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

@@ -1,19 +1,35 @@
 package com.university.chat.Client;
 
-public class ServerListener implements Runnable{
-    // TODO: store the ObjectInputStream from the user socket
-    //          (this should be the same input stream the
-    //           chatClient created when connecting)
+import com.university.chat.Common.ChatMessage;
+import com.university.chat.Common.FileMessage;
+import java.io.ObjectInputStream;
+
+public class ServerListener implements Runnable
+{
+    private final ObjectInputStream in;
+
+    public ServerListener(ObjectInputStream in)
+    {
+        this.in = in;
+    }
 
     @Override
     public void run() {
-        try {
-            // TODO: In an infinite loop read objects from the server
-            //   - if it's a ChatMessage  -> print "<sender>: <content>"
-            //   - if it's a FileMessage  -> print that a file was received
-            //                               (filename + sender), it's already
-            //                               saved to disk by the server.
-        } catch (Exception e){
+
+        try
+        {
+            while (true)
+            {
+                Object obj = in.readObject();
+
+                if (obj instanceof ChatMessage msg)
+                    System.out.println(msg.getSender() + ": " + msg.getContent());
+                else if (obj instanceof FileMessage fileMsg)
+                    System.out.println("File received from " + fileMsg.getSender() + " : " + fileMsg.getFilename());
+            }
+        }
+        catch (Exception e)
+        {
             System.out.println("Disconnected from server");
         }
     }

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

@@ -1,29 +1,133 @@
 package com.university.chat.Client;
 
-public class chatClient {
-    public static void main() {
-        // TODO: Connecting to the server
-        //  1. Create a socket and connect to the server
-        //  2. Create an ObjectOutputStream (out) and ObjectInputStream (in)
-        //      from the socket's streams — output FIRST, then input.
-        //  2. Get the username, and send a LOGIN ChatMessage with that username
-        //  3. Start a new Thread running a ServerListener(in) so incoming
-        //      messages are handled concurrently.
+import com.university.chat.Common.ChatMessage;
+import com.university.chat.Common.FileMessage;
+import com.university.chat.Common.MessageType;
+import java.io.File;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.net.Socket;
+import java.nio.file.Files;
+import java.util.Scanner;
 
-        while (true){
-            try {
-                // TODO: Program loop — read a line from the console and act on it:
-                //   - "/msg <user> <text>"        -> build & send a PRIVATE_MESSAGE
-                //   - "/users"                    -> build & send a USER_LIST request
-                //   - "/sendfile <user> <path>"   -> read the file into a byte[]
-                //                                     (you can use TransferProgress
-                //                                     to show progress)
-                //                                     and send it as a FileMessage
-                //   - anything else               -> send a PUBLIC_MESSAGE
-                //   Remember to flush() the output stream after writeObject().
-            } catch (Exception e){
-                System.out.println("command failed: " + e.getMessage());
+
+public class chatClient
+{
+    public static void main(String[] args)
+    {
+        try
+        {
+            Socket socket = new Socket("localhost", 5000);
+
+            ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
+
+            out.flush();
+
+            ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
+
+            Scanner scanner = new Scanner(System.in);
+
+            System.out.print("Username: ");
+            String username = scanner.nextLine();
+
+            ChatMessage login = new ChatMessage(MessageType.LOGIN, username, null, "");
+
+            out.writeObject(login);
+            out.flush();
+
+            new Thread(new ServerListener(in)).start();
+
+            while (true)
+            {
+                try
+                {
+                    String line = scanner.nextLine();
+
+                    if (line.startsWith("/msg "))
+                    {
+                        String[] parts = line.split(" ", 3);
+
+                        if (parts.length < 3)
+                            continue;
+
+                        ChatMessage msg =
+                                new ChatMessage(
+                                        MessageType.PRIVATE_MESSAGE,
+                                        username,
+                                        parts[1],
+                                        parts[2]
+                                );
+
+                        out.writeObject(msg);
+                        out.flush();
+                    }
+                    else if (line.equals("/users"))
+                    {
+                        ChatMessage msg =
+                                new ChatMessage(
+                                        MessageType.USER_LIST,
+                                        username,
+                                        null,
+                                        ""
+                                );
+
+                        out.writeObject(msg);
+                        out.flush();
+                    }
+                    else if (line.startsWith("/sendfile "))
+                    {
+                        String[] parts = line.split(" ", 3);
+
+                        if (parts.length < 3)
+                            continue;
+
+                        String receiver = parts[1];
+
+                        File file = new File(parts[2]);
+
+                        byte[] data = Files.readAllBytes(file.toPath());
+
+                        TransferProgress progress = new TransferProgress(data.length);
+
+                        progress.update(data.length);
+
+                        FileMessage fileMessage =
+                                new FileMessage(
+                                        username,
+                                        receiver,
+                                        file.getName(),
+                                        data
+                                );
+
+                        out.writeObject(fileMessage);
+                        out.flush();
+                    }
+                    else
+                    {
+                        ChatMessage msg =
+                                new ChatMessage(
+                                        MessageType.PUBLIC_MESSAGE,
+                                        username,
+                                        null,
+                                        line
+                                );
+
+                        out.writeObject(msg);
+                        out.flush();
+                    }
+
+                }
+                catch (Exception e)
+                {
+                    System.out.println("command failed: " + e.getMessage());
+                }
             }
+
+        }
+        catch (Exception e)
+        {
+            // just for debugging
+            e.printStackTrace();
         }
     }
-}
+}

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

@@ -1,15 +1,34 @@
 package com.university.chat.Server;
 
