Chapter 2. The Hypertext Transport Protocol

The Hypertext Transport Protocol (HTTP) is the common language that web browsers and web servers use to communicate with each other on the Internet. CGI is built on top of HTTP, so to understand CGI fully, it certainly helps to understand HTTP. One of the reasons CGI is so powerful is because it allows you to manipulate the metadata exchanged between the web browser and server and thus perform many useful tricks, including:

• Serve content of varying type, language, or other encoding according to the client's needs.

• Check the user's previous location.

• Check the browser type and version and adapt your response to it.

• Specify how long the client can cache a page before it is considered outdated and should be reloaded.