Merge branch 'develop' into b/ui-fixes

Reviewed-on: https://git.kske.dev/zdm/envoy/pulls/114
Reviewed-by: DieGurke <maxi@kske.dev>
Reviewed-by: delvh <leon@kske.dev>

Jenkinsfile

@@ -0,0 +1,37 @@
+pipeline {
+	agent any
+
+	options {
+		ansiColor('xterm')
+	}
+
+	stages {
+		stage('Build') {
+			steps {
+				sh 'mvn -DskipTests clean package'
+			}
+		}
+		stage('Test') {
+			steps {
+				sh 'mvn test'
+			}
+			post {
+				always {
+					junit '*/target/surefire-reports/*.xml'
+				}
+			}
+		}
+		stage('SonarQube Analysis') {
+			steps {
+				withSonarQubeEnv('KSKE SonarQube') {
+					sh 'mvn org.sonarsource.scanner.maven:sonar-maven-plugin:3.9.1.2184:sonar'
+				}
+			}
+		}
+	}
+	post {
+		success {
+			archiveArtifacts artifacts: 'client/target/envoy-client-*-shaded.jar, server/target/envoy-server-jar-with-dependencies.jar'
+		}
+	}
+}

README.md

@@ -17,6 +17,8 @@ If you want to transfer a file to another user, you can attach it to a message.
 
 On the settings page some convenience features can be configured, as well as the color theme.
 
+Additional info on how to use Envoy can be found [here](https://git.kske.dev/zdm/envoy/wiki) in the client section.
+
 ### System requirements
 
 To run Envoy, you have to install a Java Runtime Environment (JRE) of at least version 11.
@@ -29,7 +31,7 @@ Most major Linux distributions like Debian, Arch and Gentoo have a Noto emoji pa
 
 To set up an Envoy server, download the package from the release page.
 
-Because the project lacks external documentation for the moment, please refer to the Javadoc inside the source code to configure your Envoy instance.
+To configure the behavior of Envoy Server, please have a look at the [documentation](https://git.kske.dev/zdm/envoy/wiki), specifically the server part.
 
 ### System requirements
 

client/.classpath

@@ -21,7 +21,6 @@
 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11">
 		<attributes>
 			<attribute name="maven.pomderived" value="true"/>
-			<attribute name="module" value="true"/>
 		</attributes>
 	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">

client/src/main/java/envoy/client/data/Chat.java

@@ -22,20 +22,21 @@ import envoy.client.net.WriteProxy;
  */
 public class Chat implements Serializable {
 
-	protected boolean disabled;
+	protected transient ObservableList<Message> messages = FXCollections.observableArrayList();
+
+	protected final Contact recipient;
+
+	protected boolean	disabled;
+	protected boolean	underlyingContactDeleted;
 
 	/**
 	 * Stores the last time an {@link envoy.event.IsTyping} event has been sent.
 	 */
 	protected transient long lastWritingEvent;
 
-	protected transient ObservableList<Message> messages = FXCollections.observableArrayList();
-
 	protected int						unreadAmount;
 	protected static IntegerProperty	totalUnreadAmount	= new SimpleIntegerProperty();
 
-	protected final Contact recipient;
-
 	private static final long serialVersionUID = 2L;
 
 	/**

client/src/main/java/envoy/client/data/LocalDB.java

@@ -13,9 +13,8 @@ import java.util.stream.Stream;
 import javafx.application.Platform;
 import javafx.collections.*;
 
-import dev.kske.eventbus.Event;
-import dev.kske.eventbus.EventBus;
-import dev.kske.eventbus.EventListener;
+import dev.kske.eventbus.core.*;
+import dev.kske.eventbus.core.Event;
 
 import envoy.data.*;
 import envoy.data.Message.MessageStatus;
@@ -35,7 +34,7 @@ import envoy.client.event.*;
  * @author Kai S. K. Engelbart
  * @since Envoy Client v0.3-alpha
  */
-public final class LocalDB implements EventListener {
+public final class LocalDB {
 
 	// Data
 	private User					user;
@@ -246,8 +245,13 @@ public final class LocalDB implements EventListener {
 	 * @throws IOException if the saving process failed
 	 * @since Envoy Client v0.3-alpha
 	 */
-	@Event(eventType = EnvoyCloseEvent.class, priority = 500)
+	@Event(EnvoyCloseEvent.class)
+	@Priority(500)
 	private synchronized void save() {
+
+		// Stop saving if this account has been deleted
+		if (userFile == null)
+			return;
 		EnvoyLog.getLogger(LocalDB.class).log(Level.FINER, "Saving local database...");
 
 		// Save users
@@ -273,37 +277,66 @@ public final class LocalDB implements EventListener {
 		}
 	}
 
-	@Event(priority = 500)
+	/**
+	 * Deletes any local remnant of this user.
+	 *
+	 * @since Envoy Client v0.3-beta
+	 */
+	public void delete() {
+		try {
+
+			// Save ID generator - can be used for other users in that db
+			if (hasIDGenerator())
+				SerializationUtils.write(idGeneratorFile, idGenerator);
+		} catch (final IOException e) {
+			EnvoyLog.getLogger(LocalDB.class).log(Level.SEVERE, "Unable to save local database: ",
+				e);
+		}
+		if (lastLoginFile != null)
+			lastLoginFile.delete();
+		userFile.delete();
+		users.remove(user.getName());
+		userFile = null;
+		onLogout();
+	}
+
+	@Event
+	@Priority(500)
 	private void onMessage(Message msg) {
 		if (msg.getStatus() == MessageStatus.SENT)
 			msg.nextStatus();
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onGroupMessage(GroupMessage msg) {
 		// TODO: Cancel event once EventBus is updated
 		if (msg.getStatus() == MessageStatus.WAITING || msg.getStatus() == MessageStatus.READ)
 			logger.warning("The groupMessage has the unexpected status " + msg.getStatus());
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onMessageStatusChange(MessageStatusChange evt) {
 		getMessage(evt.getID()).ifPresent(msg -> msg.setStatus(evt.get()));
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onGroupMessageStatusChange(GroupMessageStatusChange evt) {
 		this.<GroupMessage>getMessage(evt.getID())
 			.ifPresent(msg -> msg.getMemberStatuses().replace(evt.getMemberID(), evt.get()));
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onUserStatusChange(UserStatusChange evt) {
 		getChat(evt.getID()).map(Chat::getRecipient).map(User.class::cast)
 			.ifPresent(u -> u.setStatus(evt.get()));
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onUserOperation(UserOperation operation) {
 		final var eventUser = operation.get();
 		switch (operation.getOperationType()) {
@@ -329,13 +362,15 @@ public final class LocalDB implements EventListener {
 			Platform.runLater(() -> chats.add(new GroupChat(user, newGroup)));
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onGroupResize(GroupResize evt) {
 		getChat(evt.getGroupID()).map(Chat::getRecipient).map(Group.class::cast)
 			.ifPresent(evt::apply);
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onNameChange(NameChange evt) {
 		chats.stream().map(Chat::getRecipient).filter(c -> c.getID() == evt.getID()).findAny()
 			.ifPresent(c -> c.setName(evt.get()));
@@ -357,7 +392,8 @@ public final class LocalDB implements EventListener {
 	 *
 	 * @since Envoy Client v0.2-beta
 	 */
-	@Event(eventType = Logout.class, priority = 50)
+	@Event(Logout.class)
+	@Priority(50)
 	private void onLogout() {
 		autoSaver.cancel();
 		autoSaveRestart = true;
@@ -389,21 +425,33 @@ public final class LocalDB implements EventListener {
 		});
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onOwnStatusChange(OwnStatusChange statusChange) {
 		user.setStatus(statusChange.get());
 	}
 
-	@Event(eventType = ContactsChangedSinceLastLogin.class, priority = 500)
+	@Event(ContactsChangedSinceLastLogin.class)
+	@Priority(500)
 	private void onContactsChangedSinceLastLogin() {
 		contactsChanged = true;
 	}
 
-	@Event(priority = 500)
+	@Event
+	@Priority(500)
 	private void onContactDisabled(ContactDisabled event) {
 		getChat(event.get().getID()).ifPresent(chat -> chat.setDisabled(true));
 	}
 
+	@Event
+	@Priority(500)
+	private void onAccountDeletion(AccountDeletion deletion) {
+		if (user.getID() == deletion.get())
+			logger.log(Level.WARNING,
+				"I have been informed by the server that I have been deleted without even knowing it...");
+		getChat(deletion.get()).ifPresent(chat -> chat.setDisabled(true));
+	}
+
 	/**
 	 * @return a {@code Map<String, User>} of all users stored locally with their user names as keys
 	 * @since Envoy Client v0.2-alpha
@@ -461,7 +509,8 @@ public final class LocalDB implements EventListener {
 	 * @param idGenerator the message ID generator to set
 	 * @since Envoy Client v0.3-alpha
 	 */
-	@Event(priority = 150)
+	@Event
+	@Priority(150)
 	public void setIDGenerator(IDGenerator idGenerator) { this.idGenerator = idGenerator; }
 
 	/**

client/src/main/java/envoy/client/data/Settings.java

@@ -5,8 +5,7 @@ import java.util.*;
 import java.util.logging.Level;
 import java.util.prefs.Preferences;
 
-import dev.kske.eventbus.*;
-import dev.kske.eventbus.EventListener;
+import dev.kske.eventbus.core.*;
 
 import envoy.util.*;
 
@@ -21,7 +20,7 @@ import envoy.client.event.EnvoyCloseEvent;
  * @author Kai S. K. Engelbart
  * @since Envoy Client v0.2-alpha
  */
-public final class Settings implements EventListener {
+public final class Settings {
 
 	// Actual settings accessible by the rest of the application
 	private Map<String, SettingsItem<?>> items;
@@ -69,7 +68,7 @@ public final class Settings implements EventListener {
 	 * @throws IOException if an error occurs while saving the themes
 	 * @since Envoy Client v0.2-alpha
 	 */
-	@Event(eventType = EnvoyCloseEvent.class)
+	@Event(EnvoyCloseEvent.class)
 	private void save() {
 		EnvoyLog.getLogger(Settings.class).log(Level.INFO, "Saving settings...");
 

client/src/main/java/envoy/client/data/shortcuts/EnvoyShortcutConfig.java

@@ -6,7 +6,7 @@ import envoy.data.User.UserStatus;
 
 import envoy.client.data.Context;
 import envoy.client.helper.ShutdownHelper;
-import envoy.client.ui.SceneContext.SceneInfo;
+import envoy.client.ui.SceneInfo;
 import envoy.client.util.UserUtil;
 
 /**

client/src/main/java/envoy/client/data/shortcuts/GlobalKeyShortcuts.java

@@ -4,7 +4,7 @@ import java.util.*;
 
 import javafx.scene.input.KeyCombination;
 
-import envoy.client.ui.SceneContext.SceneInfo;
+import envoy.client.ui.SceneInfo;
 
 /**
  * Contains all keyboard shortcuts used throughout the application.

client/src/main/java/envoy/client/event/AccountDeletion.java

@@ -0,0 +1,22 @@
+package envoy.client.event;
+
+import envoy.event.Event;
+
+/**
+ * Signifies the deletion of an account.
+ * 
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.3-beta
+ */
+public class AccountDeletion extends Event<Long> {
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * @param value the ID of the contact that was deleted
+	 * @since Envoy Common v0.3-beta
+	 */
+	public AccountDeletion(Long value) {
+		super(value);
+	}
+}

client/src/main/java/envoy/client/helper/ShutdownHelper.java

@@ -1,6 +1,6 @@
 package envoy.client.helper;
 
-import dev.kske.eventbus.EventBus;
+import dev.kske.eventbus.core.EventBus;
 
 import envoy.client.data.*;
 import envoy.client.event.EnvoyCloseEvent;

client/src/main/java/envoy/client/net/Client.java

@@ -5,14 +5,14 @@ import java.net.Socket;
 import java.util.concurrent.TimeoutException;
 import java.util.logging.*;
 
-import dev.kske.eventbus.*;
-import dev.kske.eventbus.Event;
+import dev.kske.eventbus.core.*;
+import dev.kske.eventbus.core.Event;
 
 import envoy.data.*;
 import envoy.event.*;
 import envoy.util.*;
 
-import envoy.client.data.*;
+import envoy.client.data.ClientConfig;
 import envoy.client.event.EnvoyCloseEvent;
 
 /**
@@ -24,7 +24,7 @@ import envoy.client.event.EnvoyCloseEvent;
  * @author Leon Hofmeister
  * @since Envoy Client v0.1-alpha
  */
-public final class Client implements EventListener, Closeable {
+public final class Client implements Closeable {
 
