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The Hypertext Transfer Protocol

The Hypertext Transfer Protocol (HTTP) is a simple protocol that describes the mechanism whereby Web clients talk to servers. The basic model is that the client sends a request to the server and receives a response back.

The first line of a request consists of a method, an identifier for the object requested and an optional HTTP version identifier, for example:

  GET /Welcome.html HTTP/1.0

If the version identifier is omitted, version 0.9 is assumed and the request just consists of the single line, otherwise the request is followed by further information expressed as mail-type headers and terminated by a blank line. All of this information is encoded using seven-bit US-ASCII. Following the request there may be an object (such as data from a form), encoded as specified by MIME headers.

The server's response consists of a status line followed by a set of headers. The status line contains the protocol version that the server is using, followed by a numeric status code and a textual representation of the status code, as shown below:

  HTTP/1.0 200 Document follows
  MIME-Version: 1.0
  Server: CERN/3.0
  Date: Monday, 14-Nov-94 17:12:29 GMT
  Content-Type: text/html
  Content-Length: 47
  Last-Modified: Saturday, 01-Oct-94 16:41:56 GMT

  <H1>Welcome!</H1>
  An empty welcome document...

Browsers actually send a lot more information to servers than has been outlined above, detailed knowledge of which is not strictly necessary for running a server. This information is currently being codified by an IETF working group, and the new HTTP specification is expected as an RFC sometime soon.

Spinning the Web by Andrew Ford
© 1995 International Thomson Publishing
© 2002 Andrew Ford and Ford & Mason Ltd
Note: this HTML document was generated in December 1994 directly from the LaTeX source files using LaTeX2HTML. It was formatted into our standard page layout using the Template Toolkit. The document is mainly of historical interest as obviously many of the sites mentioned have long since disappeared.