frankenRFC723x_sem.txt   draft-ietf-httpbis-semantics-14.txt 
Internet Engineering Task Force (IETF) R. Fielding, Ed. HTTP Working Group R. Fielding, Ed.
Request for Comments: 7231 Adobe Internet-Draft Adobe
Obsoletes: 2616 J. Reschke, Ed. Obsoletes: 2818, 7230, 7231, 7232, 7233, 7235, M. Nottingham, Ed.
Updates: 2817 greenbytes 7538, 7615, 7694 (if approved) Fastly
Category: Standards Track June 2014 Updates: 3864 (if approved) J. Reschke, Ed.
ISSN: 2070-1721 Intended status: Standards Track greenbytes
Expires: July 17, 2021 January 13, 2021
Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content HTTP Semantics
draft-ietf-httpbis-semantics-14
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is a stateless application- The Hypertext Transfer Protocol (HTTP) is a stateless application-
level protocol for distributed, collaborative, hypertext information level protocol for distributed, collaborative, hypertext information
systems. This document defines the semantics of HTTP/1.1 messages, systems. This document describes the overall architecture of HTTP,
as expressed by request methods, request header fields, response establishes common terminology, and defines aspects of the protocol
status codes, and response header fields, along with the payload of that are shared by all versions. In this definition are core
messages (metadata and body content) and mechanisms for content protocol elements, extensibility mechanisms, and the "http" and
negotiation. "https" Uniform Resource Identifier (URI) schemes.
This document obsoletes RFC 2818, RFC 7231, RFC 7232, RFC 7233, RFC
7235, RFC 7538, RFC 7615, RFC 7694, and portions of RFC 7230.
Editorial Note Editorial Note
This note is not in the original RFC. This note is to be removed before publishing as an RFC.
The purpose of this document is to produce diffs that show just the Discussion of this draft takes place on the HTTP working group
changes from text in the original RFCs that were input for http-core. mailing list (ietf-http-wg@w3.org), which is archived at
Hence, the frankenRFC documents show all of the original text (including <https://lists.w3.org/Archives/Public/ietf-http-wg/>.
stuff that has been deleted) plus some new text [in brackets] or new
headings to anchor the context, rearranged to minimize the resulting
diffs when compared to the most recently published version of
draft-ietf-httpbis-semantics.
After this document is updated to match any reorg changes in the latest Working Group information can be found at <https://httpwg.org/>;
version, the franken diffs are saved and published in this directory as source code and issues list for this draft can be found at
diff_semantics_frfc_to_NN.html (where NN is the I-D draft revision) <https://github.com/httpwg/http-core>.
The changes in this draft are summarized in Appendix C.15.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 17, 2021.
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Table of Contents Table of Contents
1. Introduction ....................................................6 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 9
1.1. Conformance and Error Handling .............................6 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2. Syntax Notation ............................................6 1.2. History and Evolution . . . . . . . . . . . . . . . . . . 10
2. Resources .......................................................7 1.3. Core Semantics . . . . . . . . . . . . . . . . . . . . . 10
3. Representations .................................................7 1.4. Specifications Obsoleted by this Document . . . . . . . . 11
3.1. Representation Metadata ....................................8 2. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.1. Processing Representation Data ......................8 2.1. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 12
3.1.2. Encoding for Compression or Integrity ..............11 2.2. Requirements Notation . . . . . . . . . . . . . . . . . . 12
3.1.3. Audience Language ..................................13 2.3. Length Requirements . . . . . . . . . . . . . . . . . . . 13
3.1.4. Identification .....................................14 2.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 14
3.2. Representation Data .......................................17 2.5. Protocol Version . . . . . . . . . . . . . . . . . . . . 14
3.3. Payload Semantics .........................................17 3. Terminology and Core Concepts . . . . . . . . . . . . . . . . 15
3.4. Content Negotiation .......................................18 3.1. Resources . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4.1. Proactive Negotiation ..............................19 3.2. Representations . . . . . . . . . . . . . . . . . . . . . 16
3.4.2. Reactive Negotiation ...............................20 3.3. Connections, Clients and Servers . . . . . . . . . . . . 16
4. Request Methods ................................................21 3.4. Messages . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Overview ..................................................21 3.5. User Agents . . . . . . . . . . . . . . . . . . . . . . . 17
4.2. Common Method Properties ..................................22 3.6. Origin Server . . . . . . . . . . . . . . . . . . . . . . 18
4.2.1. Safe Methods .......................................22 3.7. Intermediaries . . . . . . . . . . . . . . . . . . . . . 18
4.2.2. Idempotent Methods .................................23 3.8. Caches . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2.3. Cacheable Methods ..................................24 3.9. Example Message Exchange . . . . . . . . . . . . . . . . 21
4.3. Method Definitions ........................................24 4. Identifiers in HTTP . . . . . . . . . . . . . . . . . . . . . 22
4.3.1. GET ................................................24 4.1. URI References . . . . . . . . . . . . . . . . . . . . . 22
4.3.2. HEAD ...............................................25 4.2. HTTP-Related URI Schemes . . . . . . . . . . . . . . . . 23
4.3.3. POST ...............................................25 4.2.1. http URI Scheme . . . . . . . . . . . . . . . . . . . 23
4.3.4. PUT ................................................26 4.2.2. https URI Scheme . . . . . . . . . . . . . . . . . . 24
4.3.5. DELETE .............................................29 4.2.3. http(s) Normalization and Comparison . . . . . . . . 25
4.3.6. CONNECT ............................................30 4.2.4. Deprecation of userinfo in http(s) URIs . . . . . . . 25
4.3.7. OPTIONS ............................................31 4.2.5. http(s) References with Fragment Identifiers . . . . 26
4.3.8. TRACE ..............................................32 4.3. Authoritative Access . . . . . . . . . . . . . . . . . . 26
5. Request Header Fields ..........................................33 4.3.1. URI Origin . . . . . . . . . . . . . . . . . . . . . 26
5.1. Controls ..................................................33 4.3.2. http origins . . . . . . . . . . . . . . . . . . . . 27
5.1.1. Expect .............................................34 4.3.3. https origins . . . . . . . . . . . . . . . . . . . . 28
5.1.2. Max-Forwards .......................................36 4.3.4. https certificate verification . . . . . . . . . . . 29
5.2. Conditionals ..............................................36 5. Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.3. Content Negotiation .......................................37 5.1. Field Names . . . . . . . . . . . . . . . . . . . . . . . 30
5.3.1. Quality Values .....................................37 5.2. Field Lines and Combined Field Value . . . . . . . . . . 31
5.3.2. Accept .............................................38 5.3. Field Order . . . . . . . . . . . . . . . . . . . . . . . 31
5.3.3. Accept-Charset .....................................40 5.4. Field Limits . . . . . . . . . . . . . . . . . . . . . . 32
5.3.4. Accept-Encoding ....................................41 5.5. Field Values . . . . . . . . . . . . . . . . . . . . . . 33
5.3.5. Accept-Language ....................................42 5.6. Common Rules for Defining Field Values . . . . . . . . . 35
5.4. Authentication Credentials ................................44 5.6.1. Lists (#rule ABNF Extension) . . . . . . . . . . . . 35
5.5. Request Context ...........................................44 5.6.2. Tokens . . . . . . . . . . . . . . . . . . . . . . . 36
5.5.1. From ...............................................44 5.6.3. Whitespace . . . . . . . . . . . . . . . . . . . . . 36
5.5.2. Referer ............................................45 5.6.4. Quoted Strings . . . . . . . . . . . . . . . . . . . 37
5.5.3. User-Agent .........................................46 5.6.5. Comments . . . . . . . . . . . . . . . . . . . . . . 38
6. Response Status Codes ..........................................47 5.6.6. Parameters . . . . . . . . . . . . . . . . . . . . . 38
6.1. Overview of Status Codes ..................................48 5.6.7. Date/Time Formats . . . . . . . . . . . . . . . . . . 38
6.2. Informational 1xx .........................................50 6. Message Abstraction . . . . . . . . . . . . . . . . . . . . . 40
6.2.1. 100 Continue .......................................50 6.1. Framing and Completeness . . . . . . . . . . . . . . . . 41
6.2.2. 101 Switching Protocols ............................50 6.2. Control Data . . . . . . . . . . . . . . . . . . . . . . 42
6.3. Successful 2xx ............................................51 6.3. Header Fields . . . . . . . . . . . . . . . . . . . . . . 43
6.3.1. 200 OK .............................................51 6.4. Content . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.3.2. 201 Created ........................................52 6.4.1. Content Semantics . . . . . . . . . . . . . . . . . . 44
6.3.3. 202 Accepted .......................................52 6.4.2. Identifying Content . . . . . . . . . . . . . . . . . 45
6.3.4. 203 Non-Authoritative Information ..................52 6.5. Trailer Fields . . . . . . . . . . . . . . . . . . . . . 46
6.3.5. 204 No Content .....................................53 6.5.1. Limitations on use of Trailers . . . . . . . . . . . 46
6.3.6. 205 Reset Content ..................................53 6.5.2. Processing Trailer Fields . . . . . . . . . . . . . . 47
6.4. Redirection 3xx ...........................................54 7. Routing HTTP Messages . . . . . . . . . . . . . . . . . . . . 48
6.4.1. 300 Multiple Choices ...............................55 7.1. Determining the Target Resource . . . . . . . . . . . . . 48
6.4.2. 301 Moved Permanently ..............................56 7.2. Host and :authority . . . . . . . . . . . . . . . . . . . 49
6.4.3. 302 Found ..........................................56 7.3. Routing Inbound Requests . . . . . . . . . . . . . . . . 50
6.4.4. 303 See Other ......................................57 7.3.1. To a Cache . . . . . . . . . . . . . . . . . . . . . 50
6.4.5. 305 Use Proxy ......................................58 7.3.2. To a Proxy . . . . . . . . . . . . . . . . . . . . . 50
6.4.6. 306 (Unused) .......................................58 7.3.3. To the Origin . . . . . . . . . . . . . . . . . . . . 50
6.4.7. 307 Temporary Redirect .............................58 7.4. Rejecting Misdirected Requests . . . . . . . . . . . . . 50
6.5. Client Error 4xx ..........................................58 7.5. Response Correlation . . . . . . . . . . . . . . . . . . 51
6.5.1. 400 Bad Request ....................................58 7.6. Message Forwarding . . . . . . . . . . . . . . . . . . . 51
6.5.2. 402 Payment Required ...............................59 7.6.1. Connection . . . . . . . . . . . . . . . . . . . . . 51
6.5.3. 403 Forbidden ......................................59 7.6.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 53
6.5.4. 404 Not Found ......................................59 7.6.3. Via . . . . . . . . . . . . . . . . . . . . . . . . . 54
6.5.5. 405 Method Not Allowed .............................59 7.7. Message Transformations . . . . . . . . . . . . . . . . . 55
6.5.6. 406 Not Acceptable .................................60 7.8. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.5.7. 408 Request Timeout ................................60 8. Representation Data and Metadata . . . . . . . . . . . . . . 59
6.5.8. 409 Conflict .......................................60 8.1. Representation Data . . . . . . . . . . . . . . . . . . . 59
6.5.9. 410 Gone ...........................................60 8.2. Representation Metadata . . . . . . . . . . . . . . . . . 59
6.5.10. 411 Length Required ...............................61 8.3. Content-Type . . . . . . . . . . . . . . . . . . . . . . 59
6.5.11. 413 Payload Too Large .............................61 8.3.1. Media Type . . . . . . . . . . . . . . . . . . . . . 60
6.5.12. 414 URI Too Long ..................................61 8.3.2. Charset . . . . . . . . . . . . . . . . . . . . . . . 61
6.5.13. 415 Unsupported Media Type ........................62 8.3.3. Canonicalization and Text Defaults . . . . . . . . . 61
6.5.14. 417 Expectation Failed ............................62 8.3.4. Multipart Types . . . . . . . . . . . . . . . . . . . 62
6.5.15. 426 Upgrade Required ..............................62 8.4. Content-Encoding . . . . . . . . . . . . . . . . . . . . 62
6.6. Server Error 5xx ..........................................62 8.4.1. Content Codings . . . . . . . . . . . . . . . . . . . 63
6.6.1. 500 Internal Server Error ..........................63 8.5. Content-Language . . . . . . . . . . . . . . . . . . . . 64
6.6.2. 501 Not Implemented ................................63 8.5.1. Language Tags . . . . . . . . . . . . . . . . . . . . 65
6.6.3. 502 Bad Gateway ....................................63 8.6. Content-Length . . . . . . . . . . . . . . . . . . . . . 66
6.6.4. 503 Service Unavailable ............................63 8.7. Content-Location . . . . . . . . . . . . . . . . . . . . 67
6.6.5. 504 Gateway Timeout ................................63 8.8. Validator Fields . . . . . . . . . . . . . . . . . . . . 69
6.6.6. 505 HTTP Version Not Supported .....................64 8.8.1. Weak versus Strong . . . . . . . . . . . . . . . . . 70
7. Response Header Fields .........................................64 8.8.2. Last-Modified . . . . . . . . . . . . . . . . . . . . 71
7.1. Control Data ..............................................64 8.8.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . 73
7.1.1. Origination Date ...................................65 8.8.4. When to Use Entity-Tags and Last-Modified Dates . . . 77
7.1.2. Location ...........................................68 9. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.1.3. Retry-After ........................................69 9.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 77
7.1.4. Vary ...............................................70 9.2. Common Method Properties . . . . . . . . . . . . . . . . 79
7.2. Validator Header Fields ...................................71 9.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 80
7.3. Authentication Challenges .................................72 9.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 81
7.4. Response Context ..........................................72 9.2.3. Methods and Caching . . . . . . . . . . . . . . . . . 82
7.4.1. Allow ..............................................72 9.3. Method Definitions . . . . . . . . . . . . . . . . . . . 82
7.4.2. Server .............................................73 9.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 82
8. IANA Considerations ............................................73 9.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 83
8.1. Method Registry ...........................................73 9.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 84
8.1.1. Procedure ..........................................74 9.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.1.2. Considerations for New Methods .....................74 9.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 88
8.1.3. Registrations ......................................75 9.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 89
8.2. Status Code Registry ......................................75 9.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 90
8.2.1. Procedure ..........................................75 9.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 91
8.2.2. Considerations for New Status Codes ................76 10. Message Context . . . . . . . . . . . . . . . . . . . . . . . 92
8.2.3. Registrations ......................................76 10.1. Request Context Fields . . . . . . . . . . . . . . . . . 92
8.3. Header Field Registry .....................................77 10.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 92
8.3.1. Considerations for New Header Fields ...............78 10.1.2. From . . . . . . . . . . . . . . . . . . . . . . . . 94
8.3.2. Registrations ......................................80 10.1.3. Referer . . . . . . . . . . . . . . . . . . . . . . 95
8.4. Content Coding Registry ...................................81 10.1.4. TE . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.4.1. Procedure ..........................................81 10.1.5. Trailer . . . . . . . . . . . . . . . . . . . . . . 97
8.4.2. Registrations ......................................81 10.1.6. User-Agent . . . . . . . . . . . . . . . . . . . . . 97
9. Security Considerations ........................................81 10.2. Response Context Fields . . . . . . . . . . . . . . . . 98
9.1. Attacks Based on File and Path Names ......................82 10.2.1. Allow . . . . . . . . . . . . . . . . . . . . . . . 99
9.2. Attacks Based on Command, Code, or Query Injection ........82 10.2.2. Date . . . . . . . . . . . . . . . . . . . . . . . . 99
9.3. Disclosure of Personal Information ........................83 10.2.3. Location . . . . . . . . . . . . . . . . . . . . . . 100
9.4. Disclosure of Sensitive Information in URIs ...............83 10.2.4. Retry-After . . . . . . . . . . . . . . . . . . . . 102
9.5. Disclosure of Fragment after Redirects ....................84 10.2.5. Server . . . . . . . . . . . . . . . . . . . . . . . 102
9.6. Disclosure of Product Information .........................84 11. HTTP Authentication . . . . . . . . . . . . . . . . . . . . . 103
9.7. Browser Fingerprinting ....................................84 11.1. Authentication Scheme . . . . . . . . . . . . . . . . . 103
10. Acknowledgments ...............................................85 11.2. Authentication Parameters . . . . . . . . . . . . . . . 103
11. References ....................................................85 11.3. Challenge and Response . . . . . . . . . . . . . . . . . 104
11.1. Normative References .....................................85 11.4. Credentials . . . . . . . . . . . . . . . . . . . . . . 105
11.2. Informative References ...................................86 11.5. Establishing a Protection Space (Realm) . . . . . . . . 105
Appendix A. Differences between HTTP and MIME .....................89 11.6. Authenticating Users to Origin Servers . . . . . . . . . 106
A.1. MIME-Version ..............................................89 11.6.1. WWW-Authenticate . . . . . . . . . . . . . . . . . . 106
A.2. Conversion to Canonical Form ..............................89 11.6.2. Authorization . . . . . . . . . . . . . . . . . . . 107
A.3. Conversion of Date Formats ................................90 11.6.3. Authentication-Info . . . . . . . . . . . . . . . . 108
A.4. Conversion of Content-Encoding ..........................90 11.7. Authenticating Clients to Proxies . . . . . . . . . . . 108
A.5. Conversion of Content-Transfer-Encoding .................90 11.7.1. Proxy-Authenticate . . . . . . . . . . . . . . . . . 108
A.6. MHTML and Line Length Limitations .........................90 11.7.2. Proxy-Authorization . . . . . . . . . . . . . . . . 109
Appendix B. Changes from RFC 2616 .................................91 11.7.3. Proxy-Authentication-Info . . . . . . . . . . . . . 109
Appendix C. Imported ABNF .........................................93 12. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 110
Appendix D. Collected ABNF ........................................94 12.1. Proactive Negotiation . . . . . . . . . . . . . . . . . 111
Index .............................................................97 12.2. Reactive Negotiation . . . . . . . . . . . . . . . . . . 112
12.3. Request Content Negotiation . . . . . . . . . . . . . . 113
12.4. Content Negotiation Field Features . . . . . . . . . . . 113
12.4.1. Absence . . . . . . . . . . . . . . . . . . . . . . 113
12.4.2. Quality Values . . . . . . . . . . . . . . . . . . . 114
12.4.3. Wildcard Values . . . . . . . . . . . . . . . . . . 114
12.5. Content Negotiation Fields . . . . . . . . . . . . . . . 114
12.5.1. Accept . . . . . . . . . . . . . . . . . . . . . . . 115
12.5.2. Accept-Charset . . . . . . . . . . . . . . . . . . . 117
12.5.3. Accept-Encoding . . . . . . . . . . . . . . . . . . 118
12.5.4. Accept-Language . . . . . . . . . . . . . . . . . . 119
12.5.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . 121
13. Conditional Requests . . . . . . . . . . . . . . . . . . . . 122
13.1. Preconditions . . . . . . . . . . . . . . . . . . . . . 122
13.1.1. If-Match . . . . . . . . . . . . . . . . . . . . . . 123
13.1.2. If-None-Match . . . . . . . . . . . . . . . . . . . 124
13.1.3. If-Modified-Since . . . . . . . . . . . . . . . . . 126
13.1.4. If-Unmodified-Since . . . . . . . . . . . . . . . . 128
13.1.5. If-Range . . . . . . . . . . . . . . . . . . . . . . 129
13.2. Evaluation of Preconditions . . . . . . . . . . . . . . 130
13.2.1. When to Evaluate . . . . . . . . . . . . . . . . . . 131
13.2.2. Precedence of Preconditions . . . . . . . . . . . . 132
14. Range Requests . . . . . . . . . . . . . . . . . . . . . . . 133
14.1. Range Units . . . . . . . . . . . . . . . . . . . . . . 133
14.1.1. Range Specifiers . . . . . . . . . . . . . . . . . . 134
14.1.2. Byte Ranges . . . . . . . . . . . . . . . . . . . . 135
14.2. Range . . . . . . . . . . . . . . . . . . . . . . . . . 137
14.3. Accept-Ranges . . . . . . . . . . . . . . . . . . . . . 138
14.4. Content-Range . . . . . . . . . . . . . . . . . . . . . 139
14.5. Partial PUT . . . . . . . . . . . . . . . . . . . . . . 141
14.6. Media Type multipart/byteranges . . . . . . . . . . . . 141
15. Status Codes . . . . . . . . . . . . . . . . . . . . . . . . 143
15.1. Overview of Status Codes . . . . . . . . . . . . . . . . 144
15.2. Informational 1xx . . . . . . . . . . . . . . . . . . . 144
15.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 145
15.2.2. 101 Switching Protocols . . . . . . . . . . . . . . 145
15.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 145
15.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 146
15.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . 146
15.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 147
15.3.4. 203 Non-Authoritative Information . . . . . . . . . 147
15.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 147
15.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . 148
15.3.7. 206 Partial Content . . . . . . . . . . . . . . . . 148
15.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . 152
15.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 154
15.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . 155
15.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . 155
15.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . 156
15.4.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 156
15.4.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . 157
15.4.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 157
15.4.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 157
15.4.9. 308 Permanent Redirect . . . . . . . . . . . . . . . 158
15.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 158
15.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . 158
15.5.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 159
15.5.3. 402 Payment Required . . . . . . . . . . . . . . . . 159
15.5.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . 159
15.5.5. 404 Not Found . . . . . . . . . . . . . . . . . . . 159
15.5.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 160
15.5.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 160
15.5.8. 407 Proxy Authentication Required . . . . . . . . . 160
15.5.9. 408 Request Timeout . . . . . . . . . . . . . . . . 160
15.5.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 161
15.5.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 161
15.5.12. 411 Length Required . . . . . . . . . . . . . . . . 162
15.5.13. 412 Precondition Failed . . . . . . . . . . . . . . 162
15.5.14. 413 Content Too Large . . . . . . . . . . . . . . . 162
15.5.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . 162
15.5.16. 415 Unsupported Media Type . . . . . . . . . . . . . 163
15.5.17. 416 Range Not Satisfiable . . . . . . . . . . . . . 163
15.5.18. 417 Expectation Failed . . . . . . . . . . . . . . . 164
15.5.19. 418 (Unused) . . . . . . . . . . . . . . . . . . . . 164
15.5.20. 421 Misdirected Request . . . . . . . . . . . . . . 164
15.5.21. 422 Unprocessable Content . . . . . . . . . . . . . 165
15.5.22. 426 Upgrade Required . . . . . . . . . . . . . . . . 165
15.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 165
15.6.1. 500 Internal Server Error . . . . . . . . . . . . . 165
15.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . 166
15.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . 166
15.6.4. 503 Service Unavailable . . . . . . . . . . . . . . 166
15.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . 166
15.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 166
16. Extending HTTP . . . . . . . . . . . . . . . . . . . . . . . 167
16.1. Method Extensibility . . . . . . . . . . . . . . . . . . 167
16.1.1. Method Registry . . . . . . . . . . . . . . . . . . 167
16.1.2. Considerations for New Methods . . . . . . . . . . . 168
16.2. Status Code Extensibility . . . . . . . . . . . . . . . 168
16.2.1. Status Code Registry . . . . . . . . . . . . . . . . 169
16.2.2. Considerations for New Status Codes . . . . . . . . 169
16.3. Field Extensibility . . . . . . . . . . . . . . . . . . 170
16.3.1. Field Name Registry . . . . . . . . . . . . . . . . 170
16.3.2. Considerations for New Fields . . . . . . . . . . . 172
16.4. Authentication Scheme Extensibility . . . . . . . . . . 174
16.4.1. Authentication Scheme Registry . . . . . . . . . . . 174
16.4.2. Considerations for New Authentication Schemes . . . 175
16.5. Range Unit Extensibility . . . . . . . . . . . . . . . . 176
16.5.1. Range Unit Registry . . . . . . . . . . . . . . . . 176
16.5.2. Considerations for New Range Units . . . . . . . . . 176
16.6. Content Coding Extensibility . . . . . . . . . . . . . . 176
16.6.1. Content Coding Registry . . . . . . . . . . . . . . 177
16.6.2. Considerations for New Content Codings . . . . . . . 177
16.7. Upgrade Token Registry . . . . . . . . . . . . . . . . . 177
17. Security Considerations . . . . . . . . . . . . . . . . . . . 178
17.1. Establishing Authority . . . . . . . . . . . . . . . . . 178
17.2. Risks of Intermediaries . . . . . . . . . . . . . . . . 179
17.3. Attacks Based on File and Path Names . . . . . . . . . . 180
17.4. Attacks Based on Command, Code, or Query Injection . . . 181
17.5. Attacks via Protocol Element Length . . . . . . . . . . 181
17.6. Attacks using Shared-dictionary Compression . . . . . . 182
17.7. Disclosure of Personal Information . . . . . . . . . . . 182
17.8. Privacy of Server Log Information . . . . . . . . . . . 182
17.9. Disclosure of Sensitive Information in URIs . . . . . . 183
17.10. Disclosure of Fragment after Redirects . . . . . . . . . 184
17.11. Disclosure of Product Information . . . . . . . . . . . 184
17.12. Browser Fingerprinting . . . . . . . . . . . . . . . . . 184
17.13. Validator Retention . . . . . . . . . . . . . . . . . . 185
17.14. Denial-of-Service Attacks Using Range . . . . . . . . . 186
17.15. Authentication Considerations . . . . . . . . . . . . . 186
17.15.1. Confidentiality of Credentials . . . . . . . . . . 186
17.15.2. Credentials and Idle Clients . . . . . . . . . . . 187
17.15.3. Protection Spaces . . . . . . . . . . . . . . . . . 187
17.15.4. Additional Response Fields . . . . . . . . . . . . 188
18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 188
18.1. URI Scheme Registration . . . . . . . . . . . . . . . . 188
18.2. Method Registration . . . . . . . . . . . . . . . . . . 188
18.3. Status Code Registration . . . . . . . . . . . . . . . . 189
18.4. Field Name Registration . . . . . . . . . . . . . . . . 190
18.5. Authentication Scheme Registration . . . . . . . . . . . 192
18.6. Content Coding Registration . . . . . . . . . . . . . . 192
18.7. Range Unit Registration . . . . . . . . . . . . . . . . 193
18.8. Media Type Registration . . . . . . . . . . . . . . . . 193
18.9. Port Registration . . . . . . . . . . . . . . . . . . . 193
18.10. Upgrade Token Registration . . . . . . . . . . . . . . . 194
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 194
19.1. Normative References . . . . . . . . . . . . . . . . . . 194
19.2. Informative References . . . . . . . . . . . . . . . . . 196
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 202
Appendix B. Changes from previous RFCs . . . . . . . . . . . . . 207
B.1. Changes from RFC 2818 . . . . . . . . . . . . . . . . . . 207
B.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 207
B.3. Changes from RFC 7231 . . . . . . . . . . . . . . . . . . 208
B.4. Changes from RFC 7232 . . . . . . . . . . . . . . . . . . 210
B.5. Changes from RFC 7233 . . . . . . . . . . . . . . . . . . 210
B.6. Changes from RFC 7235 . . . . . . . . . . . . . . . . . . 210
B.7. Changes from RFC 7538 . . . . . . . . . . . . . . . . . . 210
B.8. Changes from RFC 7615 . . . . . . . . . . . . . . . . . . 211
B.9. Changes from RFC 7694 . . . . . . . . . . . . . . . . . . 211
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 211
C.1. Between RFC723x and draft 00 . . . . . . . . . . . . . . 211
C.2. Since draft-ietf-httpbis-semantics-00 . . . . . . . . . . 211
C.3. Since draft-ietf-httpbis-semantics-01 . . . . . . . . . . 212
C.4. Since draft-ietf-httpbis-semantics-02 . . . . . . . . . . 213
C.5. Since draft-ietf-httpbis-semantics-03 . . . . . . . . . . 214
C.6. Since draft-ietf-httpbis-semantics-04 . . . . . . . . . . 215
C.7. Since draft-ietf-httpbis-semantics-05 . . . . . . . . . . 215
C.8. Since draft-ietf-httpbis-semantics-06 . . . . . . . . . . 217
C.9. Since draft-ietf-httpbis-semantics-07 . . . . . . . . . . 218
C.10. Since draft-ietf-httpbis-semantics-08 . . . . . . . . . . 219
C.11. Since draft-ietf-httpbis-semantics-09 . . . . . . . . . . 221
C.12. Since draft-ietf-httpbis-semantics-10 . . . . . . . . . . 221
C.13. Since draft-ietf-httpbis-semantics-11 . . . . . . . . . . 222
C.14. Since draft-ietf-httpbis-semantics-12 . . . . . . . . . . 223
C.15. Since draft-ietf-httpbis-semantics-13 . . . . . . . . . . 225
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 225
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 226
1. Introduction 1. Introduction
1.1. Purpose 1.1. Purpose
[new] The Hypertext Transfer Protocol (HTTP) is a family of stateless,
application-level, request/response protocols that share a generic
interface, extensible semantics, and self-descriptive messages to
enable flexible interaction with network-based hypertext information
systems.
HTTP is a generic interface protocol for information systems. It is HTTP hides the details of how a service is implemented by presenting
designed
to hide the details of how a service is implemented by presenting
a uniform interface to clients that is independent of the types of a uniform interface to clients that is independent of the types of
resources provided. Likewise, servers do not need to be aware of resources provided. Likewise, servers do not need to be aware of
each client's purpose: an HTTP request can be considered in isolation each client's purpose: a request can be considered in isolation
rather than being associated with a specific type of client or a rather than being associated with a specific type of client or a
predetermined sequence of application steps. predetermined sequence of application steps. This allows general-
The result is a protocol that can be used effectively in many different purpose implementations to be used effectively in many different
contexts and for which implementations can evolve independently over time. contexts, reduces interaction complexity, and enables independent
evolution over time.
HTTP is also designed for use as an intermediation protocol for HTTP is also designed for use as an intermediation protocol, wherein
translating communication to and from non-HTTP information systems. proxies and gateways can translate non-HTTP information systems into
HTTP proxies and gateways can provide access to alternative a more generic interface.
information services by translating their diverse protocols into a
hypertext format that can be viewed and manipulated by clients in the
same way as HTTP services.
One consequence of this flexibility is that the protocol cannot be One consequence of this flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent of are limited to defining the syntax of communication, the intent of
received communication, and the expected behavior of recipients. If received communication, and the expected behavior of recipients. If
the communication is considered in isolation, then successful actions the communication is considered in isolation, then successful actions
ought to be reflected in corresponding changes to the observable ought to be reflected in corresponding changes to the observable
interface provided by servers. However, since multiple clients might interface provided by servers. However, since multiple clients might
act in parallel and perhaps at cross-purposes, we cannot require that act in parallel and perhaps at cross-purposes, we cannot require that
such changes be observable beyond the scope of a single response. such changes be observable beyond the scope of a single response.
1.2. History and Evolution 1.2. History and Evolution
HTTP has been in use since 1990. The first version, later referred HTTP has been the primary information transfer protocol for the World
to as HTTP/0.9, was a simple protocol for hypertext data transfer Wide Web since its introduction in 1990. It began as a trivial
across the Internet, using only a single request method (GET) and no mechanism for low-latency requests, with a single method (GET) to
metadata. request transfer of a presumed hypertext document identified by a
given pathname. As the Web grew, HTTP was extended to enclose
requests and responses within messages, transfer arbitrary data
formats using MIME-like media types, and route requests through
intermediaries. These protocols were eventually defined as HTTP/0.9
and HTTP/1.0 (see [RFC1945]).
HTTP/1.0, as defined by [RFC1945], added a range of HTTP/1.1 was designed to refine the protocol's features while
request methods and MIME-like messaging, allowing for metadata to be retaining compatibility with the existing text-based messaging
transferred and modifiers placed on the request/response semantics. syntax, improving its interoperability, scalability, and robustness
However, HTTP/1.0 did not sufficiently take into consideration the across the Internet. This included length-based data delimiters for
effects of hierarchical proxies, caching, the need for persistent both fixed and dynamic (chunked) content, a consistent framework for
connections, or name-based virtual hosts. The proliferation of content negotiation, opaque validators for conditional requests,
incompletely implemented applications calling themselves "HTTP/1.0" cache controls for better cache consistency, range requests for
further necessitated a protocol version change in order for two partial updates, and default persistent connections. HTTP/1.1 was
communicating applications to determine each other's true introduced in 1995 and published on the standards track in 1997
capabilities. [RFC2068], revised in 1999 [RFC2616], and revised again in 2014
([RFC7230] - [RFC7235]).
[new] HTTP/2 ([RFC7540]) introduced a multiplexed session layer on top of
the existing TLS and TCP protocols for exchanging concurrent HTTP
messages with efficient field compression and server push. HTTP/3
([HTTP3]) provides greater independence for concurrent messages by
using QUIC as a secure multiplexed transport over UDP instead of TCP.
[new] All three major versions of HTTP rely on the semantics defined by
this document. They have not obsoleted each other because each one
has specific benefits and limitations depending on the context of
use. Implementations are expected to choose the most appropriate
transport and messaging syntax for their particular context.
[new] This revision of HTTP separates the definition of semantics (this
document) and caching ([Caching]) from the current HTTP/1.1 messaging
syntax ([Messaging]) to allow each major protocol version to progress
independently while referring to the same core semantics.
1.3. Semantics 1.3. Core Semantics
HTTP provides a uniform interface for interacting with a resource HTTP provides a uniform interface for interacting with a resource
(Section 2), regardless of its type, nature, or implementation, via (Section 3.1) - regardless of its type, nature, or implementation -
the manipulation and transfer of representations (Section 3). by sending messages that manipulate or transfer representations
(Section 3.2).
Each Hypertext Transfer Protocol (HTTP) message is either a request Each message is either a request or a response. A client constructs
or a response. A server listens on a connection for a request, request messages that communicate its intentions and routes those
parses each message received, interprets the message semantics in messages toward an identified origin server. A server listens for
relation to the identified request target, and responds to that requests, parses each message received, interprets the message
request with one or more response messages. A client constructs semantics in relation to the identified target resource, and responds
request messages to communicate specific intentions, examines to that request with one or more response messages. The client
received responses to see if the intentions were carried out, and examines received responses to see if its intentions were carried
determines how to interpret the results. This document defines out, determining what to do next based on the status codes and
HTTP/1.1 request and response semantics in terms of the architecture content received.
defined in [RFC7230].
HTTP semantics include the intentions defined by each request method HTTP semantics include the intentions defined by each request method
(Section 4), extensions to those semantics that might be described in (Section 9), extensions to those semantics that might be described in
request header fields (Section 5), the meaning of status codes to request header fields, status codes that describe the response
indicate a machine-readable response (Section 6), and the meaning of (Section 15), and other control data and resource metadata that might
other control data and resource metadata that might be given in be given in response fields.
response header fields (Section 7).
This document also defines representation metadata that describe how Semantics also include representation metadata that describe how
a payload is intended to be interpreted by a recipient, the request content is intended to be interpreted by a recipient, request header
header fields that might influence content selection, and the various fields that might influence content selection, and the various
selection algorithms that are collectively referred to as "content selection algorithms that are collectively referred to as _content
negotiation" (Section 3.4). negotiation_ (Section 12).
This document defines HTTP/1.1 range requests, partial responses, and 1.4. Specifications Obsoleted by this Document
the multipart/byteranges media type.
This document obsoletes the following specifications:
-------------------------------------------- ----------- ---------
Title Reference Changes
-------------------------------------------- ----------- ---------
HTTP Over TLS [RFC2818] B.1
HTTP/1.1 Message Syntax and Routing [*] [RFC7230] B.2
HTTP/1.1 Semantics and Content [RFC7231] B.3
HTTP/1.1 Conditional Requests [RFC7232] B.4
HTTP/1.1 Range Requests [RFC7233] B.5
HTTP/1.1 Authentication [RFC7235] B.6
HTTP Status Code 308 (Permanent Redirect) [RFC7538] B.7
HTTP Authentication-Info and Proxy- [RFC7615] B.8
Authentication-Info Response Header Fields
HTTP Client-Initiated Content-Encoding [RFC7694] B.9
-------------------------------------------- ----------- ---------
Table 1
[*] This document only obsoletes the portions of RFC 7230 that are
independent of the HTTP/1.1 messaging syntax and connection
management; the remaining bits of RFC 7230 are obsoleted by
"HTTP/1.1" [Messaging].
2. Conformance 2. Conformance
2.1. Syntax Notation 2.1. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF) This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with a list extension, defined in Section 7 of notation of [RFC5234], extended with the notation for case-
[RFC7230], that allows for compact definition of comma-separated sensitivity in strings defined in [RFC7405].
lists using a '#' operator (similar to how the '*' operator indicates
repetition). Appendix C describes rules imported from other It also uses a list extension, defined in Section 5.6.1, that allows
documents. Appendix D shows the collected grammar with all list for compact definition of comma-separated lists using a "#" operator
operators expanded to standard ABNF notation. (similar to how the "*" operator indicates repetition). Appendix A
shows the collected grammar with all list operators expanded to
standard ABNF notation.
As a convention, ABNF rule names prefixed with "obs-" denote As a convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons. "obsolete" grammar rules that appear for historical reasons.
The following core rules are included by reference, as defined in The following core rules are included by reference, as defined in
Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return), Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF
(line feed), OCTET (any 8-bit sequence of data), SP (space), and (line feed), OCTET (any 8-bit sequence of data), SP (space), and
VCHAR (any visible US-ASCII character). VCHAR (any visible US-ASCII character).
Section 5.6 defines some generic syntactic components for field
values.
This specification uses the terms "character", "character encoding This specification uses the terms "character", "character encoding
scheme", "charset", and "protocol element" as they are defined in scheme", "charset", and "protocol element" as they are defined in
[RFC6365]. [RFC6365].
2.2. Requirements Notation 2.2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
Conformance criteria and considerations regarding error handling are capitals, as shown here.
defined in Section 2.5 of [RFC7230].
This specification targets conformance criteria according to the role This specification targets conformance criteria according to the role
of a participant in HTTP communication. Hence, HTTP requirements are of a participant in HTTP communication. Hence, requirements are
placed on senders, recipients, clients, servers, user agents, placed on senders, recipients, clients, servers, user agents,
intermediaries, origin servers, proxies, gateways, or caches, intermediaries, origin servers, proxies, gateways, or caches,
depending on what behavior is being constrained by the requirement. depending on what behavior is being constrained by the requirement.
Additional (social) requirements are placed on implementations, Additional (social) requirements are placed on implementations,
resource owners, and protocol element registrations when they apply resource owners, and protocol element registrations when they apply
beyond the scope of a single communication. beyond the scope of a single communication.
The verb "generate" is used instead of "send" where a requirement The verb "generate" is used instead of "send" where a requirement
differentiates between creating a protocol element and merely applies only to implementations that create the protocol element,
forwarding a received element downstream. rather than an implementation that forwards a received element
downstream.
An implementation is considered conformant if it complies with all of An implementation is considered conformant if it complies with all of
the requirements associated with the roles it partakes in HTTP. the requirements associated with the roles it partakes in HTTP.
Conformance includes both the syntax and semantics of protocol Conformance includes both the syntax and semantics of protocol
elements. A sender MUST NOT generate protocol elements that convey a elements. A sender MUST NOT generate protocol elements that convey a
meaning that is known by that sender to be false. A sender MUST NOT meaning that is known by that sender to be false. A sender MUST NOT
generate protocol elements that do not match the grammar defined by generate protocol elements that do not match the grammar defined by
the corresponding ABNF rules. Within a given message, a sender MUST the corresponding ABNF rules. Within a given message, a sender MUST
NOT generate protocol elements or syntax alternatives that are only NOT generate protocol elements or syntax alternatives that are only
allowed to be generated by participants in other roles (i.e., a role allowed to be generated by participants in other roles (i.e., a role
that the sender does not have for that message). that the sender does not have for that message).
2.3. Length Requirements 2.3. Length Requirements
When a received protocol element is parsed, the recipient MUST be A recipient SHOULD parse a received protocol element defensively,
able to parse any value of reasonable length that is applicable to with only marginal expectations that the element will conform to its
the recipient's role and that matches the grammar defined by the ABNF grammar and fit within a reasonable buffer size.
corresponding ABNF rules.
HTTP does not have specific length limitations for many of its HTTP does not have specific length limitations for many of its
protocol elements because the lengths that might be appropriate will protocol elements because the lengths that might be appropriate will
vary widely, depending on the deployment context and purpose of the vary widely, depending on the deployment context and purpose of the
implementation. Hence, interoperability between senders and implementation. Hence, interoperability between senders and
recipients depends on shared expectations regarding what is a recipients depends on shared expectations regarding what is a
reasonable length for each protocol element. Furthermore, what is reasonable length for each protocol element. Furthermore, what is
commonly understood to be a reasonable length for some protocol commonly understood to be a reasonable length for some protocol
elements has changed over the course of the past two decades of HTTP elements has changed over the course of the past two decades of HTTP
use and is expected to continue changing in the future. use and is expected to continue changing in the future.
At a minimum, a recipient MUST be able to parse and process protocol At a minimum, a recipient MUST be able to parse and process protocol
element lengths that are at least as long as the values that it element lengths that are at least as long as the values that it
generates for those same protocol elements in other messages. For generates for those same protocol elements in other messages. For
example, an origin server that publishes very long URI references to example, an origin server that publishes very long URI references to
its own resources needs to be able to parse and process those same its own resources needs to be able to parse and process those same
references when received as a request target. references when received as a target URI.
Note, however, that some received protocol elements might not be parsed. For Many received protocol elements are only parsed to the extent
example, an intermediary forwarding a message might parse a header-field necessary to identify and forward that element downstream. For
into generic field-name and field-value components, but then forward the example, an intermediary might parse a received field into its field
header field without further parsing inside the field-value. name and field value components, but then forward the field without
further parsing inside the field value.
2.4. Error Handling 2.4. Error Handling
A recipient MUST interpret a received protocol element according to A recipient MUST interpret a received protocol element according to
the semantics defined for it by this specification, including the semantics defined for it by this specification, including
extensions to this specification, unless the recipient has determined extensions to this specification, unless the recipient has determined
(through experience or configuration) that the sender incorrectly (through experience or configuration) that the sender incorrectly
implements what is implied by those semantics. For example, an implements what is implied by those semantics. For example, an
origin server might disregard the contents of a received origin server might disregard the contents of a received
Accept-Encoding header field if inspection of the User-Agent header Accept-Encoding header field if inspection of the User-Agent header
skipping to change at line 422 skipping to change at page 14, line 27
Unless noted otherwise, a recipient MAY attempt to recover a usable Unless noted otherwise, a recipient MAY attempt to recover a usable
protocol element from an invalid construct. HTTP does not define protocol element from an invalid construct. HTTP does not define
specific error handling mechanisms except when they have a direct specific error handling mechanisms except when they have a direct
impact on security, since different applications of the protocol impact on security, since different applications of the protocol
require different error handling strategies. For example, a Web require different error handling strategies. For example, a Web
browser might wish to transparently recover from a response where the browser might wish to transparently recover from a response where the
Location header field doesn't parse according to the ABNF, whereas a Location header field doesn't parse according to the ABNF, whereas a
systems control client might consider any form of error recovery to systems control client might consider any form of error recovery to
be dangerous. be dangerous.
[new] Some requests can be automatically retried by a client in the event
of an underlying connection failure, as described in Section 9.2.2.
2.5. Protocol Version 2.5. Protocol Version
The HTTP version number consists of two decimal digits separated by a HTTP's version number consists of two decimal digits separated by a
"." (period or decimal point). The first digit ("major version") "." (period or decimal point). The first digit ("major version")
indicates the HTTP messaging syntax, whereas the second digit ("minor indicates the messaging syntax, whereas the second digit ("minor
version") indicates the highest minor version within that major version") indicates the highest minor version within that major
version to which the sender is conformant and able to understand for version to which the sender is conformant (able to understand for
future communication. future communication).
[new] While HTTP's core semantics don't change between protocol versions,
the expression of them "on the wire" can change, and so the HTTP
version number changes when incompatible changes are made to the wire
format. Additionally, HTTP allows incremental, backwards-compatible
changes to be made to the protocol without changing its version
through the use of defined extension points (Section 16).
The protocol version as a whole indicates the sender's conformance with The protocol version as a whole indicates the sender's conformance
the set of requirements laid out in that version's corresponding with the set of requirements laid out in that version's corresponding
specification of HTTP. specification of HTTP. For example, the version "HTTP/1.1" is
defined by the combined specifications of this document, "HTTP
Caching" [Caching], and "HTTP/1.1" [Messaging].
The intention of HTTP's versioning design is that the major number HTTP's major version number is incremented when an incompatible
will only be incremented if an incompatible message syntax is message syntax is introduced. The minor number is incremented when
introduced, and that the minor number will only be incremented when
changes made to the protocol have the effect of adding to the message changes made to the protocol have the effect of adding to the message
semantics or implying additional capabilities of the sender. semantics or implying additional capabilities of the sender.
However, the minor version was not incremented for the changes
introduced between [RFC2068] and [RFC2616], and this revision has
specifically avoided any such changes to the protocol.
The minor version advertises the sender's communication capabilities The minor version advertises the sender's communication capabilities
even when the sender is only using a backwards-compatible subset of even when the sender is only using a backwards-compatible subset of
the protocol, thereby letting the recipient know that more advanced the protocol, thereby letting the recipient know that more advanced
features can be used in response (by servers) or in future requests features can be used in response (by servers) or in future requests
(by clients). (by clients).
[new] When a major version of HTTP does not define any minor versions, the
minor version "0" is implied and is used when referring to that
protocol within a protocol element that requires sending a minor
version.
3. Architecture 3. Terminology and Core Concepts
HTTP was created for the World Wide Web (WWW) architecture and has HTTP was created for the World Wide Web (WWW) architecture and has
evolved over time to support the scalability needs of a worldwide evolved over time to support the scalability needs of a worldwide
hypertext system. Much of that architecture is reflected in the hypertext system. Much of that architecture is reflected in the
terminology and syntax productions used to define HTTP. terminology and syntax productions used to define HTTP.
3.1. Resources 3.1. Resources
The target of an HTTP request is called a "resource". HTTP does not The target of an HTTP request is called a _resource_. HTTP does not
limit the nature of a resource; it merely defines an interface that limit the nature of a resource; it merely defines an interface that
might be used to interact with resources. Each resource is might be used to interact with resources. Most resources are
identified by a Uniform Resource Identifier (URI), as described in identified by a Uniform Resource Identifier (URI), as described in
Section 2.7 of [RFC7230]. Section 4.
One design goal of HTTP is to separate resource identification from One design goal of HTTP is to separate resource identification from
request semantics, which is made possible by vesting the request request semantics, which is made possible by vesting the request
semantics in the request method (Section 4) and a few semantics in the request method (Section 9) and a few request-
request-modifying header fields (Section 5). If there is a conflict modifying header fields. If there is a conflict between the method
between the method semantics and any semantic implied by the URI semantics and any semantic implied by the URI itself, as described in
itself, as described in Section 4.2.1, the method semantics take Section 9.2.1, the method semantics take precedence.
precedence.
HTTP relies upon the Uniform Resource Identifier (URI) standard HTTP relies upon the Uniform Resource Identifier (URI) standard
[RFC3986] to indicate the target resource (Section 5.1) and [RFC3986] to indicate the target resource (Section 7.1) and
relationships between resources. relationships between resources.
3.2. Representations 3.2. Representations
For the purposes of HTTP, a "representation" is information that is A _representation_ is information that is intended to reflect a past,
intended to reflect a past, current, or desired state of a given current, or desired state of a given resource, in a format that can
resource, in a format that can be readily communicated via the be readily communicated via the protocol. A representation consists
protocol, and that consists of a set of representation metadata and a of a set of representation metadata and a potentially unbounded
potentially unbounded stream of representation data. stream of representation data (Section 8).
[new] HTTP allows "information hiding" behind its uniform interface by
defining communication with respect to a transferable representation
of the resource state, rather than transferring the resource itself.
This allows the resource identified by a URI to be anything,
including temporal functions like "the current weather in Laguna
Beach", while potentially providing information that represents that
resource at the time a message is generated [REST].
Considering that a resource could be anything, and that the uniform The uniform interface is similar to a window through which one can
interface provided by HTTP is similar to a window through which one observe and act upon a thing only through the communication of
can observe and act upon such a thing only through the communication messages to an independent actor on the other side. A shared
of messages to some independent actor on the other side, an
abstraction is needed to represent ("take the place of") the current abstraction is needed to represent ("take the place of") the current
or desired state of that thing in our communications. That or desired state of that thing in our communications. When a
abstraction is called a representation [REST]. representation is hypertext, it can provide both a representation of
the resource state and processing instructions that help guide the
recipient's future interactions.
An origin server might be provided with, or be capable of generating, A target resource might be provided with, or be capable of
multiple representations that are each intended to reflect the generating, multiple representations that are each intended to
current state of a target resource. In such cases, some algorithm is reflect the resource's current state. An algorithm, usually based on
used by the origin server to select one of those representations as content negotiation (Section 12), would be used to select one of
most applicable to a given request, usually based on content those representations as being most applicable to a given request.
negotiation. This "selected representation" is used to provide the This _selected representation_ provides the data and metadata for
data and metadata for evaluating conditional requests [RFC7232] and evaluating conditional requests (Section 13) and constructing the
constructing the payload for 200 (OK) and 304 (Not Modified) content for 200 (OK), 206 (Partial Content), and 304 (Not Modified)
responses to GET (Section 4.3.1). responses to GET (Section 9.3.1).
3.3. Connections 3.3. Connections, Clients and Servers
HTTP is a stateless request/response protocol that operates by HTTP is a client/server protocol that operates over a reliable
exchanging messages (Section 3) across a reliable transport- or transport- or session-layer _connection_.
session-layer "connection" (Section 6).
An HTTP "client" is a program that establishes a connection to a An HTTP _client_ is a program that establishes a connection to a
server for the purpose of sending one or more HTTP requests. An HTTP server for the purpose of sending one or more HTTP requests. An HTTP
"server" is a program that accepts connections in order to service _server_ is a program that accepts connections in order to service
HTTP requests by sending HTTP responses. HTTP requests by sending HTTP responses.
The terms "client" and "server" refer only to the roles that these The terms "client" and "server" refer only to the roles that these
programs perform for a particular connection. The same program might programs perform for a particular connection. The same program might
act as a client on some connections and a server on others. act as a client on some connections and a server on others.
A connection might be used for multiple request/response exchanges,
as defined in Section 6.3.
3.4. Messages 3.4. Messages
The terms "sender" and "recipient" HTTP is a stateless request/response protocol for exchanging
_messages_ across a connection. The terms _sender_ and _recipient_
refer to any implementation that sends or receives a given message, refer to any implementation that sends or receives a given message,
respectively. respectively.
A client sends an HTTP request to a server in the form of a request A client sends requests to a server in the form of a _request_
message, beginning with a request-line that includes a method, URI, message with a method (Section 9) and request target (Section 7.1).
and protocol version (Section 3.1.1), followed by header fields The request might also contain header fields (Section 6.3) for
containing request modifiers, client information, and representation request modifiers, client information, and representation metadata,
metadata (Section 3.2), an empty line to indicate the end of the content (Section 6.4) intended for processing in accordance with the
header section, and finally a message body containing the payload method, and trailer fields (Section 6.5) to communicate information
body (if any, Section 3.3). collected while sending the content.
When a client constructs an HTTP/1.1 request message, it sends the
target URI in one of various forms, as defined in (Section 5.3 of
[RFC7230]). When a request is received, the server reconstructs an
effective request URI for the target resource (Section 5.5 of
[RFC7230]).
A server responds to a client's request by sending one or more A server responds to a client's request by sending one or more
HTTP response messages, each beginning with a status line that includes _response_ messages, each including a status code (Section 15). The
the protocol version, a success or error code, and textual reason response might also contain header fields for server information,
phrase (Section 3.1.2), possibly followed by header fields containing resource metadata, and representation metadata, content to be
server information, resource metadata, and representation metadata interpreted in accordance with the status code, and trailer fields to
(Section 3.2), an empty line to indicate the end of the header section, communicate information collected while sending the content.
and finally a message body containing the payload body (if any, Section
3.3).
3.5. User Agents 3.5. User Agents
The term "user agent" refers to any of the various client programs The term _user agent_ refers to any of the various client programs
that initiate a request, including (but not limited to) browsers, spiders that initiate a request.
(web-based robots), command-line tools, custom applications, and
mobile apps.
When considering the design of HTTP, it is easy to fall into a trap The most familiar form of user agent is the general-purpose Web
of thinking that all user agents are general-purpose browsers and all browser, but that's only a small percentage of implementations.
origin servers are large public websites. That is not the case in Other common user agents include spiders (web-traversing robots),
practice. Common HTTP user agents include household appliances, command-line tools, billboard screens, household appliances, scales,
stereos, scales, firmware update scripts, command-line programs, light bulbs, firmware update scripts, mobile apps, and communication
mobile apps, and communication devices in a multitude of shapes and devices in a multitude of shapes and sizes.
sizes.
The term "user agent" does not imply that there is a human user Being a user agent does not imply that there is a human user directly
directly interacting with the software agent at the time of a interacting with the software agent at the time of a request. In
request. In many cases, a user agent is installed or configured to many cases, a user agent is installed or configured to run in the
run in the background and save its results for later inspection (or background and save its results for later inspection (or save only a
save only a subset of those results that might be interesting or subset of those results that might be interesting or erroneous).
erroneous). Spiders, for example, are typically given a start URI Spiders, for example, are typically given a start URI and configured
and configured to follow certain behavior while crawling the Web as a to follow certain behavior while crawling the Web as a hypertext
hypertext graph. graph.
The implementation diversity of HTTP means that not all user agents Many user agents cannot, or choose not to, make interactive
can make interactive suggestions to their user or provide adequate suggestions to their user or provide adequate warning for security or
warning for security or privacy concerns. In the few cases where privacy concerns. In the few cases where this specification requires
this specification requires reporting of errors to the user, it is reporting of errors to the user, it is acceptable for such reporting
acceptable for such reporting to only be observable in an error to only be observable in an error console or log file. Likewise,
console or log file. Likewise, requirements that an automated action requirements that an automated action be confirmed by the user before
be confirmed by the user before proceeding might be met via advance proceeding might be met via advance configuration choices, run-time
configuration choices, run-time options, or simple avoidance of the options, or simple avoidance of the unsafe action; confirmation does
unsafe action; confirmation does not imply any specific user not imply any specific user interface or interruption of normal
interface or interruption of normal processing if the user has processing if the user has already made that choice.
already made that choice.
3.6. Origin Server 3.6. Origin Server
The term "origin server" refers to the program that can originate The term _origin server_ refers to a program that can originate
authoritative responses for a given target resource. authoritative responses for a given target resource.
Likewise, common HTTP The most familiar form of origin server are large public websites.
origin servers include home automation units, configurable However, like user agents being equated with browsers, it is easy to
be misled into thinking that all origin servers are alike. Common
origin servers also include home automation units, configurable
networking components, office machines, autonomous robots, news networking components, office machines, autonomous robots, news
feeds, traffic cameras, ad selectors, and video-delivery feeds, traffic cameras, real-time ad selectors, and video-on-demand
platforms. platforms.
Most HTTP communication consists of a retrieval request (GET) for a Most HTTP communication consists of a retrieval request (GET) for a
representation of some resource identified by a URI. In the simplest representation of some resource identified by a URI. In the simplest
case, this might be accomplished via a single bidirectional case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin connection (===) between the user agent (UA) and the origin server
server (O). (O).
request > request >
UA ======================================= O UA ======================================= O
< response < response
Figure 1
3.7. Intermediaries 3.7. Intermediaries
HTTP enables the use of intermediaries to satisfy requests through a HTTP enables the use of intermediaries to satisfy requests through a
chain of connections. There are three common forms of HTTP chain of connections. There are three common forms of HTTP
intermediary: proxy, gateway, and tunnel. In some cases, a single _intermediary_: proxy, gateway, and tunnel. In some cases, a single
intermediary might act as an origin server, proxy, gateway, or intermediary might act as an origin server, proxy, gateway, or
tunnel, switching behavior based on the nature of each request. tunnel, switching behavior based on the nature of each request.
> > > > > > > >
UA =========== A =========== B =========== C =========== O UA =========== A =========== B =========== C =========== O
< < < < < < < <
Figure 2
The figure above shows three intermediaries (A, B, and C) between the The figure above shows three intermediaries (A, B, and C) between the
user agent and origin server. A request or response message that user agent and origin server. A request or response message that
travels the whole chain will pass through four separate connections. travels the whole chain will pass through four separate connections.
Some HTTP communication options might apply only to the connection Some HTTP communication options might apply only to the connection
with the nearest, non-tunnel neighbor, only to the endpoints of the with the nearest, non-tunnel neighbor, only to the endpoints of the
chain, or to all connections along the chain. Although the diagram chain, or to all connections along the chain. Although the diagram
is linear, each participant might be engaged in multiple, is linear, each participant might be engaged in multiple,
simultaneous communications. For example, B might be receiving simultaneous communications. For example, B might be receiving
requests from many clients other than A, and/or forwarding requests requests from many clients other than A, and/or forwarding requests
to servers other than C, at the same time that it is handling A's to servers other than C, at the same time that it is handling A's
request. Likewise, later requests might be sent through a different request. Likewise, later requests might be sent through a different
path of connections, often based on dynamic configuration for load path of connections, often based on dynamic configuration for load
balancing. balancing.
skipping to change at line 641 skipping to change at page 19, line 16
with the nearest, non-tunnel neighbor, only to the endpoints of the with the nearest, non-tunnel neighbor, only to the endpoints of the
chain, or to all connections along the chain. Although the diagram chain, or to all connections along the chain. Although the diagram
is linear, each participant might be engaged in multiple, is linear, each participant might be engaged in multiple,
simultaneous communications. For example, B might be receiving simultaneous communications. For example, B might be receiving
requests from many clients other than A, and/or forwarding requests requests from many clients other than A, and/or forwarding requests
to servers other than C, at the same time that it is handling A's to servers other than C, at the same time that it is handling A's
request. Likewise, later requests might be sent through a different request. Likewise, later requests might be sent through a different
path of connections, often based on dynamic configuration for load path of connections, often based on dynamic configuration for load
balancing. balancing.
The terms "upstream" and "downstream" are used to describe The terms _upstream_ and _downstream_ are used to describe
directional requirements in relation to the message flow: all directional requirements in relation to the message flow: all
messages flow from upstream to downstream. The terms "inbound" and messages flow from upstream to downstream. The terms "inbound" and
"outbound" are used to describe directional requirements in relation "outbound" are used to describe directional requirements in relation
to the request route: "inbound" means toward the origin server and to the request route: _inbound_ means toward the origin server and
"outbound" means toward the user agent. _outbound_ means toward the user agent.
A "proxy" is a message-forwarding agent that is selected by the A _proxy_ is a message-forwarding agent that is chosen by the client,
client, usually via local configuration rules, to receive requests usually via local configuration rules, to receive requests for some
for some type(s) of absolute URI and attempt to satisfy those type(s) of absolute URI and attempt to satisfy those requests via
requests via translation through the HTTP interface. Some translation through the HTTP interface. Some translations are
translations are minimal, such as for proxy requests for "http" URIs, minimal, such as for proxy requests for "http" URIs, whereas other
whereas other requests might require translation to and from entirely requests might require translation to and from entirely different
different application-level protocols. Proxies are often used to application-level protocols. Proxies are often used to group an
group an organization's HTTP requests through a common intermediary organization's HTTP requests through a common intermediary for the
for the sake of security, annotation services, or shared caching. sake of security, annotation services, or shared caching. Some
Some proxies are designed to apply transformations to selected proxies are designed to apply transformations to selected messages or
messages or payloads while they are being forwarded, as described in content while they are being forwarded, as described in Section 7.7.
Section 5.7.2.
A "gateway" (a.k.a. "reverse proxy") is an intermediary that acts as A _gateway_ (a.k.a. _reverse proxy_) is an intermediary that acts as
an origin server for the outbound connection but translates received an origin server for the outbound connection but translates received
requests and forwards them inbound to another server or servers. requests and forwards them inbound to another server or servers.
Gateways are often used to encapsulate legacy or untrusted Gateways are often used to encapsulate legacy or untrusted
information services, to improve server performance through information services, to improve server performance through
"accelerator" caching, and to enable partitioning or load balancing _accelerator_ caching, and to enable partitioning or load balancing
of HTTP services across multiple machines. of HTTP services across multiple machines.
All HTTP requirements applicable to an origin server also apply to All HTTP requirements applicable to an origin server also apply to
the outbound communication of a gateway. A gateway communicates with the outbound communication of a gateway. A gateway communicates with
inbound servers using any protocol that it desires, including private inbound servers using any protocol that it desires, including private
extensions to HTTP that are outside the scope of this specification. extensions to HTTP that are outside the scope of this specification.
However, an HTTP-to-HTTP gateway that wishes to interoperate with However, an HTTP-to-HTTP gateway that wishes to interoperate with
third-party HTTP servers ought to conform to user agent requirements third-party HTTP servers ought to conform to user agent requirements
on the gateway's inbound connection. on the gateway's inbound connection.
A "tunnel" acts as a blind relay between two connections without A _tunnel_ acts as a blind relay between two connections without
changing the messages. Once active, a tunnel is not considered a changing the messages. Once active, a tunnel is not considered a
party to the HTTP communication, though the tunnel might have been party to the HTTP communication, though the tunnel might have been
initiated by an HTTP request. A tunnel ceases to exist when both initiated by an HTTP request. A tunnel ceases to exist when both
ends of the relayed connection are closed. Tunnels are used to ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when extend a virtual connection through an intermediary, such as when
Transport Layer Security (TLS, [RFC5246]) is used to establish Transport Layer Security (TLS, [RFC8446]) is used to establish
confidential communication through a shared firewall proxy. confidential communication through a shared firewall proxy.
The above categories for intermediary only consider those acting as The above categories for intermediary only consider those acting as
participants in the HTTP communication. There are also participants in the HTTP communication. There are also
intermediaries that can act on lower layers of the network protocol intermediaries that can act on lower layers of the network protocol
stack, filtering or redirecting HTTP traffic without the knowledge or stack, filtering or redirecting HTTP traffic without the knowledge or
permission of message senders. Network intermediaries are permission of message senders. Network intermediaries are
indistinguishable (at a protocol level) from a man-in-the-middle indistinguishable (at a protocol level) from an on-path attacker,
attack, often introducing security flaws or interoperability problems often introducing security flaws or interoperability problems due to
due to mistakenly violating HTTP semantics. mistakenly violating HTTP semantics.
For example, an "interception proxy" [RFC3040] (also commonly known For example, an _interception proxy_ [RFC3040] (also commonly known
as a "transparent proxy" [RFC1919] or "captive portal") differs from as a _transparent proxy_ [RFC1919]) differs from an HTTP proxy
an HTTP proxy because it is not selected by the client. Instead, an because it is not chosen by the client. Instead, an interception
interception proxy filters or redirects outgoing TCP port 80 packets proxy filters or redirects outgoing TCP port 80 packets (and
(and occasionally other common port traffic). Interception proxies occasionally other common port traffic). Interception proxies are
are commonly found on public network access points, as a means of commonly found on public network access points, as a means of
enforcing account subscription prior to allowing use of non-local enforcing account subscription prior to allowing use of non-local
Internet services, and within corporate firewalls to enforce network Internet services, and within corporate firewalls to enforce network
usage policies. usage policies.
HTTP is defined as a stateless protocol, meaning that each request HTTP is defined as a stateless protocol, meaning that each request
message can be understood in isolation. Many implementations depend message can be understood in isolation. Many implementations depend
on HTTP's stateless design in order to reuse proxied connections or on HTTP's stateless design in order to reuse proxied connections or
dynamically load balance requests across multiple servers. Hence, a dynamically load balance requests across multiple servers. Hence, a
server MUST NOT assume that two requests on the same connection are server MUST NOT assume that two requests on the same connection are
from the same user agent unless the connection is secured and from the same user agent unless the connection is secured and
specific to that agent. Some non-standard HTTP extensions (e.g., specific to that agent. Some non-standard HTTP extensions (e.g.,
[RFC4559]) have been known to violate this requirement, resulting in [RFC4559]) have been known to violate this requirement, resulting in
security and interoperability problems. security and interoperability problems.
3.8. Caches 3.8. Caches
A "cache" is a local store of previous response messages and the A _cache_ is a local store of previous response messages and the
subsystem that controls its message storage, retrieval, and deletion. subsystem that controls its message storage, retrieval, and deletion.
A cache stores cacheable responses in order to reduce the response A cache stores cacheable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent time and network bandwidth consumption on future, equivalent
requests. Any client or server MAY employ a cache, though a cache requests. Any client or server MAY employ a cache, though a cache
cannot be used by a server while it is acting as a tunnel. cannot be used while acting as a tunnel.
The effect of a cache is that the request/response chain is shortened The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting applicable to that request. The following illustrates the resulting
chain if B has a cached copy of an earlier response from O (via C) chain if B has a cached copy of an earlier response from O (via C)
for a request that has not been cached by UA or A. for a request that has not been cached by UA or A.
> > > >
UA =========== A =========== B - - - - - - C - - - - - - O UA =========== A =========== B - - - - - - C - - - - - - O
< < < <
A response is "cacheable" if a cache is allowed to store a copy of Figure 3
A response is _cacheable_ if a cache is allowed to store a copy of
the response message for use in answering subsequent requests. Even the response message for use in answering subsequent requests. Even
when a response is cacheable, there might be additional constraints when a response is cacheable, there might be additional constraints
placed by the client or by the origin server on when that cached placed by the client or by the origin server on when that cached
response can be used for a particular request. HTTP requirements for response can be used for a particular request. HTTP requirements for
cache behavior and cacheable responses are defined in Section 2 of cache behavior and cacheable responses are defined in Section 2 of
[RFC7234]. [Caching].
There is a wide variety of architectures and configurations of caches There is a wide variety of architectures and configurations of caches
deployed across the World Wide Web and inside large organizations. deployed across the World Wide Web and inside large organizations.
These include national hierarchies of proxy caches to save These include national hierarchies of proxy caches to save bandwidth
transoceanic bandwidth, collaborative systems that broadcast or and reduce latency, Content Delivery Networks that use gateway
multicast cache entries, archives of pre-fetched cache entries for caching to optimise regional and global distribution of popular
use in off-line or high-latency environments, and so on. sites, collaborative systems that broadcast or multicast cache
entries, archives of pre-fetched cache entries for use in off-line or
high-latency environments, and so on.
3.9. Example Request and Response 3.9. Example Message Exchange
The following example illustrates a typical message exchange for a The following example illustrates a typical HTTP/1.1 message exchange
GET request (Section 4.3.1 of [RFC7231]) on the URI for a GET request (Section 9.3.1) on the URI "http://www.example.com/
"http://www.example.com/hello.txt": hello.txt":
Client request: Client request:
GET /hello.txt HTTP/1.1 GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3 User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com Host: www.example.com
Accept-Language: en, mi Accept-Language: en, mi
Server response: Server response:
HTTP/1.1 200 OK HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00" ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes Accept-Ranges: bytes
Content-Length: 51 Content-Length: 51
Vary: Accept-Encoding Vary: Accept-Encoding
Content-Type: text/plain Content-Type: text/plain
Hello World! My payload includes a trailing CRLF. Hello World! My content includes a trailing CRLF.
4. Identifiers in HTTP 4. Identifiers in HTTP
Uniform Resource Identifiers (URIs) [RFC3986] are used throughout Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
HTTP as the means for identifying resources (Section 2 of [RFC7231]). HTTP as the means for identifying resources (Section 3.1).
4.1. URI References 4.1. URI References
URI references are used to target requests, indicate redirects, and URI references are used to target requests, indicate redirects, and
define relationships. define relationships.
The definitions of "URI-reference", "absolute-URI", "relative-part", The definitions of "URI-reference", "absolute-URI", "relative-part",
"scheme", "authority", "port", "host", "path-abempty", "segment", "authority", "port", "host", "path-abempty", "segment", and "query"
"query", and "fragment" are adopted from the URI generic syntax. An are adopted from the URI generic syntax. An "absolute-path" rule is
"absolute-path" rule is defined for protocol elements that can defined for protocol elements that can contain a non-empty path
contain a non-empty path component. (This rule differs slightly from component. (This rule differs slightly from the path-abempty rule of
the path-abempty rule of RFC 3986, which allows for an empty path to RFC 3986, which allows for an empty path to be used in references,
be used in references, and path-absolute rule, which does not allow and path-absolute rule, which does not allow paths that begin with
paths that begin with "//".) A "partial-URI" rule is defined for "//".) A "partial-URI" rule is defined for protocol elements that
protocol elements that can contain a relative URI but not a fragment can contain a relative URI but not a fragment component.
component.
URI-reference = <URI-reference, see [RFC3986], Section 4.1> URI-reference = <URI-reference, see [RFC3986], Section 4.1>
absolute-URI = <absolute-URI, see [RFC3986], Section 4.3> absolute-URI = <absolute-URI, see [RFC3986], Section 4.3>
relative-part = <relative-part, see [RFC3986], Section 4.2> relative-part = <relative-part, see [RFC3986], Section 4.2>
scheme = <scheme, see [RFC3986], Section 3.1>
authority = <authority, see [RFC3986], Section 3.2> authority = <authority, see [RFC3986], Section 3.2>
uri-host = <host, see [RFC3986], Section 3.2.2> uri-host = <host, see [RFC3986], Section 3.2.2>
port = <port, see [RFC3986], Section 3.2.3> port = <port, see [RFC3986], Section 3.2.3>
path-abempty = <path-abempty, see [RFC3986], Section 3.3> path-abempty = <path-abempty, see [RFC3986], Section 3.3>
segment = <segment, see [RFC3986], Section 3.3> segment = <segment, see [RFC3986], Section 3.3>
query = <query, see [RFC3986], Section 3.4> query = <query, see [RFC3986], Section 3.4>
fragment = <fragment, see [RFC3986], Section 3.5>
absolute-path = 1*( "/" segment ) absolute-path = 1*( "/" segment )
partial-URI = relative-part [ "?" query ] partial-URI = relative-part [ "?" query ]
Each protocol element in HTTP that allows a URI reference will Each protocol element in HTTP that allows a URI reference will
indicate in its ABNF production whether the element allows any form indicate in its ABNF production whether the element allows any form
of reference (URI-reference), only a URI in absolute form of reference (URI-reference), only a URI in absolute form (absolute-
(absolute-URI), only the path and optional query components, or some URI), only the path and optional query components, or some
combination of the above. Unless otherwise indicated, URI references combination of the above. Unless otherwise indicated, URI references
are parsed relative to the effective request URI (Section 5.5). are parsed relative to the target URI (Section 7.1).
[new] It is RECOMMENDED that all senders and recipients support, at a
minimum, URIs with lengths of 8000 octets in protocol elements. Note
that this implies some structures and on-wire representations (for
example, the request line in HTTP/1.1) will necessarily be larger in
some cases.
4.2. URI Schemes 4.2. HTTP-Related URI Schemes
IANA maintains the registry of URI Schemes [BCP115] at IANA maintains the registry of URI Schemes [BCP35] at
<http://www.iana.org/assignments/uri-schemes/>. <https://www.iana.org/assignments/uri-schemes/>. Although requests
might target any URI scheme, the following schemes are inherent to
HTTP servers:
This document defines the following URI schemes. ------------ ------------------------------------ -------
URI Scheme Description Ref.
------------ ------------------------------------ -------
http Hypertext Transfer Protocol 4.2.1
https Hypertext Transfer Protocol Secure 4.2.2
------------ ------------------------------------ -------
+------------+------------------------------------+---------------+ Table 2
| URI Scheme | Description | Reference |
+------------+------------------------------------+---------------+
| http | Hypertext Transfer Protocol | Section 2.7.1 |
| https | Hypertext Transfer Protocol Secure | Section 2.7.2 |
+------------+------------------------------------+---------------+
Note that the presence of a URI with a given authority component does Note that the presence of an "http" or "https" URI does not imply
not imply that there is always an HTTP server listening for that there is always an HTTP server at the identified origin
connections on that host and port. Anyone can mint a URI. What the listening for connections. Anyone can mint a URI, whether or not a
authority component determines is who has the right to respond server exists and whether or not that server currently maps that
authoritatively to requests that target the identified resource. The identifier to a resource. The delegated nature of registered names
delegated nature of registered names and IP addresses creates a and IP addresses creates a federated namespace whether or not an HTTP
federated namespace, based on control over the indicated host and server is present.
port, whether or not an HTTP server is present.
4.2.1. http URI Scheme 4.2.1. http URI Scheme
The "http" URI scheme is hereby defined for the purpose of minting The "http" URI scheme is hereby defined for minting identifiers
identifiers according to their association with the hierarchical within the hierarchical namespace governed by a potential HTTP origin
namespace governed by a potential HTTP origin server listening for server listening for TCP ([RFC0793]) connections on a given port.
TCP ([RFC0793]) connections on a given port.
http-URI = "http:" "//" authority path-abempty [ "?" query ] http-URI = "http" "://" authority path-abempty [ "?" query ]
[ "#" fragment ]
The origin server for an "http" URI is identified by the authority The origin server for an "http" URI is identified by the authority
component, which includes a host identifier and optional TCP port component, which includes a host identifier and optional port number
([RFC3986], Section 3.2.2). If the port subcomponent is empty or not ([RFC3986], Section 3.2.2). If the port subcomponent is empty or not
given, TCP port 80 (the reserved port for WWW services) is the given, TCP port 80 (the reserved port for WWW services) is the
default. default. The origin determines who has the right to respond
authoritatively to requests that target the identified resource, as
defined in Section 4.3.2.
A sender MUST NOT generate an "http" URI with an empty host A sender MUST NOT generate an "http" URI with an empty host
identifier. A recipient that processes such a URI reference MUST identifier. A recipient that processes such a URI reference MUST
reject it as invalid. reject it as invalid.
The hierarchical path component and optional query component serve The hierarchical path component and optional query component identify
as an identifier for a potential target resource within that the target resource within that origin server's name space.
origin server's name space.
4.2.2. https URI Scheme 4.2.2. https URI Scheme
The "https" URI scheme is hereby defined for the purpose of minting The "https" URI scheme is hereby defined for minting identifiers
identifiers according to their association with the hierarchical within the hierarchical namespace governed by a potential origin
namespace governed by a potential HTTP origin server listening to a server listening for TCP connections on a given port and capable of
given TCP port for TLS-secured connections ([RFC5246]). establishing a TLS ([RFC8446]) connection that has been secured for
HTTP communication. In this context, _secured_ specifically means
that the server has been authenticated as acting on behalf of the
identified authority and all HTTP communication with that server has
been protected for confidentiality and integrity through the use of
strong encryption.
https-URI = "https:" "//" authority path-abempty [ "?" query ] https-URI = "https" "://" authority path-abempty [ "?" query ]
[ "#" fragment ]
All of the requirements listed above for the "http" scheme are also The origin server for an "https" URI is identified by the authority
requirements for the "https" scheme, except that TCP port 443 is the component, which includes a host identifier and optional port number
default if the port subcomponent is empty or not given, and the user ([RFC3986], Section 3.2.2). If the port subcomponent is empty or not
agent MUST ensure that its connection to the origin server is secured given, TCP port 443 (the reserved port for HTTP over TLS) is the
through the use of strong encryption, end-to-end, prior to sending default. The origin determines who has the right to respond
the first HTTP request. authoritatively to requests that target the identified resource, as
defined in Section 4.3.3.
