SEBWIN-395: Fixed issue with request filter blocking load error page.

SafeExamBrowser.Browser/BrowserApplicationInstance.cs

@@ -9,6 +9,7 @@
 using System;
 using System.Net.Http;
 using System.Threading.Tasks;
+using CefSharp;
 using SafeExamBrowser.Applications.Contracts;
 using SafeExamBrowser.Applications.Contracts.Events;
 using SafeExamBrowser.Applications.Contracts.Resources.Icons;
@@ -17,7 +18,6 @@ using SafeExamBrowser.Browser.Contracts.Filters;
 using SafeExamBrowser.Browser.Events;
 using SafeExamBrowser.Browser.Filters;
 using SafeExamBrowser.Browser.Handlers;
-using SafeExamBrowser.Browser.Pages;
 using SafeExamBrowser.Configuration.Contracts;
 using SafeExamBrowser.I18n.Contracts;
 using SafeExamBrowser.Logging.Contracts;
@@ -28,6 +28,9 @@ using SafeExamBrowser.UserInterface.Contracts.Browser;
 using SafeExamBrowser.UserInterface.Contracts.Browser.Data;
 using SafeExamBrowser.UserInterface.Contracts.FileSystemDialog;
 using SafeExamBrowser.UserInterface.Contracts.MessageBox;
+using BrowserSettings = SafeExamBrowser.Settings.Browser.BrowserSettings;
+using Request = SafeExamBrowser.Browser.Contracts.Filters.Request;
+using TitleChangedEventHandler = SafeExamBrowser.Applications.Contracts.Events.TitleChangedEventHandler;
 
 namespace SafeExamBrowser.Browser
 {
@@ -112,12 +115,10 @@ namespace SafeExamBrowser.Browser
 		private void InitializeControl()
 		{
 			var contextMenuHandler = new ContextMenuHandler();
-			var controlLogger = logger.CloneFor($"{nameof(BrowserControl)} #{Id}");
 			var dialogHandler = new DialogHandler();
 			var displayHandler = new DisplayHandler();
 			var downloadLogger = logger.CloneFor($"{nameof(DownloadHandler)} #{Id}");
 			var downloadHandler = new DownloadHandler(appConfig, settings, downloadLogger);
-			var htmlLoader = new HtmlLoader(text);
 			var keyboardHandler = new KeyboardHandler();
 			var lifeSpanHandler = new LifeSpanHandler();
 			var requestFilter = new RequestFilter();
@@ -146,13 +147,12 @@ namespace SafeExamBrowser.Browser
 				dialogHandler,
 				displayHandler,
 				downloadHandler,
-				htmlLoader,
 				keyboardHandler,
 				lifeSpanHandler,
-				controlLogger,
 				requestHandler,
 				startUrl);
 			control.AddressChanged += Control_AddressChanged;
+			control.LoadFailed += Control_LoadFailed;
 			control.LoadingStateChanged += Control_LoadingStateChanged;
 			control.TitleChanged += Control_TitleChanged;
 
@@ -214,6 +214,30 @@ namespace SafeExamBrowser.Browser
 			window.UpdateAddress(address);
 		}
 
+		/// <summary>
+		/// TODO: LoadError.html is not used, as navigating back from it doesn't work! Remove page if no better solution can be found.
+		/// </summary>
+		private void Control_LoadFailed(int errorCode, string errorText, string url)
+		{
+			if (errorCode == (int) CefErrorCode.None)
+			{
+				logger.Info($"Request for '{url}' was successful.");
+			}
+			else if (errorCode == (int) CefErrorCode.Aborted)
+			{
+				logger.Info($"Request for '{url}' was aborted.");
+			}
+			else
+			{
+				var title = text.Get(TextKey.Browser_LoadErrorPageTitle);
+				var message = text.Get(TextKey.Browser_LoadErrorPageMessage).Replace("%%URL%%", url) + $" {errorText} ({errorCode})";
+
+				logger.Warn($"Request for '{url}' failed: {errorText} ({errorCode}).");
+
+				Task.Run(() => messageBox.Show(message, title, icon: MessageBoxIcon.Error, parent: window)).ContinueWith(_ => control.NavigateBackwards());
+			}
+		}
+
 		private void Control_LoadingStateChanged(bool isLoading)
 		{
 			window.CanNavigateBackwards = WindowSettings.AllowBackwardNavigation && control.CanNavigateBackwards;

SafeExamBrowser.Browser/BrowserControl.cs

@@ -8,8 +8,6 @@
 
 using CefSharp;
 using CefSharp.WinForms;
-using SafeExamBrowser.Browser.Pages;
-using SafeExamBrowser.Logging.Contracts;
 using SafeExamBrowser.UserInterface.Contracts.Browser;
 using SafeExamBrowser.UserInterface.Contracts.Browser.Events;
 
