Web Socket: Unable to Detect Client Connection on the Internet

Question

I want to detect a client connection if the client disconnects the Internet using a web socket. My code is:

 //Include util library
    var util = require('util');
    // Include underscore library
    var _ = require('underscore')._;
    //For websocket
var webSocketServer = new (require('ws')).Server({port: (process.env.PORT || 5000)}),
webSockets = {} // userID: webSocket

// CONNECT /:userID
// wscat -c ws://localhost:5000/1
webSocketServer.on('connection', function (webSocket) 
{
  var userID = webSocket.upgradeReq.url.substr(1);
  //console.log('User_id is ',userID);
  webSockets[userID] = webSocket
                   util.log('User_id: [' + userID + '] enter in connected users list of [ ' + Object.getOwnPropertyNames(webSockets)+' ]')
                   // Call function which check id exist in letswalkee DB table
                   check_userid(userID);


                   // Send msg like: [fromUserID, text]    [1, "Hello, World!"]
webSocket.on('message', function(message) {
util.log('Received from [' + userID + ']: ' + message)
var messageArray = JSON.parse(message)
                                    var toUserWebSocket = webSockets[messageArray[0]]
                                    if (toUserWebSocket) {
                                    util.log('Sent to [' + messageArray[0] + ']: ' + JSON.stringify(messageArray))
                                    messageArray[0] = userID
                                    toUserWebSocket.send(JSON.stringify(messageArray))
                                    }
                                    })

                   webSocket.on('close', function () 
                   {
                      delete webSockets[userID]
                      util.log('User_id Deleted from connected users: [ ' + userID+' ]');

                    })
webSocket.on('disconnect',function()
  {
   console.log('hello i am disconnected');  
  });
})

I used this code (webSocket.on ('disconnect', function ()), but did not work.

Answer 1

WebSocket is based on TCP, and TCP uses the FIN packet to close the connection. In the event of a sudden loss of Internet connection, both the WebSocket server and the phone are not aware of the already dead TCP connection, since no FIN packet was sent.

To fix the problem, TCP has a mechanism called keepalive.

, TCP keepalive Linux ws._socket.setKeepAlive(true).

: https://github.com/websockets/ws/issues/353

Answer 2

TCP (, Websockets) , heartbeat/ping , / , .