Call the default asp.net HttpHandler from a custom handler

Question

I\'m adding ASP.NET routing to an older webforms app. I\'m using a custom HttpHandler to process everything. In some situations I would like to map a particular pat

Answer 1

Another option is to invert the logic by handling the cases in which you do NOT want to return the default response and remap the others to your own IHttpHandler. Whenever myCondition is false, the response will be the "default". The switch is implemented as an IHttpModule:

public class SwitchModule: IHttpModule
{
    public void Init(HttpApplication context)
    {
        context.PostAuthenticateRequest += app_PostAuthenticateRequest;
    }

    void app_PostAuthenticateRequest(object sender, EventArgs e)
    {
        // Check for whatever condition you like           
        if (true)
            HttpContext.Current.RemapHandler(new CustomHandler());

    }

    public void Dispose()        
}

internal class CustomHandler: IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.Write("hallo");
    }

    public bool IsReusable { get; }
}

Answer 2

Persistence pays off! This actually works, and since this information seems to be available pretty much nowhere I thought I'd answer my own question. Thanks to Robert for this post on instantiating things with internal constructors, this is the key.

http://www.rvenables.com/2009/08/instantiating-classes-with-internal-constructors/

public void ProcessRequest(HttpContext context) {
    // the internal constructor doesn't do anything but prevent you from instantiating
    // the factory, so we can skip it.
    PageHandlerFactory factory =
        (PageHandlerFactory)System.Runtime.Serialization.FormatterServices
        .GetUninitializedObject(typeof(System.Web.UI.PageHandlerFactory));

     string newTarget  = "default.aspx"; 
     string newQueryString = // whatever you want
     string oldQueryString = context.Request.QueryString.ToString();
     string queryString = newQueryString + oldQueryString!="" ? 
         "&" + newQueryString :
         "";

     // the 3rd parameter must be just the file name.
     // the 4th parameter should be the physical path to the file, though it also
     //   works fine if you pass an empty string - perhaps that's only to override
     //   the usual presentation based on the path?

     var handler = factory.GetHandler(context, "GET",newTarget,
         context.Request.MapPath(context,newTarget));

     // Update the context object as it should appear to your page/app, and
     // assign your new handler.

     context.RewritePath(newTarget  , "", queryString);
     context.Handler = handler;

     // .. and done

     handler.ProcessRequest(context);
}

... and like some small miracle, an aspx page processes & renders completely in-process without the need to redirect.

I expect this will only work in IIS7.

Answer 3

I'm you're using Routing in webforms you should be able to just add an ignore route for the specific .aspx files you want. This will then be handled by the default HttpHandler.

http://msdn.microsoft.com/en-us/library/dd505203.aspx