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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)                      9  TCP/IP Hypertext Transfer Protocol (HTTP)                           9  HTTP Messages, Message Formats, Methods and Status Codes

HTTP Response Message Format 1 2 3 4 HTTP Status Code Format, Status Codes and Reason Phrases

A request sent by a client to a server obviously… requests that the server do something. All client/server protocols provide a way for the client to prompt the server to take action, generally by having the client give the server a series of commands. HTTP, in contrast, does not have commands but rather methods. Each client request message begins with the specification of the method that is the subject of the request.

What is the difference between a method and a command? In practical terms, nothing; they are the same. So why does HTTP use the term “method” instead of “command”? Good question. J The answer can be found in the abstract of the standard defining HTTP/1.0, RFC 1945. It states, in part, that HTTP is:

“a generic, stateless, object-oriented protocol which can be used for many tasks…”

In highly simplified terms, object-oriented programming is a technique in which software modules are described not as sets of procedures but as objects that possess attributes. These modules send messages to each other to communicate, and to cause actions to be performed, where the action taken depends on the nature of the object. In object-oriented programming, the procedures each object can perform are called methods.

HTTP is considered to be object-oriented because in many cases, the action taken by a server depends on the object that is the subject of the request. For example, if you ask a server to retrieve a text document, it will send that document, but if you ask for a directory, the server may instead return a default document for that directory. In contrast, a request that specifies the name of a program will result in the program being executed and its output returned (as opposed to the program’s source code being returned.)

HTTP Response Message Format 1 2 3 4 HTTP Status Code Format, Status Codes and Reason Phrases