-public class ChatServer {
-    // TODO: declare a single shared UserManager instance (static final)
-    //         This MUST be shared by all ClientSession threads so that
-    //         broadcasting and private messaging work correctly.
+import java.net.ServerSocket;
+import java.net.Socket;
 
-    public static void main(String[] args) {
-        // TODO: Create a ServerSocket
+public class ChatServer
+{
+    private static final UserManager USER_MANAGER = new UserManager();
 
-        // TODO: In an infinite loop:
-        //  accept an incoming client connection
-        //  make a new thread running ClientSession for each user.
+    public static void main(String[] args)
+    {
+        int port = 5000;
+
+        try (ServerSocket serverSocket = new ServerSocket(port))
+        {
+            System.out.println("Server started on port " + port);
+
+            while (true)
+            {
+                Socket socket = serverSocket.accept();
+
+                ClientSession session = new ClientSession(socket, USER_MANAGER);
+
+                new Thread(session).start();
+            }
+
+        }
+        catch (Exception e)
+        {
+            // just for debugging
+            e.printStackTrace();
+        }
     }
-}
+}

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

@@ -7,53 +7,133 @@ import java.io.IOException;
 import java.net.Socket;
 import java.nio.file.Files;
 
+import com.university.chat.Common.MessageType;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+
 public class ClientSession implements Runnable {
 
     private String username;
+    private final Socket socket;
+    private final UserManager userManager;
 
-    public ClientSession(Socket socket, UserManager userManager) {
-        // TODO : Create an ObjectOutputStream from socket.getOutputStream()
-        //         and an ObjectInputStream from socket.getInputStream().
+    private ObjectInputStream in;
+    private ObjectOutputStream out;
+
+    public ClientSession(Socket socket, UserManager userManager)
+    {
+        this.socket = socket;
+        this.userManager = userManager;
+
+        try
+        {
+            out = new ObjectOutputStream(socket.getOutputStream());
+            out.flush();
+            in = new ObjectInputStream(socket.getInputStream());
+
+        }
+        catch (Exception e)
+        {
+            throw new RuntimeException(e);
+        }
     }
 
     @Override
     public void run() {
-        try {
+        try
+        {
+            Object firstObject = in.readObject();
 
-            // TODO: Welcome the user (login step)
-            //  1. Read the first object sent by the client.
-            //  2. Check it's a ChatMessage with type LOGIN.
-            //  3. Extract the username.
-            //  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.
+            if (!(firstObject instanceof ChatMessage loginMsg)
+                    || loginMsg.getType() != MessageType.LOGIN)
+            {
+                socket.close();
+                return;
+            }
 
-            // TODO: Main message loop
-            //   In a loop, call in.readObject(), you can separate messages by their type:
-            //     - if it's a ChatMessage      -> call handleChatMessage(msg)
-            //     - if it's a FileMessage      -> call handleFileMessage(fileMsg)
-            //   Keep looping until the connection is closed (an exception will be thrown).
+            username = loginMsg.getSender();
 
-        } catch (Exception e) {
+            if (!userManager.addUser(username, this))
+            {
+                sendObject(
+                        new ChatMessage(
+                                MessageType.LOGIN_FAILED,
+                                "SERVER",
+                                username,
+                                "Username already exists"
+                        )
+                );
+
+                socket.close();
+                return;
+            }
+
+            FileManager.createUserFolders(username);
+
+            sendObject(
+                    new ChatMessage(
+                            MessageType.LOGIN_SUCCESS,
+                            "SERVER",
+                            username,
+                            "Login successful"
+                    )
+            );
+
+            System.out.println(username + " connected");
+
+            while (true)
+            {
+                Object obj = in.readObject();
+
+                if (obj instanceof ChatMessage chatMsg)
+                    handleChatMessage(chatMsg);
+                else if (obj instanceof FileMessage fileMsg)
+                    handleFileMessage(fileMsg);
+            }
+
+        }
+        catch (Exception e)
+        {
             System.out.println("Disconnected: " + username);
-        } finally {
-            // TODO: Remove the user from UserManager so they no longer
-            //        receive broadcasts or appear in users list
+        }
+        finally
+        {
+            if (username != null) {
+                userManager.removeUser(username);
+            }
         }
     }
 
 
     private void handleChatMessage(ChatMessage msg) throws IOException {
-        switch (msg.getType()) {
-            case PUBLIC_MESSAGE -> {
-                // TODO: Broadcast this message to every connected client.
+
+        switch (msg.getType())
+        {
+            case PUBLIC_MESSAGE ->
+            {
+                for (ClientSession session : userManager.getAllSessions())
+                    session.sendObject(msg);
             }
-            case PRIVATE_MESSAGE -> {
-                // TODO: Forward this message to the receiver user.
+
+            case PRIVATE_MESSAGE ->
+            {
+                ClientSession receiver = userManager.getUser(msg.getReceiver());
+
+                if (receiver != null)
+                    receiver.sendObject(msg);
             }
-            case USER_LIST -> {
-                // TODO: Reply to the requester with the list of online users.
+
+            case USER_LIST ->
+            {
+                ChatMessage response =
+                        new ChatMessage(
+                                MessageType.USER_LIST,
+                                "SERVER",
+                                username,
+                                userManager.listUsers()
+                        );
+
+                sendObject(response);
             }
         }
     }
@@ -66,6 +146,15 @@ 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());
+
+        if (receiver != null)
+            receiver.sendObject(fileMsg);
+    }
+
+    public synchronized void sendObject(Object obj) throws IOException
+    {
+        out.writeObject(obj);
+        out.flush();
     }
 }