前段时间做一个Node.js应用时，需要分配一些端口，由于没什么时间细想，只是用一系列连续而且数字比较大的端口。

下来这段来自netutil的findFreePort以后可以一看。其本质上就是在一段区间随便找一个port，先试一把，行则OK，不行则再来.

var net = require("net");var exec = require("child_process").exec;exports.findFreePort = function(start, end, hostname, callback) {    var pivot = Math.floor(Math.random() * (end-start)) + start;    var port = pivot;    asyncRepeat(function(next, done) {        var stream = net.createConnection(port, hostname);        stream.on("connect", function() {            stream.destroy();            port++;            if (port > end)                port = start;            if (port == pivot)                done("Could not find free port.");            next();        });        stream.on("error", function() {            done();        });    }, function(err) {        callback(err, port);    });};exports.isPortOpen = function(hostname, port, timeout, callback) {    var stream = net.createConnection(port, hostname);    stream.on("connect", function() {        clearTimeout(id);        stream.destroy();        callback(true);    });    stream.on("error", function() {        clearTimeout(id);        stream.destroy();        callback(false);    });    var id = setTimeout(function() {        stream.destroy();        callback(false);    }, timeout || 1000);};exports.getHostName = function(callback) {    exec("hostname", function (error, stdout, stderr) {        if (error)            return callback(stderr);        callback(null, stdout.toString().split("\n")[0]);    });};function asyncRepeat(callback, onDone) {    callback(function() {        asyncRepeat(callback, onDone);    }, onDone);}