The Hypertext Transfer Protocol (HTTP) is built on top of the TCP. When you type a URL in a browser, the browser opens a TCP channel to the server (after DNS lookup, of course) and sends an HTTP request to the web server. The server, after receiving the request, produces a response and sends it to the client. After that, the TCP channel may be closed or kept alive for further HTTP request-response pairs.
Both the request and the response contain a header and an optional (possibly zero-length) body. The header is in text format, and is separated from the body by an empty line.
More precisely, the header and the body are separated by four bytes—0x0D, 0x0A, 0x0D, and 0x0A, which are two CR, LF line separators. The HTTP protocol uses carriage return and line feed to terminate lines in the header and, thus, an empty line is two CRLF following each other.
The...
