frankenRFC723x_sem.txt   draft-ietf-httpbis-semantics-06.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: M. Nottingham, Ed.
Updates: 2817 greenbytes 2818,7230,7231,7232,7233,7235 Fastly
Category: Standards Track June 2014 ,7538,7615 (if approved) J. Reschke, Ed.
ISSN: 2070-1721 Intended status: Standards Track greenbytes
Expires: May 7, 2020 November 4, 2019
Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content HTTP Semantics
draft-ietf-httpbis-semantics-06
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 defines the semantics of HTTP: its
as expressed by request methods, request header fields, response architecture, terminology, the "http" and "https" Uniform Resource
status codes, and response header fields, along with the payload of Identifier (URI) schemes, core request methods, request header
messages (metadata and body content) and mechanisms for content fields, response status codes, response header fields, and content
negotiation. negotiation.
This document obsoletes RFC 2818, RFC 7231, RFC 7232, RFC 7233, RFC
7235, RFC 7538, RFC 7615, and portions of RFC 7230.
Editorial Note
This note is to be removed before publishing as an RFC.
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at <https://httpwg.org/>;
source code and issues list for this draft can be found at
<https://github.com/httpwg/http-core>.
The changes in this draft are summarized in Appendix J.7.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79.
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Internet Standards is available in Section 2 of RFC 5741.
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http://www.rfc-editor.org/info/rfc7231. time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 7, 2020.
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Table of Contents Table of Contents
1. Introduction ....................................................6 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1. Conformance and Error Handling .............................6 1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 9
1.2. Syntax Notation ............................................6 1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 9
2. Resources .......................................................7 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 10
3. Representations .................................................7 2.1. Client/Server Messaging . . . . . . . . . . . . . . . . . 10
3.1. Representation Metadata ....................................8 2.2. Intermediaries . . . . . . . . . . . . . . . . . . . . . 12
3.1.1. Processing Representation Data ......................8 2.3. Caches . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.2. Encoding for Compression or Integrity ..............11 2.4. Uniform Resource Identifiers . . . . . . . . . . . . . . 15
3.1.3. Audience Language ..................................13 2.5. Resources . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.4. Identification .....................................14 2.5.1. http URI Scheme . . . . . . . . . . . . . . . . . . . 16
3.2. Representation Data .......................................17 2.5.2. https URI Scheme . . . . . . . . . . . . . . . . . . 18
3.3. Payload Semantics .........................................17 2.5.3. Fragment Identifiers on http(s) URI References . . . 20
3.4. Content Negotiation .......................................18 2.5.4. http and https URI Normalization and Comparison . . . 20
3.4.1. Proactive Negotiation ..............................19 3. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4.2. Reactive Negotiation ...............................20 3.1. Implementation Diversity . . . . . . . . . . . . . . . . 21
4. Request Methods ................................................21 3.2. Role-based Requirements . . . . . . . . . . . . . . . . . 21
4.1. Overview ..................................................21 3.3. Parsing Elements . . . . . . . . . . . . . . . . . . . . 22
4.2. Common Method Properties ..................................22 3.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 23
4.2.1. Safe Methods .......................................22 3.5. Protocol Versioning . . . . . . . . . . . . . . . . . . . 23
4.2.2. Idempotent Methods .................................23 4. Header Fields . . . . . . . . . . . . . . . . . . . . . . . . 24
4.2.3. Cacheable Methods ..................................24 4.1. Header Field Names . . . . . . . . . . . . . . . . . . . 24
4.3. Method Definitions ........................................24 4.1.1. Header Field Name Registry . . . . . . . . . . . . . 27
4.3.1. GET ................................................24 4.1.2. Header Field Extensibility . . . . . . . . . . . . . 28
4.3.2. HEAD ...............................................25 4.2. Header Field Values . . . . . . . . . . . . . . . . . . . 28
4.3.3. POST ...............................................25 4.2.1. Header Field Order . . . . . . . . . . . . . . . . . 29
4.3.4. PUT ................................................26 4.2.2. Header Field Limits . . . . . . . . . . . . . . . . . 30
4.3.5. DELETE .............................................29 4.2.3. Header Field Value Components . . . . . . . . . . . . 30
4.3.6. CONNECT ............................................30 4.3. Trailer Fields . . . . . . . . . . . . . . . . . . . . . 32
4.3.7. OPTIONS ............................................31 4.3.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 32
4.3.8. TRACE ..............................................32 4.3.2. Limitations . . . . . . . . . . . . . . . . . . . . . 32
5. Request Header Fields ..........................................33 4.3.3. Trailer . . . . . . . . . . . . . . . . . . . . . . . 33
5.1. Controls ..................................................33 4.4. Considerations for New Header Fields . . . . . . . . . . 33
5.1.1. Expect .............................................34 5. Message Routing . . . . . . . . . . . . . . . . . . . . . . . 35
5.1.2. Max-Forwards .......................................36 5.1. Identifying a Target Resource . . . . . . . . . . . . . . 35
5.2. Conditionals ..............................................36 5.2. Routing Inbound . . . . . . . . . . . . . . . . . . . . . 36
5.3. Content Negotiation .......................................37 5.3. Effective Request URI . . . . . . . . . . . . . . . . . . 36
5.3.1. Quality Values .....................................37 5.4. Host . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.3.2. Accept .............................................38 5.5. Message Forwarding . . . . . . . . . . . . . . . . . . . 38
5.3.3. Accept-Charset .....................................40 5.5.1. Via . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.3.4. Accept-Encoding ....................................41 5.5.2. Transformations . . . . . . . . . . . . . . . . . . . 40
5.3.5. Accept-Language ....................................42 6. Representations . . . . . . . . . . . . . . . . . . . . . . . 41
5.4. Authentication Credentials ................................44 6.1. Representation Data . . . . . . . . . . . . . . . . . . . 42
5.5. Request Context ...........................................44 6.1.1. Media Type . . . . . . . . . . . . . . . . . . . . . 42
5.5.1. From ...............................................44 6.1.2. Content Codings . . . . . . . . . . . . . . . . . . . 44
5.5.2. Referer ............................................45 6.1.3. Language Tags . . . . . . . . . . . . . . . . . . . . 46
5.5.3. User-Agent .........................................46 6.1.4. Range Units . . . . . . . . . . . . . . . . . . . . . 47
6. Response Status Codes ..........................................47 6.2. Representation Metadata . . . . . . . . . . . . . . . . . 51
6.1. Overview of Status Codes ..................................48 6.2.1. Content-Type . . . . . . . . . . . . . . . . . . . . 51
6.2. Informational 1xx .........................................50 6.2.2. Content-Encoding . . . . . . . . . . . . . . . . . . 52
6.2.1. 100 Continue .......................................50 6.2.3. Content-Language . . . . . . . . . . . . . . . . . . 53
6.2.2. 101 Switching Protocols ............................50 6.2.4. Content-Length . . . . . . . . . . . . . . . . . . . 54
6.3. Successful 2xx ............................................51 6.2.5. Content-Location . . . . . . . . . . . . . . . . . . 55
6.3.1. 200 OK .............................................51 6.3. Payload . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.3.2. 201 Created ........................................52 6.3.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 57
6.3.3. 202 Accepted .......................................52 6.3.2. Identification . . . . . . . . . . . . . . . . . . . 58
6.3.4. 203 Non-Authoritative Information ..................52 6.3.3. Payload Body . . . . . . . . . . . . . . . . . . . . 59
6.3.5. 204 No Content .....................................53 6.3.4. Content-Range . . . . . . . . . . . . . . . . . . . . 59
6.3.6. 205 Reset Content ..................................53 6.3.5. Media Type multipart/byteranges . . . . . . . . . . . 61
6.4. Redirection 3xx ...........................................54 6.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 63
6.4.1. 300 Multiple Choices ...............................55 6.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 64
6.4.2. 301 Moved Permanently ..............................56 6.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . 65
6.4.3. 302 Found ..........................................56 7. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 66
6.4.4. 303 See Other ......................................57 7.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 66
6.4.5. 305 Use Proxy ......................................58 7.2. Common Method Properties . . . . . . . . . . . . . . . . 67
6.4.6. 306 (Unused) .......................................58 7.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 68
6.4.7. 307 Temporary Redirect .............................58 7.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 69
6.5. Client Error 4xx ..........................................58 7.2.3. Methods and Caching . . . . . . . . . . . . . . . . . 70
6.5.1. 400 Bad Request ....................................58 7.3. Method Definitions . . . . . . . . . . . . . . . . . . . 70
6.5.2. 402 Payment Required ...............................59 7.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 70
6.5.3. 403 Forbidden ......................................59 7.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 71
6.5.4. 404 Not Found ......................................59 7.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 72
6.5.5. 405 Method Not Allowed .............................59 7.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.5.6. 406 Not Acceptable .................................60 7.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 75
6.5.7. 408 Request Timeout ................................60 7.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 76
6.5.8. 409 Conflict .......................................60 7.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 78
6.5.9. 410 Gone ...........................................60 7.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 79
6.5.10. 411 Length Required ...............................61 7.4. Method Extensibility . . . . . . . . . . . . . . . . . . 79
6.5.11. 413 Payload Too Large .............................61 7.4.1. Method Registry . . . . . . . . . . . . . . . . . . . 79
6.5.12. 414 URI Too Long ..................................61 7.4.2. Considerations for New Methods . . . . . . . . . . . 80
6.5.13. 415 Unsupported Media Type ........................62 8. Request Header Fields . . . . . . . . . . . . . . . . . . . . 80
6.5.14. 417 Expectation Failed ............................62 8.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . 81
6.5.15. 426 Upgrade Required ..............................62 8.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 81
6.6. Server Error 5xx ..........................................62 8.1.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 83
6.6.1. 500 Internal Server Error ..........................63 8.2. Preconditions . . . . . . . . . . . . . . . . . . . . . . 84
6.6.2. 501 Not Implemented ................................63 8.2.1. Evaluation . . . . . . . . . . . . . . . . . . . . . 85
6.6.3. 502 Bad Gateway ....................................63 8.2.2. Precedence . . . . . . . . . . . . . . . . . . . . . 86
6.6.4. 503 Service Unavailable ............................63 8.2.3. If-Match . . . . . . . . . . . . . . . . . . . . . . 88
6.6.5. 504 Gateway Timeout ................................63 8.2.4. If-None-Match . . . . . . . . . . . . . . . . . . . . 89
6.6.6. 505 HTTP Version Not Supported .....................64 8.2.5. If-Modified-Since . . . . . . . . . . . . . . . . . . 90
7. Response Header Fields .........................................64 8.2.6. If-Unmodified-Since . . . . . . . . . . . . . . . . . 91
7.1. Control Data ..............................................64 8.2.7. If-Range . . . . . . . . . . . . . . . . . . . . . . 93
7.1.1. Origination Date ...................................65 8.3. Range . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.1.2. Location ...........................................68 8.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 95
7.1.3. Retry-After ........................................69 8.4.1. Quality Values . . . . . . . . . . . . . . . . . . . 96
7.1.4. Vary ...............................................70 8.4.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 97
7.2. Validator Header Fields ...................................71 8.4.3. Accept-Charset . . . . . . . . . . . . . . . . . . . 99
7.3. Authentication Challenges .................................72 8.4.4. Accept-Encoding . . . . . . . . . . . . . . . . . . . 100
7.4. Response Context ..........................................72 8.4.5. Accept-Language . . . . . . . . . . . . . . . . . . . 101
7.4.1. Allow ..............................................72 8.5. Authentication Credentials . . . . . . . . . . . . . . . 102
7.4.2. Server .............................................73 8.5.1. Challenge and Response . . . . . . . . . . . . . . . 102
8. IANA Considerations ............................................73 8.5.2. Protection Space (Realm) . . . . . . . . . . . . . . 104
8.1. Method Registry ...........................................73 8.5.3. Authorization . . . . . . . . . . . . . . . . . . . . 105
8.1.1. Procedure ..........................................74 8.5.4. Proxy-Authorization . . . . . . . . . . . . . . . . . 105
8.1.2. Considerations for New Methods .....................74 8.5.5. Authentication Scheme Extensibility . . . . . . . . . 106
8.1.3. Registrations ......................................75 8.6. Request Context . . . . . . . . . . . . . . . . . . . . . 108
8.2. Status Code Registry ......................................75 8.6.1. From . . . . . . . . . . . . . . . . . . . . . . . . 108
8.2.1. Procedure ..........................................75 8.6.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 109
8.2.2. Considerations for New Status Codes ................76 8.6.3. User-Agent . . . . . . . . . . . . . . . . . . . . . 110
8.2.3. Registrations ......................................76
8.3. Header Field Registry .....................................77 9. Response Status Codes . . . . . . . . . . . . . . . . . . . . 111
8.3.1. Considerations for New Header Fields ...............78 9.1. Overview of Status Codes . . . . . . . . . . . . . . . . 112
8.3.2. Registrations ......................................80 9.2. Informational 1xx . . . . . . . . . . . . . . . . . . . . 113
8.4. Content Coding Registry ...................................81 9.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 114
8.4.1. Procedure ..........................................81 9.2.2. 101 Switching Protocols . . . . . . . . . . . . . . . 114
8.4.2. Registrations ......................................81 9.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 114
9. Security Considerations ........................................81 9.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 114
9.1. Attacks Based on File and Path Names ......................82 9.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 115
9.2. Attacks Based on Command, Code, or Query Injection ........82 9.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 115
9.3. Disclosure of Personal Information ........................83 9.3.4. 203 Non-Authoritative Information . . . . . . . . . . 116
9.4. Disclosure of Sensitive Information in URIs ...............83 9.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 116
9.5. Disclosure of Fragment after Redirects ....................84 9.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 117
9.6. Disclosure of Product Information .........................84 9.3.7. 206 Partial Content . . . . . . . . . . . . . . . . . 117
9.7. Browser Fingerprinting ....................................84 9.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 120
10. Acknowledgments ...............................................85 9.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 122
11. References ....................................................85 9.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 123
11.1. Normative References .....................................85 9.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 123
11.2. Informative References ...................................86 9.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 124
Appendix A. Differences between HTTP and MIME .....................89 9.4.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 124
A.1. MIME-Version ..............................................89 9.4.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 125
A.2. Conversion to Canonical Form ..............................89 9.4.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 125
A.3. Conversion of Date Formats ................................90 9.4.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 125
A.4. Conversion of Content-Encoding ..........................90 9.4.9. 308 Permanent Redirect . . . . . . . . . . . . . . . 126
A.5. Conversion of Content-Transfer-Encoding .................90 9.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 126
A.6. MHTML and Line Length Limitations .........................90 9.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 126
Appendix B. Changes from RFC 2616 .................................91 9.5.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 126
Appendix C. Imported ABNF .........................................93 9.5.3. 402 Payment Required . . . . . . . . . . . . . . . . 127
Appendix D. Collected ABNF ........................................94 9.5.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 127
Index .............................................................97 9.5.5. 404 Not Found . . . . . . . . . . . . . . . . . . . . 127
9.5.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 128
9.5.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 128
9.5.8. 407 Proxy Authentication Required . . . . . . . . . . 128
9.5.9. 408 Request Timeout . . . . . . . . . . . . . . . . . 128
9.5.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 129
9.5.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 129
9.5.12. 411 Length Required . . . . . . . . . . . . . . . . . 129
9.5.13. 412 Precondition Failed . . . . . . . . . . . . . . . 130
9.5.14. 413 Payload Too Large . . . . . . . . . . . . . . . . 130
9.5.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . 130
9.5.16. 415 Unsupported Media Type . . . . . . . . . . . . . 130
9.5.17. 416 Range Not Satisfiable . . . . . . . . . . . . . . 131
9.5.18. 417 Expectation Failed . . . . . . . . . . . . . . . 131
9.5.19. 418 (Unused) . . . . . . . . . . . . . . . . . . . . 131
9.5.20. 422 Unprocessable Payload . . . . . . . . . . . . . . 132
9.5.21. 426 Upgrade Required . . . . . . . . . . . . . . . . 132
9.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 132
9.6.1. 500 Internal Server Error . . . . . . . . . . . . . . 133
9.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 133
9.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 133
9.6.4. 503 Service Unavailable . . . . . . . . . . . . . . . 133
9.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 133
9.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 133
9.7. Status Code Extensibility . . . . . . . . . . . . . . . . 134
9.7.1. Status Code Registry . . . . . . . . . . . . . . . . 134
9.7.2. Considerations for New Status Codes . . . . . . . . . 134
10. Response Header Fields . . . . . . . . . . . . . . . . . . . 135
10.1. Control Data . . . . . . . . . . . . . . . . . . . . . . 135
10.1.1. Origination Date . . . . . . . . . . . . . . . . . . 136
10.1.2. Location . . . . . . . . . . . . . . . . . . . . . . 139
10.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . 140
10.1.4. Vary . . . . . . . . . . . . . . . . . . . . . . . . 141
10.2. Validators . . . . . . . . . . . . . . . . . . . . . . . 142
10.2.1. Weak versus Strong . . . . . . . . . . . . . . . . . 143
10.2.2. Last-Modified . . . . . . . . . . . . . . . . . . . 144
10.2.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . 146
10.2.4. When to Use Entity-Tags and Last-Modified Dates . . 150
10.3. Authentication Challenges . . . . . . . . . . . . . . . 150
10.3.1. WWW-Authenticate . . . . . . . . . . . . . . . . . . 151
10.3.2. Proxy-Authenticate . . . . . . . . . . . . . . . . . 152
10.3.3. Authentication-Info . . . . . . . . . . . . . . . . 152
10.3.4. Proxy-Authentication-Info . . . . . . . . . . . . . 153
10.4. Response Context . . . . . . . . . . . . . . . . . . . . 154
10.4.1. Accept-Ranges . . . . . . . . . . . . . . . . . . . 154
10.4.2. Allow . . . . . . . . . . . . . . . . . . . . . . . 154
10.4.3. Server . . . . . . . . . . . . . . . . . . . . . . . 155
11. Generic Syntax . . . . . . . . . . . . . . . . . . . . . . . 156
11.1. Whitespace . . . . . . . . . . . . . . . . . . . . . . . 156
12. ABNF List Extension: #rule . . . . . . . . . . . . . . . . . 156
12.1. Sender Requirements . . . . . . . . . . . . . . . . . . 156
12.2. Recipient Requirements . . . . . . . . . . . . . . . . . 157
13. Security Considerations . . . . . . . . . . . . . . . . . . . 158
13.1. Establishing Authority . . . . . . . . . . . . . . . . . 158
13.2. Risks of Intermediaries . . . . . . . . . . . . . . . . 159
13.3. Attacks Based on File and Path Names . . . . . . . . . . 160
13.4. Attacks Based on Command, Code, or Query Injection . . . 160
13.5. Attacks via Protocol Element Length . . . . . . . . . . 161
13.6. Disclosure of Personal Information . . . . . . . . . . . 161
13.7. Privacy of Server Log Information . . . . . . . . . . . 161
13.8. Disclosure of Sensitive Information in URIs . . . . . . 162
13.9. Disclosure of Fragment after Redirects . . . . . . . . . 162
13.10. Disclosure of Product Information . . . . . . . . . . . 163
13.11. Browser Fingerprinting . . . . . . . . . . . . . . . . . 163
13.12. Validator Retention . . . . . . . . . . . . . . . . . . 164
13.13. Denial-of-Service Attacks Using Range . . . . . . . . . 165
13.14. Authentication Considerations . . . . . . . . . . . . . 165
13.14.1. Confidentiality of Credentials . . . . . . . . . . 165
13.14.2. Credentials and Idle Clients . . . . . . . . . . . 166
13.14.3. Protection Spaces . . . . . . . . . . . . . . . . . 166
13.14.4. Additional Response Header Fields . . . . . . . . . 167
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 167
14.1. URI Scheme Registration . . . . . . . . . . . . . . . . 167
14.2. Method Registration . . . . . . . . . . . . . . . . . . 167
14.3. Status Code Registration . . . . . . . . . . . . . . . . 167
14.4. Header Field Registration . . . . . . . . . . . . . . . 168
14.5. Authentication Scheme Registration . . . . . . . . . . . 168
14.6. Content Coding Registration . . . . . . . . . . . . . . 168
14.7. Range Unit Registration . . . . . . . . . . . . . . . . 169
14.8. Media Type Registration . . . . . . . . . . . . . . . . 169
14.9. Port Registration . . . . . . . . . . . . . . . . . . . 169
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 169
15.1. Normative References . . . . . . . . . . . . . . . . . . 169
15.2. Informative References . . . . . . . . . . . . . . . . . 171
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 177
Appendix B. Changes from RFC 7230 . . . . . . . . . . . . . . . 181
Appendix C. Changes from RFC 2818 . . . . . . . . . . . . . . . 182
Appendix D. Changes from RFC 7231 . . . . . . . . . . . . . . . 182
Appendix E. Changes from RFC 7232 . . . . . . . . . . . . . . . 182
Appendix F. Changes from RFC 7233 . . . . . . . . . . . . . . . 182
Appendix G. Changes from RFC 7235 . . . . . . . . . . . . . . . 182
Appendix H. Changes from RFC 7538 . . . . . . . . . . . . . . . 183
Appendix I. Changes from RFC 7615 . . . . . . . . . . . . . . . 183
Appendix J. Change Log . . . . . . . . . . . . . . . . . . . . . 183
J.1. Between RFC723x and draft 00 . . . . . . . . . . . . . . 183
J.2. Since draft-ietf-httpbis-semantics-00 . . . . . . . . . . 183
J.3. Since draft-ietf-httpbis-semantics-01 . . . . . . . . . . 184
J.4. Since draft-ietf-httpbis-semantics-02 . . . . . . . . . . 185
J.5. Since draft-ietf-httpbis-semantics-03 . . . . . . . . . . 186
J.6. Since draft-ietf-httpbis-semantics-04 . . . . . . . . . . 187
J.7. Since draft-ietf-httpbis-semantics-05 . . . . . . . . . . 187
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 196
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 197
1. Introduction 1. Introduction
The Hypertext Transfer Protocol (HTTP) is a stateless application-
level request/response protocol that uses extensible semantics and
self-descriptive messages for flexible interaction with network-based
hypertext information systems. HTTP is defined by a series of
documents that collectively form the HTTP/1.1 specification:
o "HTTP Semantics" (this document)
o "HTTP Caching" [Caching]
o "HTTP/1.1 Messaging" [Messaging]
HTTP is a generic interface protocol for information systems. It is HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by designed to hide the details of how a service is implemented by
presenting a uniform interface to clients that is independent of the presenting a uniform interface to clients that is independent of the
types of resources provided. Likewise, servers do not need to be types of resources provided. Likewise, servers do not need to be
aware of each client's purpose: an HTTP request can be considered in aware of each client's purpose: an HTTP request can be considered in
isolation rather than being associated with a specific type of client isolation rather than being associated with a specific type of client
or a predetermined sequence of application steps. The result is a or a predetermined sequence of application steps. The result is a
protocol that can be used effectively in many different contexts and protocol that can be used effectively in many different contexts and
for which implementations can evolve independently over time. for which implementations can evolve independently over time.
