Web Programming Step by Step

Lecture 23
Cookies and Sessions

References: tizag.com sessions, cookies; Codewalkers

Except where otherwise noted, the contents of this presentation are Copyright 2010 Marty Stepp and Jessica Miller.

Valid XHTML 1.1 Valid CSS!

Stateful client/server interaction

amazon cookie

Sites like amazon.com seem to "know who I am." How do they do this? How does a client uniquely identify itself to a server, and how does the server provide specific content to each client?

What is a cookie?

om nom nom

How cookies are sent

cookie exchange

Myths about cookies

A "tracking cookie"

tracking cookie figure

How long does a cookie exist?

Where are the cookies on my computer?

good enough for me

Cookies in JavaScript

document.cookie = "username=smith";   // setting two cookies
document.cookie = "password=12345";
document.cookie = "age=29; expires=Thu, 01-Jan-1970 00:00:01 GMT";  // deleting a cookie
...

// (later)
var allCookies = document.cookie.split(";");    // ["username=smith", "password=12345"]
for (var i = 0; i < allCookies.length; i++) {
	var eachCookie = allCookies[i].split("=");    // ["username", "smith"]
	var cookieName = eachCookie[0];               // "username"
	var cookieValue = eachCookie[1];              // "smith"
	...
}

CSE 190 M Cookies library

<!-- using the instructor-provided Cookies.js class -->
<script src="Cookies.js" type="text/javascript"></script>

Cookies.set("username", "smith");
// (later)
alert(Cookies.get("username"));   // smith

Setting a cookie in PHP

setcookie("name", "value");

setcookie("username", "martay");
setcookie("favoritecolor", "blue");
  • technically, a cookie is just part of an HTTP header, and it could be set using PHP's header function (but this is less convenient, so you would not want to do this):
    • header("Set-Cookie: username=martay; path=/; secure");

Retrieving information from a cookie

$variable = $_COOKIE["name"];   # retrieve value of the cookie

if (isset($_COOKIE["username"])) {
	$username = $_COOKIE["username"];
	print("Welcome back, $username.\n");
} else {
	print("Never heard of you.\n");
}
print("All cookies received:\n");
print_r($_COOKIE);
  • unset function deletes a cookie

Setting a persistent cookie in PHP

setcookie("name", "value", timeout);

$expireTime = time() + 60*60*24*7;   # 1 week from now
setcookie("CouponNumber", "389752", $expireTime);
setcookie("CouponValue", "100.00", $expireTime);

Removing a persistent cookie

setcookie("name", "", time() - 1);

setcookie("CouponNumber", "", time() - 1);

What is a session?

How sessions are established

session

Sessions in PHP: session_start

session_start();

Accessing session data

$_SESSION["name"] = value;        # store session data
$variable = $_SESSION["name"];     # read session data
if (isset($_SESSION["name"])) {  # check for session data

if (isset($_SESSION["points"])) {
	$points = $_SESSION["points"];
	print("You've earned $points points.\n");
} else {
	$_SESSION["points"] = 0;  # default
}

Where is session data stored?

session cookie

Browsers that don't support cookies

session_start();   # same as usual

# Generate a URL to link to one of our site's pages
# (you probably won't ever need to do this)
$orderUrl = "/order.php?PHPSESSID=" . session_id();

Session timeout