SEBWIN-219: Extended IPC mechanics with ping mechanism.

SafeExamBrowser.Client/Behaviour/ClientController.cs

@@ -12,6 +12,7 @@ using SafeExamBrowser.Contracts.Behaviour.Operations;
 using SafeExamBrowser.Contracts.Communication;
 using SafeExamBrowser.Contracts.Configuration;
 using SafeExamBrowser.Contracts.Configuration.Settings;
+using SafeExamBrowser.Contracts.I18n;
 using SafeExamBrowser.Contracts.Logging;
 using SafeExamBrowser.Contracts.Monitoring;
 using SafeExamBrowser.Contracts.UserInterface;
@@ -81,13 +82,21 @@ namespace SafeExamBrowser.Client.Behaviour
 
 			var success = operations.TryPerform();
 
-			// TODO
-
 			if (success)
 			{
 				RegisterEvents();
-				// TODO: Handle communication exception!
+
-				runtime.InformClientReady();
+				try
+				{
+					runtime.InformClientReady();
+				}
+				catch (Exception e)
+				{
+					logger.Error("Failed to inform runtime that client is ready!", e);
+
+					return false;
+				}
+
 				splashScreen.Hide();
 
 				logger.Info("--- Application successfully initialized ---");
@@ -110,9 +119,8 @@ namespace SafeExamBrowser.Client.Behaviour
 			splashScreen.Show();
 			splashScreen.BringToForeground();
 
-			// TODO
-
 			DeregisterEvents();
+
 			var success = operations.TryRevert();
 
 			if (success)
@@ -134,6 +142,7 @@ namespace SafeExamBrowser.Client.Behaviour
 			ClientHost.Shutdown += ClientHost_Shutdown;
 			displayMonitor.DisplayChanged += DisplayMonitor_DisplaySettingsChanged;
 			processMonitor.ExplorerStarted += ProcessMonitor_ExplorerStarted;
+			runtime.ConnectionLost += Runtime_ConnectionLost;
 			taskbar.QuitButtonClicked += Taskbar_QuitButtonClicked;
 			windowMonitor.WindowChanged += WindowMonitor_WindowChanged;
 		}
@@ -143,6 +152,7 @@ namespace SafeExamBrowser.Client.Behaviour
 			ClientHost.Shutdown -= ClientHost_Shutdown;
 			displayMonitor.DisplayChanged -= DisplayMonitor_DisplaySettingsChanged;
 			processMonitor.ExplorerStarted -= ProcessMonitor_ExplorerStarted;
+			runtime.ConnectionLost -= Runtime_ConnectionLost;
 			taskbar.QuitButtonClicked -= Taskbar_QuitButtonClicked;
 			windowMonitor.WindowChanged -= WindowMonitor_WindowChanged;
 		}
@@ -173,11 +183,31 @@ namespace SafeExamBrowser.Client.Behaviour
 			shutdown.Invoke();
 		}
 
+		private void Runtime_ConnectionLost()
+		{
+			logger.Error("Lost connection to the runtime!");
+			uiFactory.Show(TextKey.MessageBox_ApplicationError, TextKey.MessageBox_ApplicationErrorTitle, icon: MessageBoxIcon.Error);
+
+			taskbar.Close();
+			shutdown.Invoke();
+		}
+
 		private void Taskbar_QuitButtonClicked()
 		{
-			// TODO: MessageBox asking whether user really wants to quit -> only then request shutdown!
+			var result = uiFactory.Show(TextKey.MessageBox_Quit, TextKey.MessageBox_QuitTitle, MessageBoxAction.YesNo, MessageBoxIcon.Question);
-			// TODO: Handle communication exception!
+
-			runtime.RequestShutdown();
+			if (result == MessageBoxResult.Yes)
+			{
+				try
+				{
+					runtime.RequestShutdown();
+				}
+				catch (Exception e)
+				{
+					logger.Error("Failed to communicate shutdown request to the runtime!", e);
+					uiFactory.Show(TextKey.MessageBox_QuitError, TextKey.MessageBox_QuitErrorTitle, icon: MessageBoxIcon.Error);
+				}
+			}
 		}
 
 		private void WindowMonitor_WindowChanged(IntPtr window)