skipping to change at line 232 skipping to change at page 8, line 33
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.
Each Hypertext Transfer Protocol (HTTP) message is either a request Each HTTP message is either a request or a response. A server
or a response. A server listens on a connection for a request, listens on a connection for a request, parses each message received,
parses each message received, interprets the message semantics in interprets the message semantics in relation to the identified
relation to the identified request target, and responds to that request target, and responds to that request with one or more
request with one or more response messages. A client constructs response messages. A client constructs request messages to
request messages to communicate specific intentions, examines communicate specific intentions, examines received responses to see
received responses to see if the intentions were carried out, and if the intentions were carried out, and determines how to interpret
determines how to interpret the results. This document defines the results.
HTTP/1.1 request and response semantics in terms of the architecture
defined in [RFC7230].
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 2.5), regardless of its type, nature, or implementation, via
the manipulation and transfer of representations (Section 3). the manipulation and transfer of representations (Section 6).
HTTP semantics include the intentions defined by each request method This document defines semantics that are common to all versions of
(Section 4), extensions to those semantics that might be described in HTTP. HTTP semantics include the intentions defined by each request
request header fields (Section 5), the meaning of status codes to method (Section 7), extensions to those semantics that might be
indicate a machine-readable response (Section 6), and the meaning of described in request header fields (Section 8), the meaning of status
other control data and resource metadata that might be given in codes to indicate a machine-readable response (Section 9), and the
response header fields (Section 7). meaning of other control data and resource metadata that might be
given in response header fields (Section 10).
This document also defines representation metadata that describe how This document also defines representation metadata that describe how
a payload is intended to be interpreted by a recipient, the request a payload is intended to be interpreted by a recipient, the request
header fields that might influence content selection, and the various header 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 6.4).
This document defines HTTP/1.1 range requests, partial responses, and This document defines HTTP range requests, partial responses, and the
the multipart/byteranges media type. multipart/byteranges media type.
1.1. Conformance and Error Handling This document obsoletes the portions of RFC 7230 that are independent
of the HTTP/1.1 messaging syntax and connection management, with the
changes being summarized in Appendix B. The other parts of RFC 7230
are obsoleted by "HTTP/1.1 Messaging" [Messaging]. This document
also obsoletes RFC 2818 (see Appendix C), RFC 7231 (see Appendix D),
RFC 7232 (see Appendix E), RFC 7233 (see Appendix F), RFC 7235 (see
Appendix G), RFC 7538 (see Appendix H), and RFC 7615 (see
Appendix I).
1.1. 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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
Conformance criteria and considerations regarding error handling are Conformance criteria and considerations regarding error handling are
defined in Section 2.5 of [RFC7230]. defined in Section 3.
1.2. Syntax Notation 1.2. 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 12, that allows for
documents. Appendix D shows the collected grammar with all list 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 4.2.3 defines some generic syntactic components for header
field values.
The rules below are defined in [Messaging]:
obs-fold = <obs-fold, see [Messaging], Section 5.2>
protocol-name = <protocol-name, see [Messaging], Section 9.9>
protocol-version = <protocol-version, see [Messaging], Section 9.9>
request-target = <request-target, see [Messaging], Section 3.2>
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. Architecture 2. Architecture
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.
2.1. Client/Server Messaging 2.1. Client/Server Messaging
HTTP is a stateless request/response protocol that operates by HTTP is a stateless request/response protocol that operates by
exchanging messages (Section 3) across a reliable transport- or exchanging messages (Section 2 of [Messaging]) across a reliable
session-layer "connection" (Section 6). An HTTP "client" is a transport- or session-layer "connection" (Section 9 of [Messaging]).
program that establishes a connection to a server for the purpose of An HTTP "client" is a program that establishes a connection to a
sending one or more HTTP requests. An HTTP "server" is a program server for the purpose of sending one or more HTTP requests. An HTTP
that accepts connections in order to service HTTP requests by sending "server" is a program that accepts connections in order to service
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. The term act as a client on some connections and a server on others. The term
"user agent" refers to any of the various client programs that "user agent" refers to any of the various client programs that
initiate a request, including (but not limited to) browsers, spiders initiate a request, including (but not limited to) browsers, spiders
(web-based robots), command-line tools, custom applications, and (web-based robots), command-line tools, custom applications, and
mobile apps. The term "origin server" refers to the program that can mobile apps. The term "origin server" refers to the program that can
originate authoritative responses for a given target resource. The originate authoritative responses for a given target resource. The
terms "sender" and "recipient" refer to any implementation that sends terms "sender" and "recipient" refer to any implementation that sends
or receives a given message, respectively. or receives a given message, respectively.
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 5.1) and
relationships between resources. Messages are passed in a format relationships between resources.
similar to that used by Internet mail [RFC5322] and the Multipurpose
Internet Mail Extensions (MIME) [RFC2045] (see Appendix A of
[RFC7231] for the differences between HTTP and MIME messages).
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
Each major version of HTTP defines its own syntax for the inclusion
of information in messages. Nevertheless, a common abstraction is
that a message includes some form of envelope/framing, a potential
set of named header fields up front (a header section), a potential
body, and a potential set of named trailer fields.
A client sends an HTTP request to a server in the form of a request A client sends an HTTP request to a server in the form of a request
message, beginning with a request-line that includes a method, URI, message, beginning with a method (Section 7) and URI, followed by
and protocol version (Section 3.1.1), followed by header fields header fields containing request modifiers, client information, and
containing request modifiers, client information, and representation representation metadata (Section 4), and finally a payload body (if
metadata (Section 3.2), an empty line to indicate the end of the any, Section 6.3.3).
header section, and finally a message body containing the payload
body (if any, Section 3.3).
A server responds to a client's request by sending one or more HTTP 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 beginning with a success or error code
the protocol version, a success or error code, and textual reason (Section 9), possibly followed by header fields containing server
phrase (Section 3.1.2), possibly followed by header fields containing information, resource metadata, and representation metadata
server information, resource metadata, and representation metadata (Section 4), and finally a payload body (if any, Section 6.3.3).
(Section 3.2), an empty line to indicate the end of the header
section, and finally a message body containing the payload body (if
any, Section 3.3).
A connection might be used for multiple request/response exchanges, A connection might be used for multiple request/response exchanges.
as defined in Section 6.3. 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.
Responses (both final and non-final) 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.
The following example illustrates a typical message exchange for a The following example illustrates a typical message exchange for a
GET request (Section 4.3.1 of [RFC7231]) on the URI GET request (Section 7.3.1) 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:
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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 payload includes a trailing CRLF.
2.3. Intermediaries 2.2. 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
< < < < < < < <
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client, usually via local configuration rules, to receive requests client, usually via local configuration rules, to receive requests
for some type(s) of absolute URI and attempt to satisfy those for some type(s) of absolute URI and attempt to satisfy those
requests via translation through the HTTP interface. Some requests via translation through the HTTP interface. Some
translations are minimal, such as for proxy requests for "http" URIs, translations are minimal, such as for proxy requests for "http" URIs,
whereas other requests might require translation to and from entirely whereas other requests might require translation to and from entirely
different application-level protocols. Proxies are often used to different application-level protocols. Proxies are often used to
group an organization's HTTP requests through a common intermediary group an organization's HTTP requests through a common intermediary
for the sake of security, annotation services, or shared caching. for the sake of security, annotation services, or shared caching.
Some proxies are designed to apply transformations to selected Some proxies are designed to apply transformations to selected
messages or payloads while they are being forwarded, as described in messages or payloads while they are being forwarded, as described in
Section 5.7.2. Section 5.5.2.
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
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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 a man-in-the-middle
attack, often introducing security flaws or interoperability problems attack, often introducing security flaws or interoperability problems
due to mistakenly violating HTTP semantics. due to mistakenly violating HTTP semantics.
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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.
2.4. Caches 2.3. 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 by a server while it is 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
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> > > >
UA =========== A =========== B - - - - - - C - - - - - - O UA =========== A =========== B - - - - - - C - - - - - - O
< < < <
A response is "cacheable" if a cache is allowed to store a copy of 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
transoceanic bandwidth, collaborative systems that broadcast or transoceanic bandwidth, collaborative systems that broadcast or
multicast cache entries, archives of pre-fetched cache entries for multicast cache entries, archives of pre-fetched cache entries for
use in off-line or high-latency environments, and so on. use in off-line or high-latency environments, and so on.
2.7. Uniform Resource Identifiers 2.4. Uniform Resource Identifiers
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 2.5). URI
URI references are used to target requests, indicate redirects, and 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 effective request URI (Section 5.3).
2. Resources 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.
2.5. 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. Each resource is
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 2.4.
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]).
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 7) and a few request-
request-modifying header fields (Section 5). If there is a conflict modifying header fields (Section 8). If there is a conflict between
between the method semantics and any semantic implied by the URI the method semantics and any semantic implied by the URI itself, as
itself, as described in Section 4.2.1, the method semantics take described in Section 7.2.1, the method semantics take precedence.
precedence.
IANA maintains the registry of URI Schemes [BCP115] at
<http://www.iana.org/assignments/uri-schemes/>.
This document defines the following URI schemes. IANA maintains the registry of URI Schemes [BCP35] at
<https://www.iana.org/assignments/uri-schemes/>. Although requests
might target any URI scheme, the following schemes are inherent to
HTTP servers:
+------------+------------------------------------+---------------+ +------------+------------------------------------+---------------+
| URI Scheme | Description | Reference | | URI Scheme | Description | Reference |
+------------+------------------------------------+---------------+ +------------+------------------------------------+---------------+
| http | Hypertext Transfer Protocol | Section 2.7.1 | | http | Hypertext Transfer Protocol | Section 2.5.1 |
| https | Hypertext Transfer Protocol Secure | Section 2.7.2 | | https | Hypertext Transfer Protocol Secure | Section 2.5.2 |
+------------+------------------------------------+---------------+ +------------+------------------------------------+---------------+
2.7.1. http URI Scheme 2.5.1. http URI Scheme
The "http" URI scheme is hereby defined for the purpose of minting The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for namespace governed by a potential HTTP origin 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 TCP port
([RFC3986], Section 3.2.2). The hierarchical path component and ([RFC3986], Section 3.2.2). The hierarchical path component and
optional query component serve as an identifier for a potential optional query component serve as an identifier for a potential
target resource within that origin server's name space. target resource within that origin server's name space.
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.
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subcomponent is empty or not given, TCP port 80 (the reserved port subcomponent is empty or not given, TCP port 80 (the reserved port
for WWW services) is the default. for WWW services) is the default.
Note that the presence of a URI with a given authority component does Note that the presence of a URI with a given authority component does
not imply that there is always an HTTP server listening for not imply that there is always an HTTP server listening for
connections on that host and port. Anyone can mint a URI. What the connections on that host and port. Anyone can mint a URI. What the
authority component determines is who has the right to respond authority component determines is who has the right to respond
authoritatively to requests that target the identified resource. The authoritatively to requests that target the identified resource. The
delegated nature of registered names and IP addresses creates a delegated nature of registered names and IP addresses creates a
federated namespace, based on control over the indicated host and federated namespace, based on control over the indicated host and
port, whether or not an HTTP server is present. See Section 9.1 for port, whether or not an HTTP server is present. See Section 13.1 for
security considerations related to establishing authority. security considerations related to establishing authority.
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 to an IP address, establishing a TCP connection to that address
on the indicated port, and sending an HTTP request message on the indicated port, and sending an HTTP request message (Section 2
(Section 3) containing the URI's identifying data (Section 5) to the of [Messaging]) containing the URI's identifying data to the server.
server. If the server responds to that request with a non-interim If the server responds to that request with a non-interim HTTP
HTTP response message, as described in Section 6 of [RFC7231], then response message, as described in Section 9, then that response is
that response is considered an authoritative answer to the client's considered an authoritative answer to the client's request.
request.
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 is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority. An HTTP service process depends on TCP for establishing authority. An HTTP service
based on some other underlying connection protocol would presumably based on some other underlying connection protocol would presumably
be identified using a different URI scheme, just as the "https" be identified using a different URI scheme, just as the "https"
scheme (below) is used for resources that require an end-to-end scheme (below) is used for resources that require an end-to-end
secured connection. Other protocols might also be used to provide secured connection. Other protocols might also be used to provide
access to "http" identified resources -- it is only the authoritative access to "http" identified resources -- it is only the authoritative
interface that is specific to TCP. interface that is specific to TCP.
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authentication information, such as within command invocation authentication information, such as within command invocation
options, configuration files, or bookmark lists, even though such options, configuration files, or bookmark lists, even though such
usage might expose a user identifier or password. A sender MUST NOT usage might expose a user identifier or password. A sender MUST NOT
generate the userinfo subcomponent (and its "@" delimiter) when an generate the userinfo subcomponent (and its "@" delimiter) when an
"http" URI reference is generated within a message as a request "http" URI reference is generated within a message as a request
target or header field value. Before making use of an "http" URI target or header field value. Before making use of an "http" URI
reference received from an untrusted source, a recipient SHOULD parse reference received from an untrusted source, a recipient SHOULD parse
for userinfo and treat its presence as an error; it is likely being for userinfo and treat its presence as an error; it is likely being
used to obscure the authority for the sake of phishing attacks. used to obscure the authority for the sake of phishing attacks.
2.7.2. https URI Scheme 2.5.2. https URI Scheme
The "https" URI scheme is hereby defined for the purpose of minting The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening to a namespace governed by a potential HTTP origin server listening to a
given TCP port for TLS-secured connections ([RFC5246]). given TCP port for TLS-secured connections ([RFC8446]).
