404 Http module for umbraco.

umbraco404httpmodule.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Web;
using umbraco.BusinessLogic;
using umbraco.NodeFactory;

namespace Web.Modules
{
    public class Lang404Module : IHttpModule
    {
        private const string DefaultLang = "gb";
        private const string ErrorNodeType = "Error404";
        //Assumes the url contains language code ie. '/en/non-existing-pages/' 
        private static readonly Regex ReturnUrlRegex = new Regex(@"/(?<country>[a-zA-Z]{2})/");

        public void Init(HttpApplication application)
        {
            application.EndRequest += ApplicationEndRequest;
        }

        // Note: remember web.config: <httpErrors existingResponse="PassThrough" /> in system.webServer
        // Note: remember web.config: <add type="Modules.Lang404ErrorModule" name="Lang404ErrorModule" /> system.webServer.modules
        static void ApplicationEndRequest(object sender, EventArgs e)
        {
            Node currentNode = null;

            // check if we have a 404 response in progress
            var ctx = HttpContext.Current;

            // if path has extension... forget it.
            var path = ctx.Request.Url.LocalPath;
            if (path.Length - path.LastIndexOf('.') < 5) return;

            // to avoid calling the Node.GetCurrent for all image, css and js requests we check the mimetype
            if (ctx.Response.ContentType == "text/html")
                try
                {
                    currentNode = Node.GetCurrent();
                    if (currentNode.template == 0 && !ctx.Request.RawUrl.StartsWith("/umbraco/editContent.aspx", StringComparison.InvariantCultureIgnoreCase))
                        ctx.Response.StatusCode = 404;
                }
                catch { }

            // if we're not in a 404 state, return
            if (ctx.Response.StatusCode != 404) return;

            // if we're already on a 404 Node, return
            if (currentNode != null && currentNode.NodeTypeAlias == ErrorNodeType) return;

            // determine language
            var targetLang = DefaultLang; // default language

            var orgTargetUrl = ctx.Request.RawUrl;

            // if any language-matches in the original url, set this as the target language
            var match = ReturnUrlRegex.Match(orgTargetUrl);
            if (match.Success)
                targetLang = match.Groups["country"].Value.ToLower();
                       
            // if everything runs smooth, transfer the the response of the 404 page, as the current (remember to response with statuscode: 404)
            ctx.Server.TransferRequest("/404/");
        }

        public void Dispose()
        {
        }
    }
}