cloudfoundry/stratos

const net = require("net");

// call method 1: (port, cb(err, freePort))
// call method 2: (portBeg, portEnd, cb(err, freePort))
// call method 3: (portBeg, host, cb(err, freePort))
// call method 4: (portBeg, portEnd, host, cb(err, freePort))
// call method 5: (portBeg, portEnd, host, howmany, cb(err, freePort1, freePort2, ...))

function findFreePort(beg, ...rest){
  const p = rest.slice(0, rest.length - 1), cb = rest[rest.length - 1];
  let [end, ip, cnt] = Array.from(p);
  if (!ip && end && !/^\d+$/.test(end)) { // deal with method 3
    ip = end;
    end = 65534;
  } else {
    if (end == null) { end = 65534; }
  }
  if (cnt == null) { cnt = 1; }

  const retcb = cb;
  const res = [];
  const probe = function(ip, port, cb){
    const s = net.createConnection({port: port, host: ip})
    s.on('connect', function(){ s.end(); cb(null, port + 1); });
    s.on('error', err=> { cb(port); });  // can't connect, port is available
  };
  var onprobe = function(port, nextPort){
    if (port) {
      res.push(port);
      if (res.length >= cnt) {
        retcb(null, ...res)
      } else {
        setImmediate(()=> probe(ip, port+1, onprobe));
      }
    } else {
      if (nextPort>=end) {
        retcb(new Error("No available ports"));
      } else {
        setImmediate(()=> probe(ip, nextPort, onprobe));
      }
    }
  };
  return probe(ip, beg, onprobe);
};

function findFreePortPmfy(beg, ...rest) {
  const last = rest[rest.length - 1];
  if (typeof last === 'function') {
    findFreePort(beg, ...rest);
  } else {
    return new Promise((resolve, reject) => {
      findFreePort(beg, ...rest, (err, ...ports) => {
        if (err) reject(err)
        else resolve(ports);
      })
    })
  }
}
module.exports = findFreePortPmfy