Note that the "https" URI scheme depends on both TLS and TCP for A sender MUST NOT generate an "https" URI with an empty host
establishing authority. identifier. A recipient that processes such a URI reference MUST
reject it as invalid.
The process for authoritative access to an "https" identified The hierarchical path component and optional query component identify
resource is defined in [RFC2818]. the target resource within that origin server's name space.
A client MUST ensure that its HTTP requests for an "https" resource
are secured, prior to being communicated, and that it only accepts
secured responses to those requests.
Resources made available via the "https" scheme have no shared Resources made available via the "https" scheme have no shared
identity with the "http" scheme even if their resource identifiers identity with the "http" scheme. They are distinct origins with
indicate the same authority (the same host listening to the same TCP separate namespaces. However, an extension to HTTP that is defined
port). They are distinct namespaces and are considered to be distinct to apply to all origins with the same host, such as the Cookie
origin servers. However, an extension to HTTP that is defined
to apply to entire host domains, such as the Cookie
protocol [RFC6265], can allow information set by one service to protocol [RFC6265], can allow information set by one service to
impact communication with other services within a matching group of impact communication with other services within a matching group of
host domains. host domains.
4.2.3. http and https URI Normalization and Comparison 4.2.3. http(s) Normalization and Comparison
Since the "http" and "https" schemes conform to the URI generic Since the "http" and "https" schemes conform to the URI generic
syntax, such URIs are normalized and compared according to the syntax, such URIs are normalized and compared according to the
algorithm defined in Section 6 of [RFC3986], using the defaults algorithm defined in Section 6 of [RFC3986], using the defaults
described above for each scheme. described above for each scheme.
If the port is equal to the default port for a scheme, the normal If the port is equal to the default port for a scheme, the normal
form is to omit the port subcomponent. When not being used in form is to omit the port subcomponent. When not being used as the
absolute form as the request target of an OPTIONS request, an empty target of an OPTIONS request, an empty path component is equivalent
path component is equivalent to an absolute path of "/", so the to an absolute path of "/", so the normal form is to provide a path
normal form is to provide a path of "/" instead. The scheme and host of "/" instead. The scheme and host are case-insensitive and
are case-insensitive and normally provided in lowercase; all other normally provided in lowercase; all other components are compared in
components are compared in a case-sensitive manner. Characters other a case-sensitive manner. Characters other than those in the
than those in the "reserved" set are equivalent to their "reserved" set are equivalent to their percent-encoded octets: the
percent-encoded octets: the normal form is to not encode them (see normal form is to not encode them (see Sections 2.1 and 2.2 of
Sections 2.1 and 2.2 of [RFC3986]). [RFC3986]).
For example, the following three URIs are equivalent: For example, the following three URIs are equivalent:
http://example.com:80/~smith/home.html http://example.com:80/~smith/home.html
http://EXAMPLE.com/%7Esmith/home.html http://EXAMPLE.com/%7Esmith/home.html
http://EXAMPLE.com:/%7esmith/home.html http://EXAMPLE.com:/%7esmith/home.html
4.2.4. Deprecated userinfo 4.2.4. Deprecation of userinfo in http(s) URIs
The URI generic syntax for authority also includes a deprecated The URI generic syntax for authority also includes a userinfo
userinfo subcomponent ([RFC3986], Section 3.2.1) for including user subcomponent ([RFC3986], Section 3.2.1) for including user
authentication information in the URI. authentication information in the URI. In that subcomponent, the use
of the format "user:password" is deprecated.
Some implementations make use of the userinfo component for internal Some implementations make use of the userinfo component for internal
configuration of authentication information, such as within command configuration of authentication information, such as within command
invocation options, configuration files, or bookmark lists, even invocation options, configuration files, or bookmark lists, even
though such usage might expose a user identifier or password. though such usage might expose a user identifier or password.
A sender MUST NOT generate the userinfo subcomponent (and its "@" A sender MUST NOT generate the userinfo subcomponent (and its "@"
delimiter) when an "http" URI reference is generated delimiter) when an "http" or "https" URI reference is generated
within a message as a request target or header field value. within a message as a target URI or field value.
Before making use of an "http" URI reference received from Before making use of an "http" or "https" URI reference received from
an untrusted source, a recipient SHOULD parse for userinfo and treat an untrusted source, a recipient SHOULD parse for userinfo and treat
its presence as an error; it is likely being used to obscure the its presence as an error; it is likely being used to obscure the
authority for the sake of phishing attacks. authority for the sake of phishing attacks.
4.2.5. Fragment Identifiers on http(s) URI References 4.2.5. http(s) References with Fragment Identifiers
The optional fragment component allows for indirect identification of a Fragment identifiers allow for indirect identification of a secondary
secondary resource, independent of the URI scheme, as defined in Section resource, independent of the URI scheme, as defined in Section 3.5 of
3.5 of [RFC3986]. [RFC3986]. Some protocol elements that refer to a URI allow
inclusion of a fragment, while others do not. They are distinguished
by use of the ABNF rule for elements where fragment is allowed;
otherwise, a specific rule that excludes fragments is used.
[new] | *Note:* The fragment identifier component is not part of the
| scheme definition for a URI scheme (see Section 4.3 of
| [RFC3986]), thus does not appear in the ABNF definitions for
| the "http" and "https" URI schemes above.
4.3. Authoritative Access 4.3. Authoritative Access
[new] Authoritative access refers to dereferencing a given identifier, for
the sake of access to the identified resource, in a way that the
client believes is authoritative (controlled by the resource owner).
The process for determining that access is defined by the URI scheme
and often uses data within the URI components, such as the authority
component when the generic syntax is used. However, authoritative
access is not limited to the identified mechanism.
[new] Section 4.3.1 defines the concept of an origin as an aid to such
uses, and the subsequent subsections explain how to establish a
peer's association with an authority to represent an origin.
See Section 9.1 for security considerations related to establishing See Section 17.1 for security considerations related to establishing
authority. authority.
4.3.1. URI Origin 4.3.1. URI Origin
[new] The _origin_ for a given URI is the triple of scheme, host, and port
after normalizing the scheme and host to lowercase and normalizing
the port to remove any leading zeros. If port is elided from the
URI, the default port for that scheme is used. For example, the URI
[new] https://Example.Com/happy.js
[new] would have the origin
[new] { "https", "example.com", "443" }
[new] which can also be described as the normalized URI prefix with port
always present:
[new] https://example.com:443
[new] Each origin defines its own namespace and controls how identifiers
within that namespace are mapped to resources. In turn, how the
origin responds to valid requests, consistently over time, determines
the semantics that users will associate with a URI, and the
usefulness of those semantics is what ultimately transforms these
mechanisms into a "resource" for users to reference and access in the
future.
[new] Two origins are distinct if they differ in scheme, host, or port.
Even when it can be verified that the same entity controls two
distinct origins, the two namespaces under those origins are distinct
unless explicitly aliased by a server authoritative for that origin.
Origin is also used within HTML and related Web protocols, beyond the
scope of this document, as described in [RFC6454].
4.3.2. http origins 4.3.2. http origins
Although HTTP is independent of the transport protocol, the "http" Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation scheme (Section 4.2.1) is specific to associating authority with
process depends on TCP for establishing authority. An HTTP service whomever controls the origin server listening for TCP connections on
based on some other underlying connection protocol would presumably the indicated port of whatever host is identified within the
be identified using a different URI scheme, just as the "https" authority component. This is a very weak sense of authority because
scheme (below) is used for resources that require an end-to-end it depends on both client-specific name resolution mechanisms and
secured connection. Other protocols might also be used to provide communication that might not be secured from an on-path attacker.
access to "http" identified resources -- it is only the authoritative Nevertheless, it is a sufficient minimum for binding "http"
interface that is specific to TCP. identifiers to an origin server for consistent resolution within a
trusted environment.
If the host identifier is provided as an IP address, the origin If the host identifier is provided as an IP address, the origin
server is the listener (if any) on the indicated TCP port at that IP server is the listener (if any) on the indicated TCP port at that IP
address. If host is a registered name, the registered name is an address. If host is a registered name, the registered name is an
indirect identifier for use with a name resolution service, such as indirect identifier for use with a name resolution service, such as
DNS, to find an address for that origin server. DNS, to find an address for an appropriate origin server.
When an "http" URI is used within a context that calls for access to When an "http" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the the indicated resource, a client MAY attempt access by resolving the
host to an IP address, establishing a TCP connection to that address host identifier to an IP address, establishing a TCP connection to
on the indicated port, and sending an HTTP request message that address on the indicated port, and sending an HTTP request
(Section 3) containing the URI's identifying data (Section 5) to the message to the server containing the URI's identifying data.
server.
If the server responds to that request with a non-interim HTTP If the server responds to such a request with a non-interim HTTP
response message, as described in Section 6 of [RFC7231], then that response response message, as described in Section 15, then that response is
is
considered an authoritative answer to the client's request. considered an authoritative answer to the client's request.
[new] Note, however, that the above is not the only means for obtaining an
authoritative response, nor does it imply that an authoritative
response is always necessary (see [Caching]). For example, the Alt-
Svc header field [RFC7838] allows an origin server to identify other
services that are also authoritative for that origin. Access to
"http" identified resources might also be provided by protocols
outside the scope of this document.
4.3.3. https origins 4.3.3. https origins
[new] The "https" scheme (Section 4.2.2) associates authority based on the
ability of a server to use the private key corresponding to a
certificate that the client considers to be trustworthy for the
identified origin server. The client usually relies upon a chain of
trust, conveyed from some prearranged or configured trust anchor, to
deem a certificate trustworthy (Section 4.3.4).
[new] In HTTP/1.1 and earlier, a client will only attribute authority to a
server when they are communicating over a successfully established
and secured connection specifically to that URI origin's host. The
connection establishment and certificate verification are used as
proof of authority.
[new] In HTTP/2 and HTTP/3, a client will attribute authority to a server
when they are communicating over a successfully established and
secured connection if the URI origin's host matches any of the hosts
present in the server's certificate and the client believes that it
could open a connection to that host for that URI. In practice, a
client will make a DNS query to check that the origin's host contains
the same server IP address as the established connection. This
restriction can be removed by the origin server sending an equivalent
ORIGIN frame [RFC8336].
[new] The request target's host and port value are passed within each HTTP
request, identifying the origin and distinguishing it from other
namespaces that might be controlled by the same server (Section 7.2).
It is the origin's responsibility to ensure that any services
provided with control over its certificate's private key are equally
responsible for managing the corresponding "https" namespaces, or at
least prepared to reject requests that appear to have been
misdirected. A server might be unwilling to serve as the origin for
some hosts even when they have the authority to do so.
[new] For example, if a network attacker causes connections for port N to
be received at port Q, checking the target URI is necessary to ensure
that the attacker can't cause "https://example.com:N/foo" to be
replaced by "https://example.com:Q/foo" without consent.
[new] Note that the "https" scheme does not rely on TCP and the connected
port number for associating authority, since both are outside the
secured communication and thus cannot be trusted as definitive.
Hence, the HTTP communication might take place over any channel that
has been secured, as defined in Section 4.2.2, including protocols
that don't use TCP.
[new] When an "https" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the
host identifier to an IP address, establishing a TCP connection to
that address on the indicated port, securing the connection end-to-
end by successfully initiating TLS over TCP with confidentiality and
integrity protection, and sending an HTTP request message over that
connection containing the URI's identifying data.
[new] If the server responds to such a request with a non-interim HTTP
response message, as described in Section 15, then that response is
considered an authoritative answer to the client's request.
[new] Note, however, that the above is not the only means for obtaining an
authoritative response, nor does it imply that an authoritative
response is always necessary (see [Caching]).
4.3.4. https certificate verification 4.3.4. https certificate verification
In general, HTTP/TLS requests are generated by dereferencing a URI. To establish a secured connection to dereference a URI, a client MUST
As a consequence, the hostname for the server is known to the client. verify that the service's identity is an acceptable match for the
If the hostname is available, the client MUST check it against the URI's origin server. Certificate verification is used to prevent
server's identity as presented in the server's Certificate message, server impersonation by an on-path attacker or by an attacker that
in order to prevent man-in-the-middle attacks. controls name resolution. This process requires that a client be
If a subjectAltName extension of type dNSName is present, that MUST configured with a set of trust anchors.
be used as the identity. Otherwise, the (most specific) Common Name
field in the Subject field of the certificate MUST be used. Although
the use of the Common Name is existing practice, it is deprecated and
Certification Authorities are encouraged to use the dNSName instead.
Matching is performed using the matching rules specified by In general, a client MUST verify the service identity using the
[RFC2459]. If more than one identity of a given type is present in verification process defined in Section 6 of [RFC6125] (for a
the certificate (e.g., more than one dNSName name, a match in any one reference identifier of type URI-ID) unless the client has been
of the set is considered acceptable.) Names may contain the wildcard specifically configured to accept some other form of verification.
character * which is considered to match any single domain name For example, a client might be connecting to a server whose address
component or component fragment. E.g., *.a.com matches foo.a.com but and hostname are dynamic, with an expectation that the service will
not bar.foo.a.com. f*.com matches foo.com but not bar.com. present a specific certificate (or a certificate matching some
In some cases, the URI is specified as an IP address rather than a externally defined reference identity) rather than one matching the
hostname. In this case, the iPAddress subjectAltName must be present dynamic URI's origin server identifier.
in the certificate and must exactly match the IP in the URI.
If the client has external information as to the expected identity of
the server, the hostname check MAY be omitted.
(For instance, a client may be connecting to a machine whose address
and hostname are dynamic but the client knows the certificate that
the server will present.) In such cases, it is important to narrow
the scope of acceptable certificates as much as possible in order
to prevent man in the middle attacks.
In special cases, it may be appropriate for the client to simply In special cases, it might be appropriate for a client to simply
ignore the server's identity, but it must be understood that this ignore the server's identity, but it must be understood that this
leaves the connection open to active attack. leaves a connection open to active attack.
If the hostname does not match the identity in the certificate, user If the certificate is not valid for the URI's origin server, a user
oriented clients MUST either notify the user (clients MAY give the agent MUST either notify the user (user agents MAY give the user an
user the opportunity to continue with the connection in any case) or option to continue with the connection in any case) or terminate the
terminate the connection with a bad certificate error. Automated connection with a bad certificate error. Automated clients MUST log
clients MUST log the error to an appropriate audit log (if available) the error to an appropriate audit log (if available) and SHOULD
and SHOULD terminate the connection (with a bad certificate error). terminate the connection (with a bad certificate error). Automated
Automated clients MAY provide a configuration setting that disables clients MAY provide a configuration setting that disables this check,
this check, but MUST provide a setting which enables it. but MUST provide a setting which enables it.
Note that in many cases the URI itself comes from an untrusted
source. The above-described check provides no protection against
attacks where this source is compromised. For example, if the URI was
obtained by clicking on an HTML page which was itself obtained
without using HTTP/TLS, a man in the middle could have replaced the
URI. In order to prevent this form of attack, users should carefully
examine the certificate presented by the server to determine if it
meets their expectations.
*3.2. Client Identity [paras squished together to anchor context]*
Typically, the server has no external knowledge of what the client's
identity ought to be and so checks (other than that the client has a
certificate chain rooted in an appropriate CA) are not possible. If a
server has such knowledge (typically from some source external to
HTTP or TLS) it SHOULD check the identity as described above.
5. Fields 5. Fields
Header fields are key:value pairs that can be used to communicate HTTP uses _fields_ to provide data in the form of extensible key/
data about the message, its payload, the target resource, or the value pairs with a registered key namespace. Fields are sent and
connection (i.e., control data). See Section 3.2 of [RFC7230] for a received within the header and trailer sections of messages
general definition of header field syntax in HTTP messages. (Section 6).
5.1. Field Names 5.1. Field Names
The field-name token labels the corresponding field-value as having A field name labels the corresponding field value as having the
the semantics defined by that header field. For example, the Date semantics defined by that name. For example, the Date header field
header field is defined in Section 7.1.1.2 of [RFC7231] as containing is defined in Section 10.2.2 as containing the origination timestamp
the origination timestamp for the message in which it appears. for the message in which it appears.
field-name = token field-name = token
The requirements for header field names are defined in [BCP90]. Field names are case-insensitive and ought to be registered within
the "Hypertext Transfer Protocol (HTTP) Field Name Registry"; see
Section 16.3.1.
The interpretation of a header field does not change between minor versions The interpretation of a field does not change between minor versions
of the same major HTTP version, though the default behavior of a of the same major HTTP version, though the default behavior of a
recipient in the absence of such a field can change. Unless recipient in the absence of such a field can change. Unless
specified otherwise, header fields defined in HTTP/1.1 are defined specified otherwise, fields are defined for all versions of HTTP. In
for all versions of HTTP/1.x. In particular, the Host and Connection fields ought to be recognized by
particular, the Host and Connection header fields ought to be implemented by all HTTP implementations whether or not they advertise conformance
all HTTP/1.x implementations whether or not they advertise conformance
with HTTP/1.1. with HTTP/1.1.
New header fields can be introduced without changing the protocol version if New fields can be introduced without changing the protocol version if
their defined semantics allow them to be safely ignored by recipients their defined semantics allow them to be safely ignored by recipients
that do not recognize them. Header field extensibility is that do not recognize them; see Section 16.3.
discussed in Section 3.2.1.
A proxy MUST forward unrecognized header fields unless the field-name A proxy MUST forward unrecognized header fields unless the field name
is listed in the Connection header field (Section 6.1) or the proxy is listed in the Connection header field (Section 7.6.1) or the proxy
is specifically configured to block, or otherwise transform, such is specifically configured to block, or otherwise transform, such
fields. Other recipients SHOULD ignore unrecognized header fields. fields. Other recipients SHOULD ignore unrecognized header and
These requirements allow HTTP's functionality to be enhanced without trailer fields. Adhering to these requirements allows HTTP's
requiring prior update of deployed intermediaries. functionality to be extended without updating or removing deployed
intermediaries.
5.2. Field Lines and Combined Field Value
Field sections are composed of any number of _field lines_, each with
a _field name_ (see Section 5.1) identifying the field, and a _field
line value_ that conveys data for that instance of the field.
When a field name is only present once in a section, the combined
_field value_ for that field consists of the corresponding field line
value. When a field name is repeated within a section, its combined
field value consists of the list of corresponding field line values
within that section, concatenated in order, with each non-empty field
line value separated by a comma.
For example, this section:
Example-Field: Foo, Bar
Example-Field: Baz
contains two field lines, both with the field name "Example-Field".
The first field line has a field line value of "Foo, Bar", while the
second field line value is "Baz". The field value for "Example-
Field" is a list with three members: "Foo", "Bar", and "Baz".
5.3. Field Order 5.3. Field Order
A recipient MAY combine multiple header fields with the same field A recipient MAY combine multiple field lines within a field section
name into one "field-name: field-value" pair, without changing the that have the same field name into one field line, without changing
semantics of the message, by appending each subsequent field value to the semantics of the message, by appending each subsequent field line
the combined field value in order, separated by a comma. value to the initial field line value in order, separated by a comma
and OWS (optional whitespace). For consistency, use comma SP.
The order in which header fields with the same field name are received is The order in which field lines with the same name are received is
therefore significant to the interpretation of the combined field value; a therefore significant to the interpretation of the field value; a
proxy MUST NOT change the order of these field values when proxy MUST NOT change the order of these field line values when
forwarding a message. forwarding a message.
A sender MUST NOT generate multiple header fields with the same field This means that, aside from the well-known exception noted below, a
name in a message unless either the entire field value for that sender MUST NOT generate multiple field lines with the same name in a
header field is defined as a comma-separated list [i.e., #(values)] message (whether in the headers or trailers), or append a field line
or the header field is a well-known exception (as noted below). when a field line of the same name already exists in the message,
unless that field's definition allows multiple field line values to
be recombined as a comma-separated list [i.e., at least one
alternative of the field's definition allows a comma-separated list,
such as an ABNF rule of #(values) defined in Section 5.6.1].
Note: In practice, the "Set-Cookie" header field ([RFC6265]) often | *Note:* In practice, the "Set-Cookie" header field ([RFC6265])
appears multiple times in a response message and does not use the | often appears in a response message across multiple field lines
list syntax, violating the above requirements on multiple header | and does not use the list syntax, violating the above
fields with the same name. Since it cannot be combined into a | requirements on multiple field lines with the same field name.
single field-value, recipients ought to handle "Set-Cookie" as a | Since it cannot be combined into a single field value,
special case while processing header fields. (See Appendix A.2.3 | recipients ought to handle "Set-Cookie" as a special case while
of [Kri2001] for details.) | processing fields. (See Appendix A.2.3 of [Kri2001] for
| details.)
The order in which header fields with differing field names are The order in which field lines with differing field names are
received is not significant. However, it is good practice to send received in a section is not significant. However, it is good
header fields that contain control data first, such as Host on practice to send header fields that contain additional control data
requests and Date on responses, so that implementations can decide first, such as Host on requests and Date on responses, so that
when not to handle a message as early as possible. implementations can decide when not to handle a message as early as
possible.
A server MUST NOT apply a request to the target resource until the A server MUST NOT apply a request to the target resource until the
entire request header section is received, since later header fields entire request header section is received, since later header field
might include conditionals, authentication credentials, or lines might include conditionals, authentication credentials, or
deliberately misleading duplicate header fields that would impact deliberately misleading duplicate header fields that would impact
request processing. request processing.
5.4. Field Limits 5.4. Field Limits
HTTP does not place a predefined limit on the length of each header HTTP does not place a predefined limit on the length of each field
field or on the length of the header section as a whole, as described line, field value, or on the length of a header or trailer section as
in Section 2.5. Various ad hoc limitations on individual header a whole, as described in Section 2. Various ad hoc limitations on
field length are found in practice, often depending on the specific individual lengths are found in practice, often depending on the
field semantics. specific field's semantics.
A server that receives a request header field, or set of fields, A server that receives a request header field line, field value, or
larger than it wishes to process MUST respond with an appropriate 4xx set of fields larger than it wishes to process MUST respond with an
(Client Error) status code. Ignoring such header fields would appropriate 4xx (Client Error) status code. Ignoring such header
increase the server's vulnerability to request smuggling attacks fields would increase the server's vulnerability to request smuggling
(Section 9.5). attacks (Section 11.2 of [Messaging]).
A client MAY discard or truncate received header fields that are A client MAY discard or truncate received field lines that are larger
larger than the client wishes to process if the field semantics are than the client wishes to process if the field semantics are such
such that the dropped value(s) can be safely ignored without changing that the dropped value(s) can be safely ignored without changing the
the message framing or response semantics. message framing or response semantics.
5.5. Field Values 5.5. Field Values
New header field values typically have their syntax defined using HTTP field values typically have their syntax defined using ABNF
ABNF ([RFC5234]), using the extension defined in Section 7 of ([RFC5234]), using the extension defined in Section 5.6.1 as
[RFC7230] as necessary, and are usually constrained to the range of necessary, and are usually constrained to the range of US-ASCII
US-ASCII characters. Header fields needing a greater range of characters. Fields needing a greater range of characters can use an
characters can use an encoding such as the one defined in [RFC5987]. encoding such as the one defined in [RFC8187].
field-value = *( field-content / obs-fold ) field-value = *field-content
field-content = field-vchar [ 1*( SP / HTAB ) field-vchar ] field-content = field-vchar
[ 1*( SP / HTAB / field-vchar ) field-vchar ]
field-vchar = VCHAR / obs-text field-vchar = VCHAR / obs-text
Historically, HTTP has allowed field content with text in the Historically, HTTP allowed field content with text in the ISO-8859-1
ISO-8859-1 charset [ISO-8859-1], supporting other charsets only charset [ISO-8859-1], supporting other charsets only through use of
through use of [RFC2047] encoding. In practice, most HTTP header [RFC2047] encoding. In practice, most HTTP field values use only a
field values use only a subset of the US-ASCII charset [USASCII]. subset of the US-ASCII charset [USASCII]. Newly defined fields
Newly defined header fields SHOULD limit their field values to SHOULD limit their values to US-ASCII octets. A recipient SHOULD
US-ASCII octets. A recipient SHOULD treat other octets in field treat other octets in field content (obs-text) as opaque data.
content (obs-text) as opaque data.
Field values containing control (CTL) characters such as CR or LF are
invalid; recipients MUST either reject a field value containing
control characters, or convert them to SP before processing or
forwarding the message.
Leading and trailing whitespace in raw field values is removed upon Leading and trailing whitespace in raw field values is removed upon
field parsing (Section 3.2.4 of [RFC7230]). Field definitions where field parsing (e.g., Section 5.1 of [Messaging]). Field definitions
leading or trailing whitespace in values is significant will have to where leading or trailing whitespace in values is significant will
use a container syntax such as quoted-string (Section 3.2.6 of have to use a container syntax such as quoted-string (Section 5.6.4).
[RFC7230]).
[new] Commas (",") often are used to separate members in field values.
Fields that allow multiple members are referred to as _list-based
fields_. Fields that only anticipate a single member are referred to
as _singleton fields_.
Because commas (",") are used as a generic delimiter between Because commas are used as a generic delimiter between members, they
field-values, they need to be treated with care if they are allowed need to be treated with care if they are allowed as data within a
in the field-value. Typically, components that might contain a comma member. This is true for both list-based and singleton fields, since
are protected with double-quotes using the quoted-string ABNF a singleton field might be sent with multiple members erroneously;
production. being able to detect this condition improves interoperability.
Fields that expect to contain a comma within a member, such as an
HTTP-date or URI-reference element, ought to be defined with
delimiters around that element to distinguish any comma within that
data from potential list separators.
For example, a textual date and a URI (either of which might contain For example, a textual date and a URI (either of which might contain
a comma) could be safely carried in field-values like these: a comma) could be safely carried in list-based field values like
these:
Example-URI-Field: "http://example.com/a.html,foo", Example-URI-Field: "http://example.com/a.html,foo",
"http://without-a-comma.example.com/" "http://without-a-comma.example.com/"
Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005" Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
Note that double-quote delimiters almost always are used with the Note that double-quote delimiters almost always are used with the
quoted-string production; using a different syntax inside quoted-string production; using a different syntax inside double-
double-quotes will likely cause unnecessary confusion. quotes will likely cause unnecessary confusion.
Many header fields use a format including (case-insensitively) named Many fields (such as Content-Type, defined in Section 8.3) use a
parameters (for instance, Content-Type, defined in Section 3.1.1.5). common syntax for parameters that allows both unquoted (token) and
Allowing both unquoted (token) and quoted (quoted-string) syntax for quoted (quoted-string) syntax for a parameter value (Section 5.6.6).
the parameter value enables recipients to use existing parser Use of common syntax allows recipients to reuse existing parser
components. When allowing both forms, the meaning of a parameter components. When allowing both forms, the meaning of a parameter
value ought to be independent of the syntax used for it (for an value ought to be the same whether it was received as a token or a
example, see the notes on parameter handling for media types in quoted string.
Section 3.1.1.1).
Historically, HTTP header field values could be extended over Historically, HTTP field values could be extended over multiple lines
multiple lines by preceding each extra line with at least one space by preceding each extra line with at least one space or horizontal
or horizontal tab (obs-fold). tab (obs-fold). This document assumes that any such obsolete line
folding has been replaced with one or more SP octets prior to
interpreting the field value, as described in Section 5.2 of
[Messaging].
Consequently, this specification does not use ABNF rules | *Note:* This specification does not use ABNF rules to define
to define each "Field-Name: Field Value" pair, as was done in | each "Field Name: Field Value" pair, as was done in earlier
previous editions. Instead, this specification uses ABNF rules that | editions (published before [RFC7230]). Instead, ABNF rules are
are named according to each registered field name, wherein the rule | named according to each registered field name, wherein the rule
defines the valid grammar for that field's corresponding field values | defines the valid grammar for that field's corresponding field
(i.e., after the field-value has been extracted from the header | values (i.e., after the field value has been extracted by a
section by a generic field parser). | generic field parser).
5.6. Field Value Components 5.6. Common Rules for Defining Field Values
5.6.1. ABNF List Extension: #rule 5.6.1. Lists (#rule ABNF Extension)
A #rule extension to the ABNF rules of [RFC5234] is used to improve A #rule extension to the ABNF rules of [RFC5234] is used to improve
readability in the definitions of some header field values. readability in the definitions of some list-based field values.
A construct "#" is defined, similar to "*", for defining A construct "#" is defined, similar to "*", for defining comma-
comma-delimited lists of elements. The full form is "<n>#<m>element" delimited lists of elements. The full form is "<n>#<m>element"
indicating at least <n> and at most <m> elements, each separated by a indicating at least <n> and at most <m> elements, each separated by a
single comma (",") and optional whitespace (OWS). single comma (",") and optional whitespace (OWS).
5.6.1.1. Sender Requirements 5.6.1.1. Sender Requirements
In any production that uses the list construct, a sender MUST NOT In any production that uses the list construct, a sender MUST NOT
generate empty list elements. In other words, a sender MUST generate generate empty list elements. In other words, a sender MUST generate
lists that satisfy the following syntax: lists that satisfy the following syntax:
1#element => element *( OWS "," OWS element ) 1#element => element *( OWS "," OWS element )
and: and:
#element => [ 1#element ] #element => [ 1#element ]
and for n >= 1 and m > 1: and for n >= 1 and m > 1:
<n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element ) <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
Appendix B shows the collected ABNF for recipients after the list Appendix A shows the collected ABNF for senders after the list
constructs have been expanded. constructs have been expanded.
5.6.1.2. Recipient Requirements 5.6.1.2. Recipient Requirements
For compatibility with legacy list rules, a Empty elements do not contribute to the count of elements present. A
recipient MUST parse and ignore a reasonable number of empty list recipient MUST parse and ignore a reasonable number of empty list
elements: enough to handle common mistakes by senders that merge elements: enough to handle common mistakes by senders that merge
values, but not so much that they could be used as a denial-of- values, but not so much that they could be used as a denial-of-
service mechanism. In other words, a recipient MUST accept lists service mechanism. In other words, a recipient MUST accept lists
that satisfy the following syntax: that satisfy the following syntax:
#element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ] #element => [ element ] *( OWS "," OWS [ element ] )
1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
Empty elements do not contribute to the count of elements present. Note that because of the potential presence of empty list elements,
the RFC 5234 ABNF cannot enforce the cardinality of list elements,
and consequently all cases are mapped as if there was no cardinality
specified.
For example, given these ABNF productions: For example, given these ABNF productions:
example-list = 1#example-list-elmt example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 3.2.6 example-list-elmt = token ; see Section 5.6.2
Then the following are valid values for example-list (not including Then the following are valid values for example-list (not including
the double quotes, which are present for delimitation only): the double quotes, which are present for delimitation only):
"foo,bar" "foo,bar"
"foo ,bar," "foo ,bar,"
"foo , ,bar,charlie " "foo , ,bar,charlie"
In contrast, the following values would be invalid, since at least In contrast, the following values would be invalid, since at least
one non-empty element is required by the example-list production: one non-empty element is required by the example-list production:
"" ""
"," ","
", ," ", ,"
5.6.2. Tokens 5.6.2. Tokens
Most HTTP header field values are defined using common syntax Many HTTP field values are defined using common syntax components,
components (token, quoted-string, and comment) separated by separated by whitespace or specific delimiting characters.
whitespace or specific delimiting characters. Delimiters are chosen Delimiters are chosen from the set of US-ASCII visual characters not
from the set of US-ASCII visual characters not allowed in a token allowed in a token (DQUOTE and "(),/:;<=>?@[\]{}").
(DQUOTE and "(),/:;<=>?@[\]{}").
Tokens are short textual identifiers that do not include whitespace
or delimiters.
token = 1*tchar token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA / DIGIT / ALPHA
; any VCHAR, except delimiters ; any VCHAR, except delimiters
5.6.3. Whitespace 5.6.3. Whitespace
skipping to change at line 1347 skipping to change at page 37, line 9
might appear. For protocol elements where optional whitespace is might appear. For protocol elements where optional whitespace is
preferred to improve readability, a sender SHOULD generate the preferred to improve readability, a sender SHOULD generate the
optional whitespace as a single SP; otherwise, a sender SHOULD NOT optional whitespace as a single SP; otherwise, a sender SHOULD NOT
generate optional whitespace except as needed to white out invalid or generate optional whitespace except as needed to white out invalid or
unwanted protocol elements during in-place message filtering. unwanted protocol elements during in-place message filtering.
The RWS rule is used when at least one linear whitespace octet is The RWS rule is used when at least one linear whitespace octet is
required to separate field tokens. A sender SHOULD generate RWS as a required to separate field tokens. A sender SHOULD generate RWS as a
single SP. single SP.
OWS and RWS have the same semantics as a single SP. Any content
known to be defined as OWS or RWS MAY be replaced with a single SP
before interpreting it or forwarding the message downstream.
The BWS rule is used where the grammar allows optional whitespace The BWS rule is used where the grammar allows optional whitespace
only for historical reasons. A sender MUST NOT generate BWS in only for historical reasons. A sender MUST NOT generate BWS in
messages. A recipient MUST parse for such bad whitespace and remove messages. A recipient MUST parse for such bad whitespace and remove
it before interpreting the protocol element. it before interpreting the protocol element.
BWS has no semantics. Any content known to be defined as BWS MAY be
removed before interpreting it or forwarding the message downstream.
OWS = *( SP / HTAB ) OWS = *( SP / HTAB )
; optional whitespace ; optional whitespace
RWS = 1*( SP / HTAB ) RWS = 1*( SP / HTAB )
; required whitespace ; required whitespace
BWS = OWS BWS = OWS
; "bad" whitespace ; "bad" whitespace
5.6.4. Quoted Strings 5.6.4. Quoted Strings
A string of text is parsed as a single value if it is quoted using A string of text is parsed as a single value if it is quoted using
double-quote marks. double-quote marks.
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = HTAB / SP /%x21 / %x23-5B / %x5D-7E / obs-text qdtext = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
obs-text = %x80-FF obs-text = %x80-FF
The backslash octet ("\") can be used as a single-octet quoting The backslash octet ("\") can be used as a single-octet quoting
mechanism within quoted-string and comment constructs. Recipients mechanism within quoted-string and comment constructs. Recipients
that process the value of a quoted-string MUST handle a quoted-pair that process the value of a quoted-string MUST handle a quoted-pair
as if it were replaced by the octet following the backslash. as if it were replaced by the octet following the backslash.
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text ) quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
A sender SHOULD NOT generate a quoted-pair in a quoted-string except A sender SHOULD NOT generate a quoted-pair in a quoted-string except
where necessary to quote DQUOTE and backslash octets occurring within where necessary to quote DQUOTE and backslash octets occurring within
that string. A sender SHOULD NOT generate a quoted-pair in a comment that string. A sender SHOULD NOT generate a quoted-pair in a comment
except where necessary to quote parentheses ["(" and ")"] and except where necessary to quote parentheses ["(" and ")"] and
backslash octets occurring within that comment. backslash octets occurring within that comment.
5.6.5. Comments 5.6.5. Comments
Comments can be included in some HTTP header fields by surrounding Comments can be included in some HTTP fields by surrounding the
the comment text with parentheses. Comments are only allowed in comment text with parentheses. Comments are only allowed in fields
fields containing "comment" as part of their field value definition. containing "comment" as part of their field value definition.
comment = "(" *( ctext / quoted-pair / comment ) ")" comment = "(" *( ctext / quoted-pair / comment ) ")"
ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text
5.6.6. Parameters 5.6.6. Parameters
[new] Parameters are instances of name=value pairs; they are often used in
field values as a common syntax for appending auxiliary information
to an item. Each parameter is usually delimited by an immediately
preceding semicolon.
parameter = token "=" ( token / quoted-string ) parameters = *( OWS ";" OWS [ parameter ] )
parameter = parameter-name "=" parameter-value
parameter-name = token
parameter-value = ( token / quoted-string )
The parameter name tokens are case-insensitive. Parameter names are case-insensitive. Parameter values might or
Parameter values might or might not be case-sensitive, depending on might not be case-sensitive, depending on the semantics of the
the semantics of the parameter name. parameter name. Examples of parameters and some equivalent forms can
be seen in media types (Section 8.3.1) and the Accept header field
(Section 12.5.1).
A parameter value that matches the token production can be A parameter value that matches the token production can be
transmitted either as a token or within a quoted-string. The quoted transmitted either as a token or within a quoted-string. The quoted
and unquoted values are equivalent. and unquoted values are equivalent.
Note: Unlike some similar constructs in other header fields, media | *Note:* Parameters do not allow whitespace (not even "bad"
type parameters do not allow whitespace (even "bad" whitespace) | whitespace) around the "=" character.
around the "=" character.
5.6.7. Date/Time Formats 5.6.7. Date/Time Formats
Prior to 1995, there were three different formats commonly used by Prior to 1995, there were three different formats commonly used by
servers to communicate timestamps. For compatibility with old servers to communicate timestamps. For compatibility with old
implementations, all three are defined here. The preferred format is implementations, all three are defined here. The preferred format is
a fixed-length and single-zone subset of the date and time a fixed-length and single-zone subset of the date and time
specification used by the Internet Message Format [RFC5322]. specification used by the Internet Message Format [RFC5322].
HTTP-date = IMF-fixdate / obs-date HTTP-date = IMF-fixdate / obs-date
An example of the preferred format is An example of the preferred format is
Sun, 06 Nov 1994 08:49:37 GMT ; IMF-fixdate Sun, 06 Nov 1994 08:49:37 GMT ; IMF-fixdate
Examples of the two obsolete formats are Examples of the two obsolete formats are
Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
A recipient that parses a timestamp value in an HTTP header field A recipient that parses a timestamp value in an HTTP field MUST
MUST accept all three HTTP-date formats. When a sender generates a accept all three HTTP-date formats. When a sender generates a field
header field that contains one or more timestamps defined as that contains one or more timestamps defined as HTTP-date, the sender
HTTP-date, the sender MUST generate those timestamps in the MUST generate those timestamps in the IMF-fixdate format.
IMF-fixdate format.
An HTTP-date value represents time as an instance of Coordinated An HTTP-date value represents time as an instance of Coordinated
Universal Time (UTC). The first two formats indicate UTC by the Universal Time (UTC). The first two formats indicate UTC by the
three-letter abbreviation for Greenwich Mean Time, "GMT", a three-letter abbreviation for Greenwich Mean Time, "GMT", a
predecessor of the UTC name; values in the asctime format are assumed predecessor of the UTC name; values in the asctime format are assumed
to be in UTC. A sender that generates HTTP-date values from a local to be in UTC. A sender that generates HTTP-date values from a local
clock ought to use NTP ([RFC5905]) or some similar protocol to clock ought to use NTP ([RFC5905]) or some similar protocol to
synchronize its clock to UTC. synchronize its clock to UTC.
Preferred format: Preferred format:
IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT
; fixed length/zone/capitalization subset of the format ; fixed length/zone/capitalization subset of the format
; see Section 3.3 of [RFC5322] ; see Section 3.3 of [RFC5322]
day-name = %x4D.6F.6E ; "Mon", case-sensitive day-name = %s"Mon" / %s"Tue" / %s"Wed"
/ %x54.75.65 ; "Tue", case-sensitive / %s"Thu" / %s"Fri" / %s"Sat" / %s"Sun"
/ %x57.65.64 ; "Wed", case-sensitive
/ %x54.68.75 ; "Thu", case-sensitive
/ %x46.72.69 ; "Fri", case-sensitive
/ %x53.61.74 ; "Sat", case-sensitive
/ %x53.75.6E ; "Sun", case-sensitive
date1 = day SP month SP year date1 = day SP month SP year
; e.g., 02 Jun 1982 ; e.g., 02 Jun 1982
day = 2DIGIT day = 2DIGIT
month = %x4A.61.6E ; "Jan", case-sensitive month = %s"Jan" / %s"Feb" / %s"Mar" / %s"Apr"
/ %x46.65.62 ; "Feb", case-sensitive / %s"May" / %s"Jun" / %s"Jul" / %s"Aug"
/ %x4D.61.72 ; "Mar", case-sensitive / %s"Sep" / %s"Oct" / %s"Nov" / %s"Dec"
/ %x41.70.72 ; "Apr", case-sensitive
/ %x4D.61.79 ; "May", case-sensitive
/ %x4A.75.6E ; "Jun", case-sensitive
/ %x4A.75.6C ; "Jul", case-sensitive
/ %x41.75.67 ; "Aug", case-sensitive
/ %x53.65.70 ; "Sep", case-sensitive
/ %x4F.63.74 ; "Oct", case-sensitive
/ %x4E.6F.76 ; "Nov", case-sensitive
/ %x44.65.63 ; "Dec", case-sensitive
year = 4DIGIT year = 4DIGIT
GMT = %x47.4D.54 ; "GMT", case-sensitive GMT = %s"GMT"
time-of-day = hour ":" minute ":" second time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:60 (leap second) ; 00:00:00 - 23:59:60 (leap second)
hour = 2DIGIT hour = 2DIGIT
minute = 2DIGIT minute = 2DIGIT
second = 2DIGIT second = 2DIGIT
Obsolete formats: Obsolete formats:
skipping to change at line 1485 skipping to change at page 40, line 4
time-of-day = hour ":" minute ":" second time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:60 (leap second) ; 00:00:00 - 23:59:60 (leap second)
hour = 2DIGIT hour = 2DIGIT
minute = 2DIGIT minute = 2DIGIT
second = 2DIGIT second = 2DIGIT
Obsolete formats: Obsolete formats:
obs-date = rfc850-date / asctime-date obs-date = rfc850-date / asctime-date
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
date2 = day "-" month "-" 2DIGIT date2 = day "-" month "-" 2DIGIT
; e.g., 02-Jun-82 ; e.g., 02-Jun-82
day-name-l = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive day-name-l = %s"Monday" / %s"Tuesday" / %s"Wednesday"
/ %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive / %s"Thursday" / %s"Friday" / %s"Saturday"
/ %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive / %s"Sunday"
/ %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
/ %x46.72.69.64.61.79 ; "Friday", case-sensitive
/ %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
/ %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
asctime-date = day-name SP date3 SP time-of-day SP year asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT )) date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; e.g., Jun 2 ; e.g., Jun 2
HTTP-date is case sensitive. A sender MUST NOT generate additional HTTP-date is case sensitive. Note that Section 4.2 of [Caching]
whitespace in an HTTP-date beyond that specifically included as SP in relaxes this for cache recipients.
the grammar. The semantics of day-name, day, month, year, and
time-of-day are the same as those defined for the Internet Message A sender MUST NOT generate additional whitespace in an HTTP-date
Format constructs with the corresponding name ([RFC5322], Section beyond that specifically included as SP in the grammar. The
3.3). semantics of day-name, day, month, year, and time-of-day are the same
as those defined for the Internet Message Format constructs with the
corresponding name ([RFC5322], Section 3.3).
Recipients of a timestamp value in rfc850-date format, which uses a Recipients of a timestamp value in rfc850-date format, which uses a
two-digit year, MUST interpret a timestamp that appears to be more two-digit year, MUST interpret a timestamp that appears to be more
than 50 years in the future as representing the most recent year in than 50 years in the future as representing the most recent year in
the past that had the same last two digits. the past that had the same last two digits.
Recipients of timestamp values are encouraged to be robust in parsing Recipients of timestamp values are encouraged to be robust in parsing
timestamps unless otherwise restricted by the field definition. For timestamps unless otherwise restricted by the field definition. For
example, messages are occasionally forwarded over HTTP from a example, messages are occasionally forwarded over HTTP from a non-
non-HTTP source that might generate any of the date and time HTTP source that might generate any of the date and time
specifications defined by the Internet Message Format. specifications defined by the Internet Message Format.
Note: HTTP requirements for the date/time stamp format apply only | *Note:* HTTP requirements for the date/time stamp format apply
to their usage within the protocol stream. Implementations are | only to their usage within the protocol stream.
not required to use these formats for user presentation, request | Implementations are not required to use these formats for user
logging, etc. | presentation, request logging, etc.
6. Message Abstraction 6. Message Abstraction
[new] Each major version of HTTP defines its own syntax for communicating
messages. This section defines an abstract data type for HTTP
messages based on a generalization of those message characteristics,
common structure, and capacity for conveying semantics. This
abstraction is used to define requirements on senders and recipients
that are independent of the HTTP version, such that a message in one
version can be relayed through other versions without changing its
meaning.
A _message_ consists of control data to describe and route the
message, a headers lookup table of key/value pairs for extending that
control data and conveying additional information about the sender,
message, content, or context, a potentially unbounded stream of
content, and a trailers lookup table of key/value pairs for
communicating information obtained while sending the content.
Framing and control data is sent first, followed by a header section
containing fields for the headers table. When a message includes
content, the content is sent after the header section and potentially
interleaved with zero or more trailer sections containing fields for
the trailers table.
Messages are expected to be processed as a stream, wherein the
purpose of that stream and its continued processing is revealed while
being read. Hence, control data describes what the recipient needs
to know immediately, header fields describe what needs to be known
before receiving content, the content (when present) presumably
contains what the recipient wants or needs to fulfill the message
semantics, and trailer fields provide additional metadata that can be
dropped (safely ignored) when not desired.
Messages are intended to be _self-descriptive_: everything a
recipient needs to know about the message can be determined by
looking at the message itself, after decoding or reconstituting parts
that have been compressed or elided in transit, without requiring an
understanding of the sender's current application state (established
via prior messages).
Note that this message abstraction is a generalization across many
versions of HTTP, including features that might not be found in some
versions. For example, trailers were introduced within the HTTP/1.1
chunked transfer coding as a single trailer section after the
content. An equivalent feature is present in HTTP/2 and HTTP/3
within the header block that terminates each stream. However,
multiple trailer sections interleaved with content have only been
deployed as frame extensions.
6.1. Framing and Completeness 6.1. Framing and Completeness
[new] Message framing indicates how each message begins and ends, such that
each message can be distinguished from other messages or noise on the
same connection. Each major version of HTTP defines its own framing
mechanism.
[new] HTTP/0.9 and early deployments of HTTP/1.0 used closure of the
underlying connection to end a response. For backwards
compatibility, this implicit framing is also allowed in HTTP/1.1.
However, implicit framing can fail to distinguish an incomplete
response if the connection closes early. For that reason, almost all
modern implementations use explicit framing in the form of length-
delimited sequences of message data.
A message is considered _complete_ when all of the octets indicated
by its framing are available. Note that, when no explicit framing is
used, a response message that is ended by the underlying connection's
close is considered complete even though it might be
indistinguishable from an incomplete response, unless a transport-
level error indicates that it is not complete.
6.2. Control Data 6.2. Control Data
HTTP communication is initiated by a user agent for some purpose. Messages start with control data that describe its primary purpose.
The purpose is a combination of request semantics, which are defined Request message control data includes a request method (Section 9),
in [RFC7231], and a target resource upon which to apply those request target (Section 7.1), and protocol version (Section 2.5).
semantics. Response message control data includes a status code (Section 15),
optional reason phrase, and protocol version.
In HTTP/1.1 [Messaging] and earlier, control data is sent as the
first line of a message. In HTTP/2 ([RFC7540]) and HTTP/3 ([HTTP3]),
control data is sent as pseudo-header fields with a reserved name
prefix (e.g., ":authority").
Every HTTP message has a protocol version. Depending on the version
in use, it might be identified within the message explicitly or
inferred by the connection over which the message is received.
Recipients use that version information to determine limitations or
potential for later communication with that sender.
When a message is forwarded by an intermediary, the protocol version
is updated to reflect the version used by that intermediary. The Via
header field (Section 7.6.3) is used to communicate upstream protocol
information within a forwarded message.
A client SHOULD send a request version equal to the highest version A client SHOULD send a request version equal to the highest version
to which the client is conformant and whose major version is no to which the client is conformant and whose major version is no
higher than the highest version supported by the server, if this is higher than the highest version supported by the server, if this is
known. A client MUST NOT send a version to which it is not known. A client MUST NOT send a version to which it is not
conformant. conformant.
A client MAY send a lower request version if it is known that the A client MAY send a lower request version if it is known that the
server incorrectly implements the HTTP specification, but only after server incorrectly implements the HTTP specification, but only after
the client has attempted at least one normal request and determined the client has attempted at least one normal request and determined
skipping to change at line 1573 skipping to change at page 43, line 24
recipient implements, the recipient SHOULD process the message as if recipient implements, the recipient SHOULD process the message as if
it were in the highest minor version within that major version to it were in the highest minor version within that major version to
which the recipient is conformant. A recipient can assume that a which the recipient is conformant. A recipient can assume that a
message with a higher minor version, when sent to a recipient that message with a higher minor version, when sent to a recipient that
has not yet indicated support for that higher version, is has not yet indicated support for that higher version, is
sufficiently backwards-compatible to be safely processed by any sufficiently backwards-compatible to be safely processed by any
implementation of the same major version. implementation of the same major version.
6.3. Header Fields 6.3. Header Fields
[new] Fields (Section 5) that are sent/received before the content are
referred to as "header fields" (or just "headers", colloquially).
The _header section_ of a message consists of a sequence of of header
field lines. Each header field might modify or extend message
semantics, describe the sender, define the content, or provide
additional context.
| *Note:* We refer to named fields specifically as a "header
| field" when they are only allowed to be sent in the header
| section.
6.4. Content 6.4. Content
Some HTTP messages transfer a complete or partial representation as HTTP messages often transfer a complete or partial representation as
the message "payload". In some cases, a payload might contain only the message _content_: a stream of octets sent after the header
the associated representation's header fields (e.g., responses to section, as delineated by the message framing.
HEAD) or only some part(s) of the representation data (e.g., the 206
(Partial Content) status code).
[new] This abstract definition of content reflects the data after it has
been extracted from the message framing. For example, an HTTP/1.1
message body (Section 6 of [Messaging]) might consist of a stream of
data encoded with the chunked transfer coding - a sequence of data
chunks, one zero-length chunk, and a trailer section - whereas the
content of that same message includes only the data stream after the
transfer coding has been decoded; it does not include the chunk
lengths, chunked framing syntax, nor the trailer fields
(Section 6.5).
6.4.1. Content Semantics 6.4.1. Content Semantics
The purpose of a payload in a request is defined by the method The purpose of content in a request is defined by the method
semantics. semantics (Section 9).
For example, a representation in the payload of a PUT request For example, a representation in the content of a PUT request
(Section 4.3.4) represents the desired state of the target resource (Section 9.3.4) represents the desired state of the target resource
if the request is successfully applied, whereas a representation after the request is successfully applied, whereas a representation
in the payload of a POST request (Section 4.3.3) represents in the content of a POST request (Section 9.3.3) represents
information to be processed by the target resource. information to be processed by the target resource.
In a response, the payload's purpose is defined by both the request In a response, the content's purpose is defined by both the request
method and the response status code. For example, the payload of a method and the response status code (Section 15). For example, the
200 (OK) response to GET (Section 4.3.1) represents the current state content of a 200 (OK) response to GET (Section 9.3.1) represents the
of the target resource, as observed at the time of the message current state of the target resource, as observed at the time of the
origination date (Section 7.1.1.2), whereas the payload of the same message origination date (Section 10.2.2), whereas the content of the
status code in a response to POST might represent either the same status code in a response to POST might represent either the
processing result or the new state of the target resource after processing result or the new state of the target resource after
applying the processing. applying the processing.
Response messages with an error status code usually contain a payload The content of a 206 (Partial Content) response to GET contains
that represents the error condition, such that it describes either a single part of the selected representation or a multipart
the error state and what next steps are suggested for resolving it. message body containing multiple parts of that representation, as
described in Section 15.3.7.
Responses to the HEAD request method (Section 4.3.2 Response messages with an error status code usually contain content
of [RFC7231]) never include a message body because the associated that represents the error condition, such that the content describes
response header fields (e.g., Transfer-Encoding, Content-Length, the error state and what steps are suggested for resolving it.
etc.), if present, indicate only what their values would have been if
the request method had been GET (Section 4.3.1 of [RFC7231]). Responses to the HEAD request method (Section 9.3.2) never include
content; the associated response header fields indicate only what
their values would have been if the request method had been GET
(Section 9.3.1).
2xx (Successful) responses to a CONNECT request method 2xx (Successful) responses to a CONNECT request method
(Section 4.3.6 of [RFC7231]) switch to tunnel mode instead of (Section 9.3.6) switch the connection to tunnel mode instead of
having a message body. having content.
All 1xx (Informational), 204 (No Content), and 304 (Not Modified) All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
responses do not include a message body. responses do not include content.
All other responses do include a message body, although the body All other responses do include content, although that content might
might be of zero length. be of zero length.
6.4.2. Identifying Content 6.4.2. Identifying Content
When a complete or partial representation is transferred in a message When a complete or partial representation is transferred as message
payload, it is often desirable for the sender to supply, or the content, it is often desirable for the sender to supply, or the
recipient to determine, an identifier for a resource corresponding to recipient to determine, an identifier for a resource corresponding to
that representation. that representation.
For a request message: For a request message:
o If the request has a Content-Location header field, then the o If the request has a Content-Location header field, then the
sender asserts that the payload is a representation of the sender asserts that the content is a representation of the
resource identified by the Content-Location field-value. However, resource identified by the Content-Location field value. However,
such an assertion cannot be trusted unless it can be verified by such an assertion cannot be trusted unless it can be verified by
other means (not defined by this specification). The information other means (not defined by this specification). The information
might still be useful for revision history links. might still be useful for revision history links.
o Otherwise, the payload is unidentified. o Otherwise, the content is unidentified.
For a response message, the following rules are applied in order For a response message, the following rules are applied in order
until a match is found: until a match is found:
1. If the request method is GET or HEAD and the response status code 1. If the request method is HEAD or the response status code is 204
is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not (No Content) or 304 (Not Modified), there is no content in the
Modified), the payload is a representation of the resource response.
identified by the effective request URI (Section 5.5 of
[RFC7230]).
2. If the request method is GET or HEAD and the response status code 2. If the request method is GET and the response status code is 200
is 203 (Non-Authoritative Information), the payload is a potentially (OK), the content is a representation of the resource identified
by the target URI (Section 7.1).
3. If the request method is GET and the response status code is 203
(Non-Authoritative Information), the content is a potentially
modified or enhanced representation of the target resource as modified or enhanced representation of the target resource as
provided by an intermediary. provided by an intermediary.
3. If the response has a Content-Location header field and its 4. If the request method is GET and the response status code is 206
field-value is a reference to the same URI as the effective (Partial Content), the content is one or more parts of a
request URI, the payload is a representation of the resource representation of the resource identified by the target URI
identified by the effective request URI. (Section 7.1).
4. If the response has a Content-Location header field and its 5. If the response has a Content-Location header field and its field
field-value is a reference to a URI different from the effective value is a reference to the same URI as the target URI, the
request URI, then the sender asserts that the content is a representation of the target resource.
payload is a representation of the resource identified by the
Content-Location field-value. 6. If the response has a Content-Location header field and its field
value is a reference to a URI different from the target URI, then
the sender asserts that the content is a representation of the
resource identified by the Content-Location field value.
However, such an assertion cannot be trusted unless it can be However, such an assertion cannot be trusted unless it can be
verified by other means (not defined by this specification). verified by other means (not defined by this specification).
5. Otherwise, the payload is unidentified. 7. Otherwise, the content is unidentified.
6.4.3. Payload Metadata
Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing.
6.5. Trailer Fields 6.5. Trailer Fields
A trailer allows the sender to include additional fields at the end Fields (Section 5) that are sent/received after the header section
of a chunked message in order to supply metadata that might be has ended (usually after the content begins to stream) are referred
dynamically generated while the message body is sent, such as a to as "trailer fields" (or just "trailers", colloquially) and located
message integrity check, digital signature, or post-processing within a _trailer section_. Trailer fields can be useful for
status. The trailer fields are identical to header fields, except supplying message integrity checks, digital signatures, delivery
they are sent in a chunked trailer instead of the message's header metrics, or post-processing status information.
section.
Trailer fields ought to be processed and stored separately from the
fields in the header section to avoid contradicting message semantics
known at the time the header section was complete. The presence or
absence of certain header fields might impact choices made for the
routing or processing of the message as a whole before the trailers
are received; those choices cannot be unmade by the later discovery
of trailer fields.
6.5.1. Limitations on use of Trailers 6.5.1. Limitations on use of Trailers
A sender MUST NOT generate a trailer that contains a field necessary Trailer sections are only possible when supported by the version of
for message framing (e.g., Transfer-Encoding and Content-Length), HTTP in use and enabled by an explicit framing mechanism. For
routing (e.g., Host), request modifiers (e.g., controls and example, the chunked coding in HTTP/1.1 allows a trailer section to
conditionals in Section 5 of [RFC7231]), authentication (e.g., see be sent after the content (Section 7.1.2 of [Messaging]).
[RFC7235] and [RFC6265]), response control data (e.g., see Section
7.1 of [RFC7231]), or determining how to process the payload (e.g.,
Content-Encoding, Content-Type, Content-Range, and Trailer).
When a chunked message containing a non-empty trailer is received, Many fields cannot be processed outside the header section because
the recipient MAY process the fields (aside from those forbidden their evaluation is necessary prior to receiving the content, such as
above) as if they were appended to the message's header section. A those that describe message framing, routing, authentication, request
recipient MUST ignore (or consider as an error) any fields that are modifiers, response controls, or content format. A sender MUST NOT
forbidden to be sent in a trailer, since processing them as if they generate a trailer field unless the sender knows the corresponding
were present in the header section might bypass external security header field name's definition permits the field to be sent in
filters. trailers.
[new] Trailer fields can be difficult to process by intermediaries that
forward messages from one protocol version to another. If the entire
message can be buffered in transit, some intermediaries could merge
trailer fields into the header section (as appropriate) before it is
forwarded. However, in most cases, the trailers are simply
discarded. A recipient MUST NOT merge a trailer field into a header
section unless the recipient understands the corresponding header
field definition and that definition explicitly permits and defines
how trailer field values can be safely merged.
[new] The presence of the keyword "trailers" in the TE header field
(Section 10.1.4) indicates that the client is willing to accept
trailer fields, on behalf of itself and any downstream clients. For
requests from an intermediary, this implies that all downstream
clients are willing to accept trailer fields in the forwarded
response. Note that the presence of "trailers" does not mean that
the client(s) will process any particular trailer field in the
response; only that the trailer section(s) will not be dropped by any
of the clients.
Unless the request includes a TE header field indicating "trailers" Because of the potential for trailer fields to be discarded in
is acceptable, as described in Section 4.3, a server SHOULD NOT transit, a server SHOULD NOT generate trailer fields that it believes
generate trailer fields that it believes are necessary for the user are necessary for the user agent to receive.
agent to receive. Without a TE containing "trailers", the server
ought to assume that the trailer fields might be silently discarded
along the path to the user agent. This requirement allows
intermediaries to forward a de-chunked message to an HTTP/1.0
recipient without buffering the entire response.
6.5.2. Processing Trailer Fields 6.5.2. Processing Trailer Fields
[new] Like header fields, trailer fields with the same name are processed
in the order received; multiple trailer field lines with the same
name have the equivalent semantics as appending the multiple values
as a list of members, even when the field lines are received in
separate trailer sections. Trailer fields that might be generated
more than once during a message MUST be defined as a list-based field
even if each member value is only processed once per field line
received.
[new] Trailer fields are expected (but not required) to be processed one
trailer section at a time. That is, for each trailer section
received, a recipient that is looking for trailer fields will parse
the received section into fields, invoke any associated processing
for those fields at that point in the message processing, and then
append those fields to the set of trailer fields received for the
overall message.
[new] This behavior allows for iterative processing of trailer fields that
contain incremental signatures or mid-stream status information, and
fields that might refer to each other's values within the same
section. However, there is no guarantee that trailer sections won't
shift in relation to the content stream, or won't be recombined (or
dropped) in transit. Trailer fields that refer to data outside the
present trailer section need to use self-descriptive references
(i.e., refer to the data by name, ordinal position, or an octet
range) rather than assume it is the data most recently received.
[new] Likewise, at the end of a message, a recipient MAY treat the entire
set of received trailer fields as one data structure to be considered
as the message concludes. Additional processing expectations, if
any, can be defined within the field specification for a field
intended for use in trailers.
7. Routing HTTP Messages 7. Routing HTTP Messages
HTTP request message routing is determined by each client based on HTTP request message routing is determined by each client based on
the target resource, the client's proxy configuration, and the target resource, the client's proxy configuration, and
establishment or reuse of an inbound connection. The corresponding establishment or reuse of an inbound connection. The corresponding
response routing follows the same connection chain back to the response routing follows the same connection chain back to the
client. client.
7.1. Determining the Target Resource 7.1. Determining the Target Resource
HTTP is used in a wide variety of applications, ranging from Although HTTP is used in a wide variety of applications, most clients
general-purpose computers to home appliances. In some cases, rely on the same resource identification mechanism and configuration
communication options are hard-coded in a client's configuration. techniques as general-purpose Web browsers. Even when communication
However, most HTTP clients rely on the same resource identification options are hard-coded in a client's configuration, we can think of
mechanism and configuration techniques as general-purpose Web their combined effect as a URI reference (Section 4.1).
browsers.
A URI reference (Section 2.7) is typically used as an A URI reference is resolved to its absolute form in order to obtain
identifier for the "target resource", which a user agent would the _target URI_. The target URI excludes the reference's fragment
resolve to its absolute form in order to obtain the "target URI". component, if any, since fragment identifiers are reserved for
The target URI excludes the reference's fragment component, if any, client-side processing ([RFC3986], Section 3.5).
since fragment identifiers are reserved for client-side processing
([RFC3986], Section 3.5).
[new] To perform an action on a _target resource_, the client sends a
request message containing enough components of its parsed target URI
to enable recipients to identify that same resource. For historical
reasons, the parsed target URI components, collectively referred to
as the _request target_, are sent within the message control data and
the Host header field (Section 7.2).
6.1.3. Reconstructing the Target URI There are two unusual cases for which the request target components
are in a method-specific form:
Once an inbound connection is obtained, the client sends an HTTP o For CONNECT (Section 9.3.6), the request target is the host name
request message (Section 3) with a request-target derived from the and port number of the tunnel destination, separated by a colon.
target URI.
Since the request-target often contains only part of the user agent's o For OPTIONS (Section 9.3.7), the request target can be a single
target URI, a server reconstructs the intended target as an asterisk ("*").
"effective request URI" to properly service the request. This
reconstruction involves both the server's local configuration and
information communicated in the request-target, Host header field,
and connection context.
For a user agent, the effective request URI is the target URI. See the respective method definitions for details. These forms MUST
NOT be used with other methods.
Once the effective request URI has been constructed, an origin server Upon receipt of a client's request, a server reconstructs the target
needs to decide whether or not to provide service for that URI via URI from the received components in accordance with their local
the connection in which the request was received. For example, the configuration and incoming connection context. This reconstruction
request might have been misdirected, deliberately or accidentally, is specific to each major protocol version. For example, Appendix of
such that the information within a received request-target or Host [Messaging] defines how a server determines the target URI of an
header field differs from the host or port upon which the connection HTTP/1.1 request.
has been made. If the connection is from a trusted gateway, that
inconsistency might be expected; otherwise, it might indicate an | *Note:* Previous specifications defined the recomposed target
attempt to bypass security filters, trick the server into delivering | URI as a distinct concept, the _effective request URI_.
non-public content, or poison a cache. See Section 9 for security
considerations regarding message routing.
7.2. Host and :authority 7.2. Host and :authority
The "Host" header field in a request provides the host and port The "Host" header field in a request provides the host and port
information from the target URI, enabling the origin server to information from the target URI, enabling the origin server to
distinguish among resources while servicing requests for multiple distinguish among resources while servicing requests for multiple
host names on a single IP address. host names.
[new] In HTTP/2 [RFC7540] and HTTP/3 [HTTP3], the Host header field is, in
some cases, supplanted by the ":authority" pseudo-header field of a
request's control data.
Host = uri-host [ ":" port ] ; Section 2.7.1 Host = uri-host [ ":" port ] ; Section 4
Since the Host field-value is critical information for handling a The target URI's authority information is critical for handling a
request, a user agent SHOULD generate Host as the first header field request. A user agent SHOULD generate Host as the first field in the
following the request-line. header section of a request unless it has already generated that
information as an ":authority" pseudo-header field.
For example, a GET request to the origin server for For example, a GET request to the origin server for
<http://www.example.org/pub/WWW/> would begin with: <http://www.example.org/pub/WWW/> would begin with:
GET /pub/WWW/ HTTP/1.1 GET /pub/WWW/ HTTP/1.1
Host: www.example.org Host: www.example.org
Since the Host header field acts as an application-level routing Since the host and port information acts as an application-level
mechanism, it is a frequent target for malware seeking to poison a routing mechanism, it is a frequent target for malware seeking to
shared cache or redirect a request to an unintended server. An poison a shared cache or redirect a request to an unintended server.
interception proxy is particularly vulnerable if it relies on the An interception proxy is particularly vulnerable if it relies on the
Host field-value for redirecting requests to internal servers, or for host and port information for redirecting requests to internal
use as a cache key in a shared cache, without first verifying that servers, or for use as a cache key in a shared cache, without first
the intercepted connection is targeting a valid IP address for that verifying that the intercepted connection is targeting a valid IP
host. address for that host.
7.3. Routing Inbound 7.3. Routing Inbound Requests
Once the target URI is determined, a client needs to decide whether a Once the target URI and its origin are determined, a client decides
network request is necessary to accomplish the desired semantics and, whether a network request is necessary to accomplish the desired
if so, where that request is to be directed. semantics and, if so, where that request is to be directed.
If the client has a cache [RFC7234] and the request can be satisfied 7.3.1. To a Cache
If the client has a cache [Caching] and the request can be satisfied
by it, then the request is usually directed there first. by it, then the request is usually directed there first.
7.3.2. To a Proxy
If the request is not satisfied by a cache, then a typical client If the request is not satisfied by a cache, then a typical client
will check its configuration to determine whether a proxy is to be will check its configuration to determine whether a proxy is to be
used to satisfy the request. Proxy configuration is implementation- used to satisfy the request. Proxy configuration is implementation-
dependent, but is often based on URI prefix matching, selective dependent, but is often based on URI prefix matching, selective
authority matching, or both, and the proxy itself is usually authority matching, or both, and the proxy itself is usually
identified by an "http" or "https" URI. If a proxy is applicable, identified by an "http" or "https" URI. If a proxy is applicable,
the client connects inbound by establishing (or reusing) a connection the client connects inbound by establishing (or reusing) a connection
to that proxy. to that proxy.
7.3.3. To the Origin
If no proxy is applicable, a typical client will invoke a handler If no proxy is applicable, a typical client will invoke a handler
routine, usually specific to the target URI's scheme, to connect routine, usually specific to the target URI's scheme, to connect
directly to an authority for the target resource. How that is directly to an origin for the target resource. How that is
accomplished is dependent on the target URI scheme and defined by its accomplished is dependent on the target URI scheme and defined by its
associated specification, similar to how this specification defines associated specification.
origin server access for resolution of the "http" (Section 2.7.1) and
"https" (Section 2.7.2) schemes.
HTTP requirements regarding connection management are defined in
Section 6.
7.4. Rejecting Misdirected Requests 7.4. Rejecting Misdirected Requests
[new] Before performing a request, a server decides whether or not to
provide service for the target URI via the connection in which the
request is received. For example, a request might have been
misdirected, deliberately or accidentally, such that the information
within a received Host header field differs from the connection's
host or port.
[new] If the connection is from a trusted gateway, such inconsistency might
be expected; otherwise, it might indicate an attempt to bypass
security filters, trick the server into delivering non-public
content, or poison a cache. See Section 17 for security
considerations regarding message routing.
[new] The 421 (Misdirected Request) status code in a response indicates
that the origin server has rejected the request because it appears to
have been misdirected (Section 15.5.20).
7.5. Response Correlation 7.5. Response Correlation
[new] A connection might be used for multiple request/response exchanges.
The mechanism used to correlate between request and response messages
is version dependent; some versions of HTTP use implicit ordering of
messages, while others use an explicit identifier.
[new] Responses (both final and interim) can be sent at any time after a
request is received, even if it is not yet complete. However,
clients (including intermediaries) might abandon a request if the
response is not forthcoming within a reasonable period of time.
7.6. Message Forwarding 7.6. Message Forwarding
As described in Section 2.3, intermediaries can serve a variety of As described in Section 3.7, intermediaries can serve a variety of
roles in the processing of HTTP requests and responses. Some roles in the processing of HTTP requests and responses. Some
intermediaries are used to improve performance or availability. intermediaries are used to improve performance or availability.
Others are used for access control or to filter content. Since an Others are used for access control or to filter content. Since an
HTTP stream has characteristics similar to a pipe-and-filter HTTP stream has characteristics similar to a pipe-and-filter
architecture, there are no inherent limits to the extent an architecture, there are no inherent limits to the extent an
intermediary can enhance (or interfere) with either direction of the intermediary can enhance (or interfere) with either direction of the
stream. stream.
An intermediary not acting as a tunnel MUST implement the Connection An intermediary not acting as a tunnel MUST implement the Connection
header field, as specified in Section 6.1, and exclude fields from header field, as specified in Section 7.6.1, and exclude fields from
being forwarded that are only intended for the incoming connection. being forwarded that are only intended for the incoming connection.
An intermediary MUST NOT forward a message to itself unless it is An intermediary MUST NOT forward a message to itself unless it is
protected from an infinite request loop. In general, an intermediary protected from an infinite request loop. In general, an intermediary
ought to recognize its own server names, including any aliases, local ought to recognize its own server names, including any aliases, local
variations, or literal IP addresses, and respond to such requests variations, or literal IP addresses, and respond to such requests
directly. directly.
An HTTP message can be parsed as a stream for incremental processing An HTTP message can be parsed as a stream for incremental processing
or forwarding downstream. However, recipients cannot rely on or forwarding downstream. However, recipients cannot rely on
incremental delivery of partial messages, since some implementations incremental delivery of partial messages, since some implementations
will buffer or delay message forwarding for the sake of network will buffer or delay message forwarding for the sake of network
efficiency, security checks, or payload transformations. efficiency, security checks, or content transformations.
7.6.1. Connection 7.6.1. Connection
The "Connection" header field allows the sender to indicate desired The "Connection" header field allows the sender to list desired
control options for the current connection. In order to avoid control options for the current connection.
confusing downstream recipients, a proxy or gateway MUST remove or
replace any received connection options before forwarding the
message.
When a header field aside from Connection is used to supply control When a field aside from Connection is used to supply control
information for or about the current connection, the sender MUST list information for or about the current connection, the sender MUST list
the corresponding field-name within the Connection header field. the corresponding field name within the Connection header field.
Note that some versions of HTTP prohibit the use of fields for such
information, and therefore do not allow the Connection field.
A proxy or gateway MUST parse a received Connection header field before a Intermediaries MUST parse a received Connection header field before a
message is forwarded and, for each connection-option in this field, message is forwarded and, for each connection-option in this field,
remove any header field(s) from the message with the same remove any header or trailer field(s) from the message with the same
name as the connection-option, and then remove the Connection header name as the connection-option, and then remove the Connection header
field itself (or replace it with the intermediary's own connection field itself (or replace it with the intermediary's own connection
options for the forwarded message). options for the forwarded message).
Hence, the Connection header field provides a declarative way of Hence, the Connection header field provides a declarative way of
distinguishing header fields that are only intended for the immediate distinguishing fields that are only intended for the immediate
recipient ("hop-by-hop") from those fields that are intended for all recipient ("hop-by-hop") from those fields that are intended for all
recipients on the chain ("end-to-end"), enabling the message to be recipients on the chain ("end-to-end"), enabling the message to be
self-descriptive and allowing future connection-specific extensions self-descriptive and allowing future connection-specific extensions
to be deployed without fear that they will be blindly forwarded by to be deployed without fear that they will be blindly forwarded by
older intermediaries. older intermediaries.
[new] Furthermore, intermediaries SHOULD remove or replace field(s) whose
semantics are known to require removal before forwarding, whether or
not they appear as a Connection option, after applying those fields'
semantics. This includes but is not limited to:
[new] o Proxy-Connection (Appendix C.2.2 of [Messaging])
[new] o Keep-Alive (Section 19.7.1 of [RFC2068])
[new] o TE (Section 10.1.4)
[new] o Trailer (Section 10.1.5)
o Transfer-Encoding (Section 6.1 of [Messaging])
o Upgrade (Section 7.8)
The Connection header field's value has the following grammar: The Connection header field's value has the following grammar:
Connection = 1#connection-option Connection = #connection-option
connection-option = token connection-option = token
Connection options are case-insensitive. Connection options are case-insensitive.
A sender MUST NOT send a connection option corresponding to a header A sender MUST NOT send a connection option corresponding to a field
field that is intended for all recipients of the payload. For that is intended for all recipients of the content. For example,
example, Cache-Control is never appropriate as a connection option Cache-Control is never appropriate as a connection option
(Section 5.2 of [RFC7234]). (Section 5.2 of [Caching]).
The connection options do not always correspond to a header field The connection options do not always correspond to a field present in
present in the message, since a connection-specific header field the message, since a connection-specific field might not be needed if
might not be needed if there are no parameters associated with a there are no parameters associated with a connection option. In
connection option. In contrast, a connection-specific header field contrast, a connection-specific field that is received without a
that is received without a corresponding connection option usually corresponding connection option usually indicates that the field has
indicates that the field has been improperly forwarded by an been improperly forwarded by an intermediary and ought to be ignored
intermediary and ought to be ignored by the recipient. by the recipient.
When defining new connection options, specification authors ought to When defining new connection options, specification authors ought to
survey existing header field names and ensure that the new connection document it as reserved field name and register that definition in
option does not share the same name as an already deployed header the Hypertext Transfer Protocol (HTTP) Field Name Registry
field. Defining a new connection option essentially reserves that (Section 16.3.1), to avoid collisions.
potential field-name for carrying additional information related to
the connection option, since it would be unwise for senders to use
that field-name for anything else.
The "close" connection option is defined for a sender to signal that
this connection will be closed after completion of the response. For
example,
Connection: close
in either the request or the response header fields indicates that
the sender is going to close the connection after the current
request/response is complete (Section 6.6).