 	// Connection handling
 	private Socket		socket;
@@ -55,13 +55,12 @@ public final class Client implements EventListener, Closeable {
 	 * the handshake does exceed this time limit, an exception is thrown.
 	 *
 	 * @param credentials the login credentials of the user
-	 * @param cacheMap    the map of all caches needed
 	 * @throws TimeoutException     if the server could not be reached
 	 * @throws IOException          if the login credentials could not be written
 	 * @throws InterruptedException if the current thread is interrupted while waiting for the
 	 *                              handshake response
 	 */
-	public void performHandshake(LoginCredentials credentials, CacheMap cacheMap)
+	public void performHandshake(LoginCredentials credentials)
 		throws TimeoutException, IOException, InterruptedException {
 		if (online)
 			throw new IllegalStateException("Handshake has already been performed successfully");
@@ -79,7 +78,6 @@ public final class Client implements EventListener, Closeable {
 		// Register user creation processor, contact list processor, message cache and
 		// authentication token
 		receiver.registerProcessor(User.class, sender -> this.sender = sender);
-		receiver.registerProcessors(cacheMap.getMap());
 
 		// Start receiver
 		receiver.start();
@@ -101,42 +99,18 @@ public final class Client implements EventListener, Closeable {
 
 			if (System.currentTimeMillis() - start > 5000) {
 				rejected = true;
+				socket.close();
+				receiver.removeAllProcessors();
 				throw new TimeoutException("Did not log in after 5 seconds");
 			}
 			Thread.sleep(500);
 		}
 
-		online = true;
-		logger.log(Level.INFO, "Handshake completed.");
-	}
-
-	/**
-	 * Initializes the {@link Receiver} used to process data sent from the server to this client.
-	 *
-	 * @param localDB  the local database used to persist the current {@link IDGenerator}
-	 * @param cacheMap the map of all caches needed
-	 * @throws IOException if no {@link IDGenerator} is present and none could be requested from the
-	 *                     server
-	 * @since Envoy Client v0.2-alpha
-	 */
-	public void initReceiver(LocalDB localDB, CacheMap cacheMap) throws IOException {
-		checkOnline();
-
-		// Remove all processors as they are only used during the handshake
+		// Remove handshake specific processors
 		receiver.removeAllProcessors();
 
-		// Relay cached messages and message status changes
-		cacheMap.get(Message.class).setProcessor(eventBus::dispatch);
-		cacheMap.get(GroupMessage.class).setProcessor(eventBus::dispatch);
-		cacheMap.get(MessageStatusChange.class).setProcessor(eventBus::dispatch);
-		cacheMap.get(GroupMessageStatusChange.class).setProcessor(eventBus::dispatch);
-
-		// Request a generator if none is present or the existing one is consumed
-		if (!localDB.hasIDGenerator() || !localDB.getIDGenerator().hasNext())
-			requestIDGenerator();
-
-		// Relay caches
-		cacheMap.getMap().values().forEach(Cache::relay);
+		online = true;
+		logger.log(Level.INFO, "Handshake completed.");
 	}
 
 	/**
@@ -179,13 +153,15 @@ public final class Client implements EventListener, Closeable {
 		send(new IDGeneratorRequest());
 	}
 
-	@Event(eventType = HandshakeRejection.class, priority = 1000)
+	@Event(HandshakeRejection.class)
+	@Priority(1000)
 	private void onHandshakeRejection() {
 		rejected = true;
 	}
 
 	@Override
-	@Event(eventType = EnvoyCloseEvent.class, priority = 50)
+	@Event(EnvoyCloseEvent.class)
+	@Priority(50)
 	public void close() {
 		if (online) {
 			logger.log(Level.INFO, "Closing connection...");

client/src/main/java/envoy/client/net/Receiver.java

@@ -6,7 +6,7 @@ import java.util.*;
 import java.util.function.Consumer;
 import java.util.logging.*;
 
-import dev.kske.eventbus.*;
+import dev.kske.eventbus.core.EventBus;
 
 import envoy.util.*;
 
@@ -87,15 +87,17 @@ public final class Receiver extends Thread {
 					// Dispatch to the processor if present
 					if (processor != null)
 						processor.accept(obj);
-					// Dispatch to the event bus if the object is an event without a processor
-					else if (obj instanceof IEvent)
-						eventBus.dispatch((IEvent) obj);
-					// Notify if no processor could be located
+					// Dispatch to the event bus if the object has no processor
 					else
-						logger.log(Level.WARNING,
-							String.format(
-								"The received object has the %s for which no processor is defined.",
-								obj.getClass()));
+						eventBus.dispatch(obj);
+
+					// TODO: Log DeadEvent from Event Bus 1.1.0
+					// Notify if no processor could be located
+					// else
+					// logger.log(Level.WARNING,
+					// String.format(
+					// "The received object has the %s for which no processor is defined.",
+					// obj.getClass()));
 				}
 			} catch (final SocketException | EOFException e) {
 				// Connection probably closed by client.

client/src/main/java/envoy/client/ui/SceneContext.java

@@ -4,12 +4,11 @@ import java.io.IOException;
 import java.util.Stack;
 import java.util.logging.Level;
 
-import javafx.application.Platform;
 import javafx.fxml.FXMLLoader;
 import javafx.scene.*;
 import javafx.stage.Stage;
 
-import dev.kske.eventbus.*;
+import dev.kske.eventbus.core.*;
 
 import envoy.util.EnvoyLog;
 
@@ -26,53 +25,13 @@ import envoy.client.event.*;
  * @author Kai S. K. Engelbart
  * @since Envoy Client v0.1-beta
  */
-public final class SceneContext implements EventListener {
-
-	/**
-	 * Contains information about different scenes and their FXML resource files.
-	 *
-	 * @author Kai S. K. Engelbart
-	 * @since Envoy Client v0.1-beta
-	 */
-	public enum SceneInfo {
-
-		/**
-		 * The main scene in which the chat screen is displayed.
-		 *
-		 * @since Envoy Client v0.1-beta
-		 */
-		CHAT_SCENE("/fxml/ChatScene.fxml"),
-
-		/**
-		 * The scene in which the settings screen is displayed.
-		 *
-		 * @since Envoy Client v0.1-beta
-		 */
-		SETTINGS_SCENE("/fxml/SettingsScene.fxml"),
-
-		/**
-		 * The scene in which the login screen is displayed.
-		 *
-		 * @since Envoy Client v0.1-beta
-		 */
-		LOGIN_SCENE("/fxml/LoginScene.fxml");
-
-		/**
-		 * The path to the FXML resource.
-		 */
-		public final String path;
-
-		SceneInfo(String path) {
-			this.path = path;
-		}
-	}
+public final class SceneContext {
 
 	private final Stage			stage;
-	private final FXMLLoader	loader			= new FXMLLoader();
-	private final Stack<Scene>	sceneStack		= new Stack<>();
-	private final Stack<Object>	controllerStack	= new Stack<>();
+	private final Stack<Parent>	roots		= new Stack<>();
+	private final Stack<Object>	controllers	= new Stack<>();
 
-	private static final Settings settings = Settings.getInstance();
+	private Scene scene;
 
 	/**
 	 * Initializes the scene context.
@@ -88,44 +47,44 @@ public final class SceneContext implements EventListener {
 	/**
 	 * Loads a new scene specified by a scene info.
 	 *
-	 * @param sceneInfo specifies the scene to load
+	 * @param info specifies the scene to load
 	 * @throws RuntimeException if the loading process fails
 	 * @since Envoy Client v0.1-beta
 	 */
-	public void load(SceneInfo sceneInfo) {
-		EnvoyLog.getLogger(SceneContext.class).log(Level.FINER, "Loading scene " + sceneInfo);
-		loader.setRoot(null);
-		loader.setController(null);
+	public void load(SceneInfo info) {
+		EnvoyLog.getLogger(SceneContext.class).log(Level.FINER, "Loading scene " + info);
 
 		try {
-			final var	rootNode	=
-				(Parent) loader.load(getClass().getResourceAsStream(sceneInfo.path));
-			final var	scene		= new Scene(rootNode);
-			final var	controller	= loader.getController();
-			controllerStack.push(controller);
 
-			sceneStack.push(scene);
-			stage.setScene(scene);
+			// Load root node and controller
+			var		loader		= new FXMLLoader();
+			Parent	root		= loader.load(getClass().getResourceAsStream(info.path));
+			Object	controller	= loader.getController();
+			roots.push(root);
+			controllers.push(controller);
+
+			if (scene == null) {
+
+				// One-time scene initialization
+				scene = new Scene(root, stage.getWidth(), stage.getHeight());
+				applyCSS();
+				stage.setScene(scene);
+			} else {
+				scene.setRoot(root);
+			}
+
+			// Remove previous keyboard shortcuts
+			scene.getAccelerators().clear();
 
 			// Supply the global custom keyboard shortcuts for that scene
 			scene.getAccelerators()
-				.putAll(GlobalKeyShortcuts.getInstance().getKeyboardShortcuts(sceneInfo));
+				.putAll(GlobalKeyShortcuts.getInstance().getKeyboardShortcuts(info));
 
 			// Supply the scene specific keyboard shortcuts
 			if (controller instanceof KeyboardMapping)
 				scene.getAccelerators()
 					.putAll(((KeyboardMapping) controller).getKeyboardShortcuts());
-
-			// The LoginScene is the only scene not intended to be resized
-			// As strange as it seems, this is needed as otherwise the LoginScene won't be
-			// displayed on some OS (...Debian...)
-			stage.sizeToScene();
-			Platform.runLater(() -> stage.setResizable(sceneInfo != SceneInfo.LOGIN_SCENE));
-			applyCSS();
-			stage.show();
-		} catch (final IOException e) {
-			EnvoyLog.getLogger(SceneContext.class).log(Level.SEVERE,
-				String.format("Could not load scene for %s: ", sceneInfo), e);
+		} catch (IOException e) {
 			throw new RuntimeException(e);
 		}
 	}
@@ -137,42 +96,45 @@ public final class SceneContext implements EventListener {
 	 */
 	public void pop() {
 
-		// Pop scene and controller
-		sceneStack.pop();
-		controllerStack.pop();
+		// Pop current root node and controller
+		roots.pop();
+		controllers.pop();
 
 		// Apply new scene if present
-		if (!sceneStack.isEmpty()) {
-			final var newScene = sceneStack.peek();
-			stage.setScene(newScene);
-			applyCSS();
-			stage.sizeToScene();
-			// If the controller implements the Restorable interface,
-			// the actions to perform on restoration will be executed here
-			final var controller = controllerStack.peek();
+		if (!roots.isEmpty()) {
+			scene.setRoot(roots.peek());
+
+			// Invoke restore if controller is restorable
+			var controller = controllers.peek();
 			if (controller instanceof Restorable)
 				((Restorable) controller).onRestore();
+		} else {
+
+			// Remove the current scene entirely
+			scene = null;
+			stage.setScene(null);
 		}
-		stage.show();
 	}
 
 	private void applyCSS() {
-		if (!sceneStack.isEmpty()) {
-			final var	styleSheets	= stage.getScene().getStylesheets();
-			final var	themeCSS	= "/css/" + settings.getCurrentTheme() + ".css";
+		if (scene != null) {
+			var	styleSheets	= scene.getStylesheets();
+			var	themeCSS	= "/css/" + Settings.getInstance().getCurrentTheme() + ".css";
 			styleSheets.clear();
 			styleSheets.addAll(getClass().getResource("/css/base.css").toExternalForm(),
 				getClass().getResource(themeCSS).toExternalForm());
 		}
 	}
 
-	@Event(eventType = Logout.class, priority = 150)
+	@Event(Logout.class)
+	@Priority(150)
 	private void onLogout() {
-		sceneStack.clear();
-		controllerStack.clear();
+		roots.clear();
+		controllers.clear();
 	}
 
-	@Event(priority = 150, eventType = ThemeChangeEvent.class)
+	@Event(ThemeChangeEvent.class)
+	@Priority(150)
 	private void onThemeChange() {
 		applyCSS();
 	}
@@ -182,7 +144,7 @@ public final class SceneContext implements EventListener {
 	 * @return the controller used by the current scene
 	 * @since Envoy Client v0.1-beta
 	 */
-	public <T> T getController() { return (T) controllerStack.peek(); }
+	public <T> T getController() { return (T) controllers.peek(); }
 
 	/**
 	 * @return the stage in which the scenes are displayed
@@ -194,5 +156,5 @@ public final class SceneContext implements EventListener {
 	 * @return whether the scene stack is empty
 	 * @since Envoy Client v0.2-beta
 	 */
-	public boolean isEmpty() { return sceneStack.isEmpty(); }
+	public boolean isEmpty() { return roots.isEmpty(); }
 }

client/src/main/java/envoy/client/ui/SceneInfo.java

@@ -0,0 +1,40 @@
+package envoy.client.ui;
+
+/**
+ * Contains information about different scenes and their FXML resource files.
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.1-beta
+ */
+public enum SceneInfo {
+
+	/**
+	 * The main scene in which the chat screen is displayed.
+	 *
+	 * @since Envoy Client v0.1-beta
+	 */
+	CHAT_SCENE("/fxml/ChatScene.fxml"),
+
+	/**
+	 * The scene in which the settings screen is displayed.
+	 *
+	 * @since Envoy Client v0.1-beta
+	 */
+	SETTINGS_SCENE("/fxml/SettingsScene.fxml"),
+
+	/**
+	 * The scene in which the login screen is displayed.
+	 *
+	 * @since Envoy Client v0.1-beta
+	 */
+	LOGIN_SCENE("/fxml/LoginScene.fxml");
+
+	/**
+	 * The path to the FXML resource.
+	 */
+	public final String path;
+
+	SceneInfo(String path) {
+		this.path = path;
+	}
+}

client/src/main/java/envoy/client/ui/Startup.java

@@ -12,7 +12,7 @@ import javafx.stage.Stage;
 
 import envoy.data.*;
 import envoy.data.User.UserStatus;
-import envoy.event.*;
+import envoy.event.UserStatusChange;
 import envoy.exception.EnvoyException;
 import envoy.util.EnvoyLog;
 