SafeExamBrowser.Client/Communication/ClientHost.cs

@@ -17,6 +17,7 @@ namespace SafeExamBrowser.Client.Communication
 {
 	internal class ClientHost : BaseHost, IClientHost
 	{
+		private bool allowConnection = true;
 		private int processId;
 
 		public Guid StartupToken { private get; set; }
@@ -30,18 +31,24 @@ namespace SafeExamBrowser.Client.Communication
 
 		protected override bool OnConnect(Guid? token)
 		{
-			return StartupToken == token;
+			var authenticated = StartupToken == token;
+			var accepted = allowConnection && authenticated;
+
+			if (accepted)
+			{
+				allowConnection = false;
+			}
+
+			return accepted;
 		}
 
 		protected override void OnDisconnect()
 		{
-			// TODO
+			// Nothing to do here...
 		}
 
 		protected override Response OnReceive(Message message)
 		{
-			// TODO
-
 			return new SimpleResponse(SimpleResponsePurport.UnknownMessage);
 		}
 

SafeExamBrowser.Contracts/Communication/ICommunicationProxy.cs

@@ -13,7 +13,13 @@ namespace SafeExamBrowser.Contracts.Communication
 	public interface ICommunicationProxy
 	{
 		/// <summary>
-		/// Tries to establish a connection. Returns <c>true</c> if the connection has been accepted, otherwise <c>false</c>.
+		/// Fired when the connection to the proxy was lost, e.g. if a ping request failed or a communication fault occurred.
+		/// </summary>
+		event CommunicationEventHandler ConnectionLost;
+
+		/// <summary>
+		/// Tries to establish a connection. Returns <c>true</c> if the connection has been accepted, otherwise <c>false</c>. If a
+		/// connection was successfully established, a ping mechanism will be activated to periodically check the connection status.
 		/// </summary>
 		/// <exception cref="System.ServiceModel.*">If the communication failed.</exception>
 		bool Connect(Guid? token = null);

SafeExamBrowser.Contracts/Communication/Messages/Message.cs

@@ -11,7 +11,7 @@ using System;
 namespace SafeExamBrowser.Contracts.Communication.Messages
 {
 	[Serializable]
-	public class Message
+	public abstract class Message
 	{
 		/// <summary>
 		/// The communication token needed for authentication.

SafeExamBrowser.Contracts/Communication/Messages/SimpleMessagePurport.cs

@@ -28,6 +28,11 @@ namespace SafeExamBrowser.Contracts.Communication.Messages
 		/// </summary>
 		ConfigurationNeeded,
 
+		/// <summary>
+		/// Requests an interlocutor to signal that the connection status is okay.
+		/// </summary>
+		Ping,
+
 		/// <summary>
 		/// Sent from the client to the runtime to request shutting down the application.
 		/// </summary>

SafeExamBrowser.Contracts/Communication/Responses/Response.cs

@@ -11,7 +11,7 @@ using System;
 namespace SafeExamBrowser.Contracts.Communication.Responses
 {
 	[Serializable]
-	public class Response
+	public abstract class Response
 	{
 		public override string ToString()
 		{

SafeExamBrowser.Contracts/I18n/TextKey.cs

@@ -15,10 +15,18 @@ namespace SafeExamBrowser.Contracts.I18n
 	{
 		Browser_ShowDeveloperConsole,
 		LogWindow_Title,
+		MessageBox_ApplicationError,
+		MessageBox_ApplicationErrorTitle,
 		MessageBox_ConfigureClientSuccess,
 		MessageBox_ConfigureClientSuccessTitle,
+		MessageBox_Quit,
+		MessageBox_QuitTitle,
+		MessageBox_QuitError,
+		MessageBox_QuitErrorTitle,
 		MessageBox_SessionStartError,
 		MessageBox_SessionStartErrorTitle,
+		MessageBox_SessionStopError,
+		MessageBox_SessionStopErrorTitle,
 		MessageBox_ShutdownError,
 		MessageBox_ShutdownErrorTitle,
 		MessageBox_SingleInstance,

SafeExamBrowser.Core/Communication/BaseHost.cs

@@ -101,13 +101,17 @@ namespace SafeExamBrowser.Core.Communication
 
 				if (IsAuthorized(message?.CommunicationToken))
 				{
-					if (message is SimpleMessage simpleMessage)
+					switch (message)
 					{
-						response = OnReceive(simpleMessage.Purport);
+						case SimpleMessage simpleMessage when simpleMessage.Purport == SimpleMessagePurport.Ping:
-					}
+							response = new SimpleResponse(SimpleResponsePurport.Acknowledged);
-					else
+							break;
-					{
+						case SimpleMessage simpleMessage:
-						response = OnReceive(message);
+							response = OnReceive(simpleMessage.Purport);
+							break;
+						default:
+							response = OnReceive(message);
+							break;
 					}
 				}
 
