How is the WebSocket heartbeat mechanism implemented?

WebSocket heartbeat mechanism is used to detect connection activity and prevent connection disconnection due to network issues or timeouts.

Why Heartbeat is Needed

1. Detect Connection Status: Timely detect if connection is disconnected
2. Keep Connection Active: Prevent intermediate devices (such as firewalls, NAT) from closing connection due to long periods of no data transmission
3. Fast Failure Recovery: Quickly reconnect after connection disconnection

Heartbeat Implementation Methods

Client Initiates Heartbeat

javascript
// Client sends heartbeat periodically
const ws = new WebSocket('ws://example.com');
let heartbeatInterval;

function startHeartbeat() {
  heartbeatInterval = setInterval(() => {
    if (ws.readyState === WebSocket.OPEN) {
      ws.send(JSON.stringify({ type: 'ping' }));
    }
  }, 30000); // Send every 30 seconds
}

function stopHeartbeat() {
  clearInterval(heartbeatInterval);
}

ws.onopen = startHeartbeat;
ws.onclose = stopHeartbeat;

Server Responds to Heartbeat

javascript
// Server handles heartbeat
wss.on('connection', (ws) => {
  ws.on('message', (message) => {
    const data = JSON.parse(message);
    if (data.type === 'ping') {
      ws.send(JSON.stringify({ type: 'pong' }));
    }
  });
});

Heartbeat Interval Settings

• Recommended Interval: 30-60 seconds
• Too Short: Increases server load and network traffic
• Too Long: Cannot detect connection disconnection in time

Timeout Handling

javascript
let pongTimeout;
const TIMEOUT = 5000; // 5 second timeout

function sendPing() {
  ws.send(JSON.stringify({ type: 'ping' }));
  
  pongTimeout = setTimeout(() => {
    console.log('Heartbeat timeout, connection may be disconnected');
    ws.close();
  }, TIMEOUT);
}

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  if (data.type === 'pong') {
    clearTimeout(pongTimeout);
  }
};

Best Practices

1. Bidirectional Heartbeat: Both client and server can initiate heartbeat
2. Dynamic Adjustment: Dynamically adjust heartbeat interval based on network conditions
3. Exponential Backoff: Use exponential backoff strategy when reconnecting
4. Status Monitoring: Record heartbeat success/failure counts for monitoring connection quality