Response.Redirect Interceptor

Introduction

ISAPI module to intercepts IIS response.redirect calls and convert the URL to lowercase to avoid 302 or 301 Status code not good for SEOs.

Background

Main logic

From MSDN documentation It is quite clear that Response.Redirect is internally setting Location Header in Response object and luckily, not only this header is accessible but also could be alter. It means that I have to get the value of Location header and then call lower method on it and then set it back to header.

  string redirectedLocation = context.Response.Headers["Location"];
  context.Response.Headers["Location"] = redirectedLocation.ToLowerInvariant();

And there is also a property of Response object indicating redirection for the current request

IsRequestBeingRedirected

Global.asax

void Application_EndRequest(object sender, EventArgs e)
    {
        HttpApplication application = sender as HttpApplication;
        HttpContext context = application.Context;

        if (context.Response.IsRequestBeingRedirected)
        {
            string redirectedLocation = context.Response.Headers["Location"];
            context.Response.Headers["Location"] = redirectedLocation.ToLowerInvariant();
        }
    }

IHttpModule

As mentioned above IHttpModule is cleaner and more maintainable as well. Please put contants files to avoid magic strings in a separate file some where else in project better is to have them project specific.

namespace CustomizeIISPipeline
{
    public class RedirectorInterceptorModule : IHttpModule
    {
        public RedirectorInterceptorModule()
        {
            //
            // TODO: Add constructor logic here
            //
        }
        
        public void Init(HttpApplication application)
        {
            application.EndRequest +=
              (new EventHandler(this.RedirectInterceptor));
        }

        private void RedirectInterceptor(object sender, EventArgs e)
        {
            HttpApplication application = sender as HttpApplication;
            HttpContext context = application.Context;

            if (context.Response.IsRequestBeingRedirected)
            {
                string redirectedLocation = context.Response.Headers[AppConstants.RESPONSE_LOCATION_HEADER];
                context.Response.Headers[AppConstants.RESPONSE_LOCATION_HEADER] = redirectedLocation.toLowerInvariant();
            }

        }
        public void Dispose(){}
    }
    public static class AppConstants
    {
        public const string RESPONSE_LOCATION_HEADER = "Location";
    }
}

web.config entry for above module

<system.webServer>
  <modules>
      <add name="RedirectorInterceptorModule" type="CustomizeIISPipeline.RedirectorInterceptorModule"/>
     </modules>
</system.webServer>

Points of Interest

Though above is a remedy for the situation I and mine team is confronting with because of not well planned coding stratedgy. However, a better solution could be that we always have a Wrapper class whenever utliziing underlying framework specially for URL related functionality and any 3rd Party consumption in our applications.

So rule of thumb,

"Having wrapper will avoid regret in future for changes to make"