What do you mean by HTTP? Explain its headers.

The Hypertext Transfer Protocol (HTTP) is a protocol used mainly to access data on the World Wide Web. The protocol transfer all data in the form of plain text, hypertext, audio, video, and so on. However it is called the hypertext transfer protocol because its efficiency allows its use in a hypertext environment where there are rapid jumps from one document to another.

HTTP functions like a combination of FTP and SMTP. It is similar to FTP because it transfers files and uses the services of TCP. However, it is much simpler than FTP because it uses only data are transferred between the client and the server.

HTTP is like SMTP because the data transferred between the client and server look like SMTP messages. In addition, the format of the messages is controlled by MIME-like headers.

However, HTTP differs from SMTP in the way the messages are sent from the client to the server and from the server to the client. Unlike SMTP, the HTTP messages are not destined to be read by humans; they are read and interpreted by the HTTP server and HTTP client (browser). SMTP messages are stored and forwarded, but HTTP messages are delivered immediately.

The idea of HTTP is very simple. A client sends a request, which looks like mail, to the server. The server sends the response, which looks like a mail reply, to the client. The request and response messages carry data in the form of a letter with MIME-like format.

The commands from the client to the server are embedded in a letter like request message. The contents of the requested file or other information are embedded in a letter like response message.

Fig: HTTP

HTTP Transaction

Figure illustrates the HTTP transaction between the client and server. The client initializes the transaction by sending a request message. The server replies by sending a response.

Messages

There are two general types of HTTP messages, shown in figure request and response. Both message types follow almost the same format.

Request Messages

A request message consists of a request line, headers, and sometimes a body.

 Response Message

            A response message consists of a status line, headers, and sometimes a body.