Advanced Features of Socket.io

6.1. Rooms and Namespaces

Rooms and namespaces allow for more organized communication:

Rooms: Useful for broadcasting messages to specific groups of clients. For example, you might use rooms to create chat channels or multiplayer game lobbies.Server-side Example:

io.on('connection', (socket) => { console.log('A user connected'); // Join a room socket.on('join room', (room) => { socket.join(room); console.log(`User joined room: ${room}`); }); // Leave a room socket.on('leave room', (room) => { socket.leave(room); console.log(`User left room: ${room}`); }); // Broadcast message to a specific room socket.on('message to room', (room, msg) => { io.to(room).emit('room message', msg); }); });

Client-side Example:

const socket = io(); // Join room socket.emit('join room', 'room1'); // Send message to room socket.emit('message to room', 'room1', 'Hello Room 1!'); // Listen for messages from the room socket.on('room message', (msg) => { console.log('Message from room:', msg); });

Namespaces: They create separate communication channels with their own set of events and rooms. For example, you might have a chat namespace and a notifications namespace.Server-side Example:

javascriptCopy codeconst chatNamespace = io.of('/chat'); const notificationsNamespace = io.of('/notifications'); chatNamespace.on('connection', (socket) => { console.log('A user connected to chat namespace'); socket.on('chat message', (msg) => { chatNamespace.emit('chat message', msg); }); }); notificationsNamespace.on('connection', (socket) => { console.log('A user connected to notifications namespace'); socket.on('notification', (notification) => { notificationsNamespace.emit('notification', notification); }); });

Client-side Example:

<script src="/socket.io/socket.io.js"></script> <script> const chatSocket = io('/chat'); const notificationsSocket = io('/notifications'); chatSocket.on('chat message', (msg) => { console.log('Chat message:', msg); }); notificationsSocket.on('notification', (notification) => { console.log('Notification:', notification); }); chatSocket.emit('chat message', 'Hello Chat!'); notificationsSocket.emit('notification', 'New notification!'); </script>

6.2. Middleware

Socket.io allows you to use middleware for handling authentication and other pre-processing tasks before a client connects or emits an event.

Server-side Example:

const io = require('socket.io')(server);

// Middleware to authenticate clients
io.use((socket, next) => {
  const token = socket.handshake.query.token;
  if (isValidToken(token)) {
    next();
  } else {
    next(new Error('Authentication error'));
  }
});

io.on('connection', (socket) => {
  console.log('A user connected');
});

Client-side Example:

<script src="/socket.io/socket.io.js"></script>
<script>
  const socket = io({
    query: {
      token: 'your-authentication-token'
    }
  });

  socket.on('connect', () => {
    console.log('Connected to server');
  });

  socket.on('connect_error', (error) => {
    console.error('Connection error:', error);
  });
</script>

6.3. Broadcasting

You can use broadcasting to send messages to all clients except the sender or to a subset of clients.

Broadcast to All Clients Except the Sender:Server-side Example:

socket.broadcast.emit('message', 'Hello everyone except this user');

Broadcast to All Clients in a Room:Server-side Example:

io.to('room1').emit('room message', 'Hello room 1!');

6.4. Handling Disconnections

Handling disconnections gracefully is important for maintaining a good user experience.