Apache Cookbook, 2nd Edition

8.8. Invoking a CGI Program for Certain Content Types

Problem

You want to invoke a CGI program to act as a sort of content filter for certain document types. For example, a photographer may wish to create a custom handler to add a watermark to photographs served from his Web site.

Solution

Use the Action directive to create a custom handler, which will be implemented by a CGI program. Then use the AddHandler directive to associate a particular file extension with this handler:

Action watermark /cgi-bin/watermark.cgi
AddHandler watermark .gif .jpg

Or if you really want to the server to select your handler based on the type of data rather than the name of the file, you can use:

Action image/gif /cgi-bin/watermark.cgi
Action image/jpeg /cgi-bin/watermark.cgi

Discussion

This recipe creates a watermark handler that is called whenever a .gif or .jpg file is requested.

A CGI program, watermark.cgi, takes the image file as input and attaches the watermark image on top of the photograph. The path to the image file that was originally requested in the URL is available in the PATH_TRANSLATED environment variable, and the program needs to load that file, make the necessary modifications, and send the resulting content to the client, along with the appropriate HTTP headers.

Note that there is no way to circumvent this measure, as the CGI program will be called for any .gif or .jpg file that is requested from within the scope to which these directives apply.

This same technique may be used to attach a header ...