src/main/java/com/university/chat/Client/ServerListener.java

@@ -1,18 +1,32 @@
 package com.university.chat.Client;
 
+import com.university.chat.Common.ChatMessage;
+import com.university.chat.Common.FileMessage;
+
+import java.io.ObjectInputStream;
+
 public class ServerListener implements Runnable{
-    // TODO: store the ObjectInputStream from the user socket
+    private final ObjectInputStream inputStream;
-    //          (this should be the same input stream the
+
-    //           chatClient created when connecting)
+    public ServerListener(ObjectInputStream inputStream) {
+        this.inputStream = inputStream;
+    }
 
     @Override
     public void run() {
         try {
-            // TODO: In an infinite loop read objects from the server
+            while (true) {
-            //   - if it's a ChatMessage  -> print "<sender>: <content>"
+                Object obj = inputStream.readObject();
-            //   - if it's a FileMessage  -> print that a file was received
+                if (obj instanceof ChatMessage msg) {
-            //                               (filename + sender), it's already
+                    System.out.printf("%s: %s\n", msg.getSender(), msg.getContent());
-            //                               saved to disk by the server.
+                } else if (obj instanceof FileMessage fileMsg) {
+                    System.out.printf(
+                            "Received file '%s' from %s\n",
+                            fileMsg.getFilename(),
+                            fileMsg.getSender()
+                    );
+                }
+            }
         } catch (Exception e){
             System.out.println("Disconnected from server");
         }

src/main/java/com/university/chat/Client/chatClient.java

@@ -1,28 +1,138 @@
 package com.university.chat.Client;
 
+import com.university.chat.Common.ChatMessage;
+import com.university.chat.Common.FileMessage;
+import com.university.chat.Common.MessageType;
+
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.net.Socket;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Scanner;
+
 public class chatClient {
-    public static void main() {
+    public static void main(String[] args) {
-        // TODO: Connecting to the server
+        Socket socket;
-        //  1. Create a socket and connect to the server
+        try {
-        //  2. Create an ObjectOutputStream (out) and ObjectInputStream (in)
+            socket = new Socket("127.0.0.1", 555);
-        //      from the socket's streams — output FIRST, then input.
+        } catch (IOException e) {
-        //  2. Get the username, and send a LOGIN ChatMessage with that username
+            throw new RuntimeException(e);
-        //  3. Start a new Thread running a ServerListener(in) so incoming
+        }
-        //      messages are handled concurrently.
+
+        ObjectOutputStream out = null;
+        ObjectInputStream in = null;
+        try {
+            out = new ObjectOutputStream(socket.getOutputStream());
+        }
+        catch (IOException e) {
+            System.err.printf("Error: %s\n",e.getMessage());
+        }
+
+        try {
+            in = new ObjectInputStream(socket.getInputStream());
+        }
+        catch (IOException e) {
+            System.err.printf("Error: %s\n",e.getMessage());
+        }
+
+        Scanner scanner = new Scanner(System.in);
+        System.out.println("Enter your username: ");
+        String username = scanner.nextLine();
+
+        try {
+            out.writeObject(new ChatMessage(
+                MessageType.LOGIN,
+                username,
+                null,
+                username
+            ));
+            out.flush();
+
+            Object loginResponse = in.readObject();
+            if (loginResponse == MessageType.LOGIN_FAILED) {
+                System.out.println("Login failed: username is already taken.");
+                socket.close();
+                return;
+            }
+            if (loginResponse != MessageType.LOGIN_SUCCESS) {
+                System.out.println("Login failed: invalid server response.");
+                socket.close();
+                return;
+            }
+
+            Thread listenerThread = new Thread(new ServerListener(in));
+            listenerThread.start();
+        }
+        catch (IOException | ClassNotFoundException e) {
+            System.err.printf("Error: %s\n",e.getMessage());
+            return;
+        }
 
