node.js - Nodejs random free tcp ports

Question

My project need to setup a new port every time a new instance of my class is instantiated.

In Node.js how I can find a free TCP port to set in my new socket server? Or check if my specified port is already used or not.

question from:https://stackoverflow.com/questions/28050171/nodejs-random-free-tcp-ports

Answer 1

You can bind to a random, free port assigned by the OS by specifying 0 for the port. This way you are not subject to race conditions (e.g. checking for an open port and some process binding to it before you get a chance to bind to it).

Then you can get the assigned port by calling server.address().port.

Example:

var net = require('net');

var srv = net.createServer(function(sock) {
  sock.end('Hello world
');
});
srv.listen(0, function() {
  console.log('Listening on port ' + srv.address().port);
});