1 var express = require('express');

     2 var cookie  = require('cookie-parser')

     3 var crypto = require('crypto');

     4 

     5 var app = express();

     6 app.use(cookie());

     7 

     8 function mk_hash(s) {

     9     return crypto.createHash('sha1').update(s).digest('hex')

    10 }

    11 

    12 function mk_cookie(c) {

    13     return c.toString() + "-" + mk_hash(c.toString())

    14 }

    15 

    16 function gt_cookie(s) {

    17     var splits = s.split("-", 2);

    18     var counter = parseInt(splits[0])

    19     if (mk_hash(counter.toString()) == splits[1]) {

    20 	return counter

    21     } else {

    22 	return 0

    23     }

    24 }

    25 

    26 

    27 app.get('/', function(req, res){

    28     var counter = gt_cookie(req.cookies.counter) || 0;

    29     res.cookie('counter', mk_cookie(counter + 1));

    30     if (counter >= 5) {

    31 	res.write('You are a valued customer ' + 

    32 		  'visting the site ' + counter + ' times.');

    33     } else {

    34 	res.write('This is visit number '+ counter +'!');

    35     }

    36     res.end();

    37 });

    38 

    39 // starting the server

    40 app.listen(8000);

    41 console.log("Server running at http://127.0.0.1:8000/");