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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 Request Message Format 1 2 3 HTTP Methods

Status Line

The status line—not “response line”, note—is the start line used for response messages. It has two functions: to tell the client what version of the protocol the server is using, and to communicate a summary of the results of processing the client's request. The formal syntax for the status line is:

<HTTP-VERSION> <status-code> <reason-phrase>

The HTTP-VERSION label in the status line serves the same purpose as it does in the request line of a request message; here, it tells the client the version number that the server is using for its response. It uses the same format as in the request line, in upper case as “HTTP/0.9”, “HTTP/1.0” or “HTTP/1.1”. The server is required to return an HTTP version number that is no greater than that the client sent in its request.

The status code and reason phrase provide information about the results of processing the client's request in two different forms. The status code is a three-digit number that indicates the formal result that the server is communicating to the client; it is intended for the client HTTP implementation to process so the software can take appropriate action. The reason phrase is an additional, descriptive text string, which can be displayed to the human user of the HTTP client so he or she can see how the server responded. I describe status codes and reason phrases later in this section, and also list all of the standard codes.

HTTP Request Message Format 1 2 3 HTTP Methods