Added tons of javadoc, finalized server-side registration protocol.

client/src/main/java/nl/andrewl/concord_client/ConcordClient.java

@@ -1,6 +1,5 @@
 package nl.andrewl.concord_client;
 
-import com.fasterxml.jackson.databind.ObjectMapper;
 import com.googlecode.lanterna.gui2.MultiWindowTextGUI;
 import com.googlecode.lanterna.gui2.Window;
 import com.googlecode.lanterna.gui2.WindowBasedTextGUI;
@@ -9,6 +8,8 @@ import com.googlecode.lanterna.screen.TerminalScreen;
 import com.googlecode.lanterna.terminal.DefaultTerminalFactory;
 import com.googlecode.lanterna.terminal.Terminal;
 import lombok.Getter;
+import nl.andrewl.concord_client.data.ClientDataStore;
+import nl.andrewl.concord_client.data.JsonClientDataStore;
 import nl.andrewl.concord_client.event.EventManager;
 import nl.andrewl.concord_client.event.handlers.ChannelMovedHandler;
 import nl.andrewl.concord_client.event.handlers.ChatHistoryResponseHandler;
@@ -19,42 +20,41 @@ import nl.andrewl.concord_client.model.ClientModel;
 import nl.andrewl.concord_core.msg.Encryption;
 import nl.andrewl.concord_core.msg.Message;
 import nl.andrewl.concord_core.msg.Serializer;
-import nl.andrewl.concord_core.msg.types.*;
+import nl.andrewl.concord_core.msg.types.ServerMetaData;
+import nl.andrewl.concord_core.msg.types.ServerUsers;
 import nl.andrewl.concord_core.msg.types.channel.MoveToChannel;
 import nl.andrewl.concord_core.msg.types.chat.Chat;
 import nl.andrewl.concord_core.msg.types.chat.ChatHistoryRequest;
 import nl.andrewl.concord_core.msg.types.chat.ChatHistoryResponse;
-import nl.andrewl.concord_core.msg.types.client_setup.Identification;
+import nl.andrewl.concord_core.msg.types.client_setup.*;
-import nl.andrewl.concord_core.msg.types.client_setup.ServerWelcome;
 
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.Socket;
-import java.nio.file.Files;
 import java.nio.file.Path;
 import java.security.GeneralSecurityException;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 
 public class ConcordClient implements Runnable {
 	private final Socket socket;
 	private final InputStream in;
 	private final OutputStream out;
 	private final Serializer serializer;
+	private final ClientDataStore dataStore;
 
 	@Getter
-	private final ClientModel model;
+	private ClientModel model;
 
 	private final EventManager eventManager;
 
 	private volatile boolean running;
 
-	public ConcordClient(String host, int port, String nickname, Path tokensFile) throws IOException {
+	private ConcordClient(String host, int port) throws IOException {
 		this.eventManager = new EventManager(this);
 		this.socket = new Socket(host, port);
 		this.serializer = new Serializer();
+		this.dataStore = new JsonClientDataStore(Path.of("concord-session-tokens.json"));
 		try {
 			var streams = Encryption.upgrade(socket.getInputStream(), socket.getOutputStream(), this.serializer);
 			this.in = streams.first();
@@ -62,8 +62,6 @@ public class ConcordClient implements Runnable {
 		} catch (GeneralSecurityException e) {
 			throw new IOException("Could not establish secure connection to the server.", e);
 		}
-		this.model = this.initializeConnectionToServer(nickname, tokensFile);
-
 		// Add event listeners.
 		this.eventManager.addHandler(MoveToChannel.class, new ChannelMovedHandler());
 		this.eventManager.addHandler(ServerUsers.class, new ServerUsersHandler());
@@ -72,32 +70,63 @@ public class ConcordClient implements Runnable {
 		this.eventManager.addHandler(ServerMetaData.class, new ServerMetaDataHandler());
 	}
 
