answerver/index.js

incremental server port listener function

var net = require('net')

module.exports = listen

function listen(server, _port, cb){
  isPortTaken(_port, answer)
  function answer(err, b){
    if(!b) {
      server.listen(_port)
      
      server.on('listening', function(){

        cb(null, _port)
        //console.log('listening on port ' + _port)

      });
    }
    else {
      port = _port
      isPortTaken(++_port, answer)
    }
  }
}
function isPortTaken(PORT, callback) {
  var tester = net.createServer()
  tester.once('error', function (err) {
    if (err.code == 'EADDRINUSE') {
      callback(null, true)
    } else {
      callback(err)
    }
  })
  tester.once('listening', function() {
    tester.once('close', function() {
      callback(null, false)
    })
    tester.close()
  })
  tester.listen(PORT)
}