Each Request message sent by an HTTP client to a server prompts the server to send back a Response message. Actually, in certain cases, the server may send two responses: a preliminary response, followed by the real one. Usually though, one request yields one response, which indicates the results of the server's processing of the request, and a response often also carries an entity (file or resource) in the message body.
Like Request messages, Response messages use their own specific format that is based on the HTTP generic message format described earlier in this chapter. The format Response message format header is as follows (see Figure 81-2):