Sending message to a specific connected users using webSocket?

javascript

websocket

security

performance

byAlex Kataev·Mar 6, 2025

To send a specific user a message via a WebSocket, you can establish a dictionary mapping linking a userID to a WebSocket. Once a connection is established, map each user to his WebSocket. Upon doing so, you can pinpoint a particular user’s WebSocket to send them messages directly.

const wss = new WebSocket.Server({ port: 8080 });
const userSockets = {}; // A place for our friends(user sockets) to hang out

wss.on('connection', (ws) => {

  let userID; // The VIP pass for our users

  ws.on('message', (message) => {
    const { type, id, text } = JSON.parse(message);
    if (type === 'register') {
      userID = id; // Handing out the VIP pass
      userSockets[userID] = ws; // Welcome to the party!
    }
  });

  ws.on('close', () => {
    delete userSockets[userID]; // Saying goodbye isn't always easy 😢
  });
});

function sendToUser(id, text) {
  const ws = userSockets[id];
  if (ws) ws.send(text); // Special delivery! 🎁
}

Here, call sendToUser('userID', 'message') to connect with user 'userID'.

Tightening Security and Boosting Performance

Unique Identifiers

Generate individual identifiers (UIDs) for each socket to improve security and ensure proper message delivery. Remember, everyone wants to feel special, right?

Secure Authentication & Privacy

To maintain integrity and confidentiality, authenticate with access tokens, which are more secure than plain-text user IDs. Also, consider using WSS for encrypted communication. Always validate user identities to avoid any unexpected surprises.

Message Persistence

For historical purposes and search capabilities, consider preserving messages in a database.

Robust Server-Side Mechanisms

Thread Safety & Scalability

In environments like .NET, ConcurrentDictionary is your friend in ensuring thread safety and managing numerous clients.

Routing Requests

For libraries like ws, versions 3+ come in handy, allowing you to retrieve the user ID from the req.url or upgradeReq object attached to the connection event.

Tracking Active Connections

To keep track of your active connections, log user activity times and establish database tables. This approach will help you become the Sherlock Holmes of active connections.

Crafting an Advanced Messaging System

Private Messaging

For private messaging, use the user-to-WebSocket map. This approach guarantees a private, direct chat that UpHold's user-right to privacy.

Client-Side Integration

On the client-side, use event listeners for processing messages and updating the UI accordingly.

// Listening for messages
const socket = new WebSocket('ws://localhost:8080');

socket.addEventListener('message', function (event) {
  console.log('Message from server', event.data); // Received my pizza 🎉
});

// Upon connection, send a registration message
socket.addEventListener('open', function (event) {
  socket.send(JSON.stringify({ type: 'register', id: 'uniqueUserID' })); // Can I join the party please?
});

"Wscat” for Testing

Wscat command line utility simplifies testing WebSocket connections. Which can be useful in debugging and validating servers.

Libraries Exploration and WebSocket Enhancements

Optimal Libraries

To extract the full potential of WebSockets, consider exploring libraries like socket.io, ws, or WebSockets.

Superior WebSocket Servers

Fire up your WebSocket servers by experimenting with compression, binary transfer, and multiplexing. These features will keep your server optimally running even when under heavy load.