All of the requirements listed above for the "http" scheme are also All of the requirements listed above for the "http" scheme are also
requirements for the "https" scheme, except that TCP port 443 is the requirements for the "https" scheme, except that TCP port 443 is the
default if the port subcomponent is empty or not given, and the user default if the port subcomponent is empty or not given, and the user
agent MUST ensure that its connection to the origin server is secured agent MUST ensure that its connection to the origin server is secured
through the use of strong encryption, end-to-end, prior to sending through the use of strong encryption, end-to-end, prior to sending
the first HTTP request. the first HTTP request.
https-URI = "https:" "//" authority path-abempty [ "?" query ] https-URI = "https:" "//" authority path-abempty [ "?" query ]
[ "#" fragment ]
Note that the "https" URI scheme depends on both TLS and TCP for Note that the "https" URI scheme depends on both TLS and TCP for
establishing authority. Resources made available via the "https" establishing authority. Resources made available via the "https"
scheme have no shared identity with the "http" scheme even if their scheme have no shared identity with the "http" scheme even if their
resource identifiers indicate the same authority (the same host resource identifiers indicate the same authority (the same host
listening to the same TCP port). They are distinct namespaces and listening to the same TCP port). They are distinct namespaces and
are considered to be distinct origin servers. However, an extension are considered to be distinct origin servers. However, an extension
to HTTP that is defined to apply to entire host domains, such as the to HTTP that is defined to apply to entire host domains, such as the
Cookie protocol [RFC6265], can allow information set by one service Cookie protocol [RFC6265], can allow information set by one service
to impact communication with other services within a matching group to impact communication with other services within a matching group
of host domains. of host domains.
The process for authoritative access to an "https" identified 2.5.2.1. Initiating HTTP Over TLS
resource is defined in [RFC2818].
2. HTTP Over TLS
Conceptually, HTTP/TLS is very simple. Simply use HTTP over TLS Conceptually, HTTP/TLS is very simple. Simply use HTTP over TLS
precisely as you would use HTTP over TCP. precisely as you would use HTTP over TCP.
2.1. Connection Initiation
The agent acting as the HTTP client should also act as the TLS The agent acting as the HTTP client should also act as the TLS
client. It should initiate a connection to the server on the client. It should initiate a connection to the server on the
appropriate port and then send the TLS ClientHello to begin the TLS appropriate port and then send the TLS ClientHello to begin the TLS
handshake. When the TLS handshake has finished. The client may then handshake. When the TLS handshake has finished. The client may then
initiate the first HTTP request. All HTTP data MUST be sent as TLS initiate the first HTTP request. All HTTP data MUST be sent as TLS
"application data". Normal HTTP behavior, including retained "application data". Normal HTTP behavior, including retained
connections should be followed. connections should be followed.
3.1. Server Identity 2.5.2.2. Identifying HTTPS Servers
In general, HTTP/TLS requests are generated by dereferencing a URI. In general, HTTP/TLS requests are generated by dereferencing a URI.
As a consequence, the hostname for the server is known to the client. As a consequence, the hostname for the server is known to the client.
If the hostname is available, the client MUST check it against the If the hostname is available, the client MUST check it against the
server's identity as presented in the server's Certificate message, server's identity as presented in the server's Certificate message,
in order to prevent man-in-the-middle attacks. in order to prevent man-in-the-middle attacks.
If the client has external information as to the expected identity of If the client has external information as to the expected identity of
the server, the hostname check MAY be omitted. (For instance, a the server, the hostname check MAY be omitted. (For instance, a
client may be connecting to a machine whose address and hostname are client may be connecting to a machine whose address and hostname are
dynamic but the client knows the certificate that the server will dynamic but the client knows the certificate that the server will
present.) In such cases, it is important to narrow the scope of present.) In such cases, it is important to narrow the scope of
acceptable certificates as much as possible in order to prevent man acceptable certificates as much as possible in order to prevent man
in the middle attacks. In special cases, it may be appropriate for in the middle attacks. In special cases, it may be appropriate for
the client to simply ignore the server's identity, but it must be the client to simply ignore the server's identity, but it must be
understood that this leaves the connection open to active attack. understood that this leaves the connection open to active attack.
If a subjectAltName extension of type dNSName is present, that MUST If a subjectAltName extension of type dNSName is present, that MUST
be used as the identity. Otherwise, the (most specific) Common Name be used as the identity. Otherwise, the (most specific) Common Name
field in the Subject field of the certificate MUST be used. Although 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 the use of the Common Name is existing practice, it is deprecated and
Certification Authorities are encouraged to use the dNSName instead. Certification Authorities are encouraged to use the dNSName instead.
Matching is performed using the matching rules specified by Matching is performed using the matching rules specified by
[RFC2459]. If more than one identity of a given type is present in [RFC5280]. If more than one identity of a given type is present in
the certificate (e.g., more than one dNSName name, a match in any one the certificate (e.g., more than one dNSName name, a match in any one
of the set is considered acceptable.) Names may contain the wildcard of the set is considered acceptable.) Names may contain the wildcard
character * which is considered to match any single domain name character * which is considered to match any single domain name
component or component fragment. E.g., *.a.com matches foo.a.com but component or component fragment. E.g., *.a.com matches foo.a.com but
not bar.foo.a.com. f*.com matches foo.com but not bar.com. not bar.foo.a.com. f*.com matches foo.com but not bar.com.
In some cases, the URI is specified as an IP address rather than a In some cases, the URI is specified as an IP address rather than a
hostname. In this case, the iPAddress subjectAltName must be present hostname. In this case, the iPAddress subjectAltName must be present
in the certificate and must exactly match the IP in the URI. in the certificate and must exactly match the IP in the URI.
If the hostname does not match the identity in the certificate, user If the hostname does not match the identity in the certificate, user
oriented clients MUST either notify the user (clients MAY give the oriented clients MUST either notify the user (clients MAY give the
user the opportunity to continue with the connection in any case) or user the opportunity to continue with the connection in any case) or
terminate the connection with a bad certificate error. Automated terminate the connection with a bad certificate error. Automated
clients MUST log the error to an appropriate audit log (if available) clients MUST log the error to an appropriate audit log (if available)
and SHOULD terminate the connection (with a bad certificate error). and SHOULD terminate the connection (with a bad certificate error).
Automated clients MAY provide a configuration setting that disables Automated clients MAY provide a configuration setting that disables
this check, but MUST provide a setting which enables it. this check, but MUST provide a setting which enables it.
Note that in many cases the URI itself comes from an untrusted Note that in many cases the URI itself comes from an untrusted
source. The above-described check provides no protection against source. The above-described check provides no protection against
attacks where this source is compromised. For example, if the URI was attacks where this source is compromised. For example, if the URI
obtained by clicking on an HTML page which was itself obtained 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 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 URI. In order to prevent this form of attack, users should carefully
examine the certificate presented by the server to determine if it examine the certificate presented by the server to determine if it
meets their expectations. meets their expectations.
3.2. Client Identity 2.5.2.3. Identifying HTTPS Clients
Typically, the server has no external knowledge of what the client's 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 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 certificate chain rooted in an appropriate CA) are not possible. If
server has such knowledge (typically from some source external to a server has such knowledge (typically from some source external to
HTTP or TLS) it SHOULD check the identity as described above. HTTP or TLS) it SHOULD check the identity as described above.
2.5.3. Fragment Identifiers on http(s) URI References 2.5.3. Fragment Identifiers on http(s) URI References
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 (see
Section 5.1).
Note: the fragment identifier component is not part of the actual
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.
2.5.4. http and https URI Normalization and Comparison 2.5.4. http and https URI 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 in
absolute form as the request target of an OPTIONS request, an empty absolute form as the request target of an OPTIONS request, an empty
path component is equivalent to an absolute path of "/", so the path component is equivalent to an absolute path of "/", so the
normal form is to provide a path of "/" instead. The scheme and host normal form is to provide a path of "/" instead. The scheme and host
are case-insensitive and normally provided in lowercase; all other are case-insensitive and normally provided in lowercase; all other
components are compared in a case-sensitive manner. Characters other components are compared in a case-sensitive manner. Characters other
than those in the "reserved" set are equivalent to their than those in the "reserved" set are equivalent to their percent-
percent-encoded octets: the normal form is to not encode them (see encoded octets: the normal form is to not encode them (see Sections
Sections 2.1 and 2.2 of [RFC3986]). 2.1 and 2.2 of [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
X. [Conformance] 3. Conformance
2.2. Implementation Diversity 3.1. Implementation Diversity
When considering the design of HTTP, it is easy to fall into a trap When considering the design of HTTP, it is easy to fall into a trap
of thinking that all user agents are general-purpose browsers and all of thinking that all user agents are general-purpose browsers and all
origin servers are large public websites. That is not the case in origin servers are large public websites. That is not the case in
practice. Common HTTP user agents include household appliances, practice. Common HTTP user agents include household appliances,
stereos, scales, firmware update scripts, command-line programs, stereos, scales, firmware update scripts, command-line programs,
mobile apps, and communication devices in a multitude of shapes and mobile apps, and communication devices in a multitude of shapes and
sizes. Likewise, common HTTP origin servers include home automation sizes. Likewise, common HTTP origin servers include home automation
units, configurable networking components, office machines, units, configurable networking components, office machines,
autonomous robots, news feeds, traffic cameras, ad selectors, and autonomous robots, news feeds, traffic cameras, ad selectors, and
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warning for security or privacy concerns. In the few cases where warning for security or privacy concerns. In the few cases where
this specification requires reporting of errors to the user, it is this specification requires reporting of errors to the user, it is
acceptable for such reporting to only be observable in an error acceptable for such reporting to only be observable in an error
console or log file. Likewise, requirements that an automated action console or log file. Likewise, requirements that an automated action
be confirmed by the user before proceeding might be met via advance be confirmed by the user before proceeding might be met via advance
configuration choices, run-time options, or simple avoidance of the configuration choices, run-time options, or simple avoidance of the
unsafe action; confirmation does not imply any specific user unsafe action; confirmation does not imply any specific user
interface or interruption of normal processing if the user has interface or interruption of normal processing if the user has
already made that choice. already made that choice.
2.5. Conformance and Error Handling 3.2. Role-based Requirements
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, HTTP 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.
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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).
3.3. Parsing Elements
When a received protocol element is parsed, the recipient MUST be When a received protocol element is parsed, the recipient MUST be
able to parse any value of reasonable length that is applicable to able to parse any value of reasonable length that is applicable to
the recipient's role and that matches the grammar defined by the the recipient's role and that matches the grammar defined by the
corresponding ABNF rules. Note, however, that some received protocol corresponding ABNF rules. Note, however, that some received protocol
elements might not be parsed. For example, an intermediary elements might not be parsed. For example, an intermediary
forwarding a message might parse a header-field into generic forwarding a message might parse a header-field into generic field-
field-name and field-value components, but then forward the header name and field-value components, but then forward the header field
field without further parsing inside the field-value. without further parsing inside the field-value.
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 request target.
3.4. 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-
Accept-Encoding header field if inspection of the User-Agent header Encoding header field if inspection of the User-Agent header field
field indicates a specific implementation version that is known to indicates a specific implementation version that is known to fail on
fail on receipt of certain content codings. receipt of certain content codings.
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.
2.6. Protocol Versioning Some requests can be automatically retried by a client in the event
of an underlying connection failure, as described in Section 7.2.2.
3.5. Protocol Versioning
The HTTP version number consists of two decimal digits separated by a The HTTP 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 HTTP 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 and able to understand for
future communication. future communication.
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" [Messaging].
The minor version advertises the sender's The minor version advertises the sender's communication capabilities
communication capabilities even when the sender is only using a even when the sender is only using a backwards-compatible subset of
backwards-compatible subset of the protocol, thereby letting the the protocol, thereby letting the recipient know that more advanced
recipient know that more advanced features can be used in response features can be used in response (by servers) or in future requests
(by servers) or in future requests (by clients). (by clients).
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
from the response status code or header fields (e.g., Server) that from the response status code or header fields (e.g., Server) that
the server improperly handles higher request versions. the server improperly handles higher request versions.
A server SHOULD send a response version equal to the highest version A server SHOULD send a response version equal to the highest version
to which the server is conformant that has a major version less than to which the server is conformant that has a major version less than
or equal to the one received in the request. A server MUST NOT send or equal to the one received in the request. A server MUST NOT send
a version to which it is not conformant. A server can send a 505 a version to which it is not conformant. A server can send a 505
(HTTP Version Not Supported) response if it wishes, for any reason, (HTTP Version Not Supported) response if it wishes, for any reason,
to refuse service of the client's major protocol version. to refuse service of the client's major protocol version.
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.
When an HTTP message is received with a major version number that the When an HTTP message is received with a major version number that the
recipient implements, but a higher minor version number than what the recipient implements, but a higher minor version number than what the
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.
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.
4. Header Fields 4. Header Fields
This section defines the abstraction for message fields as field-name
and field-value pairs.
4.1. Header Field Names 4.1. Header Field Names
Header fields are key:value pairs that can be used to communicate Header fields are key:value pairs that can be used to communicate
data about the message, its payload, the target resource, or the data about the message, its payload, the target resource, or the
connection (i.e., control data). See Section 3.2 of [RFC7230] for a connection (i.e., control data).
general definition of header field syntax in HTTP messages.
The requirements for header field names are defined in [BCP90]. The requirements for header field names are defined in [BCP90].
The field-name token labels the corresponding field-value as having The field-name token labels the corresponding field-value as having
the semantics defined by that header field. For example, the Date the semantics defined by that header field. For example, the Date
header field is defined in Section 7.1.1.2 of [RFC7231] as containing header field is defined in Section 10.1.1.2 as containing the
the origination timestamp for the message in which it appears. origination timestamp for the message in which it appears.
field-name = token field-name = token
The interpretation of a header field does not change between minor The interpretation of a header field does not change between minor
versions of the same major HTTP version, though the default behavior versions of the same major HTTP version, though the default behavior
of a recipient in the absence of such a field can change. Unless of a recipient in the absence of such a field can change. Unless
specified otherwise, header fields defined in HTTP/1.1 are defined specified otherwise, header fields are defined for all versions of
for all versions of HTTP/1.x. In particular, the Host and Connection HTTP. In particular, the Host and Connection header fields ought to
header fields ought to be implemented by all HTTP/1.x implementations be implemented by all HTTP/1.x implementations whether or not they
whether or not they advertise conformance with HTTP/1.1. advertise conformance with HTTP/1.1.
New header fields can be introduced without changing the protocol New header fields can be introduced without changing the protocol
version if their defined semantics allow them to be safely ignored by version if their defined semantics allow them to be safely ignored by
recipients that do not recognize them. Header field extensibility is recipients that do not recognize them. Header field extensibility is
discussed in Section 3.2.1. discussed in Section 4.1.2.
The "Message Headers" registry has been updated with the following The following field names are defined by this document:
permanent registrations:
+-------------------+----------+----------+-----------------+ +---------------------------+------------+-------------------+
| Header Field Name | Protocol | Status | Reference | | Header Field Name | Status | Reference |
+-------------------+----------+----------+-----------------+ +---------------------------+------------+-------------------+
| Accept | http | standard | Section 5.3.2 | | Accept | standard | Section 8.4.2 |
| Accept-Charset | http | standard | Section 5.3.3 | | Accept-Charset | deprecated | Section 8.4.3 |
| Accept-Encoding | http | standard | Section 5.3.4 | | Accept-Encoding | standard | Section 8.4.4 |
| Accept-Language | http | standard | Section 5.3.5 | | Accept-Language | standard | Section 8.4.5 |
| Accept-Ranges | http | standard | Section 2.3 | | Accept-Ranges | standard | Section 10.4.1 |
| Allow | http | standard | Section 7.4.1 | | Allow | standard | Section 10.4.2 |
| Authorization | http | standard | Section 4.2 | | Authentication-Info | standard | Section 10.3.3 |
| Content-Encoding | http | standard | Section 3.1.2.2 | | Authorization | standard | Section 8.5.3 |
| Content-Language | http | standard | Section 3.1.3.2 | | Content-Encoding | standard | Section 6.2.2 |
| Content-Length | http | standard | Section 3.3.2 | | Content-Language | standard | Section 6.2.3 |
| Content-Location | http | standard | Section 3.1.4.2 | | Content-Length | standard | Section 6.2.4 |
| Content-Range | http | standard | Section 4.2 | | Content-Location | standard | Section 6.2.5 |
| Content-Type | http | standard | Section 3.1.1.5 | | Content-Range | standard | Section 6.3.4 |
| Date | http | standard | Section 7.1.1.2 | | Content-Type | standard | Section 6.2.1 |
| ETag | http | standard | Section 2.3 | | Date | standard | Section 10.1.1.2 |
| Expect | http | standard | Section 5.1.1 | | ETag | standard | Section 10.2.3 |
| From | http | standard | Section 5.5.1 | | Expect | standard | Section 8.1.1 |
| Host | http | standard | Section 5.4 | | From | standard | Section 8.6.1 |
| If-Match | http | standard | Section 3.1 | | Host | standard | Section 5.4 |
| If-Modified-Since | http | standard | Section 3.3 | | If-Match | standard | Section 8.2.3 |
| If-None-Match | http | standard | Section 3.2 | | If-Modified-Since | standard | Section 8.2.5 |
| If-Range | http | standard | Section 3.2 | | If-None-Match | standard | Section 8.2.4 |
| If-Unmodified-Since | http | standard | Section 3.4 | | If-Range | standard | Section 8.2.7 |
| Last-Modified | http | standard | Section 2.2 | | If-Unmodified-Since | standard | Section 8.2.6 |
| Location | http | standard | Section 7.1.2 | | Last-Modified | standard | Section 10.2.2 |
| Max-Forwards | http | standard | Section 5.1.2 | | Location | standard | Section 10.1.2 |
| Proxy-Authenticate | http | standard | Section 4.3 | | Max-Forwards | standard | Section 8.1.2 |
| Proxy-Authorization | http | standard | Section 4.4 | | Proxy-Authenticate | standard | Section 10.3.2 |
| Range | http | standard | Section 3.1 | | Proxy-Authentication-Info | standard | Section 10.3.4 |
| Referer | http | standard | Section 5.5.2 | | Proxy-Authorization | standard | Section 8.5.4 |
| Retry-After | http | standard | Section 7.1.3 | | Range | standard | Section 8.3 |
| Server | http | standard | Section 7.4.2 | | Referer | standard | Section 8.6.2 |
| Trailer | http | standard | Section 4.4 | | Retry-After | standard | Section 10.1.3 |
| User-Agent | http | standard | Section 5.5.3 | | Server | standard | Section 10.4.3 |
| Vary | http | standard | Section 7.1.4 | | Trailer | standard | Section 4.3.3 |
| Via | http | standard | Section 5.7.1 | | User-Agent | standard | Section 8.6.3 |
| WWW-Authenticate | http | standard | Section 4.1 | | Vary | standard | Section 10.1.4 |
+-------------------+----------+----------+-----------------+ | Via | standard | Section 5.5.1 |
| WWW-Authenticate | standard | Section 10.3.1 |
+---------------------------+------------+-------------------+
Table 1
4.1.1. Header Field Name Registry 4.1.1. Header Field Name Registry
HTTP header fields are registered within the "Message Headers" The "Hypertext Transfer Protocol (HTTP) Header Field Registry"
registry located at defines the namespace for HTTP header field names.