7.6.2. Max-Forwards 7.6.2. Max-Forwards
The "Max-Forwards" header field provides a mechanism with the TRACE The "Max-Forwards" header field provides a mechanism with the TRACE
(Section 4.3.8) and OPTIONS (Section 4.3.7) request methods to limit (Section 9.3.8) and OPTIONS (Section 9.3.7) request methods to limit
the number of times that the request is forwarded by proxies. This the number of times that the request is forwarded by proxies. This
can be useful when the client is attempting to trace a request that can be useful when the client is attempting to trace a request that
appears to be failing or looping mid-chain. appears to be failing or looping mid-chain.
Max-Forwards = 1*DIGIT Max-Forwards = 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded. number of times this request message can be forwarded.
Each intermediary that receives a TRACE or OPTIONS request containing Each intermediary that receives a TRACE or OPTIONS request containing
a Max-Forwards header field MUST check and update its value prior to a Max-Forwards header field MUST check and update its value prior to
forwarding the request. If the received value is zero (0), the forwarding the request. If the received value is zero (0), the
intermediary MUST NOT forward the request; instead, the intermediary intermediary MUST NOT forward the request; instead, the intermediary
MUST respond as the final recipient. If the received Max-Forwards MUST respond as the final recipient. If the received Max-Forwards
value is greater than zero, the intermediary MUST generate an updated value is greater than zero, the intermediary MUST generate an updated
Max-Forwards field in the forwarded message with a field-value that Max-Forwards field in the forwarded message with a field value that
is the lesser of a) the received value decremented by one (1) or b) is the lesser of a) the received value decremented by one (1) or b)
the recipient's maximum supported value for Max-Forwards. the recipient's maximum supported value for Max-Forwards.
A recipient MAY ignore a Max-Forwards header field received with any A recipient MAY ignore a Max-Forwards header field received with any
other request methods. other request methods.
7.6.3. Via 7.6.3. Via
The "Via" header field indicates the presence of intermediate The "Via" header field indicates the presence of intermediate
protocols and recipients between the user agent and the server (on protocols and recipients between the user agent and the server (on
requests) or between the origin server and the client (on responses), requests) or between the origin server and the client (on responses),
similar to the "Received" header field in email (Section 3.6.7 of similar to the "Received" header field in email (Section 3.6.7 of
[RFC5322]). Via can be used for tracking message forwards, avoiding [RFC5322]). Via can be used for tracking message forwards, avoiding
request loops, and identifying the protocol capabilities of senders request loops, and identifying the protocol capabilities of senders
along the request/response chain. along the request/response chain.
Via = 1#( received-protocol RWS received-by [ RWS comment ] ) Via = #( received-protocol RWS received-by [ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version received-protocol = [ protocol-name "/" ] protocol-version
; see Section 6.7 ; see Section 7.8
received-by = ( uri-host [ ":" port ] ) / pseudonym received-by = pseudonym [ ":" port ]
pseudonym = token pseudonym = token
Multiple Via field values represent each proxy or gateway that has Each member of the Via field value represents a proxy or gateway that
forwarded the message. Each intermediary appends its own information has forwarded the message. Each intermediary appends its own
about how the message was received, such that the end result is information about how the message was received, such that the end
ordered according to the sequence of forwarding recipients. result is ordered according to the sequence of forwarding recipients.
A proxy MUST send an appropriate Via header field, as described A proxy MUST send an appropriate Via header field, as described
below, in each message that it forwards. An HTTP-to-HTTP gateway below, in each message that it forwards. An HTTP-to-HTTP gateway
MUST send an appropriate Via header field in each inbound request MUST send an appropriate Via header field in each inbound request
message and MAY send a Via header field in forwarded response message and MAY send a Via header field in forwarded response
messages. messages.
For each intermediary, the received-protocol indicates the protocol For each intermediary, the received-protocol indicates the protocol
and protocol version used by the upstream sender of the message. and protocol version used by the upstream sender of the message.
Hence, the Via field value records the advertised protocol Hence, the Via field value records the advertised protocol
capabilities of the request/response chain such that they remain capabilities of the request/response chain such that they remain
visible to downstream recipients; this can be useful for determining visible to downstream recipients; this can be useful for determining
what backwards-incompatible features might be safe to use in what backwards-incompatible features might be safe to use in
response, or within a later request, as described in Section 2.6. response, or within a later request, as described in Section 2.5.
For brevity, the protocol-name is omitted when the received protocol For brevity, the protocol-name is omitted when the received protocol
is HTTP. is HTTP.
The received-by portion of the field value is normally the host and The received-by portion is normally the host and optional port number
optional port number of a recipient server or client that of a recipient server or client that subsequently forwarded the
subsequently forwarded the message. However, if the real host is message. However, if the real host is considered to be sensitive
considered to be sensitive information, a sender MAY replace it with information, a sender MAY replace it with a pseudonym. If a port is
a pseudonym. If a port is not provided, a recipient MAY interpret not provided, a recipient MAY interpret that as meaning it was
that as meaning it was received on the default TCP port, if any, for received on the default TCP port, if any, for the received-protocol.
the received-protocol.
A sender MAY generate comments in the Via header field to identify A sender MAY generate comments to identify the software of each
the software of each recipient, analogous to the User-Agent and recipient, analogous to the User-Agent and Server header fields.
Server header fields. However, all comments in the Via field are However, comments in Via are optional, and a recipient MAY remove
optional, and a recipient MAY remove them prior to forwarding the them prior to forwarding the message.
message.
For example, a request message could be sent from an HTTP/1.0 user For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which forward the request to a public proxy at p.example.net, which
completes the request by forwarding it to the origin server at completes the request by forwarding it to the origin server at
www.example.com. The request received by www.example.com would then www.example.com. The request received by www.example.com would then
have the following Via header field: have the following Via header field:
Via: 1.0 fred, 1.1 p.example.net Via: 1.0 fred, 1.1 p.example.net
An intermediary used as a portal through a network firewall SHOULD An intermediary used as a portal through a network firewall SHOULD
NOT forward the names and ports of hosts within the firewall region NOT forward the names and ports of hosts within the firewall region
unless it is explicitly enabled to do so. If not enabled, such an unless it is explicitly enabled to do so. If not enabled, such an
intermediary SHOULD replace each received-by host of any host behind intermediary SHOULD replace each received-by host of any host behind
the firewall by an appropriate pseudonym for that host. the firewall by an appropriate pseudonym for that host.
An intermediary MAY combine an ordered subsequence of Via header An intermediary MAY combine an ordered subsequence of Via header
field entries into a single such entry if the entries have identical field list members into a single member if the entries have identical
received-protocol values. For example, received-protocol values. For example,
Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
could be collapsed to could be collapsed to
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
A sender SHOULD NOT combine multiple entries unless they are all A sender SHOULD NOT combine multiple list members unless they are all
under the same organizational control and the hosts have already been under the same organizational control and the hosts have already been
replaced by pseudonyms. A sender MUST NOT combine entries that have replaced by pseudonyms. A sender MUST NOT combine members that have
different received-protocol values. different received-protocol values.
7.7. Message Transformations 7.7. Message Transformations
Some intermediaries include features for transforming messages and Some intermediaries include features for transforming messages and
their payloads. A proxy might, for example, convert between image their content. A proxy might, for example, convert between image
formats in order to save cache space or to reduce the amount of formats in order to save cache space or to reduce the amount of
traffic on a slow link. However, operational problems might occur traffic on a slow link. However, operational problems might occur
when these transformations are applied to payloads intended for when these transformations are applied to content intended for
critical applications, such as medical imaging or scientific data critical applications, such as medical imaging or scientific data
analysis, particularly when integrity checks or digital signatures analysis, particularly when integrity checks or digital signatures
are used to ensure that the payload received is identical to the are used to ensure that the content received is identical to the
original. original.
An HTTP-to-HTTP proxy is called a "transforming proxy" if it is An HTTP-to-HTTP proxy is called a _transforming proxy_ if it is
designed or configured to modify messages in a semantically designed or configured to modify messages in a semantically
meaningful way (i.e., modifications, beyond those required by normal meaningful way (i.e., modifications, beyond those required by normal
HTTP processing, that change the message in a way that would be HTTP processing, that change the message in a way that would be
significant to the original sender or potentially significant to significant to the original sender or potentially significant to
downstream recipients). For example, a transforming proxy might be downstream recipients). For example, a transforming proxy might be
acting as a shared annotation server (modifying responses to include acting as a shared annotation server (modifying responses to include
references to a local annotation database), a malware filter, a references to a local annotation database), a malware filter, a
format transcoder, or a privacy filter. Such transformations are format transcoder, or a privacy filter. Such transformations are
presumed to be desired by whichever client (or client organization) presumed to be desired by whichever client (or client organization)
selected the proxy. chose the proxy.
If a proxy receives a request-target with a host name that is not a If a proxy receives a target URI with a host name that is not a fully
fully qualified domain name, it MAY add its own domain to the host qualified domain name, it MAY add its own domain to the host name it
name it received when forwarding the request. A proxy MUST NOT received when forwarding the request. A proxy MUST NOT change the
change the host name if the request-target contains a fully qualified host name if the target URI contains a fully qualified domain name.
domain name.
A proxy MUST NOT modify the "absolute-path" and "query" parts of the A proxy MUST NOT modify the "absolute-path" and "query" parts of the
received request-target when forwarding it to the next inbound received target URI when forwarding it to the next inbound server,
server, except as noted above to replace an empty path with "/" or except as noted above to replace an empty path with "/" or "*".
"*".
A proxy MAY modify the message body through application or removal of
a transfer coding (Section 4).
A proxy MUST NOT transform the payload (Section 3.3 of [RFC7231]) of A proxy MUST NOT transform the content (Section 6.4) of a message
a message that contains a no-transform cache-control directive that contains a no-transform cache-control response directive
(Section 5.2 of [RFC7234]). (Section 5.2 of [Caching]). Note that this does not include changes
to the message body that do not affect the content, such as transfer
codings (Section 7 of [Messaging]).
A proxy MAY transform the payload of a message that does not contain A proxy MAY transform the content of a message that does not contain
a no-transform cache-control directive. A proxy that transforms a a no-transform cache-control directive. A proxy that transforms the
payload MUST add a Warning header field with the warn-code of 214 content of a 200 (OK) response can inform downstream recipients that
("Transformation Applied") if one is not already in the message (see a transformation has been applied by changing the response status
Section 5.5 of [RFC7234]). A proxy that transforms the payload of a code to 203 (Non-Authoritative Information) (Section 15.3.4).
200 (OK) response can further inform downstream recipients that a
transformation has been applied by changing the response status code
to 203 (Non-Authoritative Information) (Section 6.3.4 of [RFC7231]).
A proxy SHOULD NOT modify header fields that provide information A proxy SHOULD NOT modify header fields that provide information
about the endpoints of the communication chain, the resource state, about the endpoints of the communication chain, the resource state,
or the selected representation (other than the payload) unless the or the selected representation (other than the content) unless the
field's definition specifically allows such modification or the field's definition specifically allows such modification or the
modification is deemed necessary for privacy or security. modification is deemed necessary for privacy or security.
7.8. Upgrade 7.8. Upgrade
The "Upgrade" header field is intended to provide a simple mechanism The "Upgrade" header field is intended to provide a simple mechanism
for transitioning from HTTP/1.1 to some other protocol on the same for transitioning from HTTP/1.1 to some other protocol on the same
connection. A client MAY send a list of protocols in the Upgrade connection.
header field of a request to invite the server to switch to one or
more of those protocols, in order of descending preference, before A client MAY send a list of protocol names in the Upgrade header
field of a request to invite the server to switch to one or more of
the named protocols, in order of descending preference, before
sending the final response. A server MAY ignore a received Upgrade sending the final response. A server MAY ignore a received Upgrade
header field if it wishes to continue using the current protocol on header field if it wishes to continue using the current protocol on
that connection. Upgrade cannot be used to insist on a protocol that connection. Upgrade cannot be used to insist on a protocol
change. change.
Upgrade = 1#protocol Upgrade = #protocol
protocol = protocol-name ["/" protocol-version] protocol = protocol-name ["/" protocol-version]
protocol-name = token protocol-name = token
protocol-version = token protocol-version = token
Although protocol names are registered with a preferred case,
recipients SHOULD use case-insensitive comparison when matching each
protocol-name to supported protocols.
A server that sends a 101 (Switching Protocols) response MUST send an A server that sends a 101 (Switching Protocols) response MUST send an
Upgrade header field to indicate the new protocol(s) to which the Upgrade header field to indicate the new protocol(s) to which the
connection is being switched; if multiple protocol layers are being connection is being switched; if multiple protocol layers are being
switched, the sender MUST list the protocols in layer-ascending switched, the sender MUST list the protocols in layer-ascending
order. A server MUST NOT switch to a protocol that was not indicated order. A server MUST NOT switch to a protocol that was not indicated
by the client in the corresponding request's Upgrade header field. A by the client in the corresponding request's Upgrade header field. A
server MAY choose to ignore the order of preference indicated by the server MAY choose to ignore the order of preference indicated by the
client and select the new protocol(s) based on other factors, such as client and select the new protocol(s) based on other factors, such as
the nature of the request or the current load on the server. the nature of the request or the current load on the server.
skipping to change at line 2162 skipping to change at page 57, line 40
Upgrade header field to indicate the acceptable protocols, in order Upgrade header field to indicate the acceptable protocols, in order
of descending preference. of descending preference.
A server MAY send an Upgrade header field in any other response to A server MAY send an Upgrade header field in any other response to
advertise that it implements support for upgrading to the listed advertise that it implements support for upgrading to the listed
protocols, in order of descending preference, when appropriate for a protocols, in order of descending preference, when appropriate for a
future request. future request.
The following is a hypothetical example sent by a client: The following is a hypothetical example sent by a client:
GET /hello.txt HTTP/1.1 GET /hello HTTP/1.1
Host: www.example.com Host: www.example.com
Connection: upgrade Connection: upgrade
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11 Upgrade: websocket, IRC/6.9, RTA/x11
The capabilities and nature of the application-level communication The capabilities and nature of the application-level communication
after the protocol change is entirely dependent upon the new after the protocol change is entirely dependent upon the new
protocol(s) chosen. However, immediately after sending the 101 protocol(s) chosen. However, immediately after sending the 101
(Switching Protocols) response, the server is expected to continue (Switching Protocols) response, the server is expected to continue
responding to the original request as if it had received its responding to the original request as if it had received its
equivalent within the new protocol (i.e., the server still has an equivalent within the new protocol (i.e., the server still has an
outstanding request to satisfy after the protocol has been changed, outstanding request to satisfy after the protocol has been changed,
and is expected to do so without requiring the request to be and is expected to do so without requiring the request to be
repeated). repeated).
skipping to change at line 2192 skipping to change at page 58, line 23
to protocols with the same semantics as HTTP without the latency cost to protocols with the same semantics as HTTP without the latency cost
of an additional round trip. A server MUST NOT switch protocols of an additional round trip. A server MUST NOT switch protocols
unless the received message semantics can be honored by the new unless the received message semantics can be honored by the new
protocol; an OPTIONS request can be honored by any protocol. protocol; an OPTIONS request can be honored by any protocol.
The following is an example response to the above hypothetical The following is an example response to the above hypothetical
request: request:
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Connection: upgrade Connection: upgrade
Upgrade: HTTP/2.0 Upgrade: websocket
[... data stream switches to HTTP/2.0 with an appropriate response [... data stream switches to websocket with an appropriate response
(as defined by new protocol) to the "GET /hello.txt" request ...] (as defined by new protocol) to the "GET /hello" request ...]
When Upgrade is sent, the sender MUST also send a Connection header When Upgrade is sent, the sender MUST also send a Connection header
field (Section 6.1) that contains an "upgrade" connection option, in field (Section 7.6.1) that contains an "upgrade" connection option,
order to prevent Upgrade from being accidentally forwarded by in order to prevent Upgrade from being accidentally forwarded by
intermediaries that might not implement the listed protocols. A intermediaries that might not implement the listed protocols. A
server MUST ignore an Upgrade header field that is received in an server MUST ignore an Upgrade header field that is received in an
HTTP/1.0 request. HTTP/1.0 request.
A client cannot begin using an upgraded protocol on the connection A client cannot begin using an upgraded protocol on the connection
until it has completely sent the request message (i.e., the client until it has completely sent the request message (i.e., the client
can't change the protocol it is sending in the middle of a message). can't change the protocol it is sending in the middle of a message).
If a server receives both an Upgrade and an Expect header field with If a server receives both an Upgrade and an Expect header field with
the "100-continue" expectation (Section 5.1.1 of [RFC7231]), the the "100-continue" expectation (Section 10.1.1), the server MUST send
server MUST send a 100 (Continue) response before sending a 101 a 100 (Continue) response before sending a 101 (Switching Protocols)
(Switching Protocols) response. response.
The Upgrade header field only applies to switching protocols on top The Upgrade header field only applies to switching protocols on top
of the existing connection; it cannot be used to switch the of the existing connection; it cannot be used to switch the
underlying connection (transport) protocol, nor to switch the underlying connection (transport) protocol, nor to switch the
existing communication to a different connection. For those existing communication to a different connection. For those
purposes, it is more appropriate to use a 3xx (Redirection) response purposes, it is more appropriate to use a 3xx (Redirection) response
(Section 6.4 of [RFC7231]). (Section 15.4).
This specification only defines the protocol name "HTTP" for use by This specification only defines the protocol name "HTTP" for use by
the family of Hypertext Transfer Protocols, as defined by the HTTP the family of Hypertext Transfer Protocols, as defined by the HTTP
version rules of Section 2.6 and future updates to this version rules of Section 2.5 and future updates to this
specification. Additional tokens ought to be registered with IANA specification. Additional protocol names ought to be registered
using the registration procedure defined in Section 8.6. using the registration procedure defined in Section 16.7.
8. Representation Data and Metadata 8. Representation Data and Metadata
8.1. Representation Data 8.1. Representation Data
The representation data associated with an HTTP message is either The representation data associated with an HTTP message is either
provided as the payload body of the message or referred to by the provided as the content of the message or referred to by the message
message semantics and the effective request URI. The representation semantics and the target URI. The representation data is in a format
data is in a format and encoding defined by the representation and encoding defined by the representation metadata header fields.
metadata header fields.
The data type of the representation data is determined via the header The data type of the representation data is determined via the header
fields Content-Type and Content-Encoding. These define a two-layer, fields Content-Type and Content-Encoding. These define a two-layer,
ordered encoding model: ordered encoding model:
representation-data := Content-Encoding( Content-Type( bits ) ) representation-data := Content-Encoding( Content-Type( bits ) )
8.2. Representation Metadata 8.2. Representation Metadata
Representation header fields provide metadata about the Representation header fields provide metadata about the
representation. When a message includes a payload body, the representation. When a message includes content, the representation
representation header fields describe how to interpret the header fields describe how to interpret that data. In a response to
representation data enclosed in the payload body. In a response to a a HEAD request, the representation header fields describe the
HEAD request, the representation header fields describe the representation data that would have been enclosed in the content if
representation data that would have been enclosed in the payload body the same request had been a GET.
if the same request had been a GET.
The following header fields convey representation metadata:
8.3. Content-Type 8.3. Content-Type
The "Content-Type" header field indicates the media type of the The "Content-Type" header field indicates the media type of the
associated representation: either the representation enclosed in the associated representation: either the representation enclosed in the
message payload or the selected representation, as determined by the message content or the selected representation, as determined by the
message semantics. The indicated media type defines both the data message semantics. The indicated media type defines both the data
format and how that data is intended to be processed by a recipient, format and how that data is intended to be processed by a recipient,
within the scope of the received message semantics, after any content within the scope of the received message semantics, after any content
codings indicated by Content-Encoding are decoded. codings indicated by Content-Encoding are decoded.
Content-Type = media-type Content-Type = media-type
Media types are defined in Section 3.1.1.1. An example of the field Media types are defined in Section 8.3.1. An example of the field is
is
Content-Type: text/html; charset=ISO-8859-4 Content-Type: text/html; charset=ISO-8859-4
A sender that generates a message containing a payload body SHOULD A sender that generates a message containing content SHOULD generate
generate a Content-Type header field in that message unless the a Content-Type header field in that message unless the intended media
intended media type of the enclosed representation is unknown to the type of the enclosed representation is unknown to the sender. If a
sender. If a Content-Type header field is not present, the recipient Content-Type header field is not present, the recipient MAY either
MAY either assume a media type of "application/octet-stream" assume a media type of "application/octet-stream" ([RFC2046],
([RFC2046], Section 4.5.1) or examine the data to determine its type. Section 4.5.1) or examine the data to determine its type.
In practice, resource owners do not always properly configure their In practice, resource owners do not always properly configure their
origin server to provide the correct Content-Type for a given origin server to provide the correct Content-Type for a given
representation, with the result that some clients will examine a representation. Some user agents examine the content and, in certain
payload's content and override the specified type. Clients that do cases, override the received type (for example, see [Sniffing]).
so risk drawing incorrect conclusions, which might expose additional This "MIME sniffing" risks drawing incorrect conclusions about the
security risks (e.g., "privilege escalation"). Furthermore, it is data, which might expose the user to additional security risks (e.g.,
impossible to determine the sender's intent by examining the data "privilege escalation"). Furthermore, it is impossible to determine
format: many data formats match multiple media types that differ only the sender's intended processing model by examining the data format:
in processing semantics. Implementers are encouraged to provide a many data formats match multiple media types that differ only in
means of disabling such "content sniffing" when it is used. processing semantics. Implementers are encouraged to provide a means
to disable such sniffing.
Furthermore, although Content-Type is defined as a singleton field,
it is sometimes incorrectly generated multiple times, resulting in a
combined field value that appears to be a list. Recipients often
attempt to handle this error by using the last syntactically valid
member of the list, but note that some implementations might have
different error handling behaviors, leading to interoperability and/
or security issues.
8.3.1. Media Type 8.3.1. Media Type
HTTP uses Internet media types [RFC2046] in the Content-Type HTTP uses media types [RFC2046] in the Content-Type (Section 8.3) and
(Section 3.1.1.5) and Accept (Section 5.3.2) header fields in order Accept (Section 12.5.1) header fields in order to provide open and
to provide open and extensible data typing and type negotiation. extensible data typing and type negotiation. Media types define both
Media types define both a data format and various processing models: a data format and various processing models: how to process that data
how to process that data in accordance with each context in which it in accordance with each context in which it is received.
is received.
media-type = type "/" subtype *( OWS ";" OWS parameter ) media-type = type "/" subtype parameters
type = token type = token
subtype = token subtype = token
The type/subtype MAY be followed by parameters in the form of The type and subtype tokens are case-insensitive.
name=value pairs.
The type, subtype, and parameter name tokens are case-insensitive. The type/subtype MAY be followed by semicolon-delimited parameters
Parameter values might or might not be case-sensitive, depending on (Section 5.6.6) in the form of name=value pairs. The presence or
the semantics of the parameter name. The presence or absence of a absence of a parameter might be significant to the processing of a
parameter might be significant to the processing of a media-type, media type, depending on its definition within the media type
depending on its definition within the media type registry. registry. Parameter values might or might not be case-sensitive,
depending on the semantics of the parameter name.
For example, the following For example, the following media types are equivalent in describing
examples are all equivalent, but the first is preferred for HTML text data encoded in the UTF-8 character encoding scheme, but
consistency: the first is preferred for consistency (the "charset" parameter value
is defined as being case-insensitive in [RFC2046], Section 4.1.2):
text/html;charset=utf-8 text/html;charset=utf-8
text/html;charset=UTF-8
Text/HTML;Charset="utf-8" Text/HTML;Charset="utf-8"
text/html; charset="utf-8" text/html; charset="utf-8"
text/html;charset=UTF-8
Internet media types ought to be registered with IANA according to Media types ought to be registered with IANA according to the
the procedures defined in [BCP13]. procedures defined in [BCP13].
8.3.2. Charset 8.3.2. Charset
HTTP uses charset names to indicate or negotiate the character HTTP uses _charset_ names to indicate or negotiate the character
encoding scheme of a textual representation [RFC6365]. A charset is encoding scheme of a textual representation [RFC6365]. A charset is
identified by a case-insensitive token. identified by a case-insensitive token.
charset = token charset = token
Charset names ought to be registered in the IANA "Character Sets" Charset names ought to be registered in the IANA "Character Sets"
registry (<http://www.iana.org/assignments/character-sets>) according registry (<https://www.iana.org/assignments/character-sets>)
to the procedures defined in [RFC2978]. according to the procedures defined in Section 2 of [RFC2978].
| *Note:* In theory, charset names are defined by the "mime-
| charset" ABNF rule defined in Section 2.3 of [RFC2978] (as
| corrected in [Err1912]). That rule allows two characters that
| are not included in "token" ("{" and "}"), but no charset name
| registered at the time of this writing includes braces (see
| [Err5433]).
8.3.3. Canonicalization and Text Defaults 8.3.3. Canonicalization and Text Defaults
Internet media types are registered with a canonical form in order to Media types are registered with a canonical form in order to be
be interoperable among systems with varying native encoding formats. interoperable among systems with varying native encoding formats.
Representations selected or transferred via HTTP ought to be in Representations selected or transferred via HTTP ought to be in
canonical form, for many of the same reasons described by the canonical form, for many of the same reasons described by the
Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the
performance characteristics of email deployments (i.e., store and performance characteristics of email deployments (i.e., store and
forward messages to peers) are significantly different from those forward messages to peers) are significantly different from those
common to HTTP and the Web (server-based information services). common to HTTP and the Web (server-based information services).
Furthermore, MIME's constraints for the sake of compatibility with Furthermore, MIME's constraints for the sake of compatibility with
older mail transfer protocols do not apply to HTTP (see Appendix A). older mail transfer protocols do not apply to HTTP (see Appendix B of
[Messaging]).
MIME's canonical form requires that media subtypes of the "text" type MIME's canonical form requires that media subtypes of the "text" type
use CRLF as the text line break. HTTP allows the transfer of text use CRLF as the text line break. HTTP allows the transfer of text
media with plain CR or LF alone representing a line break, when such media with plain CR or LF alone representing a line break, when such
line breaks are consistent for an entire representation. An HTTP line breaks are consistent for an entire representation. An HTTP
sender MAY generate, and a recipient MUST be able to parse, line sender MAY generate, and a recipient MUST be able to parse, line
breaks in text media that consist of CRLF, bare CR, or bare LF. In breaks in text media that consist of CRLF, bare CR, or bare LF. In
addition, text media in HTTP is not limited to charsets that use addition, text media in HTTP is not limited to charsets that use
octets 13 and 10 for CR and LF, respectively. This flexibility octets 13 and 10 for CR and LF, respectively. This flexibility
regarding line breaks applies only to text within a representation regarding line breaks applies only to text within a representation
that has been assigned a "text" media type; it does not apply to that has been assigned a "text" media type; it does not apply to
"multipart" types or HTTP elements outside the payload body (e.g., "multipart" types or HTTP elements outside the content (e.g., header
header fields). fields).
If a representation is encoded with a content-coding, the underlying If a representation is encoded with a content-coding, the underlying
data ought to be in a form defined above prior to being encoded. data ought to be in a form defined above prior to being encoded.
8.3.4. Multipart Types 8.3.4. Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of MIME provides for a number of "multipart" types - encapsulations of
one or more representations within a single message body. All one or more representations within a single message body. All
multipart types share a common syntax, as defined in Section 5.1.1 of multipart types share a common syntax, as defined in Section 5.1.1 of
[RFC2046], and include a boundary parameter as part of the media type [RFC2046], and include a boundary parameter as part of the media type
value. The message body is itself a protocol element; a sender MUST value. The message body is itself a protocol element; a sender MUST
generate only CRLF to represent line breaks between body parts. generate only CRLF to represent line breaks between body parts.
HTTP message framing does not use the multipart boundary as an HTTP message framing does not use the multipart boundary as an
indicator of message body length, though it might be used by indicator of message body length, though it might be used by
implementations that generate or process the payload. For example, implementations that generate or process the content. For example,
the "multipart/form-data" type is often used for carrying form data the "multipart/form-data" type is often used for carrying form data
in a request, as described in [RFC2388], and the "multipart/ in a request, as described in [RFC7578], and the "multipart/
byteranges" type is defined by this specification for use in some 206 byteranges" type is defined by this specification for use in some 206
(Partial Content) responses [RFC7233]. (Partial Content) responses (see Section 15.3.7).
8.4. Content-Encoding 8.4. Content-Encoding
The "Content-Encoding" header field indicates what content codings The "Content-Encoding" header field indicates what content codings
have been applied to the representation, beyond those inherent in the have been applied to the representation, beyond those inherent in the
media type, and thus what decoding mechanisms have to be applied in media type, and thus what decoding mechanisms have to be applied in
order to obtain data in the media type referenced by the Content-Type order to obtain data in the media type referenced by the Content-Type
header field. Content-Encoding is primarily used to allow a header field. Content-Encoding is primarily used to allow a
representation's data to be compressed without losing the identity of representation's data to be compressed without losing the identity of
its underlying media type. its underlying media type.
Content-Encoding = 1#content-coding Content-Encoding = #content-coding
An example of its use is An example of its use is
Content-Encoding: gzip Content-Encoding: gzip
If one or more encodings have been applied to a representation, the If one or more encodings have been applied to a representation, the
sender that applied the encodings MUST generate a Content-Encoding sender that applied the encodings MUST generate a Content-Encoding
header field that lists the content codings in the order in which header field that lists the content codings in the order in which
they were applied. Additional information about the encoding they were applied. Note that the coding named "identity" is reserved
parameters can be provided by other header fields not defined by this for its special role in Accept-Encoding, and thus SHOULD NOT be
specification. included.
[new] Additional information about the encoding parameters can be provided
by other header fields not defined by this specification.
Unlike Transfer-Encoding (Section 3.3.1 of [RFC7230]), the codings Unlike Transfer-Encoding (Section 6.1 of [Messaging]), the codings
listed in Content-Encoding are a characteristic of the listed in Content-Encoding are a characteristic of the
representation; the representation is defined in terms of the coded representation; the representation is defined in terms of the coded
form, and all other metadata about the representation is about the form, and all other metadata about the representation is about the
coded form unless otherwise noted in the metadata definition. coded form unless otherwise noted in the metadata definition.
Typically, the representation is only decoded just prior to rendering Typically, the representation is only decoded just prior to rendering
or analogous usage. or analogous usage.
If the media type includes an inherent encoding, such as a data If the media type includes an inherent encoding, such as a data
format that is always compressed, then that encoding would not be format that is always compressed, then that encoding would not be
restated in Content-Encoding even if it happens to be the same restated in Content-Encoding even if it happens to be the same
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Content coding values indicate an encoding transformation that has Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are been or can be applied to a representation. Content codings are
primarily used to allow a representation to be compressed or primarily used to allow a representation to be compressed or
otherwise usefully transformed without losing the identity of its otherwise usefully transformed without losing the identity of its
underlying media type and without loss of information. Frequently, underlying media type and without loss of information. Frequently,
the representation is stored in coded form, transmitted directly, and the representation is stored in coded form, transmitted directly, and
only decoded by the final recipient. only decoded by the final recipient.
content-coding = token content-coding = token
All content-coding values are case-insensitive and ought to be All content codings are case-insensitive and ought to be registered
registered within the "HTTP Content Coding Registry", as defined in within the "HTTP Content Coding Registry", as described in
Section 8.4. Section 16.6
The following content-coding values are defined by this
specification:
compress (and x-compress): See Section 4.2.1 of [RFC7230].
deflate: See Section 4.2.2 of [RFC7230].
gzip (and x-gzip): See Section 4.2.3 of [RFC7230].
The codings defined below can be used to compress the payload of a Content-coding values are used in the Accept-Encoding
message. They are used in the Accept-Encoding (Section 12.5.3) and Content-Encoding (Section 8.4) header fields.
(Section 5.3.4) and Content-Encoding (Section 3.1.2.2) header fields.
8.4.1.1. Compress Coding 8.4.1.1. Compress Coding
The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
[Welch] that is commonly produced by the UNIX file compression [Welch] that is commonly produced by the UNIX file compression
program "compress". A recipient SHOULD consider "x-compress" to be program "compress". A recipient SHOULD consider "x-compress" to be
equivalent to "compress". equivalent to "compress".
8.4.1.2. Deflate Coding 8.4.1.2. Deflate Coding
The "deflate" coding is a "zlib" data format [RFC1950] containing a The "deflate" coding is a "zlib" data format [RFC1950] containing a
"deflate" compressed data stream [RFC1951] that uses a combination of "deflate" compressed data stream [RFC1951] that uses a combination of
the Lempel-Ziv (LZ77) compression algorithm and Huffman coding. the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.
Note: Some non-conformant implementations send the "deflate" | *Note:* Some non-conformant implementations send the "deflate"
compressed data without the zlib wrapper. | compressed data without the zlib wrapper.
8.4.1.3. Gzip Coding 8.4.1.3. Gzip Coding
The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy
Check (CRC) that is commonly produced by the gzip file compression Check (CRC) that is commonly produced by the gzip file compression
program [RFC1952]. A recipient SHOULD consider "x-gzip" to be program [RFC1952]. A recipient SHOULD consider "x-gzip" to be
equivalent to "gzip". equivalent to "gzip".
8.5. Content-Language 8.5. Content-Language
The "Content-Language" header field describes the natural language(s) The "Content-Language" header field describes the natural language(s)
of the intended audience for the representation. Note that this of the intended audience for the representation. Note that this
might not be equivalent to all the languages used within the might not be equivalent to all the languages used within the
representation. representation.
Content-Language = 1#language-tag Content-Language = #language-tag
Language tags are defined in Section 3.1.3.1. The primary purpose of Language tags are defined in Section 8.5.1. The primary purpose of
Content-Language is to allow a user to identify and differentiate Content-Language is to allow a user to identify and differentiate
representations according to the users' own preferred language. representations according to the users' own preferred language.
Thus, if the content is intended only for a Danish-literate audience, Thus, if the content is intended only for a Danish-literate audience,
the appropriate field is the appropriate field is
Content-Language: da Content-Language: da
If no Content-Language is specified, the default is that the content If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the is intended for all language audiences. This might mean that the
sender does not consider it to be specific to any natural language, sender does not consider it to be specific to any natural language,
skipping to change at line 2517 skipping to change at page 65, line 24
Content-Language: mi, en Content-Language: mi, en
However, just because multiple languages are present within a However, just because multiple languages are present within a
representation does not mean that it is intended for multiple representation does not mean that it is intended for multiple
linguistic audiences. An example would be a beginner's language linguistic audiences. An example would be a beginner's language
primer, such as "A First Lesson in Latin", which is clearly intended primer, such as "A First Lesson in Latin", which is clearly intended
to be used by an English-literate audience. In this case, the to be used by an English-literate audience. In this case, the
Content-Language would properly only include "en". Content-Language would properly only include "en".
Content-Language MAY be applied to any media type -- it is not Content-Language MAY be applied to any media type - it is not limited
limited to textual documents. to textual documents.
8.5.1. Language Tags 8.5.1. Language Tags
A language tag, as defined in [RFC5646], identifies a natural A language tag, as defined in [RFC5646], identifies a natural
language spoken, written, or otherwise conveyed by human beings for language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer communication of information to other human beings. Computer
languages are explicitly excluded. languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and HTTP uses language tags within the Accept-Language and
Content-Language header fields. Accept-Language uses the broader Content-Language header fields. Accept-Language uses the broader
language-range production defined in Section 5.3.5, whereas language-range production defined in Section 12.5.4, whereas
Content-Language uses the language-tag production defined below. Content-Language uses the language-tag production defined below.
language-tag = <Language-Tag, see [RFC5646], Section 2.1> language-tag = <Language-Tag, see [RFC5646], Section 2.1>
A language tag is a sequence of one or more case-insensitive subtags, A language tag is a sequence of one or more case-insensitive subtags,
each separated by a hyphen character ("-", %x2D). In most cases, a each separated by a hyphen character ("-", %x2D). In most cases, a
language tag consists of a primary language subtag that identifies a language tag consists of a primary language subtag that identifies a
broad family of related languages (e.g., "en" = English), which is broad family of related languages (e.g., "en" = English), which is
optionally followed by a series of subtags that refine or narrow that optionally followed by a series of subtags that refine or narrow that
language's range (e.g., "en-CA" = the variety of English as language's range (e.g., "en-CA" = the variety of English as
communicated in Canada). Whitespace is not allowed within a language communicated in Canada). Whitespace is not allowed within a language
tag. Example tags include: tag. Example tags include:
fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information. See [RFC5646] for further information.
8.6. Content-Length 8.6. Content-Length
The "Content-Length" header field indicates the associated
representation's data length as a decimal non-negative integer number
of octets. When transferring a representation as content, Content-
Length refers specifically to the amount of data enclosed so that it
can be used to delimit framing (e.g., Section 6.2 of [Messaging]).
In other cases, Content-Length indicates the selected
representation's current length, which can be used by recipients to
estimate transfer time or compare to previously stored
representations.
Content-Length = 1*DIGIT Content-Length = 1*DIGIT
An example is An example is
Content-Length: 3495 Content-Length: 3495
A sender MUST NOT send a Content-Length header field in any message A sender MUST NOT send a Content-Length header field in any message
that contains a Transfer-Encoding header field. that contains a Transfer-Encoding header field.
A user agent SHOULD send a Content-Length in a request message when A user agent SHOULD send a Content-Length in a request message when
no Transfer-Encoding is sent and the request method defines a meaning no Transfer-Encoding is sent and the request method defines a meaning
for an enclosed payload body. For example, a Content-Length header for enclosed content. For example, a Content-Length header field is
field is normally sent in a POST request even when the value is 0 normally sent in a POST request even when the value is 0 (indicating
(indicating an empty payload body). A user agent SHOULD NOT send a empty content). A user agent SHOULD NOT send a Content-Length header
Content-Length header field when the request message does not contain field when the request message does not contain content and the
a payload body and the method semantics do not anticipate such a method semantics do not anticipate such data.
body.
A server MAY send a Content-Length header field in a response to a A server MAY send a Content-Length header field in a response to a
HEAD request (Section 4.3.2 of [RFC7231]); a server MUST NOT send HEAD request (Section 9.3.2); a server MUST NOT send Content-Length
Content-Length in such a response unless its field-value equals the in such a response unless its field value equals the decimal number
decimal number of octets that would have been sent in the payload of octets that would have been sent in the content of a response if
body of a response if the same request had used the GET method. the same request had used the GET method.
A server MAY send a Content-Length header field in a 304 (Not A server MAY send a Content-Length header field in a 304 (Not
Modified) response to a conditional GET request (Section 4.1 of Modified) response to a conditional GET request (Section 15.4.5); a
[RFC7232]); a server MUST NOT send Content-Length in such a response server MUST NOT send Content-Length in such a response unless its
unless its field-value equals the decimal number of octets that would field value equals the decimal number of octets that would have been
have been sent in the payload body of a 200 (OK) response to the same sent in the content of a 200 (OK) response to the same request.
request.
A server MUST NOT send a Content-Length header field in any response A server MUST NOT send a Content-Length header field in any response
with a status code of 1xx (Informational) or 204 (No Content). A with a status code of 1xx (Informational) or 204 (No Content). A
server MUST NOT send a Content-Length header field in any 2xx server MUST NOT send a Content-Length header field in any 2xx
(Successful) response to a CONNECT request (Section 4.3.6 of (Successful) response to a CONNECT request (Section 9.3.6).
[RFC7231]).
Aside from the cases defined above, in the absence of Aside from the cases defined above, in the absence of Transfer-
Transfer-Encoding, an origin server SHOULD send a Content-Length Encoding, an origin server SHOULD send a Content-Length header field
header field when the payload body size is known prior to sending the when the content size is known prior to sending the complete header
complete header section. This will allow downstream recipients to section. This will allow downstream recipients to measure transfer
measure transfer progress, know when a received message is complete, progress, know when a received message is complete, and potentially
and potentially reuse the connection for additional requests. reuse the connection for additional requests.
Any Content-Length field value greater than or equal to zero is Any Content-Length field value greater than or equal to zero is
valid. Since there is no predefined limit to the length of a valid. Since there is no predefined limit to the length of content,
payload, a recipient MUST anticipate potentially large decimal a recipient MUST anticipate potentially large decimal numerals and
numerals and prevent parsing errors due to integer conversion prevent parsing errors due to integer conversion overflows
overflows (Section 9.3). (Section 17.5).
If a message is received that has multiple Content-Length header If a message is received that has a Content-Length header field value
fields with field-values consisting of the same decimal value, or a consisting of the same decimal value as a comma-separated list
single Content-Length header field with a field value containing a (Section 5.6.1) - for example, "Content-Length: 42, 42" - indicating
list of identical decimal values (e.g., "Content-Length: 42, 42"),
indicating
that duplicate Content-Length header fields have been generated or that duplicate Content-Length header fields have been generated or
combined by an upstream message processor, then the recipient MUST combined by an upstream message processor, then the recipient MUST
either reject the message as invalid or replace the duplicated either reject the message as invalid or replace the duplicated field
field-values with a single valid Content-Length field containing that values with a single valid Content-Length field containing that
decimal value prior to determining the message body length or decimal value.
forwarding the message.
8.7. Content-Location 8.7. Content-Location
The "Content-Location" header field references a URI that can be used The "Content-Location" header field references a URI that can be used
as an identifier for a specific resource corresponding to the as an identifier for a specific resource corresponding to the
representation in this message's payload. In other words, if one representation in this message's content. In other words, if one
were to perform a GET request on this URI at the time of this were to perform a GET request on this URI at the time of this
message's generation, then a 200 (OK) response would contain the same message's generation, then a 200 (OK) response would contain the same
representation that is enclosed as payload in this message. representation that is enclosed as content in this message.
Content-Location = absolute-URI / partial-URI Content-Location = absolute-URI / partial-URI
The Content-Location value is not a replacement for the effective The field value is either an absolute-URI or a partial-URI. In the
Request URI (Section 5.5 of [RFC7230]). It is representation latter case (Section 4), the referenced URI is relative to the target
metadata. It has the same syntax and semantics as the header field URI ([RFC3986], Section 5).
of the same name defined for MIME body parts in Section 4 of
[RFC2557]. However, its appearance in an HTTP message has some The Content-Location value is not a replacement for the target URI
special implications for HTTP recipients. (Section 7.1). It is representation metadata. It has the same
syntax and semantics as the header field of the same name defined for
MIME body parts in Section 4 of [RFC2557]. However, its appearance
in an HTTP message has some special implications for HTTP recipients.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its value refers (after conversion to absolute form) to a message and its value refers (after conversion to absolute form) to a
URI that is the same as the effective request URI, then the recipient URI that is the same as the target URI, then the recipient MAY
MAY consider the payload to be a current representation of that consider the content to be a current representation of that resource
resource at the time indicated by the message origination date. For at the time indicated by the message origination date. For a GET
a GET (Section 4.3.1) or HEAD (Section 4.3.2) request, this is the (Section 9.3.1) or HEAD (Section 9.3.2) request, this is the same as
same as the default semantics when no Content-Location is provided by the default semantics when no Content-Location is provided by the
the server. For a state-changing request like PUT (Section 4.3.4) or server. For a state-changing request like PUT (Section 9.3.4) or
POST (Section 4.3.3), it implies that the server's response contains POST (Section 9.3.3), it implies that the server's response contains
the new representation of that resource, thereby distinguishing it the new representation of that resource, thereby distinguishing it
from representations that might only report about the action (e.g., from representations that might only report about the action (e.g.,
"It worked!"). This allows authoring applications to update their "It worked!"). This allows authoring applications to update their
local copies without the need for a subsequent GET request. local copies without the need for a subsequent GET request.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its field-value refers to a URI that differs from the message and its field value refers to a URI that differs from the
effective request URI, then the origin server claims that the URI is target URI, then the origin server claims that the URI is an
an identifier for a different resource corresponding to the enclosed identifier for a different resource corresponding to the enclosed
representation. Such a claim can only be trusted if both identifiers representation. Such a claim can only be trusted if both identifiers
share the same resource owner, which cannot be programmatically share the same resource owner, which cannot be programmatically
determined via HTTP. determined via HTTP.
o For a response to a GET or HEAD request, this is an indication o For a response to a GET or HEAD request, this is an indication
that the effective request URI refers to a resource that is that the target URI refers to a resource that is subject to
subject to content negotiation and the Content-Location content negotiation and the Content-Location field value is a more
field-value is a more specific identifier for the selected specific identifier for the selected representation.
representation.
o For a 201 (Created) response to a state-changing method, a o For a 201 (Created) response to a state-changing method, a
Content-Location field-value that is identical to the Location Content-Location field value that is identical to the Location
field-value indicates that this payload is a current field value indicates that this content is a current
representation of the newly created resource. representation of the newly created resource.
o Otherwise, such a Content-Location indicates that this payload is o Otherwise, such a Content-Location indicates that this content is
a representation reporting on the requested action's status and a representation reporting on the requested action's status and
that the same report is available (for future access with GET) at that the same report is available (for future access with GET) at
the given URI. For example, a purchase transaction made via a the given URI. For example, a purchase transaction made via a
POST request might include a receipt document as the payload of POST request might include a receipt document as the content of
the 200 (OK) response; the Content-Location field-value provides the 200 (OK) response; the Content-Location field value provides
an identifier for retrieving a copy of that same receipt in the an identifier for retrieving a copy of that same receipt in the
future. future.
A user agent that sends Content-Location in a request message is A user agent that sends Content-Location in a request message is
stating that its value refers to where the user agent originally stating that its value refers to where the user agent originally
obtained the content of the enclosed representation (prior to any obtained the content of the enclosed representation (prior to any
modifications made by that user agent). In other words, the user modifications made by that user agent). In other words, the user
agent is providing a back link to the source of the original agent is providing a back link to the source of the original
representation. representation.
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For example, if a client makes a PUT request on a negotiated resource For example, if a client makes a PUT request on a negotiated resource
and the origin server accepts that PUT (without redirection), then and the origin server accepts that PUT (without redirection), then
the new state of that resource is expected to be consistent with the the new state of that resource is expected to be consistent with the
one representation supplied in that PUT; the Content-Location cannot one representation supplied in that PUT; the Content-Location cannot
be used as a form of reverse content selection identifier to update be used as a form of reverse content selection identifier to update
only one of the negotiated representations. If the user agent had only one of the negotiated representations. If the user agent had
wanted the latter semantics, it would have applied the PUT directly wanted the latter semantics, it would have applied the PUT directly
to the Content-Location URI. to the Content-Location URI.
8.8. Validator Header Fields 8.8. Validator Fields
Validator header fields convey metadata about the selected Validator fields convey metadata about the selected representation
representation (Section 3). In responses to safe requests, validator (Section 3.2). In responses to safe requests, validator fields
fields describe the selected representation chosen by the origin describe the selected representation chosen by the origin server
server while handling the response. Note that, depending on the while handling the response. Note that, depending on the status code
status code semantics, the selected representation for a given semantics, the selected representation for a given response is not
response is not necessarily the same as the representation enclosed necessarily the same as the representation enclosed as response
as response payload. content.
In a successful response to a state-changing request, validator In a successful response to a state-changing request, validator
fields describe the new representation that has replaced the prior fields describe the new representation that has replaced the prior
selected representation as a result of processing the request. selected representation as a result of processing the request.
For example, an ETag header field in a 201 (Created) response For example, an ETag field in a 201 (Created) response communicates
communicates the entity-tag of the newly created resource's the entity-tag of the newly created resource's representation, so
representation, so that it can be used in later conditional requests that it can be used in later conditional requests to prevent the
to prevent the "lost update" problem [RFC7232]. "lost update" problem Section 13.1.
This specification defines two forms of metadata that are commonly This specification defines two forms of metadata that are commonly
used to observe resource state and test for preconditions: used to observe resource state and test for preconditions:
modification dates (Section 2.2) and opaque entity tags modification dates (Section 8.8.2) and opaque entity tags
(Section 2.3). Additional metadata that reflects resource state has (Section 8.8.3). Additional metadata that reflects resource state
been defined by various extensions of HTTP, such as Web Distributed has been defined by various extensions of HTTP, such as Web
Authoring and Versioning (WebDAV, [RFC4918]), that are beyond the Distributed Authoring and Versioning (WebDAV, [RFC4918]), that are
scope of this specification. A resource metadata value is referred beyond the scope of this specification. A resource metadata value is
to as a "validator" when it is used within a precondition. referred to as a _validator_ when it is used within a precondition.
8.8.1. Weak versus Strong 8.8.1. Weak versus Strong
Validators come in two flavors: strong or weak. Weak validators are Validators come in two flavors: strong or weak. Weak validators are
easy to generate but are far less useful for comparisons. Strong easy to generate but are far less useful for comparisons. Strong
validators are ideal for comparisons but can be very difficult (and validators are ideal for comparisons but can be very difficult (and
occasionally impossible) to generate efficiently. Rather than impose occasionally impossible) to generate efficiently. Rather than impose
that all forms of resource adhere to the same strength of validator, that all forms of resource adhere to the same strength of validator,
HTTP exposes the type of validator in use and imposes restrictions on HTTP exposes the type of validator in use and imposes restrictions on
when weak validators can be used as preconditions. when weak validators can be used as preconditions.
A "strong validator" is representation metadata that changes value A _strong validator_ is representation metadata that changes value
whenever a change occurs to the representation data that would be whenever a change occurs to the representation data that would be
observable in the payload body of a 200 (OK) response to GET. observable in the content of a 200 (OK) response to GET.
A strong validator might change for reasons other than a change to A strong validator might change for reasons other than a change to
the representation data, such as when a semantically significant part the representation data, such as when a semantically significant part
of the representation metadata is changed (e.g., Content-Type), but of the representation metadata is changed (e.g., Content-Type), but
it is in the best interests of the origin server to only change the it is in the best interests of the origin server to only change the
value when it is necessary to invalidate the stored responses held by value when it is necessary to invalidate the stored responses held by
remote caches and authoring tools. remote caches and authoring tools.
Cache entries might persist for arbitrarily long periods, regardless Cache entries might persist for arbitrarily long periods, regardless
of expiration times. Thus, a cache might attempt to validate an of expiration times. Thus, a cache might attempt to validate an
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accessible to GET. A collision-resistant hash function applied to accessible to GET. A collision-resistant hash function applied to
the representation data is also sufficient if the data is available the representation data is also sufficient if the data is available
prior to the response header fields being sent and the digest does prior to the response header fields being sent and the digest does
not need to be recalculated every time a validation request is not need to be recalculated every time a validation request is
received. However, if a resource has distinct representations that received. However, if a resource has distinct representations that
differ only in their metadata, such as might occur with content differ only in their metadata, such as might occur with content
negotiation over media types that happen to share the same data negotiation over media types that happen to share the same data
format, then the origin server needs to incorporate additional format, then the origin server needs to incorporate additional
information in the validator to distinguish those representations. information in the validator to distinguish those representations.
In contrast, a "weak validator" is representation metadata that might In contrast, a _weak validator_ is representation metadata that might
not change for every change to the representation data. This not change for every change to the representation data. This
weakness might be due to limitations in how the value is calculated, weakness might be due to limitations in how the value is calculated,
such as clock resolution, an inability to ensure uniqueness for all such as clock resolution, an inability to ensure uniqueness for all
possible representations of the resource, or a desire of the resource possible representations of the resource, or a desire of the resource
owner to group representations by some self-determined set of owner to group representations by some self-determined set of
equivalency rather than unique sequences of data. An origin server equivalency rather than unique sequences of data. An origin server
SHOULD change a weak entity-tag whenever it considers prior SHOULD change a weak entity-tag whenever it considers prior
representations to be unacceptable as a substitute for the current representations to be unacceptable as a substitute for the current
representation. In other words, a weak entity-tag ought to change representation. In other words, a weak entity-tag ought to change
whenever the origin server wants caches to invalidate old responses. whenever the origin server wants caches to invalidate old responses.
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8.8.2. Last-Modified 8.8.2. Last-Modified
The "Last-Modified" header field in a response provides a timestamp The "Last-Modified" header field in a response provides a timestamp
indicating the date and time at which the origin server believes the indicating the date and time at which the origin server believes the
selected representation was last modified, as determined at the selected representation was last modified, as determined at the
conclusion of handling the request. conclusion of handling the request.
Last-Modified = HTTP-date Last-Modified = HTTP-date
An example of its use is An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
8.8.2.1. Generation 8.8.2.1. Generation
An origin server SHOULD send Last-Modified for any selected An origin server SHOULD send Last-Modified for any selected
representation for which a last modification date can be reasonably representation for which a last modification date can be reasonably
and consistently determined, since its use in conditional requests and consistently determined, since its use in conditional requests
and evaluating cache freshness ([RFC7234]) results in a substantial and evaluating cache freshness ([Caching]) results in a substantial
reduction of HTTP traffic on the Internet and can be a significant reduction of HTTP traffic on the Internet and can be a significant
factor in improving service scalability and reliability. factor in improving service scalability and reliability.
A representation is typically the sum of many parts behind the A representation is typically the sum of many parts behind the
resource interface. The last-modified time would usually be the most resource interface. The last-modified time would usually be the most
recent time that any of those parts were changed. How that value is recent time that any of those parts were changed. How that value is
determined for any given resource is an implementation detail beyond determined for any given resource is an implementation detail beyond
the scope of this specification. What matters to HTTP is how the scope of this specification. What matters to HTTP is how
recipients of the Last-Modified header field can use its value to recipients of the Last-Modified header field can use its value to
make conditional requests and test the validity of locally cached make conditional requests and test the validity of locally cached
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A Last-Modified time, when used as a validator in a request, is A Last-Modified time, when used as a validator in a request, is
implicitly weak unless it is possible to deduce that it is strong, implicitly weak unless it is possible to deduce that it is strong,
using the following rules: using the following rules:
o The validator is being compared by an origin server to the actual o The validator is being compared by an origin server to the actual
current validator for the representation and, current validator for the representation and,
o That origin server reliably knows that the associated o That origin server reliably knows that the associated
representation did not change twice during the second covered by representation did not change twice during the second covered by
the presented validator. the presented validator;
or or
o The validator is about to be used by a client in an o The validator is about to be used by a client in an
If-Modified-Since, If-Unmodified-Since, or If-Range header field, If-Modified-Since, If-Unmodified-Since, or If-Range header field,
because the client has a cache entry for the associated because the client has a cache entry for the associated
representation, and representation, and
o That cache entry includes a Date value, which gives the time when o That cache entry includes a Date value which is at least one
the origin server sent the original response, and second after the Last-Modified value and the client has reason to
believe that they were generated by the same clock or that there
o The presented Last-Modified time is at least 60 seconds before the is enough difference between the Last-Modified and Date values to
Date value. make clock synchronization issues unlikely;
or or
o The validator is being compared by an intermediate cache to the o The validator is being compared by an intermediate cache to the
validator stored in its cache entry for the representation, and validator stored in its cache entry for the representation, and
o That cache entry includes a Date value, which gives the time when o That cache entry includes a Date value which is at least one
the origin server sent the original response, and second after the Last-Modified value and the cache has reason to
believe that they were generated by the same clock or that there
o The presented Last-Modified time is at least 60 seconds before the is enough difference between the Last-Modified and Date values to
Date value. make clock synchronization issues unlikely.
This method relies on the fact that if two different responses were This method relies on the fact that if two different responses were
sent by the origin server during the same second, but both had the sent by the origin server during the same second, but both had the
same Last-Modified time, then at least one of those responses would same Last-Modified time, then at least one of those responses would
have a Date value equal to its Last-Modified time. The arbitrary have a Date value equal to its Last-Modified time.
60-second limit guards against the possibility that the Date and
Last-Modified values are generated from different clocks or at
somewhat different times during the preparation of the response. An
implementation MAY use a value larger than 60 seconds, if it is
believed that 60 seconds is too short.
8.8.3. ETag 8.8.3. ETag
The "ETag" header field in a response provides the current entity-tag The "ETag" field in a response provides the current entity-tag for
for the selected representation, as determined at the conclusion of the selected representation, as determined at the conclusion of
handling the request. An entity-tag is an opaque validator for handling the request. An entity-tag is an opaque validator for
differentiating between multiple representations of the same differentiating between multiple representations of the same
resource, regardless of whether those multiple representations are resource, regardless of whether those multiple representations are
due to resource state changes over time, content negotiation due to resource state changes over time, content negotiation
resulting in multiple representations being valid at the same time, resulting in multiple representations being valid at the same time,
or both. An entity-tag consists of an opaque quoted string, possibly or both. An entity-tag consists of an opaque quoted string, possibly
prefixed by a weakness indicator. prefixed by a weakness indicator.
ETag = entity-tag ETag = entity-tag
entity-tag = [ weak ] opaque-tag entity-tag = [ weak ] opaque-tag
weak = %x57.2F ; "W/", case-sensitive weak = %s"W/"
opaque-tag = DQUOTE *etagc DQUOTE opaque-tag = DQUOTE *etagc DQUOTE
etagc = %x21 / %x23-7E / obs-text etagc = %x21 / %x23-7E / obs-text
; VCHAR except double quotes, plus obs-text ; VCHAR except double quotes, plus obs-text
Note: Previously, opaque-tag was defined to be a quoted-string | *Note:* Previously, opaque-tag was defined to be a quoted-
([RFC2616], Section 3.11); thus, some recipients might perform | string ([RFC2616], Section 3.11); thus, some recipients might
backslash unescaping. Servers therefore ought to avoid backslash | perform backslash unescaping. Servers therefore ought to avoid
characters in entity tags. | backslash characters in entity tags.
An entity-tag can be more reliable for validation than a modification An entity-tag can be more reliable for validation than a modification
date in situations where it is inconvenient to store modification date in situations where it is inconvenient to store modification
dates, where the one-second resolution of HTTP date values is not dates, where the one-second resolution of HTTP date values is not
sufficient, or where modification dates are not consistently sufficient, or where modification dates are not consistently
maintained. maintained.
Examples: Examples:
ETag: "xyzzy" ETag: "xyzzy"
ETag: W/"xyzzy" ETag: W/"xyzzy"
ETag: "" ETag: ""
An entity-tag can be either a weak or strong validator, with strong An entity-tag can be either a weak or strong validator, with strong
being the default. If an origin server provides an entity-tag for a being the default. If an origin server provides an entity-tag for a
representation and the generation of that entity-tag does not satisfy representation and the generation of that entity-tag does not satisfy
all of the characteristics of a strong validator (Section 2.1), then all of the characteristics of a strong validator (Section 8.8.1),
the origin server MUST mark the entity-tag as weak by prefixing its then the origin server MUST mark the entity-tag as weak by prefixing
opaque value with "W/" (case-sensitive). its opaque value with "W/" (case-sensitive).
A sender MAY send the Etag field in a trailer section (see
Section 6.5). However, since trailers are often ignored, it is
preferable to send Etag as a header field unless the entity-tag is
generated while sending the content.
8.8.3.1. Generation 8.8.3.1. Generation
The principle behind entity-tags is that only the service author The principle behind entity-tags is that only the service author
knows the implementation of a resource well enough to select the most knows the implementation of a resource well enough to select the most
accurate and efficient validation mechanism for that resource, and accurate and efficient validation mechanism for that resource, and
that any such mechanism can be mapped to a simple sequence of octets that any such mechanism can be mapped to a simple sequence of octets
for easy comparison. Since the value is opaque, there is no need for for easy comparison. Since the value is opaque, there is no need for
the client to be aware of how each entity-tag is constructed. the client to be aware of how each entity-tag is constructed.
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applied to all changes might use an internal revision number, perhaps applied to all changes might use an internal revision number, perhaps
combined with a variance identifier for content negotiation, to combined with a variance identifier for content negotiation, to
accurately differentiate between representations. Other accurately differentiate between representations. Other
implementations might use a collision-resistant hash of implementations might use a collision-resistant hash of
representation content, a combination of various file attributes, or representation content, a combination of various file attributes, or
a modification timestamp that has sub-second resolution. a modification timestamp that has sub-second resolution.
An origin server SHOULD send an ETag for any selected representation An origin server SHOULD send an ETag for any selected representation
for which detection of changes can be reasonably and consistently for which detection of changes can be reasonably and consistently
determined, since the entity-tag's use in conditional requests and determined, since the entity-tag's use in conditional requests and
evaluating cache freshness ([RFC7234]) can result in a substantial evaluating cache freshness ([Caching]) can result in a substantial
reduction of HTTP network traffic and can be a significant factor in reduction of HTTP network traffic and can be a significant factor in
improving service scalability and reliability. improving service scalability and reliability.
8.8.3.2. Comparison 8.8.3.2. Comparison
There are two entity-tag comparison functions, depending on whether There are two entity-tag comparison functions, depending on whether
or not the comparison context allows the use of weak validators: or not the comparison context allows the use of weak validators:
o Strong comparison: two entity-tags are equivalent if both are not _Strong comparison_: two entity-tags are equivalent if both are not
weak and their opaque-tags match character-by-character. weak and their opaque-tags match character-by-character.
o Weak comparison: two entity-tags are equivalent if their _Weak comparison_: two entity-tags are equivalent if their opaque-
opaque-tags match character-by-character, regardless of either or tags match character-by-character, regardless of either or both
both being tagged as "weak". being tagged as "weak".
The example below shows the results for a set of entity-tag pairs and The example below shows the results for a set of entity-tag pairs and
both the weak and strong comparison function results: both the weak and strong comparison function results:
+--------+--------+-------------------+-----------------+ -------- -------- ------------------- -----------------
| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison | ETag 1 ETag 2 Strong Comparison Weak Comparison
+--------+--------+-------------------+-----------------+ -------- -------- ------------------- -----------------
| W/"1" | W/"1" | no match | match | W/"1" W/"1" no match match
| W/"1" | W/"2" | no match | no match | W/"1" W/"2" no match no match
| W/"1" | "1" | no match | match | W/"1" "1" no match match
| "1" | "1" | match | match | "1" "1" match match
+--------+--------+-------------------+-----------------+ -------- -------- ------------------- -----------------
Table 3
8.8.3.3. Example: Entity-Tags Varying on Content-Negotiated Resources 8.8.3.3. Example: Entity-Tags Varying on Content-Negotiated Resources
Consider a resource that is subject to content negotiation (Section Consider a resource that is subject to content negotiation
3.4 of [RFC7231]), and where the representations sent in response to (Section 12), and where the representations sent in response to a GET
a GET request vary based on the Accept-Encoding request header field request vary based on the Accept-Encoding request header field
(Section 5.3.4 of [RFC7231]): (Section 12.5.3):
>> Request: >> Request:
GET /index HTTP/1.1 GET /index HTTP/1.1
Host: www.example.com Host: www.example.com
Accept-Encoding: gzip Accept-Encoding: gzip
In this case, the response might or might not use the gzip content In this case, the response might or might not use the gzip content
coding. If it does not, the response might look like: coding. If it does not, the response might look like:
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HTTP/1.1 200 OK HTTP/1.1 200 OK
Date: Fri, 26 Mar 2010 00:05:00 GMT Date: Fri, 26 Mar 2010 00:05:00 GMT
ETag: "123-b" ETag: "123-b"
Content-Length: 43 Content-Length: 43
Vary: Accept-Encoding Vary: Accept-Encoding
Content-Type: text/plain Content-Type: text/plain
Content-Encoding: gzip Content-Encoding: gzip
...binary data... ...binary data...
Note: Content codings are a property of the representation data, | *Note:* Content codings are a property of the representation
so a strong entity-tag for a content-encoded representation has to | data, so a strong entity-tag for a content-encoded
be distinct from the entity tag of an unencoded representation to | representation has to be distinct from the entity tag of an
prevent potential conflicts during cache updates and range | unencoded representation to prevent potential conflicts during
requests. In contrast, transfer codings (Section 4 of [RFC7230]) | cache updates and range requests. In contrast, transfer
apply only during message transfer and do not result in distinct | codings (Section 7 of [Messaging]) apply only during message
entity-tags. | transfer and do not result in distinct entity-tags.
8.8.4. When to Use Entity-Tags and Last-Modified Dates 8.8.4. When to Use Entity-Tags and Last-Modified Dates
In 200 (OK) responses to GET or HEAD, an origin server: In 200 (OK) responses to GET or HEAD, an origin server:
o SHOULD send an entity-tag validator unless it is not feasible to o SHOULD send an entity-tag validator unless it is not feasible to
generate one. generate one.
o MAY send a weak entity-tag instead of a strong entity-tag, if o MAY send a weak entity-tag instead of a strong entity-tag, if
performance considerations support the use of weak entity-tags, or performance considerations support the use of weak entity-tags, or
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send both a strong entity-tag and a Last-Modified value in successful send both a strong entity-tag and a Last-Modified value in successful
responses to a retrieval request. responses to a retrieval request.
A client: A client:
o MUST send that entity-tag in any cache validation request (using o MUST send that entity-tag in any cache validation request (using
If-Match or If-None-Match) if an entity-tag has been provided by If-Match or If-None-Match) if an entity-tag has been provided by
the origin server. the origin server.
o SHOULD send the Last-Modified value in non-subrange cache o SHOULD send the Last-Modified value in non-subrange cache
validation requests (using If-Modified-Since) if only a validation requests (using If-Modified-Since) if only a Last-
Last-Modified value has been provided by the origin server. Modified value has been provided by the origin server.
o MAY send the Last-Modified value in subrange cache validation o MAY send the Last-Modified value in subrange cache validation
requests (using If-Unmodified-Since) if only a Last-Modified value requests (using If-Unmodified-Since) if only a Last-Modified value
has been provided by an HTTP/1.0 origin server. The user agent has been provided by an HTTP/1.0 origin server. The user agent
SHOULD provide a way to disable this, in case of difficulty. SHOULD provide a way to disable this, in case of difficulty.
o SHOULD send both validators in cache validation requests if both o SHOULD send both validators in cache validation requests if both
an entity-tag and a Last-Modified value have been provided by the an entity-tag and a Last-Modified value have been provided by the
origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to
respond appropriately. respond appropriately.
9. Methods 9. Methods
9.1. Overview 9.1. Overview
The request method token is the primary source of request semantics; The request method token is the primary source of request semantics;
it indicates the purpose for which the client has made this request it indicates the purpose for which the client has made this request
and what is expected by the client as a successful result. and what is expected by the client as a successful result.
The request method's semantics might be further specialized by the The request method's semantics might be further specialized by the
semantics of some header fields when present in a request (Section 5) semantics of some header fields when present in a request if those
if those additional semantics do not conflict with the method. For additional semantics do not conflict with the method. For example, a
example, a client can send conditional request header fields client can send conditional request header fields (Section 13.1) to
(Section 5.2) to make the requested action conditional on the current make the requested action conditional on the current state of the
state of the target resource ([RFC7232]). target resource.
method = token
HTTP was originally designed to be usable as an interface to HTTP was originally designed to be usable as an interface to
distributed object systems. The request method was envisioned as distributed object systems. The request method was envisioned as
applying semantics to a target resource in much the same way as applying semantics to a target resource in much the same way as
invoking a defined method on an identified object would apply invoking a defined method on an identified object would apply
semantics. semantics.
method = token
The method token is case-sensitive because it might be used as a The method token is case-sensitive because it might be used as a
gateway to object-based systems with case-sensitive method names. gateway to object-based systems with case-sensitive method names. By
By convention, standardized methods are defined in all-uppercase convention, standardized methods are defined in all-uppercase US-
US-ASCII letters. ASCII letters.
Unlike distributed objects, the standardized request methods in HTTP Unlike distributed objects, the standardized request methods in HTTP
are not resource-specific, since uniform interfaces provide for are not resource-specific, since uniform interfaces provide for
better visibility and reuse in network-based systems [REST]. Once better visibility and reuse in network-based systems [REST]. Once
defined, a standardized method ought to have the same semantics when defined, a standardized method ought to have the same semantics when
applied to any resource, though each resource determines for itself applied to any resource, though each resource determines for itself
whether those semantics are implemented or allowed. whether those semantics are implemented or allowed.
This specification defines a number of standardized methods that are This specification defines a number of standardized methods that are
commonly used in HTTP, as outlined by the following table. commonly used in HTTP, as outlined by the following table.
+---------+-------------------------------------------------+-------+ --------- -------------------------------------------- -------
| Method | Description | Sec. | Method Description Ref.
+---------+-------------------------------------------------+-------+ --------- -------------------------------------------- -------
| GET | Transfer a current representation of the target | 4.3.1 | GET Transfer a current representation of the 9.3.1
| | resource. | | target resource.
| HEAD | Same as GET, but only transfer the status line | 4.3.2 | HEAD Same as GET, but do not transfer the 9.3.2
| | and header section. | | response content.
| POST | Perform resource-specific processing on the | 4.3.3 | POST Perform resource-specific processing on 9.3.3
| | request payload. | | the request content.
| PUT | Replace all current representations of the | 4.3.4 | PUT Replace all current representations of the 9.3.4
| | target resource with the request payload. | | target resource with the request content.
| DELETE | Remove all current representations of the | 4.3.5 | DELETE Remove all current representations of the 9.3.5
| | target resource. | | target resource.
| CONNECT | Establish a tunnel to the server identified by | 4.3.6 | CONNECT Establish a tunnel to the server 9.3.6
| | the target resource. | | identified by the target resource.
| OPTIONS | Describe the communication options for the | 4.3.7 | OPTIONS Describe the communication options for the 9.3.7
| | target resource. | | target resource.
| TRACE | Perform a message loop-back test along the path | 4.3.8 | TRACE Perform a message loop-back test along the 9.3.8
| | to the target resource. | | path to the target resource.
+---------+-------------------------------------------------+-------+ --------- -------------------------------------------- -------
Table 4
All general-purpose servers MUST support the methods GET and HEAD. All general-purpose servers MUST support the methods GET and HEAD.
All other methods are OPTIONAL. All other methods are OPTIONAL.
The set of methods allowed by a target resource can be listed in an The set of methods allowed by a target resource can be listed in an
Allow header field (Section 7.4.1). However, the set of allowed Allow header field (Section 10.2.1). However, the set of allowed
methods can change dynamically. When a request method is received methods can change dynamically. When a request method is received
that is unrecognized or not implemented by an origin server, the that is unrecognized or not implemented by an origin server, the
origin server SHOULD respond with the 501 (Not Implemented) status origin server SHOULD respond with the 501 (Not Implemented) status
code. When a request method is received that is known by an origin code. When a request method is received that is known by an origin
server but not allowed for the target resource, the origin server server but not allowed for the target resource, the origin server
SHOULD respond with the 405 (Method Not Allowed) status code. SHOULD respond with the 405 (Method Not Allowed) status code.
Additional methods, outside the scope of this specification, have Additional methods, outside the scope of this specification, have
been standardized for use in HTTP. All such methods ought to be been specified for use in HTTP. All such methods ought to be
registered within the "Hypertext Transfer Protocol (HTTP) Method registered within the "Hypertext Transfer Protocol (HTTP) Method
Registry" maintained by IANA, as defined in Section 8.1. Registry", as described in Section 16.1.
9.2. Common Method Properties 9.2. Common Method Properties
9.2.1. Safe Methods 9.2.1. Safe Methods
Request methods are considered "safe" if their defined semantics are Request methods are considered _safe_ if their defined semantics are
essentially read-only; i.e., the client does not request, and does essentially read-only; i.e., the client does not request, and does
not expect, any state change on the origin server as a result of not expect, any state change on the origin server as a result of
applying a safe method to a target resource. Likewise, reasonable applying a safe method to a target resource. Likewise, reasonable
use of a safe method is not expected to cause any harm, loss of use of a safe method is not expected to cause any harm, loss of
property, or unusual burden on the origin server. property, or unusual burden on the origin server.
This definition of safe methods does not prevent an implementation This definition of safe methods does not prevent an implementation
from including behavior that is potentially harmful, that is not from including behavior that is potentially harmful, that is not
entirely read-only, or that causes side effects while invoking a safe entirely read-only, or that causes side effects while invoking a safe
method. What is important, however, is that the client did not method. What is important, however, is that the client did not
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allow automated retrieval processes (spiders) and cache performance allow automated retrieval processes (spiders) and cache performance
optimization (pre-fetching) to work without fear of causing harm. In optimization (pre-fetching) to work without fear of causing harm. In
addition, it allows a user agent to apply appropriate constraints on addition, it allows a user agent to apply appropriate constraints on
the automated use of unsafe methods when processing potentially the automated use of unsafe methods when processing potentially
untrusted content. untrusted content.
A user agent SHOULD distinguish between safe and unsafe methods when A user agent SHOULD distinguish between safe and unsafe methods when
presenting potential actions to a user, such that the user can be presenting potential actions to a user, such that the user can be
made aware of an unsafe action before it is requested. made aware of an unsafe action before it is requested.
When a resource is constructed such that parameters within the When a resource is constructed such that parameters within the target
effective request URI have the effect of selecting an action, it is URI have the effect of selecting an action, it is the resource
the resource owner's responsibility to ensure that the action is owner's responsibility to ensure that the action is consistent with
consistent with the request method semantics. For example, it is the request method semantics. For example, it is common for Web-
common for Web-based content editing software to use actions within based content editing software to use actions within query
query parameters, such as "page?do=delete". If the purpose of such a parameters, such as "page?do=delete". If the purpose of such a
resource is to perform an unsafe action, then the resource owner MUST resource is to perform an unsafe action, then the resource owner MUST
disable or disallow that action when it is accessed using a safe disable or disallow that action when it is accessed using a safe
request method. Failure to do so will result in unfortunate side request method. Failure to do so will result in unfortunate side
effects when automated processes perform a GET on every URI reference effects when automated processes perform a GET on every URI reference
for the sake of link maintenance, pre-fetching, building a search for the sake of link maintenance, pre-fetching, building a search
index, etc. index, etc.
9.2.2. Idempotent Methods 9.2.2. Idempotent Methods
A request method is considered "idempotent" if the intended effect on A request method is considered _idempotent_ if the intended effect on
the server of multiple identical requests with that method is the the server of multiple identical requests with that method is the
same as the effect for a single such request. Of the request methods same as the effect for a single such request. Of the request methods
defined by this specification, PUT, DELETE, and safe request methods defined by this specification, PUT, DELETE, and safe request methods
are idempotent. are idempotent.
Like the definition of safe, the idempotent property only applies to Like the definition of safe, the idempotent property only applies to
what has been requested by the user; a server is free to log each what has been requested by the user; a server is free to log each
request separately, retain a revision control history, or implement request separately, retain a revision control history, or implement
other non-idempotent side effects for each idempotent request. other non-idempotent side effects for each idempotent request.
Idempotent methods are distinguished because the request can be Idempotent methods are distinguished because the request can be
repeated automatically if a communication failure occurs before the repeated automatically if a communication failure occurs before the
client is able to read the server's response. For example, if a client is able to read the server's response. For example, if a
client sends a PUT request and the underlying connection is closed client sends a PUT request and the underlying connection is closed
before any response is received, then the client can establish a new before any response is received, then the client can establish a new
connection and retry the idempotent request. It knows that repeating connection and retry the idempotent request. It knows that repeating
the request will have the same intended effect, even if the original the request will have the same intended effect, even if the original
request succeeded, though the response might differ. request succeeded, though the response might differ.
