Domain Forwarding with IHttpHandler

using System;
using System.Web;
using System.Diagnostics;
using System.Configuration;

namespace DomainFilter
{
	/// <summary>
	/// Summary description for HttpHandler.
	/// </summary>
	public class DomainHandler : IHttpHandler
	{
		/// <summary>
		/// Implementing IHttpHandler
		/// </summary>
		/// <param name="context"></param>
		public void ProcessRequest(HttpContext context) 
		{
			// Extract the host name from the request url
			// an look up the redirect url in the Web.config
			String redir = ConfigurationSettings.AppSettings[context.Request.Url.Host];
			if (redir != null)
			{
				// check for valid redirect url, preventing loops
				if (RedirectIsValid(redir, context.Request.Url))
				{
					// redirect the user to the url found in web.config
					context.Response.Redirect(redir, true);
				}
				else
				{
					// display an error.
					context.Response.Write("<h1><font color=red>Error invalid DomainHandler configuration</font></h1><br><b>Please check your Web.config file.</b>");
				}
			}
		}
		// prevents possible redirect loops
		// it is not allowed to have an redirect url targeting its self
		private bool RedirectIsValid(String redir, Uri currentUri)
		{
			String val1 = redir.ToLower();
			String url = currentUri.AbsoluteUri.ToLower();
			String host = currentUri.Host.ToLower();

			if (val1 == url)						{ return false; }			
			if (val1 == ( "http://" + host))		{ return false; }
			if (val1 == ("http://" + host + "/"))	{ return false;	}
			if (val1 == host)						{ return false;	}
			if (val1 == (host + "/"))				{ return false;	}

			return true;
		}
		/// <summary>
		/// Implementing IHttpHandler
		/// </summary>
		public bool IsReusable
		{
			get
			{
				return true;
			}
		}
	}
}