@@ -218,7 +222,7 @@ namespace SafeExamBrowser.Core.Communication
 
 		private void Host_Faulted(object sender, EventArgs e)
 		{
-			logger.Debug("Communication host has faulted!");
+			logger.Error("Communication host has faulted!");
 		}
 
 		private void Host_Opened(object sender, EventArgs e)
@@ -233,7 +237,7 @@ namespace SafeExamBrowser.Core.Communication
 
 		private void Host_UnknownMessageReceived(object sender, UnknownMessageReceivedEventArgs e)
 		{
-			logger.Debug($"Communication host has received an unknown message: {e?.Message}.");
+			logger.Warn($"Communication host has received an unknown message: {e?.Message}.");
 		}
 
 		private string ToString(Message message)

SafeExamBrowser.Core/Communication/BaseProxy.cs

@@ -8,6 +8,7 @@
 
 using System;
 using System.ServiceModel;
+using System.Timers;
 using SafeExamBrowser.Contracts.Communication;
 using SafeExamBrowser.Contracts.Communication.Messages;
 using SafeExamBrowser.Contracts.Communication.Responses;
@@ -17,12 +18,18 @@ namespace SafeExamBrowser.Core.Communication
 {
 	public abstract class BaseProxy : ICommunicationProxy
 	{
+		private const int ONE_MINUTE = 60000;
+		private static readonly object @lock = new object();
+
 		private string address;
 		private ICommunication channel;
 		private Guid? communicationToken;
+		private Timer timer;
 
 		protected ILogger Logger { get; private set; }
 
+		public event CommunicationEventHandler ConnectionLost;
+
 		public BaseProxy(string address, ILogger logger)
 		{
 			this.address = address;
@@ -47,12 +54,18 @@ namespace SafeExamBrowser.Core.Communication
 			communicationToken = response.CommunicationToken;
 			Logger.Debug($"Connection was {(response.ConnectionEstablished ? "established" : "refused")}.");
 
+			if (response.ConnectionEstablished)
+			{
+				StartAutoPing();
+			}
+
 			return response.ConnectionEstablished;
 		}
 
 		public virtual bool Disconnect()
 		{
 			FailIfNotConnected(nameof(Disconnect));
+			StopAutoPing();
 
 			var message = new DisconnectionMessage { CommunicationToken = communicationToken.Value };
 			var response = channel.Disconnect(message);
@@ -80,6 +93,11 @@ namespace SafeExamBrowser.Core.Communication
 			return Send(new SimpleMessage(purport));
 		}
 
+		protected bool IsAcknowledged(Response response)
+		{
+			return response is SimpleResponse simpleResponse && simpleResponse.Purport == SimpleResponsePurport.Acknowledged;
+		}
+
 		protected string ToString(Message message)
 		{
 			return message != null ? message.ToString() : "<null>";
@@ -102,7 +120,8 @@ namespace SafeExamBrowser.Core.Communication
 
 		private void BaseProxy_Faulted(object sender, EventArgs e)
 		{
-			Logger.Debug("Communication channel has faulted!");
+			Logger.Error("Communication channel has faulted!");
+			ConnectionLost?.Invoke();
 		}
 
 		private void BaseProxy_Opened(object sender, EventArgs e)
@@ -132,5 +151,54 @@ namespace SafeExamBrowser.Core.Communication
 		{
 			return channel == null ? "null" : $"in state '{(channel as ICommunicationObject).State}'";
 		}
+
+		private void StartAutoPing()
+		{
+			lock (@lock)
+			{
+				timer = new Timer(ONE_MINUTE) { AutoReset = true };
+				timer.Elapsed += Timer_Elapsed;
+				timer.Start();
+			}
+		}
+
+		private void StopAutoPing()
+		{
+			lock (@lock)
+			{
+				timer?.Stop();
+			}
+		}
+
+		private void Timer_Elapsed(object sender, ElapsedEventArgs args)
+		{
+			lock (@lock)
+			{
+				if (timer.Enabled)
+				{
+					try
+					{
+						var response = Send(SimpleMessagePurport.Ping);
+
+						if (IsAcknowledged(response))
+						{
+							Logger.Info("Pinged proxy, connection is alive.");
+						}
+						else
+						{
+							Logger.Error($"Proxy did not acknowledge ping message! Received: {ToString(response)}.");
+							timer.Stop();
+							ConnectionLost?.Invoke();
+						}
+					}
+					catch (Exception e)
+					{
+						Logger.Error("Failed to ping proxy!", e);
+						timer.Stop();
+						ConnectionLost?.Invoke();
+					}
+				}
+			}
+		}
 	}
 }

