Table of contents
The Content-Encoding entity-header field is used as a modifier to the media-type. When present, its value indicates what additional content codings have been applied to the entity-body, and thus what decoding mechanisms must be applied in order to obtain the media-type referenced by the Content-Type header field. Content-Encoding is primarily used to allow a document to be compressed without losing the identity of its underlying media type.
Content-Encoding = "Content-Encoding" ":" 1#content-coding
Content codings are defined in section 3.5. An example of its use is
The content-coding is a characteristic of the entity identified by the Request-URI. Typically, the entity-body is stored with this encoding and is only decoded before rendering or analogous usage. However, a non-transparent proxy MAY modify the content-coding if the new coding is known to be acceptable to the recipient, unless the "no-transform" cache-control directive is present in the message.
If the content-coding of an entity is not "identity", then the response MUST include a Content-Encoding entity-header (section 14.11) that lists the non-identity content-coding(s) used.
If the content-coding of an entity in a request message is not acceptable to the origin server, the server SHOULD respond with a status code of 415 (Unsupported Media Type).
If multiple encodings have been applied to an entity, the content codings MUST be listed in the order in which they were applied. Additional information about the encoding parameters MAY be provided by other entity-header fields not defined by this specification.