<http://www.iana.org/assignments/message-headers>, as defined by
[BCP90]. Any party can request registration of a HTTP header field. See
Section 4.4 for considerations to take into account when creating a
new HTTP header field.
The "HTTP Header Field Name" registry is located at
"https://www.iana.org/assignments/http-headers/". Registration
requests can be made by following the instructions located there or
by sending an email to the "ietf-http-wg@ietf.org" mailing list.
Header field names are registered on the advice of a Designated
Expert (appointed by the IESG or their delegate). Header fields with
the status 'permanent' are Specification Required (using terminology
from [RFC8126]).
Registration requests consist of at least the following information:
o Header field name: The requested field name. It MUST conform to
the field-name syntax defined in Section 4.1, and SHOULD be
restricted to just letters, digits, hyphen ('-') and underscore
('_') characters, with the first character being a letter.
o Status: "permanent" or "provisional"
o Specification document(s): Reference to the document that
specifies the header 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.
The Expert(s) can define additional fields to be collected in the
registry, in consultation with the community.
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".
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.
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.
4.1.2. Header Field Extensibility 4.1.2. Header Field Extensibility
Header fields are fully extensible: there is no limit on the Header fields are fully extensible: there is no limit on the
introduction of new field names, each presumably defining new introduction of new field names, each presumably defining new
semantics, nor on the number of header fields used in a given semantics, nor on the number of header fields used in a given
message. Existing fields are defined in each part of this message. Existing fields are defined in each part of this
specification and in many other specifications outside this document specification and in many other specifications outside this document
set. set.
New header fields can be defined such that, when they are understood New header fields can be defined such that, when they are understood
by a recipient, they might override or enhance the interpretation of by a recipient, they might override or enhance the interpretation of
previously defined header fields, define preconditions on request previously defined header fields, define preconditions on request
evaluation, or refine the meaning of responses. evaluation, or refine the meaning of responses.
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 9.1 of [Messaging])
is specifically configured to block, or otherwise transform, such or the proxy is specifically configured to block, or otherwise
fields. Other recipients SHOULD ignore unrecognized header fields. transform, such fields. Other recipients SHOULD ignore unrecognized
These requirements allow HTTP's functionality to be enhanced without header fields. These requirements allow HTTP's functionality to be
requiring prior update of deployed intermediaries. enhanced without requiring prior update of deployed intermediaries.
All defined header fields ought to be registered with IANA in the All defined header fields ought to be registered with IANA in the
"Message Headers" registry, as described in Section 8.3 of [RFC7231]. "HTTP Header Field Name" registry.
4.2. Field Values 4.2. Header Field Values
Consequently, this specification does not use ABNF rules This specification does not use ABNF rules to define each "Field-
to define each "Field-Name: Field Value" pair, as was done in Name: Field Value" pair, as was done in earlier editions. Instead,
previous editions. Instead, this specification uses ABNF rules that this specification uses ABNF rules that are named according to each
are named according to each registered field name, wherein the rule registered field name, wherein the rule defines the valid grammar for
defines the valid grammar for that field's corresponding field values that field's corresponding field values (i.e., after the field-value
(i.e., after the field-value has been extracted from the header has been extracted by a generic field parser).
section by a generic field parser).
field-value = *( field-content / obs-fold ) field-value = *( field-content / obs-fold )
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 header field values could be extended over Historically, HTTP header field values could be extended over
multiple lines by preceding each extra line with at least one space multiple lines by preceding each extra line with at least one space
or horizontal tab (obs-fold). or horizontal tab (obs-fold). [[CREF1: This document assumes that
any such obs-fold has been replaced with one or more SP octets prior
to interpreting the field value, as described in Section 5.2 of
[Messaging].]]
Historically, HTTP has allowed field content with text in the Historically, HTTP has allowed field content with text in the
ISO-8859-1 charset [ISO-8859-1], supporting other charsets only ISO-8859-1 charset [ISO-8859-1], supporting other charsets only
through use of [RFC2047] encoding. In practice, most HTTP header through use of [RFC2047] encoding. In practice, most HTTP header
field values use only a subset of the US-ASCII charset [USASCII]. field values use only a subset of the US-ASCII charset [USASCII].
Newly defined header fields SHOULD limit their field values to Newly defined header fields SHOULD limit their field values to
US-ASCII octets. A recipient SHOULD treat other octets in field US-ASCII octets. A recipient SHOULD treat other octets in field
content (obs-text) as opaque data. content (obs-text) as opaque data.
4.2.1. Field Order 4.2.1. Header Field Order
The order in which header fields with differing field names are The order in which header fields with differing field names are
received is not significant. However, it is good practice to send received is not significant. However, it is good practice to send
header fields that contain control data first, such as Host on header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST NOT when not to handle a message as early as possible. A server MUST NOT
apply a request to the target resource until the entire request apply a request to the target resource until the entire request
header section is received, since later header fields might include header section is received, since later header fields might include
conditionals, authentication credentials, or deliberately misleading conditionals, authentication credentials, or deliberately misleading
duplicate header fields that would impact request processing. duplicate header fields that would impact request processing.
A sender MUST NOT generate multiple header fields with the same field Aside from the well-known exception noted below, a sender MUST NOT
name in a message unless either the entire field value for that generate multiple header fields with the same field name in a
header field is defined as a comma-separated list [i.e., #(values)] message, or append a header field when a field of the same name
or the header field is a well-known exception (as noted below). already exists in the message, unless that field's definition allows
multiple field 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)].
A recipient MAY combine multiple header fields with the same field A recipient MAY combine multiple header fields with the same field
name into one "field-name: field-value" pair, without changing the name into one "field-name: field-value" pair, without changing the
semantics of the message, by appending each subsequent field value to semantics of the message, by appending each subsequent field value to
the combined field value in order, separated by a comma. The order the combined field value in order, separated by a comma. The order
in which header fields with the same field name are received is in which header fields with the same field name are received is
therefore significant to the interpretation of the combined field therefore significant to the interpretation of the combined field
value; a proxy MUST NOT change the order of these field values when value; a proxy MUST NOT change the order of these field values when
forwarding a message. forwarding a message.
Note: In practice, the "Set-Cookie" header field ([RFC6265]) often Note: In practice, the "Set-Cookie" header field ([RFC6265]) often
appears multiple times in a response message and does not use the appears multiple times in a response message and does not use the
list syntax, violating the above requirements on multiple header list syntax, violating the above requirements on multiple header
fields with the same name. Since it cannot be combined into a fields with the same name. Since it cannot be combined into a
single field-value, recipients ought to handle "Set-Cookie" as a single field-value, recipients ought to handle "Set-Cookie" as a
special case while processing header fields. (See Appendix A.2.3 special case while processing header fields. (See Appendix A.2.3
of [Kri2001] for details.) of [Kri2001] for details.)
3.2.5. Field Limits 4.2.2. Header 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 header
field or on the length of the header section as a whole, as described field or on the length of the header section as a whole, as described
in Section 2.5. Various ad hoc limitations on individual header in Section 3. Various ad hoc limitations on individual header field
field length are found in practice, often depending on the specific length are found in practice, often depending on the specific field
field semantics. semantics.
A server that receives a request header field, or set of fields, A server that receives a request header field, or set of fields,
larger than it wishes to process MUST respond with an appropriate 4xx larger than it wishes to process MUST respond with an appropriate 4xx
(Client Error) status code. Ignoring such header fields would (Client Error) status code. Ignoring such header fields would
increase the server's vulnerability to request smuggling attacks increase the server's vulnerability to request smuggling attacks
(Section 9.5). (Section 11.2 of [Messaging]).
A client MAY discard or truncate received header fields that are A client MAY discard or truncate received header fields that are
larger than the client wishes to process if the field semantics are larger than the client wishes to process if the field semantics are
such that the dropped value(s) can be safely ignored without changing such that the dropped value(s) can be safely ignored without changing
the message framing or response semantics. the message framing or response semantics.
3.2.6. Field Value Components 4.2.3. Header Field Value Components
Most HTTP header field values are defined using common syntax Many HTTP header field values are defined using common syntax
components (token, quoted-string, and comment) separated by components, separated by whitespace or specific delimiting
whitespace or specific delimiting characters. Delimiters are chosen characters. Delimiters are chosen from the set of US-ASCII visual
from the set of US-ASCII visual characters not allowed in a token characters not allowed in a token (DQUOTE and "(),/:;<=>?@[\]{}").
(DQUOTE and "(),/:;<=>?@[\]{}").
4.2.3.1. Tokens
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
4.2.3.2. 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.
4.2.3.3. Comments
Comments can be included in some HTTP header fields by surrounding Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition. fields 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
parameter = token "=" ( token / quoted-string ) 4.2.3.4. Parameters
The parameter name tokens are case-insensitive. A parameter is a name=value pair that is often defined within header
Parameter values might or might not be case-sensitive, depending on field values as a common syntax for appending auxiliary information
the semantics of the parameter name. to an item. Each parameter is usually delimited by an immediately
preceding semicolon.
parameter = parameter-name "=" parameter-value
parameter-name = token
parameter-value = ( token / quoted-string )
Parameter names are case-insensitive. Parameter values might or
might not be case-sensitive, depending on the semantics of the
parameter name. Examples of parameters and some equivalent forms can
be seen in media types (Section 6.1.1) and the Accept header field
(Section 8.4.2).
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.
X.X. [Trailer Fields] 4.3. Trailer Fields
A trailer allows the sender to include additional fields at the end 4.3.1. Purpose
of a chunked message in order to supply metadata that might be
dynamically generated while the message body is sent, such as a
message integrity check, digital signature, or post-processing
status. The trailer fields are identical to header fields, except
they are sent in a chunked trailer instead of the message's header
section.
A sender MUST NOT generate a trailer that contains a field necessary In some HTTP versions, additional metadata can be sent after the
for message framing (e.g., Transfer-Encoding and Content-Length), initial header section has been completed (during or after
routing (e.g., Host), request modifiers (e.g., controls and transmission of the payload body), such as a message integrity check,
conditionals in Section 5 of [RFC7231]), authentication (e.g., see digital signature, or post-processing status. For example, the
[RFC7235] and [RFC6265]), response control data (e.g., see Section chunked coding in HTTP/1.1 allows a trailer section after the payload
7.1 of [RFC7231]), or determining how to process the payload (e.g., body (Section 7.1.2 of [Messaging]) which can contain trailer fields:
Content-Encoding, Content-Type, Content-Range, and Trailer). field names and values that share the same syntax and namespace as
header fields but are received after the header section.
When a chunked message containing a non-empty trailer is received, Trailer fields ought to be processed and stored separately from the
the recipient MAY process the fields (aside from those forbidden fields in the header section to avoid contradicting message semantics
above) as if they were appended to the message's header section. A known at the time the header section was complete. The presence or
recipient MUST ignore (or consider as an error) any fields that are absence of certain header fields might impact choices made for the
forbidden to be sent in a trailer, since processing them as if they routing or processing of the message as a whole before the trailers
were present in the header section might bypass external security are received; those choices cannot be unmade by the later discovery
filters. of trailer fields.
Unless the request includes a TE header field indicating "trailers" 4.3.2. Limitations
is acceptable, as described in Section 4.3, a server SHOULD NOT
generate trailer fields that it believes are necessary for the user Many header fields cannot be processed outside the header section
agent to receive. Without a TE containing "trailers", the server because their evaluation is necessary prior to receiving the message
ought to assume that the trailer fields might be silently discarded body, such as fields that describe message framing, routing,
along the path to the user agent. This requirement allows authentication, request modifiers, response controls, or payload
intermediaries to forward a de-chunked message to an HTTP/1.0 format. A sender MUST NOT generate a trailer field unless the sender
recipient without buffering the entire response. knows the corresponding header field name's definition permits the
field to be sent in trailers.
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.
A client can send a TE header field indicating "trailers" is
acceptable, as described in Section 7.4 of [Messaging], to inform the
server that it will not discard trailer fields.
Because of the potential for trailer fields to be discarded in
transit, a server SHOULD NOT generate trailer fields that it believes
are necessary for the user agent to receive.
4.3.3. Trailer 4.3.3. Trailer
The "Trailer" header field provides a list of field names that the
sender anticipates sending as trailer fields within that message.
This allows a recipient to prepare for receipt of the indicated
metadata before it starts processing the body.
Trailer = 1#field-name Trailer = 1#field-name
When a message includes a message body encoded with the chunked For example, a sender might indicate that a message integrity check
transfer coding and the sender desires to send metadata in the form will be computed as the payload is being streamed and provide the
of trailer fields at the end of the message, the sender SHOULD final signature as a trailer field. This allows a recipient to
generate a Trailer header field before the message body to indicate perform the same check on the fly as the payload data is received.
which fields will be present in the trailers. This allows the
recipient to prepare for receipt of that metadata before it starts A sender that intends to generate one or more trailer fields in a
processing the body, which is useful if the message is being streamed message SHOULD generate a Trailer header field in the header section
and the recipient wishes to confirm an integrity check on the fly. of that message to indicate which fields might be present in the
trailers.
4.4. Considerations for New Header Fields 4.4. Considerations for New Header Fields
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 and not to prefix the name with "X-" short but descriptive field name. Short names avoid needless data
unless the header field will never be used on the Internet. (The transmission; descriptive names avoid confusion and "squatting" on
"X-" prefix idiom has been extensively misused in practice; it was names that might have broader uses.
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 header field values typically have their syntax defined using To that end, limited-use fields (such as a header confined to a
ABNF ([RFC5234]), using the extension defined in Section 7 of single application or use case) are encouraged to use a name that
[RFC7230] as necessary, and are usually constrained to the range of includes its name (or an abbreviation) as a prefix; for example, if
US-ASCII characters. Header fields needing a greater range of the Foo Application needs a Description field, it might use "Foo-
characters can use an encoding such as the one defined in [RFC5987]. Desc"; "Description" is too generic, and "Foo-Description" is
needlessly long.
Header field names ought not be prefixed with "X-"; see [BCP178] for
further information.
Other prefixes are sometimes used in HTTP header field names; for
example, "Accept-" is used in many content negotiation headers.
These prefixes are only an aid to recognizing the purpose of a header
field, and do not trigger automatic processing.
Header field values typically have their syntax defined using ABNF
([RFC5234]), using the extension defined in Section 12 as necessary,
and are usually constrained to the range of US-ASCII characters.
Header fields needing a greater range of characters can use an
encoding such as the one defined in [RFC8187].
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 (Section 5.1 of [Messaging]). Field definitions where
leading or trailing whitespace in values is significant will have to leading or trailing whitespace in values is significant will have to
use a container syntax such as quoted-string (Section 3.2.6 of use a container syntax such as quoted-string (Section 4.2.3.2).
[RFC7230]).
Because commas (",") are used as a generic delimiter between Because commas (",") are used as a generic delimiter between field-
field-values, they need to be treated with care if they are allowed values, they need to be treated with care if they are allowed in the
in the field-value. Typically, components that might contain a comma field-value. Typically, components that might contain a comma are
are protected with double-quotes using the quoted-string ABNF protected with double-quotes using the quoted-string ABNF production.
production.
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 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 header fields (such as Content-Type, defined in Section 6.2.1)
parameters (for instance, Content-Type, defined in Section 3.1.1.5). use a common syntax for parameters that allows both unquoted (token)
Allowing both unquoted (token) and quoted (quoted-string) syntax for and quoted (quoted-string) syntax for a parameter value
the parameter value enables recipients to use existing parser (Section 4.2.3.4). Use of common syntax allows recipients to reuse
components. When allowing both forms, the meaning of a parameter existing parser components. When allowing both forms, the meaning of
value ought to be independent of the syntax used for it (for an a parameter value ought to be the same whether it was received as a
example, see the notes on parameter handling for media types in token or a quoted string.
Section 3.1.1.1).
Authors of specifications defining new header fields are advised to Authors of specifications defining new header fields are advised to
consider documenting: consider documenting:
o Whether the field is a single value or whether it can be a list o Whether the field is a single value or whether it can be a list
(delimited by commas; see Section 3.2 of [RFC7230]). (delimited by commas; see Section 4.2).
If it does not use the list syntax, document how to treat messages If it does not use the list syntax, document how to treat messages
where the field occurs multiple times (a sensible default would be where the field occurs multiple times (a sensible default would be
to ignore the field, but this might not always be the right to ignore the field, but this might not always be the right
choice). choice).
Note that intermediaries and software libraries might combine Note that intermediaries and software libraries might combine
multiple header field instances into a single one, despite the multiple header field instances into a single one, despite the
field's definition not allowing the list syntax. A robust format field's definition not allowing the list syntax. A robust format
enables recipients to discover these situations (good example: enables recipients to discover these situations (good example:
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particular request method, etc. particular request method, etc.
o Whether the field should be stored by origin servers that o Whether the field should be stored by origin servers that
understand it upon a PUT request. understand it upon a PUT request.
o Whether the field semantics are further refined by the context, o Whether the field semantics are further refined by the context,
such as by existing request methods or status codes. such as by existing request methods or status codes.
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 header field is to be hop-by-hop; see
Section 6.1 of [RFC7230]). Section 9.1 of [Messaging]).
