Entropy from ping roundtrips

ping-rng.js

#!/usr/bin/env node
// requires: npm i -g get-stdin net-ping
// usage: ping-rng [bits?] < hosts

const stdin = require('/usr/local/lib/node_modules/get-stdin')
const ping = require('/usr/local/lib/node_modules/net-ping')

let sid = 0

const probe = async (hosts) => {
  const session = ping.createSession({
    timeout: 200,
    sessionId: sid
  })
  sid = (sid + 1) % 65535
  return await Promise.all(hosts.filter(host => !!host).map((host) => (
    new Promise((resolve, reject) => {
      session.pingHost(host, (err, target, sent, rcvd) => {
        if (err) return resolve(null)
        return resolve(rcvd - sent)
      })
    })
  )))
}

stdin().then(async (str) => {
  const hosts = str.split(/\s+/g)
  const c = parseInt(process.argv[2] || -1, 10)
  let n = 0
  while (c === -1 || n < c) {
    let results = await probe(hosts)
    let nibbles = results
      .filter(time => time !== null)
      .map(time => parseInt(time % 16).toString(16))
      .join('')
    n += nibbles.length * 4
    if (c !== -1 && n >= c) {
      nibbles = nibbles.substring(0, nibbles.length - ((n - c) / 4))
    }
    process.stdout.write(nibbles)
  }
})