A user agent MUST NOT automatically retry a request with a non- A client SHOULD NOT automatically retry a request with a non-
idempotent method unless it has some means to know that the request idempotent method unless it has some means to know that the request
semantics are actually idempotent, regardless of the method, or some semantics are actually idempotent, regardless of the method, or some
means to detect that the original request was never applied. means to detect that the original request was never applied.
For example, a user agent that knows (through design or For example, a user agent that knows (through design or
configuration) that a POST request to a given resource is safe can configuration) that a POST request to a given resource is safe can
repeat that request automatically. Likewise, a user agent designed repeat that request automatically. Likewise, a user agent designed
specifically to operate on a version control repository might be able specifically to operate on a version control repository might be able
to recover from partial failure conditions by checking the target to recover from partial failure conditions by checking the target
resource revision(s) after a failed connection, reverting or fixing resource revision(s) after a failed connection, reverting or fixing
any changes that were partially applied, and then automatically any changes that were partially applied, and then automatically
retrying the requests that failed. retrying the requests that failed.
Some clients use weaker signals to initiate automatic retries. For
example, when a POST request is sent, but the underlying transport
connection is closed before any part of the response is received.
Although this is commonly implemented, it is not recommended.
A proxy MUST NOT automatically retry non-idempotent requests. A A proxy MUST NOT automatically retry non-idempotent requests. A
client SHOULD NOT automatically retry a failed automatic retry. client SHOULD NOT automatically retry a failed automatic retry.
9.2.3. Methods and Caching 9.2.3. Methods and Caching
Request methods can be defined as "cacheable" to indicate that For a cache to store and use a response, the associated method needs
responses to them are allowed to be stored for future reuse; for to explicitly allow caching, and detail under what conditions a
specific requirements see [RFC7234]. In general, safe methods that response can be used to satisfy subsequent requests; a method
do not depend on a current or authoritative response are defined as definition which does not do so cannot be cached. For additional
cacheable; this specification defines GET, HEAD, and POST as requirements see [Caching].
cacheable, although the overwhelming majority of cache
implementations only support GET and HEAD. This specification defines caching semantics for GET, HEAD, and POST,
although the overwhelming majority of cache implementations only
support GET and HEAD.
9.3. Method Definitions 9.3. Method Definitions
9.3.1. GET 9.3.1. GET
The GET method requests transfer of a current selected representation The GET method requests transfer of a current selected representation
for the target resource. GET is the primary mechanism of information for the target resource.
retrieval and the focus of almost all performance optimizations.
Hence, when people speak of retrieving some identifiable information GET is the primary mechanism of information retrieval and the focus
via HTTP, they are generally referring to making a GET request. of almost all performance optimizations. Hence, when people speak of
retrieving some identifiable information via HTTP, they are generally
referring to making a GET request. A successful response reflects
the quality of "sameness" identified by the target URI. In turn,
constructing applications such that they produce a URI for each
important resource results in more resources being available for
other applications, producing a network effect that promotes further
expansion of the Web.
It is tempting to think of resource identifiers as remote file system It is tempting to think of resource identifiers as remote file system
pathnames and of representations as being a copy of the contents of pathnames and of representations as being a copy of the contents of
such files. In fact, that is how many resources are implemented (see such files. In fact, that is how many resources are implemented (see
Section 9.1 for related security considerations). However, there are Section 17.3 for related security considerations). However, there
no such limitations in practice. The HTTP interface for a resource are no such limitations in practice.
is just as likely to be implemented as a tree of content objects, a
programmatic view on various database records, or a gateway to other The HTTP interface for a resource is just as likely to be implemented
information systems. Even when the URI mapping mechanism is tied to as a tree of content objects, a programmatic view on various database
a file system, an origin server might be configured to execute the records, or a gateway to other information systems. Even when the
files with the request as input and send the output as the URI mapping mechanism is tied to a file system, an origin server
representation rather than transfer the files directly. Regardless, might be configured to execute the files with the request as input
only the origin server needs to know how each of its resource and send the output as the representation rather than transfer the
identifiers corresponds to an implementation and how each files directly. Regardless, only the origin server needs to know how
implementation manages to select and send a current representation of each of its resource identifiers corresponds to an implementation and
the target resource in a response to GET. how each implementation manages to select and send a current
representation of the target resource in a response to GET.
A client can alter the semantics of GET to be a "range request", A client can alter the semantics of GET to be a "range request",
requesting transfer of only some part(s) of the selected requesting transfer of only some part(s) of the selected
representation, by sending a Range header field in the request representation, by sending a Range header field in the request
([RFC7233]). (Section 14.2).
A payload within a GET request message has no defined semantics; A client SHOULD NOT generate content in a GET request. Content
sending a payload body on a GET request might cause some existing received in a GET request has no defined semantics, cannot alter the
implementations to reject the request. meaning or target of the request, and might lead some implementations
to reject the request and close the connection because of its
potential as a request smuggling attack (Section 11.2 of
[Messaging]).
The response to a GET request is cacheable; a cache MAY use it to The response to a GET request is cacheable; a cache MAY use it to
satisfy subsequent GET and HEAD requests unless otherwise indicated satisfy subsequent GET and HEAD requests unless otherwise indicated
by the Cache-Control header field (Section 5.2 of [RFC7234]). by the Cache-Control header field (Section 5.2 of [Caching]).
When information retrieval is performed with a mechanism that
constructs a target URI from user-provided information, such as the
query fields of a form using GET, potentially sensitive data might be
provided that would not be appropriate for disclosure within a URI
(see Section 17.9). In some cases, the data can be filtered or
transformed such that it would not reveal such information. In
others, particularly when there is no benefit from caching a
response, using the POST method (Section 9.3.3) instead of GET can
transmit such information in the request content rather than within
the target URI.
9.3.2. HEAD 9.3.2. HEAD
The HEAD method is identical to GET except that the server MUST NOT The HEAD method is identical to GET except that the server MUST NOT
send a message body in the response (i.e., the response terminates at send content in the response and the response always terminates at
the end of the header section). the end of the header section. HEAD is used to obtain metadata about
This method can be used for obtaining metadata about the selected representation without transferring its representation
the selected representation without transferring the representation data, often for the sake of testing hypertext links or finding recent
data and is often used for testing hypertext links modifications.
for validity, accessibility, and recent modification.
The server SHOULD send the same header fields in response to a HEAD The server SHOULD send the same header fields in response to a HEAD
request as it would have sent if the request had been a GET, except request as it would have sent if the request method had been GET.
that the payload header fields (Section 3.3) MAY be omitted. However, a server MAY omit header fields for which a value is
determined only while generating the content. For example, some
servers buffer a dynamic response to GET until a minimum amount of
data is generated so that they can more efficiently delimit small
responses or make late decisions with regard to content selection.
Such a response to GET might contain Content-Length and Vary fields,
for example, that are not generated within a HEAD response. These
minor inconsistencies are considered preferable to generating and
discarding the content for a HEAD request, since HEAD is usually
requested for the sake of efficiency.
A payload within a HEAD request message has no defined semantics; A content within a HEAD request message has no defined semantics;
sending a payload body on a HEAD request might cause some existing sending content in a HEAD request might cause some existing
implementations to reject the request. implementations to reject the request.
The response to a HEAD request is cacheable; a cache MAY use it to The response to a HEAD request is cacheable; a cache MAY use it to
satisfy subsequent HEAD requests unless otherwise indicated by the satisfy subsequent HEAD requests unless otherwise indicated by the
Cache-Control header field (Section 5.2 of [RFC7234]). A HEAD Cache-Control header field (Section 5.2 of [Caching]). A HEAD
response might also have an effect on previously cached responses to response might also affect previously cached responses to GET; see
GET; see Section 4.3.5 of [RFC7234]. Section 4.3.5 of [Caching].
9.3.3. POST 9.3.3. POST
The POST method requests that the target resource process the The POST method requests that the target resource process the
representation enclosed in the request according to the resource's representation enclosed in the request according to the resource's
own specific semantics. For example, POST is used for the following own specific semantics. For example, POST is used for the following
functions (among others): functions (among others):
o Providing a block of data, such as the fields entered into an HTML o Providing a block of data, such as the fields entered into an HTML
form, to a data-handling process; form, to a data-handling process;
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blog, or similar group of articles; blog, or similar group of articles;
o Creating a new resource that has yet to be identified by the o Creating a new resource that has yet to be identified by the
origin server; and origin server; and
o Appending data to a resource's existing representation(s). o Appending data to a resource's existing representation(s).
An origin server indicates response semantics by choosing an An origin server indicates response semantics by choosing an
appropriate status code depending on the result of processing the appropriate status code depending on the result of processing the
POST request; almost all of the status codes defined by this POST request; almost all of the status codes defined by this
specification might be received in a response to POST (the exceptions specification could be received in a response to POST (the exceptions
being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not
Satisfiable)). Satisfiable)).
If one or more resources has been created on the origin server as a If one or more resources has been created on the origin server as a
result of successfully processing a POST request, the origin server result of successfully processing a POST request, the origin server
SHOULD send a 201 (Created) response containing a Location header SHOULD send a 201 (Created) response containing a Location header
field that provides an identifier for the primary resource created field that provides an identifier for the primary resource created
(Section 7.1.2) and a representation that describes the status of the (Section 10.2.3) and a representation that describes the status of
request while referring to the new resource(s). the request while referring to the new resource(s).
Responses to POST requests are only cacheable when they include Responses to POST requests are only cacheable when they include
explicit freshness information (see Section 4.2.1 of [RFC7234]). explicit freshness information (see Section 4.2.1 of [Caching]) and a
However, POST caching is not widely implemented. For cases where an
origin server wishes the client to be able to cache the result of a
POST in a way that can be reused by a later GET, the origin server
MAY send a 200 (OK) response containing the result and a
Content-Location header field that has the same value as the POST's Content-Location header field that has the same value as the POST's
effective request URI (Section 3.1.4.2). target URI (Section 8.7). A cached POST response can be reused to
satisfy a later GET or HEAD request, but not a POST request, since
POST is required to be written through to the origin server, because
it is unsafe; see Section 4 of [Caching].
If the result of processing a POST would be equivalent to a If the result of processing a POST would be equivalent to a
representation of an existing resource, an origin server MAY redirect representation of an existing resource, an origin server MAY redirect
the user agent to that resource by sending a 303 (See Other) response the user agent to that resource by sending a 303 (See Other) response
with the existing resource's identifier in the Location field. This with the existing resource's identifier in the Location field. This
has the benefits of providing the user agent a resource identifier has the benefits of providing the user agent a resource identifier
and transferring the representation via a method more amenable to and transferring the representation via a method more amenable to
shared caching, though at the cost of an extra request if the user shared caching, though at the cost of an extra request if the user
agent does not already have the representation cached. agent does not already have the representation cached.
9.3.4. PUT 9.3.4. PUT
The PUT method requests that the state of the target resource be The PUT method requests that the state of the target resource be
created or replaced with the state defined by the representation created or replaced with the state defined by the representation
enclosed in the request message payload. A successful PUT of a given enclosed in the request message content. A successful PUT of a given
representation would suggest that a subsequent GET on that same representation would suggest that a subsequent GET on that same
target resource will result in an equivalent representation being target resource will result in an equivalent representation being
sent in a 200 (OK) response. However, there is no guarantee that sent in a 200 (OK) response. However, there is no guarantee that
such a state change will be observable, since the target resource such a state change will be observable, since the target resource
might be acted upon by other user agents in parallel, or might be might be acted upon by other user agents in parallel, or might be
subject to dynamic processing by the origin server, before any subject to dynamic processing by the origin server, before any
subsequent GET is received. A successful response only implies that subsequent GET is received. A successful response only implies that
the user agent's intent was achieved at the time of its processing by the user agent's intent was achieved at the time of its processing by
the origin server. the origin server.
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origin server beyond what can be expressed by the intent of the user origin server beyond what can be expressed by the intent of the user
agent request and the semantics of the origin server response. It agent request and the semantics of the origin server response. It
does not define what a resource might be, in any sense of that word, does not define what a resource might be, in any sense of that word,
beyond the interface provided via HTTP. It does not define how beyond the interface provided via HTTP. It does not define how
resource state is "stored", nor how such storage might change as a resource state is "stored", nor how such storage might change as a
result of a change in resource state, nor how the origin server result of a change in resource state, nor how the origin server
translates resource state into representations. Generally speaking, translates resource state into representations. Generally speaking,
all implementation details behind the resource interface are all implementation details behind the resource interface are
intentionally hidden by the server. intentionally hidden by the server.
An origin server SHOULD ignore unrecognized header fields received in This extends to how header and trailer fields are stored; while
a PUT request (i.e., do not save them as part of the resource state). common header fields like Content-Type will typically be stored and
returned upon subsequent GET requests, header and trailer field
handling is specific to the resource that received the request. As a
result, an origin server SHOULD ignore unrecognized header and
trailer fields received in a PUT request (i.e., do not save them as
part of the resource state).
An origin server MUST NOT send a validator header field An origin server MUST NOT send a validator field (Section 8.8), such
(Section 7.2), such as an ETag or Last-Modified field, in a as an ETag or Last-Modified field, in a successful response to PUT
successful response to PUT unless the request's representation data unless the request's representation data was saved without any
was saved without any transformation applied to the body (i.e., the transformation applied to the content (i.e., the resource's new
resource's new representation data is identical to the representation representation data is identical to the content received in the PUT
data received in the PUT request) and the validator field value request) and the validator field value reflects the new
reflects the new representation. This requirement allows a user representation. This requirement allows a user agent to know when
agent to know when the representation body it has in memory remains the representation it has in memory remains current as a result of
current as a result of the PUT, thus not in need of being retrieved the PUT, thus not in need of being retrieved again from the origin
again from the origin server, and that the new validator(s) received server, and that the new validator(s) received in the response can be
in the response can be used for future conditional requests in order used for future conditional requests in order to prevent accidental
to prevent accidental overwrites (Section 5.2). overwrites (Section 13.1).
The fundamental difference between the POST and PUT methods is The fundamental difference between the POST and PUT methods is
highlighted by the different intent for the enclosed representation. highlighted by the different intent for the enclosed representation.
The target resource in a POST request is intended to handle the The target resource in a POST request is intended to handle the
enclosed representation according to the resource's own semantics, enclosed representation according to the resource's own semantics,
whereas the enclosed representation in a PUT request is defined as whereas the enclosed representation in a PUT request is defined as
replacing the state of the target resource. Hence, the intent of PUT replacing the state of the target resource. Hence, the intent of PUT
is idempotent and visible to intermediaries, even though the exact is idempotent and visible to intermediaries, even though the exact
effect is only known by the origin server. effect is only known by the origin server.
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A PUT request applied to the target resource can have side effects on A PUT request applied to the target resource can have side effects on
other resources. For example, an article might have a URI for other resources. For example, an article might have a URI for
identifying "the current version" (a resource) that is separate from identifying "the current version" (a resource) that is separate from
the URIs identifying each particular version (different resources the URIs identifying each particular version (different resources
that at one point shared the same state as the current version that at one point shared the same state as the current version
resource). A successful PUT request on "the current version" URI resource). A successful PUT request on "the current version" URI
might therefore create a new version resource in addition to changing might therefore create a new version resource in addition to changing
the state of the target resource, and might also cause links to be the state of the target resource, and might also cause links to be
added between the related resources. added between the related resources.
An origin server that allows PUT on a given target resource MUST send Some origin servers support use of the Content-Range header field
a 400 (Bad Request) response to a PUT request that contains a (Section 14.4) as a request modifier to perform a partial PUT, as
Content-Range header field (Section 4.2 of [RFC7233]), since the described in Section 14.5.
payload is likely to be partial content that has been mistakenly PUT
as a full representation.
Responses to the PUT method are not cacheable. If a successful PUT Responses to the PUT method are not cacheable. If a successful PUT
request passes through a cache that has one or more stored responses request passes through a cache that has one or more stored responses
for the effective request URI, those stored responses will be for the target URI, those stored responses will be invalidated (see
invalidated (see Section 4.4 of [RFC7234]). Section 4.4 of [Caching]).
9.3.5. DELETE 9.3.5. DELETE
The DELETE method requests that the origin server remove the The DELETE method requests that the origin server remove the
association between the target resource and its current association between the target resource and its current
functionality. In effect, this method is similar to the rm command functionality. In effect, this method is similar to the "rm" command
in UNIX: it expresses a deletion operation on the URI mapping of the in UNIX: it expresses a deletion operation on the URI mapping of the
origin server rather than an expectation that the previously origin server rather than an expectation that the previously
associated information be deleted. associated information be deleted.
If the target resource has one or more current representations, they If the target resource has one or more current representations, they
might or might not be destroyed by the origin server, and the might or might not be destroyed by the origin server, and the
associated storage might or might not be reclaimed, depending associated storage might or might not be reclaimed, depending
entirely on the nature of the resource and its implementation by the entirely on the nature of the resource and its implementation by the
origin server (which are beyond the scope of this specification). origin server (which are beyond the scope of this specification).
Likewise, other implementation aspects of a resource might need to be Likewise, other implementation aspects of a resource might need to be
deactivated or archived as a result of a DELETE, such as database or deactivated or archived as a result of a DELETE, such as database or
gateway connections. In general, it is assumed that the origin gateway connections. In general, it is assumed that the origin
server will only allow DELETE on resources for which it has a server will only allow DELETE on resources for which it has a
prescribed mechanism for accomplishing the deletion. prescribed mechanism for accomplishing the deletion.
Relatively few resources allow the DELETE method -- its primary use Relatively few resources allow the DELETE method - its primary use is
is for remote authoring environments, where the user has some for remote authoring environments, where the user has some direction
direction regarding its effect. For example, a resource that was regarding its effect. For example, a resource that was previously
previously created using a PUT request, or identified via the created using a PUT request, or identified via the Location header
Location header field after a 201 (Created) response to a POST field after a 201 (Created) response to a POST request, might allow a
request, might allow a corresponding DELETE request to undo those corresponding DELETE request to undo those actions. Similarly,
actions. Similarly, custom user agent implementations that implement custom user agent implementations that implement an authoring
an authoring function, such as revision control clients using HTTP function, such as revision control clients using HTTP for remote
for remote operations, might use DELETE based on an assumption that operations, might use DELETE based on an assumption that the server's
the server's URI space has been crafted to correspond to a version URI space has been crafted to correspond to a version repository.
repository.
If a DELETE method is successfully applied, the origin server SHOULD If a DELETE method is successfully applied, the origin server SHOULD
send send
a 202 (Accepted) status code if the action will likely succeed but o a 202 (Accepted) status code if the action will likely succeed but
has not yet been enacted, has not yet been enacted,
a 204 (No Content) status code if the action has been enacted and o a 204 (No Content) status code if the action has been enacted and
no further information is to be supplied, or no further information is to be supplied, or
a 200 (OK) status code if the action has been enacted and the o a 200 (OK) status code if the action has been enacted and the
response message includes a representation describing the status. response message includes a representation describing the status.
A payload within a DELETE request message has no defined semantics; A client SHOULD NOT generate content in a DELETE request. Content
sending a payload body on a DELETE request might cause some existing received in a DELETE request has no defined semantics, cannot alter
the meaning or target of the request, and might lead some
implementations to reject the request. implementations to reject the request.
Responses to the DELETE method are not cacheable. If a DELETE Responses to the DELETE method are not cacheable. If a successful
request passes through a cache that has one or more stored responses DELETE request passes through a cache that has one or more stored
for the effective request URI, those stored responses will be responses for the target URI, those stored responses will be
invalidated (see Section 4.4 of [RFC7234]). invalidated (see Section 4.4 of [Caching]).
9.3.6. CONNECT 9.3.6. CONNECT
The CONNECT method requests that the recipient establish a tunnel to The CONNECT method requests that the recipient establish a tunnel to
the destination origin server identified by the request-target and, the destination origin server identified by the request target and,
if successful, thereafter restrict its behavior to blind forwarding if successful, thereafter restrict its behavior to blind forwarding
of packets, in both directions, until the tunnel is closed. Tunnels of data, in both directions, until the tunnel is closed. Tunnels are
are commonly used to create an end-to-end virtual connection, through commonly used to create an end-to-end virtual connection, through one
one or more proxies, which can then be secured using TLS (Transport or more proxies, which can then be secured using TLS (Transport Layer
Layer Security, [RFC5246]). Security, [RFC8446]).
Because CONNECT changes the request/response nature of an HTTP
connection, specific HTTP versions might have different ways of
mapping its semantics into the protocol's wire format.
CONNECT is intended only for use in requests to a proxy. An origin CONNECT is intended only for use in requests to a proxy. An origin
server that receives a CONNECT request for itself MAY respond with a server that receives a CONNECT request for itself MAY respond with a
2xx (Successful) status code to indicate that a connection is 2xx (Successful) status code to indicate that a connection is
established. However, most origin servers do not implement CONNECT. established. However, most origin servers do not implement CONNECT.
A client sending a CONNECT request MUST send the authority form of A client sending a CONNECT request MUST send the authority component
request-target (Section 5.3 of [RFC7230]); i.e., the request-target (described in Section 3.2 of [RFC3986]) as the request target; i.e.,
consists of only the host name and port number of the tunnel the request target consists of only the host name and port number of
destination, separated by a colon. For example, the tunnel destination, separated by a colon. For example,
CONNECT server.example.com:80 HTTP/1.1 CONNECT server.example.com:80 HTTP/1.1
Host: server.example.com:80 Host: server.example.com:80
The recipient proxy can establish a tunnel either by directly The recipient proxy can establish a tunnel either by directly
connecting to the request-target or, if configured to use another connecting to the request target or, if configured to use another
proxy, by forwarding the CONNECT request to the next inbound proxy. proxy, by forwarding the CONNECT request to the next inbound proxy.
Any 2xx (Successful) response indicates that the sender (and all Any 2xx (Successful) response indicates that the sender (and all
inbound proxies) will switch to tunnel mode immediately after the inbound proxies) will switch to tunnel mode immediately after the
blank line that concludes the successful response's header section; blank line that concludes the successful response's header section;
data received after that blank line is from the server identified by data received after that blank line is from the server identified by
the request-target. Any response other than a successful response the request target. Any response other than a successful response
indicates that the tunnel has not yet been formed and that the indicates that the tunnel has not yet been formed and that the
connection remains governed by HTTP. connection remains governed by HTTP.
A tunnel is closed when a tunnel intermediary detects that either A tunnel is closed when a tunnel intermediary detects that either
side has closed its connection: the intermediary MUST attempt to send side has closed its connection: the intermediary MUST attempt to send
any outstanding data that came from the closed side to the other any outstanding data that came from the closed side to the other
side, close both connections, and then discard any remaining data side, close both connections, and then discard any remaining data
left undelivered. left undelivered.
Proxy authentication might be used to establish the authority to Proxy authentication might be used to establish the authority to
create a tunnel. For example, create a tunnel. For example,
CONNECT server.example.com:80 HTTP/1.1 CONNECT server.example.com:80 HTTP/1.1
Host: server.example.com:80 Host: server.example.com:80
Proxy-Authorization: basic aGVsbG86d29ybGQ= Proxy-Authorization: basic aGVsbG86d29ybGQ=
There are significant risks in establishing a tunnel to arbitrary There are significant risks in establishing a tunnel to arbitrary
servers, particularly when the destination is a well-known or servers, particularly when the destination is a well-known or
reserved TCP port that is not intended for Web traffic. For example, reserved TCP port that is not intended for Web traffic. For example,
a CONNECT to a request-target of "example.com:25" would suggest that a CONNECT to "example.com:25" would suggest that the proxy connect to
the proxy connect to the reserved port for SMTP traffic; if allowed, the reserved port for SMTP traffic; if allowed, that could trick the
that could trick the proxy into relaying spam email. Proxies that proxy into relaying spam email. Proxies that support CONNECT SHOULD
support CONNECT SHOULD restrict its use to a limited set of known restrict its use to a limited set of known ports or a configurable
ports or a configurable whitelist of safe request targets. whitelist of safe request targets.
A server MUST NOT send any Transfer-Encoding or Content-Length header A server MUST NOT send any Transfer-Encoding or Content-Length header
fields in a 2xx (Successful) response to CONNECT. A client MUST fields in a 2xx (Successful) response to CONNECT. A client MUST
ignore any Content-Length or Transfer-Encoding header fields received ignore any Content-Length or Transfer-Encoding header fields received
in a successful response to CONNECT. in a successful response to CONNECT.
A payload within a CONNECT request message has no defined semantics; Content within a CONNECT request message has no defined semantics;
sending a payload body on a CONNECT request might cause some existing sending content in a CONNECT request might cause some existing
implementations to reject the request. implementations to reject the request.
Responses to the CONNECT method are not cacheable. Responses to the CONNECT method are not cacheable.
9.3.7. OPTIONS 9.3.7. OPTIONS
The OPTIONS method requests information about the communication The OPTIONS method requests information about the communication
options available for the target resource, at either the origin options available for the target resource, at either the origin
server or an intervening intermediary. This method allows a client server or an intervening intermediary. This method allows a client
to determine the options and/or requirements associated with a to determine the options and/or requirements associated with a
resource, or the capabilities of a server, without implying a resource, or the capabilities of a server, without implying a
resource action. resource action.
An OPTIONS request with an asterisk ("*") as the request-target An OPTIONS request with an asterisk ("*") as the request target
(Section 5.3 of [RFC7230]) applies to the server in general rather (Section 7.1) applies to the server in general rather than to a
than to a specific resource. Since a server's communication options specific resource. Since a server's communication options typically
typically depend on the resource, the "*" request is only useful as a depend on the resource, the "*" request is only useful as a "ping" or
"ping" or "no-op" type of method; it does nothing beyond allowing the "no-op" type of method; it does nothing beyond allowing the client to
client to test the capabilities of the server. For example, this can test the capabilities of the server. For example, this can be used
be used to test a proxy for HTTP/1.1 conformance (or lack thereof). to test a proxy for HTTP/1.1 conformance (or lack thereof).
If the request-target is not an asterisk, the OPTIONS request applies If the request target is not an asterisk, the OPTIONS request applies
to the options that are available when communicating with the target to the options that are available when communicating with the target
resource. resource.
A server generating a successful response to OPTIONS SHOULD send any A server generating a successful response to OPTIONS SHOULD send any
header fields that might indicate optional features implemented by header that might indicate optional features implemented by the
the server and applicable to the target resource (e.g., Allow), server and applicable to the target resource (e.g., Allow), including
including potential extensions not defined by this specification. potential extensions not defined by this specification. The response
The response payload, if any, might also describe the communication content, if any, might also describe the communication options in a
options in a machine or human-readable representation. A standard machine or human-readable representation. A standard format for such
format for such a representation is not defined by this a representation is not defined by this specification, but might be
specification, but might be defined by future extensions to HTTP. A defined by future extensions to HTTP.
server MUST generate a Content-Length field with a value of "0" if no
payload body is to be sent in the response.
A client MAY send a Max-Forwards header field in an OPTIONS request A client MAY send a Max-Forwards header field in an OPTIONS request
to target a specific recipient in the request chain (see to target a specific recipient in the request chain (see
Section 5.1.2). A proxy MUST NOT generate a Max-Forwards header Section 7.6.2). A proxy MUST NOT generate a Max-Forwards header
field while forwarding a request unless that request was received field while forwarding a request unless that request was received
with a Max-Forwards field. with a Max-Forwards field.
A client that generates an OPTIONS request containing a payload body A client that generates an OPTIONS request containing content MUST
MUST send a valid Content-Type header field describing the send a valid Content-Type header field describing the representation
representation media type. Although this specification does not media type. Note that this specification does not define any use for
define any use for such a payload, future extensions to HTTP might such content.
use the OPTIONS body to make more detailed queries about the target
resource.
Responses to the OPTIONS method are not cacheable. Responses to the OPTIONS method are not cacheable.
9.3.8. TRACE 9.3.8. TRACE
The TRACE method requests a remote, application-level loop-back of The TRACE method requests a remote, application-level loop-back of
the request message. The final recipient of the request SHOULD the request message. The final recipient of the request SHOULD
reflect the message received, excluding some fields described below, reflect the message received, excluding some fields described below,
back to the client as the message body of a 200 (OK) response with a back to the client as the content of a 200 (OK) response with a
Content-Type of "message/http" (Section 8.3.1 of [RFC7230]). The Content-Type of "message/http" (Section 10.1 of [Messaging]). The
final recipient is either the origin server or the first server to final recipient is either the origin server or the first server to
receive a Max-Forwards value of zero (0) in the request receive a Max-Forwards value of zero (0) in the request
(Section 5.1.2). (Section 7.6.2).
A client MUST NOT generate header fields in a TRACE request A client MUST NOT generate fields in a TRACE request containing
containing sensitive data that might be disclosed by the response. sensitive data that might be disclosed by the response. For example,
For example, it would be foolish for a user agent to send stored user it would be foolish for a user agent to send stored user credentials
credentials [RFC7235] or cookies [RFC6265] in a TRACE request. The (Section 11) or cookies [RFC6265] in a TRACE request. The final
final recipient of the request SHOULD exclude any request header recipient of the request SHOULD exclude any request fields that are
fields that are likely to contain sensitive data when that recipient likely to contain sensitive data when that recipient generates the
generates the response body. response content.
TRACE allows the client to see what is being received at the other TRACE allows the client to see what is being received at the other
end of the request chain and use that data for testing or diagnostic end of the request chain and use that data for testing or diagnostic
information. The value of the Via header field (Section 5.7.1 of information. The value of the Via header field (Section 7.6.3) is of
[RFC7230]) is of particular interest, since it acts as a trace of the particular interest, since it acts as a trace of the request chain.
request chain. Use of the Max-Forwards header field allows the Use of the Max-Forwards header field allows the client to limit the
client to limit the length of the request chain, which is useful for length of the request chain, which is useful for testing a chain of
testing a chain of proxies forwarding messages in an infinite loop. proxies forwarding messages in an infinite loop.
A client MUST NOT send a message body in a TRACE request. A client MUST NOT send content in a TRACE request.
Responses to the TRACE method are not cacheable. Responses to the TRACE method are not cacheable.
10. Message Context 10. Message Context
10.1. Request Context Fields 10.1. Request Context Fields
A client sends request header fields to provide more information The request header fields below provide additional information about
about the request context, make the request conditional based on the the request context, including information about the user, user
target resource state, suggest preferred formats for the response,
supply authentication credentials, or modify the expected request
processing. These fields act as request modifiers, similar to the
parameters on a programming language method invocation.
Controls are request header fields that direct specific handling of
the request.
The following request header fields provide additional information
about the request context, including information about the user, user
agent, and resource behind the request. agent, and resource behind the request.
10.1.1. Expect 10.1.1. Expect
The "Expect" header field in a request indicates a certain set of The "Expect" header field in a request indicates a certain set of
behaviors (expectations) that need to be supported by the server in behaviors (expectations) that need to be supported by the server in
order to properly handle this request. The only such expectation order to properly handle this request.
defined by this specification is 100-continue.
Expect = "100-continue" Expect = #expectation
expectation = token [ "=" ( token / quoted-string ) parameters ]
The Expect field-value is case-insensitive. The Expect field value is case-insensitive.
[new] The only expectation defined by this specification is "100-continue"
(with no defined parameters).
A server that receives an Expect field-value other than 100-continue A server that receives an Expect field value containing a member
MAY respond with a 417 (Expectation Failed) status code to indicate other than 100-continue MAY respond with a 417 (Expectation Failed)
that the unexpected expectation cannot be met. status code to indicate that the unexpected expectation cannot be
met.
A 100-continue expectation informs recipients that the client is A _100-continue_ expectation informs recipients that the client is
about to send a (presumably large) message body in this request and about to send (presumably large) content in this request and wishes
wishes to receive a 100 (Continue) interim response if the to receive a 100 (Continue) interim response if the method, target
request-line and header fields are not sufficient to cause an URI, and header fields are not sufficient to cause an immediate
immediate success, redirect, or error response. This allows the success, redirect, or error response. This allows the client to wait
client to wait for an indication that it is worthwhile to send the for an indication that it is worthwhile to send the content before
message body before actually doing so, which can improve efficiency actually doing so, which can improve efficiency when the data is huge
when the message body is huge or when the client anticipates that an or when the client anticipates that an error is likely (e.g., when
error is likely (e.g., when sending a state-changing method, for the sending a state-changing method, for the first time, without
first time, without previously verified authentication credentials). previously verified authentication credentials).
For example, a request that begins with For example, a request that begins with
PUT /somewhere/fun HTTP/1.1 PUT /somewhere/fun HTTP/1.1
Host: origin.example.com Host: origin.example.com
Content-Type: video/h264 Content-Type: video/h264
Content-Length: 1234567890987 Content-Length: 1234567890987
Expect: 100-continue Expect: 100-continue
allows the origin server to immediately respond with an error allows the origin server to immediately respond with an error
message, such as 401 (Unauthorized) or 405 (Method Not Allowed), message, such as 401 (Unauthorized) or 405 (Method Not Allowed),
before the client starts filling the pipes with an unnecessary data before the client starts filling the pipes with an unnecessary data
transfer. transfer.
Requirements for clients: Requirements for clients:
o A client MUST NOT generate a 100-continue expectation in a request o A client MUST NOT generate a 100-continue expectation in a request
that does not include a message body. that does not include content.
o A client that will wait for a 100 (Continue) response before o A client that will wait for a 100 (Continue) response before
sending the request message body MUST send an Expect header field sending the request content MUST send an Expect header field
containing a 100-continue expectation. containing a 100-continue expectation.
o A client that sends a 100-continue expectation is not required to o A client that sends a 100-continue expectation is not required to
wait for any specific length of time; such a client MAY proceed to wait for any specific length of time; such a client MAY proceed to
send the message body even if it has not yet received a response. send the content even if it has not yet received a response.
Furthermore, since 100 (Continue) responses cannot be sent through Furthermore, since 100 (Continue) responses cannot be sent through
an HTTP/1.0 intermediary, such a client SHOULD NOT wait for an an HTTP/1.0 intermediary, such a client SHOULD NOT wait for an
indefinite period before sending the message body. indefinite period before sending the content.
o A client that receives a 417 (Expectation Failed) status code in o A client that receives a 417 (Expectation Failed) status code in
response to a request containing a 100-continue expectation SHOULD response to a request containing a 100-continue expectation SHOULD
repeat that request without a 100-continue expectation, since the repeat that request without a 100-continue expectation, since the
417 response merely indicates that the response chain does not 417 response merely indicates that the response chain does not
support expectations (e.g., it passes through an HTTP/1.0 server). support expectations (e.g., it passes through an HTTP/1.0 server).
Requirements for servers: Requirements for servers:
o A server that receives a 100-continue expectation in an HTTP/1.0 o A server that receives a 100-continue expectation in an HTTP/1.0
request MUST ignore that expectation. request MUST ignore that expectation.
o A server MAY omit sending a 100 (Continue) response if it has o A server MAY omit sending a 100 (Continue) response if it has
already received some or all of the message body for the already received some or all of the content for the corresponding
corresponding request, or if the framing indicates that there is request, or if the framing indicates that there is no content.
no message body.
o A server that sends a 100 (Continue) response MUST ultimately send o A server that sends a 100 (Continue) response MUST ultimately send
a final status code, once the message body is received and a final status code, once the request content is received and
processed, unless the connection is closed prematurely. processed, unless the connection is closed prematurely.
o A server that responds with a final status code before reading the o A server that responds with a final status code before reading the
entire message body SHOULD indicate in that response whether it entire request content SHOULD indicate whether it intends to close
intends to close the connection or continue reading and discarding the connection (e.g., see Section 9.6 of [Messaging]) or continue
the request message (see Section 6.6 of [RFC7230]). reading the request content.
An origin server MUST, upon receiving an HTTP/1.1 (or later) An origin server MUST, upon receiving an HTTP/1.1 (or later) request
request-line and a complete header section that that has a method, target URI, and complete header section that
contains a 100-continue expectation and indicates a request message contains a 100-continue expectation and an indication that request
body will follow, either send an immediate response with a final content will follow, either send an immediate response with a final
status code, if that status can be determined by examining just the status code, if that status can be determined by examining just the
request-line and header fields, or send an immediate 100 method, target URI, and header fields, or send an immediate 100
(Continue) response to encourage the client to send the request's (Continue) response to encourage the client to send the request
message body. The origin server MUST NOT wait for the message body content. The origin server MUST NOT wait for the content before
before sending the 100 (Continue) response. sending the 100 (Continue) response.
A proxy MUST, upon receiving an HTTP/1.1 (or later) request-line and A proxy MUST, upon receiving an HTTP/1.1 (or later) request that has
a complete header section that contains a 100-continue expectation and a method, target URI, and complete header section that contains a
indicates a request message body will follow, 100-continue expectation and indicates a request content will follow,
either send an immediate response with a final status code, if that either send an immediate response with a final status code, if that
status can be determined by examining just the request-line and header status can be determined by examining just the method, target URI,
fields, or begin forwarding the request toward the origin and header fields, or begin forwarding the request toward the origin
server by sending a corresponding request-line and header section to server by sending a corresponding request-line and header section to
the next inbound server. If the proxy believes (from configuration the next inbound server. If the proxy believes (from configuration
or past interaction) that the next inbound server only supports or past interaction) that the next inbound server only supports
HTTP/1.0, the proxy MAY generate an immediate 100 (Continue) response HTTP/1.0, the proxy MAY generate an immediate 100 (Continue) response
to encourage the client to begin sending the message body. to encourage the client to begin sending the content.
Note: The Expect header field was added after the original
publication of HTTP/1.1 [RFC2068] as both the means to request an
interim 100 (Continue) response and the general mechanism for
indicating must-understand extensions. However, the extension
mechanism has not been used by clients and the must-understand
requirements have not been implemented by many servers, rendering
the extension mechanism useless. This specification has removed
the extension mechanism in order to simplify the definition and
processing of 100-continue.
10.1.2. From 10.1.2. From
The "From" header field contains an Internet email address for a The "From" header field contains an Internet email address for a
human user who controls the requesting user agent. The address ought human user who controls the requesting user agent. The address ought
to be machine-usable, as defined by "mailbox" in Section 3.4 of to be machine-usable, as defined by "mailbox" in Section 3.4 of
[RFC5322]: [RFC5322]:
From = mailbox From = mailbox
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The "Referer" [sic] header field allows the user agent to specify a The "Referer" [sic] header field allows the user agent to specify a
URI reference for the resource from which the target URI was obtained URI reference for the resource from which the target URI was obtained
(i.e., the "referrer", though the field name is misspelled). A user (i.e., the "referrer", though the field name is misspelled). A user
agent MUST NOT include the fragment and userinfo components of the agent MUST NOT include the fragment and userinfo components of the
URI reference [RFC3986], if any, when generating the Referer field URI reference [RFC3986], if any, when generating the Referer field
value. value.
Referer = absolute-URI / partial-URI Referer = absolute-URI / partial-URI
The field value is either an absolute-URI or a partial-URI. In the
latter case (Section 4), the referenced URI is relative to the target
URI ([RFC3986], Section 5).
The Referer header field allows servers to generate back-links to The Referer header field allows servers to generate back-links to
other resources for simple analytics, logging, optimized caching, other resources for simple analytics, logging, optimized caching,
etc. It also allows obsolete or mistyped links to be found for etc. It also allows obsolete or mistyped links to be found for
maintenance. Some servers use the Referer header field as a means of maintenance. Some servers use the Referer header field as a means of
denying links from other sites (so-called "deep linking") or denying links from other sites (so-called "deep linking") or
restricting cross-site request forgery (CSRF), but not all requests restricting cross-site request forgery (CSRF), but not all requests
contain it. contain it.
Example: Example:
Referer: http://www.example.org/hypertext/Overview.html Referer: http://www.example.org/hypertext/Overview.html
If the target URI was obtained from a source that does not have its If the target URI was obtained from a source that does not have its
own URI (e.g., input from the user keyboard, or an entry within the own URI (e.g., input from the user keyboard, or an entry within the
user's bookmarks/favorites), the user agent MUST either exclude the user's bookmarks/favorites), the user agent MUST either exclude the
Referer field or send it with a value of "about:blank". Referer header field or send it with a value of "about:blank".
The Referer field has the potential to reveal information about the The Referer header field has the potential to reveal information
request context or browsing history of the user, which is a privacy about the request context or browsing history of the user, which is a
concern if the referring resource's identifier reveals personal privacy concern if the referring resource's identifier reveals
information (such as an account name) or a resource that is supposed personal information (such as an account name) or a resource that is
to be confidential (such as behind a firewall or internal to a supposed to be confidential (such as behind a firewall or internal to
secured service). Most general-purpose user agents do not send the a secured service). Most general-purpose user agents do not send the
Referer header field when the referring resource is a local "file" or Referer header field when the referring resource is a local "file" or
"data" URI. A user agent MUST NOT send a Referer header field in an "data" URI. A user agent MUST NOT send a Referer header field in an
unsecured HTTP request if the referring page was received with a unsecured HTTP request if the referring page was received with a
secure protocol. See Section 9.4 for additional security secure protocol. See Section 17.9 for additional security
considerations. considerations.
Some intermediaries have been known to indiscriminately remove Some intermediaries have been known to indiscriminately remove
Referer header fields from outgoing requests. This has the Referer header fields from outgoing requests. This has the
unfortunate side effect of interfering with protection against CSRF unfortunate side effect of interfering with protection against CSRF
attacks, which can be far more harmful to their users. attacks, which can be far more harmful to their users.
Intermediaries and user agent extensions that wish to limit Intermediaries and user agent extensions that wish to limit
information disclosure in Referer ought to restrict their changes to information disclosure in Referer ought to restrict their changes to
specific edits, such as replacing internal domain names with specific edits, such as replacing internal domain names with
pseudonyms or truncating the query and/or path components. An pseudonyms or truncating the query and/or path components. An
intermediary SHOULD NOT modify or delete the Referer header field intermediary SHOULD NOT modify or delete the Referer header field
when the field value shares the same scheme and host as the request when the field value shares the same scheme and host as the target
target. URI.
10.1.4. TE 10.1.4. TE
The "TE" header field in a request indicates what transfer codings, The "TE" header field in a request can be used to indicate that the
besides chunked, the client is willing to accept in response, and sender will not discard trailer fields when it contains a "trailers"
whether or not the client is willing to accept trailer fields in a member, as described in Section 6.5.
chunked transfer coding.
[new] Additionally, specific HTTP versions can use it to indicate the
transfer codings the client is willing to accept in the response. As
of publication, only HTTP/1.1 uses transfer codings (see Section 7 of
[Messaging]).
The TE field-value consists of a comma-separated list of transfer The TE field value consists of a list of tokens, each allowing for
coding names, each allowing for optional parameters (as described in optional parameters (except for the special case "trailers").
Section 4), and/or the keyword "trailers". A client MUST NOT send
the chunked transfer coding name in TE; chunked is always acceptable
for HTTP/1.1 recipients.
TE = #t-codings TE = #t-codings
t-codings = "trailers" / ( transfer-coding [ t-ranking ] ) t-codings = "trailers" / ( transfer-coding [ weight ] )
t-ranking = OWS ";" OWS "q=" rank transfer-coding = token *( OWS ";" OWS transfer-parameter )
rank = ( "0" [ "." 0*3DIGIT ] ) transfer-parameter = token BWS "=" BWS ( token / quoted-string )
/ ( "1" [ "." 0*3("0") ] )
10.1.5. Trailer 10.1.5. Trailer
This allows the recipient to prepare for receipt of that The "Trailer" header field provides a list of field names that the
metadata before it starts processing the body, which is useful sender anticipates sending as trailer fields within that message.
if the message is being streamed and the recipient wishes to This allows a recipient to prepare for receipt of the indicated
confirm an integrity check on the fly. metadata before it starts processing the content.
Trailer = 1#field-name Trailer = #field-name
[new] For example, a sender might indicate that a message integrity check
will be computed as the content is being streamed and provide the
final signature as a trailer field. This allows a recipient to
perform the same check on the fly as the content is received.
When a message includes a message body encoded with the chunked A sender that intends to generate one or more trailer fields in a
transfer coding and the sender desires to send metadata in the form message SHOULD generate a Trailer header field in the header section
of trailer fields at the end of the message, the sender SHOULD of that message to indicate which fields might be present in the
generate a Trailer header field before the message body to indicate trailers.
which fields will be present in the trailers.
10.1.6. User-Agent 10.1.6. User-Agent
The "User-Agent" header field contains information about the user The "User-Agent" header field contains information about the user
agent originating the request, which is often used by servers to help agent originating the request, which is often used by servers to help
identify the scope of reported interoperability problems, to work identify the scope of reported interoperability problems, to work
around or tailor responses to avoid particular user agent around or tailor responses to avoid particular user agent
limitations, and for analytics regarding browser or operating system limitations, and for analytics regarding browser or operating system
use. A user agent SHOULD send a User-Agent field in each request use. A user agent SHOULD send a User-Agent header field in each
unless specifically configured not to do so. request unless specifically configured not to do so.
User-Agent = product *( RWS ( product / comment ) ) User-Agent = product *( RWS ( product / comment ) )
The User-Agent field-value consists of one or more product The User-Agent field value consists of one or more product
identifiers, each followed by zero or more comments (Section 3.2 of identifiers, each followed by zero or more comments (Section 5.6.5),
[RFC7230]), which together identify the user agent software and its which together identify the user agent software and its significant
significant subproducts. By convention, the product identifiers are subproducts. By convention, the product identifiers are listed in
listed in decreasing order of their significance for identifying the decreasing order of their significance for identifying the user agent
user agent software. Each product identifier consists of a name and software. Each product identifier consists of a name and optional
optional version. version.
product = token ["/" product-version] product = token ["/" product-version]
product-version = token product-version = token
A sender SHOULD limit generated product identifiers to what is A sender SHOULD limit generated product identifiers to what is
necessary to identify the product; a sender MUST NOT generate necessary to identify the product; a sender MUST NOT generate
advertising or other nonessential information within the product advertising or other nonessential information within the product
identifier. A sender SHOULD NOT generate information in identifier. A sender SHOULD NOT generate information in
product-version that is not a version identifier (i.e., successive product-version that is not a version identifier (i.e., successive
versions of the same product name ought to differ only in the versions of the same product name ought to differ only in the
product-version portion of the product identifier). product-version portion of the product identifier).
Example: Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3 User-Agent: CERN-LineMode/2.15 libwww/2.17b3
A user agent SHOULD NOT generate a User-Agent field containing A user agent SHOULD NOT generate a User-Agent header field containing
needlessly fine-grained detail and SHOULD limit the addition of needlessly fine-grained detail and SHOULD limit the addition of
subproducts by third parties. Overly long and detailed User-Agent subproducts by third parties. Overly long and detailed User-Agent
field values increase request latency and the risk of a user being field values increase request latency and the risk of a user being
identified against their wishes ("fingerprinting"). identified against their wishes ("fingerprinting").
Likewise, implementations are encouraged not to use the product Likewise, implementations are encouraged not to use the product
tokens of other implementations in order to declare compatibility tokens of other implementations in order to declare compatibility
with them, as this circumvents the purpose of the field. If a user with them, as this circumvents the purpose of the field. If a user
agent masquerades as a different user agent, recipients can assume agent masquerades as a different user agent, recipients can assume
that the user intentionally desires to see responses tailored for that the user intentionally desires to see responses tailored for
that identified user agent, even if they might not work as well for that identified user agent, even if they might not work as well for
the actual user agent being used. the actual user agent being used.
10.2. Response Context 10.2. Response Context Fields
Response header fields can supply control data that supplements the Response header fields can supply control data that supplements the
status code, directs caching, or instructs the client where to go status code, directs caching, or instructs the client where to go
next. next.
The response header fields allow the server to pass additional The response header fields allow the server to pass additional
information about the response beyond what is placed in the information about the response beyond the status code. These header
status-line. These header fields give information about the server, fields give information about the server, about further access to the
about further access to the target resource, or about related target resource, or about related resources.
resources.
Although each response header field has a defined meaning, in Although each response header field has a defined meaning, in
general, the precise semantics might be further refined by the general, the precise semantics might be further refined by the
semantics of the request method and/or response status code. semantics of the request method and/or response status code.
The remaining response header fields provide more information about The remaining response header fields provide more information about
the target resource for potential use in later requests. the target resource for potential use in later requests.
10.2.1. Allow 10.2.1. Allow
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with the resource. with the resource.
Allow = #method Allow = #method
Example of use: Example of use:
Allow: GET, HEAD, PUT Allow: GET, HEAD, PUT
The actual set of allowed methods is defined by the origin server at The actual set of allowed methods is defined by the origin server at
the time of each request. An origin server MUST generate an Allow the time of each request. An origin server MUST generate an Allow
field in a 405 (Method Not Allowed) response and MAY do so in any header field in a 405 (Method Not Allowed) response and MAY do so in
other response. An empty Allow field value indicates that the any other response. An empty Allow field value indicates that the
resource allows no methods, which might occur in a 405 response if resource allows no methods, which might occur in a 405 response if
the resource has been temporarily disabled by configuration. the resource has been temporarily disabled by configuration.
A proxy MUST NOT modify the Allow header field -- it does not need to A proxy MUST NOT modify the Allow header field - it does not need to
understand all of the indicated methods in order to handle them understand all of the indicated methods in order to handle them
according to the generic message handling rules. according to the generic message handling rules.
10.2.2. Date 10.2.2. Date
The "Date" header field represents the date and time at which the The "Date" header field represents the date and time at which the
message was originated, having the same semantics as the Origination message was originated, having the same semantics as the Origination
Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The
field value is an HTTP-date, as defined in Section 7.1.1.1. field value is an HTTP-date, as defined in Section 5.6.7.
Date = HTTP-date Date = HTTP-date
An example is An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT Date: Tue, 15 Nov 1994 08:12:31 GMT
When a Date header field is generated, the sender SHOULD generate its When a Date header field is generated, the sender SHOULD generate its
field value as the best available approximation of the date and time field value as the best available approximation of the date and time
of message generation. In theory, the date ought to represent the of message generation. In theory, the date ought to represent the
moment just before the payload is generated. In practice, the date moment just before the content is generated. In practice, the date
can be generated at any time during message origination. can be generated at any time during message origination.
An origin server MUST NOT send a Date header field if it does not An origin server MUST NOT send a Date header field if it does not
have a clock capable of providing a reasonable approximation of the have a clock capable of providing a reasonable approximation of the
current instance in Coordinated Universal Time. An origin server MAY current instance in Coordinated Universal Time. An origin server MAY
send a Date header field if the response is in the 1xx send a Date header field if the response is in the 1xx
(Informational) or 5xx (Server Error) class of status codes. An (Informational) or 5xx (Server Error) class of status codes. An
origin server MUST send a Date header field in all other cases. origin server MUST send a Date header field in all other cases.
A recipient with a clock that receives a response message without a A recipient with a clock that receives a response message without a
Date header field MUST record the time it was received and append a Date header field MUST record the time it was received and append a
corresponding Date header field to the message's header section if it corresponding Date header field to the message's header section if it
is cached or forwarded downstream. is cached or forwarded downstream.
A recipient with a clock that receives a response with an invalid
Date header field value MAY replace that value with the time that
response was received.
A user agent MAY send a Date header field in a request, though A user agent MAY send a Date header field in a request, though
generally will not do so unless it is believed to convey useful generally will not do so unless it is believed to convey useful
information to the server. For example, custom applications of HTTP information to the server. For example, custom applications of HTTP
might convey a Date if the server is expected to adjust its might convey a Date if the server is expected to adjust its
interpretation of the user's request based on differences between the interpretation of the user's request based on differences between the
user agent and server clocks. user agent and server clocks.
10.2.3. Location 10.2.3. Location
The "Location" header field is used in some responses to refer to a The "Location" header field is used in some responses to refer to a
specific resource in relation to the response. The type of specific resource in relation to the response. The type of
relationship is defined by the combination of request method and relationship is defined by the combination of request method and
status code semantics. status code semantics.
Location = URI-reference Location = URI-reference
The field value consists of a single URI-reference. When it has the The field value consists of a single URI-reference. When it has the
form of a relative reference ([RFC3986], Section 4.2), the final form of a relative reference ([RFC3986], Section 4.2), the final
value is computed by resolving it against the effective request URI value is computed by resolving it against the target URI ([RFC3986],
([RFC3986], Section 5). Section 5).
For 201 (Created) responses, the Location value refers to the primary For 201 (Created) responses, the Location value refers to the primary
resource created by the request. For 3xx (Redirection) responses, resource created by the request. For 3xx (Redirection) responses,
the Location value refers to the preferred target resource for the Location value refers to the preferred target resource for
automatically redirecting the request. automatically redirecting the request.
If the Location value provided in a 3xx (Redirection) response does If the Location value provided in a 3xx (Redirection) response does
not have a fragment component, a user agent MUST process the not have a fragment component, a user agent MUST process the
redirection as if the value inherits the fragment component of the redirection as if the value inherits the fragment component of the
URI reference used to generate the request target (i.e., the URI reference used to generate the target URI (i.e., the redirection
redirection inherits the original reference's fragment, if any). inherits the original reference's fragment, if any).
For example, a GET request generated for the URI reference For example, a GET request generated for the URI reference
"http://www.example.org/~tim" might result in a 303 (See Other) "http://www.example.org/~tim" might result in a 303 (See Other)
response containing the header field: response containing the header field:
Location: /People.html#tim Location: /People.html#tim
which suggests that the user agent redirect to which suggests that the user agent redirect to
"http://www.example.org/People.html#tim" "http://www.example.org/People.html#tim"
skipping to change at line 4124 skipping to change at page 101, line 29
which suggests that the user agent redirect to which suggests that the user agent redirect to
"http://www.example.net/index.html#larry", preserving the original "http://www.example.net/index.html#larry", preserving the original
fragment identifier. fragment identifier.
There are circumstances in which a fragment identifier in a Location There are circumstances in which a fragment identifier in a Location
value would not be appropriate. For example, the Location header value would not be appropriate. For example, the Location header
field in a 201 (Created) response is supposed to provide a URI that field in a 201 (Created) response is supposed to provide a URI that
is specific to the created resource. is specific to the created resource.
Note: Some recipients attempt to recover from Location fields that | *Note:* Some recipients attempt to recover from Location header
are not valid URI references. This specification does not mandate | fields that are not valid URI references. This specification
or define such processing, but does allow it for the sake of | does not mandate or define such processing, but does allow it
robustness. | for the sake of robustness. A Location field value cannot
| allow a list of members because the comma list separator is a
| valid data character within a URI-reference. If an invalid
| message is sent with multiple Location field lines, a recipient
| along the path might combine those field lines into one value.
| Recovery of a valid Location field value from that situation is
| difficult and not interoperable across implementations.
Note: The Content-Location header field (Section 3.1.4.2) differs | *Note:* The Content-Location header field (Section 8.7) differs
from Location in that the Content-Location refers to the most | from Location in that the Content-Location refers to the most
specific resource corresponding to the enclosed representation. | specific resource corresponding to the enclosed representation.
It is therefore possible for a response to contain both the | It is therefore possible for a response to contain both the
Location and Content-Location header fields. | Location and Content-Location header fields.
10.2.4. Retry-After 10.2.4. Retry-After
Servers send the "Retry-After" header field to indicate how long the Servers send the "Retry-After" header field to indicate how long the
user agent ought to wait before making a follow-up request. When user agent ought to wait before making a follow-up request. When
sent with a 503 (Service Unavailable) response, Retry-After indicates sent with a 503 (Service Unavailable) response, Retry-After indicates
how long the service is expected to be unavailable to the client. how long the service is expected to be unavailable to the client.
When sent with any 3xx (Redirection) response, Retry-After indicates When sent with any 3xx (Redirection) response, Retry-After indicates
the minimum time that the user agent is asked to wait before issuing the minimum time that the user agent is asked to wait before issuing
the redirected request. the redirected request.
The value of this field can be either an HTTP-date or a number of The Retry-After field value can be either an HTTP-date or a number of
seconds to delay after the response is received. seconds to delay after the response is received.
Retry-After = HTTP-date / delay-seconds Retry-After = HTTP-date / delay-seconds
A delay-seconds value is a non-negative decimal integer, representing A delay-seconds value is a non-negative decimal integer, representing
time in seconds. time in seconds.
delay-seconds = 1*DIGIT delay-seconds = 1*DIGIT
Two examples of its use are Two examples of its use are
skipping to change at line 4169 skipping to change at page 102, line 39
In the latter example, the delay is 2 minutes. In the latter example, the delay is 2 minutes.
10.2.5. Server 10.2.5. Server
The "Server" header field contains information about the software The "Server" header field contains information about the software
used by the origin server to handle the request, which is often used used by the origin server to handle the request, which is often used
by clients to help identify the scope of reported interoperability by clients to help identify the scope of reported interoperability
problems, to work around or tailor requests to avoid particular problems, to work around or tailor requests to avoid particular
server limitations, and for analytics regarding server or operating server limitations, and for analytics regarding server or operating
system use. An origin server MAY generate a Server field in its system use. An origin server MAY generate a Server header field in
responses. its responses.
Server = product *( RWS ( product / comment ) ) Server = product *( RWS ( product / comment ) )
The Server field-value consists of one or more product identifiers, The Server header field value consists of one or more product
each followed by zero or more comments (Section 3.2 of [RFC7230]), identifiers, each followed by zero or more comments (Section 5.6.5),
which together identify the origin server software and its which together identify the origin server software and its
significant subproducts. By convention, the product identifiers are significant subproducts. By convention, the product identifiers are
listed in decreasing order of their significance for identifying the listed in decreasing order of their significance for identifying the
origin server software. Each product identifier consists of a name origin server software. Each product identifier consists of a name
and optional version, as defined in Section 5.5.3. and optional version, as defined in Section 10.1.6.
Example: Example:
Server: CERN/3.0 libwww/2.17 Server: CERN/3.0 libwww/2.17
An origin server SHOULD NOT generate a Server field containing An origin server SHOULD NOT generate a Server header field containing
needlessly fine-grained detail and SHOULD limit the addition of needlessly fine-grained detail and SHOULD limit the addition of
subproducts by third parties. Overly long and detailed Server field subproducts by third parties. Overly long and detailed Server field
values increase response latency and potentially reveal internal values increase response latency and potentially reveal internal
implementation details that might make it (slightly) easier for implementation details that might make it (slightly) easier for
attackers to find and exploit known security holes. attackers to find and exploit known security holes.
11. HTTP Authentication 11. HTTP Authentication
HTTP provides a simple challenge-response authentication framework
that can be used by a server to challenge a client request and by a
client to provide authentication information.
Two header fields are used for carrying authentication credentials,
as defined in [RFC7235].
This document defines HTTP/1.1 authentication in terms of the
architecture defined in "Hypertext Transfer Protocol (HTTP/1.1):
Message Syntax and Routing" [RFC7230], including the general
framework previously described in "HTTP Authentication: Basic and
Digest Access Authentication" [RFC2617] and the related fields and
status codes previously defined in "Hypertext Transfer Protocol --
HTTP/1.1" [RFC2616].
11.1. Authentication Scheme 11.1. Authentication Scheme
HTTP provides a general framework for access control and HTTP provides a general framework for access control and
authentication, via an extensible set of challenge-response authentication, via an extensible set of challenge-response
authentication schemes, which can be used by a server to challenge a authentication schemes, which can be used by a server to challenge a
client request and by a client to provide authentication information. client request and by a client to provide authentication information.
It uses a case-insensitive token as a means to identify the authentication It uses a case-insensitive token to identify the authentication
scheme, scheme
auth-scheme = token auth-scheme = token
The IANA Authentication Scheme Registry (Section 5.1) lists Aside from the general framework, this document does not specify any
registered authentication schemes and their corresponding authentication schemes. New and existing authentication schemes are
specifications, including the "basic" and "digest" authentication specified independently and ought to be registered within the
schemes previously defined by RFC 2617. "Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry".
For example, the "basic" and "digest" authentication schemes are
defined by RFC 7617 and RFC 7616, respectively.
11.2. Authentication Parameters 11.2. Authentication Parameters
followed by additional information The authentication scheme is followed by additional information
necessary for achieving authentication via that scheme. necessary for achieving authentication via that scheme as either a
The latter can be either a
comma-separated list of parameters or a single sequence of characters comma-separated list of parameters or a single sequence of characters
capable of holding base64-encoded information. capable of holding base64-encoded information.
token68 = 1*( ALPHA / DIGIT / token68 = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"=" "-" / "." / "_" / "~" / "+" / "/" ) *"="
The token68 syntax allows the 66 unreserved URI characters The token68 syntax allows the 66 unreserved URI characters
([RFC3986]), plus a few others, so that it can hold a base64, ([RFC3986]), plus a few others, so that it can hold a base64,
base64url (URL and filename safe alphabet), base32, or base16 (hex) base64url (URL and filename safe alphabet), base32, or base16 (hex)
encoding, with or without padding, but excluding whitespace encoding, with or without padding, but excluding whitespace
([RFC4648]). ([RFC4648]).
Authentication parameters are name=value pairs, where the name token Authentication parameters are name=value pairs, where the name token
is matched case-insensitively, and each parameter name MUST only is matched case-insensitively and each parameter name MUST only occur
occur once per challenge. once per challenge.
auth-param = token BWS "=" BWS ( token / quoted-string ) auth-param = token BWS "=" BWS ( token / quoted-string )
Parameter values can be expressed either as "token" or as "quoted- Parameter values can be expressed either as "token" or as "quoted-
string" (Section 3.2.6 of [RFC7230]). string" (Section 5.6). Authentication scheme definitions need to
Authentication scheme definitions need to allow both notations, both accept both notations, both for senders and recipients, to allow
for senders and recipients. This allows recipients to use generic parsing components regardless of the
recipients to use generic parsing components, independent of the authentication scheme.
authentication scheme in use.
For backwards compatibility, authentication scheme definitions can For backwards compatibility, authentication scheme definitions can
restrict the format for senders to one of the two variants. This can restrict the format for senders to one of the two variants. This can
be important when it is known that deployed implementations will fail be important when it is known that deployed implementations will fail
when encountering one of the two formats. when encountering one of the two formats.
11.3. Challenge and Response 11.3. Challenge and Response
A 401 (Unauthorized) response message is used by an origin server to A 401 (Unauthorized) response message is used by an origin server to
challenge the authorization of a user agent, including a challenge the authorization of a user agent, including a
WWW-Authenticate header field containing at least one challenge WWW-Authenticate header field containing at least one challenge
applicable to the requested resource. applicable to the requested resource.
A 407 (Proxy Authentication Required) response message is used by a A 407 (Proxy Authentication Required) response message is used by a
proxy to challenge the authorization of a client, including a proxy to challenge the authorization of a client, including a
Proxy-Authenticate header field containing at least one challenge Proxy-Authenticate header field containing at least one challenge
applicable to the proxy for the requested resource. applicable to the proxy for the requested resource.
challenge = auth-scheme [ 1*SP ( token68 / #auth-param ) ] challenge = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
Note: Many clients fail to parse a challenge that contains an | *Note:* Many clients fail to parse a challenge that contains an
unknown scheme. A workaround for this problem is to list well- | unknown scheme. A workaround for this problem is to list well-
supported schemes (such as "basic") first. | supported schemes (such as "basic") first.
A user agent that wishes to authenticate itself with an origin server A user agent that wishes to authenticate itself with an origin server
-- usually, but not necessarily, after receiving a 401 (Unauthorized) - usually, but not necessarily, after receiving a 401 (Unauthorized)
-- can do so by including an Authorization header field with the - can do so by including an Authorization header field with the
request. request.
A client that wishes to authenticate itself with a proxy -- usually, A client that wishes to authenticate itself with a proxy - usually,
but not necessarily, after receiving a 407 (Proxy Authentication but not necessarily, after receiving a 407 (Proxy Authentication
Required) -- can do so by including a Proxy-Authorization header Required) - can do so by including a Proxy-Authorization header field
field with the request. with the request.
11.4. Credentials 11.4. Credentials
Both the Authorization field value and the Proxy-Authorization field Both the Authorization field value and the Proxy-Authorization field
value contain the client's credentials for the realm of the resource value contain the client's credentials for the realm of the resource
being requested, based upon a challenge received in a response being requested, based upon a challenge received in a response
(possibly at some point in the past). When creating their values, (possibly at some point in the past). When creating their values,
the user agent ought to do so by selecting the challenge with what it the user agent ought to do so by selecting the challenge with what it
considers to be the most secure auth-scheme that it understands, considers to be the most secure auth-scheme that it understands,
obtaining credentials from the user as appropriate. Transmission of obtaining credentials from the user as appropriate. Transmission of
credentials within header field values implies significant security credentials within header field values implies significant security
considerations regarding the confidentiality of the underlying considerations regarding the confidentiality of the underlying
connection, as described in Section 6.1. connection, as described in Section 17.15.1.
credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ] credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
Upon receipt of a request for a protected resource that omits Upon receipt of a request for a protected resource that omits
credentials, contains invalid credentials (e.g., a bad password) or credentials, contains invalid credentials (e.g., a bad password) or
partial credentials (e.g., when the authentication scheme requires partial credentials (e.g., when the authentication scheme requires
more than one round trip), an origin server SHOULD send a 401 more than one round trip), an origin server SHOULD send a 401
(Unauthorized) response that contains a WWW-Authenticate header field (Unauthorized) response that contains a WWW-Authenticate header field
with at least one (possibly new) challenge applicable to the with at least one (possibly new) challenge applicable to the
requested resource. requested resource.
Likewise, upon receipt of a request that omits proxy credentials or Likewise, upon receipt of a request that omits proxy credentials or
contains invalid or partial proxy credentials, a proxy that requires contains invalid or partial proxy credentials, a proxy that requires
authentication SHOULD generate a 407 (Proxy Authentication Required) authentication SHOULD generate a 407 (Proxy Authentication Required)
response that contains a Proxy-Authenticate header field with at response that contains a Proxy-Authenticate header field with at
least one (possibly new) challenge applicable to the proxy. least one (possibly new) challenge applicable to the proxy.
A server that receives valid credentials that are not adequate to A server that receives valid credentials that are not adequate to
gain access ought to respond with the 403 (Forbidden) status code gain access ought to respond with the 403 (Forbidden) status code
(Section 6.5.3 of [RFC7231]). (Section 15.5.4).
HTTP does not restrict applications to this simple challenge-response HTTP does not restrict applications to this simple challenge-response
framework for access authentication. Additional mechanisms can be framework for access authentication. Additional mechanisms can be
used, such as authentication at the transport level or via message used, such as authentication at the transport level or via message
encapsulation, and with additional header fields specifying encapsulation, and with additional header fields specifying
authentication information. However, such additional mechanisms are authentication information. However, such additional mechanisms are
not defined by this specification. not defined by this specification.
Note that various custom mechanisms for user authentication use the Note that various custom mechanisms for user authentication use the
Cookie header field for this purpose, as defined in [RFC6265]. Set-Cookie and Cookie header fields, defined in [RFC6265], for
passing tokens related to authentication.
11.5. Establishing a Protection Space (Realm) 11.5. Establishing a Protection Space (Realm)
The "realm" authentication parameter is reserved for use by The _realm_ authentication parameter is reserved for use by
authentication schemes that wish to indicate a scope of protection. authentication schemes that wish to indicate a scope of protection.
A protection space is defined by the canonical root URI (the scheme A _protection space_ is defined by the origin (see Section 4.3.1) of
and authority components of the effective request URI; see Section the server being accessed, in combination with the realm value if
5.5 of [RFC7230]) of the server being accessed, in combination with present. These realms allow the protected resources on a server to
the realm value if present. These realms allow the protected be partitioned into a set of protection spaces, each with its own
resources on a server to be partitioned into a set of protection authentication scheme and/or authorization database. The realm value
spaces, each with its own authentication scheme and/or authorization is a string, generally assigned by the origin server, that can have
database. The realm value is a string, generally assigned by the additional semantics specific to the authentication scheme. Note
origin server, that can have additional semantics specific to the that a response can have multiple challenges with the same auth-
authentication scheme. Note that a response can have multiple scheme but with different realms.
challenges with the same auth-scheme but with different realms.
The protection space determines the domain over which credentials can The protection space determines the domain over which credentials can
be automatically applied. If a prior request has been authorized, be automatically applied. If a prior request has been authorized,
the user agent MAY reuse the same credentials for all other requests the user agent MAY reuse the same credentials for all other requests
within that protection space for a period of time determined by the within that protection space for a period of time determined by the
authentication scheme, parameters, and/or user preferences (such as a authentication scheme, parameters, and/or user preferences (such as a
configurable inactivity timeout). Unless specifically allowed by the configurable inactivity timeout). Unless specifically allowed by the
authentication scheme, a single protection space cannot extend authentication scheme, a single protection space cannot extend
outside the scope of its server. outside the scope of its server.
For historical reasons, a sender MUST only generate the quoted-string For historical reasons, a sender MUST only generate the quoted-string
syntax. Recipients might have to support both token and syntax. Recipients might have to support both token and quoted-
quoted-string syntax for maximum interoperability with existing string syntax for maximum interoperability with existing clients that
clients that have been accepting both notations for a long time. have been accepting both notations for a long time.
11.6. Authenticating Users to Origin Servers 11.6. Authenticating Users to Origin Servers
Authentication challenges indicate what mechanisms are available for
the client to provide authentication credentials in future requests.
This specification defines the "Authentication-Info" and "Proxy-
Authentication-Info" response header fields for use in HTTP
authentication schemes ([RFC7235]) that need to return information
once the client's authentication credentials have been accepted.
This section defines the syntax and semantics of header fields
related to the HTTP authentication framework.
11.6.1. WWW-Authenticate 11.6.1. WWW-Authenticate
The "WWW-Authenticate" header field indicates the authentication The "WWW-Authenticate" header field indicates the authentication
scheme(s) and parameters applicable to the target resource. scheme(s) and parameters applicable to the target resource.
WWW-Authenticate = 1#challenge WWW-Authenticate = #challenge
A server generating a 401 (Unauthorized) response MUST send a A server generating a 401 (Unauthorized) response MUST send a WWW-
WWW-Authenticate header field containing at least one challenge. A Authenticate header field containing at least one challenge. A
server MAY generate a WWW-Authenticate header field in other response server MAY generate a WWW-Authenticate header field in other response
messages to indicate that supplying credentials (or different messages to indicate that supplying credentials (or different
credentials) might affect the response. credentials) might affect the response.
A proxy forwarding a response MUST NOT modify any WWW-Authenticate A proxy forwarding a response MUST NOT modify any WWW-Authenticate
fields in that response. header fields in that response.
User agents are advised to take special care in parsing the field User agents are advised to take special care in parsing the field
value, as it might contain more than one challenge, and each value, as it might contain more than one challenge, and each
challenge can contain a comma-separated list of authentication challenge can contain a comma-separated list of authentication
parameters. Furthermore, the header field itself can occur multiple parameters. Furthermore, the header field itself can occur multiple
times. times.
For instance: For instance:
WWW-Authenticate: Newauth realm="apps", type=1, WWW-Authenticate: Newauth realm="apps", type=1,
title="Login to \"apps\"", Basic realm="simple" title="Login to \"apps\"", Basic realm="simple"
This header field contains two challenges; one for the "Newauth" This header field contains two challenges; one for the "Newauth"
scheme with a realm value of "apps", and two additional parameters scheme with a realm value of "apps", and two additional parameters
"type" and "title", and another one for the "Basic" scheme with a "type" and "title", and another one for the "Basic" scheme with a
realm value of "simple". realm value of "simple".
[new] Some user agents do not recognise this form, however. As a result,
sending a WWW-Authenticate field value with more than one member on
the same field line might not be interoperable.
Note: The challenge grammar production uses the list syntax as | *Note:* The challenge grammar production uses the list syntax
well. Therefore, a sequence of comma, whitespace, and comma can | as well. Therefore, a sequence of comma, whitespace, and comma
be considered either as applying to the preceding challenge, or to | can be considered either as applying to the preceding
be an empty entry in the list of challenges. In practice, this | challenge, or to be an empty entry in the list of challenges.
ambiguity does not affect the semantics of the header field value | In practice, this ambiguity does not affect the semantics of
and thus is harmless. | the header field value and thus is harmless.
11.6.2. Authorization 11.6.2. Authorization
The "Authorization" header field allows a user agent to authenticate The "Authorization" header field allows a user agent to authenticate
itself with an origin server -- usually, but not necessarily, after itself with an origin server - usually, but not necessarily, after
receiving a 401 (Unauthorized) response. Its value consists of receiving a 401 (Unauthorized) response. Its value consists of
credentials containing the authentication information of the user credentials containing the authentication information of the user
agent for the realm of the resource being requested. agent for the realm of the resource being requested.
Authorization = credentials Authorization = credentials
If a request is authenticated and a realm specified, the same If a request is authenticated and a realm specified, the same
credentials are presumed to be valid for all other requests within credentials are presumed to be valid for all other requests within
this realm (assuming that the authentication scheme itself does not this realm (assuming that the authentication scheme itself does not
require otherwise, such as credentials that vary according to a require otherwise, such as credentials that vary according to a
challenge value or using synchronized clocks). challenge value or using synchronized clocks).
A proxy forwarding a request MUST NOT modify any Authorization fields A proxy forwarding a request MUST NOT modify any Authorization header
in that request. See Section 3.2 of [RFC7234] for details of and fields in that request. See Section 3.5 of [Caching] for details of
requirements pertaining to handling of the Authorization field by and requirements pertaining to handling of the Authorization header
HTTP caches. field by HTTP caches.
11.6.3. Authentication-Info 11.6.3. Authentication-Info
HTTP authentication schemes can use the Authentication-Info response HTTP authentication schemes can use the Authentication-Info response
header field to communicate information after the client's field to communicate information after the client's authentication
authentication credentials have been accepted. This information can credentials have been accepted. This information can include a
include a finalization message from the server (e.g., it can contain finalization message from the server (e.g., it can contain the server
the server authentication). authentication).
The field value is a list of parameters (name/value pairs), using the The field value is a list of parameters (name/value pairs), using the
"auth-param" syntax defined in Section 2.1 of [RFC7235]. This "auth-param" syntax defined in Section 11.3. This specification only
specification only describes the generic format; authentication describes the generic format; authentication schemes using
schemes using Authentication-Info will define the individual Authentication-Info will define the individual parameters. The
parameters. The "Digest" Authentication Scheme, for instance, "Digest" Authentication Scheme, for instance, defines multiple
defines multiple parameters in Section 3.5 of [RFC7616]. parameters in Section 3.5 of [RFC7616].
