According to the HTTP Sepcification, a server responds with an HTTP response message:
Response = Status-Line ; Section 6.1 *(( general-header ; Section 4.5 | response-header ; Section 6.2 | entity-header ) CRLF) ; Section 7.1 CRLF [ message-body ] ; Despite being optional, some common header elements are likely to be implemented in most HTTP servers, such as 'Content-Type', 'Content-Length' etc. Who can tell me which header elements should a basic HTTP server implement.