Return the response time as a HTTP header in NodeJS

middleware.js

var time = require('./response-time');

app.configure(function(){
  app.use(time());
});

response-time.js

/*!
 * Connect - responseTime
 * Copyright(c) 2011 TJ Holowaychuk
 * MIT Licensed
*/

module.exports = function responseTime(){
  return function(req, res, next){
    var start = new Date();

    if (res._responseTime) return next();
    res._responseTime = true;

    res.on('header', function(){
      var duration = new Date() - start;
      res.setHeader('X-Response-Time', duration + 'ms');
    });

    next();
  };
};