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 it is appropriate to list the field-name in a Vary o Whether it is appropriate to list the field-name in a Vary
response header field (e.g., when the request header field is used response header field (e.g., when the request header field is used
by an origin server's content selection algorithm; see by an origin server's content selection algorithm; see
Section 7.1.4). Section 10.1.4).
o Whether the header field is useful or allowable in trailers (see o Whether the header field is useful or allowable in trailers (see
Section 4.1 of [RFC7230]). Section 7.1 of [Messaging]).
o Whether the header field ought to be preserved across redirects. o Whether the header field ought to be preserved across redirects.
o Whether it introduces any additional security considerations, such o Whether it introduces any additional security considerations, such
as disclosure of privacy-related data. as disclosure of privacy-related data.
5. Message Routing 5. Message Routing
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.
5.1. Identifying a Target Resource 5.1. Identifying a Target Resource
HTTP is used in a wide variety of applications, ranging from HTTP is used in a wide variety of applications, ranging from general-
general-purpose computers to home appliances. In some cases, purpose computers to home appliances. In some cases, communication
communication options are hard-coded in a client's configuration. options are hard-coded in a client's configuration. However, most
However, most HTTP clients rely on the same resource identification HTTP clients rely on the same resource identification mechanism and
mechanism and configuration techniques as general-purpose Web configuration techniques as general-purpose Web browsers.
browsers.
HTTP communication is initiated by a user agent for some purpose. HTTP communication is initiated by a user agent for some purpose.
The purpose is a combination of request semantics, which are defined The purpose is a combination of request semantics and a target
in [RFC7231], and a target resource upon which to apply those resource upon which to apply those semantics. A URI reference
semantics. A URI reference (Section 2.7) is typically used as an (Section 2.4) is typically used as an identifier for the "target
identifier for the "target resource", which a user agent would resource", which a user agent would resolve to its absolute form in
resolve to its absolute form in order to obtain the "target URI". order to obtain the "target URI". The target URI excludes the
The target URI excludes the reference's fragment component, if any, reference's fragment component, if any, since fragment identifiers
since fragment identifiers are reserved for client-side processing are reserved for client-side processing ([RFC3986], Section 3.5).
([RFC3986], Section 3.5).
5.2. Connecting Inbound 5.2. Routing Inbound
Once the target URI is determined, a client needs to decide whether a Once the target URI is determined, a client needs to decide whether a
network request is necessary to accomplish the desired semantics and, network request is necessary to accomplish the desired semantics and,
if so, where that request is to be directed. if so, where that request is to be directed.
If the client has a cache [RFC7234] and the request can be satisfied 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.
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.
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 authority 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, similar to how this specification defines
origin server access for resolution of the "http" (Section 2.7.1) and origin server access for resolution of the "http" (Section 2.5.1) and
"https" (Section 2.7.2) schemes. "https" (Section 2.5.2) schemes.
HTTP requirements regarding connection management are defined in HTTP requirements regarding connection management are defined in
Section 6. Section 9 of [Messaging].
5.5. Effective Request URI 5.3. Effective Request URI
Once an inbound connection is obtained, the client sends an HTTP Once an inbound connection is obtained, the client sends an HTTP
request message (Section 3) with a request-target derived from the request message (Section 2 of [Messaging]).
target URI.
Since the request-target often contains only part of the user agent's Depending on the nature of the request, the client's target URI might
target URI, a server reconstructs the intended target as an be split into components and transmitted (or implied) within various
"effective request URI" to properly service the request. This parts of a request message. These parts are recombined by each
reconstruction involves both the server's local configuration and recipient, in accordance with their local configuration and incoming
information communicated in the request-target, Host header field, connection context, to form an "effective request URI" for
and connection context. identifying the intended target resource with respect to that server.
Section 3.3 of [Messaging] defines how a server determines the
effective request URI for an HTTP/1.1 request.
For a user agent, the effective request URI is the target URI. For a user agent, the effective request URI is the target URI.
Once the effective request URI has been constructed, an origin server Once the effective request URI has been constructed, an origin server
needs to decide whether or not to provide service for that URI via needs to decide whether or not to provide service for that URI via
the connection in which the request was received. For example, the the connection in which the request was received. For example, the
request might have been misdirected, deliberately or accidentally, request might have been misdirected, deliberately or accidentally,
such that the information within a received request-target or Host such that the information within a received request-target or Host
header field differs from the host or port upon which the connection header field differs from the host or port upon which the connection
has been made. If the connection is from a trusted gateway, that has been made. If the connection is from a trusted gateway, that
inconsistency might be expected; otherwise, it might indicate an inconsistency might be expected; otherwise, it might indicate an
attempt to bypass security filters, trick the server into delivering attempt to bypass security filters, trick the server into delivering
non-public content, or poison a cache. See Section 9 for security non-public content, or poison a cache. See Section 13 for security
considerations regarding message routing. considerations regarding message routing.
5.4. Host 5.4. Host
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 on a single IP address.
Host = uri-host [ ":" port ] ; Section 2.7.1 Host = uri-host [ ":" port ] ; Section 2.4
A client MUST send a Host header field in all HTTP/1.1 request A client MUST send a Host header field in all HTTP/1.1 request
messages. If the target URI includes an authority component, then a messages. If the target URI includes an authority component, then a
client MUST send a field-value for Host that is identical to that client MUST send a field-value for Host that is identical to that
authority component, excluding any userinfo subcomponent and its "@" authority component, excluding any userinfo subcomponent and its "@"
delimiter (Section 2.7.1). If the authority component is missing or delimiter (Section 2.5.1). If the authority component is missing or
undefined for the target URI, then a client MUST send a Host header undefined for the target URI, then a client MUST send a Host header
field with an empty field-value. field with an empty field-value.
Since the Host field-value is critical information for handling a Since the Host field-value is critical information 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 header field
following the request-line. following the request-line.
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
A client MUST send a Host header field in an HTTP/1.1 request even if A client MUST send a Host header field in an HTTP/1.1 request even if
the request-target is in the absolute-form, since this allows the the request-target is in the absolute-form, since this allows the
Host information to be forwarded through ancient HTTP/1.0 proxies Host information to be forwarded through ancient HTTP/1.0 proxies
that might not have implemented Host. that might not have implemented Host.
When a proxy receives a request with an absolute-form of When a proxy receives a request with an absolute-form of request-
request-target, the proxy MUST ignore the received Host header field target, the proxy MUST ignore the received Host header field (if any)
(if any) and instead replace it with the host information of the and instead replace it with the host information of the request-
request-target. A proxy that forwards such a request MUST generate a target. A proxy that forwards such a request MUST generate a new
new Host field-value based on the received request-target rather than Host field-value based on the received request-target rather than
forward the received Host field-value. forward the received Host field-value.
Since the Host header field acts as an application-level routing Since the Host header field acts as an application-level routing
mechanism, it is a frequent target for malware seeking to poison a mechanism, it is a frequent target for malware seeking to poison a
shared cache or redirect a request to an unintended server. An shared cache or redirect a request to an unintended server. An
interception proxy is particularly vulnerable if it relies on the interception proxy is particularly vulnerable if it relies on the
Host field-value for redirecting requests to internal servers, or for Host field-value for redirecting requests to internal servers, or for
use as a cache key in a shared cache, without first verifying that use as a cache key in a shared cache, without first verifying that
the intercepted connection is targeting a valid IP address for that the intercepted connection is targeting a valid IP address for that
host. host.
A server MUST respond with a 400 (Bad Request) status code to any A server MUST respond with a 400 (Bad Request) status code to any
HTTP/1.1 request message that lacks a Host header field and to any HTTP/1.1 request message that lacks a Host header field and to any
request message that contains more than one Host header field or a request message that contains more than one Host header field or a
Host header field with an invalid field-value. Host header field with an invalid field-value.
5.7. Message Forwarding 5.5. Message Forwarding
As described in Section 2.3, intermediaries can serve a variety of As described in Section 2.2, 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 9.1 of [Messaging], and exclude
being forwarded that are only intended for the incoming connection. fields from 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 payload transformations.
5.7.1. Via 5.5.1. 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 = 1#( received-protocol RWS received-by [ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version received-protocol = [ protocol-name "/" ] protocol-version
; see Section 6.7 ; see [Messaging], Section 9.9
received-by = ( uri-host [ ":" port ] ) / pseudonym received-by = ( uri-host [ ":" port ] ) / pseudonym
pseudonym = token pseudonym = token
Multiple Via field values represent each proxy or gateway that has Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each intermediary appends its own information forwarded the message. Each intermediary appends its own information
about how the message was received, such that the end result is about how the message was received, such that the end result is
ordered according to the sequence of forwarding recipients. 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 3.5.
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 of the field value is normally the host and
optional port number of a recipient server or client that optional port number of a recipient server or client that
subsequently forwarded the message. However, if the real host is subsequently forwarded the message. However, if the real host is
considered to be sensitive information, a sender MAY replace it with considered to be sensitive information, a sender MAY replace it with
a pseudonym. If a port is not provided, a recipient MAY interpret a pseudonym. If a port is not provided, a recipient MAY interpret
that as meaning it was received on the default TCP port, if any, for that as meaning it was received on the default TCP port, if any, for
the received-protocol. the received-protocol.
skipping to change at line 1603 skipping to change at page 40, line 38
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 entries 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 entries that have
different received-protocol values. different received-protocol values.
5.7.2. Transformations 5.5.2. 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 payloads. 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 payloads 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 payload received is identical to the
original. original.
skipping to change at line 1639 skipping to change at page 41, line 26
name it received when forwarding the request. A proxy MUST NOT name it received when forwarding the request. A proxy MUST NOT
change the host name if the request-target contains a fully qualified change the host name if the request-target 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 request-target when forwarding it to the next inbound
server, except as noted above to replace an empty path with "/" or server, except as noted above to replace an empty path with "/" or
"*". "*".
A proxy MAY modify the message body through application or removal of A proxy MAY modify the message body through application or removal of
a transfer coding (Section 4). a transfer coding (Section 7 of [Messaging]).
A proxy MUST NOT transform the payload (Section 3.3 of [RFC7231]) of A proxy MUST NOT transform the payload (Section 6.3) 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]).
A proxy MAY transform the payload of a message that does not contain A proxy MAY transform the payload 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 payload 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 9.3.4).
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 payload) 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.
3. Representations 6. Representations
Considering that a resource could be anything, and that the uniform Considering that a resource could be anything, and that the uniform
interface provided by HTTP is similar to a window through which one interface provided by HTTP is similar to a window through which one
can observe and act upon such a thing only through the communication can observe and act upon such a thing only through the communication
of messages to some independent actor on the other side, an 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. That
abstraction is called a representation [REST]. abstraction is called a representation [REST].
For the purposes of HTTP, a "representation" is information that is For the purposes of HTTP, a "representation" is information that is
skipping to change at line 1682 skipping to change at page 42, line 19
resource, in a format that can be readily communicated via the resource, in a format that can be readily communicated via the
protocol, and that consists of a set of representation metadata and a protocol, and that consists of a set of representation metadata and a
potentially unbounded stream of representation data. potentially unbounded stream of representation data.
An origin server might be provided with, or be capable of generating, An origin server might be provided with, or be capable of generating,
multiple representations that are each intended to reflect the multiple representations that are each intended to reflect the
current state of a target resource. In such cases, some algorithm is current state of a target resource. In such cases, some algorithm is
used by the origin server to select one of those representations as used by the origin server to select one of those representations as
most applicable to a given request, usually based on content most applicable to a given request, usually based on content
negotiation. This "selected representation" is used to provide the negotiation. This "selected representation" is used to provide the
data and metadata for evaluating conditional requests [RFC7232] and data and metadata for evaluating conditional requests (Section 8.2)
constructing the payload for 200 (OK) and 304 (Not Modified) and constructing the payload for 200 (OK) and 304 (Not Modified)
responses to GET (Section 4.3.1). responses to GET (Section 7.3.1).
3.2. Representation Data 6.1. 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 payload body of the message or referred to by the
message semantics and the effective request URI. The representation message semantics and the effective request URI. The representation
data is in a format and encoding defined by the representation data is in a format 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 ) )
3.1.1.1. Media Type 6.1.1. Media Type
HTTP uses Internet media types [RFC2046] in the Content-Type HTTP uses media types [RFC2046] in the Content-Type (Section 6.2.1)
(Section 3.1.1.5) and Accept (Section 5.3.2) header fields in order and Accept (Section 8.4.2) 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 *( OWS ";" OWS parameter )
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 4.2.3.4) 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].
3.1.1.2. Charset 6.1.1.1. 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].
3.1.1.3. Canonicalization and Text Defaults 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]).
Internet media types are registered with a canonical form in order to 6.1.1.2. Canonicalization and Text Defaults
be interoperable among systems with varying native encoding formats.
Media types are registered with a canonical form in order to be
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 payload body (e.g.,
header fields). header 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.
3.1.1.4. Multipart Types 6.1.1.3. 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 payload. 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 9.3.7).
3.1.2.1. Content Codings 6.1.2. Content Codings
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 Content-coding values are used in the Accept-Encoding (Section 8.4.4)
registered within the "HTTP Content Coding Registry", as defined in and Content-Encoding (Section 6.2.2) header fields.
Section 8.4. They are used in the Accept-Encoding (Section 5.3.4)
and Content-Encoding (Section 3.1.2.2) header fields.
The following content-coding values are defined by this The following content-coding values are defined by this
specification: specification:
compress (and x-compress): See Section 4.2.1 of [RFC7230]. +------------+------------------------------------------+-----------+
| Name | Description | Reference |
deflate: See Section 4.2.2 of [RFC7230]. +------------+------------------------------------------+-----------+
| compress | UNIX "compress" data format [Welch] | Section 6 |
gzip (and x-gzip): See Section 4.2.3 of [RFC7230]. | | | .1.2.1 |
| deflate | "deflate" compressed data ([RFC1951]) | Section 6 |
+------------+--------------------------------------+---------------+ | | inside the "zlib" data format | .1.2.2 |
| Name | Description | Reference | | | ([RFC1950]) | |
+------------+--------------------------------------+---------------+ | gzip | GZIP file format [RFC1952] | Section 6 |
| compress | UNIX "compress" data format [Welch] | Section 4.2.1 | | | | .1.2.3 |
| deflate | "deflate" compressed data | Section 4.2.2 | | identity | Reserved (synonym for "no encoding" in | Section 8 |
| | ([RFC1951]) inside the "zlib" data | | | | Accept-Encoding) | .4.4 |
| | format ([RFC1950]) | | | x-compress | Deprecated (alias for compress) | Section 6 |
| gzip | GZIP file format [RFC1952] | Section 4.2.3 | | | | .1.2.1 |
| identity | Reserved (synonym for "no encoding" in | Section 5.3.4 | | x-gzip | Deprecated (alias for gzip) | Section 6 |
| | Accept-Encoding) | | | | | .1.2.3 |
| x-compress | Deprecated (alias for compress) | Section 4.2.1 | +------------+------------------------------------------+-----------+
| x-gzip | Deprecated (alias for gzip) | Section 4.2.3 |
+------------+--------------------------------------+---------------+
4.2. Compression Codings
The codings defined below can be used to compress the payload of a Table 2
message.
4.2.1. Compress Coding 6.1.2.1. 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".
4.2.2. Deflate Coding 6.1.2.2. 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.
4.2.3. Gzip Coding 6.1.2.3. 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".
8.4. Content Coding Registry 6.1.2.4. Content Coding Extensibility
The "HTTP Content Coding Registry" defines the namespace for content Additional content codings, outside the scope of this specification,
coding names (Section 4.2 of [RFC7230]). The content coding registry have been specified for use in HTTP. All such content codings ought
is maintained at <http://www.iana.org/assignments/http-parameters>. to be registered within the "HTTP Content Coding Registry".
8.4.1. Procedure 6.1.2.4.1. Content Coding Registry
The "HTTP Content Coding Registry", maintained by IANA at
<https://www.iana.org/assignments/http-parameters/>, registers
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 6.1.2).
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 6.1.2.
3.1.3.1. Language Tags 6.1.3. 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-
Content-Language header fields. Accept-Language uses the broader Language header fields. Accept-Language uses the broader language-
language-range production defined in Section 5.3.5, whereas range production defined in Section 8.4.5, whereas Content-Language
Content-Language uses the language-tag production defined below. 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.
2. Range Units 6.1.4. 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. This "range unit" is used in the or media type. For example, octet (a.k.a., byte) boundaries are a
Accept-Ranges (Section 2.3) response header field to advertise structural unit common to all representation data, allowing
support for range requests, the Range (Section 3.1) request header partitions of the data to be identified as a range of bytes at some
field to delineate the parts of a representation that are requested, offset from the start or end of that data.
and the Content-Range (Section 4.2) payload header field to describe
which part of a representation is being transferred.
range-unit = bytes-unit / other-range-unit This general notion of a "range unit" is used in the Accept-Ranges
(Section 10.4.1) response header field to advertise support for range
requests, the Range (Section 8.3) request header field to delineate
the parts of a representation that are requested, and the Content-
Range (Section 6.3.4) payload header field to describe which part of
a representation is being transferred.
+-------------+---------------------------------------+-------------+ range-unit = token
| Range Unit | Description | Reference |
| Name | | |
+-------------+---------------------------------------+-------------+
| bytes | a range of octets | Section 2.1 |
| none | reserved as keyword, indicating no | Section 2.3 |
| | ranges are supported | |
+-------------+---------------------------------------+-------------+
2.1. Byte Ranges The following range unit names are defined by this document:
Since representation data is transferred in payloads as a sequence of +------------+-----------------------------------------+------------+
octets, a byte range is a meaningful substructure for any | Range Unit | Description | Reference |
representation transferable over HTTP (Section 3 of [RFC7231]). The | Name | | |
"bytes" range unit is defined for expressing subranges of the data's +------------+-----------------------------------------+------------+
octet sequence. | bytes | a range of octets | Section 6. |
| | | 1.4.2 |
| none | reserved as keyword to indicate range | Section 10 |
| | requests are not supported | .4.1 |
+------------+-----------------------------------------+------------+
bytes-unit = "bytes" Table 3
A byte-range request can specify a single range of bytes or a set of 6.1.4.1. Range Specifiers
ranges within a single representation.
byte-ranges-specifier = bytes-unit "=" byte-range-set Ranges are expressed in terms of a range unit paired with a set of
byte-range-set = 1#( byte-range-spec / suffix-byte-range-spec ) range specifiers. The range unit name determines what kinds of
byte-range-spec = first-byte-pos "-" [ last-byte-pos ] range-spec are applicable to its own specifiers. Hence, the
first-byte-pos = 1*DIGIT following gramar is generic: each range unit is expected to specify
last-byte-pos = 1*DIGIT requirements on when int-range, suffix-range, and other-range are
allowed.
