1. Introduction

In HTTP, content codings allow for payload encodings such as for compression or integrity checks ([RFC7231], Section 3.1.2). In particular, the "gzip" content coding ([RFC7230], Section 4.2) 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 ([RFC7231], Section 5.3.4) for use in responses, to indicate the content codings that are supported in requests. It furthermore updates the definition of status code 415 (Unsupported Media Type) ([RFC7231], Section 6.5.13), recommending that the "Accept-Encoding" header field be included when appropriate.