@@ -20,7 +20,6 @@ import envoy.client.data.*;
 import envoy.client.data.shortcuts.EnvoyShortcutConfig;
 import envoy.client.helper.ShutdownHelper;
 import envoy.client.net.Client;
-import envoy.client.ui.SceneContext.SceneInfo;
 import envoy.client.ui.controller.LoginScene;
 import envoy.client.util.IconUtil;
 
@@ -94,7 +93,7 @@ public final class Startup extends Application {
 		final var sceneContext = new SceneContext(stage);
 		context.setSceneContext(sceneContext);
 
-		// Authenticate with token if present
+		// Authenticate with token if present or load login scene
 		if (localDB.getAuthToken() != null) {
 			logger.info("Attempting authentication with token...");
 			localDB.loadUserData();
@@ -103,8 +102,9 @@ public final class Startup extends Application {
 					VERSION, localDB.getLastSync())))
 				sceneContext.load(SceneInfo.LOGIN_SCENE);
 		} else
-			// Load login scene
 			sceneContext.load(SceneInfo.LOGIN_SCENE);
+
+		stage.show();
 	}
 
 	/**
@@ -115,21 +115,20 @@ public final class Startup extends Application {
 	 * @since Envoy Client v0.2-beta
 	 */
 	public static boolean performHandshake(LoginCredentials credentials) {
-		final var cacheMap = new CacheMap();
-		cacheMap.put(Message.class, new Cache<Message>());
-		cacheMap.put(GroupMessage.class, new Cache<GroupMessage>());
-		cacheMap.put(MessageStatusChange.class, new Cache<MessageStatusChange>());
-		cacheMap.put(GroupMessageStatusChange.class, new Cache<GroupMessageStatusChange>());
 		final var originalStatus =
 			localDB.getUser() == null ? UserStatus.ONLINE : localDB.getUser().getStatus();
 		try {
-			client.performHandshake(credentials, cacheMap);
+			client.performHandshake(credentials);
 			if (client.isOnline()) {
 
 				// Restore the original status as the server automatically returns status ONLINE
 				client.getSender().setStatus(originalStatus);
 				loadChatScene();
-				client.initReceiver(localDB, cacheMap);
+
+				// Request an ID generator if none is present or the existing one is consumed
+				if (!localDB.hasIDGenerator() || !localDB.getIDGenerator().hasNext())
+					client.requestIDGenerator();
+
 				return true;
 			} else
 				return false;
@@ -226,7 +225,7 @@ public final class Startup extends Application {
 		// Load ChatScene
 		stage.setMinHeight(400);
 		stage.setMinWidth(843);
-		context.getSceneContext().load(SceneContext.SceneInfo.CHAT_SCENE);
+		context.getSceneContext().load(SceneInfo.CHAT_SCENE);
 		stage.centerOnScreen();
 
 		// Exit or minimize the stage when a close request occurs

client/src/main/java/envoy/client/ui/StatusTrayIcon.java

@@ -9,8 +9,8 @@ import java.awt.image.BufferedImage;
 import javafx.application.Platform;
 import javafx.stage.Stage;
 
-import dev.kske.eventbus.*;
-import dev.kske.eventbus.Event;
+import dev.kske.eventbus.core.Event;
+import dev.kske.eventbus.core.EventBus;
 
 import envoy.data.Message;
 import envoy.data.User.UserStatus;
@@ -31,7 +31,7 @@ import envoy.client.util.*;
  * @author Kai S. K. Engelbart
  * @since Envoy Client v0.2-alpha
  */
-public final class StatusTrayIcon implements EventListener {
+public final class StatusTrayIcon {
 
 	/**
 	 * The {@link TrayIcon} provided by the System Tray API for controlling the system tray. This
@@ -136,7 +136,7 @@ public final class StatusTrayIcon implements EventListener {
 	 *
 	 * @since Envoy Client v0.2-beta
 	 */
-	@Event(eventType = Logout.class)
+	@Event(Logout.class)
 	public void hide() {
 		SystemTray.getSystemTray().remove(trayIcon);
 	}

client/src/main/java/envoy/client/ui/chatscene/ChatSceneCommands.java

@@ -15,7 +15,7 @@ import envoy.util.EnvoyLog;
 import envoy.client.data.Context;
 import envoy.client.data.commands.*;
 import envoy.client.helper.ShutdownHelper;
-import envoy.client.ui.SceneContext.SceneInfo;
+import envoy.client.ui.SceneInfo;
 import envoy.client.ui.controller.ChatScene;
 import envoy.client.util.*;
 
@@ -32,7 +32,7 @@ public final class ChatSceneCommands {
 	private final SystemCommandBuilder	builder					=
 		new SystemCommandBuilder(messageTextAreaCommands);
 
-	private static final String messageDependantCommandDescription =
+	private static final String messageDependentCommandDescription =
 		" the given message. Use s/S to use the selected message. Otherwise expects a number relative to the uppermost completely visible message.";
 
 	/**
@@ -141,7 +141,7 @@ public final class ChatSceneCommands {
 			else
 				useRelativeMessage(command, action, additionalCheck, positionalArgument, false);
 		}).setDefaults("s").setNumberOfArguments(1)
-			.setDescription(description.concat(messageDependantCommandDescription)).build(command);
+			.setDescription(description.concat(messageDependentCommandDescription)).build(command);
 	}
 
 	private void selectionNeighbor(Consumer<Message> action, Predicate<Message> additionalCheck,

client/src/main/java/envoy/client/ui/control/ChatControl.java

@@ -18,7 +18,7 @@ import envoy.client.util.IconUtil;
  */
 public final class ChatControl extends HBox {
 
-	private static final Image userIcon = IconUtil.loadIconThemeSensitive("user_icon", 32),
+	private static Image userIcon = IconUtil.loadIconThemeSensitive("user_icon", 32),
 		groupIcon = IconUtil.loadIconThemeSensitive("group_icon", 32);
 
 	/**
@@ -60,4 +60,14 @@ public final class ChatControl extends HBox {
 		}
 		getStyleClass().add("list-element");
 	}
+
+	/**
+	 * Reloads the default icons.
+	 *
+	 * @since Envoy Client v0.3-beta
+	 */
+	public static void reloadDefaultChatIcons() {
+		userIcon	= IconUtil.loadIconThemeSensitive("user_icon", 32);
+		groupIcon	= IconUtil.loadIconThemeSensitive("group_icon", 32);
+	}
 }

client/src/main/java/envoy/client/ui/controller/ChatScene.java

@@ -1,11 +1,14 @@
 package envoy.client.ui.controller;
 
+import static envoy.client.ui.SceneInfo.SETTINGS_SCENE;
+
 import java.awt.Toolkit;
 import java.awt.datatransfer.StringSelection;
 import java.io.*;
 import java.nio.file.Files;
 import java.time.LocalDateTime;
 import java.time.format.DateTimeFormatter;
+import java.util.Map;
 import java.util.logging.*;
 
 import javafx.animation.RotateTransition;
@@ -18,14 +21,14 @@ import javafx.scene.control.*;
 import javafx.scene.control.Alert.AlertType;
 import javafx.scene.image.*;
 import javafx.scene.input.*;
-import javafx.scene.layout.*;
+import javafx.scene.layout.HBox;
 import javafx.scene.paint.Color;
 import javafx.scene.shape.Rectangle;
 import javafx.stage.FileChooser;
 import javafx.util.Duration;
 
-import dev.kske.eventbus.*;
-import dev.kske.eventbus.Event;
+import dev.kske.eventbus.core.*;
+import dev.kske.eventbus.core.Event;
 
 import envoy.data.*;
 import envoy.data.Attachment.AttachmentType;
@@ -37,6 +40,7 @@ import envoy.util.EnvoyLog;
 
 import envoy.client.data.*;
 import envoy.client.data.audio.AudioRecorder;
+import envoy.client.data.shortcuts.KeyboardMapping;
 import envoy.client.event.*;
 import envoy.client.net.*;
 import envoy.client.ui.*;
@@ -51,7 +55,7 @@ import envoy.client.util.*;
  * @author Kai S. K. Engelbart
  * @since Envoy Client v0.1-beta
  */
-public final class ChatScene implements EventListener, Restorable {
+public final class ChatScene implements Restorable, KeyboardMapping {
 
 	@FXML
 	private ListView<Message> messageList;
@@ -216,12 +220,13 @@ public final class ChatScene implements EventListener, Restorable {
 		});
 	}
 
-	@Event(eventType = BackEvent.class)
+	@Event(BackEvent.class)
 	private void onBackEvent() {
 		tabPane.getSelectionModel().select(Tabs.CONTACT_LIST.ordinal());
 	}
 
-	@Event(includeSubtypes = true)
+	@Event
+	@Polymorphic
 	private void onMessage(Message message) {
 
 		// The sender of the message is the recipient of the chat
@@ -300,7 +305,7 @@ public final class ChatScene implements EventListener, Restorable {
 		}));
 	}
 
-	@Event(eventType = NoAttachments.class)
+	@Event(NoAttachments.class)
 	private void onNoAttachments() {
 		Platform.runLater(() -> {
 			attachmentButton.setDisable(true);
@@ -313,13 +318,15 @@ public final class ChatScene implements EventListener, Restorable {
 		});
 	}
 
-	@Event(priority = 150)
+	@Event
+	@Priority(150)
 	private void onGroupCreationResult(GroupCreationResult result) {
 		Platform.runLater(() -> newGroupButton.setDisable(result.get() == null));
 	}
 
-	@Event(eventType = ThemeChangeEvent.class)
+	@Event(ThemeChangeEvent.class)
 	private void onThemeChange() {
+		ChatControl.reloadDefaultChatIcons();
 		settingsButton.setGraphic(
 			new ImageView(IconUtil.loadIconThemeSensitive("settings", DEFAULT_ICON_SIZE)));
 		voiceButton.setGraphic(
@@ -341,11 +348,17 @@ public final class ChatScene implements EventListener, Restorable {
 				recipientProfilePic.setImage(IconUtil.loadIconThemeSensitive("group_icon", 43));
 	}
 
-	@Event(eventType = Logout.class, priority = 200)
+	@Event(Logout.class)
+	@Priority(200)
 	private void onLogout() {
 		eventBus.removeListener(this);
 	}
 
+	@Event(AccountDeletion.class)
+	private void onAccountDeletion() {
+		Platform.runLater(chatList::refresh);
+	}
+
 	@Override
 	public void onRestore() {
 		updateRemainingCharsLabel();
@@ -438,7 +451,7 @@ public final class ChatScene implements EventListener, Restorable {
 	 */
 	@FXML
 	private void settingsButtonClicked() {
-		sceneContext.load(SceneContext.SceneInfo.SETTINGS_SCENE);
+		sceneContext.load(SETTINGS_SCENE);
 	}
 
 	/**
@@ -586,7 +599,7 @@ public final class ChatScene implements EventListener, Restorable {
 		// IsTyping#millisecondsActive
 		if (client.isOnline() && currentChat.getLastWritingEvent()
 			+ IsTyping.millisecondsActive <= System.currentTimeMillis()) {
-			client.send(new IsTyping(getChatID(), currentChat.getRecipient().getID()));
+			client.send(new IsTyping(currentChat.getRecipient().getID()));
 			currentChat.lastWritingEventWasNow();
 		}
 
@@ -600,19 +613,6 @@ public final class ChatScene implements EventListener, Restorable {
 			checkPostConditions(false);
 	}
 
-	/**
-	 * Returns the id that should be used to send things to the server: the id of 'our' {@link User}
-	 * if the recipient of that object is another User, else the id of the {@link Group} 'our' user
-	 * is sending to.
-	 *
-	 * @return an id that can be sent to the server
-	 * @since Envoy Client v0.2-beta
-	 */
-	private long getChatID() {
-		return currentChat.getRecipient() instanceof User ? client.getSender().getID()
-			: currentChat.getRecipient().getID();
-	}
-
 	/**
 	 * @param e the keys that have been pressed
 	 * @since Envoy Client v0.1-beta
@@ -786,7 +786,8 @@ public final class ChatScene implements EventListener, Restorable {
 		attachmentView.setVisible(visible);
 	}
 
-	@Event(eventType = OwnStatusChange.class, priority = 50)
+	@Event(OwnStatusChange.class)
+	@Priority(50)
 	private void generateOwnStatusControl() {
 
 		// Update the own user status if present
@@ -797,7 +798,7 @@ public final class ChatScene implements EventListener, Restorable {
 			// Else prepend it to the HBox children
 			final var ownUserControl = new ContactControl(localDB.getUser());
 			ownUserControl.setAlignment(Pos.CENTER_LEFT);
-			HBox.setHgrow(ownUserControl, Priority.NEVER);
+			HBox.setHgrow(ownUserControl, javafx.scene.layout.Priority.NEVER);
 			ownContactControl.getChildren().add(1, ownUserControl);
 		}
 	}
@@ -884,4 +885,25 @@ public final class ChatScene implements EventListener, Restorable {
 			: c -> c.getRecipient().getName().toLowerCase()
 				.contains(contactSearch.getText().toLowerCase()));
 	}
+
+	@Override
+	public Map<KeyCombination, Runnable> getKeyboardShortcuts() {
+		return Map.<KeyCombination, Runnable>of(
+
+			// Delete text before the caret with "Control" + U
+			new KeyCodeCombination(KeyCode.U, KeyCombination.CONTROL_DOWN), () -> {
+				messageTextArea
+					.setText(
+						messageTextArea.getText().substring(messageTextArea.getCaretPosition()));
+				checkPostConditions(false);
+
+				// Delete text after the caret with "Control" + K
+			}, new KeyCodeCombination(KeyCode.K, KeyCombination.CONTROL_DOWN), () -> {
+				messageTextArea
+					.setText(
+						messageTextArea.getText().substring(0, messageTextArea.getCaretPosition()));
+				checkPostConditions(false);
+				messageTextArea.positionCaret(messageTextArea.getText().length());
+			});
+	}
 }

client/src/main/java/envoy/client/ui/controller/ContactSearchTab.java

@@ -7,7 +7,7 @@ import javafx.fxml.FXML;
 import javafx.scene.control.*;
 import javafx.scene.control.Alert.AlertType;
 
-import dev.kske.eventbus.*;
+import dev.kske.eventbus.core.*;
 
 import envoy.data.User;
 import envoy.event.ElementOperation;
@@ -34,7 +34,7 @@ import envoy.client.ui.listcell.ListCellFactory;
  * @author Maximilian Käfer
  * @since Envoy Client v0.1-beta
  */
-public class ContactSearchTab implements EventListener {
+public class ContactSearchTab {
 
 	@FXML
 	private TextArea searchBar;

client/src/main/java/envoy/client/ui/controller/GroupCreationTab.java

@@ -10,7 +10,7 @@ import javafx.scene.control.*;
 import javafx.scene.input.MouseEvent;
 import javafx.scene.layout.HBox;
 
-import dev.kske.eventbus.*;
+import dev.kske.eventbus.core.*;
 
 import envoy.data.*;
 import envoy.event.GroupCreation;
@@ -18,7 +18,7 @@ import envoy.event.contact.UserOperation;
 import envoy.util.Bounds;
 
 import envoy.client.data.*;
-import envoy.client.event.BackEvent;
+import envoy.client.event.*;
 import envoy.client.ui.control.*;
 import envoy.client.ui.listcell.ListCellFactory;
 
@@ -33,7 +33,7 @@ import envoy.client.ui.listcell.ListCellFactory;
  * @author Maximilian Käfer
  * @since Envoy Client v0.1-beta
  */
-public class GroupCreationTab implements EventListener {
+public class GroupCreationTab {
 
 	@FXML
 	private Button createButton;
@@ -252,4 +252,10 @@ public class GroupCreationTab implements EventListener {
 			}
 		});
 	}
+
+	@Event
+	private void onAccountDeletion(AccountDeletion deletion) {
+		final var deletedID = deletion.get();
+		Platform.runLater(() -> userList.getItems().removeIf(user -> (user.getID() == deletedID)));
+	}
 }

client/src/main/java/envoy/client/ui/controller/LoginScene.java

@@ -10,7 +10,7 @@ import javafx.scene.control.*;
 import javafx.scene.control.Alert.AlertType;
 import javafx.scene.image.ImageView;
 
-import dev.kske.eventbus.*;
+import dev.kske.eventbus.core.*;
 
 import envoy.data.LoginCredentials;
 import envoy.event.HandshakeRejection;
@@ -27,7 +27,7 @@ import envoy.client.util.IconUtil;
  * @author Maximilian Käfer
  * @since Envoy Client v0.1-beta
  */
-public final class LoginScene implements EventListener {
+public final class LoginScene {
 
 	@FXML
 	private TextField userTextField;

client/src/main/java/envoy/client/ui/settings/GeneralSettingsPane.java

@@ -2,7 +2,7 @@ package envoy.client.ui.settings;
 
 import javafx.scene.control.*;
 
-import dev.kske.eventbus.EventBus;
+import dev.kske.eventbus.core.EventBus;
 
 import envoy.data.User.UserStatus;
 

client/src/main/java/envoy/client/ui/settings/UserSettingsPane.java

@@ -13,14 +13,15 @@ import javafx.scene.image.*;
 import javafx.scene.input.InputEvent;
 import javafx.scene.layout.HBox;
 import javafx.stage.FileChooser;
+import javafx.util.Duration;
 
-import dev.kske.eventbus.EventBus;
+import dev.kske.eventbus.core.EventBus;
 
 import envoy.event.*;
 import envoy.util.*;
 
 import envoy.client.ui.control.ProfilePicImageView;
-import envoy.client.util.IconUtil;
+import envoy.client.util.*;
 
 /**
  * @author Leon Hofmeister
@@ -38,6 +39,7 @@ public final class UserSettingsPane extends OnlineOnlySettingsPane {
 	private final PasswordField	newPasswordField		= new PasswordField();
 	private final PasswordField	repeatNewPasswordField	= new PasswordField();
 	private final Button		saveButton				= new Button("Save");
+	private final Button		deleteAccountButton		= new Button("Delete Account (Locally)");
 
 	private static final EventBus	eventBus	= EventBus.getInstance();
 	private static final Logger		logger		= EnvoyLog.getLogger(UserSettingsPane.class);
@@ -112,16 +114,19 @@ public final class UserSettingsPane extends OnlineOnlySettingsPane {
 
 		final PasswordField[]					passwordFields	=
 			{ currentPasswordField, newPasswordField, repeatNewPasswordField };
-		final EventHandler<? super InputEvent>	passwordEntered	= e -> {
-																	newPassword		=
-																		newPasswordField.getText();
-																	validPassword	= newPassword
-																		.equals(
-																			repeatNewPasswordField
-																				.getText())
-																		&& !newPasswordField
-																			.getText().isBlank();
-																};
+		final EventHandler<? super InputEvent>	passwordEntered	=
+			e -> {
+																		newPassword	=
+																			newPasswordField
+																				.getText();
+																		validPassword =
+																			newPassword.equals(
+																				repeatNewPasswordField
+																					.getText())
+																				&& !newPasswordField
+																					.getText()
+																					.isBlank();
+																	};
 		newPasswordField.setOnInputMethodTextChanged(passwordEntered);
 		newPasswordField.setOnKeyTyped(passwordEntered);
 		repeatNewPasswordField.setOnInputMethodTextChanged(passwordEntered);
@@ -137,9 +142,21 @@ public final class UserSettingsPane extends OnlineOnlySettingsPane {
 
 		// Displaying the save button
 		saveButton
-			.setOnAction(e -> save(client.getSender().getID(), currentPasswordField.getText()));
+			.setOnAction(e -> save(currentPasswordField.getText()));
 		saveButton.setAlignment(Pos.BOTTOM_RIGHT);
 		getChildren().add(saveButton);
+
+		// Displaying the delete account button
+		deleteAccountButton.setAlignment(Pos.BASELINE_CENTER);
+		deleteAccountButton.setOnAction(e -> UserUtil.deleteAccount());
+		deleteAccountButton.setText("Delete Account (locally)");
+		deleteAccountButton.setPrefHeight(25);
+		deleteAccountButton.getStyleClass().clear();
+		deleteAccountButton.getStyleClass().add("danger-button");
+		final var tooltip = new Tooltip("Remote deletion is currently unsupported.");
+		tooltip.setShowDelay(Duration.millis(100));
+		deleteAccountButton.setTooltip(tooltip);
+		getChildren().add(deleteAccountButton);
 	}
 
 	/**
@@ -148,11 +165,11 @@ public final class UserSettingsPane extends OnlineOnlySettingsPane {
 	 * @param username the new username
 	 * @since Envoy Client v0.2-beta
 	 */
-	private void save(long userID, String oldPassword) {
+	private void save(String oldPassword) {
 
 		// The profile pic was changed
 		if (profilePicChanged) {
-			final var profilePicChangeEvent = new ProfilePicChange(currentImageBytes, userID);
+			final var profilePicChangeEvent = new ProfilePicChange(currentImageBytes);
 			eventBus.dispatch(profilePicChangeEvent);
 			client.send(profilePicChangeEvent);
 			logger.log(Level.INFO, "The user just changed his profile pic.");
@@ -161,7 +178,7 @@ public final class UserSettingsPane extends OnlineOnlySettingsPane {
 		// The username was changed
 		final var validContactName = Bounds.isValidContactName(newUsername);
 		if (usernameChanged && validContactName) {
-			final var nameChangeEvent = new NameChange(userID, newUsername);
+			final var nameChangeEvent = new NameChange(client.getSender().getID(), newUsername);
 			eventBus.dispatch(nameChangeEvent);
 			client.send(nameChangeEvent);
 			logger.log(Level.INFO, "The user just changed his name to " + newUsername + ".");
@@ -178,7 +195,7 @@ public final class UserSettingsPane extends OnlineOnlySettingsPane {
 
 		// The password was changed
 		if (validPassword) {
-			client.send(new PasswordChangeRequest(newPassword, oldPassword, userID));
+			client.send(new PasswordChangeRequest(newPassword, oldPassword));
 			logger.log(Level.INFO, "The user just tried to change his password!");
 		} else if (!(validPassword || newPassword.isBlank())) {
 			final var alert = new Alert(AlertType.ERROR);

client/src/main/java/envoy/client/util/MessageUtil.java

@@ -7,7 +7,7 @@ import java.util.logging.*;
 
 import javafx.stage.FileChooser;
 
-import dev.kske.eventbus.EventBus;
+import dev.kske.eventbus.core.EventBus;
 
 import envoy.data.Message;
 import envoy.util.EnvoyLog;

client/src/main/java/envoy/client/util/UserUtil.java

@@ -2,10 +2,10 @@ package envoy.client.util;
 
 import java.util.logging.*;
 
-import javafx.scene.control.Alert;
+import javafx.scene.control.*;
 import javafx.scene.control.Alert.AlertType;
 
-import dev.kske.eventbus.EventBus;
+import dev.kske.eventbus.core.EventBus;
 
 import envoy.data.*;
 import envoy.data.User.UserStatus;
@@ -16,7 +16,7 @@ import envoy.util.EnvoyLog;
 import envoy.client.data.Context;
 import envoy.client.event.*;
 import envoy.client.helper.*;
-import envoy.client.ui.SceneContext.SceneInfo;
+import envoy.client.ui.SceneInfo;
 import envoy.client.ui.controller.ChatScene;
 
 /**
@@ -121,4 +121,35 @@ public final class UserUtil {
 			});
 		}
 	}
+
+	/**
+	 * Deletes anything pointing to this user, independent of client or server. Will do nothing if
+	 * the client is currently offline.
+	 *
+	 * @since Envoy Client v0.3-beta
+	 */
+	public static void deleteAccount() {
+
+		// Show the first wall of defense, if not disabled by the user
+		final var outerAlert = new Alert(AlertType.CONFIRMATION);
+		outerAlert.setContentText(
+			"Are you sure you want to delete your account entirely? This action can seriously not be undone.");
+		outerAlert.setTitle("Delete Account?");
+		AlertHelper.confirmAction(outerAlert, () -> {
+
+			// Show the final wall of defense in every case
+			final var lastAlert = new Alert(AlertType.WARNING,
+				"Do you REALLY want to delete your account? Last Warning. Proceed?",
+				ButtonType.CANCEL, ButtonType.OK);
+			lastAlert.setTitle("Delete Account?");
+			lastAlert.showAndWait().filter(ButtonType.OK::equals).ifPresent(b2 -> {
+
+				// Delete the account
+				// TODO: Notify server of account deletion
+				context.getLocalDB().delete();
+				logger.log(Level.INFO, "The user just deleted his account. Goodbye.");
+				ShutdownHelper.exit(true);
+			});
+		});
+	}
 }

client/src/main/java/module-info.java

@@ -16,12 +16,13 @@ module envoy.client {
 	requires javafx.fxml;
 	requires javafx.base;
 	requires javafx.graphics;
+	requires dev.kske.eventbus.core;
 
-	opens envoy.client.ui to javafx.graphics, javafx.fxml, dev.kske.eventbus;
-	opens envoy.client.ui.controller to javafx.graphics, javafx.fxml, envoy.client.util, dev.kske.eventbus;
-	opens envoy.client.ui.chatscene to javafx.graphics, javafx.fxml, envoy.client.util, dev.kske.eventbus;
+	opens envoy.client.ui to javafx.graphics, javafx.fxml, dev.kske.eventbus.core;
+	opens envoy.client.ui.controller to javafx.graphics, javafx.fxml, envoy.client.util, dev.kske.eventbus.core;
+	opens envoy.client.ui.chatscene to javafx.graphics, javafx.fxml, envoy.client.util, dev.kske.eventbus.core;
 	opens envoy.client.ui.control to javafx.graphics, javafx.fxml;
 	opens envoy.client.ui.settings to envoy.client.util;
-	opens envoy.client.net to dev.kske.eventbus;
-	opens envoy.client.data to dev.kske.eventbus;
+	opens envoy.client.net to dev.kske.eventbus.core;
+	opens envoy.client.data to dev.kske.eventbus.core;
 }

client/src/main/resources/css/base.css

@@ -70,6 +70,17 @@
 	-fx-text-fill: gray;
 }
 
+.danger-button {
+	-fx-background-color: red;
+	-fx-text-fill: white;
+	-fx-background-radius: 0.2em;
+}
+
+.danger-button:hover {
+	-fx-scale-x: 1.05;
+	-fx-scale-y: 1.05;
+}
+
 .received-message {
 	-fx-alignment: center-left;
 	-fx-background-radius: 1.3em;

client/src/main/resources/css/light.css

@@ -30,6 +30,10 @@
 	-fx-background-color: black;
 }
 
+.tooltip {
+	-fx-text-fill: black;
+}
+
 #login-input-field {
 	-fx-border-color: black;
 }

client/src/main/resources/fxml/ChatScene.fxml

@@ -24,8 +24,8 @@
 
 <GridPane maxHeight="-Infinity" maxWidth="-Infinity"
 	minHeight="400.0" minWidth="500.0"
-	prefHeight="${screen.visualBounds.height}"
 	prefWidth="${screen.visualBounds.width}"
+	prefHeight="${screen.visualBounds.height}"
 	xmlns="http://javafx.com/javafx/11.0.1"
 	xmlns:fx="http://javafx.com/fxml/1"
 	fx:controller="envoy.client.ui.controller.ChatScene">
@@ -57,8 +57,7 @@
 					<content>
 						<AnchorPane minHeight="0.0" minWidth="0.0">
 							<children>
-								<VBox prefHeight="3000.0"
-									prefWidth="316.0">
+								<VBox prefHeight="3000.0" prefWidth="316.0">
 									<children>
 										<VBox id="search-panel" maxHeight="-Infinity"
 											minHeight="-Infinity" prefHeight="80.0" prefWidth="316.0">
@@ -156,8 +155,7 @@
 						<Insets left="15.0" top="5.0" right="10.0" />
 					</HBox.margin>
 				</ImageView>
-				<Region id="transparent-background"
-					HBox.hgrow="ALWAYS" />
+				<Region id="transparent-background" HBox.hgrow="ALWAYS" />
 				<Button fx:id="settingsButton" mnemonicParsing="false"
 					onAction="#settingsButtonClicked" prefHeight="30.0"
 					prefWidth="30.0" alignment="CENTER_RIGHT">
@@ -165,7 +163,7 @@
 						<Insets bottom="5.0" left="5.0" right="5.0" top="5.0" />
 					</padding>
 					<HBox.margin>
-						<Insets bottom="35.0" left="5.0" top="35.0" right="10.0"/>
+						<Insets bottom="35.0" left="5.0" top="35.0" right="10.0" />
 					</HBox.margin>
 				</Button>
 			</children>

client/src/main/resources/fxml/SettingsScene.fxml

@@ -7,11 +7,16 @@
 <?import javafx.scene.layout.HBox?>
 <?import javafx.scene.layout.VBox?>
 
-<VBox alignment="TOP_RIGHT" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="envoy.client.ui.controller.SettingsScene">
+<VBox alignment="TOP_RIGHT" maxHeight="-Infinity" minHeight="400.0"
+	minWidth="500.0" xmlns="http://javafx.com/javafx/11.0.1"
+	xmlns:fx="http://javafx.com/fxml/1"
+	fx:controller="envoy.client.ui.controller.SettingsScene">
 	<children>
 		<HBox prefHeight="389.0" prefWidth="600.0">
 			<children>
-				<ListView id="message-list" fx:id="settingsList" onMouseClicked="#settingsListClicked" prefHeight="200.0" prefWidth="200.0">
+				<ListView id="message-list" fx:id="settingsList"
+					onMouseClicked="#settingsListClicked" prefHeight="200.0"
+					prefWidth="200.0">
 					<opaqueInsets>
 						<Insets bottom="5.0" left="5.0" right="5.0" top="5.0" />
 					</opaqueInsets>
@@ -22,7 +27,8 @@
 						<Insets bottom="5.0" left="5.0" right="5.0" top="5.0" />
 					</padding>
 				</ListView>
-				<TitledPane fx:id="titledPane" collapsible="false" prefHeight="400.0" prefWidth="400.0">
+				<TitledPane fx:id="titledPane" collapsible="false"
+					prefHeight="400.0" prefWidth="400.0">
 					<HBox.margin>
 						<Insets bottom="10.0" left="5.0" right="10.0" top="10.0" />
 					</HBox.margin>
@@ -32,7 +38,8 @@
 				</TitledPane>
 			</children>
 		</HBox>
-		<Button defaultButton="true" mnemonicParsing="true" onMouseClicked="#backButtonClicked" text="_Back">
+		<Button defaultButton="true" mnemonicParsing="true"
+			onMouseClicked="#backButtonClicked" text="_Back">
 			<opaqueInsets>
 				<Insets />
 			</opaqueInsets>

common/pom.xml

@@ -12,18 +12,11 @@
 		<version>0.2-beta</version>
 	</parent>
 
-	<repositories>
-		<repository>
-			<id>kske-repo</id>
-			<url>https://kske.dev/maven-repo</url>
-		</repository>
-	</repositories>
-
 	<dependencies>
 		<dependency>
 			<groupId>dev.kske</groupId>
-			<artifactId>event-bus</artifactId>
-			<version>0.0.4</version>
+			<artifactId>event-bus-core</artifactId>
+			<version>1.0.0</version>
 		</dependency>
 		<dependency>
 			<groupId>org.junit.jupiter</groupId>

common/src/main/java/envoy/data/Attachment.java

@@ -1,6 +1,7 @@
 package envoy.data;
 
 import java.io.Serializable;
+import java.util.Objects;
 
 /**
  * This interface should be used for any type supposed to be a {@link Message} attachment (i.e.
@@ -63,9 +64,9 @@ public final class Attachment implements Serializable {
 	 * @since Envoy Common v0.1-beta
 	 */
 	public Attachment(byte[] data, String name, AttachmentType type) {
-		this.data	= data;
-		this.name	= name;
-		this.type	= type;
+		this.data	= Objects.requireNonNull(data);
+		this.name	= Objects.requireNonNull(name);
+		this.type	= Objects.requireNonNull(type);
 	}
 
 	/**

common/src/main/java/envoy/data/Contact.java

@@ -29,8 +29,8 @@ public abstract class Contact implements Serializable {
 	 */
 	public Contact(long id, String name, Set<? extends Contact> contacts) {
 		this.id			= id;
-		this.name		= name;
-		this.contacts	= contacts;
+		this.name		= Objects.requireNonNull(name);
+		this.contacts	= contacts == null ? new HashSet<>() : contacts;
 	}
 
 	/**

common/src/main/java/envoy/data/GroupMessage.java

@@ -38,7 +38,8 @@ public final class GroupMessage extends Message {
 		Map<Long, MessageStatus> memberStatuses) {
 		super(id, senderID, groupID, creationDate, receivedDate, readDate, text, attachment, status,
 			forwarded);
-		this.memberStatuses = memberStatuses;
+		this.memberStatuses =
+			memberStatuses == null ? new HashMap<>() : memberStatuses;
 	}
 
 	/**

common/src/main/java/envoy/data/IDGenerator.java

@@ -2,15 +2,13 @@ package envoy.data;
 
 import java.io.Serializable;
 
-import dev.kske.eventbus.IEvent;
-
 /**
  * Generates increasing IDs between two numbers.
  *
  * @author Kai S. K. Engelbart
  * @since Envoy Common v0.2-alpha
  */
-public final class IDGenerator implements IEvent, Serializable {
+public final class IDGenerator implements Serializable {
 
 	private final long	end;
 	private long		current;

common/src/main/java/envoy/data/LoginCredentials.java

@@ -2,6 +2,7 @@ package envoy.data;
 
 import java.io.Serializable;
 import java.time.Instant;
+import java.util.Objects;
 
 /**
  * Contains a {@link User}'s login / registration information as well as the client version.
@@ -20,15 +21,14 @@ public final class LoginCredentials implements Serializable {
 	private static final long serialVersionUID = 4;
 
 	private LoginCredentials(String identifier, String password, boolean registration,
-		boolean token, boolean requestToken, String clientVersion,
-		Instant lastSync) {
-		this.identifier		= identifier;
-		this.password		= password;
+		boolean token, boolean requestToken, String clientVersion, Instant lastSync) {
+		this.identifier		= Objects.requireNonNull(identifier);
+		this.password		= Objects.requireNonNull(password);
 		this.registration	= registration;
 		this.token			= token;
 		this.requestToken	= requestToken;
-		this.clientVersion	= clientVersion;
-		this.lastSync		= lastSync;
+		this.clientVersion	= Objects.requireNonNull(clientVersion);
+		this.lastSync		= lastSync == null ? Instant.EPOCH : lastSync;
 	}
 
 	/**
@@ -75,7 +75,8 @@ public final class LoginCredentials implements Serializable {
 	 * @since Envoy Common v0.2-beta
 	 */
 	public static LoginCredentials registration(String identifier, String password,
-		boolean requestToken, String clientVersion, Instant lastSync) {
+		boolean requestToken,
+		String clientVersion, Instant lastSync) {
 		return new LoginCredentials(identifier, password, true, false, requestToken, clientVersion,
 			lastSync);
 	}

common/src/main/java/envoy/data/Message.java

@@ -2,8 +2,7 @@ package envoy.data;
 
 import java.io.Serializable;
 import java.time.Instant;
-
-import dev.kske.eventbus.IEvent;
+import java.util.Objects;
 
 /**
  * Represents a unique message with a unique, numeric ID. Further metadata includes the sender and
@@ -13,7 +12,7 @@ import dev.kske.eventbus.IEvent;
  * @author Leon Hofmeister
  * @since Envoy Common v0.2-alpha
  */
-public class Message implements Serializable, IEvent {
+public class Message implements Serializable {
 
 	/**
 	 * This enumeration defines all possible statuses a {link Message} can have.
@@ -80,9 +79,9 @@ public class Message implements Serializable, IEvent {
 		this.creationDate	= creationDate;
 		this.receivedDate	= receivedDate;
 		this.readDate		= readDate;
-		this.text			= text;
+		this.text			= text == null ? "" : text;
 		this.attachment		= attachment;
-		this.status			= status;
+		this.status			= Objects.requireNonNull(status);
 		this.forwarded		= forwarded;
 	}
 

common/src/main/java/envoy/data/User.java

@@ -86,7 +86,7 @@ public final class User extends Contact {
 	 */
 	public User(long id, String name, UserStatus status, Set<Contact> contacts) {
 		super(id, name, contacts);
-		this.status = status;
+		this.status = Objects.requireNonNull(status);
 	}
 
 	@Override

common/src/main/java/envoy/event/Event.java

@@ -1,26 +1,33 @@
 package envoy.event;
 
 import java.io.Serializable;
-
-import dev.kske.eventbus.IEvent;
+import java.util.Objects;
 
 /**
- * This class serves as a convenience base class for all events. It implements the {@link IEvent}
- * interface and provides a generic value. For events without a value there also is
- * {@link envoy.event.Event.Valueless}.
+ * This class serves as a convenience base class for all events. It provides a generic value. For
+ * events without a value there also is {@link envoy.event.Event.Valueless}.
  *
  * @author Kai S. K. Engelbart
  * @param <T> the type of the Event
  * @since Envoy v0.2-alpha
  */
-public abstract class Event<T> implements IEvent, Serializable {
+public abstract class Event<T> implements Serializable {
 
 	protected final T value;
 
 	private static final long serialVersionUID = 0L;
 
 	protected Event(T value) {
-		this.value = value;
+		this(value, false);
+	}
+
+	/**
+	 * This constructor is reserved for {@link Valueless} events. No other event should contain null
+	 * values. Only use if really necessary. Using this constructor with {@code true} implies that
+	 * the user has to manually check if the value of the event is null.
+	 */
+	protected Event(T value, boolean canBeNull) {
+		this.value = canBeNull ? value : Objects.requireNonNull(value);
 	}
 
 	/**
@@ -46,7 +53,7 @@ public abstract class Event<T> implements IEvent, Serializable {
 		private static final long serialVersionUID = 0L;
 
 		protected Valueless() {
-			super(null);
+			super(null, true);
 		}
 
 		@Override

common/src/main/java/envoy/event/GroupCreationResult.java

@@ -20,7 +20,7 @@ public class GroupCreationResult extends Event<Group> {
 	 * @since Envoy Common v0.2-beta
 	 */
 	public GroupCreationResult() {
-		super(null);
+		super(null, true);
 	}
 
 	/**

common/src/main/java/envoy/event/GroupMessageStatusChange.java

@@ -30,7 +30,7 @@ public final class GroupMessageStatusChange extends MessageStatusChange {
 	}
 
 	/**
-	 * @return the memberID which the user who sends this event has
+	 * @return the ID of the sender of this event
 	 * @since Envoy Common v0.1-beta
 	 */
 	public long getMemberID() { return memberID; }

common/src/main/java/envoy/event/GroupResize.java

@@ -2,6 +2,8 @@ package envoy.event;
 
 import static envoy.event.ElementOperation.*;
 
+import java.util.Objects;
+
 import envoy.data.*;
 
 /**
@@ -30,7 +32,7 @@ public final class GroupResize extends Event<User> {
 	 */
 	public GroupResize(User user, Group group, ElementOperation operation) {
 		super(user);
-		this.operation = operation;
+		this.operation = Objects.requireNonNull(operation);
 		final var contained = group.getContacts().contains(user);
 		if (contained && operation.equals(ADD))
 			throw new IllegalArgumentException(String.format("Cannot add %s to %s!", user, group));

common/src/main/java/envoy/event/IsTyping.java

@@ -8,8 +8,6 @@ package envoy.event;
  */
 public final class IsTyping extends Event<Long> {
 
-	private final long destinationID;
-
 	private static final long serialVersionUID = 1L;
 
 	/**
@@ -22,20 +20,13 @@ public final class IsTyping extends Event<Long> {
 	public static final int millisecondsActive = 3500;
 
 	/**
-	 * Creates a new {@code IsTyping} event with originator and recipient.
+	 * Creates a new {@code IsTyping}. The client will only send the contact that should receive
+	 * this event. The server will send the id of the contact who sent this event.
 	 *
-	 * @param sourceID      the ID of the originator
-	 * @param destinationID the ID of the contact the user wrote to
+	 * @param id the ID of the recipient (client)/ originator(server)
 	 * @since Envoy Common v0.2-beta
 	 */
-	public IsTyping(Long sourceID, long destinationID) {
-		super(sourceID);
-		this.destinationID = destinationID;
+	public IsTyping(long id) {
+		super(id);
 	}
-
-	/**
-	 * @return the ID of the contact in whose chat the user typed something
-	 * @since Envoy Common v0.2-beta
-	 */
-	public long getDestinationID() { return destinationID; }
 }

common/src/main/java/envoy/event/IssueProposal.java

@@ -23,7 +23,7 @@ public final class IssueProposal extends Event<String> {
 	 */
 	public IssueProposal(String title, String description, boolean isBug) {
 		super(escape(title));
-		this.description	= sanitizeDescription(description);
+		this.description	= description == null ? "" : sanitizeDescription(description);
 		bug					= isBug;
 	}
 
@@ -37,8 +37,8 @@ public final class IssueProposal extends Event<String> {
 	 */
 	public IssueProposal(String title, String description, String user, boolean isBug) {
 		super(escape(title));
-		this.description	=
-			sanitizeDescription(description) + String.format("<br>Submitted by user %s.", user);
+		this.description	= description == null ? ""
+			: sanitizeDescription(description) + String.format("<br>Submitted by user %s.", user);
 		bug					= isBug;
 	}
 

common/src/main/java/envoy/event/MessageStatusChange.java

@@ -1,6 +1,7 @@
 package envoy.event;
 
 import java.time.Instant;
+import java.util.Objects;
 
 import envoy.data.Message;
 
@@ -26,7 +27,7 @@ public class MessageStatusChange extends Event<Message.MessageStatus> {
 	public MessageStatusChange(long id, Message.MessageStatus status, Instant date) {
 		super(status);
 		this.id		= id;
-		this.date	= date;
+		this.date	= Objects.requireNonNull(date);
 	}
 
 	/**

common/src/main/java/envoy/event/PasswordChangeRequest.java

@@ -1,6 +1,6 @@
 package envoy.event;
 
-import envoy.data.Contact;
+import java.util.Objects;
 
 /**
  * @author Leon Hofmeister
@@ -8,29 +8,20 @@ import envoy.data.Contact;
  */
 public final class PasswordChangeRequest extends Event<String> {
 
-	private final long		id;
-	private final String	oldPassword;
+	private final String oldPassword;
 
 	private static final long serialVersionUID = 0L;
 
 	/**
 	 * @param newPassword the new password of that user
 	 * @param oldPassword the old password of that user
-	 * @param userID      the ID of the user who wants to change his password
 	 * @since Envoy Common v0.2-beta
 	 */
-	public PasswordChangeRequest(String newPassword, String oldPassword, long userID) {
+	public PasswordChangeRequest(String newPassword, String oldPassword) {
 		super(newPassword);
-		this.oldPassword	= oldPassword;
-		id					= userID;
+		this.oldPassword = Objects.requireNonNull(oldPassword);
 	}
 
-	/**
-	 * @return the ID of the {@link Contact} this event is related to
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public long getID() { return id; }
-
 	/**
 	 * @return the old password of the underlying user
 	 * @since Envoy Common v0.2-beta
@@ -39,6 +30,6 @@ public final class PasswordChangeRequest extends Event<String> {
 
 	@Override
 	public String toString() {
-		return "PasswordChangeRequest[id=" + id + "]";
+		return "PasswordChangeRequest[]";
 	}
 }

common/src/main/java/envoy/event/ProfilePicChange.java

@@ -6,23 +6,13 @@ package envoy.event;
  */
 public final class ProfilePicChange extends Event<byte[]> {
 
-	private final long id;
-
 	private static final long serialVersionUID = 0L;
 
 	/**
-	 * @param value  the byte[] of the new image
-	 * @param userID the ID of the user who changed his profile pic
+	 * @param value the byte[] of the new image
 	 * @since Envoy Common v0.2-beta
 	 */
-	public ProfilePicChange(byte[] value, long userID) {
+	public ProfilePicChange(byte[] value) {
 		super(value);
-		id = userID;
 	}
-
-	/**
-	 * @return the ID of the user changing his profile pic
-	 * @since Envoy Common v0.2-beta
-	 */
-	public long getId() { return id; }
 }

common/src/main/java/envoy/event/contact/UserOperation.java

@@ -1,5 +1,7 @@
 package envoy.event.contact;
 
+import java.util.Objects;
+
 import envoy.data.User;
 import envoy.event.*;
 
@@ -24,7 +26,7 @@ public final class UserOperation extends Event<User> {
 	 */
 	public UserOperation(User contact, ElementOperation operationType) {
 		super(contact);
-		this.operationType = operationType;
+		this.operationType = Objects.requireNonNull(operationType);
 	}
 
 	/**

common/src/main/java/module-info.java

@@ -16,5 +16,5 @@ module envoy.common {
 	exports envoy.event.contact;
 
 	requires transitive java.logging;
-	requires transitive dev.kske.eventbus;
+	requires transitive dev.kske.eventbus.core;
 }

common/src/test/java/envoy/data/UserTest.java

@@ -18,10 +18,10 @@ import envoy.util.SerializationUtils;
  * @author Leon Hofmeister
  * @since Envoy Common v0.1-beta
  */
-class UserTest {
+public class UserTest {
 
 	@Test
-	void test() throws IOException, ClassNotFoundException {
+	public void test() throws IOException, ClassNotFoundException {
 		User	user2				= new User(2, "kai");
 		User	user3				= new User(3, "ai");
 		User	user4				= new User(4, "ki", Set.of(user2, user3));

doc/datamodel.uxf

@@ -1,285 +0,0 @@
-<?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<diagram program="umlet" version="14.3.0">
-  <zoom_level>10</zoom_level>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>50</x>
-      <y>60</y>
-      <w>210</w>
-      <h>240</h>
-    </coordinates>
-    <panel_attributes>DBUser
---
-id: Long
-nick: String
-name: String
-chats: Set&lt;DBChat&gt;
-status: UserStatus
-created: Instant
-lastSeen: Instant
-deleted: Boolean
-avatar: DBAvatar
-passwordHash: String
-authToken: String
-authTokenExpiration: Instant
---
-+toCommon(): User</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>380</x>
-      <y>330</y>
-      <w>290</w>
-      <h>160</h>
-    </coordinates>
-    <panel_attributes>DBMessage
---
-id: Long
-sender: DBUser
-forwarded: Boolean
-deleted: Boolean
-statuses: Map&lt;DBUser, DBMessageStatus&gt;
-text: String
-attachment: DBAttachment
---
-+toCommon(): Message</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>770</x>
-      <y>320</y>
-      <w>210</w>
-      <h>100</h>
-    </coordinates>
-    <panel_attributes>DBMessageStatus
---
-id: Long
-status: MessageStatus
-timestamp: Instant
---
-+toCommon(): MessageStatus</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>770</x>
-      <y>440</y>
-      <w>180</w>
-      <h>120</h>
-    </coordinates>
-    <panel_attributes>DBAttachment
---
-id: Long
-name: String
-type: AttachmentType
-url: String
---
-+toCommon(): Attachment</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>510</x>
-      <y>70</y>
-      <w>200</w>
-      <h>180</h>
-    </coordinates>
-    <panel_attributes>DBChat
---
-id: Long
-name: String
-members: Set&lt;DBUser&gt;
-admins: Set&lt;DBUser&gt;
-messages: Set&lt;DBMessage&gt;
-avatar: DBAvatar
-allowJoining: Boolean
-allowAttachments: Boolean
---
-+toCommon(): Chat</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>250</x>
-      <y>100</y>
-      <w>280</w>
-      <h>40</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;-&gt;
-m1=0..n
-m2=0..n</panel_attributes>
-    <additional_attributes>10.0;10.0;260.0;10.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>600</x>
-      <y>240</y>
-      <w>50</w>
-      <h>110</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;
-m2=0..n</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;90.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>660</x>
-      <y>360</y>
-      <w>130</w>
-      <h>40</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;
-m2=0..n</panel_attributes>
-    <additional_attributes>10.0;10.0;110.0;10.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>660</x>
-      <y>470</y>
-      <w>130</w>
-      <h>40</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;
-m2=0..1</panel_attributes>
-    <additional_attributes>10.0;10.0;110.0;10.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>140</x>
-      <y>290</y>
-      <w>260</w>
-      <h>150</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;-
-m1=0..n</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;130.0;240.0;130.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLPackage</id>
-    <coordinates>
-      <x>10</x>
-      <y>0</y>
-      <w>1010</w>
-      <h>590</h>
-    </coordinates>
-    <panel_attributes>envoy.server.data
---
-bg=#CCCCCC</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>90</x>
-      <y>680</y>
-      <w>170</w>
-      <h>130</h>
-    </coordinates>
-    <panel_attributes>User
---
-id: long
-nick: String
-name: String
-status: UserStatus
-created: Instant
-deleted: boolean</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>340</x>
-      <y>680</y>
-      <w>190</w>
-      <h>100</h>
-    </coordinates>
-    <panel_attributes>UserStatus
---
-_+ONLINE: UserStatus_
-_+AWAY: UserStatus_
-_+BUSY: UserStatus_
-_+OFFLINE: UserStatus_</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>250</x>
-      <y>730</y>
-      <w>110</w>
-      <h>30</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;-</panel_attributes>
-    <additional_attributes>90.0;10.0;10.0;10.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>340</x>
-      <y>150</y>
-      <w>100</w>
-      <h>80</h>
-    </coordinates>
-    <panel_attributes>DBAvatar
---
-id: Long
-edited: Instant
-url: String
-layer=1</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>250</x>
-      <y>190</y>
-      <w>110</w>
-      <h>40</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;-
-m1=0..1</panel_attributes>
-    <additional_attributes>90.0;10.0;10.0;10.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>430</x>
-      <y>190</y>
-      <w>100</w>
-      <h>40</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;-
-m1=0..1</panel_attributes>
-    <additional_attributes>10.0;10.0;80.0;10.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLClass</id>
-    <coordinates>
-      <x>610</x>
-      <y>680</y>
-      <w>180</w>
-      <h>130</h>
-    </coordinates>
-    <panel_attributes>Chat
---
-id: long
-name: String
-deceased: boolean
-members: Set&lt;User&gt;
-admins: Set&lt;User&gt;
-messages: List&lt;Message&gt;</panel_attributes>
-    <additional_attributes/>
-  </element>
-</diagram>

