Is sending POST data with a GET request valid?

Using Curl for example, I can "post" data (send an entity-body) in a GET request. Is this a valid thing to do? With that I mean:

• Is it not forbidden by any RFC specifi开发者_Go百科cation?
• Does someone out there use it with good reason?

See RFC2616 - Hypertext Transfer Protocol -- HTTP/1.1, section 4.3 "Message Body":

A message-body MUST NOT be included in a request if the specification of the request method (section 5.1.1) does not allow sending an entity-body in requests.

In section 9.3 "GET" including an entity-body is not forbidden.

So, yes, you are allowed to send an entity-body with a HTTP GET request.

There is a "good reason" use case out there.

elasticsearch uses entity-body data in GET requests to try to use the GET verb as a read while also allowing a more complicated specification than url alone allows (easily).