httpModule for 404

Question

I've created an httpModule to handle URL remappings, and it works great on my test system. A request for www.mydomain.com/Some_Fancy_URL gets rewritten to www.mydomain.com/some.aspx?fancy=23 and so on.

When I deploy to the actual web site, I'm getting the default IIS 404 page though.

After doing some research online, it would seem that I need to setup "Wildcard Mapping" in IIS 6 to get the request past IIS and in to my httpModule. The problem is that the site is hosted on a shared server, so it may not be possible to get the ISP to make that change.

My question is, can't I use an httpHandler to tell IIS how I want these requests handled? For example:

<httpHandlers>
  <add path="*.aspx" verb="GET,POST" type="System.Web.UI.PageHandlerFactory" validate="false"/>
</httpHandlers>

It would seem like adding this to my Web.Config should tell IIS to stop validating the existence of .aspx files, and just pass the request along for me to process. It doesn't work though.

Any suggestions?

Answer 1

The problem with IIS 6 and ASP.NET is that they're aren't integrated. IIS needs to be told about ASP.NET via script mappings (.aspx, .asmx, wildcard and so on).

None of your web.config configuration settings will influence IIS because web.config is there to configure ASP.NET's behaviour, not IIS. IIS has no knowledge of web.config.

Unless you can hand off a request to the ASP.NET pipeline (via a script map) nothing will happen and all your web.config settings will be ignored.

With IIS 7 the story is quite different. In IIS7, ASP.NET and IIS are closely integrated and share the same pipeline thus permitting you to achieve the result you're looking for.

The alternative may be to find out if your hoster runs a URL rewriter such as ISAPI_Rewrite on their servers. That way you could rewrite urls without having to map a wildcard scriptmap to IIS6.

Answer 2

Through some trial and error, along with more web searches, I found a solution. It essentially parallels Kev's answer.

IIS won't treat a request as .NET unless it has a known file extension (.aspx, .ascx, etc.). When I send along something like www.mydomain.com/anything it looks for a file or folder named "anything", and when it doesn't find one, it just drops off to the default IIS 404 handler.

That's where I took over. I changed IIS 6 to forward 404 problems to /404.aspx. I then created that page with a generic "Your file wasn't found" message in the same style as my web site.

Here's the good part: Now that IIS is sending 404's to a .NET page, the custom httpModule I created is getting fired. The request is for 404.aspx, but IIS is nice enough to also append the original URL as well. You get something like:

www.mydomain.com/404.aspx?404;http://www.mydomain.com/anything

This allows me to parse the request in the httpModule, and rewrite as needed!