Receives request of pings to desired hostnames and responds with the pongs at its arrival through WebSocket

websocket-ping-server.js

import netPing from 'net-ping';
import express from 'express';
import http from 'http';
import dns from 'dns';
import socketIO from 'socket.io';
import { BehaviorSubject, Observable } from 'rx';

const app = express();
const server = http.Server(app);
const io = socketIO(server);
const pingSession = netPing.createSession();

const resolve = Observable.fromNodeCallback(dns.resolve);
const ping = Observable.fromNodeCallback(
  pingSession.pingHost,
  pingSession,
  (host, requestTime, responseTime)=> ({
    host, requestTime, responseTime,
  })
);

app.get('/', (req, res) =>
  res.sendFile(__dirname + '/index.html')
);

function pingHostname(hostname) {
  const startTime = new Date();

  return resolve(hostname)
  .flatMap((addresses) =>
    ping(addresses[0])
    .map((pong) => ({ ...pong, startTime, hostname }))
  )
  .catch((error) =>
    Observable.return({
      hostname,
      error,
      startTime,
    })
  )
  .map(pong => ({...pong, endTime: new Date() }));
}

io
.on('connection', (socket) => {
  const hosts$ = new BehaviorSubject([]);

  // For each 10s from the connection
  const monitoring = Observable.interval(10000)

  // Gets current hosts list
  .withLatestFrom(hosts$, (interval, hosts) => hosts)

  // Sends a Ping for each hosts
  .flatMap(hosts => Observable.merge(hosts.map(pingHostname)))

  // ignores hosts no longer in the list on their arrival
  .withLatestFrom( hosts$,
    (pong, hosts) => hosts.indexOf(pong.hostname) !== -1 ? pong : null
   )
  .filter(pong => pong)

  // Emits to interested client
  .subscribe(pong => socket.emit('pong', pong));

  // Sets the hosts user is interested
  Observable.fromEvent(socket, 'setHosts')
  .map(hosts => JSON.parse(hosts))
  .subscribe(hosts$);

  // Ends monitoring on disconnect
  Observable.fromEvent(socket, 'disconnect')
  .subscribe(() => monitoring.dispose() );
});

server.listen(3000, () => {
  console.log('Listening on *:3000');
});