-	/**
+	public static ConcordClient register(String host, int port, String username, String password) throws IOException {
-	 * Initializes the communication with the server by sending an {@link Identification}
+		var client = new ConcordClient(host, port);
-	 * message, and waiting for a {@link ServerWelcome} response from the
+		client.sendMessage(new ClientRegistration(null, null, username, password));
-	 * server. After that, we request some information about the channel we were
+		Message reply = client.serializer.readMessage(client.in);
-	 * placed in by the server.
+		if (reply instanceof RegistrationStatus status) {
-	 * @param nickname The nickname to send to the server that it should know
+			if (status.type() == RegistrationStatus.Type.ACCEPTED) {
-	 *                 us by.
+				ServerWelcome welcomeData = (ServerWelcome) client.serializer.readMessage(client.in);
-	 * @param tokensFile Path to the file where session tokens are stored.
+				client.initializeClientModel(welcomeData, username);
-	 * @return The client model that contains the server's metadata and other
+			} else if (status.type() == RegistrationStatus.Type.PENDING) {
-	 * information that should be kept up-to-date at runtime.
+				System.out.println("Registration pending!");
-	 * @throws IOException If an error occurs while reading or writing the
+			}
-	 * messages, or if the server sends an unexpected response.
-	 */
-	private ClientModel initializeConnectionToServer(String nickname, Path tokensFile) throws IOException {
-		String token = this.getSessionToken(tokensFile);
-		this.serializer.writeMessage(new Identification(nickname, token), this.out);
-		Message reply = this.serializer.readMessage(this.in);
-		if (reply instanceof ServerWelcome welcome) {
-			var model = new ClientModel(welcome.clientId(), nickname, welcome.currentChannelId(), welcome.currentChannelName(), welcome.metaData());
-			this.saveSessionToken(welcome.sessionToken(), tokensFile);
-			// Start fetching initial data for the channel we were initially put into.
-			this.sendMessage(new ChatHistoryRequest(model.getCurrentChannelId(), ""));
-			return model;
 		} else {
-			throw new IOException("Unexpected response from the server after sending identification message: " + reply);
+			System.out.println(reply);
 		}
+		return client;
+	}
+
+	public static ConcordClient login(String host, int port, String username, String password) throws IOException {
+		var client = new ConcordClient(host, port);
+		client.sendMessage(new ClientLogin(username, password));
+		Message reply = client.serializer.readMessage(client.in);
+		if (reply instanceof ServerWelcome welcome) {
+			client.initializeClientModel(welcome, username);
+		} else if (reply instanceof RegistrationStatus status && status.type() == RegistrationStatus.Type.PENDING) {
+			System.out.println("Registration pending!");
+		} else {
+			System.out.println(reply);
+		}
+		return client;
+	}
+
+	public static ConcordClient loginWithToken(String host, int port) throws IOException {
+		var client = new ConcordClient(host, port);
+		var token = client.dataStore.getSessionToken(client.socket.getInetAddress().getHostName() + ":" + client.socket.getPort());
+		if (token.isPresent()) {
+			client.sendMessage(new ClientSessionResume(token.get()));
+			Message reply = client.serializer.readMessage(client.in);
+			if (reply instanceof ServerWelcome welcome) {
+				client.initializeClientModel(welcome, "unknown");
+			}
+		} else {
+			System.err.println("No session token!");
+		}
+		return client;
+	}
+
+	private void initializeClientModel(ServerWelcome welcomeData, String username) throws IOException {
+		var model = new ClientModel(
+				welcomeData.clientId(),
+				username,
+				welcomeData.currentChannelId(),
+				welcomeData.currentChannelName(),
+				welcomeData.metaData()
+		);
+		this.dataStore.saveSessionToken(this.socket.getInetAddress().getHostName() + ":" + this.socket.getPort(), welcomeData.sessionToken());
+		// Start fetching initial data for the channel we were initially put into.
+		this.sendMessage(new ChatHistoryRequest(model.getCurrentChannelId(), ""));
 	}
 
 	public void sendMessage(Message message) throws IOException {
@@ -138,46 +167,6 @@ public class ConcordClient implements Runnable {
 		}
 	}
 
-	/**
-	 * Fetches the session token that this client should use for its currently
-	 * configured server, according to the socket address and port.
-	 * @param tokensFile The file containing the session tokens.
-	 * @return The session token, or null if none was found.
-	 * @throws IOException If the tokens file could not be read.
-	 */
-	@SuppressWarnings("unchecked")
-	private String getSessionToken(Path tokensFile) throws IOException {
-		String token = null;
-		String address = this.socket.getInetAddress().getHostName() + ":" + this.socket.getPort();
-		if (Files.exists(tokensFile)) {
-			ObjectMapper mapper = new ObjectMapper();
-			Map<String, String> sessionTokens = mapper.readValue(Files.newBufferedReader(tokensFile), Map.class);
-			token = sessionTokens.get(address);
-		}
-		return token;
-	}
-
-	/**
-	 * Saves a session token that this client should use the next time it
-	 * connects to the same server.
-	 * @param token The token to save.
-	 * @param tokensFile The file containing the session tokens.
-	 * @throws IOException If the tokens file could not be read or written to.
-	 */
-	@SuppressWarnings("unchecked")
-	private void saveSessionToken(String token, Path tokensFile) throws IOException {
-		String address = this.socket.getInetAddress().getHostName() + ":" + this.socket.getPort();
-		Map<String, String> tokens = new HashMap<>();
-		ObjectMapper mapper = new ObjectMapper();
-		if (Files.exists(tokensFile)) {
-			tokens = mapper.readValue(Files.newBufferedReader(tokensFile), Map.class);
-		}
-		tokens.put(address, token);
-		mapper.writerWithDefaultPrettyPrinter().writeValue(Files.newBufferedWriter(tokensFile), tokens);
-	}
-
-
-
 	public static void main(String[] args) throws IOException {
 		Terminal term = new DefaultTerminalFactory().createTerminal();
 		Screen screen = new TerminalScreen(term);

client/src/main/java/nl/andrewl/concord_client/data/ClientDataStore.java

@@ -0,0 +1,13 @@
+package nl.andrewl.concord_client.data;
+
+import java.io.IOException;
+import java.util.Optional;
+
+/**
+ * A component which can store and retrieve persistent data which a client can
+ * use as part of its interaction with servers.
+ */
+public interface ClientDataStore {
+	Optional<String> getSessionToken(String serverName) throws IOException;
+	void saveSessionToken(String serverName, String sessionToken) throws IOException;
+}

client/src/main/java/nl/andrewl/concord_client/data/JsonClientDataStore.java

@@ -0,0 +1,42 @@
+package nl.andrewl.concord_client.data;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+public class JsonClientDataStore implements ClientDataStore {
+	private final Path file;
+
+	public JsonClientDataStore(Path file) {
+		this.file = file;
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public Optional<String> getSessionToken(String serverName) throws IOException {
+		String token = null;
+		if (Files.exists(file)) {
+			ObjectMapper mapper = new ObjectMapper();
+			Map<String, String> sessionTokens = mapper.readValue(Files.newBufferedReader(file), Map.class);
+			token = sessionTokens.get(serverName);
+		}
+		return Optional.ofNullable(token);
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public void saveSessionToken(String serverName, String sessionToken) throws IOException {
+		Map<String, String> tokens = new HashMap<>();
+		ObjectMapper mapper = new ObjectMapper();
+		if (Files.exists(file)) {
+			tokens = mapper.readValue(Files.newBufferedReader(file), Map.class);
+		}
+		tokens.put(serverName, sessionToken);
+		mapper.writerWithDefaultPrettyPrinter().writeValue(Files.newBufferedWriter(file), tokens);
+	}
+}

client/src/main/java/nl/andrewl/concord_client/gui/MainWindow.java

@@ -50,7 +50,7 @@ public class MainWindow extends BasicWindow {
 		if (nickname == null) return;
 
 		try {
-			var client = new ConcordClient(host, port, nickname, Path.of("concord-session-tokens.json"));
+			var client = ConcordClient.login(host, port, nickname, "testpass");
 			var chatPanel = new ServerPanel(client, this);
 			client.getModel().addListener(chatPanel);
 			new Thread(client).start();

client/src/main/java/nl/andrewl/concord_client/model/ClientModel.java

@@ -12,7 +12,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
 
 @Getter
 public class ClientModel {
-	private UUID id;
+	private final UUID id;
 	private String nickname;
 	private ServerMetaData serverMetaData;
 

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

@@ -1,3 +1,12 @@
+/**
+ * The core components that are used by both the Concord server and the default
+ * client implementation. Includes record-based message serialization, and some
+ * utilities for message passing.
+ * <p>
+ *     This core module defines the message protocol that clients must use to
+ *     communicate with any server.
+ * </p>
+ */
 module concord_core {
 	requires static lombok;
 

core/src/main/java/nl/andrewl/concord_core/msg/package-info.java

@@ -0,0 +1,7 @@
+/**
+ * Message components which are used by the server and the default client
+ * implementation. Notably, the {@link nl.andrewl.concord_core.msg.Serializer}
+ * within this package defines the set of supported message types, and provides
+ * the highest-level interface to client-server communication.
+ */
+package nl.andrewl.concord_core.msg;

core/src/main/java/nl/andrewl/concord_core/msg/types/Error.java

@@ -5,11 +5,10 @@ import nl.andrewl.concord_core.msg.Message;
 /**
  * Error message which can be sent between either the server or client to
  * indicate an unsavory situation.
+ * @param level The severity level of the error.
+ * @param message A message indicating what went wrong.
  */
-public record Error (
+public record Error (Level level, String message) implements Message {
-		Level level,
-		String message
-) implements Message {
 	/**
 	 * The error level gives an indication as to the severity of the error.
 	 * Warnings indicate that a user has attempted to do something which they
@@ -18,10 +17,20 @@ public record Error (
 	 */
 	public enum Level {WARNING, ERROR}
 
+	/**
+	 * Creates a warning message.
+	 * @param message The message text.
+	 * @return A warning-level error message.
+	 */
 	public static Error warning(String message) {
 		return new Error(Level.WARNING, message);
 	}
 
+	/**
+	 * Creates an error message.
+	 * @param message The message text.
+	 * @return An error-level error message.
+	 */
 	public static Error error(String message) {
 		return new Error(Level.ERROR, message);
 	}

core/src/main/java/nl/andrewl/concord_core/msg/types/channel/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Messages pertaining to channel interaction and updates.
+ */
+package nl.andrewl.concord_core.msg.types.channel;

core/src/main/java/nl/andrewl/concord_core/msg/types/chat/Chat.java

@@ -8,9 +8,7 @@ import java.util.UUID;
 /**
  * This message contains information about a chat message that a user sent.
  */
-public record Chat (
+public record Chat (UUID id, UUID senderId, String senderNickname, long timestamp, String message) implements Message {
-		UUID id, UUID senderId, String senderNickname, long timestamp, String message
-) implements Message {
 	public Chat(UUID senderId, String senderNickname, long timestamp, String message) {
 		this(null, senderId, senderNickname, timestamp, message);
 	}

core/src/main/java/nl/andrewl/concord_core/msg/types/chat/ChatHistoryRequest.java

@@ -24,6 +24,7 @@ import java.util.stream.Collectors;
  * </p>
  * <p>
  *     The following query parameters are supported:
+ * </p>
  *     <ul>
  *         <li><code>count</code> - Fetch up to N messages. Minimum of 1, and
  *         a server-specific maximum count, usually no higher than 1000.</li>
@@ -37,7 +38,6 @@ import java.util.stream.Collectors;
  *         is present, all others are ignored, and a list containing the single
  *         message is returned, if it could be found, otherwise an empty list.</li>
  *     </ul>
- * </p>
  * <p>
  *     Responses to this request are sent via {@link ChatHistoryResponse}, where
  *     the list of messages is always sorted by the timestamp.

core/src/main/java/nl/andrewl/concord_core/msg/types/chat/ChatHistoryResponse.java

@@ -7,5 +7,7 @@ import java.util.UUID;
 /**
  * The response that a server sends to a {@link ChatHistoryRequest}. The list of
  * messages is ordered by timestamp, with the newest messages appearing first.
+ * @param channelId The id of the channel that the chat messages belong to.
+ * @param messages The list of messages that comprises the history.
  */
 public record ChatHistoryResponse (UUID channelId, Chat[] messages) implements Message {}

core/src/main/java/nl/andrewl/concord_core/msg/types/chat/package-info.java

@@ -0,0 +1,5 @@
+/**
+ * Messages pertaining to chat messages and other auxiliary messages regarding
+ * the management of chat information.
+ */
+package nl.andrewl.concord_core.msg.types.chat;

core/src/main/java/nl/andrewl/concord_core/msg/types/client_setup/KeyData.java

@@ -5,5 +5,8 @@ import nl.andrewl.concord_core.msg.Message;
 /**
  * This message is sent as the first message from both the server and the client
  * to establish an end-to-end encryption via a key exchange.
+ * @param iv The initialization vector bytes.
+ * @param salt The salt bytes.
+ * @param publicKey The public key.
  */
 public record KeyData (byte[] iv, byte[] salt, byte[] publicKey) implements Message {}

core/src/main/java/nl/andrewl/concord_core/msg/types/client_setup/RegistrationStatus.java

@@ -6,10 +6,10 @@ import nl.andrewl.concord_core.msg.Message;
  * A response from the server which indicates the current status of the client's
  * registration request.
  */
-public record RegistrationStatus (Type type) implements Message {
+public record RegistrationStatus (Type type, String reason) implements Message {
 	public enum Type {PENDING, ACCEPTED, REJECTED}
 
 	public static RegistrationStatus pending() {
-		return new RegistrationStatus(Type.PENDING);
+		return new RegistrationStatus(Type.PENDING, null);
 	}
 }

core/src/main/java/nl/andrewl/concord_core/msg/types/client_setup/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Messages pertaining to the establishment of a connection with clients.
+ */
+package nl.andrewl.concord_core.msg.types.client_setup;

core/src/main/java/nl/andrewl/concord_core/msg/types/package-info.java

@@ -0,0 +1,10 @@
+/**
+ * Contains all the various message types which can be sent between the server
+ * and client.
+ * <p>
+ *     <em>Note that not all message types defined here may be supported by the
+ *     latest version of Concord. See {@link nl.andrewl.concord_core.msg.Serializer}
+ *     for the definitive list.</em>
+ * </p>
+ */
+package nl.andrewl.concord_core.msg.types;

core/src/main/java/nl/andrewl/concord_core/util/Pair.java

@@ -1,3 +1,8 @@
 package nl.andrewl.concord_core.util;
 
+/**
+ * Simple generic pair of two objects.
+ * @param <A> The first object.
+ * @param <B> The second object.
+ */
 public record Pair<A, B>(A first, B second) {}

core/src/main/java/nl/andrewl/concord_core/util/Triple.java

@@ -1,3 +1,9 @@
 package nl.andrewl.concord_core.util;
 
+/**
+ * Simple generic triple of objects.
+ * @param <A> The first object.
+ * @param <B> The second object.
+ * @param <C> The third object.
+ */
 public record Triple<A, B, C> (A first, B second, C third) {}

core/src/main/java/nl/andrewl/concord_core/util/package-info.java

@@ -0,0 +1,5 @@
+/**
+ * Contains some useful one-off utility classes that any consumer of Concord
+ * messages could benefit from.
+ */
+package nl.andrewl.concord_core.util;

pom.xml

@@ -16,9 +16,10 @@
     </modules>
 
     <properties>
-        <maven.compiler.source>16</maven.compiler.source>
+        <maven.compiler.source>17</maven.compiler.source>
-        <maven.compiler.target>16</maven.compiler.target>
+        <maven.compiler.target>17</maven.compiler.target>
-        <java.version>16</java.version>
+        <maven.compiler.release>17</maven.compiler.release>
+        <java.version>17</java.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
 
@@ -47,6 +48,18 @@
                     </annotationProcessorPaths>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <version>3.3.1</version>
+                <configuration>
+                    <detectLinks>false</detectLinks>
+                    <detectOfflineLinks>false</detectOfflineLinks>
+                    <failOnError>false</failOnError>
+                    <failOnWarnings>false</failOnWarnings>
+                    <show>private</show>
+                </configuration>
+            </plugin>
         </plugins>
     </build>
 </project>

server/src/main/java/nl/andrewl/concord_server/ConcordServer.java

@@ -124,6 +124,9 @@ public class ConcordServer implements Runnable {
 		}
 	}
 
+	/**
+	 * @return The server's metadata.
+	 */
 	public ServerMetaData getMetaData() {
 		return new ServerMetaData(
 				this.config.getName(),

server/src/main/java/nl/andrewl/concord_server/channel/Channel.java

@@ -33,7 +33,7 @@ public class Channel implements Comparable<Channel> {
 
 	/**
 	 * A document collection which holds all messages created in this channel,
-	 * indexed on id, timestamp, message, and sender's nickname.
+	 * indexed on id, timestamp, message, and sender's username.
 	 */
 	private final NitriteCollection messageCollection;
 

server/src/main/java/nl/andrewl/concord_server/client/AuthenticationService.java

@@ -24,8 +24,6 @@ import java.util.UUID;
  * and logging in.
  */
 public class AuthenticationService {
-	public static record ClientConnectionData(UUID id, String nickname, String sessionToken, boolean newClient) {}
-
 	private final NitriteCollection userCollection;
 	private final NitriteCollection sessionTokenCollection;
 	private final ConcordServer server;

server/src/main/java/nl/andrewl/concord_server/client/ClientConnectionData.java

@@ -0,0 +1,15 @@
+package nl.andrewl.concord_server.client;
+
+import java.util.UUID;
+
+/**
+ * Some common data that's used when dealing with a client who has just joined
+ * the server.
+ * @param id The user's unique id.
+ * @param username The user's unique username.
+ * @param sessionToken The user's new session token that can be used the next
+ *                     time they want to log in.
+ * @param newClient True if this client is connecting for the first time, or
+ *                  false otherwise.
+ */
+public record ClientConnectionData(UUID id, String username, String sessionToken, boolean newClient) {}

server/src/main/java/nl/andrewl/concord_server/client/ClientManager.java

@@ -27,9 +27,12 @@ public class ClientManager {
 	private final Map<UUID, ClientThread> clients;
 	private final Map<UUID, ClientThread> pendingClients;
 	private final NitriteCollection userCollection;
-
 	private final AuthenticationService authService;
 
+	/**
+	 * Constructs a new client manager for the given server.
+	 * @param server The server that the client manager is for.
+	 */
 	public ClientManager(ConcordServer server) {
 		this.server = server;
 		this.clients = new ConcurrentHashMap<>();
@@ -45,12 +48,28 @@ public class ClientManager {
 		server.getScheduledExecutorService().scheduleAtFixedRate(this.authService::removeExpiredSessionTokens, 1, 1, TimeUnit.DAYS);
 	}
 
+	/**
+	 * Handles an attempt by a new client to register as a user for this server.
+	 * If the server is set to automatically accept all new clients, the new
+	 * user is registered and the client is sent a {@link RegistrationStatus}
+	 * with the {@link RegistrationStatus.Type#ACCEPTED} value, closely followed
+	 * by a {@link ServerWelcome} message. Otherwise, the client is sent a
+	 * {@link RegistrationStatus.Type#PENDING} response, which indicates that
+	 * the client's registration is pending approval. The client can choose to
+	 * remain connected and wait for approval, or disconnect and try logging in
+	 * later.
+	 *
+	 * @param registration The client's registration information.
+	 * @param clientThread The client thread.
+	 * @throws InvalidIdentificationException If the user's registration info is
+	 * not valid.
+	 */
 	public void handleRegistration(ClientRegistration registration, ClientThread clientThread) throws InvalidIdentificationException {
 		Document userDoc = this.userCollection.find(Filters.eq("username", registration.username())).firstOrDefault();
 		if (userDoc != null) throw new InvalidIdentificationException("Username is taken.");
 		if (this.server.getConfig().isAcceptAllNewClients()) {
 			var clientData = this.authService.registerNewClient(registration);
-			clientThread.sendToClient(new RegistrationStatus(RegistrationStatus.Type.ACCEPTED));
+			clientThread.sendToClient(new RegistrationStatus(RegistrationStatus.Type.ACCEPTED, null));
 			this.initializeClientConnection(clientData, clientThread);
 		} else {
 			var clientId = this.authService.registerPendingClient(registration);
@@ -58,6 +77,23 @@ public class ClientManager {
 		}
 	}
 
