UrlRewriter+HttpModule+Session problem

Question

I need to write a custom "UrlRewriter" using a HttpModule, in the moment of "rewriting" I need access to the Session and has followed the advice from another SO thread:

Can I access session state from an HTTPModule?

Everything works, except the RewritePath/Redirect part. I don't get any exceptions, but the browser takes forever to load. Is this really the best way to build a urlrewriter like this?

using System;
using System.Web;
using System.Web.SessionState;
using System.Diagnostics;

namespace MyCompany.Campaigns
{

    public class CampaignRewriteModule : IHttpModule
    {
        public void Init(HttpApplication application)
        {
            application.PostAcquireRequestState += new EventHandler(Application_PostAcquireRequestState);
            application.PostMapRequestHandler += new EventHandler(Application_PostMapRequestHandler);
        }

        void Application_PostMapRequestHandler(object source, EventArgs e)
        {
            HttpApplication app = (HttpApplication)source;

            if (app.Context.Handler is IReadOnlySessionState || app.Context.Handler is IRequiresSessionState)
            {
                return;
            }

            app.Context.Handler = new MyHttpHandler(app.Context.Handler);
        }

        void Application_PostAcquireRequestState(object source, EventArgs e)
        {
            HttpApplication app = (HttpApplication)source;

            MyHttpHandler resourceHttpHandler = HttpContext.Current.Handler as MyHttpHandler;

            if (resourceHttpHandler != null)
            {
                HttpContext.Current.Handler = resourceHttpHandler.OriginalHandler;
            }

            Debug.Assert(app.Session != null);


            string path = HttpUtils.Path();

            if (!CampaignCodeMethods.IsValidCampaignCode(path)) return;

            string domain = HttpUtils.Domain();

            CampaignCode code = CampaignManager.RegisterCode(path, domain.Equals(Config.Instance.Domain.ToLower()) ? null : domain);

            if (code != null)
            {
               //app.Context.RewritePath(code.CampaignCodePath.Path, false);
               app.Context.Response.Redirect(code.CampaignCodePath.Path, true);
            }


        }

        public void Dispose() { }

        public class MyHttpHandler : IHttpHandler, IRequiresSessionState
        {
            internal readonly IHttpHandler OriginalHandler;

            public MyHttpHandler(IHttpHandler originalHandler)
            {
                OriginalHandler = originalHandler;
            }

            public void ProcessRequest(HttpContext context)
            {
                throw new InvalidOperationException("MyHttpHandler cannot process requests.");
            }

            public bool IsReusable
            {
                get { return false; }
            }
        }

    }

}

Answer 1

I think I know what it is. Your module is executed on ALL requests and assigns a handler that throws an error unless there is a valid campaign code (where a rewrite/redirect occurs).

But because this is not just for your "handler campaign code" url it is causing an error to be thrown, which is causing you to be redirected to your error page, which is being caught by the module, which is assigning the handler, which is throwing an error, which is redirecting... I think you get where I'm going ;)

Otherwise I'd try a few things:

• Setup Fiddler and check for an infinite redirect loop
• Put a breakpoint on app.Context.Response.Redirect - make sure your not in an infinite loop
• Put a breakpoint on MyHttpHandler.ProcessRequest - make sure it's not being called and the exception swallowed