socket.io: clientsCount and on connection and on disconnect events - node.js

Question

I count the number of online websockets via onConnection and onDisconnect events:
const socketIo = require('socket.io');
var on_connect = 0;
var on_disconnect = 0;
var port = 6001;
var io = socketIo(port, {
pingTimeout: 5000,
pingInterval: 10000
});
//I have only one NameSpace and root NS is not used
var ns1 = io.of('ns1');
ns1
.on('connection', function (socket) {
on_connect += 1;
socket.on('disconnect', function (reason) {
on_disconnect += 1;
});
});
...
var online = on_connect - on_disconnect;
...
But online value not equal io.engine.clientsCount value.
And over time the difference between online value and io.engine.clientsCount value is growing up.
Why this is happens?
What is needed to make to fix this?

Answer 1

on_connect and on_disconnect variables are updates in the callback events, whereas the online variable is not recalculated. So you will need to recalculate the online variable every time the other variable change.

Answer 2

It might be easier to use only one variable to count connections. Increment it on connection, and decrement it on disconnect. That's how I keep track of the number of connections. Then there isn't a need to calculate it every time its value is needed.
Also, the line that states var online = on_connect - on_disconnect; Is occurring before either is modified... That's what #gvmani is trying to tell you.
Here's an example of some of what I'm doing. The code below sets up to listen for connections & disconnections and maintains a count of current connections. I should note that I'm not using a namespace like the OP, but the counting portion is what's of importance. I'll also note that I use connCount > 0 in the send() function. Which in my application is used to broadcast to all connected clients.
/* ******************************************************************** */
// initialize the server
const http = require('http');
const server = http.createServer();
// Socket.io listens to our server
const io = require('socket.io').listen(server);
// Count connections as they occur, decrement when a client disconnects.
// If the counter is zero then we won't send anything over the socket.
var connCount = 0;
// A client has connected,
io.on('connection', function(socket) {
// Increment the connection counter
connCount += 1;
// log the new connection for debugging purposes.
console.log(`on connect - ${socket.id} ${connCount}`);
// The client that initiated the connection has disconnected.
socket.on('disconnect', function () {
connCount -= 1;
console.log(`on disconnect - ${socket.id} ${connCount}`);
});
});
// Start listening...
server.listen(3000);
// Send something to all connected clients (a broadcast) the
// 'channel' will indicate the destination within the client
// and 'data' becomes the payload.
function send(channel, data) {
console.log(`send() - channel = ${channel} payload = ${JSON.stringify(data)}`);
if(connCount > 0) io.emit(channel, {payload: data});
else console.log('send() - no connections');
};