+	/**
+	 * Handles an attempt by a new client to login as an existing user to the
+	 * server. If the user's credentials are valid, then the following can
+	 * result:
+	 * <ul>
+	 *     <li>If the user's registration is still pending, they will be sent a
+	 *     {@link RegistrationStatus.Type#PENDING} response, to indicate that
+	 *     their registration is still pending approval.</li>
+	 *     <li>For non-pending (normal) users, they will be logged into the
+	 *     server and sent a {@link ServerWelcome} message.</li>
+	 * </ul>
+	 *
+	 * @param login The client's login credentials.
+	 * @param clientThread The client thread managing the connection.
+	 * @throws InvalidIdentificationException If the client's credentials are
+	 * incorrect.
+	 */
 	public void handleLogin(ClientLogin login, ClientThread clientThread) throws InvalidIdentificationException {
 		Document userDoc = this.authService.findAndAuthenticateUser(login);
 		if (userDoc == null) throw new InvalidIdentificationException("Username or password is incorrect.");
@@ -68,20 +104,38 @@ public class ClientManager {
 			this.initializePendingClientConnection(userId, username, clientThread);
 		} else {
 			String sessionToken = this.authService.generateSessionToken(userId);
-			this.initializeClientConnection(new AuthenticationService.ClientConnectionData(userId, username, sessionToken, false), clientThread);
+			this.initializeClientConnection(new ClientConnectionData(userId, username, sessionToken, false), clientThread);
 		}
 	}
 
+	/**
+	 * Handles an attempt by a new client to login as an existing user to the
+	 * server with a session token from their previous session. If the token is
+	 * valid, the user will be logged in and sent a {@link ServerWelcome}
+	 * response.
+	 *
+	 * @param sessionResume The session token data.
+	 * @param clientThread The client thread managing the connection.
+	 * @throws InvalidIdentificationException If the token is invalid or refers
+	 * to a non-existent user.
+	 */
 	public void handleSessionResume(ClientSessionResume sessionResume, ClientThread clientThread) throws InvalidIdentificationException {
 		Document userDoc = this.authService.findAndAuthenticateUser(sessionResume);
 		if (userDoc == null) throw new InvalidIdentificationException("Invalid session. Log in to obtain a new session token.");
 		UUID userId = userDoc.get("id", UUID.class);
 		String username = userDoc.get("username", String.class);
 		String sessionToken = this.authService.generateSessionToken(userId);
-		this.initializeClientConnection(new AuthenticationService.ClientConnectionData(userId, username, sessionToken, false), clientThread);
+		this.initializeClientConnection(new ClientConnectionData(userId, username, sessionToken, false), clientThread);
 	}
 
