rfc2616.md

https://www.ietf.org/rfc/rfc2616.txt

  3.If a Content-Length header field (section 14.13) is present, its
     decimal value in OCTETs represents both the entity-length and the
     transfer-length. The Content-Length header field MUST NOT be sent
     if these two lengths are different (i.e., if a Transfer-Encoding



Fielding, et al.            Standards Track                    [Page 33]

RFC 2616                        HTTP/1.1                       June 1999


     header field is present). If a message is received with both a
     Transfer-Encoding header field and a Content-Length header field,
     the latter MUST be ignored.