SafeExamBrowser.Core/Communication/ClientProxy.cs

@@ -6,6 +6,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+using System.ServiceModel;
 using SafeExamBrowser.Contracts.Communication;
 using SafeExamBrowser.Contracts.Communication.Messages;
 using SafeExamBrowser.Contracts.Communication.Responses;
@@ -23,9 +24,9 @@ namespace SafeExamBrowser.Core.Communication
 		{
 			var response = Send(SimpleMessagePurport.Shutdown);
 
-			if (response is SimpleResponse simpleMessage && simpleMessage.Purport == SimpleResponsePurport.Acknowledged)
+			if (!IsAcknowledged(response))
 			{
-				// TODO
+				throw new CommunicationException($"Runtime did not acknowledge shutdown request! Received: {ToString(response)}.");
 			}
 		}
 
@@ -33,7 +34,12 @@ namespace SafeExamBrowser.Core.Communication
 		{
 			var response = Send(SimpleMessagePurport.Authenticate);
 
-			return response as AuthenticationResponse;
+			if (response is AuthenticationResponse authenticationResponse)
+			{
+				return authenticationResponse;
+			}
+
+			throw new CommunicationException($"Did not receive authentication response! Received: {ToString(response)}.");
 		}
 	}
 }

SafeExamBrowser.Core/Communication/RuntimeProxy.cs

@@ -52,10 +52,5 @@ namespace SafeExamBrowser.Core.Communication
 				throw new CommunicationException($"Runtime did not acknowledge shutdown request! Response: {ToString(response)}.");
 			}
 		}
-
-		private bool IsAcknowledged(Response response)
-		{
-			return response is SimpleResponse simpleResponse && simpleResponse.Purport == SimpleResponsePurport.Acknowledged;
-		}
 	}
 }

SafeExamBrowser.Core/I18n/Text.xml

@@ -6,18 +6,42 @@
   <Entry key="LogWindow_Title">
     Application Log
   </Entry>
+  <Entry key="MessageBox_ApplicationError">
+    An unrecoverable error has occurred! Please consult the application log for more information. The application will now shut down...
+  </Entry>
+  <Entry key="MessageBox_ApplicationErrorTitle">
+    Application Error
+  </Entry>
   <Entry key="MessageBox_ConfigureClientSuccess">
     The client configuration has been saved and will be used when you start the application the next time. Do you want to quit for now?
   </Entry>
   <Entry key="MessageBox_ConfigureClientSuccessTitle">
     Configuration Successful
   </Entry>
+  <Entry key="MessageBox_Quit">
+    Would you really like to quit the application?
+  </Entry>
+  <Entry key="MessageBox_QuitTitle">
+    Quit?
+  </Entry>
+  <Entry key="MessageBox_QuitError">
+    The client failed to communicate the shutdown request to the runtime! Please try again...
+  </Entry>
+  <Entry key="MessageBox_QuitErrorTitle">
+    Quit Error
+  </Entry>
   <Entry key="MessageBox_SessionStartError">
     The application failed to start a new session. Please consult the application log for more information...
   </Entry>
   <Entry key="MessageBox_SessionStartErrorTitle">
     Session Start Error
   </Entry>
+  <Entry key="MessageBox_SessionStopError">
+    The application failed to properly stop the running session. Please consult the application log for more information...
+  </Entry>
+  <Entry key="MessageBox_SessionStopErrorTitle">
+    Session Stop Error
+  </Entry>
   <Entry key="MessageBox_ShutdownError">
     An unexpected error occurred during the shutdown procedure! Please consult the application log for more information...
   </Entry>