         while (true){
             try {
-                // TODO: Program loop — read a line from the console and act on it:
+                String input = scanner.nextLine();
-                //   - "/msg <user> <text>"        -> build & send a PRIVATE_MESSAGE
+                if (input.isBlank()) {
-                //   - "/users"                    -> build & send a USER_LIST request
+                    continue;
-                //   - "/sendfile <user> <path>"   -> read the file into a byte[]
+                }
-                //                                     (you can use TransferProgress
+
-                //                                     to show progress)
+                String[] tokens = input.split("\\s+", 3);
-                //                                     and send it as a FileMessage
+
-                //   - anything else               -> send a PUBLIC_MESSAGE
+                switch (tokens[0]) {
-                //   Remember to flush() the output stream after writeObject().
+                    case "/msg" ->{
+                        if (tokens.length < 3) {
+                            System.err.println("Usage: /msg <user> <text>");
+                            continue;
+                        }
+                        out.writeObject(new ChatMessage(
+                                MessageType.PRIVATE_MESSAGE,
+                                username,
+                                tokens[1],
+                                tokens[2]
+                        ));
+                        out.flush();
+                    }
+                    case "/users" ->{
+                        out.writeObject(new ChatMessage(
+                                MessageType.USER_LIST,
+                                username,
+                                null,
+                                ""
+                        ));
+                        out.flush();
+                    }
+                    case "/sendfile" ->{
+                        if (tokens.length < 3) {
+                            System.err.println("Usage: /sendfile <user> <path>");
+                            continue;
+                        }
+
+                        Path path = Path.of(tokens[2]);
+                        byte[] data = Files.readAllBytes(path);
+                        TransferProgress progress = new TransferProgress(data.length);
+                        progress.update(data.length);
+
+                        out.writeObject(new FileMessage(
+                                username,
+                                tokens[1],
+                                path.getFileName().toString(),
+                                data
+                        ));
+                        out.flush();
+                    }
+                    default -> {
+                        out.writeObject(new ChatMessage(
+                                MessageType.PUBLIC_MESSAGE,
+                                username,
+                                null,
+                                input
+                        ));
+                        out.flush();
+                    }
+                }
             } catch (Exception e){
-                System.out.println("command failed: " + e.getMessage());
+                System.err.println("command failed: " + e.getMessage());
             }
         }
     }

src/main/java/com/university/chat/Server/ChatServer.java

@@ -1,15 +1,28 @@
 package com.university.chat.Server;
 
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+
 public class ChatServer {
-    // TODO: declare a single shared UserManager instance (static final)
+    public static final UserManager userManager = new UserManager();
-    //         This MUST be shared by all ClientSession threads so that
+    private static ServerSocket serverSocket;
-    //         broadcasting and private messaging work correctly.
-
     public static void main(String[] args) {
-        // TODO: Create a ServerSocket
+        try {
+            serverSocket = new ServerSocket(555);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
 
-        // TODO: In an infinite loop:
+	        while (true){
-        //  accept an incoming client connection
+	            try {
-        //  make a new thread running ClientSession for each user.
+	                Socket socket = serverSocket.accept();
+	                System.out.println("New client accepted");
+	                ClientSession session = new ClientSession(socket, userManager);
+	                new Thread(session).start();
+	            } catch (IOException e) {
+	                System.err.println("Unable to establish connection");
+	            }
+	        }
+	    }
 	}
-}

src/main/java/com/university/chat/Server/ClientSession.java

@@ -2,44 +2,89 @@ package com.university.chat.Server;
 
 import com.university.chat.Common.ChatMessage;
 import com.university.chat.Common.FileMessage;
+import com.university.chat.Common.MessageType;
 
 import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.OutputStream;
 import java.net.Socket;
 import java.nio.file.Files;
 
 public class ClientSession implements Runnable {
 
+    private final Socket socket;
+    private final UserManager userManager;
     private String username;
+    private ObjectOutputStream outputStream;
+    private ObjectInputStream inputStream;
 
     public ClientSession(Socket socket, UserManager userManager) {
-        // TODO : Create an ObjectOutputStream from socket.getOutputStream()
+        this.userManager = userManager;
-        //         and an ObjectInputStream from socket.getInputStream().
+        this.socket = socket;
+        try {
+             outputStream = new ObjectOutputStream(socket.getOutputStream());
+        }
+        catch (IOException e) {
+            System.err.printf("Error: %s\n",e.getMessage());
+        }
+
+        try {
+             inputStream = new ObjectInputStream(socket.getInputStream());
+        }
+        catch (IOException e) {
+            System.err.printf("Error: %s\n",e.getMessage());
+        }
     }
 
     @Override
     public void run() {
         try {
+            System.out.println("Welcome.");
 
