The HTTP QUERY Method

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Table of Contents

1. Introduction

This specification defines the HTTP QUERY request method as a means of making a safe, idempotent request that contains content.¶

Most often, this is desirable when the data conveyed in a request is too voluminous to be encoded into the request's URI. For example, this is a common query pattern:¶

GET /feed?q=foo&limit=10&sort=-published HTTP/1.1
Host: example.org

However, for a query with parameters that are complex or large in size, encoding it in the request URI may not be the best option because¶

• often size limits are not known ahead of time because a request can pass through many uncoordinated system,¶
• expressing certain kinds of data in the target URI is inefficient because of the overhead of encoding that data into a valid URI, and¶
• encoding query parameters directly into the request URI effectively casts every possible combination of query inputs as distinct resources.¶

As an alternative to using GET, many implementations make use of the HTTP POST method to perform queries, as illustrated in the example below. In this case, the input parameters to the query operation are passed along within the request content as opposed to using the request URI.¶

A typical use of HTTP POST for requesting a query:¶

POST /feed HTTP/1.1
Host: example.org
Content-Type: application/x-www-form-urlencoded

q=foo&limit=10&sort=-published

This variation, however, suffers from the same basic limitation as GET in that it is not readily apparent -- absent specific knowledge of the resource and server to which the request is being sent -- that a safe, idempotent query is being performed.¶

The QUERY method provides a solution that spans the gap between the use of GET and POST, with the example above being expressed as:¶

QUERY /feed HTTP/1.1
Host: example.org
Content-Type: application/x-www-form-urlencoded

q=foo&limit=10&sort=-published

As with POST, the input to the query operation is passed along within the content of the request rather than as part of the request URI. Unlike POST, however, the method is explicitly safe and idempotent, allowing functions like caching and automatic retries to operate.¶

Summarizing:¶

2. QUERY

The QUERY method is used to initiate a server-side query. Unlike the HTTP GET method, which requests that a server return a representation of the resource identified by the target URI (as defined by Section 7.1 of [HTTP]), the QUERY method is used to ask the server to perform a query operation (described by the request content) over some set of data scoped to the target URI. The content returned in response to a QUERY cannot be assumed to be a representation of the resource identified by the target URI.¶

The content of the request defines the query. Implementations MAY use a request content of any media type with the QUERY method, provided that it has appropriate query semantics.¶

QUERY requests are both safe and idempotent with regards to the resource identified by the request URI. That is, QUERY requests do not alter the state of the targeted resource. However, while processing a QUERY request, a server can be expected to allocate computing and memory resources or even create additional HTTP resources through which the response can be retrieved.¶

A successful response to a QUERY request is expected to provide some indication as to the final disposition of the operation. For instance, a successful query that yields no results can be represented by a 204 No Content response. If the response includes content, it is expected to describe the results of the operation.¶

3. The "Accept-Query" Header Field

The "Accept-Query" response header field can be used by a resource to directly signal support for the QUERY method while identifying the specific query format media type(s) that may be used.¶

"Accept-Query" contains a list of media ranges (Section 12.5.1 of [HTTP]) using "Structured Fields" syntax ([STRUCTURED-FIELDS]). Media ranges are represented by a List Structured Header Field of either Tokens or Strings, containing the media range value without parameters. Parameters, if any, are mapped to Parameters of type String.¶

The choice of Token vs. String is semantically insignificant. That is, recipients MAY convert Tokens to Strings, but MUST NOT process them differently based on the received type.¶

Media types do not exactly map to Tokens, for instance they allow a leading digit. In cases like these, the String format needs to be used.¶

The only supported uses of wildcards are "*/*", which matches any type, or "xxxx/*", which matches any subtype of the indicated type.¶

The order of types listed in the field value is not significant.¶

The only allowed format for parameters is String.¶

Accept-Query's value applies to every URI on the server that shares the same path; in other words, the query component is ignored. If requests to the same resource return different Accept-Query values, the most recently received fresh value (per Section 4.2 of [HTTP-CACHING]) is used.¶

Example:¶

Accept-Query: "application/jsonpath", application/sql;charset="UTF-8"

Although the syntax for this field appears to be similar to other fields, such as "Accept" (Section 12.5.1 of [HTTP]), it is a Structured Field and thus MUST be processed as specified in Section 4 of [STRUCTURED-FIELDS].¶

5. IANA Considerations

Appendix A. Examples

The non-normative examples in this section make use of a simple, hypothetical plain-text based query syntax based on SQL with results returned as comma-separated values. This is done for illustration purposes only. Implementations are free to use any format they wish on both the request and response.¶

QUERY /contacts HTTP/1.1
Host: example.org
Content-Type: application/sql
Accept: text/csv

select surname, givenname, email limit 10

HTTP/1.1 200 OK
Content-Type: text/csv

surname, givenname, email
Smith, John, john.smith@example.org
Jones, Sally, sally.jones@example.com
Dubois, Camille, camille.dubois@example.net

QUERY /contacts HTTP/1.1
Host: example.org
Content-Type: application/sql
Accept: text/csv

select surname, givenname, email limit 10

HTTP/1.1 200 OK
Content-Type: text/csv
Content-Location: /contacts/responses/42
Location: /contacts/queries/17

surname, givenname, email
Smith, John, john.smith@example.org
Jones, Sally, sally.jones@example.com
Dubois, Camille, camille.dubois@example.net

GET /contacts/queries/17 HTTP/1.1
Host: example.org
Accept: text/csv

HTTP/1.1 200 OK
Content-Type: text/csv
Content-Location: /contacts/responses/43

surname, givenname, email
Jones, Sally, sally.jones@example.com
Dubois, Camille, camille.dubois@example.net

QUERY /contacts HTTP/1.1
Host: example.org
Content-Type: application/sql
Accept: text/csv

select surname, givenname, email limit 10

HTTP/1.1 303 See Other
Location: /contacts/query123

GET /contacts/query123 HTTP/1.1
Host: example.org

HTTP/1.1 200 OK
Content-Type: text/csv

surname, givenname, email
Smith, John, john.smith@example.org
Jones, Sally, sally.jones@example.com
Dubois, Camille, camille.dubois@example.net

QUERY /contacts HTTP/1.1
Host: example.org
Content-Type: application/sql
Accept: text/csv

select surname, givenname, email limit 10

HTTP/1.1 308 Moved Permanently
Location: /morecontacts

QUERY /morecontacts HTTP/1.1
Host: example.org
Content-Type: application/sql
Accept: text/csv

select surname, givenname, email limit 10

HTTP/1.1 200 OK
Content-Type: text/csv

surname, givenname, email
Smith, John, john.smith@example.org
Jones, Sally, sally.jones@example.com
Dubois, Camille, camille.dubois@example.net

Appendix B. Change Log

This section is to be removed before publishing as an RFC.¶

Authors' Addresses