findAvailablePort

function findAvailablePort(app, done) {
  var port = portrange;
  portrange += 1;

  var server = http.createServer(app);

  server.listen(port, function (err) {
    done(server, port);
  });

  server.on('error', function (err) {
    findAvailablePort(app, done);
  });
}