src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/ServerApp.java

@@ -1,5 +1,11 @@
 package ch.unibas.dmi.dbis.cs108.casono.server;
 
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick.CheckUsernameHandler;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick.CheckUsernameParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick.CheckUsernameRequest;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping.PingHandler;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping.PingParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping.PingRequest;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserCleanupJob;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserRegistry;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.NetworkManager;
@@ -7,6 +13,7 @@ import ch.unibas.dmi.dbis.cs108.casono.server.network.command.execution.CommandR
 import ch.unibas.dmi.dbis.cs108.casono.server.network.command.parsing.CommandParserDispatcher;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.events.DisconnectEvent;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.events.EventBus;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionDisconnectJob;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionManager;
 import java.time.Duration;
@@ -58,6 +65,31 @@ public class ServerApp {
                 SESSION_DISCONNECT_JOB_PERIOD,
                 TimeUnit.SECONDS);
 
+        ResponseDispatcher responseDispatcher = new ResponseDispatcher(sessionManager);
+
+        registerCommands(dispatcher, router, responseDispatcher, userRegistry);
+
         networkManager.start();
     }
+
+    /**
+     * Registers command parsers and handlers.
+     *
+     * @param parserDispatcher the dispatcher responsible for parsing incoming commands
+     * @param commandRouter the router that dispatches parsed commands to appropriate handlers
+     * @param responseDispatcher the dispatcher responsible for sending responses back to clients
+     */
+    private static void registerCommands(
+            CommandParserDispatcher parserDispatcher,
+            CommandRouter commandRouter,
+            ResponseDispatcher responseDispatcher,
+            UserRegistry userRegistry) {
+        parserDispatcher.register("PING", new PingParser());
+        commandRouter.register(PingRequest.class, new PingHandler(responseDispatcher));
+
+        parserDispatcher.register("CHECK_USERNAME", new CheckUsernameParser());
+        commandRouter.register(
+                CheckUsernameRequest.class,
+                new CheckUsernameHandler(responseDispatcher, userRegistry));
+    }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameHandler.java

@@ -0,0 +1,44 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.User;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserRegistry;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.execution.CommandHandler;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
+import java.util.Optional;
+
+/** Handles {@link CheckUsernameRequest}s to check whether a username is available. */
+public class CheckUsernameHandler implements CommandHandler<CheckUsernameRequest> {
+    private final ResponseDispatcher responseDispatcher;
+    private final UserRegistry userRegistry;
+
+    /**
+     * Creates a new handler for checking username availability.
+     *
+     * @param responseDispatcher the dispatcher used to send the response
+     * @param userRegistry the registry used to look up existing users
+     */
+    public CheckUsernameHandler(ResponseDispatcher responseDispatcher, UserRegistry userRegistry) {
+        this.responseDispatcher = responseDispatcher;
+        this.userRegistry = userRegistry;
+    }
+
+    /**
+     * Executes the username availability check for the given request.
+     *
+     * <p>If no user exists for the requested username, the username is reported as {@link
+     * UsernameAvailability#FREE}; otherwise, it is reported as {@link UsernameAvailability#TAKEN}.
+     *
+     * @param request the request to execute
+     */
+    @Override
+    public void execute(CheckUsernameRequest request) {
+        Optional<User> user = userRegistry.getByUsername(request.getUsername());
+        UsernameAvailability availability;
+        if (user.isEmpty()) {
+            availability = UsernameAvailability.FREE;
+        } else {
+            availability = UsernameAvailability.TAKEN;
+        }
+        responseDispatcher.dispatch(new CheckUsernameResponse(request.getContext(), availability));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameParser.java

@@ -0,0 +1,21 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.parsing.CommandParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.PrimitiveRequest;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.accessor.RequestParameterAccessor;
+
+/** Parses a primitive request into a {@link CheckUsernameRequest}. */
+public class CheckUsernameParser implements CommandParser<CheckUsernameRequest> {
+    /**
+     * Extracts the required {@code USERNAME} parameter from the incoming request.
+     *
+     * @param primitiveRequest the request to parse
+     * @return {@link CheckUsernameRequest} containing the username
+     */
+    @Override
+    public CheckUsernameRequest parse(PrimitiveRequest primitiveRequest) {
+        RequestParameterAccessor accessor =
+                new RequestParameterAccessor(primitiveRequest.parameters());
+        return new CheckUsernameRequest(primitiveRequest.context(), accessor.require("USERNAME"));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameRequest.java

@@ -0,0 +1,30 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+
+/** Request implementation used to check whether a username is available or already taken */
+public class CheckUsernameRequest extends Request {
+    private final String username;
+
+    /**
+     * Constructs a new CheckUsernameRequest with the given context and username to check
+     *
+     * @param context the {@link RequestContext} containing information for responding to the
+     *     request
+     * @param username the username to check for availability
+     */
+    public CheckUsernameRequest(RequestContext context, String username) {
+        super(context);
+        this.username = username;
+    }
+
+    /**
+     * Returns the provided username in the request
+     *
+     * @return username to check
+     */
+    public String getUsername() {
+        return username;
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameResponse.java