@@ -21,14 +19,12 @@ namespace SafeExamBrowser.Browser
 		private IDialogHandler dialogHandler;
 		private IDisplayHandler displayHandler;
 		private IDownloadHandler downloadHandler;
-		private string errorPage;
-		private HtmlLoader htmlLoader;
 		private IKeyboardHandler keyboardHandler;
 		private ILifeSpanHandler lifeSpanHandler;
-		private ILogger logger;
 		private IRequestHandler requestHandler;
 
 		private AddressChangedEventHandler addressChanged;
+		private LoadFailedEventHandler loadFailed;
 		private LoadingStateChangedEventHandler loadingStateChanged;
 		private TitleChangedEventHandler titleChanged;
 
@@ -41,6 +37,12 @@ namespace SafeExamBrowser.Browser
 			remove { addressChanged -= value; }
 		}
 
+		event LoadFailedEventHandler IBrowserControl.LoadFailed
+		{
+			add { loadFailed += value; }
+			remove { loadFailed -= value; }
+		}
+
 		event LoadingStateChangedEventHandler IBrowserControl.LoadingStateChanged
 		{
 			add { loadingStateChanged += value; }
@@ -58,10 +60,8 @@ namespace SafeExamBrowser.Browser
 			IDialogHandler dialogHandler,
 			IDisplayHandler displayHandler,
 			IDownloadHandler downloadHandler,
-			HtmlLoader htmlLoader,
 			IKeyboardHandler keyboardHandler,
 			ILifeSpanHandler lifeSpanHandler,
-			ILogger logger,
 			IRequestHandler requestHandler,
 			string url) : base(url)
 		{
@@ -69,10 +69,8 @@ namespace SafeExamBrowser.Browser
 			this.dialogHandler = dialogHandler;
 			this.displayHandler = displayHandler;
 			this.downloadHandler = downloadHandler;
-			this.htmlLoader = htmlLoader;
 			this.keyboardHandler = keyboardHandler;
 			this.lifeSpanHandler = lifeSpanHandler;
-			this.logger = logger;
 			this.requestHandler = requestHandler;
 		}
 
@@ -90,8 +88,6 @@ namespace SafeExamBrowser.Browser
 			LifeSpanHandler = lifeSpanHandler;
 			MenuHandler = contextMenuHandler;
 			RequestHandler = requestHandler;
-
-			errorPage = htmlLoader.LoadErrorPage();
 		}
 
 		public void NavigateBackwards()
@@ -126,25 +122,7 @@ namespace SafeExamBrowser.Browser
 
 		private void BrowserControl_LoadError(object sender, LoadErrorEventArgs e)
 		{
-			if (e.ErrorCode == CefErrorCode.None)
+			loadFailed?.Invoke((int) e.ErrorCode, e.ErrorText, e.FailedUrl);
-			{
-				logger.Info($"Request for '{e.FailedUrl}' was successful.");
-			}
-			else if (e.ErrorCode == CefErrorCode.Aborted)
-			{
-				logger.Info($"Request for '{e.FailedUrl}' was aborted.");
-			}
-			else
-			{
-				var html = string.Copy(errorPage);
-
-				logger.Warn($"Request for '{e.FailedUrl}' failed: {e.ErrorText} ({e.ErrorCode}).");
-
-				html = html.Replace("%%STATUS%%", $"{e.ErrorText} ({e.ErrorCode})");
-				html = html.Replace("%%URL%%", e.FailedUrl);
-
-				e.Frame.LoadHtml(html, true);
-			}
 		}
 	}
 }

SafeExamBrowser.UserInterface.Contracts/Browser/Events/LoadFailedEventHandler.cs

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2020 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+namespace SafeExamBrowser.UserInterface.Contracts.Browser.Events
+{
+	/// <summary>
+	/// Indicates a load error for a browser request.
+	/// </summary>
+	public delegate void LoadFailedEventHandler(int errorCode, string errorText, string url);
+}

SafeExamBrowser.UserInterface.Contracts/Browser/IBrowserControl.cs

@@ -36,6 +36,11 @@ namespace SafeExamBrowser.UserInterface.Contracts.Browser
 		/// </summary>
 		event AddressChangedEventHandler AddressChanged;
 
+		/// <summary>
+		/// Event fired when a load error occurs.
+		/// </summary>
+		event LoadFailedEventHandler LoadFailed;
+
 		/// <summary>
 		/// Event fired when the loading state of the browser control changes.
 		/// </summary>

SafeExamBrowser.UserInterface.Contracts/SafeExamBrowser.UserInterface.Contracts.csproj

@@ -56,6 +56,7 @@
   <ItemGroup>
     <Compile Include="Browser\Data\DownloadItemState.cs" />
     <Compile Include="Browser\Events\AddressChangedEventHandler.cs" />
+    <Compile Include="Browser\Events\LoadFailedEventHandler.cs" />
     <Compile Include="Browser\Events\LoadingStateChangedEventHandler.cs" />
     <Compile Include="Browser\Events\TitleChangedEventHandler.cs" />
     <Compile Include="Browser\IBrowserControl.cs" />