Is this statement correct? HTTP GET method always has no message body

Question

Is this statement correct? HTTP GET method always has no message body. I didn't find any part of RFC2616 explicitly say this.

And if this is not true, then in what circumstances will an Http GET request include a message body

Answer 1

Neither restclient nor REST console support this but curl does.

The original HTTP 1.1 specification says in section 4.3

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.

Section 5.1.1 redirects us to section 9.x for the various methods. None of them explicitly prohibit the inclusion of a message body. However...

Section 5.2 says

The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.

and Section 9.3 says

The GET method means retrieve whatever information (in the form of an entity) is identified by the Request-URI.

Which together suggest that when processing a GET request, a server is not required to examine anything other that the Request-URI and Host header field.

In summary, the HTTP spec doesn't prevent you from sending a message-body with GET, but there is sufficient ambiguity that it wouldn't surprise me if it was not supported by all servers.

Answer 2

The old RFC2616 has been superseded and it was replaced by multiple RFCs (7230-7237).

New RFC 7230 on HTTP/1.1 clearly says about message body:

The message body (if any) of an HTTP message is used to carry the
payload body of that request or response. The message body is
identical to the payload body unless a transfer coding has been
applied, as described in Section 3.3.1.

 message-body = *OCTET

The rules for when a message body is allowed in a message differ for requests and responses.

The presence of a message body in a request is signaled by a
Content-Length or Transfer-Encoding header field. Request message
framing is independent of method semantics, even if the method does
not define any use for a message body.

So new standard clearly answer the initial question. But there are some old software which can ignore message-body into GET request, so you need be cautious and check this case.