Apache: The Definitive Guide, 3rd Edition

A Closer Look at HTTP

In publishing a site, we’ve been focusing on only one method of the HTTP protocol, GET. Apache’s basic handling of GET is more than adequate for sites that just need to publish information from files, but HTTP (and Apache) can support a much wider range of options. Developers who want to create interactive sites will have to write some programs to supply the basic logic. However, many useful tasks are simple to create, and Apache is quite capable of supporting much more complex applications, including applications that connect to databases or other information sources.

Every HTTP request must specify a method. This tells the server how to handle the incoming data. For a complete account, see the HTTP 1.1 specification (http://www.w3.org/Protocols/rfc2616/rfc2616.html). Briefly, however, the methods are as follows:

GET

Returns the data asked for. To save network traffic, a “conditional GET " only generates a return if the condition is satisfied. For instance, a page that alters frequently may be transmitted. The client asks for it again: if it hasn’t changed since last time, the conditional GET generates a response telling the client to get it from its local cache. (GET may also include extra path information, as well as a query string with information an application needs to process.)

HEAD

Returns the headers that a GET would have included, but without data. They can be used to test the freshness of the client’s cache without the bandwidth expense of retrieving ...