Retrieving subscriber count using zeromq PUB/SUB sockets

Question

Is it possible to get the total count of subscribers from a PUB socket in zeromq?

Thanks!

Answer 1

This is implementation on NodeJS for rep, I think for pub it's the same.

Like Jakob Möllås said, need to use monitor.

const zmq = require('zmq')
        , rep = zmq.socket('rep');

let counter = 0;

rep.bind('tcp://*:5560', function (err) {
    if (err) {
        console.log(err);
    } else {
        console.log("Listening on 5560…");
        rep.monitor(500, 0);
    }
});

// Register to monitoring events
rep.on('connect', function (fd, ep) {
    console.log('connect, endpoint:', ep);
});
rep.on('connect_delay', function (fd, ep) {
    console.log('connect_delay, endpoint:', ep);
});
rep.on('connect_retry', function (fd, ep) {
    console.log('connect_retry, endpoint:', ep);
});
rep.on('listen', function (fd, ep) {
    console.log('listen, endpoint:', ep);
});
rep.on('bind_error', function (fd, ep) {
    console.log('bind_error, endpoint:', ep);
});
rep.on('accept', function (fd, ep) {
    console.log('accept, endpoint:', ep);
    counter++;
});
rep.on('accept_error', function (fd, ep) {
    console.log('accept_error, endpoint:', ep);
});
rep.on('close', function (fd, ep) {
    console.log('close, endpoint:', ep);
});
rep.on('close_error', function (fd, ep) {
    console.log('close_error, endpoint:', ep);
});
rep.on('disconnect', function (fd, ep) {
    console.log('disconnect, endpoint:', ep);
    counter--;
});

// Handle monitor error
rep.on('monitor_error', function(err) {
    console.log('Error in monitoring: %s, will restart monitoring in 5 seconds', err);
    setTimeout(function() { rep.monitor(500, 0); }, 5000);
});

rep.on('message', function (msg) {
    console.log(`recieve: `, JSON.parse(msg));
    rep.send(JSON.stringify({ "status": FAIL, "code": 3666 }));
});

---

console

recieve:  { method: 'login', login: 'a', password: 'b1' }
accept, endpoint: tcp://0.0.0.0:5560
accept, endpoint: tcp://0.0.0.0:5560
login: a, password: b1
recieve:  { method: 'login', login: 'a', password: 'b1' }
disconnect, endpoint: tcp://0.0.0.0:5560
login: a, password: b1
disconnect, endpoint: tcp://0.0.0.0:5560