Authentication-Info = #auth-param Authentication-Info = #auth-param
The Authentication-Info header field can be used in any HTTP The Authentication-Info field can be used in any HTTP response,
response, independently of request method and status code. Its independently of request method and status code. Its semantics are
semantics are defined by the authentication scheme indicated by the defined by the authentication scheme indicated by the Authorization
Authorization header field ([RFC7235], Section 4.2) of the header field (Section 11.6.2) of the corresponding request.
corresponding request.
A proxy forwarding a response is not allowed to modify the field A proxy forwarding a response is not allowed to modify the field
value in any way. value in any way.
Authentication-Info can be used inside trailers ([RFC7230], Authentication-Info can be sent as a trailer field (Section 6.5) when
Section 4.1.2) when the authentication scheme explicitly allows this. the authentication scheme explicitly allows this.
11.7. Authenticating Clients to Proxies 11.7. Authenticating Clients to Proxies
11.7.1. Proxy-Authenticate 11.7.1. Proxy-Authenticate
The "Proxy-Authenticate" header field consists of at least one The "Proxy-Authenticate" header field consists of at least one
challenge that indicates the authentication scheme(s) and parameters challenge that indicates the authentication scheme(s) and parameters
applicable to the proxy for this effective request URI (Section 5.5 applicable to the proxy for this request. A proxy MUST send at least
of [RFC7230]). A proxy MUST send at least one Proxy-Authenticate one Proxy-Authenticate header field in each 407 (Proxy Authentication
header field in each 407 (Proxy Authentication Required) response Required) response that it generates.
that it generates.
Proxy-Authenticate = 1#challenge Proxy-Authenticate = #challenge
Unlike WWW-Authenticate, the Proxy-Authenticate header field applies Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
only to the next outbound client on the response chain. This is only to the next outbound client on the response chain. This is
because only the client that chose a given proxy is likely to have because only the client that chose a given proxy is likely to have
the credentials necessary for authentication. However, when multiple the credentials necessary for authentication. However, when multiple
proxies are used within the same administrative domain, such as proxies are used within the same administrative domain, such as
office and regional caching proxies within a large corporate network, office and regional caching proxies within a large corporate network,
it is common for credentials to be generated by the user agent and it is common for credentials to be generated by the user agent and
passed through the hierarchy until consumed. Hence, in such a passed through the hierarchy until consumed. Hence, in such a
configuration, it will appear as if Proxy-Authenticate is being configuration, it will appear as if Proxy-Authenticate is being
forwarded because each proxy will send the same challenge set. forwarded because each proxy will send the same challenge set.
Note that the parsing considerations for WWW-Authenticate apply to Note that the parsing considerations for WWW-Authenticate apply to
this header field as well; see Section 4.1 for details. this header field as well; see Section 11.6.1 for details.
11.7.2. Proxy-Authorization 11.7.2. Proxy-Authorization
The "Proxy-Authorization" header field allows the client to identify The "Proxy-Authorization" header field allows the client to identify
itself (or its user) to a proxy that requires authentication. Its itself (or its user) to a proxy that requires authentication. Its
value consists of credentials containing the authentication value consists of credentials containing the authentication
information of the client for the proxy and/or realm of the resource information of the client for the proxy and/or realm of the resource
being requested. being requested.
Proxy-Authorization = credentials Proxy-Authorization = credentials
Unlike Authorization, the Proxy-Authorization header field applies Unlike Authorization, the Proxy-Authorization header field applies
only to the next inbound proxy that demanded authentication using the only to the next inbound proxy that demanded authentication using the
Proxy-Authenticate field. When multiple proxies are used in a chain, Proxy-Authenticate header field. When multiple proxies are used in a
the Proxy-Authorization header field is consumed by the first inbound chain, the Proxy-Authorization header field is consumed by the first
proxy that was expecting to receive credentials. A proxy MAY relay inbound proxy that was expecting to receive credentials. A proxy MAY
the credentials from the client request to the next proxy if that is relay the credentials from the client request to the next proxy if
the mechanism by which the proxies cooperatively authenticate a given that is the mechanism by which the proxies cooperatively authenticate
request. a given request.
11.7.3. Proxy-Authentication-Info 11.7.3. Proxy-Authentication-Info
The Proxy-Authentication-Info response header field is equivalent to The Proxy-Authentication-Info response header field is equivalent to
Authentication-Info, except that it applies to proxy authentication Authentication-Info, except that it applies to proxy authentication
([RFC7235], Section 2) and its semantics are defined by the (Section 11.3) and its semantics are defined by the authentication
authentication scheme indicated by the Proxy-Authorization header scheme indicated by the Proxy-Authorization header field
field ([RFC7235], Section 4.4) of the corresponding request: (Section 11.7.2) of the corresponding request:
Proxy-Authentication-Info = #auth-param Proxy-Authentication-Info = #auth-param
However, unlike Authentication-Info, the Proxy-Authentication-Info However, unlike Authentication-Info, the Proxy-Authentication-Info
header field applies only to the next outbound client on the response header field applies only to the next outbound client on the response
chain. This is because only the client that chose a given proxy is chain. This is because only the client that chose a given proxy is
likely to have the credentials necessary for authentication. likely to have the credentials necessary for authentication.
However, when multiple proxies are used within the same However, when multiple proxies are used within the same
administrative domain, such as office and regional caching proxies administrative domain, such as office and regional caching proxies
within a large corporate network, it is common for credentials to be within a large corporate network, it is common for credentials to be
generated by the user agent and passed through the hierarchy until generated by the user agent and passed through the hierarchy until
consumed. Hence, in such a configuration, it will appear as if consumed. Hence, in such a configuration, it will appear as if
Proxy-Authentication-Info is being forwarded because each proxy will Proxy-Authentication-Info is being forwarded because each proxy will
send the same field value. send the same field value.
12. Content Negotiation 12. Content Negotiation
When responses convey payload information, whether indicating a When responses convey content, whether indicating a success or an
success or an error, the origin server often has different ways of error, the origin server often has different ways of representing
representing that information; for example, in different formats, that information; for example, in different formats, languages, or
languages, or encodings. Likewise, different users or user agents encodings. Likewise, different users or user agents might have
might have differing capabilities, characteristics, or preferences differing capabilities, characteristics, or preferences that could
that could influence which representation, among those available, influence which representation, among those available, would be best
would be best to deliver. For this reason, HTTP provides mechanisms to deliver. For this reason, HTTP provides mechanisms for content
for content negotiation. negotiation.
This specification defines two patterns of content negotiation that This specification defines three patterns of content negotiation that
can be made visible within the protocol: "proactive", where the can be made visible within the protocol: "proactive" negotiation,
server selects the representation based upon the user agent's stated where the server selects the representation based upon the user
preferences, and "reactive" negotiation, where the server provides a agent's stated preferences, "reactive" negotiation, where the server
list of representations for the user agent to choose from. provides a list of representations for the user agent to choose from,
and "request content" negotiation, where the user agent selects the
representation for a future request based upon the server's stated
preferences in past responses.
Other patterns of content negotiation include "conditional content", Other patterns of content negotiation include "conditional content",
where the representation consists of multiple parts that are where the representation consists of multiple parts that are
selectively rendered based on user agent parameters, "active selectively rendered based on user agent parameters, "active
content", where the representation contains a script that makes content", where the representation contains a script that makes
additional (more specific) requests based on the user agent additional (more specific) requests based on the user agent
characteristics, and "Transparent Content Negotiation" ([RFC2295]), characteristics, and "Transparent Content Negotiation" ([RFC2295]),
where content selection is performed by an intermediary. These where content selection is performed by an intermediary. These
patterns are not mutually exclusive, and each has trade-offs in patterns are not mutually exclusive, and each has trade-offs in
applicability and practicality. applicability and practicality.
Note that, in all cases, HTTP is not aware of the resource semantics. Note that, in all cases, HTTP is not aware of the resource semantics.
The consistency with which an origin server responds to requests, The consistency with which an origin server responds to requests,
over time and over the varying dimensions of content negotiation, and over time and over the varying dimensions of content negotiation, and
thus the "sameness" of a resource's observed representations over thus the "sameness" of a resource's observed representations over
time, is determined entirely by whatever entity or algorithm selects time, is determined entirely by whatever entity or algorithm selects
or generates those responses. HTTP pays no attention to the man or generates those responses.
behind the curtain.
12.1. Proactive Negotiation 12.1. Proactive Negotiation
When content negotiation preferences are sent by the user agent in a When content negotiation preferences are sent by the user agent in a
request to encourage an algorithm located at the server to select the request to encourage an algorithm located at the server to select the
preferred representation, it is called proactive negotiation (a.k.a., preferred representation, it is called _proactive negotiation_
server-driven negotiation). Selection is based on the available (a.k.a., _server-driven negotiation_). Selection is based on the
representations for a response (the dimensions over which it might available representations for a response (the dimensions over which
vary, such as language, content-coding, etc.) compared to various it might vary, such as language, content-coding, etc.) compared to
information supplied in the request, including both the explicit various information supplied in the request, including both the
negotiation fields of Section 5.3 and implicit characteristics, such explicit negotiation header fields below and implicit
as the client's network address or parts of the User-Agent field. characteristics, such as the client's network address or parts of the
User-Agent field.
Proactive negotiation is advantageous when the algorithm for Proactive negotiation is advantageous when the algorithm for
selecting from among the available representations is difficult to selecting from among the available representations is difficult to
describe to a user agent, or when the server desires to send its describe to a user agent, or when the server desires to send its
"best guess" to the user agent along with the first response (hoping "best guess" to the user agent along with the first response (hoping
to avoid the round trip delay of a subsequent request if the "best to avoid the round trip delay of a subsequent request if the "best
guess" is good enough for the user). In order to improve the guess" is good enough for the user). In order to improve the
server's guess, a user agent MAY send request header fields that server's guess, a user agent MAY send request header fields that
describe its preferences. describe its preferences.
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algorithms for generating responses to a request; and, algorithms for generating responses to a request; and,
o It limits the reusability of responses for shared caching. o It limits the reusability of responses for shared caching.
A user agent cannot rely on proactive negotiation preferences being A user agent cannot rely on proactive negotiation preferences being
consistently honored, since the origin server might not implement consistently honored, since the origin server might not implement
proactive negotiation for the requested resource or might decide that proactive negotiation for the requested resource or might decide that
sending a response that doesn't conform to the user agent's sending a response that doesn't conform to the user agent's
preferences is better than sending a 406 (Not Acceptable) response. preferences is better than sending a 406 (Not Acceptable) response.
A Vary header field (Section 7.1.4) is often sent in a response A Vary header field (Section 12.5.5) is often sent in a response
subject to proactive negotiation to indicate what parts of the subject to proactive negotiation to indicate what parts of the
request information were used in the selection algorithm. request information were used in the selection algorithm.
The following request header fields are sent by a user agent to The request header fields Accept, Accept-Charset, Accept-Encoding,
engage in proactive negotiation of the response content, as defined and Accept-Language are defined below for a user agent to engage in
in Section 3.4.1. The preferences sent in these fields apply to any proactive negotiation of the response content. The preferences sent
content in the response, including representations of the target in these fields apply to any content in the response, including
resource, representations of error or processing status, and representations of the target resource, representations of error or
potentially even the miscellaneous text strings that might appear processing status, and potentially even the miscellaneous text
within the protocol. strings that might appear within the protocol.
12.2. Reactive Negotiation 12.2. Reactive Negotiation
With reactive negotiation (a.k.a., agent-driven negotiation), With _reactive negotiation_ (a.k.a., _agent-driven negotiation_),
selection of the best response representation (regardless of the selection of the best response representation (regardless of the
status code) is performed by the user agent after receiving an status code) is performed by the user agent after receiving an
initial response from the origin server that contains a list of initial response from the origin server that contains a list of
resources for alternative representations. If the user agent is not resources for alternative representations.
satisfied by the initial response representation, it can perform a
GET request on one or more of the alternative resources, selected If the user agent is not satisfied by the initial response
based on metadata included in the list, to obtain a different form of representation, it can perform a GET request on one or more of the
representation for that response. Selection of alternatives might be alternative resources, selected based on metadata included in the
performed automatically by the user agent or manually by the user list, to obtain a different form of representation for that response.
selecting from a generated (possibly hypertext) menu. Selection of alternatives might be performed automatically by the
user agent or manually by the user selecting from a generated
(possibly hypertext) menu.
Note that the above refers to representations of the response, in Note that the above refers to representations of the response, in
general, not representations of the resource. The alternative general, not representations of the resource. The alternative
representations are only considered representations of the target representations are only considered representations of the target
resource if the response in which those alternatives are provided has resource if the response in which those alternatives are provided has
the semantics of being a representation of the target resource (e.g., the semantics of being a representation of the target resource (e.g.,
a 200 (OK) response to a GET request) or has the semantics of a 200 (OK) response to a GET request) or has the semantics of
providing links to alternative representations for the target providing links to alternative representations for the target
resource (e.g., a 300 (Multiple Choices) response to a GET request). resource (e.g., a 300 (Multiple Choices) response to a GET request).
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Reactive negotiation suffers from the disadvantages of transmitting a Reactive negotiation suffers from the disadvantages of transmitting a
list of alternatives to the user agent, which degrades user-perceived list of alternatives to the user agent, which degrades user-perceived
latency if transmitted in the header section, and needing a second latency if transmitted in the header section, and needing a second
request to obtain an alternate representation. Furthermore, this request to obtain an alternate representation. Furthermore, this
specification does not define a mechanism for supporting automatic specification does not define a mechanism for supporting automatic
selection, though it does not prevent such a mechanism from being selection, though it does not prevent such a mechanism from being
developed as an extension. developed as an extension.
12.3. Request Content Negotiation 12.3. Request Content Negotiation
[new] When content negotiation preferences are sent in a server's response,
the listed preferences are called _request content negotiation_
because they intend to influence selection of an appropriate content
for subsequent requests to that resource. For example, the Accept
(Section 12.5.1) and Accept-Encoding (Section 12.5.3) header fields
can be sent in a response to indicate preferred media types and
content codings for subsequent requests to that resource.
Similarly, Section 3.1 of [RFC5789] defines the "Accept-Patch"
response header field which allows discovery of which content types
are accepted in PATCH requests.
12.4. Content Negotiation Field Features 12.4. Content Negotiation Field Features
12.4.1. Absence 12.4.1. Absence
A request without any Accept header field implies that the user agent For each of the content negotiation fields, a request that does not
will accept any media type in response. contain the field implies that the sender has no preference on that
axis of negotiation.
If the header field is present in a request and If a content negotiation header field is present in a request and
none of the available representations for the response have a media none of the available representations for the response can be
type that is listed as acceptable, the origin server can either considered acceptable according to it, the origin server can either
honor the header field by sending a 406 (Not Acceptable) response or honor the header field by sending a 406 (Not Acceptable) response or
disregard the header field by treating the response as if it is not disregard the header field by treating the response as if it is not
subject to content negotiation. subject to content negotiation for that request header field. This
does not imply, however, that the client will be able to use the
representation.
| *Note:* Sending these header fields makes it easier for a
| server to identify an individual by virtue of the user agent's
| request characteristics (Section 17.12).
12.4.2. Quality Values 12.4.2. Quality Values
Many of the request header fields for proactive negotiation use a The content negotiation fields defined by this specification use a
common parameter, named "q" (case-insensitive), to assign a relative common parameter, named "q" (case-insensitive), to assign a relative
"weight" to the preference for that associated kind of content. This "weight" to the preference for that associated kind of content. This
weight is referred to as a "quality value" (or "qvalue") because the weight is referred to as a "quality value" (or "qvalue") because the
same parameter name is often used within server configurations to same parameter name is often used within server configurations to
assign a weight to the relative quality of the various assign a weight to the relative quality of the various
representations that can be selected for a resource. representations that can be selected for a resource.
The weight is normalized to a real number in the range 0 through 1, The weight is normalized to a real number in the range 0 through 1,
where 0.001 is the least preferred and 1 is the most preferred; a where 0.001 is the least preferred and 1 is the most preferred; a
value of 0 means "not acceptable". If no "q" parameter is present, value of 0 means "not acceptable". If no "q" parameter is present,
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weight = OWS ";" OWS "q=" qvalue weight = OWS ";" OWS "q=" qvalue
qvalue = ( "0" [ "." 0*3DIGIT ] ) qvalue = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] ) / ( "1" [ "." 0*3("0") ] )
A sender of qvalue MUST NOT generate more than three digits after the A sender of qvalue MUST NOT generate more than three digits after the
decimal point. User configuration of these values ought to be decimal point. User configuration of these values ought to be
limited in the same fashion. limited in the same fashion.
12.4.3. Wildcard Values 12.4.3. Wildcard Values
[new] Most of these header fields, where indicated, define a wildcard value
("*") to select unspecified values. If no wildcard is present,
values that are not explicitly mentioned in the field are considered
unacceptable, except for within Vary where it means the variance is
unlimited.
| *Note:* In practice, using wildcards in content negotiation has
| limited practical value, because it is seldom useful to say,
| for example, "I prefer image/* more or less than (some other
| specific value)". Clients can explicitly request a 406 (Not
| Acceptable) response if a more preferred format is not
| available by sending Accept: */*;q=0, but they still need to be
| able to handle a different response, since the server is
| allowed to ignore their preference.
12.5. Content Negotiation Fields 12.5. Content Negotiation Fields
12.5.1. Accept 12.5.1. Accept
The "Accept" header field can be used by user agents to specify The "Accept" header field can be used by user agents to specify their
response media types that are acceptable. Accept header fields can preferences regarding response media types. For example, Accept
be used to indicate that the request is specifically limited to a header fields can be used to indicate that the request is
small set of desired types, as in the case of a request for an specifically limited to a small set of desired types, as in the case
in-line image. of a request for an in-line image.
[new] When sent by a server in a response, Accept provides information
about what content types are preferred in the content of a subsequent
request to the same resource.
Accept = #( media-range [ accept-params ] ) Accept = #( media-range [ weight ] )
media-range = ( "*/*" media-range = ( "*/*"
/ ( type "/" "*" ) / ( type "/" "*" )
/ ( type "/" subtype ) / ( type "/" subtype )
) *( OWS ";" OWS parameter ) ) parameters
accept-params = weight *( accept-ext )
accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
The asterisk "*" character is used to group media types into ranges, The asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The media-range can include media type subtypes of that type. The media-range can include media type
parameters that are applicable to that range. parameters that are applicable to that range.
Each media-range might be followed by zero or more applicable media Each media-range might be followed by optional applicable media type
type parameters (e.g., charset), an optional "q" parameter for parameters (e.g., charset), followed by an optional "q" parameter for
indicating a relative weight (Section 5.3.1), indicating a relative weight (Section 12.4.2).
and then zero or more Previous specifications allowed additional extension parameters to
extension parameters. The "q" parameter is necessary if any appear after the weight parameter. The accept extension grammar
extensions (accept-ext) are present, since it acts as a separator (accept-ext) has been removed because it had a complicated
between the two parameter sets. definition, was not being used in practice, and is more easily
deployed through new header fields. Senders using weights SHOULD
send "q" last (after all media-range parameters). Recipients SHOULD
process any parameter named "q" as weight, regardless of parameter
ordering.
Note: Use of the "q" parameter name to separate media type | *Note:* Use of the "q" parameter name to control content
parameters from Accept extension parameters is due to historical | negotiation is due to historical practice. Although this
practice. Although this prevents any media type parameter named | prevents any media type parameter named "q" from being used
"q" from being used with a media range, such an event is believed | with a media range, such an event is believed to be unlikely
to be unlikely given the lack of any "q" parameters in the IANA | given the lack of any "q" parameters in the IANA media type
media type registry and the rare usage of any media type | registry and the rare usage of any media type parameters in
parameters in Accept. Future media types are discouraged from | Accept. Future media types are discouraged from registering
registering any parameter named "q". | any parameter named "q".
The example The example
Accept: audio/*; q=0.2, audio/basic Accept: audio/*; q=0.2, audio/basic
is interpreted as "I prefer audio/basic, but send me any audio type is interpreted as "I prefer audio/basic, but send me any audio type
if it is the best available after an 80% markdown in quality". if it is the best available after an 80% markdown in quality".
A more elaborate example is A more elaborate example is
Accept: text/plain; q=0.5, text/html, Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8, text/x-c text/x-dvi; q=0.8, text/x-c
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2. text/plain 2. text/plain
3. text/* 3. text/*
4. */* 4. */*
The media type quality factor associated with a given type is The media type quality factor associated with a given type is
determined by finding the media range with the highest precedence determined by finding the media range with the highest precedence
that matches the type. For example, that matches the type. For example,
Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1, Accept: text/*;q=0.3, text/plain;q=0.7, text/plain;format=flowed,
text/html;level=2;q=0.4, */*;q=0.5 text/plain;format=fixed;q=0.4, */*;q=0.5
would cause the following values to be associated: would cause the following values to be associated:
+-------------------+---------------+ -------------------------- ---------------
| Media Type | Quality Value | Media Type Quality Value
+-------------------+---------------+ -------------------------- ---------------
| text/html;level=1 | 1 | text/plain;format=flowed 1
| text/html | 0.7 | text/plain 0.7
| text/plain | 0.3 | text/html 0.3
| image/jpeg | 0.5 | image/jpeg 0.5
| text/html;level=2 | 0.4 | text/plain;format=fixed 0.4
| text/html;level=3 | 0.7 | text/html;level=3 0.7
+-------------------+---------------+ -------------------------- ---------------
Note: A user agent might be provided with a default set of quality Table 5
values for certain media ranges. However, unless the user agent is a
closed system that cannot interact with other rendering agents, this | *Note:* A user agent might be provided with a default set of
default set ought to be configurable by the user. | quality values for certain media ranges. However, unless the
| user agent is a closed system that cannot interact with other
| rendering agents, this default set ought to be configurable by
| the user.
12.5.2. Accept-Charset 12.5.2. Accept-Charset
The "Accept-Charset" header field can be sent by a user agent to The "Accept-Charset" header field can be sent by a user agent to
indicate what charsets are acceptable in textual response content. indicate its preferences for charsets in textual response content.
This field allows user agents capable of understanding more For example, this field allows user agents capable of understanding
comprehensive or special-purpose charsets to signal that capability more comprehensive or special-purpose charsets to signal that
to an origin server that is capable of representing information in capability to an origin server that is capable of representing
those charsets. information in those charsets.
Accept-Charset = 1#( ( charset / "*" ) [ weight ] ) Accept-Charset = #( ( charset / "*" ) [ weight ] )
Charset names are defined in Section 3.1.1.2. A user agent MAY Charset names are defined in Section 8.3.2. A user agent MAY
associate a quality value with each charset to indicate the user's associate a quality value with each charset to indicate the user's
relative preference for that charset, as defined in Section 5.3.1. relative preference for that charset, as defined in Section 12.4.2.
An example is An example is
Accept-Charset: iso-8859-5, unicode-1-1;q=0.8 Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
The special value "*", if present in the Accept-Charset field, The special value "*", if present in the Accept-Charset header field,
matches every charset that is not mentioned elsewhere in the matches every charset that is not mentioned elsewhere in the field.
Accept-Charset field. If no "*" is present in an Accept-Charset
field, then any charsets not explicitly mentioned in the field are
considered "not acceptable" to the client.
A request without any Accept-Charset header field implies that the
user agent will accept any charset in response. Most general-purpose
user agents do not send Accept-Charset, unless specifically
configured to do so, because a detailed list of supported charsets
makes it easier for a server to identify an individual by virtue of
the user agent's request characteristics (Section 9.7).
If an Accept-Charset header field is present in a request and none of | *Note:* Accept-Charset is deprecated because UTF-8 has become
the available representations for the response has a charset that is | nearly ubiquitous and sending a detailed list of user-preferred
listed as acceptable, the origin server can either honor the header | charsets wastes bandwidth, increases latency, and makes passive
field, by sending a 406 (Not Acceptable) response, or disregard the | fingerprinting far too easy (Section 17.12). Most general-
header field by treating the resource as if it is not subject to | purpose user agents do not send Accept-Charset, unless
content negotiation. | specifically configured to do so.
12.5.3. Accept-Encoding 12.5.3. Accept-Encoding
The "Accept-Encoding" header field can be used by user agents to The "Accept-Encoding" header field can be used to indicate
indicate what response content-codings (Section 3.1.2.1) are preferences regarding the use of content codings (Section 8.4.1).
acceptable in the response.
[new] When sent by a user agent in a request, Accept-Encoding indicates the
content codings acceptable in a response.
[new] When sent by a server in a response, Accept-Encoding provides
information about what content codings are preferred in the content
of a subsequent request to the same resource.
An "identity" token is used as a synonym for "no encoding" in order An "identity" token is used as a synonym for "no encoding" in order
to communicate when no encoding is preferred. to communicate when no encoding is preferred.
Accept-Encoding = #( codings [ weight ] ) Accept-Encoding = #( codings [ weight ] )
codings = content-coding / "identity" / "*" codings = content-coding / "identity" / "*"
Each codings value MAY be given an associated quality value Each codings value MAY be given an associated quality value
representing the preference for that encoding, as defined in representing the preference for that encoding, as defined in
Section 5.3.1. The asterisk "*" symbol in an Accept-Encoding field Section 12.4.2. The asterisk "*" symbol in an Accept-Encoding field
matches any available content-coding not explicitly listed in the matches any available content-coding not explicitly listed in the
header field. field.
For example, For example,
Accept-Encoding: compress, gzip Accept-Encoding: compress, gzip
Accept-Encoding: Accept-Encoding:
Accept-Encoding: * Accept-Encoding: *
Accept-Encoding: compress;q=0.5, gzip;q=1.0 Accept-Encoding: compress;q=0.5, gzip;q=1.0
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0 Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
A request without an Accept-Encoding header field implies that the
user agent has no preferences regarding content-codings. Although
this allows the server to use any content-coding in a response, it
does not imply that the user agent will be able to correctly process
all encodings.
A server tests whether a content-coding for a given representation is A server tests whether a content-coding for a given representation is
acceptable using these rules: acceptable using these rules:
1. If no Accept-Encoding field is in the request, any content-coding 1. If no Accept-Encoding header field is in the request, any
is considered acceptable by the user agent. content-coding is considered acceptable by the user agent.
2. If the representation has no content-coding, then it is 2. If the representation has no content-coding, then it is
acceptable by default unless specifically excluded by the acceptable by default unless specifically excluded by the Accept-
Accept-Encoding field stating either "identity;q=0" or "*;q=0" Encoding header field stating either "identity;q=0" or "*;q=0"
without a more specific entry for "identity". without a more specific entry for "identity".
3. If the representation's content-coding is one of the 3. If the representation's content-coding is one of the content-
content-codings listed in the Accept-Encoding field, then it is codings listed in the Accept-Encoding field value, then it is
acceptable unless it is accompanied by a qvalue of 0. (As acceptable unless it is accompanied by a qvalue of 0. (As
defined in Section 5.3.1, a qvalue of 0 means "not acceptable".) defined in Section 12.4.2, a qvalue of 0 means "not acceptable".)
4. If multiple content-codings are acceptable, then the acceptable 4. If multiple content-codings are acceptable, then the acceptable
content-coding with the highest non-zero qvalue is preferred. content-coding with the highest non-zero qvalue is preferred.
An Accept-Encoding header field with a combined field-value that is An Accept-Encoding header field with a field value that is empty
empty implies that the user agent does not want any content-coding in implies that the user agent does not want any content-coding in
response. If an Accept-Encoding header field is present in a request response. If an Accept-Encoding header field is present in a request
and none of the available representations for the response have a and none of the available representations for the response have a
content-coding that is listed as acceptable, the origin server SHOULD content-coding that is listed as acceptable, the origin server SHOULD
send a response without any content-coding. send a response without any content-coding.
[new] When the Accept-Encoding header field is present in a response, it
indicates what content codings the resource was willing to accept in
the associated request. The field value is evaluated the same way as
in a request.
[new] Note that this information is specific to the associated request; the
set of supported encodings might be different for other resources on
the same server and could change over time or depend on other aspects
of the request (such as the request method).
[new] Servers that fail a request due to an unsupported content coding
ought to respond with a 415 (Unsupported Media Type) status and
include an Accept-Encoding header field in that response, allowing
clients to distinguish between issues related to content codings and
media types. In order to avoid confusion with issues related to
media types, servers that fail a request with a 415 status for
reasons unrelated to content codings MUST NOT include the Accept-
Encoding header field.
[new] The most common use of Accept-Encoding is in responses with a 415
(Unsupported Media Type) status code, in response to optimistic use
of a content coding by clients. However, the header field can also
be used to indicate to clients that content codings are supported, to
optimize future interactions. For example, a resource might include
it in a 2xx (Successful) response when the request content was big
enough to justify use of a compression coding but the client failed
do so.
Note: Most HTTP/1.0 applications do not recognize or obey qvalues | *Note:* Most HTTP/1.0 applications do not recognize or obey
associated with content-codings. This means that qvalues might | qvalues associated with content-codings. This means that
not work and are not permitted with x-gzip or x-compress. | qvalues might not work and are not permitted with x-gzip or
| x-compress.
12.5.4. Accept-Language 12.5.4. Accept-Language
The "Accept-Language" header field can be used by user agents to The "Accept-Language" header field can be used by user agents to
indicate the set of natural languages that are preferred in the indicate the set of natural languages that are preferred in the
response. Language tags are defined in Section 3.1.3.1. response. Language tags are defined in Section 8.5.1.
Accept-Language = 1#( language-range [ weight ] ) Accept-Language = #( language-range [ weight ] )
language-range = language-range =
<language-range, see [RFC4647], Section 2.1> <language-range, see [RFC4647], Section 2.1>
Each language-range can be given an associated quality value Each language-range can be given an associated quality value
representing an estimate of the user's preference for the languages representing an estimate of the user's preference for the languages
specified by that range, as defined in Section 5.3.1. For example, specified by that range, as defined in Section 12.4.2. For example,
Accept-Language: da, en-gb;q=0.8, en;q=0.7 Accept-Language: da, en-gb;q=0.8, en;q=0.7
would mean: "I prefer Danish, but will accept British English and would mean: "I prefer Danish, but will accept British English and
other types of English". other types of English".
A request without any Accept-Language header field implies that the
user agent will accept any language in response. If the header field
is present in a request and none of the available representations for
the response have a matching language tag, the origin server can
either disregard the header field by treating the response as if it
is not subject to content negotiation or honor the header field by
sending a 406 (Not Acceptable) response. However, the latter is not
encouraged, as doing so can prevent users from accessing content that
they might be able to use (with translation software, for example).
Note that some recipients treat the order in which language tags are Note that some recipients treat the order in which language tags are
listed as an indication of descending priority, particularly for tags listed as an indication of descending priority, particularly for tags
that are assigned equal quality values (no value is the same as q=1). that are assigned equal quality values (no value is the same as q=1).
However, this behavior cannot be relied upon. For consistency and to However, this behavior cannot be relied upon. For consistency and to
maximize interoperability, many user agents assign each language tag maximize interoperability, many user agents assign each language tag
a unique quality value while also listing them in order of decreasing a unique quality value while also listing them in order of decreasing
quality. Additional discussion of language priority lists can be quality. Additional discussion of language priority lists can be
found in Section 2.3 of [RFC4647]. found in Section 2.3 of [RFC4647].
For matching, Section 3 of [RFC4647] defines several matching For matching, Section 3 of [RFC4647] defines several matching
schemes. Implementations can offer the most appropriate matching schemes. Implementations can offer the most appropriate matching
scheme for their requirements. The "Basic Filtering" scheme scheme for their requirements. The "Basic Filtering" scheme
([RFC4647], Section 3.3.1) is identical to the matching scheme that ([RFC4647], Section 3.3.1) is identical to the matching scheme that
was previously defined for HTTP in Section 14.4 of [RFC2616]. was previously defined for HTTP in Section 14.4 of [RFC2616].
It might be contrary to the privacy expectations of the user to send It might be contrary to the privacy expectations of the user to send
an Accept-Language header field with the complete linguistic an Accept-Language header field with the complete linguistic
preferences of the user in every request (Section 9.7). preferences of the user in every request (Section 17.12).
Since intelligibility is highly dependent on the individual user, Since intelligibility is highly dependent on the individual user,
user agents need to allow user control over the linguistic preference user agents need to allow user control over the linguistic preference
(either through configuration of the user agent itself or by (either through configuration of the user agent itself or by
defaulting to a user controllable system setting). A user agent that defaulting to a user controllable system setting). A user agent that
does not provide such control to the user MUST NOT send an does not provide such control to the user MUST NOT send an Accept-
Accept-Language header field. Language header field.
Note: User agents ought to provide guidance to users when setting | *Note:* User agents ought to provide guidance to users when
a preference, since users are rarely familiar with the details of | setting a preference, since users are rarely familiar with the
language matching as described above. For example, users might | details of language matching as described above. For example,
assume that on selecting "en-gb", they will be served any kind of | users might assume that on selecting "en-gb", they will be
English document if British English is not available. A user | served any kind of English document if British English is not
agent might suggest, in such a case, to add "en" to the list for | available. A user agent might suggest, in such a case, to add
better matching behavior. | "en" to the list for better matching behavior.
12.5.5. Vary 12.5.5. Vary
The "Vary" header field in a response describes what parts of a The "Vary" header field in a response describes what parts of a
request message, aside from the method, Host header field, and request message, aside from the method and target URI, might
request target, might influence the origin server's process for influence the origin server's process for selecting and representing
selecting and representing this response. The value consists of this response.
either a single asterisk ("*") or a list of header field names
(case-insensitive).
Vary = "*" / 1#field-name Vary = #( "*" / field-name )
A Vary field value consisting of a comma-separated list of names A Vary field value is a list of request field names, known as the
indicates that the named request header fields, known as the selecting header fields, that might have a role in selecting the
selecting header fields, might have a role in selecting the representation for this response. Potential selecting header fields
representation. The potential selecting header fields are not are not limited to those defined by this specification.
limited to those defined by this specification.
A Vary field value of "*" signals that anything about the request If the list contains "*", it signals that other aspects of the
might play a role in selecting the response representation, possibly request might play a role in selecting the response representation,
including elements outside the message syntax (e.g., the client's possibly including elements outside the message syntax (e.g., the
network address). A recipient will not be able to determine whether client's network address). A recipient will not be able to determine
this response is appropriate for a later request without forwarding whether this response is appropriate for a later request without
the request to the origin server. A proxy MUST NOT generate a Vary forwarding the request to the origin server. A proxy MUST NOT
field with a "*" value. generate "*" in a Vary field value.
For example, a response that contains For example, a response that contains
Vary: accept-encoding, accept-language Vary: accept-encoding, accept-language
indicates that the origin server might have used the request's indicates that the origin server might have used the request's
Accept-Encoding and Accept-Language fields (or lack thereof) as Accept-Encoding and Accept-Language header fields (or lack thereof)
determining factors while choosing the content for this response. as determining factors while choosing the content for this response.
An origin server might send Vary with a list of fields for two An origin server might send Vary with a list of header fields for two
purposes: purposes:
1. To inform cache recipients that they MUST NOT use this response 1. To inform cache recipients that they MUST NOT use this response
to satisfy a later request unless the later request has the same to satisfy a later request unless the later request has the same
values for the listed fields as the original request (Section 4.1 values for the listed header fields as the original request
of [RFC7234]). In other words, Vary expands the cache key (Section 4.1 of [Caching]). In other words, Vary expands the
required to match a new request to the stored cache entry. cache key required to match a new request to the stored cache
entry.
2. To inform user agent recipients that this response is subject to 2. To inform user agent recipients that this response is subject to
content negotiation (Section 5.3) and that a different content negotiation (Section 12) and that a different
representation might be sent in a subsequent request if representation might be sent in a subsequent request if
additional parameters are provided in the listed header fields additional parameters are provided in the listed header fields
(proactive negotiation). (proactive negotiation).
An origin server SHOULD send a Vary header field when its algorithm An origin server SHOULD send a Vary header field when its algorithm
for selecting a representation varies based on aspects of the request for selecting a representation varies based on aspects of the request
message other than the method and request target, unless the variance message other than the method and target URI, unless the variance
cannot be crossed or the origin server has been deliberately cannot be crossed or the origin server has been deliberately
configured to prevent cache transparency. For example, there is no configured to prevent cache transparency. For example, there is no
need to send the Authorization field name in Vary because reuse need to send the Authorization field name in Vary because reuse
across users is constrained by the field definition (Section 4.2 of across users is constrained by the field definition (Section 11.6.2).
[RFC7235]). Likewise, an origin server might use Cache-Control Likewise, an origin server might use Cache-Control response
directives (Section 5.2 of [RFC7234]) to supplant Vary if it directives (Section 5.2 of [Caching]) to supplant Vary if it
considers the variance less significant than the performance cost of considers the variance less significant than the performance cost of
Vary's impact on caching. Vary's impact on caching.
13. Conditional Requests 13. Conditional Requests
Conditional requests are HTTP requests [RFC7231] that include one or A conditional request is an HTTP request with one or more request
more header fields indicating a precondition to be tested before header fields that indicate a precondition to be tested before
applying the method semantics to the target resource. Section 5 applying the request method to the target resource. Section 13.2
defines when the preconditions are applied. Section 6 defines the defines when to evaluate preconditions and their order of precedence
order of evaluation when more than one precondition is present. when more than one precondition is present.
Conditional GET requests are the most efficient mechanism for HTTP Conditional GET requests are the most efficient mechanism for HTTP
cache updates [RFC7234]. Conditionals can also be applied to cache updates [Caching]. Conditionals can also be applied to state-
state-changing methods, such as PUT and DELETE, to prevent the "lost changing methods, such as PUT and DELETE, to prevent the "lost
update" problem: one client accidentally overwriting the work of update" problem: one client accidentally overwriting the work of
another client that has been acting in parallel. another client that has been acting in parallel.
Conditional request preconditions are based on the state of the Conditional request preconditions are based on the state of the
target resource as a whole (its current value set) or the state as target resource as a whole (its current value set) or the state as
observed in a previously obtained representation (one value in that observed in a previously obtained representation (one value in that
set). A resource might have multiple current representations, each set). A resource might have multiple current representations, each
with its own observable state. The conditional request mechanisms with its own observable state. The conditional request mechanisms
assume that the mapping of requests to a "selected representation" assume that the mapping of requests to a selected representation
(Section 3 of [RFC7231]) will be consistent over time if the server (Section 3.2) will be consistent over time if the server intends to
intends to take advantage of conditionals. Regardless, if the take advantage of conditionals. Regardless, if the mapping is
mapping is inconsistent and the server is unable to select the inconsistent and the server is unable to select the appropriate
appropriate representation, then no harm will result when the representation, then no harm will result when the precondition
precondition evaluates to false. evaluates to false.
13.1. Preconditions 13.1. Preconditions
The HTTP conditional request header fields [RFC7232] allow a client The request header fields below allow a client to place a
to place a precondition on the state of the target resource, so that precondition on the state of the target resource, so that the action
the action corresponding to the method semantics will not be applied corresponding to the method semantics will not be applied if the
if the precondition evaluates to false. Each precondition defined by precondition evaluates to false. Each precondition defined by this
this specification consists of a comparison between a set of specification consists of a comparison between a set of validators
validators obtained from prior representations of the target resource obtained from prior representations of the target resource to the
to the current state of validators for the selected representation current state of validators for the selected representation
(Section 7.2). Hence, these preconditions evaluate whether the state (Section 8.8). Hence, these preconditions evaluate whether the state
of the target resource has changed since a given state known by the of the target resource has changed since a given state known by the
client. The effect of such an evaluation depends on the method client. The effect of such an evaluation depends on the method
semantics and choice of conditional, as defined in Section 5 of semantics and choice of conditional, as defined in Section 13.2.
[RFC7232].
The conditional request preconditions defined by this specification
(Section 3) are evaluated when applicable to the recipient
(Section 5) according to their order of precedence (Section 6).
This section defines the syntax and semantics of HTTP/1.1 header
fields for applying preconditions on requests.
13.1.1. If-Match 13.1.1. If-Match
The "If-Match" header field makes the request method conditional on The "If-Match" header field makes the request method conditional on
the recipient origin server either having at least one current the recipient origin server either having at least one current
representation of the target resource, when the field-value is "*", representation of the target resource, when the field value is "*",
or having a current representation of the target resource that has an or having a current representation of the target resource that has an
entity-tag matching a member of the list of entity-tags provided in entity-tag matching a member of the list of entity-tags provided in
the field-value. the field value.
An origin server MUST use the strong comparison function when An origin server MUST use the strong comparison function when
comparing entity-tags for If-Match (Section 2.3.2), since the client comparing entity-tags for If-Match (Section 8.8.3.2), since the
intends this precondition to prevent the method from being applied if client intends this precondition to prevent the method from being
there have been any changes to the representation data. applied if there have been any changes to the representation data.
If-Match = "*" / 1#entity-tag If-Match = "*" / #entity-tag
Examples: Examples:
If-Match: "xyzzy" If-Match: "xyzzy"
If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-Match: * If-Match: *
If-Match is most often used with state-changing methods (e.g., POST, If-Match is most often used with state-changing methods (e.g., POST,
PUT, DELETE) to prevent accidental overwrites when multiple user PUT, DELETE) to prevent accidental overwrites when multiple user
agents might be acting in parallel on the same resource (i.e., to agents might be acting in parallel on the same resource (i.e., to
prevent the "lost update" problem). It can also be used with safe prevent the "lost update" problem). It can also be used with any
methods to abort a request if the selected representation does not method to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request. match one that the client has already stored (or partially stored)
from a prior request.
An origin server that receives an If-Match header field MUST evaluate An origin server that receives an If-Match header field MUST evaluate
the condition prior to performing the method (Section 5). the condition as per Section 13.2 prior to performing the method.
If the field-value is "*", the condition is false if the origin To evaluate a received If-Match header field:
server does not have a current representation for the target resource.
If the field-value is a list of entity-tags, the condition is false 1. If the field value is "*", the condition is true if the origin
if none of the listed tags match the entity-tag of the server has a current representation for the target resource.
selected representation.
2. If the field value is a list of entity-tags, the condition is
true if any of the listed tags match the entity-tag of the
selected representation.
3. Otherwise, the condition is false.
An origin server MUST NOT perform the requested method if a received An origin server MUST NOT perform the requested method if a received
If-Match condition evaluates to false; instead, the origin server If-Match condition evaluates to false. Instead, the origin server
MUST respond with either a) the 412 (Precondition Failed) status code MAY indicate that the conditional request failed by responding with a
or b) one of the 2xx (Successful) status codes if the origin server 412 (Precondition Failed) status code. Alternatively, if the request
has verified that a state change is being requested and the final is a state-changing operation that appears to have already been
state is already reflected in the current state of the target applied to the selected representation, the origin server MAY respond
resource (i.e., the change requested by the user agent has already with a 2xx (Successful) status code (i.e., the change requested by
succeeded, but the user agent might not be aware of it, perhaps the user agent has already succeeded, but the user agent might not be
because the prior response was lost or a compatible change was made aware of it, perhaps because the prior response was lost or an
by some other user agent). In the latter case, the origin server equivalent change was made by some other user agent).
MUST NOT send a validator header field in the response unless it can
verify that the request is a duplicate of an immediately prior change
made by the same user agent.
[new] Allowing an origin server to send a success response when a change
request appears to have already been applied is more efficient for
many authoring use cases, but comes with some risk if multiple user
agents are making change requests that are very similar but not
cooperative. For example, multiple user agents writing to a common
resource as a semaphore (e.g., a non-atomic increment) are likely to
collide and potentially lose important state transitions. For those
kinds of resources, an origin server is better off being stringent in
sending 412 for every failed precondition on an unsafe method. In
other cases, excluding the ETag field from a success response might
encourage the user agent to perform a GET as its next request to
eliminate confusion about the resource's current state.
The If-Match header field can be ignored by caches and intermediaries The If-Match header field can be ignored by caches and intermediaries
because it is not applicable to a stored response. because it is not applicable to a stored response.
[new] Note that an If-Match header field with a list value containing "*"
and other values (including other instances of "*") is unlikely to be
interoperable.
13.1.2. If-None-Match 13.1.2. If-None-Match
The "If-None-Match" header field makes the request method conditional The "If-None-Match" header field makes the request method conditional
on a recipient cache or origin server either not having any current on a recipient cache or origin server either not having any current
representation of the target resource, when the field-value is "*", representation of the target resource, when the field value is "*",
or having a selected representation with an entity-tag that does not or having a selected representation with an entity-tag that does not
match any of those listed in the field-value. match any of those listed in the field value.
A recipient MUST use the weak comparison function when comparing A recipient MUST use the weak comparison function when comparing
entity-tags for If-None-Match (Section 2.3.2), since weak entity-tags entity-tags for If-None-Match (Section 8.8.3.2), since weak entity-
can be used for cache validation even if there have been changes to tags can be used for cache validation even if there have been changes
the representation data. to the representation data.
If-None-Match = "*" / 1#entity-tag If-None-Match = "*" / #entity-tag
Examples: Examples:
If-None-Match: "xyzzy" If-None-Match: "xyzzy"
If-None-Match: W/"xyzzy" If-None-Match: W/"xyzzy"
If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz" If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
If-None-Match: * If-None-Match: *
If-None-Match is primarily used in conditional GET requests to enable If-None-Match is primarily used in conditional GET requests to enable
skipping to change at line 5196 skipping to change at page 125, line 24
stored responses that have entity-tags, the client SHOULD generate an stored responses that have entity-tags, the client SHOULD generate an
If-None-Match header field containing a list of those entity-tags If-None-Match header field containing a list of those entity-tags
when making a GET request; this allows recipient servers to send a when making a GET request; this allows recipient servers to send a
304 (Not Modified) response to indicate when one of those stored 304 (Not Modified) response to indicate when one of those stored
responses matches the selected representation. responses matches the selected representation.
If-None-Match can also be used with a value of "*" to prevent an If-None-Match can also be used with a value of "*" to prevent an
unsafe request method (e.g., PUT) from inadvertently modifying an unsafe request method (e.g., PUT) from inadvertently modifying an
existing representation of the target resource when the client existing representation of the target resource when the client
believes that the resource does not have a current representation believes that the resource does not have a current representation
(Section 4.2.1 of [RFC7231]). This is a variation on the "lost (Section 9.2.1). This is a variation on the "lost update" problem
update" problem that might arise if more than one client attempts to that might arise if more than one client attempts to create an
create an initial representation for the target resource. initial representation for the target resource.
An origin server that receives an If-None-Match header field MUST An origin server that receives an If-None-Match header field MUST
evaluate the condition prior to performing the method (Section 5). evaluate the condition as per Section 13.2 prior to performing the
method.
[new] To evaluate a received If-None-Match header field:
If the field-value is "*", the condition is false if the origin 1. If the field value is "*", the condition is false if the origin
server has a current representation for the target resource. server has a current representation for the target resource.
If the field-value is a list of entity-tags, the condition is false if 2. If the field value is a list of entity-tags, the condition is
one of the listed tags match the entity-tag of the false if one of the listed tags matches the entity-tag of the
selected representation. selected representation.
[new] 3. Otherwise, the condition is true.
An origin server MUST NOT perform the requested method if the An origin server MUST NOT perform the requested method if a received
condition evaluates to false; instead, the origin server MUST respond If-None-Match condition evaluates to false; instead, the origin
with either a) the 304 (Not Modified) status code if the request server MUST respond with either a) the 304 (Not Modified) status code
method is GET or HEAD or b) the 412 (Precondition Failed) status code if the request method is GET or HEAD or b) the 412 (Precondition
for all other request methods. Failed) status code for all other request methods.
Requirements on cache handling of a received If-None-Match header Requirements on cache handling of a received If-None-Match header
field are defined in Section 4.3.2 of [RFC7234]. field are defined in Section 4.3.2 of [Caching].
Note that an If-None-Match header field with a list value containing
"*" and other values (including other instances of "*") is unlikely
to be interoperable.
13.1.3. If-Modified-Since 13.1.3. If-Modified-Since
The "If-Modified-Since" header field makes a GET or HEAD request The "If-Modified-Since" header field makes a GET or HEAD request
method conditional on the selected representation's modification date method conditional on the selected representation's modification date
being more recent than the date provided in the field-value. being more recent than the date provided in the field value.
Transfer of the selected representation's data is avoided if that Transfer of the selected representation's data is avoided if that
data has not changed. data has not changed.
If-Modified-Since = HTTP-date If-Modified-Since = HTTP-date
An example of the field is: An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A recipient MUST ignore If-Modified-Since if the request contains an A recipient MUST ignore If-Modified-Since if the request contains an
If-None-Match header field; the condition in If-None-Match is If-None-Match header field; the condition in If-None-Match is
considered to be a more accurate replacement for the condition in considered to be a more accurate replacement for the condition in If-
If-Modified-Since, and the two are only combined for the sake of Modified-Since, and the two are only combined for the sake of
interoperating with older intermediaries that might not implement interoperating with older intermediaries that might not implement
If-None-Match. If-None-Match.
A recipient MUST ignore the If-Modified-Since header field if the A recipient MUST ignore the If-Modified-Since header field if the
received field-value is not a valid HTTP-date, or if the request received field value is not a valid HTTP-date, the field value has
method is neither GET nor HEAD. more than one member, or if the request method is neither GET nor
HEAD.
A recipient MUST interpret an If-Modified-Since field-value's A recipient MUST interpret an If-Modified-Since field value's
timestamp in terms of the origin server's clock. timestamp in terms of the origin server's clock.
If-Modified-Since is typically used for two distinct purposes: 1) to If-Modified-Since is typically used for two distinct purposes: 1) to
allow efficient updates of a cached representation that does not have allow efficient updates of a cached representation that does not have
an entity-tag and 2) to limit the scope of a web traversal to an entity-tag and 2) to limit the scope of a web traversal to
resources that have recently changed. resources that have recently changed.
When used for cache updates, a cache will typically use the value of When used for cache updates, a cache will typically use the value of
the cached message's Last-Modified field to generate the field value the cached message's Last-Modified header field to generate the field
of If-Modified-Since. This behavior is most interoperable for cases value of If-Modified-Since. This behavior is most interoperable for
where clocks are poorly synchronized or when the server has chosen to cases where clocks are poorly synchronized or when the server has
only honor exact timestamp matches (due to a problem with chosen to only honor exact timestamp matches (due to a problem with
Last-Modified dates that appear to go "back in time" when the origin Last-Modified dates that appear to go "back in time" when the origin
server's clock is corrected or a representation is restored from an server's clock is corrected or a representation is restored from an
archived backup). However, caches occasionally generate the field archived backup). However, caches occasionally generate the field
value based on other data, such as the Date header field of the value based on other data, such as the Date header field of the
cached message or the local clock time that the message was received, cached message or the local clock time that the message was received,
particularly when the cached message does not contain a Last-Modified particularly when the cached message does not contain a Last-Modified
field. header field.
When used for limiting the scope of retrieval to a recent time When used for limiting the scope of retrieval to a recent time
window, a user agent will generate an If-Modified-Since field value window, a user agent will generate an If-Modified-Since field value
based on either its own local clock or a Date header field received based on either its own local clock or a Date header field received
from the server in a prior response. Origin servers that choose an from the server in a prior response. Origin servers that choose an
exact timestamp match based on the selected representation's exact timestamp match based on the selected representation's
Last-Modified field will not be able to help the user agent limit its Last-Modified header field will not be able to help the user agent
data transfers to only those changed during the specified window. limit its data transfers to only those changed during the specified
window.
An origin server that receives an If-Modified-Since header field An origin server that receives an If-Modified-Since header field
SHOULD evaluate the condition prior to performing the method SHOULD evaluate the condition as per Section 13.2 prior to performing
(Section 5). the method.
The origin server SHOULD NOT perform the requested To evaluate a received If-Modified-Since header field:
method if the selected representation's last modification date is
earlier than or equal to the date provided in the field-value; 1. If the selected representation's last modification date is
instead, the origin server SHOULD generate a 304 (Not Modified) earlier or equal to the date provided in the field value, the
response, including only those metadata that are useful for condition is false.
identifying or updating a previously cached response.
2. Otherwise, the condition is true.
An origin server SHOULD NOT perform the requested method if a
received If-Modified-Since condition evaluates to false; instead, the
origin server SHOULD generate a 304 (Not Modified) response,
including only those metadata that are useful for identifying or
updating a previously cached response.
Requirements on cache handling of a received If-Modified-Since header Requirements on cache handling of a received If-Modified-Since header
field are defined in Section 4.3.2 of [RFC7234]. field are defined in Section 4.3.2 of [Caching].
13.1.4. If-Unmodified-Since 13.1.4. If-Unmodified-Since
The "If-Unmodified-Since" header field makes the request method The "If-Unmodified-Since" header field makes the request method
conditional on the selected representation's last modification date conditional on the selected representation's last modification date
being earlier than or equal to the date provided in the field-value. being earlier than or equal to the date provided in the field value.
This field accomplishes the same purpose as If-Match for cases where This field accomplishes the same purpose as If-Match for cases where
the user agent does not have an entity-tag for the representation. the user agent does not have an entity-tag for the representation.
If-Unmodified-Since = HTTP-date If-Unmodified-Since = HTTP-date
An example of the field is: An example of the field is:
If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A recipient MUST ignore If-Unmodified-Since if the request contains A recipient MUST ignore If-Unmodified-Since if the request contains
an If-Match header field; the condition in If-Match is considered to an If-Match header field; the condition in If-Match is considered to
be a more accurate replacement for the condition in be a more accurate replacement for the condition in If-Unmodified-
If-Unmodified-Since, and the two are only combined for the sake of Since, and the two are only combined for the sake of interoperating
interoperating with older intermediaries that might not implement with older intermediaries that might not implement If-Match.
If-Match.
A recipient MUST ignore the If-Unmodified-Since header field if the A recipient MUST ignore the If-Unmodified-Since header field if the
received field-value is not a valid HTTP-date. received field value is not a valid HTTP-date (including when the
field value appears to be a list of dates).
A recipient MUST interpret an If-Unmodified-Since field-value's A recipient MUST interpret an If-Unmodified-Since field value's
timestamp in terms of the origin server's clock. timestamp in terms of the origin server's clock.
If-Unmodified-Since is most often used with state-changing methods If-Unmodified-Since is most often used with state-changing methods
(e.g., POST, PUT, DELETE) to prevent accidental overwrites when (e.g., POST, PUT, DELETE) to prevent accidental overwrites when
multiple user agents might be acting in parallel on a resource that multiple user agents might be acting in parallel on a resource that
does not supply entity-tags with its representations (i.e., to does not supply entity-tags with its representations (i.e., to
prevent the "lost update" problem). It can also be used with safe prevent the "lost update" problem). It can also be used with any
methods to abort a request if the selected representation does not method to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request. match one that the client already stored (or partially stored) from a
prior request.
An origin server that receives an If-Unmodified-Since header field An origin server that receives an If-Unmodified-Since header field
MUST evaluate the condition prior to performing the method without an If-Match header field MUST evaluate the condition as per
(Section 5). Section 13.2 prior to performing the method.
[new] To evaluate a received If-Unmodified-Since header field:
[new] 1. If the selected representation's last modification date is
earlier than or equal to the date provided in the field value,
the condition is true.
[new] 2. Otherwise, the condition is false.
The origin server MUST NOT perform the requested method An origin server MUST NOT perform the requested method if an If-
if the selected representation's last modification date is Unmodified-Since condition evaluates to false. Instead, the origin
more recent than the date provided in the field-value; instead the origin server MAY indicate that the conditional request failed by responding
server MUST respond with either a) the 412 (Precondition Failed) with a 412 (Precondition Failed) status code. Alternatively, if the
status code or b) one of the 2xx (Successful) status codes if the request is a state-changing operation that appears to have already
origin server has verified that a state change is being requested and been applied to the selected representation, the origin server MAY
the final state is already reflected in the current state of the respond with a 2xx (Successful) status code (i.e., the change
target resource (i.e., the change requested by the user agent has requested by the user agent has already succeeded, but the user agent
already succeeded, but the user agent might not be aware of that might not be aware of it, perhaps because the prior response was lost
because the prior response message was lost or a compatible change or an equivalent change was made by some other user agent).
was made by some other user agent). In the latter case, the origin
server MUST NOT send a validator header field in the response unless
it can verify that the request is a duplicate of an immediately prior
change made by the same user agent.
[new] Allowing an origin server to send a success response when a change
request appears to have already been applied is more efficient for
many authoring use cases, but comes with some risk if multiple user
agents are making change requests that are very similar but not
cooperative. In those cases, an origin server is better off being
stringent in sending 412 for every failed precondition on an unsafe
method.
The If-Unmodified-Since header field can be ignored by caches and The If-Unmodified-Since header field can be ignored by caches and
intermediaries because it is not applicable to a stored response. intermediaries because it is not applicable to a stored response.
13.1.5. If-Range 13.1.5. If-Range
The "If-Range" header field provides a special conditional request The "If-Range" header field provides a special conditional request
mechanism that is similar to the If-Match and If-Unmodified-Since mechanism that is similar to the If-Match and If-Unmodified-Since
header fields but that instructs the recipient to ignore the Range header fields but that instructs the recipient to ignore the Range
header field if the validator doesn't match, resulting in transfer of header field if the validator doesn't match, resulting in transfer of
the new selected representation instead of a 412 (Precondition the new selected representation instead of a 412 (Precondition
Failed) response. If-Range is defined in Section 3.2 of [RFC7233]. Failed) response.
If a client has a partial copy of a representation and wishes to have If a client has a partial copy of a representation and wishes to have
an up-to-date copy of the entire representation, it could use the an up-to-date copy of the entire representation, it could use the
Range header field with a conditional GET (using either or both of Range header field with a conditional GET (using either or both of
If-Unmodified-Since and If-Match.) However, if the precondition If-Unmodified-Since and If-Match.) However, if the precondition
fails because the representation has been modified, the client would fails because the representation has been modified, the client would
then have to make a second request to obtain the entire current then have to make a second request to obtain the entire current
representation. representation.
The "If-Range" header field allows a client to "short-circuit" the The "If-Range" header field allows a client to "short-circuit" the
second request. Informally, its meaning is as follows: if the second request. Informally, its meaning is as follows: if the
representation is unchanged, send me the part(s) that I am requesting representation is unchanged, send me the part(s) that I am requesting
in Range; otherwise, send me the entire representation. in Range; otherwise, send me the entire representation.
If-Range = entity-tag / HTTP-date If-Range = entity-tag / HTTP-date
A valid entity-tag can be distinguished from a valid HTTP-date by A valid entity-tag can be distinguished from a valid HTTP-date by
examining the first two characters for a DQUOTE. examining the first three characters for a DQUOTE.
A client MUST NOT generate an If-Range header field in a request that A client MUST NOT generate an If-Range header field in a request that
does not contain a Range header field. A server MUST ignore an does not contain a Range header field. A server MUST ignore an If-
If-Range header field received in a request that does not contain a Range header field received in a request that does not contain a
Range header field. An origin server MUST ignore an If-Range header Range header field. An origin server MUST ignore an If-Range header
field received in a request for a target resource that does not field received in a request for a target resource that does not
support Range requests. support Range requests.
A client MUST NOT generate an If-Range header field containing an A client MUST NOT generate an If-Range header field containing an
entity-tag that is marked as weak. A client MUST NOT generate an entity-tag that is marked as weak. A client MUST NOT generate an If-
If-Range header field containing an HTTP-date unless the client has Range header field containing an HTTP-date unless the client has no
no entity-tag for the corresponding representation and the date is a entity-tag for the corresponding representation and the date is a
strong validator in the sense defined by Section 2.2.2 of [RFC7232]. strong validator in the sense defined by Section 8.8.2.2.
A server that evaluates an If-Range precondition MUST use the strong A server that receives an If-Range header field on a Range request
comparison function when comparing entity-tags (Section 2.3.2 of MUST evaluate the condition as per Section 13.2 prior to performing
[RFC7232]) and MUST evaluate the condition as false if an HTTP-date the method.
validator is provided that is not a strong validator in the sense
defined by Section 2.2.2 of [RFC7232].
[new] To evaluate a received If-Range header field containing an HTTP-date:
[new] 1. If the HTTP-date validator provided is not a strong validator in
the sense defined by Section 8.8.2.2, the condition is false.
[new] 2. If the HTTP-date validator provided exactly matches the
Last-Modified field value for the selected representation, the
condition is true.
[new] 3. Otherwise, the condition is false.
[new] To evaluate a received If-Range header field containing an
entity-tag:
[new] 1. If the entity-tag validator provided exactly matches the ETag
field value for the selected representation using the strong
comparison function (Section 8.8.3.2), the condition is true.
[new] 2. Otherwise, the condition is false.
If the validator given in the If-Range header field matches the A recipient of an If-Range header field MUST ignore the Range header
current validator for the selected representation of the target field if the If-Range condition evaluates to false. Otherwise, the
resource, then the server SHOULD process the Range header field as recipient SHOULD process the Range header field as requested.
requested. If the validator does not match, the server MUST ignore
the Range header field.
Note that this comparison by exact match, including when the Note that the If-Range comparison by exact match, including when the
validator is an HTTP-date, differs from the "earlier than or equal validator is an HTTP-date, differs from the "earlier than or equal
to" comparison used when evaluating an If-Unmodified-Since to" comparison used when evaluating an If-Unmodified-Since
conditional. conditional.
13.2. Evaluation of Preconditions 13.2. Evaluation of Preconditions
13.2.1. When to Evaluate 13.2.1. When to Evaluate
Except when excluded below, a recipient cache or origin server MUST Except when excluded below, a recipient cache or origin server MUST
evaluate received request preconditions after it has successfully evaluate received request preconditions after it has successfully
performed its normal request checks and just before it would perform performed its normal request checks and just before it would process
the action associated with the request method. A server MUST ignore the request content (if any) or perform the action associated with
all received preconditions if its response to the same request the request method. A server MUST ignore all received preconditions
without those conditions would have been a status code other than a if its response to the same request without those conditions, prior
2xx (Successful) or 412 (Precondition Failed). In other words, to processing the request content, would have been a status code
redirects and failures take precedence over the evaluation of other than a 2xx (Successful) or 412 (Precondition Failed). In other
preconditions in conditional requests. words, redirects and failures that can be detected before significant
processing occurs take precedence over the evaluation of
preconditions.
A server that is not the origin server for the target resource and A server that is not the origin server for the target resource and
cannot act as a cache for requests on the target resource MUST NOT cannot act as a cache for requests on the target resource MUST NOT
evaluate the conditional request header fields defined by this evaluate the conditional request header fields defined by this
specification, and it MUST forward them if the request is forwarded, specification, and it MUST forward them if the request is forwarded,
since the generating client intends that they be evaluated by a since the generating client intends that they be evaluated by a
server that can provide a current representation. Likewise, a server server that can provide a current representation. Likewise, a server
MUST ignore the conditional request header fields defined by this MUST ignore the conditional request header fields defined by this
specification when received with a request method that does not specification when received with a request method that does not
involve the selection or modification of a selected representation, involve the selection or modification of a selected representation,
such as CONNECT, OPTIONS, or TRACE. such as CONNECT, OPTIONS, or TRACE.
Note that protocol extensions can modify the conditions under which
revalidation is triggered. For example, the "immutable" cache
directive (defined by [RFC8246]) instructs caches to forgo
revalidation of fresh responses even when requested by the client.
Conditional request header fields that are defined by extensions to Conditional request header fields that are defined by extensions to
HTTP might place conditions on all recipients, on the state of the HTTP might place conditions on all recipients, on the state of the
target resource in general, or on a group of resources. For target resource in general, or on a group of resources. For
instance, the "If" header field in WebDAV can make a request instance, the "If" header field in WebDAV can make a request
conditional on various aspects of multiple resources, such as locks, conditional on various aspects of multiple resources, such as locks,
if the recipient understands and implements that field ([RFC4918], if the recipient understands and implements that field ([RFC4918],
Section 10.4). Section 10.4).
Although conditional request header fields are defined as being Although conditional request header fields are defined as being
usable with the HEAD method (to keep HEAD's semantics consistent with usable with the HEAD method (to keep HEAD's semantics consistent with
skipping to change at line 5483 skipping to change at page 132, line 22
validation, a validated cache is more efficient than a partial validation, a validated cache is more efficient than a partial
response, and entity tags are presumed to be more accurate than date response, and entity tags are presumed to be more accurate than date
validators. validators.
A recipient cache or origin server MUST evaluate the request A recipient cache or origin server MUST evaluate the request
preconditions defined by this specification in the following order: preconditions defined by this specification in the following order:
1. When recipient is the origin server and If-Match is present, 1. When recipient is the origin server and If-Match is present,
evaluate the If-Match precondition: evaluate the If-Match precondition:
* if true, continue to step 3 o if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be o if false, respond 412 (Precondition Failed) unless it can be
determined that the state-changing request has already determined that the state-changing request has already
succeeded (see Section 3.1) succeeded (see Section 13.1.1)
2. When recipient is the origin server, If-Match is not present, and 2. When recipient is the origin server, If-Match is not present, and
If-Unmodified-Since is present, evaluate the If-Unmodified-Since If-Unmodified-Since is present, evaluate the If-Unmodified-Since
precondition: precondition:
* if true, continue to step 3 o if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be o if false, respond 412 (Precondition Failed) unless it can be
determined that the state-changing request has already determined that the state-changing request has already
succeeded (see Section 3.4) succeeded (see Section 13.1.4)
3. When If-None-Match is present, evaluate the If-None-Match 3. When If-None-Match is present, evaluate the If-None-Match
precondition: precondition:
* if true, continue to step 5 o if true, continue to step 5
* if false for GET/HEAD, respond 304 (Not Modified) o if false for GET/HEAD, respond 304 (Not Modified)
* if false for other methods, respond 412 (Precondition Failed) o if false for other methods, respond 412 (Precondition Failed)
4. When the method is GET or HEAD, If-None-Match is not present, and 4. When the method is GET or HEAD, If-None-Match is not present, and
If-Modified-Since is present, evaluate the If-Modified-Since If-Modified-Since is present, evaluate the If-Modified-Since
precondition: precondition:
* if true, continue to step 5 o if true, continue to step 5
o if false, respond 304 (Not Modified)
* if false, respond 304 (Not Modified)
5. When the method is GET and both Range and If-Range are present, 5. When the method is GET and both Range and If-Range are present,
evaluate the If-Range precondition: evaluate the If-Range precondition:
* if the validator matches and the Range specification is o if the validator matches and the Range specification is
applicable to the selected representation, respond 206 applicable to the selected representation, respond 206
(Partial Content) [RFC7233] (Partial Content)
6. Otherwise, 6. Otherwise,
* all conditions are met, so perform the requested action and o all conditions are met, so perform the requested action and
respond according to its success or failure. respond according to its success or failure.
Any extension to HTTP/1.1 that defines additional conditional request Any extension to HTTP that defines additional conditional request
header fields ought to define its own expectations regarding the header fields ought to define its own expectations regarding the
order for evaluating such fields in relation to those defined in this order for evaluating such fields in relation to those defined in this
document and other conditionals that might be found in practice. document and other conditionals that might be found in practice.
14. Range Requests 14. Range Requests
Hypertext Transfer Protocol (HTTP) clients often encounter Clients often encounter interrupted data transfers as a result of
interrupted data transfers as a result of canceled requests or canceled requests or dropped connections. When a client has stored a
dropped connections. When a client has stored a partial partial representation, it is desirable to request the remainder of
representation, it is desirable to request the remainder of that that representation in a subsequent request rather than transfer the
representation in a subsequent request rather than transfer the
entire representation. Likewise, devices with limited local storage entire representation. Likewise, devices with limited local storage
might benefit from being able to request only a subset of a larger might benefit from being able to request only a subset of a larger
representation, such as a single page of a very large document, or representation, such as a single page of a very large document, or
the dimensions of an embedded image. the dimensions of an embedded image.
Range requests are an OPTIONAL Range requests are an OPTIONAL feature of HTTP, designed so that
feature of HTTP, designed so that recipients not implementing this recipients not implementing this feature (or not supporting it for
feature (or not supporting it for the target resource) can respond as the target resource) can respond as if it is a normal GET request
if it is a normal GET request without impacting interoperability. without impacting interoperability. Partial responses are indicated
Partial responses are indicated by a distinct status code to not be by a distinct status code to not be mistaken for full responses by
mistaken for full responses by caches that might not implement the caches that might not implement the feature.
feature.
14.1. Range Units 14.1. Range Units
A representation can be partitioned into subranges according to Representation data can be partitioned into subranges when there are
various structural units, depending on the structure inherent in the addressable structural units inherent to that data's content coding
representation's media type. or media type. For example, octet (a.k.a., byte) boundaries are a
structural unit common to all representation data, allowing
partitions of the data to be identified as a range of bytes at some
offset from the start or end of that data.
This "range unit" is used in the Accept-Ranges This general notion of a _range unit_ is used in the Accept-Ranges
(Section 2.3) response header field to advertise support for range (Section 14.3) response header field to advertise support for range
requests, the Range (Section 3.1) request header field to delineate requests, the Range (Section 14.2) request header field to delineate
the parts of a representation that are requested, and the the parts of a representation that are requested, and the
Content-Range (Section 4.2) payload header field to describe which Content-Range (Section 14.4) header field to describe which part of a
part of a representation is being transferred. representation is being transferred.
range-unit = bytes-unit / other-range-unit
other-range-unit = token range-unit = token
[new] All range unit names are case-insensitive and ought to be registered
within the "HTTP Range Unit Registry", as defined in Section 16.5.1
Range units are intended to be extensible. New range units ought to Range units are intended to be extensible, as described in
be registered with IANA, as defined in Section 5.1. Section 16.5.
14.1.1. Range Specifiers 14.1.1. Range Specifiers
[Ranges are expressed ... Ranges are expressed in terms of a range unit paired with a set of
. range specifiers. The range unit name determines what kinds of
. range-spec are applicable to its own specifiers. Hence, the
: following gramar is generic: each range unit is expected to specify
, requirements on when int-range, suffix-range, and other-range are
.] allowed.
A byte-range request can specify a single range of bytes or a set of A range request can specify a single range or a set of ranges within
ranges within a single representation. a single representation.
byte-ranges-specifier = bytes-unit "=" byte-range-set ranges-specifier = range-unit "=" range-set
byte-range-set = 1#( byte-range-spec / suffix-byte-range-spec ) range-set = 1#range-spec
range-spec = int-range
/ suffix-range
/ other-range
[new] An int-range is a range expressed as two non-negative integers or as
one non-negative integer through to the end of the representation
data. The range unit specifies what the integers mean (e.g., they
might indicate unit offsets from the beginning, inclusive numbered
parts, etc.).
byte-range-spec = first-byte-pos "-" [ last-byte-pos ] int-range = first-pos "-" [ last-pos ]
first-byte-pos = 1*DIGIT first-pos = 1*DIGIT
last-byte-pos = 1*DIGIT last-pos = 1*DIGIT
[new] An int-range is invalid if the last-pos value is present and less
than the first-pos.
[new] A suffix-range is a range expressed as a suffix of the representation
data with the provided non-negative integer maximum length (in range
units). In other words, the last N units of the representation data.
suffix-byte-range-spec = "-" suffix-length suffix-range = "-" suffix-length
suffix-length = 1*DIGIT suffix-length = 1*DIGIT
[new] To provide for extensibility, the other-range rule is a mostly
unconstrained grammar that allows application-specific or future
range units to define additional range specifiers.
[new] other-range = 1*( %x21-2B / %x2D-7E )
; 1*(VCHAR excluding comma)
14.1.2. Byte Ranges 14.1.2. Byte Ranges
Since representation data is transferred in payloads as a sequence of The "bytes" range unit is used to express subranges of a
octets, a byte range is a meaningful substructure for any representation data's octet sequence. Each byte range is expressed
representation transferable over HTTP (Section 3 of [RFC7231]). The as an integer range at some offset, relative to either the beginning
"bytes" range unit is defined for expressing subranges of the data's (int-range) or end (suffix-range) of the representation data. Byte
octet sequence. ranges do not use the other-range specifier.
bytes-unit = "bytes" The first-pos value in a bytes int-range gives the offset of the
first byte in a range. The last-pos value gives the offset of the
last byte in the range; that is, the byte positions specified are
inclusive. Byte offsets start at zero.
The first-byte-pos value in a byte-range-spec gives the byte-offset If the representation data has a content coding applied, each byte
of the first byte in a range. The last-byte-pos value gives the range is calculated with respect to the encoded sequence of bytes,
byte-offset of the last byte in the range; that is, the byte not the sequence of underlying bytes that would be obtained after
positions specified are inclusive. Byte offsets start at zero. decoding.
Examples of byte-ranges-specifier values: Examples of bytes range specifiers:
o The first 500 bytes (byte offsets 0-499, inclusive): o The first 500 bytes (byte offsets 0-499, inclusive):
bytes=0-499 bytes=0-499
o The second 500 bytes (byte offsets 500-999, inclusive): o The second 500 bytes (byte offsets 500-999, inclusive):
bytes=500-999 bytes=500-999
A byte-range-spec is invalid if the last-byte-pos value is present
and less than the first-byte-pos.
A client can limit the number of bytes requested without knowing the A client can limit the number of bytes requested without knowing the
size of the selected representation. If the last-byte-pos value is size of the selected representation. If the last-pos value is
absent, or if the value is greater than or equal to the current absent, or if the value is greater than or equal to the current
length of the representation data, the byte range is interpreted as length of the representation data, the byte range is interpreted as
the remainder of the representation (i.e., the server replaces the the remainder of the representation (i.e., the server replaces the
value of last-byte-pos with a value that is one less than the current value of last-pos with a value that is one less than the current
length of the selected representation). length of the selected representation).
A client can request the last N bytes of the selected representation A client can request the last N bytes (N > 0) of the selected
using a suffix-byte-range-spec. representation using a suffix-range. If the selected representation
is shorter than the specified suffix-length, the entire
If the selected representation is shorter than the specified representation is used.
suffix-length, the entire representation is used.
Additional examples, assuming a representation of length 10000: Additional examples, assuming a representation of length 10000:
o The final 500 bytes (byte offsets 9500-9999, inclusive): o The final 500 bytes (byte offsets 9500-9999, inclusive):
bytes=-500 bytes=-500
Or: Or:
bytes=9500- bytes=9500-
o The first and last bytes only (bytes 0 and 9999): o The first and last bytes only (bytes 0 and 9999):
bytes=0-0,-1 bytes=0-0,-1
o The first, middle, and last 1000 bytes:
bytes= 0-999, 4500-5499, -1000
o Other valid (but not canonical) specifications of the second 500 o Other valid (but not canonical) specifications of the second 500
bytes (byte offsets 500-999, inclusive): bytes (byte offsets 500-999, inclusive):
bytes=500-600,601-999 bytes=500-600,601-999
bytes=500-700,601-999 bytes=500-700,601-999
If a valid byte-range-set includes at least one byte-range-spec with If a valid bytes range-set includes at least one range-spec with a
a first-byte-pos that is less than the current length of the first-pos that is less than the current length of the representation,
representation, or at least one suffix-byte-range-spec with a or at least one suffix-range with a non-zero suffix-length, then the
non-zero suffix-length, then the byte-range-set is satisfiable. bytes range-set is satisfiable. Otherwise, the bytes range-set is
Otherwise, the byte-range-set is unsatisfiable. unsatisfiable.
