HTTP messages consist of requests from client to server and responses from server to client.
HTTP-message = Request | Response ; HTTP/1.1 messages
Request (section 5) and Response (section 6) messages use the generic message format of RFC 822 [9] for transferring entities (the payload of the message). Both types of message consist of a start-line, one or more header fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header fields, and an optional message-body.
generic-message = start-line *message-header CRLF [ message-body ] start-line = Request-Line | Status-Line
In the interest of robustness, servers SHOULD ignore any empty line(s) received where a Request-Line is expected. In other words, if the server is reading the protocol stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF.