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/ui/controller/ChatScene.java

@@ -593,7 +593,7 @@ 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();
 		}
 
@@ -607,19 +607,6 @@ 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

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

@@ -137,7 +137,7 @@ 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);
 	}
@@ -148,11 +148,11 @@ 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 +161,7 @@ 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 +178,7 @@ 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);

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/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

@@ -2,6 +2,7 @@ package envoy.data;
 
 import java.io.Serializable;
 import java.time.Instant;
+import java.util.Objects;
 
 import dev.kske.eventbus.IEvent;
 
@@ -80,9 +81,9 @@ 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

@@ -1,6 +1,7 @@
 package envoy.event;
 
 import java.io.Serializable;
+import java.util.Objects;
 
 import dev.kske.eventbus.IEvent;
 
@@ -20,7 +21,16 @@ public abstract class Event<T> implements IEvent, Serializable {
 	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 +56,7 @@ 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);
 	}
 
 	/**

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.*;
@@ -223,6 +223,9 @@ 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 +239,9 @@ 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 +283,18 @@ 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 +316,18 @@ 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 +341,36 @@ 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/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
@@ -28,6 +29,14 @@ 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());
 
 		// Any other status than READ is not supposed to be sent to the server

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

@@ -123,7 +123,6 @@ 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
@@ -139,7 +138,6 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 			persistenceManager.updateContact(user);
 			writeProxy.write(socketID, new NewAuthToken(token));
 		}
-
 		final var pendingMessages =
 			PersistenceManager.getInstance().getPendingMessages(user, credentials.getLastSync());
 		pendingMessages.removeIf(GroupMessage.class::isInstance);

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/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/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;
+	}
+}