The first-byte-pos value in a byte-range-spec gives the byte-offset A range request can specify a single range or a set of ranges within
of the first byte in a range. The last-byte-pos value gives the a single representation.
byte-offset of the last byte in the range; that is, the byte
positions specified are inclusive. Byte offsets start at zero.
Examples of byte-ranges-specifier values: ranges-specifier = range-unit "=" range-set
range-set = 1#range-spec
range-spec = int-range
/ suffix-range
/ other-range
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.).
int-range = first-pos "-" [ last-pos ]
first-pos = 1*DIGIT
last-pos = 1*DIGIT
An int-range is invalid if the last-pos value is present and less
than the first-pos.
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-range = "-" suffix-length
suffix-length = 1*DIGIT
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.
other-range = 1*( %x21-2B / %x2D-7E )
; 1*(VCHAR excluding comma)
6.1.4.2. Byte Ranges
The "bytes" range unit is used to express subranges of a
representation data's octet sequence. Each byte range is expressed
as an integer range at some offset, relative to either the beginning
(int-range) or end (suffix-range) of the representation data. Byte
ranges do not use the other-range specifier.
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.
If the representation data has a content coding applied, each byte
range is calculated with respect to the encoded sequence of bytes,
not the sequence of underlying bytes that would be obtained after
decoding.
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 of the selected representation
using a suffix-byte-range-spec. using a suffix-range. If the selected representation is shorter than
the specified suffix-length, the entire representation is used.
suffix-byte-range-spec = "-" suffix-length
suffix-length = 1*DIGIT
If the selected representation is shorter than the specified
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.
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 a payload, 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.
2.2. Other Range Units 6.1.4.3. Other Range Units
Range units are intended to be extensible. New range units ought to Other range units, such as format-specific boundaries like pages,
be registered with IANA, as defined in Section 5.1. 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.
other-range-unit = token Range units are intended to be extensible. New range units ought to
be registered with IANA, as defined in Section 6.1.4.4.
5.1. Range Unit Registry 6.1.4.4. 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>.
5.1.1. Procedure
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).
3.1. Representation Metadata 6.2. 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 a payload body, the
representation header fields describe how to interpret the representation header fields describe how to interpret the
representation data enclosed in the payload body. In a response to a representation data enclosed in the payload body. In a response to 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 payload body representation data that would have been enclosed in the payload body
if the same request had been a GET. if the same request had been a GET.
The following header fields convey representation metadata: The following header fields convey representation metadata:
+-------------------+-----------------+ +-------------------+---------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+-----------------+ +-------------------+---------------+
| Content-Type | Section 3.1.1.5 | | Content-Type | Section 6.2.1 |
| Content-Encoding | Section 3.1.2.2 | | Content-Encoding | Section 6.2.2 |
| Content-Language | Section 3.1.3.2 | | Content-Language | Section 6.2.3 |
| Content-Location | Section 3.1.4.2 | | Content-Length | Section 6.2.4 |
+-------------------+-----------------+ | Content-Location | Section 6.2.5 |
+-------------------+---------------+
3.1.1. Processing Representation Data
3.1.1.5. Content-Type 6.2.1. 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 payload 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 6.1.1. 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 a payload body SHOULD
generate a Content-Type header field in that message unless the generate a Content-Type header field in that message unless the
intended media type of the enclosed representation is unknown to the intended media type of the enclosed representation is unknown to the
sender. If a Content-Type header field is not present, the recipient sender. If a Content-Type header field is not present, the recipient
MAY either assume a media type of "application/octet-stream" MAY either assume a media type of "application/octet-stream"
([RFC2046], Section 4.5.1) or examine the data to determine its type. ([RFC2046], 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 a payload's content and, in
payload's content and override the specified type. Clients that do certain cases, override the received type (for example, see
so risk drawing incorrect conclusions, which might expose additional [Sniffing]). This "MIME sniffing" risks drawing incorrect
conclusions about the data, which might expose the user to additional
security risks (e.g., "privilege escalation"). Furthermore, it is security risks (e.g., "privilege escalation"). Furthermore, it is
impossible to determine the sender's intent by examining the data impossible to determine the sender's intended processing model by
format: many data formats match multiple media types that differ only examining the data format: many data formats match multiple media
in processing semantics. Implementers are encouraged to provide a types that differ only in processing semantics. Implementers are
means of disabling such "content sniffing" when it is used. encouraged to provide a means to disable such sniffing.
3.1.2. Encoding for Compression or Integrity
3.1.2.2. Content-Encoding 6.2.2. 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 = 1#content-coding
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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. Additional information about the encoding
parameters can be provided by other header fields not defined by this parameters can be provided by other header fields not defined by this
specification. 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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choose to publish the same data as multiple representations that choose to publish the same data as multiple representations that
differ only in whether the coding is defined as part of Content-Type differ only in whether the coding is defined as part of Content-Type
or Content-Encoding, since some user agents will behave differently or Content-Encoding, since some user agents will behave differently
in their handling of each response (e.g., open a "Save as ..." dialog in their handling of each response (e.g., open a "Save as ..." dialog
instead of automatic decompression and rendering of content). instead of automatic decompression and rendering of content).
An origin server MAY respond with a status code of 415 (Unsupported An origin server MAY respond with a status code of 415 (Unsupported
Media Type) if a representation in the request message has a content Media Type) if a representation in the request message has a content
coding that is not acceptable. coding that is not acceptable.
3.1.3. Audience Language 6.2.3. Content-Language
3.1.3.2. 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 = 1#language-tag
Language tags are defined in Section 3.1.3.1. The primary purpose of Language tags are defined in Section 6.1.3. 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,
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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 to textual documents. limited to textual documents.
3.3.2. Content-Length 6.2.4. Content-Length
[[CREF2: The "Content-Length" header field indicates the number of
data octets (body length) for the representation. In some cases,
Content-Length is used to define or estimate message framing. ]]
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 an enclosed payload body. For example, a Content-Length header
field is normally sent in a POST request even when the value is 0 field is normally sent in a POST request even when the value is 0
(indicating an empty payload body). A user agent SHOULD NOT send a (indicating an empty payload body). A user agent SHOULD NOT send a
Content-Length header field when the request message does not contain Content-Length header field when the request message does not contain
a payload body and the method semantics do not anticipate such a a payload body and the method semantics do not anticipate such a
body. 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 7.3.2); 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 payload body of a response
body of a response if the same request had used the GET method. if 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 9.4.5); 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 payload body 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 7.3.6).
[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 payload body size is known prior to sending the complete
complete header section. This will allow downstream recipients to header section. This will allow downstream recipients to measure
measure transfer progress, know when a received message is complete, transfer progress, know when a received message is complete, and
and potentially reuse the connection for additional requests. potentially 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 a
payload, a recipient MUST anticipate potentially large decimal payload, a recipient MUST anticipate potentially large decimal
numerals and prevent parsing errors due to integer conversion numerals and prevent parsing errors due to integer conversion
overflows (Section 9.3). overflows (Section 13.5).
If a message is received that has multiple Content-Length header If a message is received that has multiple Content-Length header
fields with field-values consisting of the same decimal value, or a fields with field-values consisting of the same decimal value, or a
single Content-Length header field with a field value containing a single Content-Length header field with a field value containing a
list of identical decimal values (e.g., "Content-Length: 42, 42"), list of identical decimal values (e.g., "Content-Length: 42, 42"),
indicating that duplicate Content-Length header fields have been indicating that duplicate Content-Length header fields have been
generated or combined by an upstream message processor, then the generated or combined by an upstream message processor, then the
recipient MUST either reject the message as invalid or replace the recipient MUST either reject the message as invalid or replace the
duplicated field-values with a single valid Content-Length field duplicated field-values with a single valid Content-Length field
containing that decimal value prior to determining the message body containing that decimal value prior to determining the message body
length or forwarding the message. length or forwarding the message.
3.1.4. Identification 6.2.5. Content-Location
3.1.4.2. 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 payload. 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 payload 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 Content-Location value is not a replacement for the effective
Request URI (Section 5.5 of [RFC7230]). It is representation Request URI (Section 5.3). It is representation metadata. It has
metadata. It has the same syntax and semantics as the header field the same syntax and semantics as the header field of the same name
of the same name defined for MIME body parts in Section 4 of defined for MIME body parts in Section 4 of [RFC2557]. However, its
[RFC2557]. However, its appearance in an HTTP message has some appearance in an HTTP message has some special implications for HTTP
special implications for HTTP recipients. 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 effective request URI, then the recipient
MAY consider the payload to be a current representation of that MAY consider the payload to be a current representation of that
resource at the time indicated by the message origination date. For resource at the time indicated by the message origination date. For
a GET (Section 4.3.1) or HEAD (Section 4.3.2) request, this is the a GET (Section 7.3.1) or HEAD (Section 7.3.2) request, this is the
same as the default semantics when no Content-Location is provided by same as the default semantics when no Content-Location is provided by
the server. For a state-changing request like PUT (Section 4.3.4) or the server. For a state-changing request like PUT (Section 7.3.4) or
POST (Section 4.3.3), it implies that the server's response contains POST (Section 7.3.3), 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 effective request URI, then the origin server claims that the URI is
an identifier for a different resource corresponding to the enclosed an 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 effective request URI refers to a resource that is
subject to content negotiation and the Content-Location subject to content negotiation and the Content-Location field-
field-value is a more specific identifier for the selected value is a more 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 payload 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 payload 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
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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.
3.3. Payload Semantics 6.3. Payload
Some HTTP messages transfer a complete or partial representation as Some HTTP messages transfer a complete or partial representation as
the message "payload". In some cases, a payload might contain only the message "payload". In some cases, a payload might contain only
the associated representation's header fields (e.g., responses to the associated representation's header fields (e.g., responses to
HEAD) or only some part(s) of the representation data (e.g., the 206 HEAD) or only some part(s) of the representation data (e.g., the 206
(Partial Content) status code). (Partial Content) status code).
Header fields that specifically describe the payload, rather than the Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing. specification, due to their impact on message parsing.
+-------------------+----------------------------+ +-------------------+----------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+----------------------------+ +-------------------+----------------------------+
| Content-Length | Section 3.3.2 of [RFC7230] | | Content-Range | Section 6.3.4 |
| Content-Range | Section 4.2 of [RFC7233] | | Trailer | Section 4.3.3 |
| Trailer | Section 4.4 of [RFC7230] | | Transfer-Encoding | Section 6.1 of [Messaging] |
| Transfer-Encoding | Section 3.3.1 of [RFC7230] |
+-------------------+----------------------------+ +-------------------+----------------------------+
X.X.X. [Purpose] 6.3.1. Purpose
The purpose of a payload in a request is defined by the method The purpose of a payload in a request is defined by the method
semantics. For example, a representation in the payload of a PUT semantics. For example, a representation in the payload of a PUT
request (Section 4.3.4) represents the desired state of the target request (Section 7.3.4) represents the desired state of the target
resource if the request is successfully applied, whereas a resource if the request is successfully applied, whereas a
representation in the payload of a POST request (Section 4.3.3) representation in the payload of a POST request (Section 7.3.3)
represents information to be processed by the target resource. represents 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 payload'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. For example, the payload of a
200 (OK) response to GET (Section 4.3.1) represents the current state 200 (OK) response to GET (Section 7.3.1) represents the current state
of the target resource, as observed at the time of the message of the target resource, as observed at the time of the message
origination date (Section 7.1.1.2), whereas the payload of the same origination date (Section 10.1.1.2), whereas the payload of the same
status code in a response to POST might represent either the 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. Response messages with an error status code applying the processing. Response messages with an error status code
usually contain a payload that represents the error condition, such usually contain a payload that represents the error condition, such
that it describes the error state and what next steps are suggested that it describes the error state and what next steps are suggested
for resolving it. for resolving it.
3.1.4.1. Identifying a Representation 6.3.2. Identification
When a complete or partial representation is transferred in a message When a complete or partial representation is transferred in a message
payload, it is often desirable for the sender to supply, or the payload, 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 payload is a representation of the
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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 payload 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 GET or HEAD and the response status code
is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not
Modified), the payload is a representation of the resource Modified), the payload is a representation of the resource
identified by the effective request URI (Section 5.5 of identified by the effective request URI (Section 5.3).
[RFC7230]).
2. If the request method is GET or HEAD and the response status code 2. If the request method is GET or HEAD and the response status code
is 203 (Non-Authoritative Information), the payload is a is 203 (Non-Authoritative Information), the payload is a
potentially modified or enhanced representation of the target potentially modified or enhanced representation of the target
resource as provided by an intermediary. resource as provided by an intermediary.
3. If the response has a Content-Location header field and its 3. If the response has a Content-Location header field and its
field-value is a reference to the same URI as the effective field-value is a reference to the same URI as the effective
request URI, the payload is a representation of the resource request URI, the payload is a representation of the resource
identified by the effective request URI. identified by the effective request URI.
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request URI, then the sender asserts that the payload is a request URI, then the sender asserts that the payload is a
representation of the resource identified by the Content-Location representation of the resource identified by the Content-Location
field-value. However, such an assertion cannot be trusted unless field-value. However, such an assertion cannot be trusted unless
it can be verified by other means (not defined by this it can be verified by other means (not defined by this
specification). specification).
5. Otherwise, the payload is unidentified. 5. Otherwise, the payload is unidentified.
6.3.3. Payload Body 6.3.3. Payload Body
Responses to the HEAD request method (Section 4.3.2 The payload body contains the data of a request or response. This is
of [RFC7231]) never include a message body because the associated distinct from the message body (e.g., Section 6 of [Messaging]),
response header fields (e.g., Transfer-Encoding, Content-Length, which is how the payload body is transferred "on the wire", and might
etc.), if present, indicate only what their values would have been if be encoded, depending on the HTTP version in use.
the request method had been GET (Section 4.3.1 of [RFC7231]).
It is also distinct from a request or response's representation data
(Section 6.1), which can be inferred from protocol operation, rather
than necessarily appearing "on the wire."
The presence of a payload body in a request depends on whether the
request method used defines semantics for it.
The presence of a payload body in a response depends on both the
request method to which it is responding and the response status code
(Section 9).
Responses to the HEAD request method (Section 7.3.2) never include a
payload body because the associated response header fields indicate
only what their values would have been if the request method had been
GET (Section 7.3.1).
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 7.3.6) switch the connection to tunnel mode instead of
having a message body. having a payload body.
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 a payload body.
All other responses do include a message body, although the body All other responses do include a payload body, although that body
might be of zero length. might be of zero length.
4.2. Content-Range 6.3.4. 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 payload, 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 6.1.4) 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.
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.
skipping to change at line 2499 skipping to change at page 60, line 37
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
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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
Appendix A. Internet Media Type multipart/byteranges 6.3.5. 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".
The multipart/byteranges media type includes one or more body parts, The multipart/byteranges media type includes one or more body parts,
each with its own Content-Type and Content-Range fields. The each with its own Content-Type and Content-Range fields. The
required boundary parameter specifies the boundary string used to required boundary parameter specifies the boundary string used to
separate each body part. separate each body part.
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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--
5.4.1. Internet Media Type multipart/byteranges The following information serves as the registration form for the
multipart/byteranges media type.
This document serves as the specification for the Internet media type
"multipart/byteranges". The following has been registered with IANA.
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 13
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: This specification (see Section 6.3.5).
Published specification: This specification (see Appendix A).
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
3.4. Content Negotiation 6.4. Content Negotiation
When responses convey payload information, whether indicating a When responses convey payload information, whether indicating a
success or an error, the origin server often has different ways of success or an error, the origin server often has different ways of
representing that information; for example, in different formats, representing that information; for example, in different formats,
languages, or encodings. Likewise, different users or user agents languages, or encodings. Likewise, different users or user agents
might have differing capabilities, characteristics, or preferences might have differing capabilities, characteristics, or preferences
that could influence which representation, among those available, that could influence which representation, among those available,
would be best to deliver. For this reason, HTTP provides mechanisms would be best to deliver. For this reason, HTTP provides mechanisms
for content negotiation. for content negotiation.
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practicality. 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. HTTP pays no attention to the man
behind the curtain. behind the curtain.
3.4.1. Proactive Negotiation 6.4.1. 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 (a.k.a.,
server-driven negotiation). Selection is based on the available server-driven negotiation). Selection is based on the available
representations for a response (the dimensions over which it might representations for a response (the dimensions over which it might
vary, such as language, content-coding, etc.) compared to various vary, such as language, content-coding, etc.) compared to various
information supplied in the request, including both the explicit information supplied in the request, including both the explicit
negotiation fields of Section 5.3 and implicit characteristics, such negotiation fields of Section 8.4 and implicit characteristics, such
as the client's network address or parts of the User-Agent field. 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 10.1.4) 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.
3.4.2. Reactive Negotiation 6.4.2. 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. If the user agent is not
satisfied by the initial response representation, it can perform a satisfied by the initial response representation, it can perform a
GET request on one or more of the alternative resources, selected GET request on one or more of the alternative resources, selected
based on metadata included in the list, to obtain a different form of based on metadata included in the list, to obtain a different form of
representation for that response. Selection of alternatives might be representation for that response. Selection of alternatives might be
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caches are used to distribute server load and reduce network usage. caches are used to distribute server load and reduce network usage.
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.
4. Request Methods 7. Request Methods
4.1. Overview 7.1. 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 (Section 8)
if those additional semantics do not conflict with the method. For if those additional semantics do not conflict with the method. For
example, a client can send conditional request header fields example, a client can send conditional request header fields
(Section 5.2) to make the requested action conditional on the current (Section 8.2) to make the requested action conditional on the current
state of the target resource ([RFC7232]). state of the target resource.
method = token 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. The method token is case-sensitive because it might be semantics.
used as a gateway to object-based systems with case-sensitive method
names. The method token is case-sensitive because it might be used as a
gateway to object-based systems with case-sensitive method names. By
convention, standardized methods are defined in all-uppercase US-
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. By commonly used in HTTP, as outlined by the following table.
convention, standardized methods are defined in all-uppercase
US-ASCII letters.
