BVNetwork.NotFound.Core.Custom404Handler.FileNotFoundHandler C# (CSharp) Method

        public static void FileNotFoundHandler(object sender, EventArgs evt)
        {
            // Check if this should be enabled
            if (Configuration.Configuration.FileNotFoundHandlerMode == FileNotFoundMode.Off)
                return;

            HttpContext context = GetContext();
            if (context == null)
                return;

            if (context.Response.StatusCode != 404)
                return;

            // If we're only doing this for remote users, we need to test for local host
            if (Configuration.Configuration.FileNotFoundHandlerMode == FileNotFoundMode.RemoteOnly)
            {
                // Determine if we're on localhost
                bool localHost = IsLocalhost();
                if (localHost)
                {
                    Logger.Debug("Determined to be localhost, returning");
                    return;
                }
                Logger.Debug("Not localhost, handling error");
            }

            Logger.Debug("FileNotFoundHandler called");

            Uri notFoundUri = context.Request.Url;

            // Skip resource files
            if (IsResourceFile(notFoundUri))
                return;

            string query = context.Request.ServerVariables["QUERY_STRING"];

            // avoid duplicate log entries
            if ((query != null) && query.StartsWith("404;"))
            {
                return;
            }

            CustomRedirect newUrl;
            var canHandleRedirect = HandleRequest(GetReferer(context.Request.UrlReferrer), notFoundUri, out newUrl);
            if (canHandleRedirect && newUrl.State == (int)DataStoreHandler.State.Saved)
            {
                context.Response.Clear();
                context.Response.TrySkipIisCustomErrors = true;
                context.Server.ClearError();
                context.Response.RedirectPermanent(newUrl.NewUrl);
                context.Response.End();
            }
            else if (canHandleRedirect && newUrl.State == (int)DataStoreHandler.State.Deleted)
            {
                SetStatusCodeAndShow404(context, 410);
            }
            else
            {
                SetStatusCodeAndShow404(context, 404);
            }
        }