[new] If the selected representation has zero length, the only satisfiable
form of range-spec is a suffix-range with a non-zero suffix-length.
In the byte-range syntax, first-byte-pos, last-byte-pos, and In the byte-range syntax, first-pos, last-pos, and suffix-length are
suffix-length are expressed as decimal number of octets. Since there expressed as decimal number of octets. Since there is no predefined
is no predefined limit to the length of a payload, recipients MUST limit to the length of content, recipients MUST anticipate
anticipate potentially large decimal numerals and prevent parsing potentially large decimal numerals and prevent parsing errors due to
errors due to integer conversion overflows. integer conversion overflows.
14.2. Range 14.2. Range
The "Range" header field on a GET request modifies the method The "Range" header field on a GET request modifies the method
semantics to request transfer of only one or more subranges of the semantics to request transfer of only one or more subranges of the
selected representation data, rather than the entire selected selected representation data (Section 8.1), rather than the entire
representation data. selected representation.
Range = byte-ranges-specifier / other-ranges-specifier Range = ranges-specifier
other-ranges-specifier = other-range-unit "=" other-range-set
other-range-set = 1*VCHAR
A server MAY ignore the Range header field. However, origin servers A server MAY ignore the Range header field. However, origin servers
and intermediate caches ought to support byte ranges when possible, and intermediate caches ought to support byte ranges when possible,
since Range supports efficient recovery from partially failed since they support efficient recovery from partially failed transfers
transfers and partial retrieval of large representations. A server and partial retrieval of large representations.
MUST ignore a Range header field received with a request method other
than GET.
Although the range request mechanism is designed to allow for A server MUST ignore a Range header field received with a request
extensible range types, this specification only defines requests for method which is unrecognized or for which range handling is not
byte ranges. defined. For this specification, GET is the only method for which
range handling is defined.
An origin server MUST ignore a Range header field that contains a An origin server MUST ignore a Range header field that contains a
range unit it does not understand. A proxy MAY discard a Range range unit it does not understand. A proxy MAY discard a Range
header field that contains a range unit it does not understand. header field that contains a range unit it does not understand.
A server that supports range requests MAY ignore or reject a Range A server that supports range requests MAY ignore or reject a Range
header field that consists of more than two overlapping ranges, or a header field that consists of more than two overlapping ranges, or a
set of many small ranges that are not listed in ascending order, set of many small ranges that are not listed in ascending order,
since both are indications of either a broken client or a deliberate since both are indications of either a broken client or a deliberate
denial-of-service attack (Section 6.1). A client SHOULD NOT request denial-of-service attack (Section 17.14). A client SHOULD NOT
multiple ranges that are inherently less efficient to process and request multiple ranges that are inherently less efficient to process
transfer than a single range that encompasses the same data. and transfer than a single range that encompasses the same data.
A server that supports range requests MAY ignore a Range header field
when the selected representation has no content (i.e., the selected
representation's data is of zero length).
A client that is requesting multiple ranges SHOULD list those ranges A client that is requesting multiple ranges SHOULD list those ranges
in ascending order (the order in which they would typically be in ascending order (the order in which they would typically be
received in a complete representation) unless there is a specific received in a complete representation) unless there is a specific
need to request a later part earlier. For example, a user agent need to request a later part earlier. For example, a user agent
processing a large representation with an internal catalog of parts processing a large representation with an internal catalog of parts
might need to request later parts first, particularly if the might need to request later parts first, particularly if the
representation consists of pages stored in reverse order and the user representation consists of pages stored in reverse order and the user
agent wishes to transfer one page at a time. agent wishes to transfer one page at a time.
The Range header field is evaluated after evaluating the precondition The Range header field is evaluated after evaluating the precondition
header fields defined in [RFC7232], and only if the result in absence header fields defined in Section 13.1, and only if the result in
of the Range header field would be a 200 (OK) response. In other absence of the Range header field would be a 200 (OK) response. In
words, Range is ignored when a conditional GET would result in a 304 other words, Range is ignored when a conditional GET would result in
(Not Modified) response. a 304 (Not Modified) response.
The If-Range header field (Section 3.2) can be used as a precondition The If-Range header field (Section 13.1.5) can be used as a
to applying the Range header field. precondition to applying the Range header field.
If all of the preconditions are true, the server supports the Range If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are header field for the target resource, and the specified range(s) are
valid and satisfiable (as defined in Section 2.1), the server SHOULD valid and satisfiable (as defined in Section 14.1.2), the server
send a 206 (Partial Content) response with a payload containing one SHOULD send a 206 (Partial Content) response with a content
or more partial representations that correspond to the satisfiable containing one or more partial representations that correspond to the
ranges requested, as defined in Section 4. satisfiable ranges requested.
The above does not imply that a server will send all requested
ranges. In some cases, it may only be possible (or efficient) to
send a portion of the requested ranges first, while expecting the
client to re-request the remaining portions later if they are still
desired (see Section 15.3.7).
If all of the preconditions are true, the server supports the Range If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are header field for the target resource, and the specified range(s) are
invalid or unsatisfiable, the server SHOULD send a 416 (Range Not invalid or unsatisfiable, the server SHOULD send a 416 (Range Not
Satisfiable) response. Satisfiable) response.
14.3. Accept-Ranges 14.3. Accept-Ranges
The "Accept-Ranges" header field allows a server to indicate that it The "Accept-Ranges" header field allows a server to indicate that it
supports range requests for the target resource. supports range requests for the target resource.
skipping to change at line 5762 skipping to change at page 139, line 7
Accept-Ranges = acceptable-ranges Accept-Ranges = acceptable-ranges
acceptable-ranges = 1#range-unit / "none" acceptable-ranges = 1#range-unit / "none"
An origin server that supports byte-range requests for a given target An origin server that supports byte-range requests for a given target
resource MAY send resource MAY send
Accept-Ranges: bytes Accept-Ranges: bytes
to indicate what range units are supported. A client MAY generate to indicate what range units are supported. A client MAY generate
range requests without having received this header field for the range requests without having received this header field for the
resource involved. Range units are defined in Section 2. resource involved. Range units are defined in Section 14.1.
A server that does not support any kind of range request for the A server that does not support any kind of range request for the
target resource MAY send target resource MAY send
Accept-Ranges: none Accept-Ranges: none
to advise the client not to attempt a range request. to advise the client not to attempt a range request.
14.4. Content-Range 14.4. Content-Range
The "Content-Range" header field is sent in a single part 206 The "Content-Range" header field is sent in a single part 206
(Partial Content) response to indicate the partial range of the (Partial Content) response to indicate the partial range of the
selected representation enclosed as the message payload, sent in each selected representation enclosed as the message content, sent in each
part of a multipart 206 response to indicate the range enclosed part of a multipart 206 response to indicate the range enclosed
within each body part, and sent in 416 (Range Not Satisfiable) within each body part, and sent in 416 (Range Not Satisfiable)
responses to provide information about the selected representation. responses to provide information about the selected representation.
Content-Range = byte-content-range Content-Range = range-unit SP
/ other-content-range ( range-resp / unsatisfied-range )
byte-content-range = bytes-unit SP
( byte-range-resp / unsatisfied-range )
byte-range-resp = byte-range "/" ( complete-length / "*" ) range-resp = incl-range "/" ( complete-length / "*" )
byte-range = first-byte-pos "-" last-byte-pos incl-range = first-pos "-" last-pos
unsatisfied-range = "*/" complete-length unsatisfied-range = "*/" complete-length
complete-length = 1*DIGIT complete-length = 1*DIGIT
other-content-range = other-range-unit SP other-range-resp
other-range-resp = *CHAR
If a 206 (Partial Content) response contains a Content-Range header If a 206 (Partial Content) response contains a Content-Range header
field with a range unit (Section 2) that the recipient does not field with a range unit (Section 14.1) that the recipient does not
understand, the recipient MUST NOT attempt to recombine it with a understand, the recipient MUST NOT attempt to recombine it with a
stored representation. A proxy that receives such a message SHOULD stored representation. A proxy that receives such a message SHOULD
forward it downstream. forward it downstream.
Content-Range might also be sent as a request modifier to request a
partial PUT, as described in Section 14.5, based on private
agreements between client and origin server. A server MUST ignore a
Content-Range header field received in a request with a method for
which Content-Range support is not defined.
For byte ranges, a sender SHOULD indicate the complete length of the For byte ranges, a sender SHOULD indicate the complete length of the
representation from which the range has been extracted, unless the representation from which the range has been extracted, unless the
complete length is unknown or difficult to determine. An asterisk complete length is unknown or difficult to determine. An asterisk
character ("*") in place of the complete-length indicates that the character ("*") in place of the complete-length indicates that the
representation length was unknown when the header field was representation length was unknown when the header field was
generated. generated.
The following example illustrates when the complete length of the The following example illustrates when the complete length of the
selected representation is known by the sender to be 1234 bytes: selected representation is known by the sender to be 1234 bytes:
Content-Range: bytes 42-1233/1234 Content-Range: bytes 42-1233/1234
and this second example illustrates when the complete length is and this second example illustrates when the complete length is
unknown: unknown:
Content-Range: bytes 42-1233/* Content-Range: bytes 42-1233/*
A Content-Range field value is invalid if it contains a A Content-Range field value is invalid if it contains a range-resp
byte-range-resp that has a last-byte-pos value less than its that has a last-pos value less than its first-pos value, or a
first-byte-pos value, or a complete-length value less than or equal complete-length value less than or equal to its last-pos value. The
to its last-byte-pos value. The recipient of an invalid recipient of an invalid Content-Range MUST NOT attempt to recombine
Content-Range MUST NOT attempt to recombine the received content with the received content with a stored representation.
a stored representation.
A server generating a 416 (Range Not Satisfiable) response to a A server generating a 416 (Range Not Satisfiable) response to a byte-
byte-range request SHOULD send a Content-Range header field with an range request SHOULD send a Content-Range header field with an
unsatisfied-range value, as in the following example: unsatisfied-range value, as in the following example:
Content-Range: bytes */1234 Content-Range: bytes */1234
The complete-length in a 416 response indicates the current length of The complete-length in a 416 response indicates the current length of
the selected representation. the selected representation.
The Content-Range header field has no meaning for status codes that The Content-Range header field has no meaning for status codes that
do not explicitly describe its semantic. For this specification, do not explicitly describe its semantic. For this specification,
only the 206 (Partial Content) and 416 (Range Not Satisfiable) status only the 206 (Partial Content) and 416 (Range Not Satisfiable) status
codes describe a meaning for Content-Range. codes describe a meaning for Content-Range.
The following are examples of Content-Range values in which the The following are examples of Content-Range values in which the
selected representation contains a total of 1234 bytes: selected representation contains a total of 1234 bytes:
o The first 500 bytes: o The first 500 bytes:
Content-Range: bytes 0-499/1234 Content-Range: bytes 0-499/1234
o The second 500 bytes: o The second 500 bytes:
Content-Range: bytes 500-999/1234 Content-Range: bytes 500-999/1234
o All except for the first 500 bytes: o All except for the first 500 bytes:
Content-Range: bytes 500-1233/1234 Content-Range: bytes 500-1233/1234
o The last 500 bytes: o The last 500 bytes:
Content-Range: bytes 734-1233/1234 Content-Range: bytes 734-1233/1234
14.5. Partial PUT 14.5. Partial PUT
[new] Some origin servers support PUT of a partial representation when a
Content-Range header field (Section 14.4) is sent in the request,
though such support is inconsistent and depends on private agreements
with user agents. In general, it requests that the state of the
target resource be partly replaced with the enclosed content at an
offset and length indicated by the Content-Range value, where the
offset is relative to the current selected representation.
[new] An origin server SHOULD respond with a 400 (Bad Request) status code
if it receives Content-Range on a PUT for a target resource that does
not support partial PUT requests.
[new] Partial PUT is not backwards compatible with the original definition
of PUT. It may result in the content being written as a complete
replacement for the current representation.
Partial content updates are possible by targeting a separately Partial resource updates are also possible by targeting a separately
identified resource with state that overlaps a portion of identified resource with state that overlaps or extends a portion of
the larger resource, or by using a different method that has been the larger resource, or by using a different method that has been
specifically defined for partial updates (for example, the PATCH specifically defined for partial updates (for example, the PATCH
method defined in [RFC5789]). method defined in [RFC5789]).
14.6. Media Type multipart/byteranges 14.6. Media Type multipart/byteranges
When a 206 (Partial Content) response message includes the content of When a 206 (Partial Content) response message includes the content of
multiple ranges, they are transmitted as body parts in a multipart multiple ranges, they are transmitted as body parts in a multipart
message body ([RFC2046], Section 5.1) with the media type of message body ([RFC2046], Section 5.1) with the media type of
"multipart/byteranges". "multipart/byteranges".
skipping to change at line 5895 skipping to change at page 142, line 7
1. Additional CRLFs might precede the first boundary string in the 1. Additional CRLFs might precede the first boundary string in the
body. body.
2. Although [RFC2046] permits the boundary string to be quoted, some 2. Although [RFC2046] permits the boundary string to be quoted, some
existing implementations handle a quoted boundary string existing implementations handle a quoted boundary string
incorrectly. incorrectly.
3. A number of clients and servers were coded to an early draft of 3. A number of clients and servers were coded to an early draft of
the byteranges specification that used a media type of multipart/ the byteranges specification that used a media type of multipart/
x-byteranges, which is almost (but not quite) compatible with x-byteranges , which is almost (but not quite) compatible with
this type. this type.
Despite the name, the "multipart/byteranges" media type is not Despite the name, the "multipart/byteranges" media type is not
limited to byte ranges. The following example uses an "exampleunit" limited to byte ranges. The following example uses an "exampleunit"
range unit: range unit:
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Date: Tue, 14 Nov 1995 06:25:24 GMT Date: Tue, 14 Nov 1995 06:25:24 GMT
Last-Modified: Tue, 14 July 04:58:08 GMT Last-Modified: Tue, 14 July 04:58:08 GMT
Content-Length: 2331785 Content-Length: 2331785
skipping to change at line 5920 skipping to change at page 142, line 32
Content-Range: exampleunit 1.2-4.3/25 Content-Range: exampleunit 1.2-4.3/25
...the first range... ...the first range...
--THIS_STRING_SEPARATES --THIS_STRING_SEPARATES
Content-Type: video/example Content-Type: video/example
Content-Range: exampleunit 11.2-14.3/25 Content-Range: exampleunit 11.2-14.3/25
...the second range ...the second range
--THIS_STRING_SEPARATES-- --THIS_STRING_SEPARATES--
This document serves as the specification for the Internet media type The following information serves as the registration form for the
"multipart/byteranges". The following has been registered with IANA. multipart/byteranges media type.
Type name: multipart Type name: multipart
Subtype name: byteranges Subtype name: byteranges
Required parameters: boundary Required parameters: boundary
Optional parameters: N/A Optional parameters: N/A
Encoding considerations: only "7bit", "8bit", or "binary" are Encoding considerations: only "7bit", "8bit", or "binary" are
permitted permitted
Security considerations: see Section 6 Security considerations: see Section 17
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: This specification (see Appendix A). Published specification: This specification (see Section 14.6).
Applications that use this media type: HTTP components supporting Applications that use this media type: HTTP components supporting
multiple ranges in a single request. multiple ranges in a single request.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information: Additional information: Deprecated alias names for this type: N/A
Deprecated alias names for this type: N/A
Magic number(s): N/A Magic number(s): N/A
File extension(s): N/A File extension(s): N/A
Macintosh file type code(s): N/A Macintosh file type code(s): N/A
Person and email address to contact for further information: See Person and email address to contact for further information: See Aut
Authors' Addresses section. hors' Addresses section.
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: N/A Restrictions on usage: N/A
Author: See Authors' Addresses section. Author: See Authors' Addresses section.
Change controller: IESG Change controller: IESG
15. Status Codes 15. Status Codes
The status-code element is a three-digit integer code giving the The (response) status code is a three-digit integer code giving the
result of the attempt to understand and satisfy the request. result of the attempt to understand and satisfy the request.
HTTP status codes are extensible. HTTP clients are not required to HTTP status codes are extensible. HTTP clients are not required to
understand the meaning of all registered status codes, though such understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, a client MUST understanding is obviously desirable. However, a client MUST
understand the class of any status code, as indicated by the first understand the class of any status code, as indicated by the first
digit, and treat an unrecognized status code as being equivalent to digit, and treat an unrecognized status code as being equivalent to
the x00 status code of that class, with the exception that a the x00 status code of that class.
recipient MUST NOT cache a response with an unrecognized status code.
For example, if an unrecognized status code of 471 is received by a For example, if an unrecognized status code of 471 is received by a
client, the client can assume that there was something wrong with its client, the client can assume that there was something wrong with its
request and treat the response as if it had received a 400 (Bad request and treat the response as if it had received a 400 (Bad
Request) status code. The response message will usually contain a Request) status code. The response message will usually contain a
representation that explains the status. representation that explains the status.
The first digit of the status-code defines the class of response. The first digit of the status code defines the class of response.
The last two digits do not have any categorization role. There are The last two digits do not have any categorization role. There are
five values for the first digit: five values for the first digit:
o 1xx (Informational): The request was received, continuing process o 1xx (Informational): The request was received, continuing process
o 2xx (Successful): The request was successfully received, o 2xx (Successful): The request was successfully received,
understood, and accepted understood, and accepted
o 3xx (Redirection): Further action needs to be taken in order to o 3xx (Redirection): Further action needs to be taken in order to
complete the request complete the request
o 4xx (Client Error): The request contains bad syntax or cannot be o 4xx (Client Error): The request contains bad syntax or cannot be
fulfilled fulfilled
o 5xx (Server Error): The server failed to fulfill an apparently o 5xx (Server Error): The server failed to fulfill an apparently
skipping to change at line 6002 skipping to change at page 144, line 16
o 3xx (Redirection): Further action needs to be taken in order to o 3xx (Redirection): Further action needs to be taken in order to
complete the request complete the request
o 4xx (Client Error): The request contains bad syntax or cannot be o 4xx (Client Error): The request contains bad syntax or cannot be
fulfilled fulfilled
o 5xx (Server Error): The server failed to fulfill an apparently o 5xx (Server Error): The server failed to fulfill an apparently
valid request valid request
[new] A single request can have multiple associated responses: zero or more
_interim_ (non-final) responses with status codes in the
"informational" (1xx) range, followed by exactly one _final_ response
with a status code in one of the other ranges.
15.1. Overview of Status Codes 15.1. Overview of Status Codes
The status codes listed below are defined in this specification, The status codes listed below are defined in this specification. The
Section 4 of [RFC7232], Section 4 of [RFC7233], and Section 3 of reason phrases listed here are only recommendations - they can be
[RFC7235]. The replaced by local equivalents or left out altogether without
reason phrases listed here are only recommendations -- they can be affecting the protocol.
replaced by local equivalents without affecting the protocol.
Responses with status codes that are defined as cacheable by default Responses with status codes that are defined as heuristically
(e.g., 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, and 501 in cacheable (e.g., 200, 203, 204, 206, 300, 301, 308, 404, 405, 410,
this specification) can be reused by a cache with heuristic 414, and 501 in this specification) can be reused by a cache with
expiration unless otherwise indicated by the method definition or heuristic expiration unless otherwise indicated by the method
explicit cache controls [RFC7234]; all other status codes are not definition or explicit cache controls [Caching]; all other status
cacheable by default. codes are not heuristically cacheable.
Note that this list is not exhaustive -- it does not include Additional status codes, outside the scope of this specification,
extension status codes defined in other specifications. The complete have been specified for use in HTTP. All such status codes ought to
list of status codes is maintained by IANA. See Section 8.2 for be registered within the "Hypertext Transfer Protocol (HTTP) Status
details. Code Registry", as described in Section 16.2.
15.2. Informational 1xx 15.2. Informational 1xx
The 1xx (Informational) class of status code indicates an interim The _1xx (Informational)_ class of status code indicates an interim
response for communicating connection status or request progress response for communicating connection status or request progress
prior to completing the requested action and sending a final prior to completing the requested action and sending a final
response. Since HTTP/1.0 did not define any 1xx status codes, a response. Since HTTP/1.0 did not define any 1xx status codes, a
server MUST NOT send a 1xx response to an HTTP/1.0 client. server MUST NOT send a 1xx response to an HTTP/1.0 client.
1xx responses are terminated by the first empty line after the A 1xx response is terminated by the end of the header section; it
status-line (the empty line signaling the end of the header section). cannot contain content or trailers.
A client MUST be able to parse one or more 1xx responses received A client MUST be able to parse one or more 1xx responses received
prior to a final response, even if the client does not expect one. A prior to a final response, even if the client does not expect one. A
user agent MAY ignore unexpected 1xx responses. user agent MAY ignore unexpected 1xx responses.
A proxy MUST forward 1xx responses unless the proxy itself requested A proxy MUST forward 1xx responses unless the proxy itself requested
the generation of the 1xx response. For example, if a proxy adds an the generation of the 1xx response. For example, if a proxy adds an
"Expect: 100-continue" field when it forwards a request, then it need "Expect: 100-continue" header field when it forwards a request, then
not forward the corresponding 100 (Continue) response(s). it need not forward the corresponding 100 (Continue) response(s).
15.2.1. 100 Continue 15.2.1. 100 Continue
The 100 (Continue) status code indicates that the initial part of a The _100 (Continue)_ status code indicates that the initial part of a
request has been received and has not yet been rejected by the request has been received and has not yet been rejected by the
server. The server intends to send a final response after the server. The server intends to send a final response after the
request has been fully received and acted upon. request has been fully received and acted upon.
When the request contains an Expect header field that includes a When the request contains an Expect header field that includes a
100-continue expectation, the 100 response indicates that the server 100-continue expectation, the 100 response indicates that the server
wishes to receive the request payload body, as described in wishes to receive the request content, as described in
Section 5.1.1. The client ought to continue sending the request and Section 10.1.1. The client ought to continue sending the request and
discard the 100 response. discard the 100 response.
If the request did not contain an Expect header field containing the If the request did not contain an Expect header field containing the
100-continue expectation, the client can simply discard this interim 100-continue expectation, the client can simply discard this interim
response. response.
15.2.2. 101 Switching Protocols 15.2.2. 101 Switching Protocols
The 101 (Switching Protocols) status code indicates that the server The _101 (Switching Protocols)_ status code indicates that the server
understands and is willing to comply with the client's request, via understands and is willing to comply with the client's request, via
the Upgrade header field (Section 6.7 of [RFC7230]), for a change in the Upgrade header field (Section 7.8), for a change in the
the application protocol being used on this connection. The server application protocol being used on this connection. The server MUST
MUST generate an Upgrade header field in the response that indicates generate an Upgrade header field in the response that indicates which
which protocol(s) will be switched to immediately after the empty protocol(s) will be switched to immediately after the empty line that
line that terminates the 101 response. terminates the 101 response.
It is assumed that the server will only agree to switch protocols It is assumed that the server will only agree to switch protocols
when it is advantageous to do so. For example, switching to a newer when it is advantageous to do so. For example, switching to a newer
version of HTTP might be advantageous over older versions, and version of HTTP might be advantageous over older versions, and
switching to a real-time, synchronous protocol might be advantageous switching to a real-time, synchronous protocol might be advantageous
when delivering resources that use such features. when delivering resources that use such features.
15.3. Successful 2xx 15.3. Successful 2xx
The 2xx (Successful) class of status code indicates that the client's The _2xx (Successful)_ class of status code indicates that the
request was successfully received, understood, and accepted. client's request was successfully received, understood, and accepted.
15.3.1. 200 OK 15.3.1. 200 OK
The 200 (OK) status code indicates that the request has succeeded. The _200 (OK)_ status code indicates that the request has succeeded.
The payload sent in a 200 response depends on the request method. The content sent in a 200 response depends on the request method.
For the methods defined by this specification, the intended meaning For the methods defined by this specification, the intended meaning
of the payload can be summarized as: of the content can be summarized as:
GET a representation of the target resource;
HEAD the same representation as GET, but without the representation
data;
POST a representation of the status of, or results obtained from,
the action;
PUT, DELETE a representation of the status of the action;
OPTIONS a representation of the communications options; ---------------- --------------------------------------------
request method response content is a representation of
---------------- --------------------------------------------
GET the target resource
HEAD the target resource, like GET, but without
transferring the representation data
POST the status of, or results obtained from,
the action
PUT, DELETE the status of the action
OPTIONS communication options for the target
resource
TRACE the request message as received by the
server returning the trace
---------------- --------------------------------------------
TRACE a representation of the request message as received by the end Table 6
server.
Aside from responses to CONNECT, a 200 response always has a payload, Aside from responses to CONNECT, a 200 response always has content,
though an origin server MAY generate a payload body of zero length. though an origin server MAY generate content of zero length. If no
If no payload is desired, an origin server ought to send 204 (No content is desired, an origin server ought to send _204 (No Content)_
Content) instead. For CONNECT, no payload is allowed because the instead. For CONNECT, no content is allowed because the successful
successful result is a tunnel, which begins immediately after the 200 result is a tunnel, which begins immediately after the 200 response
response header section. header section.
A 200 response is cacheable by default; i.e., unless otherwise A 200 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.3.2. 201 Created 15.3.2. 201 Created
The 201 (Created) status code indicates that the request has been The _201 (Created)_ status code indicates that the request has been
fulfilled and has resulted in one or more new resources being fulfilled and has resulted in one or more new resources being
created. The primary resource created by the request is identified created. The primary resource created by the request is identified
by either a Location header field in the response or, if no Location by either a Location header field in the response or, if no Location
field is received, by the effective request URI. header field is received, by the target URI.
The 201 response payload typically describes and links to the The 201 response content typically describes and links to the
resource(s) created. See Section 7.2 for a discussion of the meaning resource(s) created. See Section 8.8 for a discussion of the meaning
and purpose of validator header fields, such as ETag and and purpose of validator fields, such as ETag and Last-Modified, in a
Last-Modified, in a 201 response. 201 response.
15.3.3. 202 Accepted 15.3.3. 202 Accepted
The 202 (Accepted) status code indicates that the request has been The _202 (Accepted)_ status code indicates that the request has been
accepted for processing, but the processing has not been completed. accepted for processing, but the processing has not been completed.
The request might or might not eventually be acted upon, as it might The request might or might not eventually be acted upon, as it might
be disallowed when processing actually takes place. There is no be disallowed when processing actually takes place. There is no
facility in HTTP for re-sending a status code from an asynchronous facility in HTTP for re-sending a status code from an asynchronous
operation. operation.
The 202 response is intentionally noncommittal. Its purpose is to The 202 response is intentionally noncommittal. Its purpose is to
allow a server to accept a request for some other process (perhaps a allow a server to accept a request for some other process (perhaps a
batch-oriented process that is only run once per day) without batch-oriented process that is only run once per day) without
requiring that the user agent's connection to the server persist requiring that the user agent's connection to the server persist
until the process is completed. The representation sent with this until the process is completed. The representation sent with this
response ought to describe the request's current status and point to response ought to describe the request's current status and point to
(or embed) a status monitor that can provide the user with an (or embed) a status monitor that can provide the user with an
estimate of when the request will be fulfilled. estimate of when the request will be fulfilled.
15.3.4. 203 Non-Authoritative Information 15.3.4. 203 Non-Authoritative Information
The 203 (Non-Authoritative Information) status code indicates that The _203 (Non-Authoritative Information)_ status code indicates that
the request was successful but the enclosed payload has been modified the request was successful but the enclosed content has been modified
from that of the origin server's 200 (OK) response by a transforming from that of the origin server's 200 (OK) response by a transforming
proxy (Section 5.7.2 of [RFC7230]). This status code allows the proxy (Section 7.7). This status code allows the proxy to notify
proxy to notify recipients when a transformation has been applied, recipients when a transformation has been applied, since that
since that knowledge might impact later decisions regarding the knowledge might impact later decisions regarding the content. For
content. For example, future cache validation requests for the example, future cache validation requests for the content might only
content might only be applicable along the same request path (through be applicable along the same request path (through the same proxies).
the same proxies).
The 203 response is similar to the Warning code of 214 Transformation
Applied (Section 5.5 of [RFC7234]), which has the advantage of being
applicable to responses with any status code.
A 203 response is cacheable by default; i.e., unless otherwise A 203 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.3.5. 204 No Content 15.3.5. 204 No Content
The 204 (No Content) status code indicates that the server has The _204 (No Content)_ status code indicates that the server has
successfully fulfilled the request and that there is no additional successfully fulfilled the request and that there is no additional
content to send in the response payload body. Metadata in the content to send in the response content. Metadata in the response
response header fields refer to the target resource and its selected header fields refer to the target resource and its selected
representation after the requested action was applied. representation after the requested action was applied.
For example, if a 204 status code is received in response to a PUT For example, if a 204 status code is received in response to a PUT
request and the response contains an ETag header field, then the PUT request and the response contains an ETag field, then the PUT was
was successful and the ETag field-value contains the entity-tag for successful and the ETag field value contains the entity-tag for the
the new representation of that target resource. new representation of that target resource.
The 204 response allows a server to indicate that the action has been The 204 response allows a server to indicate that the action has been
successfully applied to the target resource, while implying that the successfully applied to the target resource, while implying that the
user agent does not need to traverse away from its current "document user agent does not need to traverse away from its current "document
view" (if any). The server assumes that the user agent will provide view" (if any). The server assumes that the user agent will provide
some indication of the success to its user, in accord with its own some indication of the success to its user, in accord with its own
interface, and apply any new or updated metadata in the response to interface, and apply any new or updated metadata in the response to
its active representation. its active representation.
For example, a 204 status code is commonly used with document editing For example, a 204 status code is commonly used with document editing
interfaces corresponding to a "save" action, such that the document interfaces corresponding to a "save" action, such that the document
being saved remains available to the user for editing. It is also being saved remains available to the user for editing. It is also
frequently used with interfaces that expect automated data transfers frequently used with interfaces that expect automated data transfers
to be prevalent, such as within distributed version control systems. to be prevalent, such as within distributed version control systems.
A 204 response is terminated by the first empty line after the header A 204 response is terminated by the end of the header section; it
fields because it cannot contain a message body. cannot contain content or trailers.
A 204 response is cacheable by default; i.e., unless otherwise A 204 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.3.6. 205 Reset Content 15.3.6. 205 Reset Content
The 205 (Reset Content) status code indicates that the server has The _205 (Reset Content)_ status code indicates that the server has
fulfilled the request and desires that the user agent reset the fulfilled the request and desires that the user agent reset the
"document view", which caused the request to be sent, to its original "document view", which caused the request to be sent, to its original
state as received from the origin server. state as received from the origin server.
This response is intended to support a common data entry use case This response is intended to support a common data entry use case
where the user receives content that supports data entry (a form, where the user receives content that supports data entry (a form,
notepad, canvas, etc.), enters or manipulates data in that space, notepad, canvas, etc.), enters or manipulates data in that space,
causes the entered data to be submitted in a request, and then the causes the entered data to be submitted in a request, and then the
data entry mechanism is reset for the next entry so that the user can data entry mechanism is reset for the next entry so that the user can
easily initiate another input action. easily initiate another input action.
Since the 205 status code implies that no additional content will be Since the 205 status code implies that no additional content will be
provided, a server MUST NOT generate a payload in a 205 response. In provided, a server MUST NOT generate content in a 205 response.
other words, a server MUST do one of the following for a 205
response: a) indicate a zero-length body for the response by
including a Content-Length header field with a value of 0; b)
indicate a zero-length payload for the response by including a
Transfer-Encoding header field with a value of chunked and a message
body consisting of a single chunk of zero-length; or, c) close the
connection immediately after sending the blank line terminating the
header section.
15.3.7. 206 Partial Content 15.3.7. 206 Partial Content
The 206 (Partial Content) status code indicates that the server is The _206 (Partial Content)_ status code indicates that the server is
successfully fulfilling a range request for the target resource by successfully fulfilling a range request for the target resource by
transferring one or more parts of the selected representation that transferring one or more parts of the selected representation.
correspond to the satisfiable ranges found in the request's Range
header field (Section 3.1). A server that supports range requests (Section 14) will usually
attempt to satisfy all of the requested ranges, since sending less
data will likely result in another client request for the remainder.
However, a server might want to send only a subset of the data
requested for reasons of its own, such as temporary unavailability,
cache efficiency, load balancing, etc. Since a 206 response is self-
descriptive, the client can still understand a response that only
partially satisfies its range request.
A client MUST inspect a 206 response's Content-Type and Content-Range
field(s) to determine what parts are enclosed and whether additional
requests are needed.
When a 206 response is generated, the server MUST generate the When a 206 response is generated, the server MUST generate the
following header fields, in addition to those required above, if the following header fields, in addition to those required in the
field would have been sent in a 200 (OK) response to the same subsections below, if the field would have been sent in a 200 (OK)
request: Date, Cache-Control, ETag, Expires, Content-Location, and response to the same request: Date, Cache-Control, ETag, Expires,
Vary. Content-Location, and Vary.
A Content-Length header field present in a 206 response indicates the
number of octets in the content of this message, which is usually not
the complete length of the selected representation. Each
Content-Range header field includes information about the selected
representation's complete length.
If a 206 is generated in response to a request with an If-Range If a 206 is generated in response to a request with an If-Range
header field, the sender SHOULD NOT generate other representation header field, the sender SHOULD NOT generate other representation
header fields beyond those required above, because the client is header fields beyond those required, because the client is understood
understood to already have a prior response containing those header to already have a prior response containing those header fields.
fields. Otherwise, the sender MUST generate all of the Otherwise, the sender MUST generate all of the representation header
representation header fields that would have been sent in a 200 (OK) fields that would have been sent in a 200 (OK) response to the same
response to the same request. request.
A 206 response is cacheable by default; i.e., unless otherwise A 206 response is heuristically cacheable; i.e., unless otherwise
indicated by explicit cache controls (see Section 4.2.2 of indicated by explicit cache controls (see Section 4.2.2 of
[RFC7234]). [Caching]).
15.3.7.1. Single Part
If a single part is being transferred, the server generating the 206 If a single part is being transferred, the server generating the 206
response MUST generate a Content-Range header field, describing what response MUST generate a Content-Range header field, describing what
range of the selected representation is enclosed, and a payload range of the selected representation is enclosed, and a content
consisting of the range. For example: consisting of the range. For example:
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Date: Wed, 15 Nov 1995 06:25:24 GMT Date: Wed, 15 Nov 1995 06:25:24 GMT
Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
Content-Range: bytes 21010-47021/47022 Content-Range: bytes 21010-47021/47022
Content-Length: 26012 Content-Length: 26012
Content-Type: image/gif Content-Type: image/gif
... 26012 bytes of partial image data ... ... 26012 bytes of partial image data ...
15.3.7.2. Multiple Parts
If multiple parts are being transferred, the server generating the If multiple parts are being transferred, the server generating the
206 response MUST generate a "multipart/byteranges" payload, as 206 response MUST generate "multipart/byteranges" content, as defined
defined in Appendix A, and a Content-Type header field containing the in Section 14.6, and a Content-Type header field containing the
multipart/byteranges media type and its required boundary parameter. multipart/byteranges media type and its required boundary parameter.
To avoid confusion with single-part responses, a server MUST NOT To avoid confusion with single-part responses, a server MUST NOT
generate a Content-Range header field in the HTTP header section of a generate a Content-Range header field in the HTTP header section of a
multiple part response (this field will be sent in each part multiple part response (this field will be sent in each part
instead). instead).
Within the header area of each body part in the multipart payload, Within the header area of each body part in the multipart content,
the server MUST generate a Content-Range header field corresponding the server MUST generate a Content-Range header field corresponding
to the range being enclosed in that body part. If the selected to the range being enclosed in that body part. If the selected
representation would have had a Content-Type header field in a 200 representation would have had a Content-Type header field in a 200
(OK) response, the server SHOULD generate that same Content-Type (OK) response, the server SHOULD generate that same Content-Type
field in the header area of each body part. For example: header field in the header area of each body part. For example:
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Date: Wed, 15 Nov 1995 06:25:24 GMT Date: Wed, 15 Nov 1995 06:25:24 GMT
Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
Content-Length: 1741 Content-Length: 1741
Content-Type: multipart/byteranges; boundary=THIS_STRING_SEPARATES Content-Type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
--THIS_STRING_SEPARATES --THIS_STRING_SEPARATES
Content-Type: application/pdf Content-Type: application/pdf
Content-Range: bytes 500-999/8000 Content-Range: bytes 500-999/8000
skipping to change at line 6302 skipping to change at page 150, line 44
--THIS_STRING_SEPARATES --THIS_STRING_SEPARATES
Content-Type: application/pdf Content-Type: application/pdf
Content-Range: bytes 7000-7999/8000 Content-Range: bytes 7000-7999/8000
...the second range ...the second range
--THIS_STRING_SEPARATES-- --THIS_STRING_SEPARATES--
When multiple ranges are requested, a server MAY coalesce any of the When multiple ranges are requested, a server MAY coalesce any of the
ranges that overlap, or that are separated by a gap that is smaller ranges that overlap, or that are separated by a gap that is smaller
than the overhead of sending multiple parts, regardless of the order than the overhead of sending multiple parts, regardless of the order
in which the corresponding byte-range-spec appeared in the received in which the corresponding range-spec appeared in the received Range
Range header field. Since the typical overhead between parts of a header field. Since the typical overhead between each part of a
multipart/byteranges payload is around 80 bytes, depending on the multipart/byteranges is around 80 bytes, depending on the selected
selected representation's media type and the chosen boundary representation's media type and the chosen boundary parameter length,
parameter length, it can be less efficient to transfer many small it can be less efficient to transfer many small disjoint parts than
disjoint parts than it is to transfer the entire selected it is to transfer the entire selected representation.
representation.
A server MUST NOT generate a multipart response to a request for a A server MUST NOT generate a multipart response to a request for a
single range, since a client that does not request multiple parts single range, since a client that does not request multiple parts
might not support multipart responses. However, a server MAY might not support multipart responses. However, a server MAY
generate a multipart/byteranges payload with only a single body part generate a multipart/byteranges response with only a single body part
if multiple ranges were requested and only one range was found to be if multiple ranges were requested and only one range was found to be
satisfiable or only one range remained after coalescing. A client satisfiable or only one range remained after coalescing. A client
that cannot process a multipart/byteranges response MUST NOT generate that cannot process a multipart/byteranges response MUST NOT generate
a request that asks for multiple ranges. a request that asks for multiple ranges.
When a multipart response payload is generated, the server SHOULD When a multipart response is generated, the server SHOULD send the
send the parts in the same order that the corresponding parts in the same order that the corresponding range-spec appeared in
byte-range-spec appeared in the received Range header field, the received Range header field, excluding those ranges that were
excluding those ranges that were deemed unsatisfiable or that were deemed unsatisfiable or that were coalesced into other ranges. A
coalesced into other ranges. A client that receives a multipart client that receives a multipart response MUST inspect the
response MUST inspect the Content-Range header field present in each Content-Range header field present in each body part in order to
body part in order to determine which range is contained in that body determine which range is contained in that body part; a client cannot
part; a client cannot rely on receiving the same ranges that it rely on receiving the same ranges that it requested, nor the same
requested, nor the same order that it requested. order that it requested.
15.3.7.3. Combining Parts 15.3.7.3. Combining Parts
A response might transfer only a subrange of a representation if the A response might transfer only a subrange of a representation if the
connection closed prematurely or if the request used one or more connection closed prematurely or if the request used one or more
Range specifications. After several such transfers, a client might Range specifications. After several such transfers, a client might
have received several ranges of the same representation. These have received several ranges of the same representation. These
ranges can only be safely combined if they all have in common the ranges can only be safely combined if they all have in common the
same strong validator (Section 2.1 of [RFC7232]). same strong validator (Section 8.8.1).
A client that has received multiple partial responses to GET requests A client that has received multiple partial responses to GET requests
on a target resource MAY combine those responses into a larger on a target resource MAY combine those responses into a larger
continuous range if they share the same strong validator. continuous range if they share the same strong validator.
If the most recent response is an incomplete 200 (OK) response, then If the most recent response is an incomplete 200 (OK) response, then
the header fields of that response are used for any combined response the header fields of that response are used for any combined response
and replace those of the matching stored responses. and replace those of the matching stored responses.
If the most recent response is a 206 (Partial Content) response and If the most recent response is a 206 (Partial Content) response and
at least one of the matching stored responses is a 200 (OK), then the at least one of the matching stored responses is a 200 (OK), then the
combined response header fields consist of the most recent 200 combined response header fields consist of the most recent 200
response's header fields. If all of the matching stored responses response's header fields. If all of the matching stored responses
are 206 responses, then the stored response with the most recent are 206 responses, then the stored response with the most recent
header fields is used as the source of header fields for the combined header fields is used as the source of header fields for the combined
response, except that the client MUST use other header fields response, except that the client MUST use other header fields
provided in the new response, aside from Content-Range, to replace provided in the new response, aside from Content-Range, to replace
all instances of the corresponding header fields in the stored all instances of the corresponding header fields in the stored
response. response.
The combined response message body consists of the union of partial The combined response content consists of the union of partial
content ranges in the new response and each of the selected content ranges in the new response and each of the selected
responses. If the union consists of the entire range of the responses. If the union consists of the entire range of the
representation, then the client MUST process the combined response as representation, then the client MUST process the combined response as
if it were a complete 200 (OK) response, including a Content-Length if it were a complete 200 (OK) response, including a Content-Length
header field that reflects the complete length. Otherwise, the header field that reflects the complete length. Otherwise, the
client MUST process the set of continuous ranges as one of the client MUST process the set of continuous ranges as one of the
following: an incomplete 200 (OK) response if the combined response following: an incomplete 200 (OK) response if the combined response
is a prefix of the representation, a single 206 (Partial Content) is a prefix of the representation, a single 206 (Partial Content)
response containing a multipart/byteranges body, or multiple 206 response containing multipart/byteranges content, or multiple 206
(Partial Content) responses, each with one continuous range that is (Partial Content) responses, each with one continuous range that is
indicated by a Content-Range header field. indicated by a Content-Range header field.
15.4. Redirection 3xx 15.4. Redirection 3xx
The 3xx (Redirection) class of status code indicates that further The _3xx (Redirection)_ class of status code indicates that further
action needs to be taken by the user agent in order to fulfill the action needs to be taken by the user agent in order to fulfill the
request. request. There are several types of redirects:
There are several types of redirects:
1. Redirects that indicate the resource might be available at a 1. Redirects that indicate this resource might be available at a
different URI, as provided by the Location field, as in the different URI, as provided by the Location header field, as in
status codes 301 (Moved Permanently), 302 (Found), and 307 the status codes 301 (Moved Permanently), 302 (Found), 307
(Temporary Redirect). (Temporary Redirect), and 308 (Permanent Redirect).
2. Redirection that offers a choice of matching resources, each 2. Redirection that offers a choice among matching resources capable
capable of representing the original request target, as in the of representing this resource, as in the 300 (Multiple Choices)
300 (Multiple Choices) status code. status code.
3. Redirection to a different resource, identified by the Location 3. Redirection to a different resource, identified by the Location
field, that can represent an indirect response to the request, as header field, that can represent an indirect response to the
in the 303 (See Other) status code. request, as in the 303 (See Other) status code.
4. Redirection to a previously cached result, as in the 304 (Not 4. Redirection to a previously stored result, as in the 304 (Not
Modified) status code. Modified) status code.
If a Location header field (Section 7.1.2) is provided, the user If a Location header field (Section 10.2.3) is provided, the user
agent MAY automatically redirect its request to the URI agent MAY automatically redirect its request to the URI referenced by
referenced by the Location field value, even if the specific status the Location field value, even if the specific status code is not
code is not understood. Automatic redirection needs to done with understood. Automatic redirection needs to be done with care for
care for methods not known to be safe, as defined in Section 4.2.1, methods not known to be safe, as defined in Section 9.2.1, since the
since the user might not wish to redirect an unsafe request. user might not wish to redirect an unsafe request.
[new] When automatically following a redirected request, the user agent
SHOULD resend the original request message with the following
modifications:
[new] 1. Replace the target URI with the URI referenced by the redirection
response's Location header field value after resolving it
relative to the original request's target URI.
[new] 2. Remove header fields that were automatically generated by the
implementation, replacing them with updated values as appropriate
to the new request. This includes:
[new] 1. Connection-specific header fields (see Section 7.6.1),
[new] 2. Header fields specific to the client's proxy configuration,
including (but not limited to) Proxy-Authorization,
[new] 3. Origin-specific header fields (if any), including (but not
limited to) Host,
[new] 4. Validating header fields that were added by the
implementation's cache (e.g., If-None-Match,
If-Modified-Since),
[new] 5. Resource-specific header fields, including (but not limited
to) Referer, Origin, Authorization, and Cookie.
[new] 3. Consider removing header fields that were not automatically
generated by the implementation (i.e., those present in the
request because they were added by the calling context) where
there are security implications; this includes but is not limited
to Authorization and Cookie.
[new] 4. Change the request method according to the redirecting status
code's semantics, if applicable.
[new] 5. If the request method has been changed to GET or HEAD, remove
content-specific header fields, including (but not limited to)
Content-Encoding, Content-Language, Content-Location,
Content-Type, Content-Length, Digest, ETag, Last-Modified.
Note: In HTTP/1.0, the status codes 301 (Moved Permanently) and | *Note:* In HTTP/1.0, the status codes 301 (Moved Permanently)
302 (Found) were defined for the first type of redirect | and 302 (Found) were defined for the first type of redirect
([RFC1945], Section 9.3). Early user agents split on whether the | ([RFC1945], Section 9.3). Early user agents split on whether
method applied to the redirect target would be the same as the | the method applied to the redirect target would be the same as
original request or would be rewritten as GET. Although HTTP | the original request or would be rewritten as GET. Although
originally defined the former semantics for 301 and 302 (to match | HTTP originally defined the former semantics for 301 and 302
its original implementation at CERN), and defined 303 (See Other) | (to match its original implementation at CERN), and defined 303
to match the latter semantics, prevailing practice gradually | (See Other) to match the latter semantics, prevailing practice
converged on the latter semantics for 301 and 302 as well. The | gradually converged on the latter semantics for 301 and 302 as
first revision of HTTP/1.1 added 307 (Temporary Redirect) to | well. The first revision of HTTP/1.1 added 307 (Temporary
indicate the former semantics without being impacted by divergent | Redirect) to indicate the former semantics of 302 without being
practice. Over 10 years later, most user agents still do method | impacted by divergent practice. For the same reason, 308
rewriting for 301 and 302; therefore, this specification makes | (Permanent Redirect) was later on added in [RFC7538] to match
that behavior conformant when the original request is POST. | 301. Over 10 years later, most user agents still do method
| rewriting for 301 and 302; therefore, [RFC7231] made that
| behavior conformant when the original request is POST.
A client SHOULD detect and intervene in cyclical redirections (i.e., A client SHOULD detect and intervene in cyclical redirections (i.e.,
"infinite" redirection loops). "infinite" redirection loops).
Note: An earlier version of this specification recommended a | *Note:* An earlier version of this specification recommended a
maximum of five redirections ([RFC2068], Section 10.3). Content | maximum of five redirections ([RFC2068], Section 10.3).
developers need to be aware that some clients might implement such | Content developers need to be aware that some clients might
a fixed limitation. | implement such a fixed limitation.
15.4.1. 300 Multiple Choices 15.4.1. 300 Multiple Choices
The 300 (Multiple Choices) status code indicates that the target The _300 (Multiple Choices)_ status code indicates that the target
resource has more than one representation, each with its own more resource has more than one representation, each with its own more
specific identifier, and information about the alternatives is being specific identifier, and information about the alternatives is being
provided so that the user (or user agent) can select a preferred provided so that the user (or user agent) can select a preferred
representation by redirecting its request to one or more of those representation by redirecting its request to one or more of those
identifiers. In other words, the server desires that the user agent identifiers. In other words, the server desires that the user agent
engage in reactive negotiation to select the most appropriate engage in reactive negotiation to select the most appropriate
representation(s) for its needs (Section 3.4). representation(s) for its needs (Section 12).
If the server has a preferred choice, the server SHOULD generate a If the server has a preferred choice, the server SHOULD generate a
Location header field containing a preferred choice's URI reference. Location header field containing a preferred choice's URI reference.
The user agent MAY use the Location field value for automatic The user agent MAY use the Location field value for automatic
redirection. redirection.
For request methods other than HEAD, the server SHOULD generate a For request methods other than HEAD, the server SHOULD generate
payload in the 300 response containing a list of representation content in the 300 response containing a list of representation
metadata and URI reference(s) from which the user or user agent can metadata and URI reference(s) from which the user or user agent can
choose the one most preferred. The user agent MAY make a selection choose the one most preferred. The user agent MAY make a selection
from that list automatically if it understands the provided media from that list automatically if it understands the provided media
type. A specific format for automatic selection is not defined by type. A specific format for automatic selection is not defined by
this specification because HTTP tries to remain orthogonal to the this specification because HTTP tries to remain orthogonal to the
definition of its payloads. In practice, the representation is definition of its content. In practice, the representation is
provided in some easily parsed format believed to be acceptable to provided in some easily parsed format believed to be acceptable to
the user agent, as determined by shared design or content the user agent, as determined by shared design or content
negotiation, or in some commonly accepted hypertext format. negotiation, or in some commonly accepted hypertext format.
A 300 response is cacheable by default; i.e., unless otherwise A 300 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
Note: The original proposal for the 300 status code defined the | *Note:* The original proposal for the 300 status code defined
URI header field as providing a list of alternative | the URI header field as providing a list of alternative
representations, such that it would be usable for 200, 300, and | representations, such that it would be usable for 200, 300, and
406 responses and be transferred in responses to the HEAD method. | 406 responses and be transferred in responses to the HEAD
However, lack of deployment and disagreement over syntax led to | method. However, lack of deployment and disagreement over
both URI and Alternates (a subsequent proposal) being dropped from | syntax led to both URI and Alternates (a subsequent proposal)
this specification. It is possible to communicate the list using | being dropped from this specification. It is possible to
a set of Link header fields [RFC5988], each with a relationship of | communicate the list as a Link header field value [RFC8288]
"alternate", though deployment is a chicken-and-egg problem. | whose members have a relationship of "alternate", though
| deployment is a chicken-and-egg problem.
15.4.2. 301 Moved Permanently 15.4.2. 301 Moved Permanently
The 301 (Moved Permanently) status code indicates that the target The _301 (Moved Permanently)_ status code indicates that the target
resource has been assigned a new permanent URI and any future resource has been assigned a new permanent URI and any future
references to this resource ought to use one of the enclosed URIs. references to this resource ought to use one of the enclosed URIs.
Clients with link-editing capabilities ought to automatically re-link Clients with link-editing capabilities ought to automatically re-link
references to the effective request URI to one or more of the new references to the target URI to one or more of the new references
references sent by the server, where possible. sent by the server, where possible.
The server SHOULD generate a Location header field in the response The server SHOULD generate a Location header field in the response
containing a preferred URI reference for the new permanent URI. The containing a preferred URI reference for the new permanent URI. The
user agent MAY use the Location field value for automatic user agent MAY use the Location field value for automatic
redirection. The server's response payload usually contains a short redirection. The server's response content usually contains a short
hypertext note with a hyperlink to the new URI(s). hypertext note with a hyperlink to the new URI(s).
Note: For historical reasons, a user agent MAY change the request | *Note:* For historical reasons, a user agent MAY change the
method from POST to GET for the subsequent request. If this | request method from POST to GET for the subsequent request. If
behavior is undesired, the 307 (Temporary Redirect) status code | this behavior is undesired, the 308 (Permanent Redirect) status
can be used instead. | code can be used instead.
A 301 response is cacheable by default; i.e., unless otherwise A 301 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.4.3. 302 Found 15.4.3. 302 Found
The 302 (Found) status code indicates that the target resource The _302 (Found)_ status code indicates that the target resource
resides temporarily under a different URI. Since the redirection resides temporarily under a different URI. Since the redirection
might be altered on occasion, the client ought to continue to use the might be altered on occasion, the client ought to continue to use the
effective request URI for future requests. target URI for future requests.
The server SHOULD generate a Location header field in the response The server SHOULD generate a Location header field in the response
containing a URI reference for the different URI. The user agent MAY containing a URI reference for the different URI. The user agent MAY
use the Location field value for automatic redirection. The server's use the Location field value for automatic redirection. The server's
response payload usually contains a short hypertext note with a response content usually contains a short hypertext note with a
hyperlink to the different URI(s). hyperlink to the different URI(s).
Note: For historical reasons, a user agent MAY change the request | *Note:* For historical reasons, a user agent MAY change the
method from POST to GET for the subsequent request. If this | request method from POST to GET for the subsequent request. If
behavior is undesired, the 307 (Temporary Redirect) status code | this behavior is undesired, the 307 (Temporary Redirect) status
can be used instead. | code can be used instead.
15.4.4. 303 See Other 15.4.4. 303 See Other
The 303 (See Other) status code indicates that the server is The _303 (See Other)_ status code indicates that the server is
redirecting the user agent to a different resource, as indicated by a redirecting the user agent to a different resource, as indicated by a
URI in the Location header field, which is intended to provide an URI in the Location header field, which is intended to provide an
indirect response to the original request. A user agent can perform indirect response to the original request. A user agent can perform
a retrieval request targeting that URI (a GET or HEAD request if a retrieval request targeting that URI (a GET or HEAD request if
using HTTP), which might also be redirected, and present the eventual using HTTP), which might also be redirected, and present the eventual
result as an answer to the original request. Note that the new URI result as an answer to the original request. Note that the new URI
in the Location header field is not considered equivalent to the in the Location header field is not considered equivalent to the
effective request URI. target URI.
This status code is applicable to any HTTP method. It is primarily This status code is applicable to any HTTP method. It is primarily
used to allow the output of a POST action to redirect the user agent used to allow the output of a POST action to redirect the user agent
to a selected resource, since doing so provides the information to a selected resource, since doing so provides the information
corresponding to the POST response in a form that can be separately corresponding to the POST response in a form that can be separately
identified, bookmarked, and cached, independent of the original identified, bookmarked, and cached, independent of the original
request. request.
A 303 response to a GET request indicates that the origin server does A 303 response to a GET request indicates that the origin server does
not have a representation of the target resource that can be not have a representation of the target resource that can be
skipping to change at line 6566 skipping to change at page 156, line 46
answers to the questions of what can be represented, what answers to the questions of what can be represented, what
representations are adequate, and what might be a useful description representations are adequate, and what might be a useful description
are outside the scope of HTTP. are outside the scope of HTTP.
Except for responses to a HEAD request, the representation of a 303 Except for responses to a HEAD request, the representation of a 303
response ought to contain a short hypertext note with a hyperlink to response ought to contain a short hypertext note with a hyperlink to
the same URI reference provided in the Location header field. the same URI reference provided in the Location header field.
15.4.5. 304 Not Modified 15.4.5. 304 Not Modified
The 304 (Not Modified) status code indicates that a conditional GET The _304 (Not Modified)_ status code indicates that a conditional GET
or HEAD request has been received and would have resulted in a 200 or HEAD request has been received and would have resulted in a 200
(OK) response if it were not for the fact that the condition (OK) response if it were not for the fact that the condition
evaluated to false. In other words, there is no need for the server evaluated to false. In other words, there is no need for the server
to transfer a representation of the target resource because the to transfer a representation of the target resource because the
request indicates that the client, which made the request request indicates that the client, which made the request
conditional, already has a valid representation; the server is conditional, already has a valid representation; the server is
therefore redirecting the client to make use of that stored therefore redirecting the client to make use of that stored
representation as if it were the payload of a 200 (OK) response. representation as if it were the content of a 200 (OK) response.
The server generating a 304 response MUST generate any of the The server generating a 304 response MUST generate any of the
following header fields that would have been sent in a 200 (OK) following header fields that would have been sent in a 200 (OK)
response to the same request: Cache-Control, Content-Location, Date, response to the same request: Cache-Control, Content-Location, Date,
ETag, Expires, and Vary. ETag, Expires, and Vary.
Since the goal of a 304 response is to minimize information transfer Since the goal of a 304 response is to minimize information transfer
when the recipient already has one or more cached representations, a when the recipient already has one or more cached representations, a
sender SHOULD NOT generate representation metadata other than the sender SHOULD NOT generate representation metadata other than the
above listed fields unless said metadata exists for the purpose of above listed fields unless said metadata exists for the purpose of
guiding cache updates (e.g., Last-Modified might be useful if the guiding cache updates (e.g., Last-Modified might be useful if the
response does not have an ETag field). response does not have an ETag field).
Requirements on a cache that receives a 304 response are defined in Requirements on a cache that receives a 304 response are defined in
Section 4.3.4 of [RFC7234]. If the conditional request originated Section 4.3.4 of [Caching]. If the conditional request originated
with an outbound client, such as a user agent with its own cache with an outbound client, such as a user agent with its own cache
sending a conditional GET to a shared proxy, then the proxy SHOULD sending a conditional GET to a shared proxy, then the proxy SHOULD
forward the 304 response to that client. forward the 304 response to that client.
A 304 response cannot contain a message-body; it is always terminated A 304 response is terminated by the end of the header section; it
by the first empty line after the header fields. cannot contain content or trailers.
15.4.6. 305 Use Proxy 15.4.6. 305 Use Proxy
The 305 (Use Proxy) status code was defined in a previous version of The _305 (Use Proxy)_ status code was defined in a previous version
this specification and is now deprecated (Appendix B). of this specification and is now deprecated (Appendix B of
[RFC7231]).
15.4.7. 306 (Unused) 15.4.7. 306 (Unused)
The 306 status code was defined in a previous version of this The 306 status code was defined in a previous version of this
specification, is no longer used, and the code is reserved. specification, is no longer used, and the code is reserved.
15.4.7. 307 Temporary Redirect 15.4.8. 307 Temporary Redirect
The 307 (Temporary Redirect) status code indicates that the target The _307 (Temporary Redirect)_ status code indicates that the target
resource resides temporarily under a different URI and the user agent resource resides temporarily under a different URI and the user agent
MUST NOT change the request method if it performs an automatic MUST NOT change the request method if it performs an automatic
redirection to that URI. Since the redirection can change over time, redirection to that URI. Since the redirection can change over time,
the client ought to continue using the original effective request URI the client ought to continue using the original target URI for future
for future requests. requests.
The server SHOULD generate a Location header field in the response The server SHOULD generate a Location header field in the response
containing a URI reference for the different URI. The user agent MAY containing a URI reference for the different URI. The user agent MAY
use the Location field value for automatic redirection. The server's use the Location field value for automatic redirection. The server's
response payload usually contains a short hypertext note with a response content usually contains a short hypertext note with a
hyperlink to the different URI(s). hyperlink to the different URI(s).
Note: This status code is similar to 302 (Found), except that it
does not allow changing the request method from POST to GET. This
specification defines no equivalent counterpart for 301 (Moved
Permanently) ([RFC7238], however, defines the status code 308
(Permanent Redirect) for this purpose).
15.4.9. 308 Permanent Redirect 15.4.9. 308 Permanent Redirect
The 308 (Permanent Redirect) status code indicates that the target The _308 (Permanent Redirect)_ status code indicates that the target
resource has been assigned a new permanent URI and any future resource has been assigned a new permanent URI and any future
references to this resource ought to use one of the enclosed URIs. references to this resource ought to use one of the enclosed URIs.
Clients with link editing capabilities ought to automatically re-link Clients with link editing capabilities ought to automatically re-link
references to the effective request URI (Section 5.5 of [RFC7230]) to references to the target URI to one or more of the new references
one or more of the new references sent by the server, where possible. sent by the server, where possible.
The server SHOULD generate a Location header field ([RFC7231], The server SHOULD generate a Location header field in the response
Section 7.1.2) in the response containing a preferred URI reference containing a preferred URI reference for the new permanent URI. The
for the new permanent URI. The user agent MAY use the Location field user agent MAY use the Location field value for automatic
value for automatic redirection. The server's response payload redirection. The server's response content usually contains a short
usually contains a short hypertext note with a hyperlink to the new hypertext note with a hyperlink to the new URI(s).
URI(s).
A 308 response is cacheable by default; i.e., unless otherwise A 308 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
[RFC7234], Section 4.2.2). Section 4.2.2 of [Caching]).
Note: This status code is similar to 301 (Moved Permanently) | *Note:* This status code is much younger (June 2014) than its
([RFC7231], Section 6.4.2), except that it does not allow changing | sibling codes, and thus might not be recognized everywhere.
the request method from POST to GET. | See Section 4 of [RFC7538] for deployment considerations.
15.5. Client Error 4xx 15.5. Client Error 4xx
The 4xx (Client Error) class of status code indicates that the client The _4xx (Client Error)_ class of status code indicates that the
seems to have erred. Except when responding to a HEAD request, the client seems to have erred. Except when responding to a HEAD
server SHOULD send a representation containing an explanation of the request, the server SHOULD send a representation containing an
error situation, and whether it is a temporary or permanent explanation of the error situation, and whether it is a temporary or
condition. These status codes are applicable to any request method. permanent condition. These status codes are applicable to any
User agents SHOULD display any included representation to the user. request method. User agents SHOULD display any included
representation to the user.
15.5.1. 400 Bad Request 15.5.1. 400 Bad Request
The 400 (Bad Request) status code indicates that the server cannot or The _400 (Bad Request)_ status code indicates that the server cannot
will not process the request due to something that is perceived to be or will not process the request due to something that is perceived to
a client error (e.g., malformed request syntax, invalid request be a client error (e.g., malformed request syntax, invalid request
message framing, or deceptive request routing). message framing, or deceptive request routing).
15.5.2. 401 Unauthorized 15.5.2. 401 Unauthorized
The 401 (Unauthorized) status code indicates that the request has not The _401 (Unauthorized)_ status code indicates that the request has
been applied because it lacks valid authentication credentials for not been applied because it lacks valid authentication credentials
the target resource. The server generating a 401 response MUST send for the target resource. The server generating a 401 response MUST
a WWW-Authenticate header field (Section 4.1) containing at least one send a WWW-Authenticate header field (Section 11.6.1) containing at
challenge applicable to the target resource. least one challenge applicable to the target resource.
If the request included authentication credentials, then the 401 If the request included authentication credentials, then the 401
response indicates that authorization has been refused for those response indicates that authorization has been refused for those
credentials. The user agent MAY repeat the request with a new or credentials. The user agent MAY repeat the request with a new or
replaced Authorization header field (Section 4.2). If the 401 replaced Authorization header field (Section 11.6.2). If the 401
response contains the same challenge as the prior response, and the response contains the same challenge as the prior response, and the
user agent has already attempted authentication at least once, then user agent has already attempted authentication at least once, then
the user agent SHOULD present the enclosed representation to the the user agent SHOULD present the enclosed representation to the
user, since it usually contains relevant diagnostic information. user, since it usually contains relevant diagnostic information.
15.5.3. 402 Payment Required 15.5.3. 402 Payment Required
The 402 (Payment Required) status code is reserved for future use. The _402 (Payment Required)_ status code is reserved for future use.
15.5.4. 403 Forbidden 15.5.4. 403 Forbidden
The 403 (Forbidden) status code indicates that the server understood The _403 (Forbidden)_ status code indicates that the server
the request but refuses to authorize it. A server that wishes to understood the request but refuses to fulfill it. A server that
make public why the request has been forbidden can describe that wishes to make public why the request has been forbidden can describe
reason in the response payload (if any). that reason in the response content (if any).
If authentication credentials were provided in the request, the If authentication credentials were provided in the request, the
server considers them insufficient to grant access. The client server considers them insufficient to grant access. The client
SHOULD NOT automatically repeat the request with the same SHOULD NOT automatically repeat the request with the same
credentials. The client MAY repeat the request with new or different credentials. The client MAY repeat the request with new or different
credentials. However, a request might be forbidden for reasons credentials. However, a request might be forbidden for reasons
unrelated to the credentials. unrelated to the credentials.
An origin server that wishes to "hide" the current existence of a An origin server that wishes to "hide" the current existence of a
forbidden target resource MAY instead respond with a status code of forbidden target resource MAY instead respond with a status code of
404 (Not Found). 404 (Not Found).
15.5.5. 404 Not Found 15.5.5. 404 Not Found
The 404 (Not Found) status code indicates that the origin server did The _404 (Not Found)_ status code indicates that the origin server
not find a current representation for the target resource or is not did not find a current representation for the target resource or is
willing to disclose that one exists. A 404 status code does not not willing to disclose that one exists. A 404 status code does not
indicate whether this lack of representation is temporary or indicate whether this lack of representation is temporary or
permanent; the 410 (Gone) status code is preferred over 404 if the permanent; the 410 (Gone) status code is preferred over 404 if the
origin server knows, presumably through some configurable means, that origin server knows, presumably through some configurable means, that
the condition is likely to be permanent. the condition is likely to be permanent.
A 404 response is cacheable by default; i.e., unless otherwise A 404 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.5.6. 405 Method Not Allowed 15.5.6. 405 Method Not Allowed
The 405 (Method Not Allowed) status code indicates that the method The _405 (Method Not Allowed)_ status code indicates that the method
received in the request-line is known by the origin server but not received in the request-line is known by the origin server but not
supported by the target resource. The origin server MUST generate an supported by the target resource. The origin server MUST generate an
Allow header field in a 405 response containing a list of the target Allow header field in a 405 response containing a list of the target
resource's currently supported methods. resource's currently supported methods.
A 405 response is cacheable by default; i.e., unless otherwise A 405 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.5.7. 406 Not Acceptable 15.5.7. 406 Not Acceptable
The 406 (Not Acceptable) status code indicates that the target The _406 (Not Acceptable)_ status code indicates that the target
resource does not have a current representation that would be resource does not have a current representation that would be
acceptable to the user agent, according to the proactive negotiation acceptable to the user agent, according to the proactive negotiation
header fields received in the request (Section 5.3), and the server header fields received in the request (Section 12.1), and the server
is unwilling to supply a default representation. is unwilling to supply a default representation.
The server SHOULD generate a payload containing a list of available The server SHOULD generate content containing a list of available
representation characteristics and corresponding resource identifiers representation characteristics and corresponding resource identifiers
from which the user or user agent can choose the one most from which the user or user agent can choose the one most
appropriate. A user agent MAY automatically select the most appropriate. A user agent MAY automatically select the most
appropriate choice from that list. However, this specification does appropriate choice from that list. However, this specification does
not define any standard for such automatic selection, as described in not define any standard for such automatic selection, as described in
Section 6.4.1. Section 15.4.1.
15.5.8. 407 Proxy Authentication Required 15.5.8. 407 Proxy Authentication Required
The 407 (Proxy Authentication Required) status code is similar to 401 The _407 (Proxy Authentication Required)_ status code is similar to
(Unauthorized), but it indicates that the client needs to 401 (Unauthorized), but it indicates that the client needs to
authenticate itself in order to use a proxy. The proxy MUST send a authenticate itself in order to use a proxy for this request. The
Proxy-Authenticate header field (Section 4.3) containing a challenge proxy MUST send a Proxy-Authenticate header field (Section 11.7.1)
applicable to that proxy for the target resource. The client MAY containing a challenge applicable to that proxy for the request. The
repeat the request with a new or replaced Proxy-Authorization header client MAY repeat the request with a new or replaced
field (Section 4.4). Proxy-Authorization header field (Section 11.7.2).
15.5.9. 408 Request Timeout 15.5.9. 408 Request Timeout
The 408 (Request Timeout) status code indicates that the server did The _408 (Request Timeout)_ status code indicates that the server did
not receive a complete request message within the time that it was not receive a complete request message within the time that it was
prepared to wait. A server SHOULD send the "close" connection option prepared to wait.
(Section 6.1 of [RFC7230]) in the response, since 408 implies that
the server has decided to close the connection rather than continue If the client has an outstanding request in transit, it MAY repeat
waiting. If the client has an outstanding request in transit, the that request. If the current connection is not usable (e.g., as it
client MAY repeat that request on a new connection. would be in HTTP/1.1, because request delimitation is lost), a new
connection will be used.
15.5.10. 409 Conflict 15.5.10. 409 Conflict
The 409 (Conflict) status code indicates that the request could not The _409 (Conflict)_ status code indicates that the request could not
be completed due to a conflict with the current state of the target be completed due to a conflict with the current state of the target
resource. This code is used in situations where the user might be resource. This code is used in situations where the user might be
able to resolve the conflict and resubmit the request. The server able to resolve the conflict and resubmit the request. The server
SHOULD generate a payload that includes enough information for a user SHOULD generate content that includes enough information for a user
to recognize the source of the conflict. to recognize the source of the conflict.
Conflicts are most likely to occur in response to a PUT request. For Conflicts are most likely to occur in response to a PUT request. For
example, if versioning were being used and the representation being example, if versioning were being used and the representation being
PUT included changes to a resource that conflict with those made by PUT included changes to a resource that conflict with those made by
an earlier (third-party) request, the origin server might use a 409 an earlier (third-party) request, the origin server might use a 409
response to indicate that it can't complete the request. In this response to indicate that it can't complete the request. In this
case, the response representation would likely contain information case, the response representation would likely contain information
useful for merging the differences based on the revision history. useful for merging the differences based on the revision history.
15.5.11. 410 Gone 15.5.11. 410 Gone
The 410 (Gone) status code indicates that access to the target The _410 (Gone)_ status code indicates that access to the target
resource is no longer available at the origin server and that this resource is no longer available at the origin server and that this
condition is likely to be permanent. If the origin server does not condition is likely to be permanent. If the origin server does not
know, or has no facility to determine, whether or not the condition know, or has no facility to determine, whether or not the condition
is permanent, the status code 404 (Not Found) ought to be used is permanent, the status code 404 (Not Found) ought to be used
instead. instead.
The 410 response is primarily intended to assist the task of web The 410 response is primarily intended to assist the task of web
maintenance by notifying the recipient that the resource is maintenance by notifying the recipient that the resource is
intentionally unavailable and that the server owners desire that intentionally unavailable and that the server owners desire that
remote links to that resource be removed. Such an event is common remote links to that resource be removed. Such an event is common
for limited-time, promotional services and for resources belonging to for limited-time, promotional services and for resources belonging to
individuals no longer associated with the origin server's site. It individuals no longer associated with the origin server's site. It
is not necessary to mark all permanently unavailable resources as is not necessary to mark all permanently unavailable resources as
"gone" or to keep the mark for any length of time -- that is left to "gone" or to keep the mark for any length of time - that is left to
the discretion of the server owner. the discretion of the server owner.
A 410 response is cacheable by default; i.e., unless otherwise A 410 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.5.12. 411 Length Required 15.5.12. 411 Length Required
The 411 (Length Required) status code indicates that the server The _411 (Length Required)_ status code indicates that the server
refuses to accept the request without a defined Content-Length refuses to accept the request without a defined Content-Length
(Section 3.3.2 of [RFC7230]). The client MAY repeat the request if (Section 8.6). The client MAY repeat the request if it adds a valid
it adds a valid Content-Length header field containing the length of Content-Length header field containing the length of the request
the message body in the request message. content.
15.5.13. 412 Precondition Failed 15.5.13. 412 Precondition Failed
The 412 (Precondition Failed) status code indicates that one or more The _412 (Precondition Failed)_ status code indicates that one or
conditions given in the request header fields evaluated to false when more conditions given in the request header fields evaluated to false
tested on the server. This response code allows the client to place when tested on the server. This response status code allows the
preconditions on the current resource state (its current client to place preconditions on the current resource state (its
representations and metadata) and, thus, prevent the request method current representations and metadata) and, thus, prevent the request
from being applied if the target resource is in an unexpected state. method from being applied if the target resource is in an unexpected
state.
15.5.14. 413 Payload Too Large 15.5.14. 413 Content Too Large
The 413 (Payload Too Large) status code indicates that the server is The _413 (Content Too Large)_ status code indicates that the server
refusing to process a request because the request payload is larger is refusing to process a request because the request content is
than the server is willing or able to process. The server MAY close larger than the server is willing or able to process. The server MAY
the connection to prevent the client from continuing the request. terminate the request, if the protocol version in use allows it;
otherwise, the server MAY close the connection.
If the condition is temporary, the server SHOULD generate a If the condition is temporary, the server SHOULD generate a
Retry-After header field to indicate that it is temporary and after Retry-After header field to indicate that it is temporary and after
what time the client MAY try again. what time the client MAY try again.
15.5.15. 414 URI Too Long 15.5.15. 414 URI Too Long
The 414 (URI Too Long) status code indicates that the server is The _414 (URI Too Long)_ status code indicates that the server is
refusing to service the request because the request-target (Section refusing to service the request because the target URI is longer than
5.3 of [RFC7230]) is longer than the server is willing to interpret. the server is willing to interpret. This rare condition is only
This rare condition is only likely to occur when a client has likely to occur when a client has improperly converted a POST request
improperly converted a POST request to a GET request with long query to a GET request with long query information, when the client has
information, when the client has descended into a "black hole" of descended into a "black hole" of redirection (e.g., a redirected URI
redirection (e.g., a redirected URI prefix that points to a suffix of prefix that points to a suffix of itself) or when the server is under
itself) or when the server is under attack by a client attempting to attack by a client attempting to exploit potential security holes.
exploit potential security holes.
A 414 response is cacheable by default; i.e., unless otherwise A 414 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.5.16. 415 Unsupported Media Type 15.5.16. 415 Unsupported Media Type
The 415 (Unsupported Media Type) status code indicates that the The _415 (Unsupported Media Type)_ status code indicates that the
origin server is refusing to service the request because the payload origin server is refusing to service the request because the content
is in a format not supported by this method on the target resource. is in a format not supported by this method on the target resource.
The format problem might be due to the request's indicated The format problem might be due to the request's indicated
Content-Type or Content-Encoding, or as a result of inspecting the Content-Type or Content-Encoding, or as a result of inspecting the
data directly. data directly.
[new] If the problem was caused by an unsupported content coding, the
Accept-Encoding response header field (Section 12.5.3) ought to be
used to indicate what (if any) content codings would have been
accepted in the request.
[new] On the other hand, if the cause was an unsupported media type, the
Accept response header field (Section 12.5.1) can be used to indicate
what media types would have been accepted in the request.
15.5.17. 416 Range Not Satisfiable 15.5.17. 416 Range Not Satisfiable
The 416 (Range Not Satisfiable) status code indicates that none of The _416 (Range Not Satisfiable)_ status code indicates that the set
the ranges in the request's Range header field (Section 3.1) overlap of ranges in the request's Range header field (Section 14.2) has been
the current extent of the selected resource or that the set of ranges rejected either because none of the requested ranges are satisfiable
requested has been rejected due to invalid ranges or an excessive or because the client has requested an excessive number of small or
request of small or overlapping ranges. overlapping ranges (a potential denial of service attack).