doc/handshake_sequence_uml.uxf

@@ -1,501 +0,0 @@
-<?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<diagram program="umlet" version="14.3.0">
-  <zoom_level>9</zoom_level>
-  <element>
-    <id>UMLActor</id>
-    <coordinates>
-      <x>72</x>
-      <y>540</y>
-      <w>54</w>
-      <h>99</h>
-    </coordinates>
-    <panel_attributes>Client1</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>2196</x>
-      <y>504</y>
-      <w>198</w>
-      <h>171</h>
-    </coordinates>
-    <panel_attributes>Database
-halign=center
-bg=orange
---</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>351</x>
-      <y>513</y>
-      <w>90</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>Main</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>531</x>
-      <y>513</y>
-      <w>90</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>Startup
-bg=orange</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>702</x>
-      <y>513</y>
-      <w>90</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>Client
-bg=yellow</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>873</x>
-      <y>513</y>
-      <w>90</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>LocalDB
-bg=pink</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>1548</x>
-      <y>522</y>
-      <w>189</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>LoginCredentialsProcessor
-bg=cyan</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>1809</x>
-      <y>522</y>
-      <w>135</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>PersistenceManager
-bg=gray</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>396</x>
-      <y>729</y>
-      <w>189</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-start javaFX app</panel_attributes>
-    <additional_attributes>190.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>387</x>
-      <y>720</y>
-      <w>18</w>
-      <h>54</h>
-    </coordinates>
-    <panel_attributes/>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>387</x>
-      <y>621</y>
-      <w>27</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;110.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>567</x>
-      <y>621</y>
-      <w>27</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;110.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>738</x>
-      <y>621</y>
-      <w>27</w>
-      <h>216</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;220.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>909</x>
-      <y>621</y>
-      <w>27</w>
-      <h>153</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;150.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>567</x>
-      <y>720</y>
-      <w>18</w>
-      <h>396</h>
-    </coordinates>
-    <panel_attributes>bg=orange</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>738</x>
-      <y>819</y>
-      <w>18</w>
-      <h>558</h>
-    </coordinates>
-    <panel_attributes>bg=yellow</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>909</x>
-      <y>756</y>
-      <w>18</w>
-      <h>621</h>
-    </coordinates>
-    <panel_attributes>bg=pink</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>576</x>
-      <y>756</y>
-      <w>351</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-initialize</panel_attributes>
-    <additional_attributes>370.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>1062</x>
-      <y>513</y>
-      <w>90</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>Receiver
-bg=red</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1098</x>
-      <y>621</y>
-      <w>27</w>
-      <h>270</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;280.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>1098</x>
-      <y>873</y>
-      <w>18</w>
-      <h>504</h>
-    </coordinates>
-    <panel_attributes>bg=red</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>576</x>
-      <y>1071</y>
-      <w>180</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-init receivers
-layer=0</panel_attributes>
-    <additional_attributes>180.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>576</x>
-      <y>828</y>
-      <w>180</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-perform handshake</panel_attributes>
-    <additional_attributes>180.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>747</x>
-      <y>873</y>
-      <w>369</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-init handhake receivers
-layer=0</panel_attributes>
-    <additional_attributes>390.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>747</x>
-      <y>1071</y>
-      <w>369</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-init permanent receivers
-layer=0</panel_attributes>
-    <additional_attributes>390.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1638</x>
-      <y>630</y>
-      <w>27</w>
-      <h>306</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;320.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>1638</x>
-      <y>918</y>
-      <w>18</w>
-      <h>558</h>
-    </coordinates>
-    <panel_attributes>bg=cyan</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>747</x>
-      <y>918</y>
-      <w>909</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-send login credentials
-layer=0</panel_attributes>
-    <additional_attributes>990.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1872</x>
-      <y>630</y>
-      <w>27</w>
-      <h>306</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;320.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>1872</x>
-      <y>918</y>
-      <w>18</w>
-      <h>558</h>
-    </coordinates>
-    <panel_attributes>bg=gray</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1881</x>
-      <y>918</y>
-      <w>423</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-use queries
-layer=0</panel_attributes>
-    <additional_attributes>450.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>2286</x>
-      <y>666</y>
-      <w>27</w>
-      <h>270</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;280.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>2286</x>
-      <y>918</y>
-      <w>18</w>
-      <h>558</h>
-    </coordinates>
-    <panel_attributes>bg=orange</panel_attributes>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1647</x>
-      <y>918</y>
-      <w>243</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=&lt;&lt;-
-aquire data
-layer=0</panel_attributes>
-    <additional_attributes>250.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1881</x>
-      <y>954</y>
-      <w>423</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;&gt;
-send query responses
-layer=0</panel_attributes>
-    <additional_attributes>450.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1647</x>
-      <y>954</y>
-      <w>243</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;&gt;
-send aquired data
-layer=0</panel_attributes>
-    <additional_attributes>250.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>1107</x>
-      <y>990</y>
-      <w>549</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;&gt;
-send user, chats, pending messages, etc.
-layer=0</panel_attributes>
-    <additional_attributes>590.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>918</x>
-      <y>990</y>
-      <w>198</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;&gt;
-store data
-layer=0</panel_attributes>
-    <additional_attributes>200.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>99</x>
-      <y>729</y>
-      <w>306</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;
-start app</panel_attributes>
-    <additional_attributes>10.0;20.0;320.0;20.0</additional_attributes>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>90</x>
-      <y>621</y>
-      <w>27</w>
-      <h>117</h>
-    </coordinates>
-    <panel_attributes>lt=.</panel_attributes>
-    <additional_attributes>10.0;10.0;10.0;110.0</additional_attributes>
-  </element>
-  <element>
-    <id>UMLGeneric</id>
-    <coordinates>
-      <x>90</x>
-      <y>720</y>
-      <w>18</w>
-      <h>54</h>
-    </coordinates>
-    <panel_attributes/>
-    <additional_attributes/>
-  </element>
-  <element>
-    <id>Relation</id>
-    <coordinates>
-      <x>747</x>
-      <y>1026</y>
-      <w>369</w>
-      <h>36</h>
-    </coordinates>
-    <panel_attributes>lt=-&gt;&gt;
-online
-layer=0</panel_attributes>
-    <additional_attributes>390.0;20.0;10.0;20.0</additional_attributes>
-  </element>
-</diagram>

pom.xml

@@ -28,6 +28,13 @@
 				</plugin>
 			</plugins>
 		</pluginManagement>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<version>3.0.0-M5</version>
+			</plugin>
+		</plugins>
 	</build>
 
 	<modules>

server/src/main/java/envoy/server/data/PersistenceManager.java

@@ -1,7 +1,7 @@
 package envoy.server.data;
 
 import java.time.Instant;
-import java.util.List;
+import java.util.*;
 import java.util.logging.Level;
 
 import javax.persistence.*;
@@ -121,8 +121,9 @@ public final class PersistenceManager {
 		transaction(() -> {
 
 			// Remove this contact from the contact list of his contacts
-			for (final var remainingContact : contact.getContacts())
+			for (final var remainingContact : contact.contacts)
 				remainingContact.getContacts().remove(contact);
+			contact.contacts.clear();
 		});
 		remove(contact);
 	}
@@ -223,6 +224,9 @@ public final class PersistenceManager {
 	 * @since Envoy Server Standalone v0.2-beta
 	 */
 	public List<Message> getPendingMessages(User user, Instant lastSync) {
+		if (user == null)
+			return new ArrayList<>();
+		lastSync = Objects.requireNonNullElse(lastSync, Instant.EPOCH);
 		return entityManager.createNamedQuery(Message.getPending).setParameter("user", user)
 			.setParameter("lastSeen", lastSync).getResultList();
 	}
@@ -236,6 +240,9 @@ public final class PersistenceManager {
 	 * @since Envoy Server Standalone v0.2-beta
 	 */
 	public List<GroupMessage> getPendingGroupMessages(User user, Instant lastSync) {
+		if (user == null)
+			return new ArrayList<>();
+		lastSync = Objects.requireNonNullElse(lastSync, Instant.EPOCH);
 		return entityManager.createNamedQuery(GroupMessage.getPendingGroupMsg)
 			.setParameter("userId", user.getID())
 			.setParameter("lastSeen", lastSync)
@@ -277,16 +284,18 @@ public final class PersistenceManager {
 	 * @since Envoy Server v0.3-beta
 	 */
 	public void addContactBidirectional(Contact contact1, Contact contact2) {
+		if (!(contact1 == null || contact2 == null)) {
 
-		// Add users to each others contact list
-		contact1.getContacts().add(contact2);
-		contact2.getContacts().add(contact1);
+			// Add users to each others contact list
+			contact1.getContacts().add(contact2);
+			contact2.getContacts().add(contact1);
 
-		// Synchronize changes with the database
-		transaction(() -> {
-			entityManager.merge(contact1);
-			entityManager.merge(contact2);
-		});
+			// Synchronize changes with the database
+			transaction(() -> {
+				entityManager.merge(contact1);
+				entityManager.merge(contact2);
+			});
+		}
 	}
 
 	/**
@@ -308,16 +317,18 @@ public final class PersistenceManager {
 	 * @since Envoy Server v0.3-beta
 	 */
 	public void removeContactBidirectional(Contact contact1, Contact contact2) {
+		if (!(contact1 == null || contact2 == null)) {
 
-		// Remove users from each others contact list
-		contact1.getContacts().remove(contact2);
-		contact2.getContacts().remove(contact1);
+			// Remove users from each others contact list
+			contact1.getContacts().remove(contact2);
+			contact2.getContacts().remove(contact1);
 
-		// Synchronize changes with the database
-		transaction(() -> {
-			entityManager.merge(contact1);
-			entityManager.merge(contact2);
-		});
+			// Synchronize changes with the database
+			transaction(() -> {
+				entityManager.merge(contact1);
+				entityManager.merge(contact2);
+			});
+		}
 	}
 
 	/**
@@ -331,15 +342,36 @@ public final class PersistenceManager {
 	}
 
 	private void persist(Object obj) {
-		transaction(() -> entityManager.persist(obj));
+		try {
+			transaction(() -> entityManager.persist(obj));
+		} catch (EntityExistsException e) {
+			if (transaction.isActive())
+				transaction.rollback();
+			EnvoyLog.getLogger(PersistenceManager.class).log(Level.WARNING,
+				String.format("Could not persist %s: entity exists already.", obj));
+		}
 	}
 
 	private void merge(Object obj) {
-		transaction(() -> entityManager.merge(obj));
+		try {
+			transaction(() -> entityManager.merge(obj));
+		} catch (IllegalArgumentException e) {
+			if (transaction.isActive())
+				transaction.rollback();
+			EnvoyLog.getLogger(PersistenceManager.class).log(Level.WARNING,
+				String.format("Could not merge %s: entity doesn't exist.", obj));
+		}
 	}
 
 	private void remove(Object obj) {
-		transaction(() -> entityManager.remove(obj));
+		try {
+			transaction(() -> entityManager.remove(obj));
+		} catch (IllegalArgumentException e) {
+			if (transaction.isActive())
+				transaction.rollback();
+			EnvoyLog.getLogger(PersistenceManager.class).log(Level.WARNING,
+				String.format("Could not remove %s: entity didn't exist (for the database).", obj));
+		}
 	}
 
 	/**

server/src/main/java/envoy/server/net/ConnectionManager.java

@@ -49,8 +49,10 @@ public final class ConnectionManager implements ISocketIdListener {
 			// Notify contacts of this users offline-going
 			final envoy.server.data.User user =
 				PersistenceManager.getInstance().getUserByID(getUserIDBySocketID(socketID));
-			user.setLastSeen(Instant.now());
-			UserStatusChangeProcessor.updateUserStatus(user, UserStatus.OFFLINE);
+			if (user != null) {
+				user.setLastSeen(Instant.now());
+				UserStatusChangeProcessor.updateUserStatus(user, UserStatus.OFFLINE);
+			}
 
 			// Remove the socket
 			sockets.entrySet().removeIf(e -> e.getValue() == socketID);

server/src/main/java/envoy/server/net/ObjectMessageProcessor.java

@@ -33,7 +33,6 @@ public final class ObjectMessageProcessor implements IMessageProcessor {
 		this.processors = processors;
 	}
 
-	@SuppressWarnings("unchecked")
 	@Override
 	public void process(Message message, WriteProxy writeProxy) {
 		try (ObjectInputStream in =
@@ -45,23 +44,34 @@ public final class ObjectMessageProcessor implements IMessageProcessor {
 				return;
 			}
 
-			logger.fine("Received " + obj);
+			logger.log(Level.INFO, "Received " + obj);
 
