In HTTP, "Content Codings" allow for payload encodings such as for compression or integrity checks. In particular, the "gzip" content coding is widely used for payload data sent in response messages.¶
Content Codings can be used in request messages as well, however discoverability is not on par with response messages. This document extends the HTTP "Accept-Encoding" header field for use in responses.¶
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In HTTP, "Content Codings" allow for payload encodings such as for compression or integrity checks ([HTTPSEM], Section 3.1.2). In particular, the "gzip" content coding is widely used for payload data sent in response messages.¶
This specification extends that definition to allow "Accept-Encoding" as response header field as well. When present, it indicates what content codings a server is willing to accept in requests. In particular, a field value that contains "identity" only implies that no content codings are supported at all.¶
Note that this information applies to the resource to which the request was addressed. The set of supported encodings might vary for different resources on the same server, and could also vary depending on other aspects of the request (such as the request method).¶
Servers that fail a request due to an unsupported content coding SHOULD respond with a 415 status and SHOULD include an "Accept-Encoding" header in that response, allowing clients to distinguish between content coding related issues and media type related issues.¶
POST /edit/ HTTP/1.1 Host: example.org Content-Type: application/atom+xml;type=entry Content-Encoding: compress ...compressed payload...
Server rejects request because it only allows the "gzip" content coding:¶
HTTP/1.1 415 Unsupported Media Type Date: Fri, 09 May 2014 11:43:53 GMT Accept-Encoding: gzip Content-Length: 68 Content-Type: text/plain This resource only supports the "gzip" content coding in requests.
...at which point the client can retry the request with the supported "gzip" content coding.¶
Alternatively, a server that does not support any content codings in requests could answer with:¶
HTTP/1.1 415 Unsupported Media Type Date: Fri, 09 May 2014 11:43:53 GMT Accept-Encoding: identity Content-Length: 61 Content-Type: text/plain This resource does not support content codings in requests.
This document updates the definition of the "Accept-Encoding" header field, so the "Permanent Message Header Field Names" registry shall be updated accordingly:¶