SafeExamBrowser.Runtime/Behaviour/Operations/SessionSequenceOperation.cs

@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-using System;
 using System.Threading;
 using SafeExamBrowser.Contracts.Behaviour.Operations;
 using SafeExamBrowser.Contracts.Communication;
@@ -65,14 +64,7 @@ namespace SafeExamBrowser.Runtime.Behaviour.Operations
 			logger.Info("Initializing service session...");
 			service.StartSession(session.Id, configuration.CurrentSettings);
 
-			try
+			sessionRunning = TryStartClient();
-			{
-				sessionRunning = TryStartClient();
-			}
-			catch (Exception e)
-			{
-				logger.Error("Failed to start client!", e);
-			}
 
 			if (sessionRunning)
 			{
@@ -96,14 +88,10 @@ namespace SafeExamBrowser.Runtime.Behaviour.Operations
 				logger.Info("Stopping service session...");
 				service.StopSession(session.Id);
 
-				try
+				if (!session.ClientProcess.HasTerminated)
 				{
 					StopClient();
 				}
-				catch (Exception e)
-				{
-					logger.Error("Failed to terminate client!", e);
-				}
 
 				sessionRunning = false;
 				logger.Info($"Successfully stopped session with identifier '{session.Id}'.");
@@ -204,7 +192,7 @@ namespace SafeExamBrowser.Runtime.Behaviour.Operations
 			}
 			else
 			{
-				logger.Warn("Attempting to kill client process since graceful shutdown failed!");
+				logger.Warn("Attempting to kill client process since graceful termination failed!");
 				KillClient();
 			}
 		}

SafeExamBrowser.Runtime/Behaviour/RuntimeController.cs

@@ -75,12 +75,12 @@ namespace SafeExamBrowser.Runtime.Behaviour
 
 			if (initialized)
 			{
+				RegisterEvents();
+
 				logger.Info("--- Application successfully initialized ---");
 				logger.Log(string.Empty);
 				logger.Subscribe(runtimeWindow);
-
 				splashScreen.Hide();
-				runtimeHost.ShutdownRequested += RuntimeHost_ShutdownRequested;
 
 				StartSession(true);
 			}
@@ -88,6 +88,8 @@ namespace SafeExamBrowser.Runtime.Behaviour
 			{
 				logger.Info("--- Application startup aborted! ---");
 				logger.Log(string.Empty);
+
+				uiFactory.Show(TextKey.MessageBox_StartupError, TextKey.MessageBox_StartupErrorTitle, icon: MessageBoxIcon.Error);
 			}
 
 			return initialized && sessionRunning;
@@ -95,8 +97,11 @@ namespace SafeExamBrowser.Runtime.Behaviour
 
 		public void Terminate()
 		{
+			DeregisterEvents();
+
 			if (sessionRunning)
 			{
+				DeregisterSessionEvents();
 				StopSession();
 			}
 
@@ -119,6 +124,8 @@ namespace SafeExamBrowser.Runtime.Behaviour
 			{
 				logger.Info("--- Shutdown procedure failed! ---");
 				logger.Log(string.Empty);
+
+				uiFactory.Show(TextKey.MessageBox_ShutdownError, TextKey.MessageBox_ShutdownErrorTitle, icon: MessageBoxIcon.Error);
 			}
 
 			splashScreen?.Close();
@@ -127,13 +134,20 @@ namespace SafeExamBrowser.Runtime.Behaviour
 		private void StartSession(bool initial = false)
 		{
 			runtimeWindow.Show();
-			logger.Info(">------ Initiating session procedure ------<");
+			logger.Info(">>>--- Initiating session procedure ---<<<");
+
+			if (sessionRunning)
+			{
+				DeregisterSessionEvents();
+			}
 
 			sessionRunning = initial ? sessionSequence.TryPerform() : sessionSequence.TryRepeat();
 
 			if (sessionRunning)
 			{
-				logger.Info(">------ Session is running ------<");
+				RegisterSessionEvents();
+
+				logger.Info(">>>--- Session is running ---<<<");
 				runtimeWindow.HideProgressBar();
 				runtimeWindow.UpdateText(TextKey.RuntimeWindow_ApplicationRunning);
 