-			// Get processor and input class and process object
-			for (@SuppressWarnings("rawtypes")
-			ObjectProcessor p : processors) {
-				Class<?> c = (Class<?>) ((ParameterizedType) p.getClass().getGenericInterfaces()[0])
-					.getActualTypeArguments()[0];
-				if (c.equals(obj.getClass()))
-					try {
-						p.process(c.cast(obj), message.socketId, new ObjectWriteProxy(writeProxy));
-						break;
-					} catch (IOException e) {
-						logger.log(Level.SEVERE, "Exception during processor execution: ", e);
-					}
-			}
+			refer(message.socketId, writeProxy, obj);
 		} catch (IOException | ClassNotFoundException e) {
-			e.printStackTrace();
+			logger.log(Level.WARNING,
+				"An exception occurred when reading in an object: " + e);
+		}
+	}
+
+	/**
+	 * Executes the appropriate {@link ObjectProcessor} for the given input ({@code obj}), if any is
+	 * present.
+	 */
+	@SuppressWarnings("unchecked")
+	private void refer(long socketID, WriteProxy writeProxy, Object obj) {
+
+		// Get processor and input class and process object
+		for (@SuppressWarnings("rawtypes")
+		ObjectProcessor p : processors) {
+			Class<?> c = (Class<?>) ((ParameterizedType) p.getClass().getGenericInterfaces()[0])
+				.getActualTypeArguments()[0];
+			if (c.equals(obj.getClass()))
+				try {
+					p.process(c.cast(obj), socketID, new ObjectWriteProxy(writeProxy));
+					break;
+				} catch (IOException e) {
+					logger.log(Level.SEVERE, "Exception during processor execution: ", e);
+				}
 		}
 	}
 }

server/src/main/java/envoy/server/processors/GroupMessageProcessor.java

@@ -5,7 +5,7 @@ import static envoy.server.Startup.config;
 
 import java.time.Instant;
 import java.util.Collections;
-import java.util.logging.Logger;
+import java.util.logging.*;
 
 import javax.persistence.EntityExistsException;
 
@@ -15,6 +15,7 @@ import envoy.util.EnvoyLog;
 
 import envoy.server.data.PersistenceManager;
 import envoy.server.net.*;
+import envoy.server.util.UserAuthenticationUtil;
 
 /**
  * @author Maximilian Käfer
@@ -29,6 +30,15 @@ public final class GroupMessageProcessor implements ObjectProcessor<GroupMessage
 
 	@Override
 	public void process(GroupMessage groupMessage, long socketID, ObjectWriteProxy writeProxy) {
+
+		// Check whether the message has the expected parameters
+		if (!UserAuthenticationUtil.isExpectedUser(groupMessage.getSenderID(), socketID)
+			|| persistenceManager.getContactByID(groupMessage.getRecipientID()) == null) {
+			logger.log(Level.INFO,
+				"Received a group message with invalid parameters");
+			return;
+		}
+
 		groupMessage.nextStatus();
 
 		// Update statuses to SENT / RECEIVED depending on online status

server/src/main/java/envoy/server/processors/GroupMessageStatusChangeProcessor.java

@@ -12,6 +12,7 @@ import envoy.util.EnvoyLog;
 
 import envoy.server.data.*;
 import envoy.server.net.*;
+import envoy.server.util.UserAuthenticationUtil;
 
 /**
  * @author Maximilian Käfer
@@ -28,7 +29,17 @@ public final class GroupMessageStatusChangeProcessor
 	@Override
 	public void process(GroupMessageStatusChange statusChange, long socketID,
 		ObjectWriteProxy writeProxy) {
+
+		// Check whether the message has the expected parameters
+		if (!UserAuthenticationUtil.isExpectedUser(statusChange.getMemberID(), socketID)) {
+			logger.log(Level.INFO,
+				"Received a group message with invalid parameters");
+			return;
+		}
+		
 		GroupMessage gmsg = (GroupMessage) persistenceManager.getMessageByID(statusChange.getID());
+		if (gmsg == null)
+			return;
 
 		// Any other status than READ is not supposed to be sent to the server
 		if (statusChange.get() != MessageStatus.READ) {

server/src/main/java/envoy/server/processors/GroupResizeProcessor.java

@@ -24,6 +24,10 @@ public final class GroupResizeProcessor implements ObjectProcessor<GroupResize>
 		final var	group	= persistenceManager.getGroupByID(groupResize.getGroupID());
 		final var	sender	= persistenceManager.getUserByID(groupResize.get().getID());
 
+		// TODO: Inform the sender that this group has already been deleted
+		if (group == null)
+			return;
+
 		// Perform the desired operation
 		switch (groupResize.getOperation()) {
 			case ADD:

server/src/main/java/envoy/server/processors/IsTypingProcessor.java

@@ -23,10 +23,11 @@ public final class IsTypingProcessor implements ObjectProcessor<IsTyping> {
 		throws IOException {
 		final var contact = persistenceManager.getContactByID(event.get());
 		if (contact instanceof User) {
-			final var destinationID = event.getDestinationID();
-			if (connectionManager.isOnline(destinationID))
-				writeProxy.write(connectionManager.getSocketID(destinationID), event);
+			if (connectionManager.isOnline(event.get()))
+				writeProxy.write(connectionManager.getSocketID(event.get()),
+					new IsTyping(connectionManager.getUserIDBySocketID(socketID)));
 		} else
-			writeProxy.writeToOnlineContacts(contact.getContacts(), event);
+			writeProxy.writeToOnlineContacts(contact.getContacts(),
+				new IsTyping(connectionManager.getUserIDBySocketID(socketID)));
 	}
 }

server/src/main/java/envoy/server/processors/LoginCredentialProcessor.java

@@ -40,6 +40,7 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 		// Cache this write proxy for user-independent notifications
 		UserStatusChangeProcessor.setWriteProxy(writeProxy);
 
+		// Check for compatible versions
 		if (!VersionUtil.verifyCompatibility(credentials.getClientVersion())) {
 			logger.info("The client has the wrong version.");
 			writeProxy.write(socketID, new HandshakeRejection(WRONG_VERSION));
@@ -70,10 +71,10 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 						writeProxy.write(socketID, new HandshakeRejection(INVALID_TOKEN));
 						return;
 					}
-				} else
+				} else if (!PasswordUtil.validate(credentials.getPassword(),
+					user.getPasswordHash())) {
 
-				// Check the password hash
-				if (!PasswordUtil.validate(credentials.getPassword(), user.getPasswordHash())) {
+					// Check the password hash
 					logger.info(user + " has entered the wrong password.");
 					writeProxy.write(socketID, new HandshakeRejection(WRONG_PASSWORD_OR_USER));
 					return;
@@ -101,7 +102,8 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 				writeProxy.write(socketID, new HandshakeRejection(USERNAME_TAKEN));
 				return;
 			} catch (final NoResultException e) {
-				// Creation of a new user
+
+				// Create a new user
 				user = new User();
 				user.setName(credentials.getIdentifier());
 				user.setLastSeen(Instant.now());
@@ -123,7 +125,6 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 		// Process token request
 		if (credentials.requestToken()) {
 			String token;
-
 			if (user.getAuthToken() != null && user.getAuthTokenExpiration().isAfter(Instant.now()))
 
 				// Reuse existing token and delay expiration date
@@ -140,6 +141,14 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 			writeProxy.write(socketID, new NewAuthToken(token));
 		}
 
+		// Notify the user if a contact deletion has happened since he last logged in
+		if (user.getLatestContactDeletion().isAfter(user.getLastSeen()))
+			writeProxy.write(socketID, new ContactsChangedSinceLastLogin());
+
+		// Complete the handshake
+		writeProxy.write(socketID, user.toCommon());
+
+		// Send pending (group) messages and status changes
 		final var pendingMessages =
 			PersistenceManager.getInstance().getPendingMessages(user, credentials.getLastSync());
 		pendingMessages.removeIf(GroupMessage.class::isInstance);
@@ -164,8 +173,9 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 					writeProxy.write(connectionManager.getSocketID(msg.getSender().getID()),
 						new MessageStatusChange(msgCommon));
 				}
-			} else
+			} else {
 				writeProxy.write(socketID, new MessageStatusChange(msgCommon));
+			}
 		}
 
 		final List<GroupMessage> pendingGroupMessages = PersistenceManager.getInstance()
@@ -199,10 +209,11 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 					}
 
 					PersistenceManager.getInstance().updateMessage(gmsg);
-				} else
+				} else {
 
 					// Just send the message without updating if it was received in the past
 					writeProxy.write(socketID, gmsgCommon);
+				}
 			} else {
 
 				// Sending group message status changes
@@ -222,11 +233,5 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 					writeProxy.write(socketID, new MessageStatusChange(gmsgCommon));
 			}
 		}
-		// Notify the user if a contact deletion has happened since he last logged in
-		if (user.getLatestContactDeletion().isAfter(user.getLastSeen()))
-			writeProxy.write(socketID, new ContactsChangedSinceLastLogin());
-
-		// Complete the handshake
-		writeProxy.write(socketID, user.toCommon());
 	}
 }

server/src/main/java/envoy/server/processors/MessageProcessor.java

@@ -12,6 +12,7 @@ import envoy.util.EnvoyLog;
 
 import envoy.server.data.PersistenceManager;
 import envoy.server.net.*;
+import envoy.server.util.UserAuthenticationUtil;
 
 /**
  * This {@link ObjectProcessor} handles incoming {@link Message}s.
@@ -29,6 +30,15 @@ public final class MessageProcessor implements ObjectProcessor<Message> {
 
 	@Override
 	public void process(Message message, long socketID, ObjectWriteProxy writeProxy) {
+
+		// Check whether the message has the expected parameters
+		if (!UserAuthenticationUtil.isExpectedUser(message.getSenderID(), socketID)
+			|| persistenceManager.getContactByID(message.getRecipientID()) == null) {
+			logger.log(Level.INFO,
+				"Received a message with invalid parameters");
+			return;
+		}
+
 		message.nextStatus();
 
 		// Convert to server message

server/src/main/java/envoy/server/processors/MessageStatusChangeProcessor.java

@@ -32,6 +32,8 @@ public final class MessageStatusChangeProcessor implements ObjectProcessor<Messa
 		}
 
 		final var msg = persistenceManager.getMessageByID(statusChange.getID());
+		if (msg == null)
+			return;
 		msg.read();
 		persistenceManager.updateMessage(msg);
 

server/src/main/java/envoy/server/processors/PasswordChangeRequestProcessor.java

@@ -7,7 +7,7 @@ import envoy.event.*;
 import envoy.util.EnvoyLog;
 
 import envoy.server.data.PersistenceManager;
-import envoy.server.net.ObjectWriteProxy;
+import envoy.server.net.*;
 import envoy.server.util.PasswordUtil;
 
 /**
@@ -21,7 +21,8 @@ public final class PasswordChangeRequestProcessor
 	public void process(PasswordChangeRequest event, long socketID, ObjectWriteProxy writeProxy)
 		throws IOException {
 		final var	persistenceManager		= PersistenceManager.getInstance();
-		final var	user					= persistenceManager.getUserByID(event.getID());
+		final var	user					= persistenceManager
+			.getUserByID(ConnectionManager.getInstance().getUserIDBySocketID(socketID));
 		final var	logger					=
 			EnvoyLog.getLogger(PasswordChangeRequestProcessor.class);
 		final var	correctAuthentication	=

server/src/main/java/envoy/server/processors/UserOperationProcessor.java

@@ -22,10 +22,16 @@ public final class UserOperationProcessor implements ObjectProcessor<UserOperati
 	private static final PersistenceManager	persistenceManager	= PersistenceManager.getInstance();
 
 	@Override
-	public void process(UserOperation evt, long socketId, ObjectWriteProxy writeProxy) {
-		final long	userID		= ConnectionManager.getInstance().getUserIDBySocketID(socketId);
+	public void process(UserOperation evt, long socketID, ObjectWriteProxy writeProxy) {
+		final long	userID		= ConnectionManager.getInstance().getUserIDBySocketID(socketID);
 		final long	contactID	= evt.get().getID();
-		final var	sender		= persistenceManager.getUserByID(userID);
+		final var	recipient	= persistenceManager.getUserByID(contactID);
+
+		// TODO: Inform the sender if the requested contact has already been deleted
+		if (recipient == null)
+			return;
+
+		final var sender = persistenceManager.getUserByID(userID);
 		switch (evt.getOperationType()) {
 			case ADD:
 				logger.log(Level.FINE,
@@ -45,7 +51,7 @@ public final class UserOperationProcessor implements ObjectProcessor<UserOperati
 				sender.setLatestContactDeletion(Instant.now());
 
 				// Notify the removed contact on next startup(s) of this deletion
-				persistenceManager.getUserByID(contactID).setLatestContactDeletion(Instant.now());
+				recipient.setLatestContactDeletion(Instant.now());
 
 				// Notify the removed contact if online
 				if (connectionManager.isOnline(contactID))

server/src/main/java/envoy/server/util/UserAuthenticationUtil.java

@@ -0,0 +1,24 @@
+package envoy.server.util;
+
+import envoy.server.net.ConnectionManager;
+
+/**
+ * @author Leon Hofmeister
+ * @since Envoy Server v0.3-beta
+ */
+public final class UserAuthenticationUtil {
+
+	private UserAuthenticationUtil() {}
+
+	/**
+	 * Checks whether a user is really who he claims to be.
+	 *
+	 * @param expectedID the expected user ID
+	 * @param socketID   the socket ID of the user making a request
+	 * @return whether this user is who he claims to be
+	 * @since Envoy Server v0.3-beta
+	 */
+	public static boolean isExpectedUser(long expectedID, long socketID) {
+		return ConnectionManager.getInstance().getUserIDBySocketID(socketID) == expectedID;
+	}
+}