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| Method | Description | Sec. | | Method | Description | Sec. |
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| GET | Transfer a current representation of the target | 4.3.1 | | GET | Transfer a current representation of the target | 7.3.1 |
| | resource. | | | | resource. | |
| HEAD | Same as GET, but only transfer the status line | 4.3.2 | | HEAD | Same as GET, but only transfer the status line | 7.3.2 |
| | and header section. | | | | and header section. | |
| POST | Perform resource-specific processing on the | 4.3.3 | | POST | Perform resource-specific processing on the | 7.3.3 |
| | request payload. | | | | request payload. | |
| PUT | Replace all current representations of the | 4.3.4 | | PUT | Replace all current representations of the | 7.3.4 |
| | target resource with the request payload. | | | | target resource with the request payload. | |
| DELETE | Remove all current representations of the | 4.3.5 | | DELETE | Remove all current representations of the | 7.3.5 |
| | target resource. | | | | target resource. | |
| CONNECT | Establish a tunnel to the server identified by | 4.3.6 | | CONNECT | Establish a tunnel to the server identified by | 7.3.6 |
| | the target resource. | | | | the target resource. | |
| OPTIONS | Describe the communication options for the | 4.3.7 | | OPTIONS | Describe the communication options for the | 7.3.7 |
| | 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 path | 7.3.8 |
| | to the target resource. | | | | 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 10.4.2). 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.
4.2. Common Method Properties 7.2. Common Method Properties
+---------+------+------------+----------------+
| Method | Safe | Idempotent | Reference |
+---------+------+------------+----------------+
| CONNECT | no | no | Section 7.3.6 |
| DELETE | no | yes | Section 7.3.5 |
| GET | yes | yes | Section 7.3.1 |
| HEAD | yes | yes | Section 7.3.2 |
| OPTIONS | yes | yes | Section 7.3.7 |
| POST | no | no | Section 7.3.3 |
| PUT | no | yes | Section 7.3.4 |
| TRACE | yes | yes | Section 7.3.8 |
+---------+------+------------+----------------+
+---------+------+------------+---------------+ Table 5
| Method | Safe | Idempotent | Reference |
+---------+------+------------+---------------+
| CONNECT | no | no | Section 4.3.6 |
| DELETE | no | yes | Section 4.3.5 |
| GET | yes | yes | Section 4.3.1 |
| HEAD | yes | yes | Section 4.3.2 |
| OPTIONS | yes | yes | Section 4.3.7 |
| POST | no | no | Section 4.3.3 |
| PUT | no | yes | Section 4.3.4 |
| TRACE | yes | yes | Section 4.3.8 |
+---------+------+------------+---------------+
4.2.1. Safe Methods 7.2.1. 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
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consistent with the request method semantics. For example, it is consistent with the request method semantics. For example, it is
common for Web-based content editing software to use actions within common for Web-based content editing software to use actions within
query parameters, such as "page?do=delete". If the purpose of such a query 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.
4.2.2. Idempotent Methods 7.2.2. 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
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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.
7.2.3. Methods and Caching 7.2.3. 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.
4.3. Method Definitions This specification defines caching semantics for GET, HEAD, and POST,
although the overwhelming majority of cache implementations only
support GET and HEAD.
4.3.1. GET 7.3. Method Definitions
7.3.1. 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. GET is the primary mechanism of information
retrieval and the focus of almost all performance optimizations. retrieval and the focus of almost all performance optimizations.
Hence, when people speak of retrieving some identifiable information Hence, when people speak of retrieving some identifiable information
via HTTP, they are generally referring to making a GET request. via HTTP, they are generally referring to making a GET request.
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 13.3 for related security considerations). However, there
no such limitations in practice. The HTTP interface for a resource are no such limitations in practice. The HTTP interface for a
is just as likely to be implemented as a tree of content objects, a resource is just as likely to be implemented as a tree of content
programmatic view on various database records, or a gateway to other objects, a programmatic view on various database records, or a
information systems. Even when the URI mapping mechanism is tied to gateway to other information systems. Even when the URI mapping
a file system, an origin server might be configured to execute the mechanism is tied to a file system, an origin server might be
files with the request as input and send the output as the configured to execute the files with the request as input and send
representation rather than transfer the files directly. Regardless, the output as the representation rather than transfer the files
only the origin server needs to know how each of its resource directly. Regardless, only the origin server needs to know how each
identifiers corresponds to an implementation and how each of its resource identifiers corresponds to an implementation and how
implementation manages to select and send a current representation of each implementation manages to select and send a current
the target resource in a response to GET. 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 8.3).
A payload within a GET request message has no defined semantics; The GET method is specifically intended to reflect the quality of
sending a payload body on a GET request might cause some existing "sameness" identified by the request URI as if it were referenced as
implementations to reject the request. an ordinary hypertext link. A client SHOULD NOT generate a body in a
GET request. A payload received in a GET request has no defined
semantics, cannot alter the 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]). A
cache that receives a payload in a GET request is likely to ignore
that payload and cache regardless of the payload contents.
4.3.2. HEAD 7.3.2. 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 a message body in the response (i.e., the response terminates at
the end of the header section). The server SHOULD send the same the end of the header section). The server SHOULD send the same
header fields in response to a HEAD request as it would have sent if header fields in response to a HEAD request as it would have sent if
the request had been a GET, except that the payload header fields the request had been a GET, except that the payload header fields
(Section 3.3) MAY be omitted. This method can be used for obtaining (Section 6.3) MAY be omitted. This method can be used for obtaining
metadata about the selected representation without transferring the metadata about the selected representation without transferring the
representation data and is often used for testing hypertext links for representation data and is often used for testing hypertext links for
validity, accessibility, and recent modification. validity, accessibility, and recent modification.
A payload within a HEAD request message has no defined semantics; A payload within a HEAD request message has no defined semantics;
sending a payload body on a HEAD request might cause some existing sending a payload body on 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 have an effect on previously cached responses to
GET; see Section 4.3.5 of [RFC7234]. GET; see Section 4.3.5 of [Caching].
4.3.3. POST 7.3.3. 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;
o Posting a message to a bulletin board, newsgroup, mailing list, o Posting a message to a bulletin board, newsgroup, mailing list,
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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 might 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 10.1.2) 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). effective request URI (Section 6.2.5). 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.
4.3.4. PUT 7.3.4. 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 payload. 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
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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 MUST NOT send a validator header field An origin server MUST NOT send a validator header field
(Section 7.2), such as an ETag or Last-Modified field, in a (Section 10.2), such as an ETag or Last-Modified field, in a
successful response to PUT unless the request's representation data successful response to PUT unless the request's representation data
was saved without any transformation applied to the body (i.e., the was saved without any transformation applied to the body (i.e., the
resource's new representation data is identical to the representation resource's new representation data is identical to the representation
data received in the PUT request) and the validator field value data received in the PUT request) and the validator field value
reflects the new representation. This requirement allows a user reflects the new representation. This requirement allows a user
agent to know when the representation body it has in memory remains agent to know when the representation body it has in memory remains
current as a result of the PUT, thus not in need of being retrieved current as a result of the PUT, thus not in need of being retrieved
again from the origin server, and that the new validator(s) received again from the origin server, and that the new validator(s) received
in the response can be used for future conditional requests in order in the response can be used for future conditional requests in order
to prevent accidental overwrites (Section 5.2). to prevent accidental overwrites (Section 8.2).
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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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 An origin server that allows PUT on a given target resource MUST send
a 400 (Bad Request) response to a PUT request that contains a a 400 (Bad Request) response to a PUT request that contains a
Content-Range header field (Section 4.2 of [RFC7233]), since the Content-Range header field (Section 6.3.4), since the payload is
payload is likely to be partial content that has been mistakenly PUT likely to be partial content that has been mistakenly PUT as a full
as a full representation. Partial content updates are possible by representation. Partial content updates are possible by targeting a
targeting a separately identified resource with state that overlaps a separately identified resource with state that overlaps a portion of
portion of the larger resource, or by using a different method that the larger resource, or by using a different method that has been
has been specifically defined for partial updates (for example, the specifically defined for partial updates (for example, the PATCH
PATCH method defined in [RFC5789]). method defined in [RFC5789]).
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 effective request URI, those stored responses will be
invalidated (see Section 4.4 of [RFC7234]). invalidated (see Section 4.4 of [Caching]).
4.3.5. DELETE 7.3.5. 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
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previously created using a PUT request, or identified via the previously created using a PUT request, or identified via the
Location header field after a 201 (Created) response to a POST Location header field after a 201 (Created) response to a POST
request, might allow a corresponding DELETE request to undo those request, might allow a corresponding DELETE request to undo those
actions. Similarly, custom user agent implementations that implement actions. Similarly, custom user agent implementations that implement
an authoring function, such as revision control clients using HTTP an authoring function, such as revision control clients using HTTP
for remote operations, might use DELETE based on an assumption that for remote operations, might use DELETE based on an assumption that
the server's URI space has been crafted to correspond to a version the server's 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 a 202 (Accepted) status code if the action will likely succeed send
but has not yet been enacted, a 204 (No Content) status code if the
action has been enacted and no further information is to be supplied, o a 202 (Accepted) status code if the action will likely succeed but
or a 200 (OK) status code if the action has been enacted and the has not yet been enacted,
response message includes a representation describing the status.
o a 204 (No Content) status code if the action has been enacted and
no further information is to be supplied, or
o a 200 (OK) status code if the action has been enacted and the
response message includes a representation describing the status.
A payload within a DELETE request message has no defined semantics; A payload within a DELETE request message has no defined semantics;
sending a payload body on a DELETE request might cause some existing sending a payload body on a DELETE request might cause some existing
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 effective request URI, those stored responses will
invalidated (see Section 4.4 of [RFC7234]). be invalidated (see Section 4.4 of [Caching]).
4.3.6. CONNECT 7.3.6. 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 packets, in both directions, until the tunnel is closed. Tunnels
are commonly used to create an end-to-end virtual connection, through are commonly used to create an end-to-end virtual connection, through
one or more proxies, which can then be secured using TLS (Transport one or more proxies, which can then be secured using TLS (Transport
Layer Security, [RFC5246]). Layer Security, [RFC8446]).
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 form of
request-target (Section 5.3 of [RFC7230]); i.e., the request-target request-target (Section 3.2 of [Messaging]); i.e., the request-target
consists of only the host name and port number of the tunnel consists of only the host name and port number of the tunnel
destination, separated by a colon. For example, 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
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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; A payload within a CONNECT request message has no defined semantics;
sending a payload body on a CONNECT request might cause some existing sending a payload body on 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.
4.3.7. OPTIONS 7.3.7. 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 3.2 of [Messaging]) applies to the server in general rather
than to a specific resource. Since a server's communication options than to a specific resource. Since a server's communication options
typically depend on the resource, the "*" request is only useful as a typically depend on the resource, the "*" request is only useful as a
"ping" or "no-op" type of method; it does nothing beyond allowing the "ping" or "no-op" type of method; it does nothing beyond allowing the
client to test the capabilities of the server. For example, this can client to test the capabilities of the server. For example, this can
be used to test a proxy for HTTP/1.1 conformance (or lack thereof). be used 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 fields that might indicate optional features implemented by
the server and applicable to the target resource (e.g., Allow), the server and applicable to the target resource (e.g., Allow),
including potential extensions not defined by this specification. including potential extensions not defined by this specification.
The response payload, if any, might also describe the communication The response payload, if any, might also describe the communication
options in a machine or human-readable representation. A standard options in a machine or human-readable representation. A standard
format for such a representation is not defined by this format for such a representation is not defined by this
specification, but might be defined by future extensions to HTTP. A specification, but might be 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 8.1.2). 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 a payload body
MUST send a valid Content-Type header field describing the MUST send a valid Content-Type header field describing the
representation media type. Although this specification does not representation media type. Note that this specification does not
define any use for such a payload, future extensions to HTTP might define any use for such a payload.
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.
4.3.8. TRACE 7.3.8. 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 message body 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 8.1.2).
A client MUST NOT generate header fields in a TRACE request A client MUST NOT generate header fields in a TRACE request
containing sensitive data that might be disclosed by the response. containing sensitive data that might be disclosed by the response.
For example, it would be foolish for a user agent to send stored user For example, it would be foolish for a user agent to send stored user
credentials [RFC7235] or cookies [RFC6265] in a TRACE request. The credentials Section 8.5 or cookies [RFC6265] in a TRACE request. The
final recipient of the request SHOULD exclude any request header final recipient of the request SHOULD exclude any request header
fields that are likely to contain sensitive data when that recipient fields that are likely to contain sensitive data when that recipient
generates the response body. generates the response body.
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 5.5.1) 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 a message body in a TRACE request.
Responses to the TRACE method are not cacheable. Responses to the TRACE method are not cacheable.
X.X. [Method Extensibility] 7.4. Method Extensibility
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".
8.1. Method Registry
The "Hypertext Transfer Protocol (HTTP) Method Registry" defines the 7.4.1. Method Registry
namespace for the request method token (Section 4). The method
registry has been created and is now maintained at
<http://www.iana.org/assignments/http-methods>.
8.1.1. Procedure The "Hypertext Transfer Protocol (HTTP) Method Registry", maintained
by IANA at <https://www.iana.org/assignments/http-methods>, registers
method names.
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 7)
o Safe ("yes" or "no", see Section 7.2.1)
o Safe ("yes" or "no", see Section 4.2.1)
o Idempotent ("yes" or "no", see Section 4.2.2) o Idempotent ("yes" or "no", see Section 7.2.2)
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).
8.1.2. Considerations for New Methods 7.4.2. 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 a message body 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 message body is allowed by requiring a Content-Length
header field with a value of "0". header field with a value of "0".
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 7.2.1), idempotent (Section 7.2.2), cacheable
(Section 4.2.3), what semantics are to be associated with the payload (Section 7.2.3), what semantics are to be associated with the payload
body if any is present in the request and what refinements the method body if any is present in the request and what refinements the method
makes to header field or status code semantics. If the new method is makes to header field or status code semantics. If the new method is
cacheable, its definition ought to describe how, and under what cacheable, its definition ought to describe how, and under what
conditions, a cache can store a response and use it to satisfy a conditions, a cache can store a response and use it to satisfy a
subsequent request. The new method ought to describe whether it can subsequent request. The new method ought to describe whether it can
be made conditional (Section 5.2) and, if so, how a server responds be made conditional (Section 8.2) and, if so, how a server responds
when the condition is false. Likewise, if the new method might have when the condition is false. Likewise, if the new method might have
some use for partial response semantics ([RFC7233]), it ought to some use for partial response semantics (Section 8.3), it ought to
document this, too. document this, too.
Note: Avoid defining a method name that starts with "M-", since Note: Avoid defining a method name that starts with "M-", since
that prefix might be misinterpreted as having the semantics that prefix might be misinterpreted as having the semantics
assigned to it by [RFC2774]. assigned to it by [RFC2774].
5. Request Header Fields 8. Request Header Fields
A client sends request header fields to provide more information A client sends request header fields to provide more information
about the request context, make the request conditional based on the about the request context, make the request conditional based on the
target resource state, suggest preferred formats for the response, target resource state, suggest preferred formats for the response,
supply authentication credentials, or modify the expected request supply authentication credentials, or modify the expected request
processing. These fields act as request modifiers, similar to the processing. These fields act as request modifiers, similar to the
parameters on a programming language method invocation. parameters on a programming language method invocation.
5.1. Controls 8.1. Controls
Controls are request header fields that direct specific handling of Controls are request header fields that direct specific handling of
the request. the request.
+-------------------+--------------------------+ +-------------------+----------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+--------------------------+ +-------------------+----------------------------+
| Cache-Control | Section 5.2 of [RFC7234] | | Cache-Control | Section 5.2 of [Caching] |
| Expect | Section 5.1.1 | | Expect | Section 8.1.1 |
| Host | Section 5.4 of [RFC7230] | | Host | Section 5.4 |
| Max-Forwards | Section 5.1.2 | | Max-Forwards | Section 8.1.2 |
| Pragma | Section 5.4 of [RFC7234] | | Pragma | Section 5.4 of [Caching] |
| Range | Section 3.1 of [RFC7233] | | TE | Section 7.4 of [Messaging] |
| TE | Section 4.3 of [RFC7230] | +-------------------+----------------------------+
+-------------------+--------------------------+
5.1.1. Expect 8.1.1. 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. The only such expectation
defined by this specification is 100-continue. defined by this specification is 100-continue.
Expect = "100-continue" Expect = "100-continue"
The Expect field-value is case-insensitive. The Expect field-value is case-insensitive.
A server that receives an Expect field-value other than 100-continue A server that receives an Expect field-value other than 100-continue
MAY respond with a 417 (Expectation Failed) status code to indicate MAY respond with a 417 (Expectation Failed) status code to indicate
that the unexpected expectation cannot be met. 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 a (presumably large) message body in this request and
wishes to receive a 100 (Continue) interim response if the wishes to receive a 100 (Continue) interim response if the request-
request-line and header fields are not sufficient to cause an line 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 message body
message body before actually doing so, which can improve efficiency before actually doing so, which can improve efficiency when the
when the message body is huge or when the client anticipates that an message body is huge or when the client anticipates that an error is
error is likely (e.g., when sending a state-changing method, for the likely (e.g., when sending a state-changing method, for the first
first time, without previously verified authentication credentials). time, without 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.
skipping to change at line 3537 skipping to change at page 83, line 6
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 message body for the
corresponding request, or if the framing indicates that there is corresponding request, or if the framing indicates that there is
no message body. 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 message body 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 payload body SHOULD indicate whether it intends to
intends to close the connection or continue reading and discarding close the connection (see Section 9.7 of [Messaging]) or continue
the request message (see Section 6.6 of [RFC7230]). reading the payload body.
