Hypertext Transfer Protocol (HTTP) is an application-level protocol.HTTP is a request/response standard between a client and a server. A client is the end-user, the server is the web site. The client making a HTTP request�using a web browser, spider, or other end-user tool�is referred to as the user agent. The responding server�which stores or creates resources such as HTML files and images�is called the origin server. In between the user agent and origin server may be several intermediaries, such as proxies, gateways, and tunnels. HTTP is not constrained to using TCP/IP and its supporting layers, although this is its most popular application on the Internet. Indeed HTTP can be "implemented on top of any other protocol on the Internet, or on other networks.
Request message
The request message consists of the following:
* Request line, such as GET /images/logo.gif HTTP/1.1, which requests a resource called /images/logo.gif from server
* Headers, such as Accept-Language: en
* An empty line
* An optional message body
Request methods
HTTP defines eight methods indicating the desired action to be performed on the identified resource.
HTTP is a stateless protocol. The advantage of a stateless protocol is that hosts do not need to retain information about users between requests, but this forces web developers to use alternative methods for maintaining users’ states.