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 var salt = 'secret key' 

     9 

    10 function mk_hash(s) {

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

    12 }

    13 

    14 function mk_cookie(c) {

    15     return c.toString() + '-' + mk_hash(c.toString() + salt)

    16 }

    17 

    18 function gt_cookie(s) {

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

    20     var counter = parseInt(splits[0])

    21     var hash = splits[1]

    22     if (mk_hash(counter.toString() + salt) == hash) {

    23 	return counter

    24     } else {

    25 	return 0

    26     }

    27 }

    28 

    29 

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

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

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

    33     if (counter >= 5) {

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

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

    36     } else {

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

    38     }

    39     res.end();

    40 });

    41 

    42 // starting the server

    43 app.listen(8000);

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