-            // TODO: Welcome the user (login step)
+            boolean isLogin = false;
-            //  1. Read the first object sent by the client.
+            Object firstOjbect = inputStream.readObject();
-            //  2. Check it's a ChatMessage with type LOGIN.
+            if (firstOjbect instanceof ChatMessage){
-            //  3. Extract the username.
+                isLogin = ((ChatMessage)firstOjbect).getType() == MessageType.LOGIN;
-            //  4. Try to register the user via userManager.addUser(...).
+            }
-            //  5. If the username is taken, send back LOGIN_FAILED and close the socket.
-            //  6. Otherwise, create the user's folders with FileManager.createUserFolders(...)
-            //      and send back LOGIN_SUCCESS.
 
-            // TODO: Main message loop
+            if (!isLogin) {
-            //   In a loop, call in.readObject(), you can separate messages by their type:
+                socket.close();
-            //     - if it's a ChatMessage      -> call handleChatMessage(msg)
+                return;
-            //     - if it's a FileMessage      -> call handleFileMessage(fileMsg)
+            }
-            //   Keep looping until the connection is closed (an exception will be thrown).
 
-        } catch (Exception e) {
+            username = ((ChatMessage)firstOjbect).getContent();
+            if (userManager.addUser(username, this)){
+                System.out.printf("Successfully registered: %s\n", username);
+                FileManager.createUserFolders(username);
+                outputStream.writeObject(MessageType.LOGIN_SUCCESS);
+                outputStream.flush();
+            }
+            else {
+                System.err.printf("Error: a user with username: %s already exists.\n",username);
+                outputStream.writeObject(MessageType.LOGIN_FAILED);
+                outputStream.flush();
+                socket.close();
+                return;
+            }
+
+            while (true) {
+                Object obj = inputStream.readObject();
+
+                if (obj instanceof ChatMessage) {
+                    handleChatMessage((ChatMessage) obj);
+                }
+                else if (obj instanceof FileMessage) {
+                    handleFileMessage((FileMessage) obj);
+                }
+            }
+        }
+        catch (Exception e) {
             System.out.println("Disconnected: " + username);
-        } finally {
+        }
-            // TODO: Remove the user from UserManager so they no longer
+        finally {
-            //        receive broadcasts or appear in users list
+
+            userManager.removeUser(username);
         }
     }
 
@@ -47,17 +92,43 @@ public class ClientSession implements Runnable {
     private void handleChatMessage(ChatMessage msg) throws IOException {
         switch (msg.getType()) {
             case PUBLIC_MESSAGE -> {
-                // TODO: Broadcast this message to every connected client.
+                Iterable<ClientSession> users = userManager.getAllSessions();
+                for (ClientSession user : users) {
+                    if (user != this) {
+                        user.sendObject(msg);
+                    }
+                }
             }
             case PRIVATE_MESSAGE -> {
-                // TODO: Forward this message to the receiver user.
+                ClientSession receiver = userManager.getUser(msg.getReceiver());
+                if (receiver != null) {
+                    receiver.sendObject(msg);
+                }
+                else {
+                    sendObject(new ChatMessage(
+                            MessageType.PRIVATE_MESSAGE,
+                            "server",
+                            username,
+                            "User not found: " + msg.getReceiver()
+                    ));
+                }
             }
             case USER_LIST -> {
-                // TODO: Reply to the requester with the list of online users.
+                sendObject(new ChatMessage(
+                        MessageType.USER_LIST,
+                        "server",
+                        username,
+                        userManager.listUsers()
+                ));
             }
         }
     }
 
+    private synchronized void sendObject(Object obj) throws IOException {
+        outputStream.writeObject(obj);
+        outputStream.flush();
+    }
+
     private void handleFileMessage(FileMessage fileMsg) throws IOException {
         // Storing the file
         var sentPath = FileManager.getSentPath(fileMsg.getSender(), fileMsg.getFilename());
@@ -66,6 +137,7 @@ public class ClientSession implements Runnable {
         Files.write(sentPath, fileMsg.getData());
         Files.write(recvPath, fileMsg.getData());
 
-        // TODO: Forward the received file-message to the destination user.
+        ClientSession receiver = userManager.getUser(fileMsg.getReceiver());
+        receiver.sendObject(fileMsg);
     }
 }