Sitecore CMS - PageNotFound 404 handling using a Sitecore Item as ErrorPage

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using Sitecore;
using Sitecore.Configuration;
using Sitecore.Diagnostics;
using Sitecore.Layouts;
using Sitecore.Pipelines.HttpRequest;
using Sitecore.Sites;
using Sitecore.Web;

namespace SitecoreExtensions.Pipelines.HttpRequest
{
    /// <summary>
    /// Instead of overridding the last pipeline element and returning a html error page 
    /// We override just after the ItemResolver and return the error page if the item is empty, allowing the layoutResolver to run on the error Item.
    /// The error handling is copied from the Sitecore.Pipelines.HttpRequest.ExecuteRequest 
    /// </summary>
    /// <remarks>
    ///  Installation: 
    ///     Add to HttpRequestBegin after Sitecore.Pipelines.HttpRequest.ItemResolver and before Sitecore.Pipelines.HttpRequest.LayoutResolver 
    ///     and add httpErrors existingResponse="PassThrough" to system.webServer for allowing the 404 header to be returned by the page
    /// </remarks>
    /// <example>
    ///  Rendering to be added to the 404 page for returning correct status code 
    /// 
    ///  public partial class PageNotFoundResponseHeader : System.Web.UI.UserControl
    ///  {
    ///    protected void Page_Load(object sender, EventArgs e)
    ///    {
    ///        Log.Error("Request 404 Page not found - " + Sitecore.Context.RawUrl, typeof(PageNotFoundResponseHeader));
    ///        Response.TrySkipIisCustomErrors = true;
    ///        Response.StatusCode = 404;
    ///        Response.StatusDescription = "Page not found";
    ///    }
    ///  }
    /// </example>
    public class ItemNotFoundResolver : Sitecore.Pipelines.HttpRequest.HttpRequestProcessor
    {
        /// <summary>
        /// Pipeline processor implementation.
        /// </summary>
        /// <param name="args">Pipeline processor arguments.</param>
        public override void Process(Sitecore.Pipelines.HttpRequest.HttpRequestArgs args)
        {
            Assert.ArgumentNotNull(args, "args");

            if (Sitecore.Context.Item != null)
            {
                // Fall through to default handler
                return;
            }

            SiteContext site = Context.Site;
            if (((site != null) && !SiteManager.CanEnter(site.Name, Context.User)))
            {
                // Fall through to default handler
                return;
            }

            PageContext page = Context.Page;
            Assert.IsNotNull(page, "No page context in processor.");
            string filePath = page.FilePath;
            if (filePath.Length > 0)
            {
                if (WebUtil.IsExternalUrl(filePath))
                {
                    args.Context.Response.Redirect(filePath, true);
                }
                else
                {
                    args.Context.RewritePath(filePath, args.Context.Request.PathInfo, args.Url.QueryString, false);
                }
            }
            else if (Context.Item == null)
            {
                this.HandleItemNotFound(args);
            }
        }

        private void HandleItemNotFound(HttpRequestArgs args)
        {
            string localPath = args.LocalPath;
            string name = Context.User.Name;
            bool flag = false;
            string itemNotFoundUrl = Settings.ItemNotFoundUrl;
            if (args.PermissionDenied)
            {
                flag = true;
                // Fall through to default handler
                return;
                ////itemNotFoundUrl = this.GetNoAccessUrl(out loginPage);
            }
            SiteContext site = Context.Site;
            string str4 = (site != null) ? site.Name : string.Empty;
            List<string> list = new List<string>(new string[] { "item", localPath, "user", name, "site", str4 });
            if (Settings.Authentication.SaveRawUrl)
            {
                list.AddRange(new string[] { "url", HttpUtility.UrlEncode(Context.RawUrl) });
            }
            itemNotFoundUrl = WebUtil.AddQueryString(itemNotFoundUrl, list.ToArray());
            if (!flag)
            {

                if (Context.Database == null)
                {
                    // Fall through to default handler
                    return;
                }

                // Find context site root
                var root = args.GetItem(Context.Site.StartPath);
                if (root == null)
                {
                    // Fall through to default handler
                    return;
                }

                // Find context site pagenotfound pages // Must be located straight under the root 
                IEnumerable<PageNotFoundPageItem> pageNotFoundItems = root.GetChildren<PageNotFoundPageItem>();
                foreach (PageNotFoundPageItem item in pageNotFoundItems)
	            {
		             if ((item != null) && (item.InnerItem.Versions.Count > 0))
                     {
                         Context.Item = item;
                         break;
                     }
	            }
            }
        }
    }
}