For byte ranges, failing to overlap the current extent means that the Each range unit defines what is required for its own range sets to be
first-byte-pos of all of the byte-range-spec values were greater than satisfiable. For example, Section 14.1.2 defines what makes a bytes
the current length of the selected representation. range set satisfiable.
When this status code is generated in response to a byte-range When this status code is generated in response to a byte-range
request, the sender SHOULD generate a Content-Range header field request, the sender SHOULD generate a Content-Range header field
specifying the current length of the selected representation specifying the current length of the selected representation
(Section 4.2). (Section 14.4).
For example: For example:
HTTP/1.1 416 Range Not Satisfiable HTTP/1.1 416 Range Not Satisfiable
Date: Fri, 20 Jan 2012 15:41:54 GMT Date: Fri, 20 Jan 2012 15:41:54 GMT
Content-Range: bytes */47022 Content-Range: bytes */47022
Note: Because servers are free to ignore Range, many | *Note:* Because servers are free to ignore Range, many
implementations will simply respond with the entire selected | implementations will respond with the entire selected
representation in a 200 (OK) response. That is partly because | representation in a 200 (OK) response. That is partly because
most clients are prepared to receive a 200 (OK) to complete the | most clients are prepared to receive a 200 (OK) to complete the
task (albeit less efficiently) and partly because clients might | task (albeit less efficiently) and partly because clients might
not stop making an invalid partial request until they have | not stop making an invalid range request until they have
received a complete representation. Thus, clients cannot depend | received a complete representation. Thus, clients cannot
on receiving a 416 (Range Not Satisfiable) response even when it | depend on receiving a 416 (Range Not Satisfiable) response even
is most appropriate. | when it is most appropriate.
15.5.18. 417 Expectation Failed 15.5.18. 417 Expectation Failed
The 417 (Expectation Failed) status code indicates that the The _417 (Expectation Failed)_ status code indicates that the
expectation given in the request's Expect header field expectation given in the request's Expect header field
(Section 5.1.1) could not be met by at least one of the inbound (Section 10.1.1) could not be met by at least one of the inbound
servers. servers.
15.5.19. 418 (Unused) 15.5.19. 418 (Unused)
[new] [RFC2324] was an April 1 RFC that lampooned the various ways HTTP was
abused; one such abuse was the definition of an application-specific
418 status code. In the intervening years, this status code has been
widely implemented as an "Easter Egg", and therefore is effectively
consumed by this use.
[new] Therefore, the 418 status code is reserved in the IANA HTTP Status
Code Registry. This indicates that the status code cannot be
assigned to other applications currently. If future circumstances
require its use (e.g., exhaustion of 4NN status codes), it can be re-
assigned to another use.
15.5.20. 421 Misdirected Request 15.5.20. 421 Misdirected Request
[new] The 421 (Misdirected Request) status code indicates that the request
was directed at a server that is unable or unwilling to produce an
authoritative response for the target URI. A 421 is sent when an
origin server (or gateway acting on behalf of the origin server)
rejects a target URI that does not match an origin for which the
server has been configured (Section 4.3.1) or does not match the
connection context over which the request was received (Section 7.4).
[new] A client that receives a 421 (Misdirected Request) response MAY retry
the request, whether or not the request method is idempotent, over a
different connection, such as a fresh connection specific to the
target resource's origin, or via an alternative service [RFC7838].
[new] A proxy MUST NOT generate a 421 response.
15.5.21. 422 Unprocessable Payload 15.5.21. 422 Unprocessable Content
[new] The 422 (Unprocessable Content) status code indicates that the server
understands the content type of the request content (hence a 415
(Unsupported Media Type) status code is inappropriate), and the
syntax of the request content is correct, but was unable to process
the contained instructions. For example, this status code can be
sent if an XML request content contains well-formed (i.e.,
syntactically correct), but semantically erroneous XML instructions.
15.5.22. 426 Upgrade Required 15.5.22. 426 Upgrade Required
The 426 (Upgrade Required) status code indicates that the server The _426 (Upgrade Required)_ status code indicates that the server
refuses to perform the request using the current protocol but might refuses to perform the request using the current protocol but might
be willing to do so after the client upgrades to a different be willing to do so after the client upgrades to a different
protocol. The server MUST send an Upgrade header field in a 426 protocol. The server MUST send an Upgrade header field in a 426
response to indicate the required protocol(s) (Section 6.7 of response to indicate the required protocol(s) (Section 7.8).
[RFC7230]).
Example: Example:
HTTP/1.1 426 Upgrade Required HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/3.0 Upgrade: HTTP/3.0
Connection: Upgrade Connection: Upgrade
Content-Length: 53 Content-Length: 53
Content-Type: text/plain Content-Type: text/plain
This service requires use of the HTTP/3.0 protocol. This service requires use of the HTTP/3.0 protocol.
15.6. Server Error 5xx 15.6. Server Error 5xx
The 5xx (Server Error) class of status code indicates that the server The _5xx (Server Error)_ class of status code indicates that the
is aware that it has erred or is incapable of performing the server is aware that it has erred or is incapable of performing the
requested method. Except when responding to a HEAD request, the requested method. Except when responding to a HEAD request, the
server SHOULD send a representation containing an explanation of the server SHOULD send a representation containing an explanation of the
error situation, and whether it is a temporary or permanent error situation, and whether it is a temporary or permanent
condition. A user agent SHOULD display any included representation condition. A user agent SHOULD display any included representation
to the user. These response codes are applicable to any request to the user. These response codes are applicable to any request
method. method.
15.6.1. 500 Internal Server Error 15.6.1. 500 Internal Server Error
The 500 (Internal Server Error) status code indicates that the server The _500 (Internal Server Error)_ status code indicates that the
encountered an unexpected condition that prevented it from fulfilling server encountered an unexpected condition that prevented it from
the request. fulfilling the request.
15.6.2. 501 Not Implemented 15.6.2. 501 Not Implemented
The 501 (Not Implemented) status code indicates that the server does The _501 (Not Implemented)_ status code indicates that the server
not support the functionality required to fulfill the request. This does not support the functionality required to fulfill the request.
is the appropriate response when the server does not recognize the This is the appropriate response when the server does not recognize
request method and is not capable of supporting it for any resource. the request method and is not capable of supporting it for any
resource.
A 501 response is cacheable by default; i.e., unless otherwise A 501 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [Caching]).
15.6.3. 502 Bad Gateway 15.6.3. 502 Bad Gateway
The 502 (Bad Gateway) status code indicates that the server, while The _502 (Bad Gateway)_ status code indicates that the server, while
acting as a gateway or proxy, received an invalid response from an acting as a gateway or proxy, received an invalid response from an
inbound server it accessed while attempting to fulfill the request. inbound server it accessed while attempting to fulfill the request.
15.6.4. 503 Service Unavailable 15.6.4. 503 Service Unavailable
The 503 (Service Unavailable) status code indicates that the server The _503 (Service Unavailable)_ status code indicates that the server
is currently unable to handle the request due to a temporary overload is currently unable to handle the request due to a temporary overload
or scheduled maintenance, which will likely be alleviated after some or scheduled maintenance, which will likely be alleviated after some
delay. The server MAY send a Retry-After header field delay. The server MAY send a Retry-After header field
(Section 7.1.3) to suggest an appropriate amount of time for the (Section 10.2.4) to suggest an appropriate amount of time for the
client to wait before retrying the request. client to wait before retrying the request.
Note: The existence of the 503 status code does not imply that a | *Note:* The existence of the 503 status code does not imply
server has to use it when becoming overloaded. Some servers might | that a server has to use it when becoming overloaded. Some
simply refuse the connection. | servers might simply refuse the connection.
15.6.5. 504 Gateway Timeout 15.6.5. 504 Gateway Timeout
The 504 (Gateway Timeout) status code indicates that the server, The _504 (Gateway Timeout)_ status code indicates that the server,
while acting as a gateway or proxy, did not receive a timely response while acting as a gateway or proxy, did not receive a timely response
from an upstream server it needed to access in order to complete the from an upstream server it needed to access in order to complete the
request. request.
15.6.6. 505 HTTP Version Not Supported 15.6.6. 505 HTTP Version Not Supported
The 505 (HTTP Version Not Supported) status code indicates that the The _505 (HTTP Version Not Supported)_ status code indicates that the
server does not support, or refuses to support, the major version of server does not support, or refuses to support, the major version of
HTTP that was used in the request message. The server is indicating HTTP that was used in the request message. The server is indicating
that it is unable or unwilling to complete the request using the same that it is unable or unwilling to complete the request using the same
major version as the client, as described in Section 2.6 of major version as the client, as described in Section 2.5, other than
[RFC7230], other than with this error message. The server SHOULD with this error message. The server SHOULD generate a representation
generate a representation for the 505 response that describes why for the 505 response that describes why that version is not supported
that version is not supported and what other protocols are supported and what other protocols are supported by that server.
by that server.
16. Extending HTTP 16. Extending HTTP
HTTP defines a number of generic extension points that can be used to
introduce capabilities to the protocol without introducing a new
version, including methods, status codes, field names, and further
extensibility points within defined fields, such as authentication
schemes and cache-directives (see Cache-Control extensions in
Section 5.2.3 of [Caching]). Because the semantics of HTTP are not
versioned, these extension points are persistent; the version of the
protocol in use does not affect their semantics.
Version-independent extensions are discouraged from depending on or
interacting with the specific version of the protocol in use. When
this is unavoidable, careful consideration needs to be given to how
the extension can interoperate across versions.
Additionally, specific versions of HTTP might have their own
extensibility points, such as transfer-codings in HTTP/1.1
(Section 6.1 of [Messaging]) and HTTP/2 ([RFC7540]) SETTINGS or frame
types. These extension points are specific to the version of the
protocol they occur within.
Version-specific extensions cannot override or modify the semantics
of a version-independent mechanism or extension point (like a method
or header field) without explicitly being allowed by that protocol
element. For example, the CONNECT method (Section 9.3.6) allows
this.
These guidelines assure that the protocol operates correctly and
predictably, even when parts of the path implement different versions
of HTTP.
16.1. Method Extensibility 16.1. Method Extensibility
16.1.1. Method Registry 16.1.1. Method Registry
The "Hypertext Transfer Protocol (HTTP) Method Registry" defines the The "Hypertext Transfer Protocol (HTTP) Method Registry", maintained
namespace for the request method token (Section 4). The method by IANA at <https://www.iana.org/assignments/http-methods>, registers
registry has been created and is now maintained at method names.
<http://www.iana.org/assignments/http-methods>.
HTTP method registrations MUST include the following fields: HTTP method registrations MUST include the following fields:
o Method Name (see Section 4) o Method Name (see Section 9)
o Safe ("yes" or "no", see Section 4.2.1)
o Idempotent ("yes" or "no", see Section 4.2.2) o Safe ("yes" or "no", see Section 9.2.1)
o Idempotent ("yes" or "no", see Section 9.2.2)
o Pointer to specification text o Pointer to specification text
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
[RFC5226], Section 4.1). [RFC8126], Section 4.8).
16.1.2. Considerations for New Methods 16.1.2. Considerations for New Methods
Standardized methods are generic; that is, they are potentially Standardized methods are generic; that is, they are potentially
applicable to any resource, not just one particular media type, kind applicable to any resource, not just one particular media type, kind
of resource, or application. As such, it is preferred that new of resource, or application. As such, it is preferred that new
methods be registered in a document that isn't specific to a single methods be registered in a document that isn't specific to a single
application or data format, since orthogonal technologies deserve application or data format, since orthogonal technologies deserve
orthogonal specification. orthogonal specification.
Since message parsing (Section 3.3 of [RFC7230]) needs to be Since message parsing (Section 6 of [Messaging]) needs to be
independent of method semantics (aside from responses to HEAD), independent of method semantics (aside from responses to HEAD),
definitions of new methods cannot change the parsing algorithm or definitions of new methods cannot change the parsing algorithm or
prohibit the presence of a message body on either the request or the prohibit the presence of content on either the request or the
response message. Definitions of new methods can specify that only a response message. Definitions of new methods can specify that only a
zero-length message body is allowed by requiring a Content-Length zero-length content is allowed by requiring a Content-Length header
header field with a value of "0". field with a value of "0".
Likewise, new methods cannot use the special host:port and asterisk
forms of request target that are allowed for CONNECT and OPTIONS,
respectively (Section 7.1). A full URI in absolute form is needed
for the target URI, which means either the request target needs to be
sent in absolute form or the target URI will be reconstructed from
the request context in the same way it is for other methods.
A new method definition needs to indicate whether it is safe A new method definition needs to indicate whether it is safe
(Section 4.2.1), idempotent (Section 4.2.2), cacheable (Section 9.2.1), idempotent (Section 9.2.2), cacheable
(Section 4.2.3), what semantics are to be associated with the payload (Section 9.2.3), what semantics are to be associated with the request
body if any is present in the request and what refinements the method content (if any), and what refinements the method makes to header
makes to header field or status code semantics. If the new method is field or status code semantics. If the new method is cacheable, its
cacheable, its definition ought to describe how, and under what definition ought to describe how, and under what conditions, a cache
conditions, a cache can store a response and use it to satisfy a can store a response and use it to satisfy a subsequent request. The
subsequent request. The new method ought to describe whether it can new method ought to describe whether it can be made conditional
be made conditional (Section 5.2) and, if so, how a server responds (Section 13.1) and, if so, how a server responds when the condition
when the condition is false. Likewise, if the new method might have is false. Likewise, if the new method might have some use for
some use for partial response semantics ([RFC7233]), it ought to partial response semantics (Section 14.2), it ought to document this,
document this, too. too.
Note: Avoid defining a method name that starts with "M-", since | *Note:* Avoid defining a method name that starts with "M-",
that prefix might be misinterpreted as having the semantics | since that prefix might be misinterpreted as having the
assigned to it by [RFC2774]. | semantics assigned to it by [RFC2774].
16.2. Status Code Extensibility 16.2. Status Code Extensibility
16.2.1. Status Code Registry 16.2.1. Status Code Registry
The "Hypertext Transfer Protocol (HTTP) Status Code Registry" defines The "Hypertext Transfer Protocol (HTTP) Status Code Registry",
the namespace for the response status-code token (Section 6). The maintained by IANA at <https://www.iana.org/assignments/http-status-
status code registry is maintained at codes>, registers status code numbers.
<http://www.iana.org/assignments/http-status-codes>.
This section replaces the registration procedure for HTTP Status
Codes previously defined in Section 7.1 of [RFC2817].
A registration MUST include the following fields: A registration MUST include the following fields:
o Status Code (3 digits) o Status Code (3 digits)
o Short Description o Short Description
o Pointer to specification text o Pointer to specification text
Values to be added to the HTTP status code namespace require IETF Values to be added to the HTTP status code namespace require IETF
Review (see [RFC5226], Section 4.1). Review (see [RFC8126], Section 4.8).
16.2.2. Considerations for New Status Codes 16.2.2. Considerations for New Status Codes
When it is necessary to express semantics for a response that are not When it is necessary to express semantics for a response that are not
defined by current status codes, a new status code can be registered. defined by current status codes, a new status code can be registered.
Status codes are generic; they are potentially applicable to any Status codes are generic; they are potentially applicable to any
resource, not just one particular media type, kind of resource, or resource, not just one particular media type, kind of resource, or
application of HTTP. As such, it is preferred that new status codes application of HTTP. As such, it is preferred that new status codes
be registered in a document that isn't specific to a single be registered in a document that isn't specific to a single
application. application.
New status codes are required to fall under one of the categories New status codes are required to fall under one of the categories
defined in Section 6. To allow existing parsers to process the defined in Section 15. To allow existing parsers to process the
response message, new status codes cannot disallow a payload, response message, new status codes cannot disallow content, although
although they can mandate a zero-length payload body. they can mandate a zero-length content.
Proposals for new status codes that are not yet widely deployed ought Proposals for new status codes that are not yet widely deployed ought
to avoid allocating a specific number for the code until there is to avoid allocating a specific number for the code until there is
clear consensus that it will be registered; instead, early drafts can clear consensus that it will be registered; instead, early drafts can
use a notation such as "4NN", or "3N0" .. "3N9", to indicate the use a notation such as "4NN", or "3N0" .. "3N9", to indicate the
class of the proposed status code(s) without consuming a number class of the proposed status code(s) without consuming a number
prematurely. prematurely.
The definition of a new status code ought to explain the request The definition of a new status code ought to explain the request
conditions that would cause a response containing that status code conditions that would cause a response containing that status code
(e.g., combinations of request header fields and/or method(s)) along (e.g., combinations of request header fields and/or method(s)) along
with any dependencies on response header fields (e.g., what fields with any dependencies on response header fields (e.g., what fields
are required, what fields can modify the semantics, and what header are required, what fields can modify the semantics, and what field
field semantics are further refined when used with the new status semantics are further refined when used with the new status code).
code).
By default, a status code applies only to the request corresponding
to the response it occurs within. If a status code applies to a
larger scope of applicability - for example, all requests to the
resource in question, or all requests to a server - this must be
explicitly specified. When doing so, it should be noted that not all
clients can be expected to consistently apply a larger scope, because
they might not understand the new status code.
The definition of a new status code ought to specify whether or not The definition of a new status code ought to specify whether or not
it is cacheable. Note that all status codes can be cached if the it is cacheable. Note that all status codes can be cached if the
response they occur in has explicit freshness information; however, response they occur in has explicit freshness information; however,
status codes that are defined as being cacheable are allowed to be status codes that are defined as being cacheable are allowed to be
cached without explicit freshness information. Likewise, the cached without explicit freshness information. Likewise, the
definition of a status code can place constraints upon cache definition of a status code can place constraints upon cache
behavior. See [RFC7234] for more information. behavior. See [Caching] for more information.
Finally, the definition of a new status code ought to indicate Finally, the definition of a new status code ought to indicate
whether the payload has any implied association with an identified whether the content has any implied association with an identified
resource (Section 3.1.4.1). resource (Section 6.4.2).
16.3. Field Extensibility 16.3. Field Extensibility
Header fields are fully extensible: there is no limit on the HTTP's most widely used extensibility point is the definition of new
introduction of new field names, each presumably defining new header and trailer fields.
semantics, nor on the number of header fields used in a given
message. Existing fields are defined in each part of this
specification and in many other specifications outside this document
set.
New header fields can be defined such that, when they are understood by a New fields can be defined such that, when they are understood by a
recipient, they might override or enhance the interpretation of previously recipient, they override or enhance the interpretation of previously
defined header fields, define preconditions on request evaluation, or refine defined fields, define preconditions on request evaluation, or refine
the meaning of responses. the meaning of responses.
However, defining a field doesn't guarantee its deployment or
recognition by recipients. Most fields are designed with the
expectation that a recipient can safely ignore (but forward
downstream) any field not recognized. In other cases, the sender's
ability to understand a given field might be indicated by its prior
communication, perhaps in the protocol version or fields that it sent
in prior messages, or its use of a specific media type. Likewise,
direct inspection of support might be possible through an OPTIONS
request or by interacting with a defined well-known URI [RFC8615] if
such inspection is defined along with the field being introduced.
16.3.1. Field Name Registry 16.3.1. Field Name Registry
[new] The "Hypertext Transfer Protocol (HTTP) Field Name Registry" defines
the namespace for HTTP field names.
[new] Any party can request registration of a HTTP field. See
Section 16.3.2 for considerations to take into account when creating
a new HTTP field.
HTTP header fields are registered within the "Message Headers" The "Hypertext Transfer Protocol (HTTP) Field Name Registry" is
registry located at located at <https://www.iana.org/assignments/http-fields/>.
<http://www.iana.org/assignments/message-headers>, as defined by Registration requests can be made by following the instructions
[BCP90]. located there or by sending an email to the "ietf-http-wg@ietf.org"
mailing list.
All defined header fields ought to be registered with IANA in the Field names are registered on the advice of a Designated Expert
"Message Headers" registry, as described in Section 8.3 of [RFC7231]. (appointed by the IESG or their delegate). Fields with the status
'permanent' are Specification Required ([RFC8126], Section 4.6).
[new] Registration requests consist of at least the following information:
[new] Field name:
The requested field name. It MUST conform to the field-name
syntax defined in Section 5.1, and SHOULD be restricted to just
letters, digits, hyphen ('-') and underscore ('_') characters,
with the first character being a letter.
[new] Status:
"permanent" or "provisional".
[new] Specification document(s):
Reference to the document that specifies the field, preferably
including a URI that can be used to retrieve a copy of the
document. An indication of the relevant section(s) can also be
included, but is not required.
[new] And, optionally:
[new] Comments: Additional information, such as about reserved entries.
[new] The Expert(s) can define additional fields to be collected in the
registry, in consultation with the community.
[new] Standards-defined names have a status of "permanent". Other names
can also be registered as permanent, if the Expert(s) find that they
are in use, in consultation with the community. Other names should
be registered as "provisional".
[new] Provisional entries can be removed by the Expert(s) if - in
consultation with the community - the Expert(s) find that they are
not in use. The Experts can change a provisional entry's status to
permanent at any time.
[new] Note that names can be registered by third parties (including the
Expert(s)), if the Expert(s) determines that an unregistered name is
widely deployed and not likely to be registered in a timely manner
otherwise.
16.3.2. Considerations for New Fields 16.3.2. Considerations for New Fields
[new] HTTP header and trailer fields are a widely-used extension point for
the protocol. While they can be used in an ad hoc fashion, fields
that are intended for wider use need to be carefully documented to
ensure interoperability.
[new] In particular, authors of specifications defining new fields are
advised to consider and, where appropriate, document the following
aspects:
o Under what conditions the header field can be used; e.g., only in o Under what conditions the field can be used; e.g., only in
responses or requests, in all messages, only on responses to a responses or requests, in all messages, only on responses to a
particular request method, etc. particular request method, etc.
o Whether the field semantics are further refined by the context, o Whether the field semantics are further refined by their context,
such as by existing request methods or status codes. such as their use with certain request methods or status codes.
o [new] o The scope of applicability for the information conveyed. By
default, fields apply only to the message they are associated
with, but some response fields are designed to apply to all
representations of a resource, the resource itself, or an even
broader scope. Specifications that expand the scope of a response
field will need to carefully consider issues such as content
negotiation, the time period of applicability, and (in some cases)
multi-tenant server deployments.
o Under what conditions intermediaries are allowed to insert, o Under what conditions intermediaries are allowed to insert,
delete, or modify the field's value. delete, or modify the field's value.
o Whether the header field is useful or allowable in trailers (see o If the field is allowable in trailers; by default, it will not be
Section 4.1 of [RFC7230]). (see Section 6.5.1).
o Whether it is appropriate to list the field-name in the Connection o Whether it is appropriate to list the field name in the Connection
header field (i.e., if the header field is to be hop-by-hop; see header field (i.e., if the field is to be hop-by-hop; see
Section 6.1 of [RFC7230]). Section 7.6.1).
o Whether it introduces any additional security considerations, such o Whether the field introduces any additional security
as disclosure of privacy-related data. considerations, such as disclosure of privacy-related data.
[new] Request header fields have additional considerations that need to be
documented if the default behaviour is not appropriate:
o Whether it is appropriate to list the field-name in a Vary o If it is appropriate to list the field name in a Vary response
response header field (e.g., when the request header field is used header field (e.g., when the request header field is used by an
by an origin server's content selection algorithm; see origin server's content selection algorithm; see Section 12.5.5).
Section 7.1.4).
o Whether the field should be stored by origin servers that o If the field is intended to be stored when received in a PUT
understand it upon a PUT request. request (see Section 9.3.4).
o Whether the header field ought to be preserved across redirects. o If the field ought to be removed when automatically redirecting a
request, due to security concerns (see Section 15.4).
16.3.2.1. Considerations for New Field Names 16.3.2.1. Considerations for New Field Names
Authors of specifications defining new fields are advised to keep the Authors of specifications defining new fields are advised to choose a
name as short as practical short but descriptive field name. Short names avoid needless data
transmission; descriptive names avoid confusion and "squatting" on
[new] names that might have broader uses.
[new] To that end, limited-use fields (such as a header confined to a
single application or use case) are encouraged to use a name that
includes that use (or an abbreviation) as a prefix; for example, if
the Foo Application needs a Description field, it might use "Foo-
Desc"; "Description" is too generic, and "Foo-Description" is
needlessly long.
[new] While the field-name syntax is defined to allow any token character,
in practice some implementations place limits on the characters they
accept in field-names. To be interoperable, new field names SHOULD
constrain themselves to alphanumeric characters, "-", and ".", and
SHOULD begin with an alphanumeric character.
and not to prefix the name with "X-" Field names ought not be prefixed with "X-"; see [BCP178] for further
unless the header field will never be used on the Internet. (The information.
"X-" prefix idiom has been extensively misused in practice; it was
intended to only be used as a mechanism for avoiding name collisions
inside proprietary software or intranet processing, since the prefix
would ensure that private names never collide with a newly registered
Internet name; see [BCP178] for further information).
[new] Other prefixes are sometimes used in HTTP field names; for example,
"Accept-" is used in many content negotiation headers. These
prefixes are only an aid to recognizing the purpose of a field, and
do not trigger automatic processing.
16.3.2.2. Considerations for New Field Values 16.3.2.2. Considerations for New Field Values
[new] A major task in the definition of a new HTTP field is the
specification of the field value syntax: what senders should
generate, and how recipients should infer semantics from what is
received.
Authors of specifications defining new header fields are advised to Authors are encouraged (but not required) to use either the ABNF
consider documenting: rules in this specification or those in [RFCSTRF] to define the
syntax of new field values.
o Whether the field is a single value or whether it can be a list Authors are advised to carefully consider how the combination of
(delimited by commas; see Section 3.2 of [RFC7230]). multiple field lines will impact them (see Section 5.3). Because
senders might send erroneously send multiple values, and both
intermediaries and HTTP libraries can perform combination
automatically, this applies to all field values - even when only a
single value is anticipated.
If it does not use the list syntax, document how to treat messages Therefore, authors are advised to delimit or encode values that
where the field occurs multiple times (a sensible default would be contain commas (e.g., with the quoted-string rule of Section 5.6.4,
to ignore the field, but this might not always be the right the String data type of [RFCSTRF]), or a field-specific encoding).
choice). This ensures that commas within field data are not confused with the
commas that delimit a list value.
Note that intermediaries and software libraries might combine For example, the Content-Type field value only allows commas inside
multiple header field instances into a single one, despite the quoted strings, which can be reliably parsed even when multiple
field's definition not allowing the list syntax. A robust format values are present. The Location field value provides a counter-
enables recipients to discover these situations (good example: example that should not be emulated: because URIs can include commas,
"Content-Type", as the comma can only appear inside quoted it is not possible to reliably distinguish between a single value
strings; bad example: "Location", as a comma can occur inside a that includes a comma from two values.
URI).
[new] Authors of fields with a singleton value (see Section 5.5) are
additionally advised to document how to treat messages where the
multiple members are present (a sensible default would be to ignore
the field, but this might not always be the right choice).
16.4. Authentication Scheme Extensibility 16.4. Authentication Scheme Extensibility
16.4.1. Authentication Scheme Registry 16.4.1. Authentication Scheme Registry
The "Hypertext Transfer Protocol (HTTP) Authentication Scheme The "Hypertext Transfer Protocol (HTTP) Authentication Scheme
Registry" defines the namespace for the authentication schemes in Registry" defines the namespace for the authentication schemes in
challenges and credentials. It has been created and is now challenges and credentials. It is maintained at
maintained at <http://www.iana.org/assignments/http-authschemes>. <https://www.iana.org/assignments/http-authschemes>.
Registrations MUST include the following fields: Registrations MUST include the following fields:
o Authentication Scheme Name o Authentication Scheme Name
o Pointer to specification text o Pointer to specification text
o Notes (optional) o Notes (optional)
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
[RFC5226], Section 4.1). [RFC8126], Section 4.8).
16.4.2. Considerations for New Authentication Schemes 16.4.2. Considerations for New Authentication Schemes
There are certain aspects of the HTTP Authentication Framework that There are certain aspects of the HTTP Authentication framework that
put constraints on how new authentication schemes can work: put constraints on how new authentication schemes can work:
o HTTP authentication is presumed to be stateless: all of the o HTTP authentication is presumed to be stateless: all of the
information necessary to authenticate a request MUST be provided information necessary to authenticate a request MUST be provided
in the request, rather than be dependent on the server remembering in the request, rather than be dependent on the server remembering
prior requests. Authentication based on, or bound to, the prior requests. Authentication based on, or bound to, the
underlying connection is outside the scope of this specification underlying connection is outside the scope of this specification
and inherently flawed unless steps are taken to ensure that the and inherently flawed unless steps are taken to ensure that the
connection cannot be used by any party other than the connection cannot be used by any party other than the
authenticated user (see Section 2.3 of [RFC7230]). authenticated user (see Section 3.7).
o The authentication parameter "realm" is reserved for defining o The authentication parameter "realm" is reserved for defining
protection spaces as described in Section 2.2. New schemes MUST protection spaces as described in Section 11.5. New schemes MUST
NOT use it in a way incompatible with that definition. NOT use it in a way incompatible with that definition.
o The "token68" notation was introduced for compatibility with o The "token68" notation was introduced for compatibility with
existing authentication schemes and can only be used once per existing authentication schemes and can only be used once per
challenge or credential. Thus, new schemes ought to use the challenge or credential. Thus, new schemes ought to use the auth-
auth-param syntax instead, because otherwise future extensions param syntax instead, because otherwise future extensions will be
will be impossible. impossible.
o The parsing of challenges and credentials is defined by this o The parsing of challenges and credentials is defined by this
specification and cannot be modified by new authentication specification and cannot be modified by new authentication
schemes. When the auth-param syntax is used, all parameters ought schemes. When the auth-param syntax is used, all parameters ought
to support both token and quoted-string syntax, and syntactical to support both token and quoted-string syntax, and syntactical
constraints ought to be defined on the field value after parsing constraints ought to be defined on the field value after parsing
(i.e., quoted-string processing). This is necessary so that (i.e., quoted-string processing). This is necessary so that
recipients can use a generic parser that applies to all recipients can use a generic parser that applies to all
authentication schemes. authentication schemes.
Note: The fact that the value syntax for the "realm" parameter is *Note:* The fact that the value syntax for the "realm" parameter
restricted to quoted-string was a bad design choice not to be is restricted to quoted-string was a bad design choice not to be
repeated for new parameters. repeated for new parameters.
o Definitions of new schemes ought to define the treatment of o Definitions of new schemes ought to define the treatment of
unknown extension parameters. In general, a "must-ignore" rule is unknown extension parameters. In general, a "must-ignore" rule is
preferable to a "must-understand" rule, because otherwise it will preferable to a "must-understand" rule, because otherwise it will
be hard to introduce new parameters in the presence of legacy be hard to introduce new parameters in the presence of legacy
recipients. Furthermore, it's good to describe the policy for recipients. Furthermore, it's good to describe the policy for
defining new parameters (such as "update the specification" or defining new parameters (such as "update the specification" or
"use this registry"). "use this registry").
o Authentication schemes need to document whether they are usable in o Authentication schemes need to document whether they are usable in
origin-server authentication (i.e., using WWW-Authenticate), origin-server authentication (i.e., using WWW-Authenticate), and/
and/or proxy authentication (i.e., using Proxy-Authenticate). or proxy authentication (i.e., using Proxy-Authenticate).
o The credentials carried in an Authorization header field are o The credentials carried in an Authorization header field are
specific to the user agent and, therefore, have the same effect on specific to the user agent and, therefore, have the same effect on
HTTP caches as the "private" Cache-Control response directive HTTP caches as the "private" Cache-Control response directive
(Section 5.2.2.6 of [RFC7234]), within the scope of the request in (Section 5.2.2.7 of [Caching]), within the scope of the request in
which they appear. which they appear.
Therefore, new authentication schemes that choose not to carry Therefore, new authentication schemes that choose not to carry
credentials in the Authorization header field (e.g., using a newly credentials in the Authorization header field (e.g., using a newly
defined header field) will need to explicitly disallow caching, by defined header field) will need to explicitly disallow caching, by
mandating the use of either Cache-Control request directives mandating the use of Cache-Control response directives (e.g.,
(e.g., "no-store", Section 5.2.1.5 of [RFC7234]) or response "private").
directives (e.g., "private").
o Schemes using Authentication-Info, Proxy-Authentication-Info, or
any other authentication related response header field need to
consider and document the related security considerations (see
Section 17.15.4).
16.5. Range Unit Extensibility 16.5. Range Unit Extensibility
16.5.1. Range Unit Registry 16.5.1. Range Unit Registry
The "HTTP Range Unit Registry" defines the namespace for the range The "HTTP Range Unit Registry" defines the namespace for the range
unit names and refers to their corresponding specifications. The unit names and refers to their corresponding specifications. It is
registry has been created and is now maintained at maintained at <https://www.iana.org/assignments/http-parameters>.
<http://www.iana.org/assignments/http-parameters>.
Registration of an HTTP Range Unit MUST include the following fields: Registration of an HTTP Range Unit MUST include the following fields:
o Name o Name
o Description o Description
o Pointer to specification text o Pointer to specification text
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
[RFC5226], Section 4.1). [RFC8126], Section 4.8).
16.5.2. Considerations for New Range Units 16.5.2. Considerations for New Range Units
[new] Other range units, such as format-specific boundaries like pages,
sections, records, rows, or time, are potentially usable in HTTP for
application-specific purposes, but are not commonly used in practice.
Implementors of alternative range units ought to consider how they
would work with content codings and general-purpose intermediaries.
16.6. Content Coding Extensibility 16.6. Content Coding Extensibility
16.6.1. Content Coding Registry 16.6.1. Content Coding Registry
The "HTTP Content Coding Registry" defines the namespace for content The "HTTP Content Coding Registry", maintained by IANA at
coding names (Section 4.2 of [RFC7230]). The content coding registry <https://www.iana.org/assignments/http-parameters/>, registers
is maintained at <http://www.iana.org/assignments/http-parameters>. content-coding names.
Content coding registrations MUST include the following fields: Content coding registrations MUST include the following fields:
o Name o Name
o Description o Description
o Pointer to specification text o Pointer to specification text
Names of content codings MUST NOT overlap with names of transfer Names of content codings MUST NOT overlap with names of transfer
codings (Section 4 of [RFC7230]), unless the encoding transformation codings (Section 7 of [Messaging]), unless the encoding
is identical (as is the case for the compression codings defined in transformation is identical (as is the case for the compression
Section 4.2 of [RFC7230]). codings defined in Section 8.4.1).
Values to be added to this namespace require IETF Review (see Section Values to be added to this namespace require IETF Review (see
4.1 of [RFC5226]) and MUST conform to the purpose of content coding Section 4.8 of [RFC8126]) and MUST conform to the purpose of content
defined in this section. coding defined in Section 8.4.1.
16.6.2. Considerations for New Content Codings 16.6.2. Considerations for New Content Codings
[new] New content codings ought to be self-descriptive whenever possible,
with optional parameters discoverable within the coding format
itself, rather than rely on external metadata that might be lost
during transit.
16.7. Upgrade Token Registry 16.7. Upgrade Token Registry
The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry" The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry"
defines the namespace for protocol-name tokens used to identify defines the namespace for protocol-name tokens used to identify
protocols in the Upgrade header field. The registry is maintained at protocols in the Upgrade header field. The registry is maintained at
<http://www.iana.org/assignments/http-upgrade-tokens>. <https://www.iana.org/assignments/http-upgrade-tokens>.
Each registered protocol name is associated with contact information Each registered protocol name is associated with contact information
and an optional set of specifications that details how the connection and an optional set of specifications that details how the connection
will be processed after it has been upgraded. will be processed after it has been upgraded.
Registrations happen on a "First Come First Served" basis (see Registrations happen on a "First Come First Served" basis (see
Section 4.1 of [RFC5226]) and are subject to the following rules: Section 4.4 of [RFC8126]) and are subject to the following rules:
1. A protocol-name token, once registered, stays registered forever. 1. A protocol-name token, once registered, stays registered forever.
2. The registration MUST name a responsible party for the 2. A protocol-name token is case-insensitive and registered with the
preferred case to be generated by senders.
3. The registration MUST name a responsible party for the
registration. registration.
3. The registration MUST name a point of contact. 4. The registration MUST name a point of contact.
4. The registration MAY name a set of specifications associated with 5. The registration MAY name a set of specifications associated with
that token. Such specifications need not be publicly available. that token. Such specifications need not be publicly available.
5. The registration SHOULD name a set of expected "protocol-version" 6. The registration SHOULD name a set of expected "protocol-version"
tokens associated with that token at the time of registration. tokens associated with that token at the time of registration.
6. The responsible party MAY change the registration at any time. 7. The responsible party MAY change the registration at any time.
The IANA will keep a record of all such changes, and make them The IANA will keep a record of all such changes, and make them
available upon request. available upon request.
7. The IESG MAY reassign responsibility for a protocol token. This 8. The IESG MAY reassign responsibility for a protocol token. This
will normally only be used in the case when a responsible party will normally only be used in the case when a responsible party
cannot be contacted. cannot be contacted.
This registration procedure for HTTP Upgrade Tokens replaces that
previously defined in Section 7.2 of [RFC2817].
17. Security Considerations 17. Security Considerations
This section is meant to inform developers, information providers, This section is meant to inform developers, information providers,
and users of known security concerns relevant to HTTP semantics and and users of known security concerns relevant to HTTP semantics and
its use for transferring information over the Internet. its use for transferring information over the Internet.
Considerations related to message syntax, parsing, and routing are Considerations related to caching are discussed in Section 7 of
discussed in Section 9 of [RFC7230]. [Caching] and considerations related to HTTP/1.1 message syntax and
parsing are discussed in Section 11 of [Messaging].
The list of considerations below is not exhaustive. Most security The list of considerations below is not exhaustive. Most security
concerns related to HTTP semantics are about securing server-side concerns related to HTTP semantics are about securing server-side
applications (code behind the HTTP interface), securing user agent applications (code behind the HTTP interface), securing user agent
processing of payloads received via HTTP, or secure use of the processing of content received via HTTP, or secure use of the
Internet in general, rather than security of the protocol. Various Internet in general, rather than security of the protocol. Various
organizations maintain topical information and links to current organizations maintain topical information and links to current
research on Web application security (e.g., [OWASP]). research on Web application security (e.g., [OWASP]).
17.1. Establishing Authority 17.1. Establishing Authority
HTTP relies on the notion of an authoritative response: a response HTTP relies on the notion of an _authoritative response_: a response
that has been determined by (or at the direction of) the authority that has been determined by (or at the direction of) the origin
identified within the target URI to be the most appropriate response server identified within the target URI to be the most appropriate
for that request given the state of the target resource at the time response for that request given the state of the target resource at
of response message origination. the time of response message origination.
When a registered name is used in the authority component, the "http" When a registered name is used in the authority component, the "http"
URI scheme (Section 2.7.1) relies on the user's local name resolution URI scheme (Section 4.2.1) relies on the user's local name resolution
service to determine where it can find authoritative responses. This service to determine where it can find authoritative responses. This
means that any attack on a user's network host table, cached names, means that any attack on a user's network host table, cached names,
or name resolution libraries becomes an avenue for attack on or name resolution libraries becomes an avenue for attack on
establishing authority. Likewise, the user's choice of server for establishing authority for "http" URIs. Likewise, the user's choice
Domain Name Service (DNS), and the hierarchy of servers from which it of server for Domain Name Service (DNS), and the hierarchy of servers
obtains resolution results, could impact the authenticity of address from which it obtains resolution results, could impact the
mappings; DNS Security Extensions (DNSSEC, [RFC4033]) are one way to authenticity of address mappings; DNS Security Extensions (DNSSEC,
improve authenticity. [RFC4033]) are one way to improve authenticity.
Furthermore, after an IP address is obtained, establishing authority Furthermore, after an IP address is obtained, establishing authority
for an "http" URI is vulnerable to attacks on Internet Protocol for an "http" URI is vulnerable to attacks on Internet Protocol
routing. routing.
The "https" scheme (Section 2.7.2) is intended to prevent (or at The "https" scheme (Section 4.2.2) is intended to prevent (or at
least reveal) many of these potential attacks on establishing least reveal) many of these potential attacks on establishing
authority, provided that the negotiated TLS connection is secured and authority, provided that the negotiated connection is secured and the
the client properly verifies that the communicating server's identity client properly verifies that the communicating server's identity
matches the target URI's authority component (see [RFC2818]). matches the target URI's authority component (Section 4.3.4).
Correctly implementing such verification can be difficult (see Correctly implementing such verification can be difficult (see
[Georgiev]). [Georgiev]).
Authority for a given origin server can be delegated through protocol
extensions; for example, [RFC7838]. Likewise, the set of servers for
which a connection is considered authoritative can be changed with a
protocol extension like [RFC8336].
Providing a response from a non-authoritative source, such as a Providing a response from a non-authoritative source, such as a
shared cache, is often useful to improve performance and shared proxy cache, is often useful to improve performance and
availability, but only to the extent that the source can be trusted availability, but only to the extent that the source can be trusted
or the distrusted response can be safely used. or the distrusted response can be safely used.
Unfortunately, establishing authority can be difficult. For example, Unfortunately, communicating authority to users can be difficult.
phishing is an attack on the user's perception of authority, where For example, _phishing_ is an attack on the user's perception of
that perception can be misled by presenting similar branding in authority, where that perception can be misled by presenting similar
hypertext, possibly aided by userinfo obfuscating the authority branding in hypertext, possibly aided by userinfo obfuscating the
component (see Section 2.7.1). User agents can reduce the impact of authority component (see Section 4.2.1). User agents can reduce the
phishing attacks by enabling users to easily inspect a target URI impact of phishing attacks by enabling users to easily inspect a
prior to making an action, by prominently distinguishing (or target URI prior to making an action, by prominently distinguishing
rejecting) userinfo when present, and by not sending stored (or rejecting) userinfo when present, and by not sending stored
credentials and cookies when the referring document is from an credentials and cookies when the referring document is from an
unknown or untrusted source. unknown or untrusted source.
17.2. Risks of Intermediaries 17.2. Risks of Intermediaries
By their very nature, HTTP intermediaries are men-in-the-middle and, HTTP intermediaries are inherently situated for on-path attacks.
thus, represent an opportunity for man-in-the-middle attacks.
Compromise of the systems on which the intermediaries run can result Compromise of the systems on which the intermediaries run can result
in serious security and privacy problems. Intermediaries might have in serious security and privacy problems. Intermediaries might have
access to security-related information, personal information about access to security-related information, personal information about
individual users and organizations, and proprietary information individual users and organizations, and proprietary information
belonging to users and content providers. A compromised belonging to users and content providers. A compromised
intermediary, or an intermediary implemented or configured without intermediary, or an intermediary implemented or configured without
regard to security and privacy considerations, might be used in the regard to security and privacy considerations, might be used in the
commission of a wide range of potential attacks. commission of a wide range of potential attacks.
Intermediaries that contain a shared cache are especially vulnerable Intermediaries that contain a shared cache are especially vulnerable
to cache poisoning attacks, as described in Section 8 of [RFC7234]. to cache poisoning attacks, as described in Section 7 of [Caching].
Implementers need to consider the privacy and security implications Implementers need to consider the privacy and security implications
of their design and coding decisions, and of the configuration of their design and coding decisions, and of the configuration
options they provide to operators (especially the default options they provide to operators (especially the default
configuration). configuration).
Users need to be aware that intermediaries are no more trustworthy Users need to be aware that intermediaries are no more trustworthy
than the people who run them; HTTP itself cannot solve this problem. than the people who run them; HTTP itself cannot solve this problem.
17.3. Attacks Based on File and Path Names 17.3. Attacks Based on File and Path Names
Origin servers frequently make use of their local file system to Origin servers frequently make use of their local file system to
manage the mapping from effective request URI to resource manage the mapping from target URI to resource representations. Most
representations. Most file systems are not designed to protect file systems are not designed to protect against malicious file or
against malicious file or path names. Therefore, an origin server path names. Therefore, an origin server needs to avoid accessing
needs to avoid accessing names that have a special significance to names that have a special significance to the system when mapping the
the system when mapping the request target to files, folders, or target resource to files, folders, or directories.
directories.
For example, UNIX, Microsoft Windows, and other operating systems use For example, UNIX, Microsoft Windows, and other operating systems use
".." as a path component to indicate a directory level above the ".." as a path component to indicate a directory level above the
current one, and they use specially named paths or file names to send current one, and they use specially named paths or file names to send
data to system devices. Similar naming conventions might exist data to system devices. Similar naming conventions might exist
within other types of storage systems. Likewise, local storage within other types of storage systems. Likewise, local storage
systems have an annoying tendency to prefer user-friendliness over systems have an annoying tendency to prefer user-friendliness over
security when handling invalid or unexpected characters, security when handling invalid or unexpected characters,
recomposition of decomposed characters, and case-normalization of recomposition of decomposed characters, and case-normalization of
case-insensitive names. case-insensitive names.
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of-service (e.g., telling the server to read from a COM port) or of-service (e.g., telling the server to read from a COM port) or
disclosure of configuration and source files that are not meant to be disclosure of configuration and source files that are not meant to be
served. served.
17.4. Attacks Based on Command, Code, or Query Injection 17.4. Attacks Based on Command, Code, or Query Injection
Origin servers often use parameters within the URI as a means of Origin servers often use parameters within the URI as a means of
identifying system services, selecting database entries, or choosing identifying system services, selecting database entries, or choosing
a data source. However, data received in a request cannot be a data source. However, data received in a request cannot be
trusted. An attacker could construct any of the request data trusted. An attacker could construct any of the request data
elements (method, request-target, header fields, or body) to contain elements (method, target URI, header fields, or content) to contain
data that might be misinterpreted as a command, code, or query when data that might be misinterpreted as a command, code, or query when
passed through a command invocation, language interpreter, or passed through a command invocation, language interpreter, or
database interface. database interface.
For example, SQL injection is a common attack wherein additional For example, SQL injection is a common attack wherein additional
query language is inserted within some part of the request-target or query language is inserted within some part of the target URI or
header fields (e.g., Host, Referer, etc.). If the received data is header fields (e.g., Host, Referer, etc.). If the received data is
used directly within a SELECT statement, the query language might be used directly within a SELECT statement, the query language might be
interpreted as a database command instead of a simple string value. interpreted as a database command instead of a simple string value.
This type of implementation vulnerability is extremely common, in This type of implementation vulnerability is extremely common, in
spite of being easy to prevent. spite of being easy to prevent.
In general, resource implementations ought to avoid use of request In general, resource implementations ought to avoid use of request
data in contexts that are processed or interpreted as instructions. data in contexts that are processed or interpreted as instructions.
Parameters ought to be compared to fixed strings and acted upon as a Parameters ought to be compared to fixed strings and acted upon as a
result of that comparison, rather than passed through an interface result of that comparison, rather than passed through an interface
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Similar considerations apply to request data when it is stored and Similar considerations apply to request data when it is stored and
later processed, such as within log files, monitoring tools, or when later processed, such as within log files, monitoring tools, or when
included within a data format that allows embedded scripts. included within a data format that allows embedded scripts.
17.5. Attacks via Protocol Element Length 17.5. Attacks via Protocol Element Length
Because HTTP uses mostly textual, character-delimited fields, parsers Because HTTP uses mostly textual, character-delimited fields, parsers
are often vulnerable to attacks based on sending very long (or very are often vulnerable to attacks based on sending very long (or very
slow) streams of data, particularly where an implementation is slow) streams of data, particularly where an implementation is
expecting a protocol element with no predefined length. expecting a protocol element with no predefined length (Section 2.3).
To promote interoperability, specific recommendations are made for To promote interoperability, specific recommendations are made for
minimum size limits on request-line (Section 3.1.1) and header fields minimum size limits on fields (Section 5.4). These are minimum
(Section 3.2). These are minimum recommendations, chosen to be recommendations, chosen to be supportable even by implementations
supportable even by implementations with limited resources; it is with limited resources; it is expected that most implementations will
expected that most implementations will choose substantially higher choose substantially higher limits.
limits.
A server can reject a message that has a request-target that is too A server can reject a message that has a target URI that is too long
long (Section 6.5.12 of [RFC7231]) or a request payload that is too (Section 15.5.15) or request content that is too large
large (Section 6.5.11 of [RFC7231]). Additional status codes related (Section 15.5.14). Additional status codes related to capacity
to capacity limits have been defined by extensions to HTTP [RFC6585]. limits have been defined by extensions to HTTP [RFC6585].
Recipients ought to carefully limit the extent to which they process Recipients ought to carefully limit the extent to which they process
other protocol elements, including (but not limited to) request other protocol elements, including (but not limited to) request
methods, response status phrases, header field-names, numeric values, methods, response status phrases, field names, numeric values, and
and body chunks. Failure to limit such processing can result in chunk lengths. Failure to limit such processing can result in buffer
buffer overflows, arithmetic overflows, or increased vulnerability to overflows, arithmetic overflows, or increased vulnerability to
denial-of-service attacks. denial-of-service attacks.
17.6. Attacks using Shared-dictionary Compression 17.6. Attacks using Shared-dictionary Compression
[new] Some attacks on encrypted protocols use the differences in size
created by dynamic compression to reveal confidential information;
for example, [BREACH]. These attacks rely on creating a redundancy
between attacker-controlled content and the confidential information,
such that a dynamic compression algorithm using the same dictionary
for both content will compress more efficiently when the attacker-
controlled content matches parts of the confidential content.
HTTP messages can be compressed in a number of ways, including using
TLS compression, content-codings, transfer-codings, and other
extension or version-specific mechanisms.
The most effective mitigation for this risk is to disable compression
on sensitive data, or to strictly separate sensitive data from
attacker-controlled data so that they cannot share the same
compression dictionary. With careful design, a compression scheme
can be designed in a way that is not considered exploitable in
limited use cases, such as HPACK ([RFC7541]).
17.7. Disclosure of Personal Information 17.7. Disclosure of Personal Information
Clients are often privy to large amounts of personal information, Clients are often privy to large amounts of personal information,
including both information provided by the user to interact with including both information provided by the user to interact with
resources (e.g., the user's name, location, mail address, passwords, resources (e.g., the user's name, location, mail address, passwords,
encryption keys, etc.) and information about the user's browsing encryption keys, etc.) and information about the user's browsing
activity over time (e.g., history, bookmarks, etc.). Implementations activity over time (e.g., history, bookmarks, etc.). Implementations
need to prevent unintentional disclosure of personal information. need to prevent unintentional disclosure of personal information.
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A server is in the position to save personal data about a user's A server is in the position to save personal data about a user's
requests over time, which might identify their reading patterns or requests over time, which might identify their reading patterns or
subjects of interest. In particular, log information gathered at an subjects of interest. In particular, log information gathered at an
intermediary often contains a history of user agent interaction, intermediary often contains a history of user agent interaction,
across a multitude of sites, that can be traced to individual users. across a multitude of sites, that can be traced to individual users.
HTTP log information is confidential in nature; its handling is often HTTP log information is confidential in nature; its handling is often
constrained by laws and regulations. Log information needs to be constrained by laws and regulations. Log information needs to be
securely stored and appropriate guidelines followed for its analysis. securely stored and appropriate guidelines followed for its analysis.
Anonymization of personal information within individual entries Anonymization of personal information within individual entries
helps, but it is generally not sufficient to prevent real log traces helps, but it is generally not sufficient to prevent real log traces
from being re-identified based on correlation with other access from being re-identified based on correlation with other access
characteristics. As such, access traces that are keyed to a specific characteristics. As such, access traces that are keyed to a specific
client are unsafe to publish even if the key is pseudonymous. client are unsafe to publish even if the key is pseudonymous.
To minimize the risk of theft or accidental publication, log To minimize the risk of theft or accidental publication, log
information ought to be purged of personally identifiable information ought to be purged of personally identifiable
information, including user identifiers, IP addresses, and information, including user identifiers, IP addresses, and user-
user-provided query parameters, as soon as that information is no provided query parameters, as soon as that information is no longer
longer necessary to support operational needs for security, auditing, necessary to support operational needs for security, auditing, or
or fraud control. fraud control.
17.9. Disclosure of Sensitive Information in URIs 17.9. Disclosure of Sensitive Information in URIs
URIs are intended to be shared, not secured, even when they identify URIs are intended to be shared, not secured, even when they identify
secure resources. URIs are often shown on displays, added to secure resources. URIs are often shown on displays, added to
templates when a page is printed, and stored in a variety of templates when a page is printed, and stored in a variety of
unprotected bookmark lists. It is therefore unwise to include unprotected bookmark lists. Many servers, proxies, and user agents
information within a URI that is sensitive, personally identifiable, log or display the target URI in places where it might be visible to
or a risk to disclose. third parties. It is therefore unwise to include information within
a URI that is sensitive, personally identifiable, or a risk to
disclose.
Authors of services ought to avoid GET-based forms for the submission When an application uses client-side mechanisms to construct a target
of sensitive data because that data will be placed in the URI out of user-provided information, such as the query fields of a
request-target. Many existing servers, proxies, and user agents log form using GET, potentially sensitive data might be provided that
or display the request-target in places where it might be visible to would not be appropriate for disclosure within a URI. POST is often
third parties. Such services ought to use POST-based form submission preferred in such cases because it usually doesn't construct a URI;
instead. instead, POST of a form transmits the potentially sensitive data in
the request content. However, this hinders caching and uses an
unsafe method for what would otherwise be a safe request.
Alternative workarounds include transforming the user-provided data
prior to constructing the URI, or filtering the data to only include
common values that are not sensitive. Likewise, redirecting the
result of a query to a different (server-generated) URI can remove
potentially sensitive data from later links and provide a cacheable
response for later reuse.
Since the Referer header field tells a target site about the context Since the Referer header field tells a target site about the context
that resulted in a request, it has the potential to reveal that resulted in a request, it has the potential to reveal
information about the user's immediate browsing history and any information about the user's immediate browsing history and any
personal information that might be found in the referring resource's personal information that might be found in the referring resource's
URI. Limitations on the Referer header field are described in URI. Limitations on the Referer header field are described in
Section 5.5.2 to address some of its security considerations. Section 10.1.3 to address some of its security considerations.
17.10. Disclosure of Fragment after Redirects 17.10. Disclosure of Fragment after Redirects
Although fragment identifiers used within URI references are not sent Although fragment identifiers used within URI references are not sent
in requests, implementers ought to be aware that they will be visible in requests, implementers ought to be aware that they will be visible
to the user agent and any extensions or scripts running as a result to the user agent and any extensions or scripts running as a result
of the response. In particular, when a redirect occurs and the of the response. In particular, when a redirect occurs and the
original request's fragment identifier is inherited by the new original request's fragment identifier is inherited by the new
reference in Location (Section 7.1.2), this might have the effect of reference in Location (Section 10.2.3), this might have the effect of
disclosing one site's fragment to another site. If the first site disclosing one site's fragment to another site. If the first site
uses personal information in fragments, it ought to ensure that uses personal information in fragments, it ought to ensure that
redirects to other sites include a (possibly empty) fragment redirects to other sites include a (possibly empty) fragment
component in order to block that inheritance. component in order to block that inheritance.
17.11. Disclosure of Product Information 17.11. Disclosure of Product Information
The User-Agent (Section 5.5.3), Via (Section 5.7.1 of [RFC7230]), and The User-Agent (Section 10.1.6), Via (Section 7.6.3), and Server
Server (Section 7.4.2) header fields often reveal information about (Section 10.2.5) header fields often reveal information about the
the respective sender's software systems. In theory, this can make respective sender's software systems. In theory, this can make it
it easier for an attacker to exploit known security holes; in easier for an attacker to exploit known security holes; in practice,
practice, attackers tend to try all potential holes regardless of the attackers tend to try all potential holes regardless of the apparent
apparent software versions being used. software versions being used.
Proxies that serve as a portal through a network firewall ought to Proxies that serve as a portal through a network firewall ought to
take special precautions regarding the transfer of header information take special precautions regarding the transfer of header information
that might identify hosts behind the firewall. The Via header field that might identify hosts behind the firewall. The Via header field
allows intermediaries to replace sensitive machine names with allows intermediaries to replace sensitive machine names with
pseudonyms. pseudonyms.
17.12. Browser Fingerprinting 17.12. Browser Fingerprinting
Browser fingerprinting is a set of techniques for identifying a Browser fingerprinting is a set of techniques for identifying a
specific user agent over time through its unique set of specific user agent over time through its unique set of
characteristics. These characteristics might include information characteristics. These characteristics might include information
related to its TCP behavior, feature capabilities, and scripting related to its TCP behavior, feature capabilities, and scripting
environment, though of particular interest here is the set of unique environment, though of particular interest here is the set of unique
characteristics that might be communicated via HTTP. Fingerprinting characteristics that might be communicated via HTTP. Fingerprinting
is considered a privacy concern because it enables tracking of a user is considered a privacy concern because it enables tracking of a user
agent's behavior over time without the corresponding controls that agent's behavior over time ([Bujlow]) without the corresponding
the user might have over other forms of data collection (e.g., controls that the user might have over other forms of data collection
cookies). Many general-purpose user agents (i.e., Web browsers) have (e.g., cookies). Many general-purpose user agents (i.e., Web
taken steps to reduce their fingerprints. browsers) have taken steps to reduce their fingerprints.
There are a number of request header fields that might reveal There are a number of request header fields that might reveal
information to servers that is sufficiently unique to enable information to servers that is sufficiently unique to enable
fingerprinting. The From header field is the most obvious, though it fingerprinting. The From header field is the most obvious, though it
is expected that From will only be sent when self-identification is is expected that From will only be sent when self-identification is
desired by the user. Likewise, Cookie header fields are deliberately desired by the user. Likewise, Cookie header fields are deliberately
designed to enable re-identification, so fingerprinting concerns only designed to enable re-identification, so fingerprinting concerns only
apply to situations where cookies are disabled or restricted by the apply to situations where cookies are disabled or restricted by the
user agent's configuration. user agent's configuration.
The User-Agent header field might contain enough information to The User-Agent header field might contain enough information to
uniquely identify a specific device, usually when combined with other uniquely identify a specific device, usually when combined with other
characteristics, particularly if the user agent sends excessive characteristics, particularly if the user agent sends excessive
details about the user's system or extensions. However, the source details about the user's system or extensions. However, the source
of unique information that is least expected by users is proactive of unique information that is least expected by users is proactive
negotiation (Section 5.3), including the Accept, Accept-Charset, negotiation (Section 12.1), including the Accept, Accept-Charset,
Accept-Encoding, and Accept-Language header fields. Accept-Encoding, and Accept-Language header fields.
In addition to the fingerprinting concern, detailed use of the In addition to the fingerprinting concern, detailed use of the
Accept-Language header field can reveal information the user might Accept-Language header field can reveal information the user might
consider to be of a private nature. For example, understanding a consider to be of a private nature. For example, understanding a
given language set might be strongly correlated to membership in a given language set might be strongly correlated to membership in a
particular ethnic group. An approach that limits such loss of particular ethnic group. An approach that limits such loss of
privacy would be for a user agent to omit the sending of privacy would be for a user agent to omit the sending of Accept-
Accept-Language except for sites that have been whitelisted, perhaps Language except for sites that have been whitelisted, perhaps via
via interaction after detecting a Vary header field that indicates interaction after detecting a Vary header field that indicates
language negotiation might be useful. language negotiation might be useful.
In environments where proxies are used to enhance privacy, user In environments where proxies are used to enhance privacy, user
agents ought to be conservative in sending proactive negotiation agents ought to be conservative in sending proactive negotiation
header fields. General-purpose user agents that provide a high header fields. General-purpose user agents that provide a high
degree of header field configurability ought to inform users about degree of header field configurability ought to inform users about
the loss of privacy that might result if too much detail is provided. the loss of privacy that might result if too much detail is provided.
As an extreme privacy measure, proxies could filter the proactive As an extreme privacy measure, proxies could filter the proactive
negotiation header fields in relayed requests. negotiation header fields in relayed requests.
17.13. Validator Retention 17.13. Validator Retention
This section is meant to inform developers, information providers,
and users of known security concerns specific to the HTTP conditional
request mechanisms. More general security considerations are
addressed in HTTP "Message Syntax and Routing" [RFC7230] and
"Semantics and Content" [RFC7231].
The validators defined by this specification are not intended to The validators defined by this specification are not intended to
ensure the validity of a representation, guard against malicious ensure the validity of a representation, guard against malicious
changes, or detect man-in-the-middle attacks. At best, they enable changes, or detect on-path attacks. At best, they enable more
more efficient cache updates and optimistic concurrent writes when efficient cache updates and optimistic concurrent writes when all
all participants are behaving nicely. At worst, the conditions will participants are behaving nicely. At worst, the conditions will fail
fail and the client will receive a response that is no more harmful and the client will receive a response that is no more harmful than
than an HTTP exchange without conditional requests. an HTTP exchange without conditional requests.
An entity-tag can be abused in ways that create privacy risks. For An entity-tag can be abused in ways that create privacy risks. For
example, a site might deliberately construct a semantically invalid example, a site might deliberately construct a semantically invalid
entity-tag that is unique to the user or user agent, send it in a entity-tag that is unique to the user or user agent, send it in a
cacheable response with a long freshness time, and then read that cacheable response with a long freshness time, and then read that
entity-tag in later conditional requests as a means of re-identifying entity-tag in later conditional requests as a means of re-identifying
that user or user agent. Such an identifying tag would become a that user or user agent. Such an identifying tag would become a
persistent identifier for as long as the user agent retained the persistent identifier for as long as the user agent retained the
original cache entry. User agents that cache representations ought original cache entry. User agents that cache representations ought
to ensure that the cache is cleared or replaced whenever the user to ensure that the cache is cleared or replaced whenever the user
performs privacy-maintaining actions, such as clearing stored cookies performs privacy-maintaining actions, such as clearing stored cookies
or changing to a private browsing mode. or changing to a private browsing mode.
17.14. Denial-of-Service Attacks Using Range 17.14. Denial-of-Service Attacks Using Range
This section is meant to inform developers, information providers,
and users of known security concerns specific to the HTTP range
request mechanisms. More general security considerations are
addressed in HTTP messaging [RFC7230] and semantics [RFC7231].
Unconstrained multiple range requests are susceptible to denial-of- Unconstrained multiple range requests are susceptible to denial-of-
service attacks because the effort required to request many service attacks because the effort required to request many
overlapping ranges of the same data is tiny compared to the time, overlapping ranges of the same data is tiny compared to the time,
memory, and bandwidth consumed by attempting to serve the requested memory, and bandwidth consumed by attempting to serve the requested
data in many parts. Servers ought to ignore, coalesce, or reject data in many parts. Servers ought to ignore, coalesce, or reject
egregious range requests, such as requests for more than two egregious range requests, such as requests for more than two
overlapping ranges or for many small ranges in a single set, overlapping ranges or for many small ranges in a single set,
particularly when the ranges are requested out of order for no particularly when the ranges are requested out of order for no
apparent reason. Multipart range requests are not designed to apparent reason. Multipart range requests are not designed to
support random access. support random access.
17.15. Authentication Considerations 17.15. Authentication Considerations
This section is meant to inform developers, information providers,
and users of known security concerns specific to HTTP authentication.
More general security considerations are addressed in HTTP messaging
[RFC7230] and semantics [RFC7231].
Everything about the topic of HTTP authentication is a security Everything about the topic of HTTP authentication is a security
consideration, so the list of considerations below is not exhaustive. consideration, so the list of considerations below is not exhaustive.
Furthermore, it is limited to security considerations regarding the Furthermore, it is limited to security considerations regarding the
authentication framework, in general, rather than discussing all of authentication framework, in general, rather than discussing all of
the potential considerations for specific authentication schemes the potential considerations for specific authentication schemes
(which ought to be documented in the specifications that define those (which ought to be documented in the specifications that define those
schemes). Various organizations maintain topical information and schemes). Various organizations maintain topical information and
links to current research on Web application security (e.g., links to current research on Web application security (e.g.,
[OWASP]), including common pitfalls for implementing and using the [OWASP]), including common pitfalls for implementing and using the
authentication schemes found in practice. authentication schemes found in practice.
skipping to change at line 7825 skipping to change at page 187, line 7
of future authentication schemes, it is inadequate for the protection of future authentication schemes, it is inadequate for the protection
of existing schemes that provide no confidentiality on their own, or of existing schemes that provide no confidentiality on their own, or
that do not sufficiently protect against replay attacks. that do not sufficiently protect against replay attacks.
Furthermore, if the server expects credentials that are specific to Furthermore, if the server expects credentials that are specific to
each individual user, the exchange of those credentials will have the each individual user, the exchange of those credentials will have the
effect of identifying that user even if the content within effect of identifying that user even if the content within
credentials remains confidential. credentials remains confidential.
HTTP depends on the security properties of the underlying transport- HTTP depends on the security properties of the underlying transport-
or session-level connection to provide confidential transmission of or session-level connection to provide confidential transmission of
header fields. In other words, if a server limits access to fields. Services that depend on individual user authentication
authenticated users using this framework, the server needs to ensure require a secured connection prior to exchanging credentials
that the connection is properly secured in accordance with the nature (Section 4.2.2).
of the authentication scheme used. For example, services that depend
on individual user authentication often require a connection to be
secured with TLS ("Transport Layer Security", [RFC5246]) prior to
exchanging any credentials.
17.15.2. Credentials and Idle Clients 17.15.2. Credentials and Idle Clients
Existing HTTP clients and user agents typically retain authentication Existing HTTP clients and user agents typically retain authentication
information indefinitely. HTTP does not provide a mechanism for the information indefinitely. HTTP does not provide a mechanism for the
origin server to direct clients to discard these cached credentials, origin server to direct clients to discard these cached credentials,
since the protocol has no awareness of how credentials are obtained since the protocol has no awareness of how credentials are obtained
or managed by the user agent. The mechanisms for expiring or or managed by the user agent. The mechanisms for expiring or
revoking credentials can be specified as part of an authentication revoking credentials can be specified as part of an authentication
scheme definition. scheme definition.
skipping to change at line 7870 skipping to change at page 188, line 6
Authentication schemes that solely rely on the "realm" mechanism for Authentication schemes that solely rely on the "realm" mechanism for
establishing a protection space will expose credentials to all establishing a protection space will expose credentials to all
resources on an origin server. Clients that have successfully made resources on an origin server. Clients that have successfully made
authenticated requests with a resource can use the same authenticated requests with a resource can use the same
authentication credentials for other resources on the same origin authentication credentials for other resources on the same origin
server. This makes it possible for a different resource to harvest server. This makes it possible for a different resource to harvest
authentication credentials for other resources. authentication credentials for other resources.
This is of particular concern when an origin server hosts resources This is of particular concern when an origin server hosts resources
for multiple parties under the same canonical root URI (Section 2.2). for multiple parties under the same origin (Section 11.5). Possible
Possible mitigation strategies include restricting direct access to mitigation strategies include restricting direct access to
authentication credentials (i.e., not making the content of the authentication credentials (i.e., not making the content of the
Authorization request header field available), and separating Authorization request header field available), and separating
protection spaces by using a different host name (or port number) for protection spaces by using a different host name (or port number) for
each party. each party.
17.15.4. Additional Response Fields 17.15.4. Additional Response Fields
Adding information to HTTP responses that are sent over an Adding information to responses that are sent over an unencrypted
unencrypted channel can affect security and privacy. The presence of channel can affect security and privacy. The presence of the
the header fields alone indicates that HTTP authentication is in use. Authentication-Info and Proxy-Authentication-Info header fields alone
Additional information could be exposed by the contents of the indicates that HTTP authentication is in use. Additional information
authentication-scheme specific parameters; this will have to be could be exposed by the contents of the authentication-scheme
considered in the definitions of these schemes. specific parameters; this will have to be considered in the
definitions of these schemes.
18. IANA Considerations 18. IANA Considerations
The change controller for the above registrations is: "IETF The change controller for the following registrations is: "IETF
(iesg@ietf.org) - Internet Engineering Task Force". (iesg@ietf.org) - Internet Engineering Task Force".
18.1. URI Scheme Registration 18.1. URI Scheme Registration
IANA maintains the registry of URI Schemes [BCP115] at Please update the registry of URI Schemes [BCP35] at
<http://www.iana.org/assignments/uri-schemes/>. <https://www.iana.org/assignments/uri-schemes/> with the permanent
schemes listed in the table in Section 4.2.
This document defines the following URI schemes, so the "Permanent
URI Schemes" registry has been updated accordingly.
18.2. Method Registration 18.2. Method Registration
The "Hypertext Transfer Protocol (HTTP) Method Registry" has been Please update the "Hypertext Transfer Protocol (HTTP) Method
populated with the registrations below: Registry" at <https://www.iana.org/assignments/http-methods> with the
registration procedure of Section 16.1.1 and the method names
summarized in the following table.
+---------+------+------------+----------------+ --------- ------ ------------ -------
| Method | Safe | Idempotent | Reference | Method Safe Idempotent Ref.
+---------+------+------------+----------------+ --------- ------ ------------ -------
| CONNECT | no | no | Section 4.3.6 | CONNECT no no 9.3.6
| DELETE | no | yes | Section 4.3.5 | DELETE no yes 9.3.5
| GET | yes | yes | Section 4.3.1 | GET yes yes 9.3.1
| HEAD | yes | yes | Section 4.3.2 | HEAD yes yes 9.3.2
| OPTIONS | yes | yes | Section 4.3.7 | OPTIONS yes yes 9.3.7
| POST | no | no | Section 4.3.3 | POST no no 9.3.3
| PUT | no | yes | Section 4.3.4 | PUT no yes 9.3.4
| TRACE | yes | yes | Section 4.3.8 | TRACE yes yes 9.3.8
+---------+------+------------+----------------+ * no no 18.2
--------- ------ ------------ -------
Table 7
The method name "*" is reserved, since using that name as HTTP method
name might conflict with special semantics in fields such as "Access-
Control-Request-Method".
18.3. Status Code Registration 18.3. Status Code Registration
The status code registry has been updated with the registrations Please update the "Hypertext Transfer Protocol (HTTP) Status Code
below: Registry" at <https://www.iana.org/assignments/http-status-codes>
with the registration procedure of Section 16.2.1 and the status code
values summarized in the following table.
+------+-------------------------------+--------------------------+ ------- ------------------------------- ---------
| Code | Reason-Phrase | Defined in... | Value Description Ref.
+------+-------------------------------+--------------------------+ ------- ------------------------------- ---------
| 100 | Continue | Section 6.2.1 | 100 Continue 15.2.1
| 101 | Switching Protocols | Section 6.2.2 | 101 Switching Protocols 15.2.2
| 200 | OK | Section 6.3.1 | 200 OK 15.3.1
| 201 | Created | Section 6.3.2 | 201 Created 15.3.2
| 202 | Accepted | Section 6.3.3 | 202 Accepted 15.3.3
| 203 | Non-Authoritative Information | Section 6.3.4 | 203 Non-Authoritative Information 15.3.4
| 204 | No Content | Section 6.3.5 | 204 No Content 15.3.5
| 205 | Reset Content | Section 6.3.6 | 205 Reset Content 15.3.6
| 206 | Partial Content | Section 4.1 of [RFC7233] | 206 Partial Content 15.3.7
| 300 | Multiple Choices | Section 6.4.1 | 300 Multiple Choices 15.4.1
| 301 | Moved Permanently | Section 6.4.2 | 301 Moved Permanently 15.4.2
| 302 | Found | Section 6.4.3 | 302 Found 15.4.3
| 303 | See Other | Section 6.4.4 | 303 See Other 15.4.4
| 304 | Not Modified | Section 4.1 of [RFC7232] | 304 Not Modified 15.4.5
| 305 | Use Proxy | Section 6.4.5 | 305 Use Proxy 15.4.6
| 307 | Temporary Redirect | Section 6.4.7 | 306 (Unused) 15.4.7
| 400 | Bad Request | Section 6.5.1 | 307 Temporary Redirect 15.4.8
| 401 | Unauthorized | Section 3.1 of [RFC7235] | 308 Permanent Redirect 15.4.9
| 402 | Payment Required | Section 6.5.2 | 400 Bad Request 15.5.1
| 403 | Forbidden | Section 6.5.3 | 401 Unauthorized 15.5.2
| 404 | Not Found | Section 6.5.4 | 402 Payment Required 15.5.3
| 405 | Method Not Allowed | Section 6.5.5 | 403 Forbidden 15.5.4
| 406 | Not Acceptable | Section 6.5.6 | 404 Not Found 15.5.5
| 407 | Proxy Authentication Required | Section 3.2 of [RFC7235] | 405 Method Not Allowed 15.5.6
| 408 | Request Timeout | Section 6.5.7 | 406 Not Acceptable 15.5.7
| 409 | Conflict | Section 6.5.8 | 407 Proxy Authentication Required 15.5.8
| 410 | Gone | Section 6.5.9 | 408 Request Timeout 15.5.9
| 411 | Length Required | Section 6.5.10 | 409 Conflict 15.5.10
| 412 | Precondition Failed | Section 4.2 of [RFC7232] | 410 Gone 15.5.11
| 413 | Payload Too Large | Section 6.5.11 | 411 Length Required 15.5.12
| 414 | URI Too Long | Section 6.5.12 | 412 Precondition Failed 15.5.13
| 415 | Unsupported Media Type | Section 6.5.13 | 413 Content Too Large 15.5.14
| 416 | Range Not Satisfiable | Section 4.4 of [RFC7233] | 414 URI Too Long 15.5.15
| 417 | Expectation Failed | Section 6.5.14 | 415 Unsupported Media Type 15.5.16
| 426 | Upgrade Required | Section 6.5.15 | 416 Range Not Satisfiable 15.5.17
| 500 | Internal Server Error | Section 6.6.1 | 417 Expectation Failed 15.5.18
| 501 | Not Implemented | Section 6.6.2 | 418 (Unused) 15.5.19
| 502 | Bad Gateway | Section 6.6.3 | 421 Misdirected Request 15.5.20
| 503 | Service Unavailable | Section 6.6.4 | 422 Unprocessable Content 15.5.21
| 504 | Gateway Timeout | Section 6.6.5 | 426 Upgrade Required 15.5.22
| 505 | HTTP Version Not Supported | Section 6.6.6 | 500 Internal Server Error 15.6.1
+------+-------------------------------+--------------------------+ 501 Not Implemented 15.6.2
502 Bad Gateway 15.6.3
503 Service Unavailable 15.6.4
504 Gateway Timeout 15.6.5
505 HTTP Version Not Supported 15.6.6
------- ------------------------------- ---------
Table 8
18.4. Field Name Registration 18.4. Field Name Registration
[new] This specification updates the HTTP related aspects of the existing
registration procedures for message header fields defined in
[RFC3864]. It defines both a new registration procedure and moves
HTTP field definitions into a separate registry.
