[ExpressJS] ExpressJS www없이 접속 www로 리다이렉트(Redirect) 처리

var express = require("express");
var app = express.createServer();

app.all(/.*/, function(req, res, next) {
  var host = req.header("host");
  if (host.match(/^www\..*/i)) {
    next();
  } else {
    res.redirect(301, "http://www." + host + req.url);
  }
});