@@ -0,0 +1,18 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.SuccessResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBodyBuilder;
+
+/** Response indicating the availability status of a username check. */
+public class CheckUsernameResponse extends SuccessResponse {
+    /**
+     * Creates a new response to respond to the username availability check to
+     *
+     * @param context the {@link RequestContext} associated with the request
+     * @param availability the availability status of the requested username
+     */
+    public CheckUsernameResponse(RequestContext context, UsernameAvailability availability) {
+        super(context, new ResponseBodyBuilder().param("STATUS", availability).build());
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/UsernameAvailability.java

@@ -0,0 +1,10 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+/** Represents the availability status of a username */
+enum UsernameAvailability {
+    /** Username is available */
+    FREE,
+
+    /** Username is already in use */
+    TAKEN
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/ping/PingHandler.java

@@ -0,0 +1,29 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.execution.CommandHandler;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.OkResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
+
+/** Handler for {@link PingRequest}. */
+public class PingHandler implements CommandHandler<PingRequest> {
+    private final ResponseDispatcher responseDispatcher;
+
+    /**
+     * Create a new PingHandler to execute {@link PingRequest}s
+     *
+     * @param responseDispatcher dispatcher used to send responses back to clients
+     */
+    public PingHandler(ResponseDispatcher responseDispatcher) {
+        this.responseDispatcher = responseDispatcher;
+    }
+
+    /**
+     * Execute the ping request.
+     *
+     * @param request the ping request to handle
+     */
+    @Override
+    public void execute(PingRequest request) {
+        responseDispatcher.dispatch(new OkResponse(request.getContext()));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/ping/PingParser.java

@@ -0,0 +1,22 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.parsing.CommandParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.PrimitiveRequest;
+
+/**
+ * Parser for the Ping command.
+ *
+ * <p>Converts a low-level {@link PrimitiveRequest} into a {@link PingRequest}.
+ */
+public class PingParser implements CommandParser<PingRequest> {
+    /**
+     * Parse the given primitive request into a {@link PingRequest}.
+     *
+     * @param primitiveRequest the raw request to parse
+     * @return {@link PingRequest}
+     */
+    @Override
+    public PingRequest parse(PrimitiveRequest primitiveRequest) {
+        return new PingRequest(primitiveRequest.context());
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/ping/PingRequest.java

@@ -0,0 +1,19 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+
+/**
+ * Represents a "PING" request sent by a client to check server availability and keep the connection
+ * alive.
+ */
+public class PingRequest extends Request {
+    /**
+     * Constructs a new PingRequest with the given context.
+     *
+     * @param context the request context associated with this request
+     */
+    public PingRequest(RequestContext context) {
+        super(context);
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/user/UserRegistry.java

@@ -86,15 +86,38 @@ public class UserRegistry {
     }
 
     /**
-     * Looks up a user by their session ID.
+     * Looks up a user by their {@link SessionId}.
      *
-     * @param sessionId the session ID to look up
-     * @return an Optional containing the user, or empty if no user is associated with this session
+     * @param sessionId the SessionId to look up
+     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     *     SessionId
      */
-    public Optional<User> findBySessionId(SessionId sessionId) {
+    public Optional<User> getBySessionId(SessionId sessionId) {
         return Optional.ofNullable(bySessionId.get(sessionId));
     }
 
+    /**
+     * Looks up a user by their {@link UserId}.
+     *
+     * @param userId the UserId to look up
+     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     *     UserId
+     */
+    public Optional<User> getByUserId(UserId userId) {
+        return Optional.ofNullable(byId.get(userId));
+    }
+
+    /**
+     * Looks up a user by their username.
+     *
+     * @param username the username to look up
+     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     *     username
+     */
+    public Optional<User> getByUsername(String username) {
+        return Optional.ofNullable(byName.get(username));
+    }
+
     /**
      * Returns all currently registered users.
      *

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/sessions/SessionReader.java

@@ -12,6 +12,7 @@ import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Primitive
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RawRequest;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.accessor.MissingParameterException;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.ErrorResponse;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.PrimitiveResponse;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatchException;
@@ -94,6 +95,14 @@ public class SessionReader implements Runnable {
                         "Unexpected ResponseDispatchException exception while dispatching request",
                         e);
 
+            } catch (MissingParameterException e) {
+                logger.error(
+                        "Recieved request for command '{}' was missing the '{}' parameter",
+                        rawRequest.command(),
+                        e.getParameterKey());
+                sendErrorResponse(
+                        new ErrorResponse(requestContext, "MISSING_PARAMETER", e.getMessage()));
+
             } catch (IOException e) {
                 logger.error("Unexpected IO exception while reading from transport", e);