A quick and easy way of doing URL rewriting or responding to requests for static resources is to use the Application_BeginRequest event. This event will fire each time a page is requested. In there, you could do something like the following to serve a different file when a specific URL is requested to your site:

// get the current URL
string sUrl = Request.Url.PathAndQuery;
if (sUrl == "/my-pretty-url/some-page")
{
    // rewrite the URL to a different path 
    // (NOTE: user's browser's address will stay the same)
    HttpContext.Current.RewritePath("/SomeOtherUrl.aspx");
}

You could also block access to a static resource like an image from being served based on some criteria. In this code sample, I’ve blocked access to an image if the caller is a specific website I don’t want to serve my images to:

// get the current URL
string sUrl = Request.Url.PathAndQuery;
// check the IP address of the caller
if (Request.UserHostAddress == "122.134.54.234" && sUrl == "/images/my-image-name.png")
{
    // serve up 404 error because we don't want this client to get access 
    // to this image resource
    Response.Status = "404 Not Found";
    Response.StatusCode = 404;
    Response.End();
}

These code samples will run great in your Visual Studio 2008 or 2010 Cassini built-in web server, but if you deploy them to a standard IIS 6 or IIS 7 server, you will be scratching your head because your Global.asax events will not fire when static resources are requested.

Problem in IIS 6

For IIS 6, the reason for this is that the IIS pipeline does not support native .NET IHttpModules. Pre-IIS 7, .NET was an ISAPI plug-in for IIS instead of native to the server. Static resources get served by IIS using the built-in IIS services. Therefore, static resources do not go through the ASP.NET pipeline and your events are not fired.

IIS 6 Solution

There are several solutions to get IIS 6 to run your Global.asax file events whenever a static resource is served. The easiest to implement is to add a wild card mapping to your server to run all requests through the .NET run-time. To do this, first right-click on your IIS web site instance that you want to change and choose properties.

Click on the Home Directory tab and then click "Configuration" next to your web application instance.

On the Wildcard application maps section, click "Insert" (NOTE: don’t click "Add")

Enter the path to your ASP.NET ISAPI dll. For instance, if you are using .NET 2.0, then your path would like this:

C:\windows\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll

If you are using .NET 4.0, then it will have a similar path.
Make sure to NOT check the box "Verify that file exists" and then click OK.

There are other solutions as well but this one is simplest. On high performance, high traffic sites, you may want to consider alternatives because this solution could affect performance since all static resources will be served by ASP.NET instead of the native IIS server (which could be slower in some cases). Other solutions and more information this is in this great article here:

http://blog.stevensanderson.com/2008/07/04/options-for-deploying-aspnet-mvc-to-iis-6/

Problem in IIS 7

In IIS 7, the .NET pipeline is fully integrated into IIS but by default, IIS does not serve static resources through your ASP.NET application. So your events will not fire for these types of resources.

IIS 7 Solution

The easy solution in IIS 7 is to add a setting in your web.config file to tell IIS to process all requests through your Global.asax events. Just add or change this section in your web.config to enable requests:

<system.webServer>
  <modules runAllManagedModulesForAllRequests="true" />
</system.webServer>