-	public void decidePendingUser(UUID userId, boolean accepted) {
+	/**
+	 * Used to accept or reject a pending user's registration. If the given user
+	 * is not pending approval, this method does nothing.
+	 * @param userId The id of the pending user.
+	 * @param accepted Whether to accept or reject.
+	 * @param reason The reason for rejection (or acceptance). This may be null.
+	 */
+	public void decidePendingUser(UUID userId, boolean accepted, String reason) {
 		Document userDoc = this.userCollection.find(Filters.and(Filters.eq("id", userId), Filters.eq("pending", true))).firstOrDefault();
 		if (userDoc != null) {
 			if (accepted) {
@@ -90,16 +144,16 @@ public class ClientManager {
 				// If the pending user is still connected, upgrade them to a normal connected client.
 				var clientThread = this.pendingClients.remove(userId);
 				if (clientThread != null) {
-					clientThread.sendToClient(new RegistrationStatus(RegistrationStatus.Type.ACCEPTED));
+					clientThread.sendToClient(new RegistrationStatus(RegistrationStatus.Type.ACCEPTED, reason));
 					String username = userDoc.get("username", String.class);
 					String sessionToken = this.authService.generateSessionToken(userId);
-					this.initializeClientConnection(new AuthenticationService.ClientConnectionData(userId, username, sessionToken, true), clientThread);
+					this.initializeClientConnection(new ClientConnectionData(userId, username, sessionToken, true), clientThread);
 				}
 			} else {
 				this.userCollection.remove(userDoc);
 				var clientThread = this.pendingClients.remove(userId);
 				if (clientThread != null) {
-					clientThread.sendToClient(new RegistrationStatus(RegistrationStatus.Type.REJECTED));
+					clientThread.sendToClient(new RegistrationStatus(RegistrationStatus.Type.REJECTED, reason));
 				}
 			}
 		}
@@ -111,22 +165,30 @@ public class ClientManager {
 	 * @param clientData The data about the client that has connected.
 	 * @param clientThread The thread managing the client's connection.
 	 */
-	private void initializeClientConnection(AuthenticationService.ClientConnectionData clientData, ClientThread clientThread) {
+	private void initializeClientConnection(ClientConnectionData clientData, ClientThread clientThread) {
-		this.clients.put(clientData.id(), clientThread);
 		clientThread.setClientId(clientData.id());
-		clientThread.setClientNickname(clientData.nickname());
+		clientThread.setClientNickname(clientData.username());
 		var defaultChannel = this.server.getChannelManager().getDefaultChannel().orElseThrow();
 		clientThread.sendToClient(new ServerWelcome(clientData.id(), clientData.sessionToken(), defaultChannel.getId(), defaultChannel.getName(), this.server.getMetaData()));
+		this.clients.put(clientData.id(), clientThread); // We only add the client after sending the welcome, to make sure that we send the welcome packet first.
 		defaultChannel.addClient(clientThread);
 		clientThread.setCurrentChannel(defaultChannel);
 		this.broadcast(new ServerUsers(this.getConnectedClients().toArray(new UserData[0])));
 	}
 
+	/**
+	 * Initializes a connection to a client whose registration is pending, thus
+	 * they should simply keep their connection alive, and receive a {@link RegistrationStatus.Type#PENDING}
+	 * message, instead of a {@link ServerWelcome}.
+	 * @param clientId The id of the client.
+	 * @param pendingUsername The client's username.
+	 * @param clientThread The thread managing the client's connection.
+	 */
 	private void initializePendingClientConnection(UUID clientId, String pendingUsername, ClientThread clientThread) {
-		this.pendingClients.put(clientId, clientThread);
 		clientThread.setClientId(clientId);
 		clientThread.setClientNickname(pendingUsername);
 		clientThread.sendToClient(RegistrationStatus.pending());
+		this.pendingClients.put(clientId, clientThread);
 	}
 
 	/**
@@ -166,6 +228,9 @@ public class ClientManager {
 		}
 	}
 
+	/**
+	 * @return The list of connected clients.
+	 */
 	public List<UserData> getConnectedClients() {
 		return this.clients.values().stream()
 				.sorted(Comparator.comparing(ClientThread::getClientNickname))
@@ -173,6 +238,9 @@ public class ClientManager {
 				.collect(Collectors.toList());
 	}
 
+	/**
+	 * @return The list of connected, pending clients.
+	 */
 	public List<UserData> getPendingClients() {
 		return this.pendingClients.values().stream()
 				.sorted(Comparator.comparing(ClientThread::getClientNickname))
@@ -180,14 +248,27 @@ public class ClientManager {
 				.collect(Collectors.toList());
 	}
 
+	/**
+	 * @return The set of ids of all connected clients.
+	 */
 	public Set<UUID> getConnectedIds() {
 		return this.clients.keySet();
 	}
 
+	/**
+	 * Tries to find a connected client with the given id.
+	 * @param id The id to look for.
+	 * @return An optional client thread.
+	 */
 	public Optional<ClientThread> getClientById(UUID id) {
 		return Optional.ofNullable(this.clients.get(id));
 	}
 
+	/**
+	 * Tries to find a pending client with the given id.
+	 * @param id The id to look for.
+	 * @return An optional client thread.
+	 */
 	public Optional<ClientThread> getPendingClientById(UUID id) {
 		return Optional.ofNullable(this.pendingClients.get(id));
 	}