[new] Please create a new registry as outlined in Section 16.3.1.
[new] After creating the registry, all entries in the Permanent and
Provisional Message Header Registries with the protocol 'http' are to
be moved to it, with the following changes applied:
[new] 1. The 'Applicable Protocol' field is to be omitted.
[new] 2. Entries with a status of 'standard', 'experimental', 'reserved',
or 'informational' are to have a status of 'permanent'.
[new] 3. Provisional entries without a status are to have a status of
'provisional'.
[new] 4. Permanent entries without a status (after confirmation that the
registration document did not define one) will have a status of
'provisional'. The Expert(s) can choose to update their status
if there is evidence that another is more appropriate.
[new] Please annotate the Permanent and Provisional Message Header
registries to indicate that HTTP field name registrations have moved,
with an appropriate link.
The "Message Headers" registry has been updated with the following After that is complete, please update the new registry with the field
permanent registrations: names listed in the following table.
+-------------------+----------+----------+-----------------+ --------------------------- ------------ -------- ------------
| Header Field Name | Protocol | Status | Reference | Field Name Status Ref. Comments
+-------------------+----------+----------+-----------------+ --------------------------- ------------ -------- ------------
| Accept | http | standard | Section 5.3.2 | Accept standard 12.5.1
| Accept-Charset | http | standard | Section 5.3.3 | Accept-Charset deprecated 12.5.2
| Accept-Encoding | http | standard | Section 5.3.4 | Accept-Encoding standard 12.5.3
| Accept-Language | http | standard | Section 5.3.5 | Accept-Language standard 12.5.4
| Accept-Ranges | http | standard | Section 2.3 | Accept-Ranges standard 14.3
| Allow | http | standard | Section 7.4.1 | Allow standard 10.2.1
| Authorization | http | standard | Section 4.2 | Authentication-Info standard 11.6.3
| Connection | http | standard | Section 6.1 | Authorization standard 11.6.2
| Content-Encoding | http | standard | Section 3.1.2.2 | Connection standard 7.6.1
| Content-Language | http | standard | Section 3.1.3.2 | Content-Encoding standard 8.4
| Content-Length | http | standard | Section 3.3.2 | Content-Language standard 8.5
| Content-Location | http | standard | Section 3.1.4.2 | Content-Length standard 8.6
| Content-Range | http | standard | Section 4.2 | Content-Location standard 8.7
| Content-Type | http | standard | Section 3.1.1.5 | Content-Range standard 14.4
| Date | http | standard | Section 7.1.1.2 | Content-Type standard 8.3
| ETag | http | standard | Section 2.3 | Date standard 10.2.2
| Expect | http | standard | Section 5.1.1 | ETag standard 8.8.3
| From | http | standard | Section 5.5.1 | Expect standard 10.1.1
| Host | http | standard | Section 5.4 | From standard 10.1.2
| If-Match | http | standard | Section 3.1 | Host standard 7.2
| If-Modified-Since | http | standard | Section 3.3 | If-Match standard 13.1.1
| If-None-Match | http | standard | Section 3.2 | If-Modified-Since standard 13.1.3
| If-Range | http | standard | Section 3.2 | If-None-Match standard 13.1.2
| If-Unmodified-Since | http | standard | Section 3.4 | If-Range standard 13.1.5
| Last-Modified | http | standard | Section 2.2 | If-Unmodified-Since standard 13.1.4
| Location | http | standard | Section 7.1.2 | Last-Modified standard 8.8.2
| Max-Forwards | http | standard | Section 5.1.2 | Location standard 10.2.3
| Proxy-Authenticate | http | standard | Section 4.3 | Max-Forwards standard 7.6.2
| Proxy-Authorization | http | standard | Section 4.4 | Proxy-Authenticate standard 11.7.1
| Range | http | standard | Section 3.1 | Proxy-Authentication-Info standard 11.7.3
| Referer | http | standard | Section 5.5.2 | Proxy-Authorization standard 11.7.2
| Retry-After | http | standard | Section 7.1.3 | Range standard 14.2
| Server | http | standard | Section 7.4.2 | Referer standard 10.1.3
| TE | http | standard | Section 4.3 | Retry-After standard 10.2.4
| Trailer | http | standard | Section 4.4 | Server standard 10.2.5
| Upgrade | http | standard | Section 6.7 | TE standard 10.1.4
| User-Agent | http | standard | Section 5.5.3 | Trailer standard 10.1.5
| Vary | http | standard | Section 7.1.4 | Upgrade standard 7.8
| Via | http | standard | Section 5.7.1 | User-Agent standard 10.1.6
| WWW-Authenticate | http | standard | Section 4.1 | Vary standard 12.5.5
+-------------------+----------+----------+-----------------+ Via standard 7.6.3
WWW-Authenticate standard 11.6.1
* standard 12.5.5 (reserved)
--------------------------- ------------ -------- ------------
Table 9
The field name "*" is reserved, since using that name as an HTTP
header field might conflict with its special semantics in the Vary
header field (Section 12.5.5).
Finally, please update the "Content-MD5" entry in the new registry to
have a status of 'obsoleted' with references to Section 14.15 of
[RFC2616] (for the definition of the header field) and Appendix B of
[RFC7231] (which removed the field definition from the updated
specification).
18.5. Authentication Scheme Registration 18.5. Authentication Scheme Registration
The "Hypertext Transfer Protocol (HTTP) Authentication Scheme Please update the "Hypertext Transfer Protocol (HTTP) Authentication
Registry" defines the namespace for the authentication schemes in Scheme Registry" at <https://www.iana.org/assignments/http-
challenges and credentials. It has been created and is now authschemes> with the registration procedure of Section 16.4.1. No
maintained at <http://www.iana.org/assignments/http-authschemes>. authentication schemes are defined in this document.
18.6. Content Coding Registration 18.6. Content Coding Registration
IANA maintains the "HTTP Content Coding Registry" at Please update the "HTTP Content Coding Registry" at
<http://www.iana.org/assignments/http-parameters>. <https://www.iana.org/assignments/http-parameters/> with the
The "HTTP Content Coding Registry" has been updated with the registration procedure of Section 16.6.1 and the content coding names
registrations below: summarized in the table below.
+------------+--------------------------------------+---------------+ ------------ ------------------------------------------- ---------
| Name | Description | Reference | Name Description Ref.
+------------+--------------------------------------+---------------+ ------------ ------------------------------------------- ---------
| compress | UNIX "compress" data format [Welch] | Section 4.2.1 | compress UNIX "compress" data format [Welch] 8.4.1.1
| deflate | "deflate" compressed data | Section 4.2.2 | deflate "deflate" compressed data ([RFC1951]) 8.4.1.2
| | ([RFC1951]) inside the "zlib" data | | inside the "zlib" data format ([RFC1950])
| | format ([RFC1950]) | | gzip GZIP file format [RFC1952] 8.4.1.3
| gzip | GZIP file format [RFC1952] | Section 4.2.3 | identity Reserved 12.5.3
| identity | Reserved (synonym for "no encoding" in | Section 5.3.4 | x-compress Deprecated (alias for compress) 8.4.1.1
| | Accept-Encoding) | | x-gzip Deprecated (alias for gzip) 8.4.1.3
| x-compress | Deprecated (alias for compress) | Section 4.2.1 | ------------ ------------------------------------------- ---------
| x-gzip | Deprecated (alias for gzip) | Section 4.2.3 |
+------------+--------------------------------------+---------------+ Table 10
18.7. Range Unit Registration 18.7. Range Unit Registration
The initial range unit registry contains the registrations below: Please update the "HTTP Range Unit Registry" at
<https://www.iana.org/assignments/http-parameters/> with the
registration procedure of Section 16.5.1 and the range unit names
summarized in the table below.
+------------+-----------------------------------------+------------+ ----------------- ---------------------------------- --------
Range Unit Name Description Ref. Range Unit Name Description Ref.
| Name | | | ----------------- ---------------------------------- --------
+------------+-----------------------------------------+------------+ bytes a range of octets 14.1.2
| bytes | a range of octets | Section 2.1 | none reserved as keyword to indicate 14.3
| none | reserved as keyword, indicating no | Section 2.3 | range requests are not supported
| | ranges are supported | | ----------------- ---------------------------------- --------
+------------+-----------------------------------------+------------+
Table 11
18.8. Media Type Registration 18.8. Media Type Registration
IANA maintains the registry of Internet media types [BCP13] at Please update the "Media Types" registry at
<http://www.iana.org/assignments/media-types>. <https://www.iana.org/assignments/media-types> with the registration
information in Section 14.6 for the media type "multipart/
byteranges".
18.9. Port Registration 18.9. Port Registration
[new] Please update the "Service Name and Transport Protocol Port Number"
registry at <https://www.iana.org/assignments/service-names-port-
numbers/> for the services on ports 80 and 443 that use UDP or TCP
to:
1. use this document as "Reference", and
2. when currently unspecified, set "Assignee" to "IESG" and
"Contact" to "IETF_Chair".
18.10. Upgrade Token Registration 18.10. Upgrade Token Registration
The "HTTP" entry in the upgrade token registry has been updated with Please update the "Hypertext Transfer Protocol (HTTP) Upgrade Token
the registration below: Registry" at <https://www.iana.org/assignments/http-upgrade-tokens>
with the registration procedure of Section 16.7 and the upgrade token
names summarized in the following table.
+-------+----------------------+----------------------+-------------+ ------ ------------------- ------------------------- ------
| Value | Description | Expected Version | Reference | Name Description Expected Version Tokens Ref.
| | | Tokens | | ------ ------------------- ------------------------- ------
+-------+----------------------+----------------------+-------------+ HTTP Hypertext any DIGIT.DIGIT (e.g, 2.5
| HTTP | Hypertext Transfer | any DIGIT.DIGIT | Section 2.6 | Transfer Protocol "2.0")
| | Protocol | (e.g, "2.0") | | ------ ------------------- ------------------------- ------
+-------+----------------------+----------------------+-------------+
Table 12
19. References 19. References
19.1. Normative References 19.1. Normative References
[new] [Caching] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", Work in Progress, Internet-Draft,
draft-ietf-httpbis-cache-14, January 13, 2021,
<https://tools.ietf.org/html/draft-ietf-httpbis-cache-14>.
[new] [Messaging]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", Work in Progress, Internet-Draft, draft-
ietf-httpbis-messaging-14, January 13, 2021,
<https://tools.ietf.org/html/draft-ietf-httpbis-messaging-
14>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC1950] Deutsch, L.P. and J-L. Gailly, "ZLIB Compressed Data
Format Specification version 3.3", RFC 1950,
DOI 10.17487/RFC1950, May 1996,
<https://www.rfc-editor.org/info/rfc1950>.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, DOI 10.17487/RFC1951, May 1996,
<https://www.rfc-editor.org/info/rfc1951>.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L.P., and
G. Randers-Pehrson, "GZIP file format specification
version 4.3", RFC 1952, DOI 10.17487/RFC1952, May 1996,
<https://www.rfc-editor.org/info/rfc1952>.
[RFC2045] Freed, N. and N.S. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996. Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996. DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005. RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4647] Phillips, A., Ed. and M. Davis, Ed., "Matching of Language [RFC4647] Phillips, A., Ed. and M. Davis, Ed., "Matching of Language
Tags", BCP 47, RFC 4647, September 2006. Tags", BCP 47, RFC 4647, DOI 10.17487/RFC4647, September
2006, <https://www.rfc-editor.org/info/rfc4647>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006. Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, September 2009. Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365, Internationalization in the IETF", BCP 166, RFC 6365,
September 2011. DOI 10.17487/RFC6365, September 2011,
<https://www.rfc-editor.org/info/rfc6365>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7405, DOI 10.17487/RFC7405, December 2014,
RFC 7230, June 2014. <https://www.rfc-editor.org/info/rfc7405>.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
Protocol (HTTP/1.1): Conditional Requests", RFC 7232, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
June 2014. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests", Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
RFC 7233, June 2014. <https://www.rfc-editor.org/info/rfc8446>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [USASCII] American National Standards Institute, "Coded Character
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", Set -- 7-bit American Standard Code for Information
RFC 7234, June 2014. Interchange", ANSI X3.4, 1986.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [Welch] Welch, T. A., "A Technique for High-Performance Data
Protocol (HTTP/1.1): Authentication", RFC 7235, June 2014. Compression", IEEE Computer 17(6),
DOI 10.1109/MC.1984.1659158, June 1984,
<https://ieeexplore.ieee.org/document/1659158/>.
19.2. Informative References 19.2. Informative References
[BCP115] Hansen, T., Hardie, T., and L. Masinter, "Guidelines
and Registration Procedures for New URI Schemes",
BCP 115, RFC 4395, February 2006.
[BCP13] Freed, N., Klensin, J., and T. Hansen, "Media Type [BCP13] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, January 2013. RFC 6838, January 2013,
<https://www.rfc-editor.org/info/bcp13>.
[BCP178] Saint-Andre, P., Crocker, D., and M. Nottingham, [BCP178] Saint-Andre, P., Crocker, D., and M. Nottingham,
"Deprecating the "X-" Prefix and Similar Constructs in "Deprecating the "X-" Prefix and Similar Constructs in
Application Protocols", BCP 178, RFC 6648, June 2012. Application Protocols", BCP 178, RFC 6648, June 2012,
<https://www.rfc-editor.org/info/bcp178>.
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration [BCP35] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
Procedures for Message Header Fields", BCP 90, RFC 3864, and Registration Procedures for URI Schemes", BCP 35,
September 2004. RFC 7595, June 2015,
<https://www.rfc-editor.org/info/bcp35>.
[Georgiev] Georgiev, M., Iyengar, S., Jana, S., Anubhai, R., [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the
Boneh, D., and V. Shmatikov, "The Most Dangerous Code CRIME Attack", July 2013,
in the World: Validating SSL Certificates in Non- <http://breachattack.com/resources/
browser Software", In Proceedings of the 2012 ACM BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
Conference on Computer and Communications Security (CCS
'12), pp. 38-49, October 2012, [Bujlow] Bujlow, T., Carela-Espanol, V., Sole-Pareta, J., and P.
<http://doi.acm.org/10.1145/2382196.2382204>. Barlet-Ros, "A Survey on Web Tracking: Mechanisms,
Implications, and Defenses",
DOI 10.1109/JPROC.2016.2637878, Proceedings of the
IEEE 105(8), August 2017,
<https://doi.org/10.1109/JPROC.2016.2637878>.
[Err1912] RFC Errata, Erratum ID 1912, RFC 2978,
<https://www.rfc-editor.org/errata/eid1912>.
[Err5433] RFC Errata, Erratum ID 5433, RFC 2978,
<https://www.rfc-editor.org/errata/eid5433>.
[Georgiev] Georgiev, M., Iyengar, S., Jana, S., Anubhai, R., Boneh,
D., and V. Shmatikov, "The Most Dangerous Code in the
World: Validating SSL Certificates in Non-browser
Software", DOI 10.1145/2382196.2382204, In Proceedings of
the 2012 ACM Conference on Computer and Communications
Security (CCS '12), pp. 38-49, October 2012,
<https://doi.org/10.1145/2382196.2382204>.
[HTTP3] Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-33, December 15, 2020,
<https://tools.ietf.org/html/draft-ietf-quic-http-33>.
[ISO-8859-1]
International Organization for Standardization,
"Information technology -- 8-bit single-byte coded graphic
character sets -- Part 1: Latin alphabet No. 1", ISO/
IEC 8859-1:1998, 1998.
[Kri2001] Kristol, D., "HTTP Cookies: Standards, Privacy, and
Politics", ACM Transactions on Internet Technology 1(2),
November 2001, <http://arxiv.org/abs/cs.SE/0105018>.
[OWASP] van der Stock, A., Ed., "A Guide to Building Secure Web [OWASP] van der Stock, A., Ed., "A Guide to Building Secure Web
Applications and Web Services", The Open Web Application Applications and Web Services", The Open Web Application
Security Project (OWASP) 2.0.1, July 2005, Security Project (OWASP) 2.0.1, July 27, 2005,
<https://www.owasp.org/>. <https://www.owasp.org/>.
[REST] Fielding, R., "Architectural Styles and the Design of [REST] Fielding, R.T., "Architectural Styles and the Design of
Network-based Software Architectures", Network-based Software Architectures",
Doctoral Dissertation, University of California, Irvine, Doctoral Dissertation, University of California, Irvine,
September 2000, September 2000,
<http://roy.gbiv.com/pubs/dissertation/top.htm>. <https://roy.gbiv.com/pubs/dissertation/top.htm>.
[RFC1919] Chatel, M., "Classical versus Transparent IP Proxies", [RFC1919] Chatel, M., "Classical versus Transparent IP Proxies",
RFC 1919, March 1996. RFC 1919, DOI 10.17487/RFC1919, March 1996,
<https://www.rfc-editor.org/info/rfc1919>.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext [RFC1945] Berners-Lee, T., Fielding, R.T., and H.F. Nielsen,
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. "Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945,
DOI 10.17487/RFC1945, May 1996,
<https://www.rfc-editor.org/info/rfc1945>.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, DOI 10.17487/RFC2047, November 1996,
<https://www.rfc-editor.org/info/rfc2047>.
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. [RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2068, January 1997. RFC 2068, DOI 10.17487/RFC2068, January 1997,
<https://www.rfc-editor.org/info/rfc2068>.
[RFC2145] Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, [RFC2145] Mogul, J.C., Fielding, R.T., Gettys, J., and H.F. Nielsen,
"Use and Interpretation of HTTP Version Numbers", "Use and Interpretation of HTTP Version Numbers",
RFC 2145, May 1997. RFC 2145, DOI 10.17487/RFC2145, May 1997,
<https://www.rfc-editor.org/info/rfc2145>.
[RFC2295] Holtman, K. and A. Mutz, "Transparent Content Negotiation [RFC2295] Holtman, K. and A.H. Mutz, "Transparent Content
in HTTP", RFC 2295, March 1998. Negotiation in HTTP", RFC 2295, DOI 10.17487/RFC2295,
March 1998, <https://www.rfc-editor.org/info/rfc2295>.
[RFC2388] Masinter, L., "Returning Values from Forms: multipart/ [RFC2324] Masinter, L., "Hyper Text Coffee Pot Control Protocol
form-data", RFC 2388, August 1998. (HTCPCP/1.0)", RFC 2324, DOI 10.17487/RFC2324, April 1,
1998, <https://www.rfc-editor.org/info/rfc2324>.
[RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud, [RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud,
"MIME Encapsulation of Aggregate Documents, such as HTML "MIME Encapsulation of Aggregate Documents, such as HTML
(MHTML)", RFC 2557, March 1999. (MHTML)", RFC 2557, DOI 10.17487/RFC2557, March 1999,
<https://www.rfc-editor.org/info/rfc2557>.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Transfer Protocol -- HTTP/1.1", RFC 2616,
DOI 10.17487/RFC2616, June 1999,
<https://www.rfc-editor.org/info/rfc2616>.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., [RFC2617] Franks, J., Hallam-Baker, P.M., Hostetler, J.L., Lawrence,
Leach, P., Luotonen, A., and L. Stewart, "HTTP S.D., Leach, P.J., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication", Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999. RFC 2617, DOI 10.17487/RFC2617, June 1999,
<https://www.rfc-editor.org/info/rfc2617>.
[RFC2774] Frystyk, H., Leach, P., and S. Lawrence, "An HTTP [RFC2774] Frystyk, H., Leach, P., and S. Lawrence, "An HTTP
Extension Framework", RFC 2774, February 2000. Extension Framework", RFC 2774, DOI 10.17487/RFC2774,
February 2000, <https://www.rfc-editor.org/info/rfc2774>.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, May 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC2978] Freed, N. and J. Postel, "IANA Charset Registration [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, October 2000. Procedures", BCP 19, RFC 2978, DOI 10.17487/RFC2978,
October 2000, <https://www.rfc-editor.org/info/rfc2978>.
[RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC 3040,
January 2001.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
Rose, "DNS Security Introduction and Requirements", Replication and Caching Taxonomy", RFC 3040,
RFC 4033, March 2005. DOI 10.17487/RFC3040, January 2001,
<https://www.rfc-editor.org/info/rfc3040>.
[RFC4559] Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Kerberos and NTLM HTTP Authentication in Microsoft Procedures for Message Header Fields", BCP 90, RFC 3864,
Windows", RFC 4559, June 2006. DOI 10.17487/RFC3864, September 2004,
<https://www.rfc-editor.org/info/rfc3864>.
[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Authoring and Versioning (WebDAV)", RFC 4918, June 2007. Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC4559] Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based
IANA Considerations Section in RFCs", BCP 26, RFC 5226, Kerberos and NTLM HTTP Authentication in Microsoft
May 2008. Windows", RFC 4559, DOI 10.17487/RFC4559, June 2006,
<https://www.rfc-editor.org/info/rfc4559>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC4918] Dusseault, L.M., Ed., "HTTP Extensions for Web Distributed
(TLS) Protocol Version 1.2", RFC 5246, August 2008. Authoring and Versioning (WebDAV)", RFC 4918,
DOI 10.17487/RFC4918, June 2007,
<https://www.rfc-editor.org/info/rfc4918>.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322, [RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008. DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP", [RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, March 2010. RFC 5789, DOI 10.17487/RFC5789, March 2010,
<https://www.rfc-editor.org/info/rfc5789>.
[RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale
Content", RFC 5861, April 2010.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms "Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010. Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC5987] Reschke, J., "Character Set and Language Encoding for [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
Hypertext Transfer Protocol (HTTP) Header Field DOI 10.17487/RFC6265, April 2011,
Parameters", RFC 5987, August 2010. <https://www.rfc-editor.org/info/rfc6265>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010. [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/info/rfc6454>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
April 2011. Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012,
<https://www.rfc-editor.org/info/rfc6585>.
[RFC6266] Reschke, J., "Use of the Content-Disposition Header Field [RFC7230] Fielding, R., Ed. and J. F. Reschke, Ed., "Hypertext
in the Hypertext Transfer Protocol (HTTP)", RFC 6266, Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
June 2011. RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7238] Reschke, J., "The Hypertext Transfer Protocol (HTTP) [RFC7231] Fielding, R., Ed. and J. F. Reschke, Ed., "Hypertext
Status Code 308 (Permanent Redirect)", RFC 7238, Transfer Protocol (HTTP/1.1): Semantics and Content",
June 2014. RFC 7231, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7232] Fielding, R., Ed. and J. F. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Conditional Requests",
RFC 7232, DOI 10.17487/RFC7232, June 2014,
<https://www.rfc-editor.org/info/rfc7232>.
[RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. F. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
RFC 7233, DOI 10.17487/RFC7233, June 2014,
<https://www.rfc-editor.org/info/rfc7233>.
[RFC7235] Fielding, R., Ed. and J. F. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014,
<https://www.rfc-editor.org/info/rfc7235>.
[RFC7538] Reschke, J. F., "The Hypertext Transfer Protocol Status
Code 308 (Permanent Redirect)", RFC 7538,
DOI 10.17487/RFC7538, April 2015,
<https://www.rfc-editor.org/info/rfc7538>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<https://www.rfc-editor.org/info/rfc7541>.
[RFC7578] Masinter, L., "Returning Values from Forms: multipart/
form-data", RFC 7578, DOI 10.17487/RFC7578, July 2015,
<https://www.rfc-editor.org/info/rfc7578>.
[RFC7615] Reschke, J. F., "HTTP Authentication-Info and Proxy-
Authentication-Info Response Header Fields", RFC 7615,
DOI 10.17487/RFC7615, September 2015,
<https://www.rfc-editor.org/info/rfc7615>.
[RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
Digest Access Authentication", RFC 7616,
DOI 10.17487/RFC7616, September 2015,
<https://www.rfc-editor.org/info/rfc7616>.
[RFC7617] Reschke, J. F., "The 'Basic' HTTP Authentication Scheme",
RFC 7617, DOI 10.17487/RFC7617, September 2015,
<https://www.rfc-editor.org/info/rfc7617>.
[RFC7694] Reschke, J. F., "Hypertext Transfer Protocol (HTTP)
Client-Initiated Content-Encoding", RFC 7694,
DOI 10.17487/RFC7694, November 2015,
<https://www.rfc-editor.org/info/rfc7694>.
[RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
April 2016, <https://www.rfc-editor.org/info/rfc7838>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8187] Reschke, J. F., "Indicating Character Encoding and
Language for HTTP Header Field Parameters", RFC 8187,
DOI 10.17487/RFC8187, September 2017,
<https://www.rfc-editor.org/info/rfc8187>.
[RFC8246] McManus, P., "HTTP Immutable Responses", RFC 8246,
DOI 10.17487/RFC8246, September 2017,
<https://www.rfc-editor.org/info/rfc8246>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
[RFC8336] Nottingham, M. and E. Nygren, "The ORIGIN HTTP/2 Frame",
RFC 8336, DOI 10.17487/RFC8336, March 2018,
<https://www.rfc-editor.org/info/rfc8336>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
[RFCSTRF] Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-header-structure-19, June 2020,
<https://tools.ietf.org/html/draft-ietf-httpbis-header-
structure-19>.
[Sniffing] WHATWG, "MIME Sniffing",
<https://mimesniff.spec.whatwg.org>.
Appendix A. Collected ABNF Appendix A. Collected ABNF
In the collected ABNF below, list rules are expanded as per In the collected ABNF below, list rules are expanded as per
Section 1.2 of [RFC7230]. Section 5.6.1.1.
Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [ Accept = [ ( media-range [ weight ] ) *( OWS "," OWS ( media-range [
OWS ( media-range [ accept-params ] ) ] ) ] weight ] ) ) ]
Accept-Charset = *( "," OWS ) ( ( charset / "*" ) [ weight ] ) *( OWS Accept-Charset = [ ( ( charset / "*" ) [ weight ] ) *( OWS "," OWS (
"," [ OWS ( ( charset / "*" ) [ weight ] ) ] ) ( charset / "*" ) [ weight ] ) ) ]
Accept-Encoding = [ ( "," / ( codings [ weight ] ) ) *( OWS "," [ OWS Accept-Encoding = [ ( codings [ weight ] ) *( OWS "," OWS ( codings [
( codings [ weight ] ) ] ) ] weight ] ) ) ]
Accept-Language = *( "," OWS ) ( language-range [ weight ] ) *( OWS Accept-Language = [ ( language-range [ weight ] ) *( OWS "," OWS (
"," [ OWS ( language-range [ weight ] ) ] ) language-range [ weight ] ) ) ]
Allow = [ ( "," / method ) *( OWS "," [ OWS method ] ) ] Accept-Ranges = acceptable-ranges
Allow = [ method *( OWS "," OWS method ) ]
Authentication-Info = [ auth-param *( OWS "," OWS auth-param ) ]
Authorization = credentials
BWS = <BWS, see [RFC7230], Section 3.2.3> BWS = OWS
Content-Encoding = *( "," OWS ) content-coding *( OWS "," [ OWS Connection = [ connection-option *( OWS "," OWS connection-option )
content-coding ] ) ]
Content-Language = *( "," OWS ) language-tag *( OWS "," [ OWS Content-Encoding = [ content-coding *( OWS "," OWS content-coding )
language-tag ] ) ]
Content-Language = [ language-tag *( OWS "," OWS language-tag ) ]
Content-Length = 1*DIGIT
Content-Location = absolute-URI / partial-URI Content-Location = absolute-URI / partial-URI
Content-Range = range-unit SP ( range-resp / unsatisfied-range )
Content-Type = media-type Content-Type = media-type
Date = HTTP-date Date = HTTP-date
Expect = "100-continue" ETag = entity-tag
Expect = [ expectation *( OWS "," OWS expectation ) ]
From = mailbox From = mailbox
GMT = %x47.4D.54 ; GMT GMT = %x47.4D.54 ; GMT
HTTP-date = IMF-fixdate / obs-date HTTP-date = IMF-fixdate / obs-date
Host = uri-host [ ":" port ]
IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT
If-Match = "*" / [ entity-tag *( OWS "," OWS entity-tag ) ]
If-Modified-Since = HTTP-date
If-None-Match = "*" / [ entity-tag *( OWS "," OWS entity-tag ) ]
If-Range = entity-tag / HTTP-date
If-Unmodified-Since = HTTP-date
Last-Modified = HTTP-date
Location = URI-reference Location = URI-reference
Max-Forwards = 1*DIGIT Max-Forwards = 1*DIGIT
OWS = <OWS, see [RFC7230], Section 3.2.3> OWS = *( SP / HTAB )
RWS = <RWS, see [RFC7230], Section 3.2.3> Proxy-Authenticate = [ challenge *( OWS "," OWS challenge ) ]
Proxy-Authentication-Info = [ auth-param *( OWS "," OWS auth-param )
]
Proxy-Authorization = credentials
RWS = 1*( SP / HTAB )
Range = ranges-specifier
Referer = absolute-URI / partial-URI Referer = absolute-URI / partial-URI
Retry-After = HTTP-date / delay-seconds Retry-After = HTTP-date / delay-seconds
Server = product *( RWS ( product / comment ) ) Server = product *( RWS ( product / comment ) )
URI-reference = <URI-reference, see [RFC7230], Section 2.7> TE = [ t-codings *( OWS "," OWS t-codings ) ]
Trailer = [ field-name *( OWS "," OWS field-name ) ]
URI-reference = <URI-reference, see [RFC3986], Section 4.1>
Upgrade = [ protocol *( OWS "," OWS protocol ) ]
User-Agent = product *( RWS ( product / comment ) ) User-Agent = product *( RWS ( product / comment ) )
Vary = "*" / ( *( "," OWS ) field-name *( OWS "," [ OWS field-name ] Vary = [ ( "*" / field-name ) *( OWS "," OWS ( "*" / field-name ) )
) ) ]
Via = [ ( received-protocol RWS received-by [ RWS comment ] ) *( OWS
"," OWS ( received-protocol RWS received-by [ RWS comment ] ) ) ]
absolute-URI = <absolute-URI, see [RFC7230], Section 2.7> WWW-Authenticate = [ challenge *( OWS "," OWS challenge ) ]
accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
accept-params = weight *accept-ext absolute-URI = <absolute-URI, see [RFC3986], Section 4.3>
absolute-path = 1*( "/" segment )
acceptable-ranges = ( range-unit *( OWS "," OWS range-unit ) ) /
"none"
asctime-date = day-name SP date3 SP time-of-day SP year asctime-date = day-name SP date3 SP time-of-day SP year
auth-param = token BWS "=" BWS ( token / quoted-string )
auth-scheme = token
authority = <authority, see [RFC3986], Section 3.2>
challenge = auth-scheme [ 1*SP ( token68 / [ auth-param *( OWS ","
OWS auth-param ) ] ) ]
charset = token charset = token
codings = content-coding / "identity" / "*" codings = content-coding / "identity" / "*"
comment = <comment, see [RFC7230], Section 3.2.6> comment = "(" *( ctext / quoted-pair / comment ) ")"
complete-length = 1*DIGIT
connection-option = token
content-coding = token content-coding = token
credentials = auth-scheme [ 1*SP ( token68 / [ auth-param *( OWS ","
OWS auth-param ) ] ) ]
ctext = HTAB / SP / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
date1 = day SP month SP year date1 = day SP month SP year
date2 = day "-" month "-" 2DIGIT date2 = day "-" month "-" 2DIGIT
date3 = month SP ( 2DIGIT / ( SP DIGIT ) ) date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
day = 2DIGIT day = 2DIGIT
day-name = %x4D.6F.6E ; Mon day-name = %x4D.6F.6E ; Mon
/ %x54.75.65 ; Tue / %x54.75.65 ; Tue
/ %x57.65.64 ; Wed / %x57.65.64 ; Wed
/ %x54.68.75 ; Thu / %x54.68.75 ; Thu
/ %x46.72.69 ; Fri / %x46.72.69 ; Fri
skipping to change at line 8375 skipping to change at page 205, line 11
/ %x53.75.6E ; Sun / %x53.75.6E ; Sun
day-name-l = %x4D.6F.6E.64.61.79 ; Monday day-name-l = %x4D.6F.6E.64.61.79 ; Monday
/ %x54.75.65.73.64.61.79 ; Tuesday / %x54.75.65.73.64.61.79 ; Tuesday
/ %x57.65.64.6E.65.73.64.61.79 ; Wednesday / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
/ %x54.68.75.72.73.64.61.79 ; Thursday / %x54.68.75.72.73.64.61.79 ; Thursday
/ %x46.72.69.64.61.79 ; Friday / %x46.72.69.64.61.79 ; Friday
/ %x53.61.74.75.72.64.61.79 ; Saturday / %x53.61.74.75.72.64.61.79 ; Saturday
/ %x53.75.6E.64.61.79 ; Sunday / %x53.75.6E.64.61.79 ; Sunday
delay-seconds = 1*DIGIT delay-seconds = 1*DIGIT
field-name = <comment, see [RFC7230], Section 3.2> entity-tag = [ weak ] opaque-tag
etagc = "!" / %x23-7E ; '#'-'~'
/ obs-text
expectation = token [ "=" ( token / quoted-string ) parameters ]
field-content = field-vchar [ 1*( SP / HTAB / field-vchar )
field-vchar ]
field-name = token
field-value = *field-content
field-vchar = VCHAR / obs-text
first-pos = 1*DIGIT
hour = 2DIGIT hour = 2DIGIT
http-URI = "http://" authority path-abempty [ "?" query ]
https-URI = "https://" authority path-abempty [ "?" query ]
incl-range = first-pos "-" last-pos
int-range = first-pos "-" [ last-pos ]
language-range = <language-range, see [RFC4647], Section 2.1> language-range = <language-range, see [RFC4647], Section 2.1>
language-tag = <Language-Tag, see [RFC5646], Section 2.1> language-tag = <Language-Tag, see [RFC5646], Section 2.1>
last-pos = 1*DIGIT
mailbox = <mailbox, see [RFC5322], Section 3.4> mailbox = <mailbox, see [RFC5322], Section 3.4>
media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) )
";" OWS parameter ) parameters
media-type = type "/" subtype parameters
media-type = type "/" subtype *( OWS ";" OWS parameter )
method = token method = token
minute = 2DIGIT minute = 2DIGIT
month = %x4A.61.6E ; Jan month = %x4A.61.6E ; Jan
/ %x46.65.62 ; Feb / %x46.65.62 ; Feb
/ %x4D.61.72 ; Mar / %x4D.61.72 ; Mar
/ %x41.70.72 ; Apr / %x41.70.72 ; Apr
/ %x4D.61.79 ; May / %x4D.61.79 ; May
/ %x4A.75.6E ; Jun / %x4A.75.6E ; Jun
/ %x4A.75.6C ; Jul / %x4A.75.6C ; Jul
/ %x41.75.67 ; Aug / %x41.75.67 ; Aug
/ %x53.65.70 ; Sep / %x53.65.70 ; Sep
/ %x4F.63.74 ; Oct / %x4F.63.74 ; Oct
/ %x4E.6F.76 ; Nov / %x4E.6F.76 ; Nov
/ %x44.65.63 ; Dec / %x44.65.63 ; Dec
obs-date = rfc850-date / asctime-date obs-date = rfc850-date / asctime-date
obs-text = %x80-FF
opaque-tag = DQUOTE *etagc DQUOTE
other-range = 1*( %x21-2B ; '!'-'+'
/ %x2D-7E ; '-'-'~'
)
parameter = token "=" ( token / quoted-string ) parameter = parameter-name "=" parameter-value
partial-URI = <partial-URI, see [RFC7230], Section 2.7> parameter-name = token
parameter-value = ( token / quoted-string )
parameters = *( OWS ";" OWS [ parameter ] )
partial-URI = relative-part [ "?" query ]
path-abempty = <path-abempty, see [RFC3986], Section 3.3>
port = <port, see [RFC3986], Section 3.2.3>
product = token [ "/" product-version ] product = token [ "/" product-version ]
product-version = token product-version = token
quoted-string = <quoted-string, see [RFC7230], Section 3.2.6> protocol = protocol-name [ "/" protocol-version ]
protocol-name = token
protocol-version = token
pseudonym = token
qdtext = HTAB / SP / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
query = <query, see [RFC3986], Section 3.4>
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] ) qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
range-resp = incl-range "/" ( complete-length / "*" )
range-set = range-spec *( OWS "," OWS range-spec )
range-spec = int-range / suffix-range / other-range
range-unit = token
ranges-specifier = range-unit "=" range-set
received-by = pseudonym [ ":" port ]
received-protocol = [ protocol-name "/" ] protocol-version
relative-part = <relative-part, see [RFC3986], Section 4.2>
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
second = 2DIGIT second = 2DIGIT
segment = <segment, see [RFC3986], Section 3.3>
subtype = token subtype = token
suffix-length = 1*DIGIT
suffix-range = "-" suffix-length
t-codings = "trailers" / ( transfer-coding [ weight ] )
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
"^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
time-of-day = hour ":" minute ":" second time-of-day = hour ":" minute ":" second
token = <token, see [RFC7230], Section 3.2.6> token = 1*tchar
token68 = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" )
*"="
transfer-coding = token *( OWS ";" OWS transfer-parameter )
transfer-parameter = token BWS "=" BWS ( token / quoted-string )
type = token type = token
unsatisfied-range = "*/" complete-length
uri-host = <host, see [RFC3986], Section 3.2.2>
weak = %x57.2F ; W/
weight = OWS ";" OWS "q=" qvalue weight = OWS ";" OWS "q=" qvalue
year = 4DIGIT year = 4DIGIT
Appendix B. Changes from RFC 2616 Appendix B. Changes from previous RFCs
[elided]
B.1. Changes from RFC 2818 B.1. Changes from RFC 2818
None.
B.2. Changes from RFC 7230 B.2. Changes from RFC 7230
The sections introducing HTTP's design goals, history, architecture,
conformance criteria, protocol versioning, URIs, message routing, and
header fields have been moved here (without substantive change).
The description of an origin and authoritative access to origin
servers has been extended for both "http" and "https" URIs to account
for alternative services and secured connections that are not
necessarily based on TCP. (Section 4.2.1, Section 4.2.2,
Section 4.3.1, Section 7.3.3)
"Field value" now refers to the value after multiple field lines are
combined with commas - by far the most common use. To refer to a
single header line's value, use "field line value". (Section 6.3)
Parameters in media type, media range, and expectation can be empty
via one or more trailing semicolons. (Section 5.6.6)
Trailer field semantics now transcend the specifics of chunked
encoding. Use of trailer fields has been further limited to only
allow generation as a trailer field when the sender knows the field
defines that usage and to only allow merging into the header section
if the recipient knows the corresponding field definition permits and
defines how to merge. In all other cases, implementations are
encouraged to either store the trailer fields separately or discard
them instead of merging. (Section 6.5.1)
Trailer fields can now potentially appear as multiple trailer
sections, if allowed by the HTTP version and framing in use, with
processing described as being iterative as each section is received.
(Section 6.5.2)
Made the priority of the absolute form of the request URI over the
Host header by origin servers explicit, to align with proxy handling.
(Section 7.2)
The grammar definition for the Via field's "received-by" was expanded
in 7230 due to changes in the URI grammar for host [RFC3986] that are
not desirable for Via. For simplicity, we have removed uri-host from
the received-by production because it can be encompassed by the
existing grammar for pseudonym. In particular, this change removed
comma from the allowed set of charaters for a host name in received-
by. (Section 7.6.3)
B.3. Changes from RFC 7231 B.3. Changes from RFC 7231
Minimum URI lengths to be supported by implementations are now
recommended. (Section 3.1)
Clarify that control characters in field values are to be rejected or
mapped to SP. (Section 5.5)
Parameters in media type, media range, and expectation can be empty
via one or more trailing semicolons. (Section 5.6.6)
An abstract data type for HTTP messages has been introduced to define
the components of a message and their semantics as an abstraction
across multiple HTTP versions, rather than in terms of the specific
syntax form of HTTP/1.1 in [Messaging], and reflect the contents
after the message is parsed. This makes it easier to distinguish
between requirements on the content (what is conveyed) versus
requirements on the messaging syntax (how it is conveyed) and avoids
baking limitations of early protocol versions into the future of
HTTP. (Section 6)
The term "effective request URI" has been replaced with "target URI".
(Section 7.1)
Restrictions on client retries have been loosened, to reflect
implementation behavior. (Section 9.2.2)
Clarified that request bodies on GET and DELETE are not
interoperable. (Section 9.3.1, Section 9.3.5)
Removed a superfluous requirement about setting Content-Length from
the description of the OPTIONS method. (Section 9.3.7)
Restore list-based grammar for Expect for compatibility with RFC
2616. (Section 10.1.1)
Allow Accept and Accept-Encoding in response messages; the latter was
introduced by [RFC7694]. (Section 12.3)
"Accept Parameters" (accept-params) have been removed from the
definition of the Accept field. (Section 12.5.1)
The semantics of "*" in the Vary header field when other values are
present was clarified. (Section 12.5.5)
Range units are compared in a case insensitive fashion.
(Section 14.1)
The process of creating a redirected request has been clarified.
(Section 15.4)
Added status code 308 (previously defined in [RFC7538]) so that it's
defined closer to status codes 301, 302, and 307. (Section 15.4.9)
Added status code 421 (previously defined in Section 9.1.2 of
[RFC7540]) because of its general applicability. 421 is no longer
defined as heuristically cacheable, since the response is specific to
the connection (not the target resource). (Section 15.5.20)
Added status code 422 (previously defined in Section 11.2 of
[RFC4918]) because of its general applicability. (Section 15.5.21)
Allowed use of the Content-Range header field (Section 14.4) as a
request modifier on PUT. (Section 9.3.4)
B.4. Changes from RFC 7232 B.4. Changes from RFC 7232
Previous revisions of HTTP imposed an arbitrary 60-second limit on
the determination of whether Last-Modified was a strong validator to
guard against the possibility that the Date and Last-Modified values
are generated from different clocks or at somewhat different times
during the preparation of the response. This specification has
relaxed that to allow reasonable discretion. (Section 8.8.2.2)
Removed edge case requirement on If-Match and If-Unmodified-Since
that a validator not be sent in a 2xx response when validation fails
and the server decides that the same change request has already been
applied. (Section 13.1.1 and Section 13.1.4)
Clarified that If-Unmodified-Since doesn't apply to a resource
without a concept of modification time. (Section 13.1.4)
Preconditions can now be evaluated before the request content is
processed rather than waiting until the response would otherwise be
successful. (Section 13.2)
B.5. Changes from RFC 7233 B.5. Changes from RFC 7233
Refactored the range-unit and ranges-specifier grammars to simplify
and reduce artificial distinctions between bytes and other
(extension) range units, removing the overlapping grammar of other-
range-unit by defining range units generically as a token and placing
extensions within the scope of a range-spec (other-range). This
disambiguates the role of list syntax (commas) in all range sets,
including extension range units, for indicating a range-set of more
than one range. Moving the extension grammar into range specifiers
also allows protocol specific to byte ranges to be specified
separately.
It is now possible to define Range handling on extension methods.
(Section 14.2)
Described use of the Content-Range header field (Section 14.4) as a
request modifier to perform a partial PUT. (Section 14.5)
B.6. Changes from RFC 7235 B.6. Changes from RFC 7235
None.
B.7. Changes from RFC 7538 B.7. Changes from RFC 7538
None.
B.8. Changes from RFC 7615 B.8. Changes from RFC 7615
None.
B.9. Changes from RFC 7694 B.9. Changes from RFC 7694
This specification includes the extension defined in [RFC7694], but
leaves out examples and deployment considerations.
Appendix C. Change Log Appendix C. Change Log
This section is to be removed before publishing as an RFC.
C.1. Between RFC723x and draft 00 C.1. Between RFC723x and draft 00
The changes were purely editorial:
o Change boilerplate and abstract to indicate the "draft" status,
and update references to ancestor specifications.
o Remove version "1.1" from document title, indicating that this
specification applies to all HTTP versions.
o Adjust historical notes.
o Update links to sibling specifications.
o Replace sections listing changes from RFC 2616 by new empty
sections referring to RFC 723x.
o Remove acknowledgements specific to RFC 723x.
o Move "Acknowledgements" to the very end and make them unnumbered.
C.2. Since draft-ietf-httpbis-semantics-00 C.2. Since draft-ietf-httpbis-semantics-00
The changes in this draft are editorial, with respect to HTTP as a
whole, to merge core HTTP semantics into this document:
o Merged introduction, architecture, conformance, and ABNF
extensions from RFC 7230 (Messaging).
o Rearranged architecture to extract conformance, http(s) schemes,
and protocol versioning into a separate major section.
o Moved discussion of MIME differences to [Messaging] since that is
primarily concerned with transforming 1.1 messages.
o Merged entire content of RFC 7232 (Conditional Requests).
o Merged entire content of RFC 7233 (Range Requests).
o Merged entire content of RFC 7235 (Auth Framework).
o Moved all extensibility tips, registration procedures, and
registry tables from the IANA considerations to normative
sections, reducing the IANA considerations to just instructions
that will be removed prior to publication as an RFC.
C.3. Since draft-ietf-httpbis-semantics-01 C.3. Since draft-ietf-httpbis-semantics-01
o Improve [Welch] citation (<https://github.com/httpwg/http-core/
issues/63>)
o Remove HTTP/1.1-ism about Range Requests
(<https://github.com/httpwg/http-core/issues/71>)
o Cite RFC 8126 instead of RFC 5226 (<https://github.com/httpwg/
http-core/issues/75>)
o Cite RFC 7538 instead of RFC 7238 (<https://github.com/httpwg/
http-core/issues/76>)
o Cite RFC 8288 instead of RFC 5988 (<https://github.com/httpwg/
http-core/issues/77>)
o Cite RFC 8187 instead of RFC 5987 (<https://github.com/httpwg/
http-core/issues/78>)
o Cite RFC 7578 instead of RFC 2388 (<https://github.com/httpwg/
http-core/issues/79>)
o Cite RFC 7595 instead of RFC 4395 (<https://github.com/httpwg/
http-core/issues/80>)
o improve ABNF readability for qdtext (<https://github.com/httpwg/
http-core/issues/81>, <https://www.rfc-editor.org/errata/eid4891>)
o Clarify "resource" vs "representation" in definition of status
code 416 (<https://github.com/httpwg/http-core/issues/83>,
<https://www.rfc-editor.org/errata/eid4664>)
o Resolved erratum 4072, no change needed here
(<https://github.com/httpwg/http-core/issues/84>,
<https://www.rfc-editor.org/errata/eid4072>)
o Clarify DELETE status code suggestions
(<https://github.com/httpwg/http-core/issues/85>,
<https://www.rfc-editor.org/errata/eid4436>)
o In Section 14.4, fix ABNF for "other-range-resp" to use VCHAR
instead of CHAR (<https://github.com/httpwg/http-core/issues/86>,
<https://www.rfc-editor.org/errata/eid4707>)
o Resolved erratum 5162, no change needed here
(<https://github.com/httpwg/http-core/issues/89>,
<https://www.rfc-editor.org/errata/eid5162>)
o Replace "response code" with "response status code" and "status-
code" (the ABNF production name from the HTTP/1.1 message format)
by "status code" (<https://github.com/httpwg/http-core/issues/94>,
<https://www.rfc-editor.org/errata/eid4050>)
o Added a missing word in Section 15.4 (<https://github.com/httpwg/
http-core/issues/98>, <https://www.rfc-editor.org/errata/eid4452>)
o In Section 5.6.1, fixed an example that had trailing whitespace
where it shouldn't (<https://github.com/httpwg/http-core/
issues/104>, <https://www.rfc-editor.org/errata/eid4169>)
o In Section 15.3.7, remove words that were potentially misleading
with respect to the relation to the requested ranges
(<https://github.com/httpwg/http-core/issues/102>,
<https://www.rfc-editor.org/errata/eid4358>)
C.4. Since draft-ietf-httpbis-semantics-02 C.4. Since draft-ietf-httpbis-semantics-02
o Included (Proxy-)Auth-Info header field definition from RFC 7615
(<https://github.com/httpwg/http-core/issues/9>)
o In Section 9.3.3, clarify POST caching
(<https://github.com/httpwg/http-core/issues/17>)
o Add Section 15.5.19 to reserve the 418 status code
(<https://github.com/httpwg/http-core/issues/43>)
o In Section 3.4 and Section 10.1.1, clarified when a response can
be sent (<https://github.com/httpwg/http-core/issues/82>)
o In Section 8.3.2, explain the difference between the "token"
production, the RFC 2978 ABNF for charset names, and the actual
registration practice (<https://github.com/httpwg/http-core/
issues/100>, <https://www.rfc-editor.org/errata/eid4689>)
o In Section 3.1, removed the fragment component in the URI scheme
definitions as per Section 4.3 of [RFC3986], furthermore moved
fragment discussion into a separate section
(<https://github.com/httpwg/http-core/issues/103>,
<https://www.rfc-editor.org/errata/eid4251>, <https://www.rfc-
editor.org/errata/eid4252>)
o In Section 2.5, add language about minor HTTP version number
defaulting (<https://github.com/httpwg/http-core/issues/115>)
o Added Section 15.5.21 for status code 422, previously defined in
Section 11.2 of [RFC4918] (<https://github.com/httpwg/http-core/
issues/123>)
o In Section 15.5.17, fixed prose about byte range comparison
(<https://github.com/httpwg/http-core/issues/135>,
<https://www.rfc-editor.org/errata/eid5474>)
o In Section 3.4, explain that request/response correlation is
version specific (<https://github.com/httpwg/http-core/
issues/145>)
C.5. Since draft-ietf-httpbis-semantics-03 C.5. Since draft-ietf-httpbis-semantics-03
o In Section 15.4.9, include status code 308 from RFC 7538
(<https://github.com/httpwg/http-core/issues/3>)
o In Section 8.3.1, clarify that the charset parameter value is
case-insensitive due to the definition in RFC 2046
(<https://github.com/httpwg/http-core/issues/13>)
o Define a separate registry for HTTP header field names
(<https://github.com/httpwg/http-core/issues/42>)
o In Section 12.1, refactor and clarify description of wildcard
("*") handling (<https://github.com/httpwg/http-core/issues/46>)
o Deprecate Accept-Charset (<https://github.com/httpwg/http-core/
issues/61>)
o In Section 13.2, mention Cache-Control: immutable
(<https://github.com/httpwg/http-core/issues/69>)
o In Section 5.3, clarify when header field combination is allowed
(<https://github.com/httpwg/http-core/issues/74>)
o In Section 18.4, instruct IANA to mark Content-MD5 as obsolete
(<https://github.com/httpwg/http-core/issues/93>)
o Use RFC 7405 ABNF notation for case-sensitive string constants
(<https://github.com/httpwg/http-core/issues/133>)
o Rework Section 3.4 to be more version-independent
(<https://github.com/httpwg/http-core/issues/142>)
o In Section 9.3.5, clarify that DELETE needs to be successful to
invalidate cache (<https://github.com/httpwg/http-core/
issues/167>, <https://www.rfc-editor.org/errata/eid5541>)
C.6. Since draft-ietf-httpbis-semantics-04 C.6. Since draft-ietf-httpbis-semantics-04
o In Section 5.5, fix field-content ABNF
(<https://github.com/httpwg/http-core/issues/19>,
<https://www.rfc-editor.org/errata/eid4189>)
o Move Section 5.6.6 into its own section
(<https://github.com/httpwg/http-core/issues/45>)
o In Section 8.3, reference MIME Sniffing
(<https://github.com/httpwg/http-core/issues/51>)
o In Section 5.6.1, simplify the #rule mapping for recipients
(<https://github.com/httpwg/http-core/issues/164>,
<https://www.rfc-editor.org/errata/eid5257>)
o In Section 9.3.7, remove misleading text about "extension" of HTTP
is needed to define method content (<https://github.com/httpwg/
http-core/issues/204>)
o Fix editorial issue in Section 3.2 (<https://github.com/httpwg/
http-core/issues/223>)
o In Section 15.5.21, rephrase language not to use "entity" anymore,
and also avoid lowercase "may" (<https://github.com/httpwg/http-
core/issues/224>)
o Move discussion of retries from [Messaging] into Section 9.2.2
(<https://github.com/httpwg/http-core/issues/230>)
C.7. Since draft-ietf-httpbis-semantics-05 C.7. Since draft-ietf-httpbis-semantics-05
o Moved transport-independent part of the description of trailers
into Section 6.5 (<https://github.com/httpwg/http-core/issues/16>)
o Loosen requirements on retries based upon implementation behavior
(<https://github.com/httpwg/http-core/issues/27>)
o In Section 18.9, update IANA port registry for TCP/UDP on ports 80
and 443 (<https://github.com/httpwg/http-core/issues/36>)
o In Section 16.3.2.2, revise guidelines for new header field names
(<https://github.com/httpwg/http-core/issues/47>)
o In Section 9.2.3, remove concept of "cacheable methods" in favor
of prose (<https://github.com/httpwg/http-core/issues/54>,
<https://www.rfc-editor.org/errata/eid5300>)
o In Section 17.1, mention that the concept of authority can be
modified by protocol extensions (<https://github.com/httpwg/http-
core/issues/143>)
o Create new subsection on content in Section 6.4, taken from
portions of message body (<https://github.com/httpwg/http-core/
issues/159>)
o Moved definition of "Whitespace" into new container "Generic
Syntax" (<https://github.com/httpwg/http-core/issues/162>)
o In Section 3.1, recommend minimum URI size support for
implementations (<https://github.com/httpwg/http-core/issues/169>)
o In Section 14.1, refactored the range-unit and ranges-specifier
grammars (<https://github.com/httpwg/http-core/issues/196>,
<https://www.rfc-editor.org/errata/eid5620>)
o In Section 9.3.1, caution against a request content more strongly
(<https://github.com/httpwg/http-core/issues/202>)
o Reorganized text in Section 16.3.2.2 (<https://github.com/httpwg/
http-core/issues/214>)
o In Section 15.5.4, replace "authorize" with "fulfill"
(<https://github.com/httpwg/http-core/issues/218>)
o In Section 9.3.7, removed a misleading statement about Content-
Length (<https://github.com/httpwg/http-core/issues/235>,
<https://www.rfc-editor.org/errata/eid5806>)
o In Section 17.1, add text from RFC 2818
(<https://github.com/httpwg/http-core/issues/236>)
o Changed "cacheable by default" to "heuristically cacheable"
throughout (<https://github.com/httpwg/http-core/issues/242>)
C.8. Since draft-ietf-httpbis-semantics-06 C.8. Since draft-ietf-httpbis-semantics-06
o In Section 7.6.3, simplify received-by grammar (and disallow comma
character) (<https://github.com/httpwg/http-core/issues/24>)
o In Section 5.1, give guidance on interoperable field names
(<https://github.com/httpwg/http-core/issues/30>)
o In Section 5.6.3, define the semantics and possible replacement of
whitespace when it is known to occur (<https://github.com/httpwg/
http-core/issues/53>, <https://www.rfc-editor.org/errata/eid5163>)
o In Section 6.3, introduce field terminology and distinguish
between field line values and field values; use terminology
consistently throughout (<https://github.com/httpwg/http-core/
issues/111>)
o Moved #rule definition into Section 5.5 and whitespace into
Section 2.1 (<https://github.com/httpwg/http-core/issues/162>)
o In Section 14.1, explicitly call out range unit names as case-
insensitive, and encourage registration
(<https://github.com/httpwg/http-core/issues/179>)
o In Section 8.4.1, explicitly call out content codings as case-
insensitive, and encourage registration
(<https://github.com/httpwg/http-core/issues/179>)
o In Section 5.1, explicitly call out field names as case-
insensitive (<https://github.com/httpwg/http-core/issues/179>)
o In Section 17.12, cite [Bujlow] (<https://github.com/httpwg/http-
core/issues/185>)
o In Section 15, formally define "final" and "interim" status codes
(<https://github.com/httpwg/http-core/issues/245>)
o In Section 9.3.5, caution against a request content more strongly
(<https://github.com/httpwg/http-core/issues/258>)
o In Section 8.8.3, note that Etag can be used in trailers
(<https://github.com/httpwg/http-core/issues/262>)
o In Section 18.4, consider reserved fields as well
(<https://github.com/httpwg/http-core/issues/273>)
o In Section 4.2.4, be more correct about what was deprecated by RFC
3986 (<https://github.com/httpwg/http-core/issues/278>,
<https://www.rfc-editor.org/errata/eid5964>)
o In Section 5.3, recommend comma SP when combining field lines
(<https://github.com/httpwg/http-core/issues/148>)
o In Section 7.2, make explicit requirements on origin server to use
authority from absolute-form when available
(<https://github.com/httpwg/http-core/issues/191>)
o In Section 4.2.1, Section 4.2.2, Section 4.3.1, and Section 7.3.3,
refactored schemes to define origin and authoritative access to an
origin server for both "http" and "https" URIs to account for
alternative services and secured connections that are not
necessarily based on TCP (<https://github.com/httpwg/http-core/
issues/237>)
o In Section 2.2, reference RFC 8174 as well
(<https://github.com/httpwg/http-core/issues/303>)
C.9. Since draft-ietf-httpbis-semantics-07 C.9. Since draft-ietf-httpbis-semantics-07
o In Section 14.2, explicitly reference the definition of
representation data as including any content codings
(<https://github.com/httpwg/http-core/issues/11>)
o Move TE: trailers from [Messaging] into Section 6.5.1
(<https://github.com/httpwg/http-core/issues/18>)
o In Section 8.6, adjust requirements for handling multiple content-
length values (<https://github.com/httpwg/http-core/issues/59>)
o In Section 13.1.1 and Section 13.1.2, clarified condition
evaluation (<https://github.com/httpwg/http-core/issues/72>)
o In Section 5.5, remove concept of obs-fold, as that is
HTTP/1-specific (<https://github.com/httpwg/http-core/issues/116>)
o In Section 12, introduce the concept of request content
negotiation (Section 12.3) and define for Accept-Encoding
(<https://github.com/httpwg/http-core/issues/119>)
o In Section 15.3.6, Section 15.5.9, and Section 15.5.14, remove
HTTP/1-specific, connection-related requirements
(<https://github.com/httpwg/http-core/issues/144>)
o In Section 9.3.6, correct language about what is forwarded
(<https://github.com/httpwg/http-core/issues/170>)
o Throughout, replace "effective request URI", "request-target" and
similar with "target URI" (<https://github.com/httpwg/http-core/
issues/259>)
o In Section 16.3.2.2 and Section 16.2.2, describe how extensions
should consider scope of applicability
(<https://github.com/httpwg/http-core/issues/265>)
o In Section 3.4, don't rely on the HTTP/1.1 Messaging specification
to define "message" (<https://github.com/httpwg/http-core/
issues/311>)
o In Section 8.7 and Section 10.1.3, note that URL resolution is
necessary (<https://github.com/httpwg/http-core/issues/321>)
o In Section 3.2, explicitly reference 206 as one of the status
codes that provide representation data
(<https://github.com/httpwg/http-core/issues/325>)
o In Section 13.1.4, refine requirements so that they don't apply to
resources without a concept of modification time
(<https://github.com/httpwg/http-core/issues/326>)
o In Section 11.7.1, specify the scope as a request, not a target
resource (<https://github.com/httpwg/http-core/issues/331>)
o In Section 3.4, introduce concept of "complete" messages
(<https://github.com/httpwg/http-core/issues/334>)
o In Section 7.1, Section 9.3.6, and Section 9.3.7, refine use of
"request target" (<https://github.com/httpwg/http-core/
issues/340>)
o Throughout, remove "status-line" and "request-line", as these are
HTTP/1.1-specific (<https://github.com/httpwg/http-core/
issues/361>)
C.10. Since draft-ietf-httpbis-semantics-08 C.10. Since draft-ietf-httpbis-semantics-08
o In Section 15.5.17, remove duplicate definition of what makes a
range satisfiable and refer instead to each range unit's
definition (<https://github.com/httpwg/http-core/issues/12>)
o In Section 14.1.2 and Section 14.2, clarify that a selected
representation of zero length can only be satisfiable as a suffix
range and that a server can still ignore Range for that case
(<https://github.com/httpwg/http-core/issues/12>)
o In Section 12.5.1 and Section 15.5.16, allow "Accept" as response
field (<https://github.com/httpwg/http-core/issues/48>)
o Appendix A now uses the sender variant of the "#" list expansion
(<https://github.com/httpwg/http-core/issues/192>)
o In Section 12.5.5, make the field list-based even when "*" is
present (<https://github.com/httpwg/http-core/issues/272>)
o In Section 16.3.1, add optional "Comments" entry
(<https://github.com/httpwg/http-core/issues/273>)
o In Section 18.4, reserve "*" as field name
(<https://github.com/httpwg/http-core/issues/274>)
o In Section 18.2, reserve "*" as method name
(<https://github.com/httpwg/http-core/issues/274>)
o In Section 13.1.1 and Section 13.1.2, state that multiple "*" is
unlikely to be interoperable (<https://github.com/httpwg/http-
core/issues/305>)
o In Section 12.5.1, avoid use of obsolete media type parameter on
text/html (<https://github.com/httpwg/http-core/issues/375>,
<https://www.rfc-editor.org/errata/eid6149>)
o Rephrase prose in Section 3.4 to become version-agnostic
(<https://github.com/httpwg/http-core/issues/372>)
o In Section 5.5, instruct recipients how to deal with control
characters in field values (<https://github.com/httpwg/http-core/
issues/377>)
o In Section 5.5, update note about field ABNF
(<https://github.com/httpwg/http-core/issues/380>)
o Add Section 16 about Extending and Versioning HTTP
(<https://github.com/httpwg/http-core/issues/384>)
o In Section 15.1, include status 308 in list of heuristically
cacheable status codes (<https://github.com/httpwg/http-core/
issues/385>)
o In Section 8.4, make it clearer that "identity" is not to be
included (<https://github.com/httpwg/http-core/issues/388>)
C.11. Since draft-ietf-httpbis-semantics-09 C.11. Since draft-ietf-httpbis-semantics-09
o Switch to xml2rfc v3 mode for draft generation
(<https://github.com/httpwg/http-core/issues/394>)
C.12. Since draft-ietf-httpbis-semantics-10 C.12. Since draft-ietf-httpbis-semantics-10
o In Section 17.6, mention compression attacks
(<https://github.com/httpwg/http-core/issues/6>)
o In Section 16.6.1, advise to make new content codings self-
descriptive (<https://github.com/httpwg/http-core/issues/21>)
o In Section 5.6.6, introduced the "parameters" ABNF rule, allowing
empty parameters and trailing semicolons within media type, media
range, and expectation (<https://github.com/httpwg/http-core/
issues/33>)
o In Section 15.4, explain how to create a redirected request
(<https://github.com/httpwg/http-core/issues/38>)
o In Section 8.3, defined error handling for multiple members
(<https://github.com/httpwg/http-core/issues/39>)
o In Section 1, revise the introduction and introduce HTTP/2 and
HTTP/3 (<https://github.com/httpwg/http-core/issues/64>)
o In Section 8.6, added a definition for Content-Length that
encompasses its various roles in describing message content or
selected representation length; in Section 15.3.7, noted that
Content-Length counts only the message content (not the selected
representation) and that the representation length is in each
Content-Range (<https://github.com/httpwg/http-core/issues/118>)
o Noted that "WWW-Authenticate" with more than one value on a line
is sometimes not interoperable [Messaging]
(<https://github.com/httpwg/http-core/issues/136>)
o In Section 13.1.1 and Section 13.1.4, removed requirement that a
validator not be sent in a 2xx response when validation fails and
the server decides that the same change request has already been
applied (<https://github.com/httpwg/http-core/issues/166>)
o Moved requirements specific to HTTP/1.1 from Section 7.2 to
[Messaging] (<https://github.com/httpwg/http-core/issues/182>)
o In Section 5.5, introduce the terms "singleton field" and "list-
based field" (also - in various places - discuss what to do when a
singleton field is received as a list)
(<https://github.com/httpwg/http-core/issues/193>)
o In Section 10.1.1, change the ABNF back to be a list of
expectations, as defined in RFC 2616 (<https://github.com/httpwg/
http-core/issues/203>)
o In Section 10.1.5 (Trailer), Section 7.6.3 (Via), Section 7.8
(Upgrade), Section 7.6.1 (Connection), Section 8.4
(Content-Encoding), Section 8.5 (Content-Language), Section 10.1.1
(Expect), Section 13.1.1 (If-Match), Section 13.1.2
(If-None-Match), Section 12.5.2 (Accept-Charset), Section 12.5.4
(Accept-Language), Section 12.5.5 (Vary), Section 11.6.1
(WWW-Authenticate), and Section 11.7.1 (Proxy-Authenticate),
adjust ABNF to allow empty lists (<https://github.com/httpwg/http-
core/issues/210>)
o In Section 9.3.1 and Section 17.9, provide a more nuanced
explanation of sensitive data in GET-based forms and describe
workarounds (<https://github.com/httpwg/http-core/issues/277>)
o In Section 13.2, allow preconditions to be evaluated before the
request content (if any) is processed (<https://github.com/httpwg/
http-core/issues/261>)
o In Section 6.3 and Section 6.5.2, allow for trailer fields in
multiple trailer sections, depending on the HTTP version and
framing in use, with processing being iterative as each section is
received (<https://github.com/httpwg/http-core/issues/313>)
o Moved definitions of "TE" and "Upgrade" from [Messaging]
(<https://github.com/httpwg/http-core/issues/392>)
o Moved 1.1-specific discussion of TLS to Messaging and rewrote
Section 4.3.4 to refer to RFC6125 (<https://github.com/httpwg/
http-core/issues/404>)
o Moved definition of "Connection" from [Messaging]
(<https://github.com/httpwg/http-core/issues/407>)
C.13. Since draft-ietf-httpbis-semantics-11 C.13. Since draft-ietf-httpbis-semantics-11
o The entire document has been reorganized, with no changes to
content except editorial for the reorganization
(<https://github.com/httpwg/http-core/issues/368>)
o Move IANA Upgrade Token Registry instructions from [Messaging]
(<https://github.com/httpwg/http-core/issues/450>)
C.14. Since draft-ietf-httpbis-semantics-12 C.14. Since draft-ietf-httpbis-semantics-12
o In Appendix "Acknowledgments" (Appendix D), added acks for the
work since 2014 (<https://github.com/httpwg/http-core/issues/442>)
o In Section 15.3.7, specifically require that a client check the
206 response header fields to determine what ranges are enclosed,
since it cannot assume they exactly match those requested
(<https://github.com/httpwg/http-core/issues/445>)
o In Section 16.3, explain why new fields need to be backwards-
compatible (<https://github.com/httpwg/http-core/issues/448>)
o In Section 5.3, constrain field combination to be within a section
(<https://github.com/httpwg/http-core/issues/454>)
o In Section 5.6.7, mention that caching relaxes date sensitivity
(<https://github.com/httpwg/http-core/issues/473>)
o In Section 18.4, moved "*" field registration into main table
(<https://github.com/httpwg/http-core/issues/476>)
o In Section 1.2, reference HTTP/0.9 (<https://github.com/httpwg/
http-core/issues/497>)
o In Section 9.3.4, clarify handling of unrecognized fields
(<https://github.com/httpwg/http-core/issues/502>)
o In Section 15.2, align language about bodies and trailers with 204
and 304 (<https://github.com/httpwg/http-core/issues/503>)
o Moved table of content codings into Section 18.6, moved table of
range units into Section 18.7 (<https://github.com/httpwg/http-
core/issues/506>)
o In Section 6, add an abstract data type for message to help define
semantics without being dependent on the specific structure of
HTTP/1.1 (<https://github.com/httpwg/http-core/issues/557>)
o In Section 8.8.2.2, relax arbitrary 60-second comparison limit
(<https://github.com/httpwg/http-core/issues/510>)
o In Section 7.2, add ":authority" pseudo-header to Host discussion
and make section applicable to both (<https://github.com/httpwg/
http-core/issues/511>)
o In Section 18.4, note that this document updates [RFC3864]
(<https://github.com/httpwg/http-core/issues/515>)
o Moved transfer-coding ABNF from [Messaging] to Section 10.1.4 and
replaced "t-ranking" ABNF by equivalent "weight"
(<https://github.com/httpwg/http-core/issues/531>)
o In Section 11.5, replace "canonical root URI" by "origin"
(<https://github.com/httpwg/http-core/issues/542>)
o In Section 10.1.1, remove obsolete note about a change in RFC 723x
(<https://github.com/httpwg/http-core/issues/547>)
o Changed to using "payload" when defining requirements about the
data being conveyed within a message, instead of the terms
"payload body" or "response body" or "representation body", since
they often get confused with the HTTP/1.1 message body (which
includes transfer coding) (<https://github.com/httpwg/http-core/
issues/553>)
o Rewrite definition of HEAD method (<https://github.com/httpwg/
http-core/issues/559>)
o In Section 13.1.5, fix an off-by-one bug about how many chars to
consider when checking for etags (<https://github.com/httpwg/http-
core/issues/570>)
o In Section 15.1, clarify that "no reason phrase" is fine as well
(<https://github.com/httpwg/http-core/issues/571>)
o In Section 15.3.4, remove an obsolete reference to the Warning
response header field (<https://github.com/httpwg/http-core/
issues/573>)
o In Section 15.5.9, rephrase prose about connection re-use
(<https://github.com/httpwg/http-core/issues/579>)
o In Section 14.2, potentially allow Range handling on methods other
than GET (<https://github.com/httpwg/http-core/issues/581>)
o In Section 18.3, remove redundant text about status code 418
(<https://github.com/httpwg/http-core/issues/583>)
o In Section 17.15.1, rewrite requirement to refer to "secured
connection" (<https://github.com/httpwg/http-core/issues/587>)
o Make reference to [RFC8446] normative (<https://github.com/httpwg/
http-core/issues/589>)
C.15. Since draft-ietf-httpbis-semantics-13 C.15. Since draft-ietf-httpbis-semantics-13
o In Section 12.5.1, remove the unused "accept parameters"
(<https://github.com/httpwg/http-core/issues/568>)
o In Section 1.2, mention that RFC 1945 describes HTTP/0.9 as well
(<https://github.com/httpwg/http-core/issues/614>)
o In Section 14.5, describe non-standard use of the Content-Range
header field (Section 14.4) as a request modifier to perform a
partial PUT (<https://github.com/httpwg/http-core/issues/618>)
o In Section 15.5.20, import the 421 (Misdirected Request) status
code from [RFC7540] (<https://github.com/httpwg/http-core/
issues/622>)
o In Section 2.3, rephrase the actual recipient parsing requirements
(<https://github.com/httpwg/http-core/issues/634>)
o In Section 16.1.2, mention request target forms in considerations
for new methods (<https://github.com/httpwg/http-core/issues/636>)
o Changed to using "content" instead of "payload" or "payload data"
to avoid confusion with the payload of version-specific messaging
frames (<https://github.com/httpwg/http-core/issues/654>)
o In Section 13.1.3, Section 13.1.4, and Section 13.1.5, specify
evaluation in a way similar to other conditional header fields
(<https://github.com/httpwg/http-core/issues/665>)
o In Section 10.2.2, specify that recipients can replace an invalid
Date header field value with the time received
(<https://github.com/httpwg/http-core/issues/669>)
Acknowledgments Acknowledgments
See Section 10 of [RFC7230]. This edition of the HTTP specification builds on the many
contributions that went into RFC 1945, RFC 2068, RFC 2145, RFC 2616,
and RFC 2818, including substantial contributions made by the
previous authors, editors, and Working Group Chairs: Tim Berners-Lee,
Jean-François Groff, Ari Luotonen, Roy T. Fielding, Henrik Frystyk
Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter, Paul J.
Leach, Eric Rescorla, and Yves Lafon.
This specification takes over the definition of the HTTP In addition, this document has reincorporated the HTTP Authentication
Authentication Framework, previously defined in RFC 2617. We thank Framework, previously defined in RFC 7235 and RFC 2617. We thank
John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D. John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott
Lawrence, Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart for D. Lawrence, Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart
their work on that specification. See Section 6 of [RFC2617] for for their work on that specification. See Section 6 of [RFC2617] for
further acknowledgements. further acknowledgements.
Since 2014, the following contributors have helped improve the HTTP
specification by reporting bugs, asking smart questions, drafting or
reviewing text, and evaluating open issues:
Alan Egerton, Alex Rousskov, Amichai Rothman, Amos Jeffries, Anders
Kaseorg, Andreas Gebhardt, Anne van Kesteren, Armin Abfalterer, Aron
Duby, Asanka Herath, Asbjørn Ulsberg, Attila Gulyas, Austin Wright,
Barry Pollard, Ben Burkert, Björn Höhrmann, Brad Fitzpatrick, Chris
Pacejo, Colin Bendell, Cory Benfield, Cory Nelson, Daisuke Miyakawa,
Daniel Stenberg, Danil Suits, David Benjamin, David Matson, David
Schinazi, Дилян Палаузов (Dilyan Palauzov), Eric Anderson, Eric
Rescorla, Erwin Pe, Etan Kissling, Evert Pot, Evgeny Vrublevsky,
Florian Best, Igor Lubashev, James Callahan, James Peach, Jeffrey
Yasskin, Kalin Gyokov, Kannan Goundan, 奥 一穂 (Kazuho Oku), Ken
Murchison, Lucas Pardue, Martin Dürst, Martin Thomson, Martynas
Jusevičius, Matt Menke, Matthias Pigulla, Michael Osipov, Mike
Bishop, Mike Pennisi, Mike West, Nicholas Hurley, Nikita Piskunov,
Patrick McManus, Piotr Sikora, Poul-Henning Kamp, Rick van Rein,
Roberto Polli, Semyon Kholodnov, Simon Pieters, Simon Schüppel, Todd
Greer, Tommy Pauly, Vasiliy Faronov, Vladimir Lashchev, Wenbo Zhu,
William A. Rowe Jr., Willy Tarreau, Xingwei Liu, and Yishuai Li.
See Section 10 of [RFC7230] for further acknowledgements from prior
revisions.
Authors' Addresses Authors' Addresses
Roy T. Fielding (editor) Roy T. Fielding (editor)
Adobe Systems Incorporated Adobe
345 Park Ave 345 Park Ave
San Jose, CA 95110 San Jose, CA 95110
USA United States of America
EMail: fielding@gbiv.com Email: fielding@gbiv.com
URI: http://roy.gbiv.com/ URI: https://roy.gbiv.com/
Mark Nottingham (editor)
Fastly
Prahran VIC
Australia
Julian F. Reschke (editor) Email: mnot@mnot.net
URI: https://www.mnot.net/
Julian Reschke (editor)
greenbytes GmbH greenbytes GmbH
Hafenweg 16 Hafenweg 16
Muenster, NW 48155 48155 Münster
Germany Germany
EMail: julian.reschke@greenbytes.de Email: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/ URI: https://greenbytes.de/tech/webdav/
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