How to defer to the "default" HttpHandler for ASP.NET MVC after handling a potential override?

Question

I need to implement a custom handler for MVC that gives me the first look at URLs requests to determine if it should rewrite the urls before submitting the URL to the routing engine. Any pattern is a candidate for the redirect, so I need to intercept the URL request before the standard MVC routing engine takes a look at it.

After looking at a whole bunch of examples, blogs, articles, etc. of implementing custom routing for ASP.NET MVC, I still haven't found a use-case that fits my scenario. We have an existing implementation for ASP.NET that works fine, but we're returning the "standard" handler when no overrides are matched. The technique we're currently using is very similar to that described in this MSDN article: http://msdn.microsoft.com/en-us/library/ms972974.aspx#urlrewriting_topic5 which says "the HTTP handler factory can return the HTTP handler returned by the System.Web.UI.PageParser class's GetCompiledPageInstance() method. (This is the same technique by which the built-in ASP.NET Web page HTTP handler factory, PageHandlerFactory, works.)".

What I'm trying to figure out is: how can I get the first look at the incoming request, then pass it to the MVC routing if the current request doesn't match any of the dynamically configured (via a data table) values?

Answer 1

You would need to:

1. Not use the standard MapRoute extension method in global.asax (this is what sets up the route handler).
2. Instead, write your own route subtype, like this.

Answer 2

Although I explained to Craig I may not need to override scenario any more (favoring the future rather than the past), I realized there is an easy and reasonably clean place this override could be implemented - in the Default.aspx code behind file. Here's the standard Page_Load method:

    public void Page_Load(object sender, System.EventArgs e)
    {
        // Change the current path so that the Routing handler can correctly interpret
        // the request, then restore the original path so that the OutputCache module
        // can correctly process the response (if caching is enabled).

        string originalPath = Request.Path;
        HttpContext.Current.RewritePath(Request.ApplicationPath, false);
        IHttpHandler httpHandler = new MvcHttpHandler();
        httpHandler.ProcessRequest(HttpContext.Current);
        HttpContext.Current.RewritePath(originalPath, false);
    }

As you can see, it would be very easy to stick a url processing interceptor in front of the MVC handler. This changes the standard default page behavior and would need to be reflected in any other MVC app you'd want to create with this same method, but it sure looks like it would work.