Project: WebSocket Chat Server

In this project, we will build a real-time, multi-client chat server using the native Node.js net module (TCP sockets). Clients will connect to the server using standard terminal tools like Telnet or Netcat.

1. Project Specifications

• Protocol: TCP Socket connections handled by Node.js net module.
• Broadcasting: Every incoming message from a client is broadcasted to all other active sockets.
• Events: Handle new connections, client exits, and system errors without crashing.

2. Implementing the TCP Chat Server

Create a new file named chatServer.js and paste the following implementation:

import net from "net";

// Store all active client sockets
const clients = new Set();

const server = net.createServer((socket) => {
  // Set encoding to read string input instead of raw Buffers
  socket.setEncoding("utf8");

  // Add the new client connection to the active list
  clients.add(socket);
  
  const clientAddress = `${socket.remoteAddress}:${socket.remotePort}`;
  console.log(`[JOIN] New client connected from ${clientAddress}`);
  
  socket.write("Welcome to the Node.js TCP Chat Room!\n");
  broadcast(`[SYSTEM] User from ${clientAddress} has joined the room.\n`, socket);

  // Listen for incoming messages from this client
  socket.on("data", (message) => {
    const cleanMessage = message.trim();
    if (cleanMessage) {
      console.log(`[MSG] ${clientAddress}: ${cleanMessage}`);
      broadcast(`[${clientAddress}]: ${cleanMessage}\n`, socket);
    }
  });

  // Handle client disconnection
  socket.on("end", () => {
    clients.delete(socket);
    console.log(`[LEAVE] Client ${clientAddress} disconnected`);
    broadcast(`[SYSTEM] User from ${clientAddress} has left the room.\n`);
  });

  // Handle connection errors
  socket.on("error", (err) => {
    clients.delete(socket);
    console.log(`[ERROR] Connection error for ${clientAddress}: ${err.message}`);
  });
});

// Broadcast helper function to send messages to all active clients
function broadcast(message, senderSocket = null) {
  for (const client of clients) {
    // Write message to everyone except the sender
    if (client !== senderSocket && client.writable) {
      client.write(message);
    }
  }
}

const PORT = 4000;
server.listen(PORT, () => {
  console.log(`TCP Chat Server is running on port ${PORT}`);
});

3. Running and Testing the Server

First, launch the server in your terminal:

# Start the TCP chat server
node chatServer.js

Next, open multiple separate terminal windows to simulate different users connecting via Netcat (nc) or Telnet:

# User 1 connection
nc localhost 4000

# User 2 connection (in a separate terminal)
nc localhost 4000

When User 1 types a message and presses Enter, it will immediately broadcast to the User 2 terminal, creating a real-time terminal chat room.