Accept: being optional

[decoderwheel]

Accept: being optional

[bbarry]

https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1

If no Accept header field is present, then it is assumed that the client accepts all media types. If an Accept header field is present, and if the server cannot send a response which is acceptable according to the combined Accept field value, then the server SHOULD send a 406 (not acceptable) response.

[decoderwheel]

@bbarry Yes, that's what I said. However, the REST guidelines say (my emphasis):

Per the HTTP guidelines, this is just a hint and responses MAY have a different content type,
such as a blob fetch where a successful response will just be the blob stream as the payload.

However, I've just answered my own question; RFC2616 was obsoleted by RFC 7231 (amongst others), which now says this in Section 5.3.2:

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.

I'd argue that's bad practice, but it is part of the spec.