Using ColdFusion to Handle 404 Errors (Page Not Found) On Development Server

Handling 404 errors can be tricky no matter what. On your live, production server, you can set up custom 404 handling on a site-by-site basis via IIS custom error templates. However, for many of us, this is trickier on the development server where there are no site. Its just one web server with many sub directories, none of which are usually virtual sites.

To remedy this situation, I have developed a 404 error handler that is defined at the root of the developmental web server. This 404 error handler catches 404 errors and attempts to forward the errors to individual "site" error handlers in an attempt to mimic 404 error handling on a live site. This setup makes a few assumptions:

1. Your 404 errors are handled by a ColdFusion template named "cferror.cfm"
   
2. Your cferror.cfm template is located either in the root of the site (a sub directory on the development server) or at least that it is in the same directory or a parent directory of the requested non-existent page.

The system works by catching the 404 error at the root of the ColdFusion web server. It then takes the requested page and starts crawling up the directories url. For each directory, it check for the existence of the cferror.cfm template. If it is found, the root 404 error handler performs a CFLocation to that cferror.cfm template, sending, as the query string, the same "404;" query string that IIS has defined.

As the system crawls up the directory path, after checking for cferror.cfm, it checks for either an Application.cfm or Application.cfc file. If it hits one of these files, it stops crawling and displays its own Page Not Found message. The idea here is that we don't want to leave the context of the application when search for a 404 error handler.

I have prevented infinite loops (the root 404 error handler constantly CFLocating to itself) by stopping the search once there is no more directory to crawl (signaling that we are in the root directory). I have not tested this, but I assume this means that if the development server's cferror.cfm template is NOT IN THE ROOT of the web server, the infinite looping IS possible.

A word of caution: This template is done to help develop 404 error handling by simulating 404 error handling on the live, production server. It DOES NOT MIMIC live 404 error handling. On the live server, IIS will pass control directly to your site's 404 error handler without doing any URL location changes. Therefore, from your BROWSER's PERSPECTIVE, on the live server, your missing page URL may be in a different directory as your 404 error handler. On the development server, however, the missing page URL is ALWAYS in the same directory as the 404 error handler.

For example, let's say you request a non-existent page "ben-nadel/is/cool.htm" on the live server.

Browser sees:
ben-nadel/is/cool.htm

ColdFusion sees:
cferror.cfm

The web browser is TWO directories down in the site structure. The relative paths would start with "../../".

If you do the same thing on the development server:

Browser sees:
cferror.cfm?404;http://..../ben-nadel/is/cool.htm

ColdFusion sees:
cferror.cfm

Both the web browser and the 404 error handler are in the SAME directory (due to the root 404 error handler's CFLocation). The relative paths would be empty since there is no sub-folder URL.

The cferror.cfm template as it exists in the root of my development server:

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