@@ -144,7 +158,7 @@ namespace SafeExamBrowser.Runtime.Behaviour
 			}
 			else
 			{
-				logger.Info(">------ Session procedure was aborted! ------<");
+				logger.Info(">>>--- Session procedure was aborted! ---<<<");
 				// TODO: Not when user chose to terminate after reconfiguration! Probably needs IOperationSequenceResult or alike...
 				uiFactory.Show(TextKey.MessageBox_SessionStartError, TextKey.MessageBox_SessionStartErrorTitle, icon: MessageBoxIcon.Error);
 
@@ -160,28 +174,65 @@ namespace SafeExamBrowser.Runtime.Behaviour
 			runtimeWindow.Show();
 			runtimeWindow.BringToForeground();
 			runtimeWindow.ShowProgressBar();
-			logger.Info(">------ Reverting session operations ------<");
+			logger.Info(">>>--- Reverting session operations ---<<<");
 
 			var success = sessionSequence.TryRevert();
 
 			if (success)
 			{
-				logger.Info(">------ Session is terminated ------<");
+				logger.Info(">>>--- Session is terminated ---<<<");
 				sessionRunning = false;
-
-				// TODO
 			}
 			else
 			{
-				logger.Info(">------ Session reversion was erroneous! ------<");
+				logger.Info(">>>--- Session reversion was erroneous! ---<<<");
-
+				uiFactory.Show(TextKey.MessageBox_SessionStopError, TextKey.MessageBox_SessionStopErrorTitle, icon: MessageBoxIcon.Error);
-				// TODO
 			}
 		}
 
+		private void RegisterEvents()
+		{
+			client.ConnectionLost += Client_ConnectionLost;
+			runtimeHost.ShutdownRequested += RuntimeHost_ShutdownRequested;
+		}
+
+		private void RegisterSessionEvents()
+		{
+			configuration.CurrentSession.ClientProcess.Terminated += ClientProcess_Terminated;
+		}
+
+		private void DeregisterEvents()
+		{
+			client.ConnectionLost -= Client_ConnectionLost;
+			runtimeHost.ShutdownRequested -= RuntimeHost_ShutdownRequested;
+		}
+
+		private void DeregisterSessionEvents()
+		{
+			configuration.CurrentSession.ClientProcess.Terminated -= ClientProcess_Terminated;
+		}
+
+		private void ClientProcess_Terminated(int exitCode)
+		{
+			logger.Error($"Client application has unexpectedly terminated with exit code {exitCode}!");
+			// TODO: Check if message box is rendered on new desktop as well -> otherwise shutdown is blocked!
+			uiFactory.Show(TextKey.MessageBox_ApplicationError, TextKey.MessageBox_ApplicationErrorTitle, icon: MessageBoxIcon.Error);
+
+			shutdown.Invoke();
+		}
+
+		private void Client_ConnectionLost()
+		{
+			logger.Error("Lost connection to the client application!");
+			// TODO: Check if message box is rendered on new desktop as well -> otherwise shutdown is blocked!
+			uiFactory.Show(TextKey.MessageBox_ApplicationError, TextKey.MessageBox_ApplicationErrorTitle, icon: MessageBoxIcon.Error);
+
+			shutdown.Invoke();
+		}
+
 		private void RuntimeHost_ShutdownRequested()
 		{
-			logger.Info("Received shutdown request from client application.");
+			logger.Info("Received shutdown request from the client application.");
 			shutdown.Invoke();
 		}
 	}

SafeExamBrowser.Runtime/Communication/RuntimeHost.cs

@@ -18,6 +18,7 @@ namespace SafeExamBrowser.Runtime.Communication
 {
 	internal class RuntimeHost : BaseHost, IRuntimeHost
 	{
+		private bool allowConnection = true;
 		private IConfigurationRepository configuration;
 
 		public Guid StartupToken { private get; set; }
@@ -33,7 +34,15 @@ namespace SafeExamBrowser.Runtime.Communication
 
 		protected override bool OnConnect(Guid? token = null)
 		{
-			return StartupToken == token;
+			var authenticated = StartupToken == token;
+			var accepted = allowConnection && authenticated;
+
+			if (accepted)
+			{
+				allowConnection = false;
+			}
+
+			return accepted;
 		}
 
 		protected override void OnDisconnect()
@@ -43,7 +52,6 @@ namespace SafeExamBrowser.Runtime.Communication
 
 		protected override Response OnReceive(Message message)
 		{
-			// TODO
 			return new SimpleResponse(SimpleResponsePurport.UnknownMessage);
 		}