HTTP: The Definitive Guide

Step 5: Building Responses

Once the web server has identified the resource, it performs the action described in the request method and returns the response message. The response message contains a response status code, response headers, and a response body if one was generated. HTTP response codes were detailed in Section 3.4 in Chapter 3.

Response Entities

If the transaction generated a response body, the content is sent back with the response message. If there was a body, the response message usually contains:

• A Content-Type header, describing the MIME type of the response body

• A Content-Length header, describing the size of the response body

• The actual message body content

MIME Typing

The web server is responsible for determining the MIME type of the response body. There are many ways to configure servers to associate MIME types with resources:

mime.types

The web server can use the extension of the filename to indicate MIME type. The web server scans a file containing MIME types for each extension to compute the MIME type for each resource. This extension-based type association is the most common; it is illustrated in Figure 5-12.

Figure 5-12. A web server uses MIME types file to set outgoing Content-Type of resources

Magic typing

The Apache web server can scan the contents of each resource and pattern-match the content against a table of known patterns (called the magic file) to determine ...