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 contains a line and a complete header section that contains a 100-continue
100-continue expectation and indicates a request message body will expectation and indicates a request message body will follow, either
follow, either send an immediate response with a final status code, send an immediate response with a final status code, if that status
if that status can be determined by examining just the request-line can be determined by examining just the request-line and header
and header fields, or send an immediate 100 (Continue) response to fields, or send an immediate 100 (Continue) response to encourage the
encourage the client to send the request's message body. The origin client to send the request's message body. The origin server MUST
server MUST NOT wait for the message body before sending the 100 NOT wait for the message body before sending the 100 (Continue)
(Continue) response. 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-line and
a complete header section that contains a 100-continue expectation a complete header section that contains a 100-continue expectation
and indicates a request message body will follow, either send an and indicates a request message body will follow, either send an
immediate response with a final status code, if that status can be immediate response with a final status code, if that status can be
determined by examining just the request-line and header fields, or determined by examining just the request-line and header fields, or
begin forwarding the request toward the origin server by sending a begin forwarding the request toward the origin server by sending a
corresponding request-line and header section to the next inbound corresponding request-line and header section to the next inbound
server. If the proxy believes (from configuration or past server. If the proxy believes (from configuration or past
interaction) that the next inbound server only supports HTTP/1.0, the interaction) that the next inbound server only supports HTTP/1.0, the
skipping to change at line 3573 skipping to change at page 83, line 42
Note: The Expect header field was added after the original Note: The Expect header field was added after the original
publication of HTTP/1.1 [RFC2068] as both the means to request an publication of HTTP/1.1 [RFC2068] as both the means to request an
interim 100 (Continue) response and the general mechanism for interim 100 (Continue) response and the general mechanism for
indicating must-understand extensions. However, the extension indicating must-understand extensions. However, the extension
mechanism has not been used by clients and the must-understand mechanism has not been used by clients and the must-understand
requirements have not been implemented by many servers, rendering requirements have not been implemented by many servers, rendering
the extension mechanism useless. This specification has removed the extension mechanism useless. This specification has removed
the extension mechanism in order to simplify the definition and the extension mechanism in order to simplify the definition and
processing of 100-continue. processing of 100-continue.
5.1.2. Max-Forwards 8.1.2. 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 7.3.8) and OPTIONS (Section 7.3.7) 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
skipping to change at line 3599 skipping to change at page 84, line 21
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.
5.2. Conditionals 8.2. Preconditions
Conditional requests are HTTP requests [RFC7231] that include one or
more header fields indicating a precondition to be tested before
applying the method semantics to the target resource. This document
defines the HTTP/1.1 conditional request mechanisms in terms of the
architecture, syntax notation, and conformance criteria defined in
[RFC7230].
3. Precondition Header Fields
This section defines the syntax and semantics of HTTP/1.1 header A conditional request is an HTTP request with one or more request
fields for applying preconditions on requests. Section 5 defines header fields that indicate a precondition to be tested before
when the preconditions are applied. Section 6 defines the order of applying the request method to the target resource. Section 8.2.1
evaluation when more than one precondition is present. defines when preconditions are applied. Section 8.2.2 defines the
order of evaluation 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 6) 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.
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).
The HTTP conditional request header fields [RFC7232] allow a client The following request header fields 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 10.2). Hence, these preconditions evaluate whether the
of the target resource has changed since a given state known by the state of the target resource has changed since a given state known by
client. The effect of such an evaluation depends on the method the 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 8.2.1.
[RFC7232].
+---------------------+--------------------------+ +---------------------+---------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+---------------------+--------------------------+ +---------------------+---------------+
| If-Match | Section 3.1 of [RFC7232] | | If-Match | Section 8.2.3 |
| If-None-Match | Section 3.2 of [RFC7232] | | If-None-Match | Section 8.2.4 |
| If-Modified-Since | Section 3.3 of [RFC7232] | | If-Modified-Since | Section 8.2.5 |
| If-Unmodified-Since | Section 3.4 of [RFC7232] | | If-Unmodified-Since | Section 8.2.6 |
| If-Range | Section 3.2 of [RFC7233] | | If-Range | Section 8.2.7 |
+---------------------+--------------------------+ +---------------------+---------------+
5. Evaluation 8.2.1. Evaluation
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 perform
the action associated with the request method. A server MUST ignore the action associated with the request method. A server MUST ignore
all received preconditions if its response to the same request all received preconditions if its response to the same request
without those conditions would have been a status code other than a without those conditions would have been a status code other than a
2xx (Successful) or 412 (Precondition Failed). In other words, 2xx (Successful) or 412 (Precondition Failed). In other words,
redirects and failures take precedence over the evaluation of redirects and failures take precedence over the evaluation of
preconditions in conditional requests. preconditions in conditional requests.
skipping to change at line 3683 skipping to change at page 85, line 43
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
those of GET), there is no point in sending a conditional HEAD those of GET), there is no point in sending a conditional HEAD
because a successful response is around the same size as a 304 (Not because a successful response is around the same size as a 304 (Not
Modified) response and more useful than a 412 (Precondition Failed) Modified) response and more useful than a 412 (Precondition Failed)
response. response.
6. Precedence 8.2.2. Precedence
When more than one conditional request header field is present in a When more than one conditional request header field is present in a
request, the order in which the fields are evaluated becomes request, the order in which the fields are evaluated becomes
important. In practice, the fields defined in this document are important. In practice, the fields defined in this document are
consistently implemented in a single, logical order, since "lost consistently implemented in a single, logical order, since "lost
update" preconditions have more strict requirements than cache update" preconditions have more strict requirements than cache
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 * if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be * 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 8.2.3)
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 * if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be * 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 8.2.6)
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 * if true, continue to step 5
* if false for GET/HEAD, respond 304 (Not Modified) * if false for GET/HEAD, respond 304 (Not Modified)
* if false for other methods, respond 412 (Precondition Failed) * if false for other methods, respond 412 (Precondition Failed)
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* if true, continue to step 5 * if true, continue to step 5
* 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 * 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 * 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/1.1 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.
3.1. If-Match 8.2.3. 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 10.2.3.2), 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 = "*" / 1#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 safe
methods to abort a request if the selected representation does not methods to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request. match one 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). If the the condition prior to performing the method (Section 8.2.1). If the
field-value is "*", the condition is false if the origin server does field-value is "*", the condition is false if the origin server does
not have a current representation for the target resource. If the not have a current representation for the target resource. If the
field-value is a list of entity-tags, the condition is false if none field-value is a list of entity-tags, the condition is false if none
of the listed tags match the entity-tag of the selected of the listed tags match the entity-tag of the selected
representation. representation.
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 MUST respond with either a) the 412 (Precondition Failed) status code
or b) one of the 2xx (Successful) status codes if the origin server or b) one of the 2xx (Successful) status codes if the origin server
skipping to change at line 3819 skipping to change at page 89, line 15
succeeded, but the user agent might not be aware of it, perhaps succeeded, but the user agent might not be aware of it, perhaps
because the prior response was lost or a compatible change was made because the prior response was lost or a compatible change was made
by some other user agent). In the latter case, the origin server 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 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 verify that the request is a duplicate of an immediately prior change
made by the same user agent. made by the same user agent.
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.
3.2. If-None-Match 8.2.4. 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 10.2.3.2), 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 = "*" / 1#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: *
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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 7.2.1). 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 prior to performing the method
If the field-value is "*", the condition is false if the origin (Section 8.2.1). If the field-value is "*", the condition is false
server has a current representation for the target resource. If the if the origin server has a current representation for the target
field-value is a list of entity-tags, the condition is false if one resource. If the field-value is a list of entity-tags, the condition
of the listed tags match the entity-tag of the selected is false if one of the listed tags match the entity-tag of the
representation. selected representation.
An origin server MUST NOT perform the requested method if the An origin server MUST NOT perform the requested method if the
condition evaluates to false; instead, the origin server MUST respond condition evaluates to false; instead, the origin server MUST respond
with either a) the 304 (Not Modified) status code if the request with either a) the 304 (Not Modified) status code if the request
method is GET or HEAD or b) the 412 (Precondition Failed) status code method is GET or HEAD or b) the 412 (Precondition Failed) status code
for all other request methods. 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].
3.3. If-Modified-Since 8.2.5. 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-
If-None-Match. 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, or if the request
method is neither GET nor HEAD. 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 field to generate the field value
of If-Modified-Since. This behavior is most interoperable for cases of If-Modified-Since. This behavior is most interoperable for cases
where clocks are poorly synchronized or when the server has chosen to where clocks are poorly synchronized or when the server has chosen to
only honor exact timestamp matches (due to a problem with only honor exact timestamp matches (due to a problem with Last-
Last-Modified dates that appear to go "back in time" when the origin 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. 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-
Last-Modified field will not be able to help the user agent limit its Modified field will not be able to help the user agent limit its data
data transfers to only those changed during the specified window. 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 prior to performing the method
(Section 5). The origin server SHOULD NOT perform the requested (Section 8.2.1). The origin server SHOULD NOT perform the requested
method if the selected representation's last modification date is method if the selected representation's last modification date is
earlier than or equal to the date provided in the field-value; earlier than or equal to the date provided in the field-value;
instead, the origin server SHOULD generate a 304 (Not Modified) instead, the origin server SHOULD generate a 304 (Not Modified)
response, including only those metadata that are useful for response, including only those metadata that are useful for
identifying or updating a previously cached response. 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].
3.4. If-Unmodified-Since 8.2.6. 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.
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 safe
methods to abort a request if the selected representation does not methods to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request. match one 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 MUST evaluate the condition prior to performing the method
(Section 5). The origin server MUST NOT perform the requested method (Section 8.2.1). The origin server MUST NOT perform the requested
if the selected representation's last modification date is more method if the selected representation's last modification date is
recent than the date provided in the field-value; instead the origin more recent than the date provided in the field-value; instead the
server MUST respond with either a) the 412 (Precondition Failed) origin server MUST respond with either a) the 412 (Precondition
status code or b) one of the 2xx (Successful) status codes if the Failed) status code or b) one of the 2xx (Successful) status codes if
origin server has verified that a state change is being requested and the origin server has verified that a state change is being requested
the final state is already reflected in the current state of the and the final state is already reflected in the current state of the
target resource (i.e., the change requested by the user agent has target resource (i.e., the change requested by the user agent has
already succeeded, but the user agent might not be aware of that already succeeded, but the user agent might not be aware of that
because the prior response message was lost or a compatible change because the prior response message was lost or a compatible change
was made by some other user agent). In the latter case, the origin 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 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 it can verify that the request is a duplicate of an immediately prior
change made by the same user agent. change made by the same user agent.
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.
3.5. If-Range 8.2.7. 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 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 10.2.2.2.
A server that evaluates an If-Range precondition MUST use the strong A server that evaluates an If-Range precondition MUST use the strong
comparison function when comparing entity-tags (Section 2.3.2 of comparison function when comparing entity-tags (Section 10.2.3.2) and
[RFC7232]) and MUST evaluate the condition as false if an HTTP-date MUST evaluate the condition as false if an HTTP-date validator is
validator is provided that is not a strong validator in the sense provided that is not a strong validator in the sense defined by
defined by Section 2.2.2 of [RFC7232]. A valid entity-tag can be Section 10.2.2.2. A valid entity-tag can be distinguished from a
distinguished from a valid HTTP-date by examining the first two valid HTTP-date by examining the first two characters for a DQUOTE.
characters for a DQUOTE.
If the validator given in the If-Range header field matches the If the validator given in the If-Range header field matches the
current validator for the selected representation of the target current validator for the selected representation of the target
resource, then the server SHOULD process the Range header field as resource, then the server SHOULD process the Range header field as
requested. If the validator does not match, the server MUST ignore requested. If the validator does not match, the server MUST ignore
the Range header field. Note that this comparison by exact match, the Range header field. Note that this comparison by exact match,
including when the validator is an HTTP-date, differs from the including when the validator is an HTTP-date, differs from the
"earlier than or equal to" comparison used when evaluating an "earlier than or equal to" comparison used when evaluating an If-
If-Unmodified-Since conditional. Unmodified-Since conditional.
3.1. Range 8.3. 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, rather than the entire selected
representation data. representation data.
Range = byte-ranges-specifier / other-ranges-specifier Range = ranges-specifier
other-ranges-specifier = other-range-unit "=" other-range-set
other-range-set = 1*VCHAR
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.
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. A server MUST ignore
MUST ignore a Range header field received with a request method other a Range header field received with a request method other than GET.
than GET.
Although the range request mechanism is designed to allow for Although the range request mechanism is designed to allow for
extensible range types, this specification only defines requests for extensible range types, this specification only defines requests for
byte ranges. byte ranges.
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 13.13). 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 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 8.2, 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 8.2.7) 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 6.1.4.2), the server
send a 206 (Partial Content) response with a payload containing one SHOULD send a 206 (Partial Content) response with a payload
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.
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.
5.3. Content Negotiation 8.4. Content Negotiation
The following request header fields are sent by a user agent to The following request header fields are sent by a user agent to
engage in proactive negotiation of the response content, as defined engage in proactive negotiation of the response content, as defined
in Section 3.4.1. The preferences sent in these fields apply to any in Section 6.4.1. The preferences sent in these fields apply to any
content in the response, including representations of the target content in the response, including representations of the target
resource, representations of error or processing status, and resource, representations of error or processing status, and
potentially even the miscellaneous text strings that might appear potentially even the miscellaneous text strings that might appear
within the protocol. within the protocol.
+-------------------+---------------+ +-------------------+---------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+---------------+ +-------------------+---------------+
| Accept | Section 5.3.2 | | Accept | Section 8.4.2 |
| Accept-Charset | Section 5.3.3 | | Accept-Charset | Section 8.4.3 |
| Accept-Encoding | Section 5.3.4 | | Accept-Encoding | Section 8.4.4 |
| Accept-Language | Section 5.3.5 | | Accept-Language | Section 8.4.5 |
+-------------------+---------------+ +-------------------+---------------+
For each of these header fields, a request that does not contain it
implies that the user agent has no preference on that axis of
negotiation. If the header field is present in a request and none of
the available representations for the response can be considered
acceptable according to it, the origin server can either 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 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 13.11).
Each of these header fields defines a wildcard value (often, "*") to
select unspecified values. If no wildcard is present, all values not
explicitly mentioned in the field are considered "not acceptable" to
the client.
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.
8.4.1. Quality Values 8.4.1. Quality Values
Many of the request header fields for proactive negotiation use a Many of the request header fields for proactive negotiation 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.
skipping to change at line 4175 skipping to change at page 97, line 18
the default weight is 1. the default weight is 1.
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.
5.3.2. Accept 8.4.2. 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.
Accept = #( media-range [ accept-params ] ) Accept = #( media-range [ accept-params ] )
media-range = ( "*/*" media-range = ( "*/*"
/ ( type "/" "*" ) / ( type "/" "*" )
/ ( type "/" subtype ) / ( type "/" subtype )
) *( OWS ";" OWS parameter ) ) *( OWS ";" OWS parameter )
accept-params = weight *( accept-ext ) accept-params = weight *( accept-ext )
accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ] 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 zero or more applicable media
type parameters (e.g., charset), an optional "q" parameter for type parameters (e.g., charset), an optional "q" parameter for
indicating a relative weight (Section 5.3.1), and then zero or more indicating a relative weight (Section 8.4.1), and then zero or more
extension parameters. The "q" parameter is necessary if any extension parameters. The "q" parameter is necessary if any
extensions (accept-ext) are present, since it acts as a separator extensions (accept-ext) are present, since it acts as a separator
between the two parameter sets. between the two parameter sets.
Note: Use of the "q" parameter name to separate media type Note: Use of the "q" parameter name to separate media type
parameters from Accept extension parameters is due to historical parameters from Accept extension parameters is due to historical
practice. Although this prevents any media type parameter named practice. Although this prevents any media type parameter named
"q" from being used with a media range, such an event is believed "q" from being used with a media range, such an event is believed
to be unlikely given the lack of any "q" parameters in the IANA to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type media type registry and the rare usage of any media type
parameters in Accept. Future media types are discouraged from parameters in Accept. Future media types are discouraged from
registering any parameter named "q". registering 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 request without any Accept header field implies that the user agent
will accept any media type in response. If the header field is
present in a request and none of the available representations for
the response have a media type that is listed as acceptable, the
origin server can either 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 subject to content negotiation.
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
Verbally, this would be interpreted as "text/html and text/x-c are Verbally, this would be interpreted as "text/html and text/x-c are
the equally preferred media types, but if they do not exist, then the equally preferred media types, but if they do not exist, then
send the text/x-dvi representation, and if that does not exist, send send the text/x-dvi representation, and if that does not exist, send
the text/plain representation". the text/plain representation".
skipping to change at line 4279 skipping to change at page 99, line 21
| image/jpeg | 0.5 | | image/jpeg | 0.5 |
| text/html;level=2 | 0.4 | | text/html;level=2 | 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 Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is a values for certain media ranges. However, unless the user agent is a
closed system that cannot interact with other rendering agents, this closed system that cannot interact with other rendering agents, this
default set ought to be configurable by the user. default set ought to be configurable by the user.
5.3.3. Accept-Charset 8.4.3. 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 = 1#( ( charset / "*" ) [ weight ] )
Charset names are defined in Section 3.1.1.2. A user agent MAY Charset names are defined in Section 6.1.1.1. 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 8.4.1.
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 field,
matches every charset that is not mentioned elsewhere in the matches every charset that is not mentioned elsewhere in the Accept-
Accept-Charset field. If no "*" is present in an Accept-Charset Charset field.
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 nearly
the available representations for the response has a charset that is ubiquitous and sending a detailed list of user-preferred charsets
listed as acceptable, the origin server can either honor the header wastes bandwidth, increases latency, and makes passive fingerprinting
field, by sending a 406 (Not Acceptable) response, or disregard the far too easy (Section 13.11). Most general-purpose user agents do
header field by treating the resource as if it is not subject to not send Accept-Charset, unless specifically configured to do so.
content negotiation.
5.3.4. Accept-Encoding 8.4.4. Accept-Encoding
The "Accept-Encoding" header field can be used by user agents to The "Accept-Encoding" header field can be used by user agents to
indicate what response content-codings (Section 3.1.2.1) are indicate their preferences regarding response content-codings
acceptable in the response. An "identity" token is used as a synonym (Section 6.1.2). An "identity" token is used as a synonym for "no
for "no encoding" in order to communicate when no encoding is encoding" in order to communicate when no encoding is preferred.
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 8.4.1. 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. header 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 field is in the request, any content-coding
is considered acceptable by the user agent. 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 field stating either "identity;q=0" or "*;q=0" without a
without a more specific entry for "identity". 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, 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 8.4.1, 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 combined field-value that is
empty implies that the user agent does not want any content-coding in empty 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.
Note: Most HTTP/1.0 applications do not recognize or obey qvalues Note: Most HTTP/1.0 applications do not recognize or obey qvalues
associated with content-codings. This means that qvalues might associated with content-codings. This means that qvalues might
not work and are not permitted with x-gzip or x-compress. not work and are not permitted with x-gzip or x-compress.
5.3.5. Accept-Language 8.4.5. 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 6.1.3.
Accept-Language = 1#( language-range [ weight ] ) Accept-Language = 1#( 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 8.4.1. 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