如何在javascript中实现对webSocket连接的Ping / Pong请求？

Question

I use websocket in javascript. But the connection close after one minute.

I am wondering somethings:

1- Is not Websocket naturaly providing with Ping/Pong messages not to close the connection? I think it have to. Otherwise what is the difference between websocket and TCP connection?

2- If I have to send the ping/pong messages, how is the ping message sent? What am I need to do? Is WebSocket object provide a ping method? Or should I call a method as websocket.send("ping") ? I am use naturaly WebSocket object in javascipt.

3- Should the server respond to Ping requests with Pong? Should this be implemented separately on the server side?

Note:Sorry for my english.

Answer 1

Yes, there are ping/pong frames in websockets. Here is an example using the ws module, where the server is initiating the ping request:

const http = require('http');
const ws = require('ws');

const server = http.createServer(function(req_stream_in, res_stream_out) {
  // handle regular HTTP requests here
});
const webSocketServer = new ws.Server({
  path: "/websocket",
  server: server
});

const connected_clients = new Map();

webSocketServer.on('connection', function connection(ws_client_stream) {
  // NOTE: only for demonstration, will cause collisions.  Use a UUID or some other identifier that's actually unique.
  const this_stream_id = Array.from(connected_clients.values()).length;

  // Keep track of the stream, so that we can send all of them messages.
  connected_clients.set(this_stream_id, ws_client_stream);

  // Attach event handler to mark this client as alive when pinged.
  ws_client_stream.is_alive = true;
  ws_client_stream.on('pong', () => { ws_client_stream.is_alive = true; });

  // When the stream is closed, clean up the stream reference.
  ws_client_stream.on('close', function() {
    connected_clients.delete(this_stream_id);
  });
});

setInterval(function ping() {
  Array.from(connected_clients.values()).forEach(function each(client_stream) {
    if (!client_stream.is_alive) { client_stream.terminate(); return; }
    client_stream.is_alive = false;
    client_stream.ping();
  });
}, 1000);

Answer 2

At this point in time, heartbeats are normally implemented on the server side: there's not much you can do from the client end.

However, if the server keeps killing your socket connection, and you have no control over it, it is possible for the client to send arbitrary data to the websocket on an interval:

let socket = null;

function connect_socket() {
  socket = new WebSocket(ws_url);
  socket.on("close", connect_socket); // <- rise from your grave!
  heartbeat();
}

function heartbeat() {
  if (!socket) return;
  if (socket.readyState !== 1) return;
  socket.send("heartbeat");
  setTimeout(heartbeat, 500);
}

connect_socket();

I strongly recommend trying to sort out what's happening on the server end, rather than trying to work around it on the client.

Answer 3

In ouni's solution, heartbeat() wasn't kicking in. It works when it's put in an open event like this:

let socket = null;

function connect_socket() {
  socket = new WebSocket(ws_url);
  socket.on("close", connect_socket); // <- rise from your grave!
  socket.on("open", heartbeat); // heartbeat when the socket is open
}

function heartbeat() {
  if (!socket) return;
  if (socket.readyState !== 1) return;
  socket.send("heartbeat");
  setTimeout(heartbeat, 500);
}

connect_socket();

Answer 4

According to Mozilla there is a dedicated convention for Ping Pong

At any point after the handshake, either the client or the server can choose to send a ping to the other party. When the ping is received, the recipient must send back a pong as soon as possible. You can use this to make sure that the client is still connected, for example.

A ping or pong is just a regular frame, but it's a control frame. Pings have an opcode of 0x9, and pongs have an opcode of 0xA. When you get a ping, send back a pong with the exact same Payload Data as the ping (for pings and pongs, the max payload length is 125). You might also get a pong without ever sending a ping; ignore this if it happens.

If you have gotten more than one ping before you get the chance to send a pong, you only send one pong.

https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_servers#Pings_and_Pongs_The_Heartbeat_of_WebSockets

Find more in depth discussion about ping/pong from the browser side here: Sending websocket ping/pong frame from browser