app.js

const PORT = process.env.PORT || 3001;
const STR_REGEX = 'socket\\-[a-z0-9]+';

var express = require('express');
var app = express();

var http = require('http').createServer(app);

var io = require('socket.io')(http, {
    handlePreflightRequest: (req, res) => {
        const headers = {
            "Access-Control-Allow-Headers": "Content-Type, Authorization",
            "Access-Control-Allow-Origin": req.headers.origin,
            "Access-Control-Allow-Credentials": true
        };
        res.writeHead(200, headers);
        res.end();
    }
});

// endpoint
app.use(express.json());
app.post(`/:ns(${STR_REGEX})`, function (req, res) {
    var ns = io.of(req.params.ns);
    if (req.body.users) {
        req.body.users.forEach(function (id) {
            ns.to(`user-${id}`).volatile.emit(req.body.name, req.body.data);
        });
    } else if (req.body.room) {
        ns.to(req.body.room).volatile.emit(req.body.name, req.body.data);
    } else {
        ns.volatile.emit(req.body.name, req.body.data);
    }
    res.json({status: true});
});
app.get(`/:ns(${STR_REGEX})`, function (req, res) {
    var ns = io.of(req.params.ns);
    ns.clients((error, clients) => {
        res.json(error ? {error: error} : {count: clients.length});
    });
});

http.listen(PORT, function () {
    console.log('listening on *:' + PORT);
});