The presence of a message-body in a request is signaled by the
inclusion of a Content-Length or Transfer-Encoding header field in
the request's message-headers. 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.
Based on my understanding of HTTP, I would assume this means that a GET
request cannot have a Content-Length header. However, I cannot find any
place in the spec that says the GET request method does not allow
sending of an entity-body.