Implementation of "get next available TCP port"

node-is-a-liar-snippet-4.js

var net = require('net');
var os = require('os');

function getLocalHosts() {
    var hosts = ['0.0.0.0', '::'];
    var interfaces = os.networkInterfaces();
    Object.keys(interfaces).forEach(function(interfaceName) {
        var interface = interfaces[interfaceName];
        interface.forEach(function(info) {
            var address = info.address;
            // append the interface name onto link-local IPv6 addresses
            // http://stackoverflow.com/a/34275391
            if (address.indexOf('fe80:') === 0) {
                address += '%' + interfaceName;
            }
            hosts.push(address);
        });
    });
    return hosts;
}

function createServer(port, host) {
    return new Promise(function(resolve, reject) {
        var server = net.createServer();
        server.listen(port, host, function() {
            server.once('close', function() {
                resolve(true);
            });
            server.close();
        });
        server.on('error', reject);
    });
}

function _getNextAvailableTcpPort(port, hosts, callback) {
    if (port < 1 || port > 65535) {
        callback(new RangeError('expected port to be from 1 to 65535, got ' + port));
        return;
    }
    var servers = hosts.reduce(function(lastServer, host) {
        return lastServer
            ? lastServer.then(function() { return createServer(port, host); })
            : createServer(port, host);
    }, null);

    servers.then(function() {
        callback(null, port);
    }, function(error) {
        _getNextAvailableTcpPort(port + 1, hosts, callback);
    });
}

function getNextAvailableTcpPort(port, callback) {
    if (typeof callback !== 'function') {
        throw new TypeError('expected callback to be a function, got ' + typeof callback);
    }
    if (typeof port !== 'number') {
        callback(new TypeError('expected port to be a number, got ' + typeof port));
        return;
    }
    var hosts = getLocalHosts();
    return _getNextAvailableTcpPort(port, hosts, callback);
}

module.exports = getNextAvailableTcpPort;