Kevin Wang knwang

How Does a Web Application Keep Track of its Users?

If you have an Gmail account, you have probably observed that when you visit http://www.gmail.com, sometimes it asks for your username and password, but sometimes it takes you directly into your inbox; Similarly, when you visit http://www.amazon.com, you may be surprised that the front page has your first name on it! How do websites like Google and Amazon keep track of user identity and information? In this article, we are going to explore this topic, and explain how web applications use cookies to track their users over time.

Web applications do not track users by default

The core technologies that power the Internet are designed such that when you make requests to web servers, for example, Google's front page http://www.google.com, the web server does not know who you are, nor does it have any memory of its past interactions with you. The protocol that governs the transportation of data between your browser and Google's server, which is called

	.search
	= form_tag search_candidates_path, method: :post do
	%fieldset
	= text_field_tag :search, params[:search]
	= submit_tag "Search"

	%table.standard
	%thead
	%tr
	- ["Name", "Phone", "Email", "Github", "Twitter", "Local", "Willing to Relocate"].each do \|th\|

	class CandidatesController < ApplicationController
	expose(:candidates) { Candidate.search(params[:search]).order(:first_name) }

	def search
	render :index
	end
	end

	<body>
	<div id="hug_a_rocketeer">
	<ul id="rocketeers">
	<li>
	<div id='pic_and_name'>
	<img src='http://dummyimage.com/50x50/574b57/bcbfeb.png'/>
	<span> Marian Phalen </span>
	</div>
	<ul id="props">
	<li> 3 Hugs </li>

	$(function(){
	var Person = Backbone.Model.extend({
	defaults: {
	img_url: '',
	name: '',
	hugs: 0,
	},
	refresh_hugs: function() {
	var self = this;
	$.getJSON(this.get("search_url"), function(data) {

	....

	returned_results: 0,

	initialize: function() {
	var self = this;
	this.collection = new People();

	_.each(rocketeers, function(person) {
	$.getJSON(person.get("search_url"), function(data) {

	require 'spec_helper'

	feature 'User invites a friend' do
	context 'User successfully invites friend to join' do
	Given(:alice) { Fabricate(:user) }

	When do
	sign_in(alice)
	invite_a_friend
	friend_accepts_invitation

	require 'rack'
	require './extract_data'

	surfing_app = Surfing.new
	run surfing_app

	at_exit do
	data = YAML.dump(surfing_app.journal_entries)
	File.open("data/journal_entries.yml", 'w') do \|file\|
	file.write(data)

	Simplest Rails

	1. Route, ApplicationsController that renders some HTML
	2. Separate content and flow control - HTML as "views"
	3. dynamically generated pages
	- data with different time
	- render template, passing in the data
	- render "dir/hello_world.html", locals: {time: "am"}

	- data from the URL

	local ret_status="%(?:%{$fg_bold[green]%}➜ :%{$fg_bold[red]%}➜ %s)"
	PROMPT='${ret_status}%{$fg_bold[green]%}%p %{$fg[cyan]%}%c %{$reset_color%}$(git_prompt_info)% %{$reset_color%}'

	git_prompt_info () {
	local g="$(git rev-parse --git-dir 2>/dev/null)"
	if [ -n "$g" ]; then
	local r
	local b
	local d
	local s