Hyper Text Transfer Protocol is  the underlying protocol used by the World Wide Web.   HTTP defines how messages are formatted and transmitted, and what action web server and browsers should take in response to various commands.  For example, when the user enters a URL in a browser, the browser actually sends and HTTP command to web server directing it to fetch and transmit the requested web page.

HTTP Working functionality

HTTP is based on request / response model.  The client connects to the server and sends a request  to the server.  The request contains the following: request method, URL, Protocol version.  The client then sends some header information.  The server’s response includes the return of the protocol version, status code, followed by a header that contains server information , and then the requested data.  The connection is then closed.

These are the four stages behind HTTP.  They are

 REQUEST – client send request to server for example you want to access the page named   http://tut2learn.com/  is a request for the document named login.html.  The browser maps this string into an HTTP request.

Headers – After the requests, the client can include additional information for the server.  These     headers state some key facts about the clients.

RESPONSE – after the client sends the request, the server processes it and returns a response.  The first line of the response is the status line, which states the status of the request.  After the status line, the server sends response headers that states facts about the responses.

GET/POST methods  – HTTP  responses can be one of several types, called methods.  The two most important methods are get and post.

The Get method is used for retrieving information from the server;  the post method is used for sending information to a server, for example, placing an order for  a book at Amazon.  When you type an URL into your browser or click a link the GET method is being used.  When you submit a  complicated  form the POST method is typically being used.  The difference between GET and POST is that GET requests are intended to be used to send only a relatively small amount of information to a server.  POST commands, on the other hand, can be used to send a virtually unlimited amount of data to the server.

HTTP is stateless protocol which means that a different connection between a client and server is established for each request.

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