Socket.IO：检测断开的套接字

Question

I have a socket.io server/client. When a client safely disconnects, on the server side, the line

socket.on('disconnect', function() {

});

is called.

However, if the client server crashes, then socket.on('disconnect') is never called; I know this because I recursively print out wss.sockets.connected.length and the number does not decrease.

How can I check that such a crash has happened on the server?

Answer 1

You should eventually receive the disconnect event, because socket.io has a heartbeat mechanism. I don't think there is any other way to detect a client crash. It does take some time though.

Heartbeat has been explained well here:

Advantage/disadvantage of using socketio heartbeats

Answer 2

When server calls disconnect(), the reason given to disconnect handler is: io server disconnect. And when server stops, the reason is: transport close. So you can check this by adding a condition:

socket.on('disconnect', function(reason) {
  if (reason === 'transport close'){
    console.log('Server Crashed');
  } 
});