Is the Content-Type header appropriate for any HTTP verb other than PUT or POST?

I'm trying out the REST API of the CollectionSpace software, and noticed that sending it a Content-Type header as part of a GET request results in the following error:

HTTP Status 415 - Cannot consume content type

Both of the python REST client libraries I've tried, restclient on github and python-rest-client on google code, do send a Content-Type header when making GET requests.

My understanding from reviewing http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html is that clients should only send Content-Type headers on POST and PUT requests. Is that correct?

The fact that both of these libraries do sen开发者_开发问答t the header makes me think that servers typically ignore it, rather than return a client error code.

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Although not explicitly outlined in the spec, one could make some inferences. Section 7.2.1 states

Any HTTP/1.1 message containing an entity-body SHOULD include a Content-Type header field defining the media type of that body.

That's pretty obvious, and makes sense. Given that, we can have a look at Section 9 (Method Definitions) to see which ones mention that they'd possibly have an entity in the request body. Three of them mention it:

OPTIONS

If the OPTIONS request includes an entity-body (as indicated by the presence of Content-Length or Transfer-Encoding)...

POST

...used to request that the origin server accept the entity enclosed in the request...

PUT

...requests that the enclosed entity be stored under the supplied Request-URI

And one method specificially disallows entities, TRACE:

A TRACE request MUST NOT include an entity.

In reality you could send any method (except TRACE) with an entity in the body and a Content-Type header. However, per the spec, I wouldn't expect the server to do anything with it unless it were one of the three methods above.

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I would also say that the software you're using that responds with the HTTP Status 415 is in violation of the specification.

Section 4.3 says:

...if the request method does not include defined semantics for an entity-body, then the message-body SHOULD be ignored when handling the request.

Since the spec doesn't include defined semantics for an entity body with a GET request, the server should ignore it.

Additionally if no entity was provided in the request, and the Content-Length is zero (assuming the Transfer-Encoding header is not set and is not "identity"), the server should not try to consume an entity, regardless of of the request method or whether or not there's a Content-Type header present. This can be backed up by the order of precedence for determining the message length described in Section 4.4.

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415 Cannot consume content type

This problem happens if the REST Resource has @Consumes suggesting to accept a particular MIME Type. To fix this set the correct "Accept" Header in the Request/Resource call along with "Content-Type" header. For MockHttpRequest from RESTEasy it can be done simply as

request.accept(MediaType.APPLICATION_JSON); request.contentType(MediaType.APPLICATION_JSON);