Apache Cookbook, 2nd Edition

5.14. Redirecting Unreferred Requests to an Explanation Page

Problem

When a request comes to your server without a referring URL being mentioned, you want to redirect it to a page that explains why you’re not satisfying it.

Solution

Add lines such as the following to your configuration files:

RewriteEngine On
RewriteCond "%{HTTP_REFERER}" "^$"
RewriteRule "(.*)" "/cgi-bin/need-referer" [PT,E=ORIG:$1]

Tip

Be sure to put these directives in an appropriate scope, or people won’t be able to type in your site’s URLs at all!

Discussion

The specific problem being addressed in the Solution is requests coming to your server with no information about where they got the URL (which is passed in the Referer request header field). This frequently indicates someone surfing directly to the page rather than following a link, and in the case of images informaltable may be the result of a “Save As” request on the user’s part. If you want to only serve requests that came from links on your own site, you can change the RewriteCond directive to:

RewriteCond "%{HTTP_REFERER}" "!http://%{SERVER_NAME}/" [NC]

The RewriteRule will pass the request to a CGI script named need-referer, and will put the original URI into the environment variable ORIG for the script to reference. Note that only the local portion of the URI is included; the hostname will not be, for instance.

Warning

The lack of a Referer request header field does not always signify skulduggery. Some people consider it none of a site’s business how they came ...