How to terminate a WebSocket connection?

Question

Is it possible to terminate a websocket connection from server without closing the entire server? If it is then, how can I achieve it?

Note: I'm using NodeJS as back-end and 'ws' websocket module.

Answer 1

So because of some sort of omission in the documentation regarding ws.close() and ws.terminate() I think the solutions in provided answers won't close the sockets gracefully in some cases, thus keeping them hanging in the Event Loop.

Compare the next two methods of ws package:

• ws.close():

Initializes close handshake, sending close frame to the peer and awaiting to receive close frame from the peer, after that sending FIN packet in attempt to perform a clean socket close. When answer received, the socket is destroyed. However, there is a closeTimeout that will destroy socket only as a worst case scenario, and it potentially could keep socket for additional 30 seconds, preventing the graceful exit with your custom timeout:

// ws/lib/WebSocket.js:21
const closeTimeout = 30 * 1000; // Allow 30 seconds to terminate the connection cleanly.

• ws.terminate():

Forcibly destroys the socket without closing frames or fin packets exchange, and does it instantly, without any timeout.

Hard shutdown

Considering all of the above, the "hard landing" scenario would be as follows:

wss.clients.forEach((socket) => {
  // Soft close
  socket.close();

  process.nextTick(() => {
    if ([socket.OPEN, socket.CLOSING].includes(socket.readyState)) {
      // Socket still hangs, hard close
      socket.terminate();
    }
  });
});

Soft shutdown

You can give your clients some time to respond, if you could allow yourself to wait for a while (but not 30 seconds):

// First sweep, soft close
wss.clients.forEach((socket) => {
  socket.close();
});

setTimeout(() => {
  // Second sweep, hard close
  // for everyone who's left
  wss.clients.forEach((socket) => {
    if ([socket.OPEN, socket.CLOSING].includes(socket.readyState)) {
      socket.terminate();
    }
  });
}, 10000);

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Important: proper execution of close() method will emit 1000 close code for close event, while terminate() will signal abnormal close with 1006 (MDN WebSocket Close event).