Developing State-enabled Applications With PHP

Installment 1

Developing State-enabled Applications With PHP

When a user is browsing through a website and is surfing from one web page to another, sometimes the website needs to remember the actions (e.g. choices) performed by the user. For example, in a website that sells DVDs, the user typically browses through a list of DVDs and selects individual DVDs for check out at the end of the shopping session. The website needs to remember which DVDs the user has selected because the selected items needs to be presented again to the user when the user checks out. In other words, the website needs to remember the State - i.e. the selected items - of the user's browsing activities.

However, HTTP is a Stateless protocol and is ill-equipped to handle States. A standard HTML website basically provides information to the user and a series of links that simply directs the user to other related web pages. This Stateless nature of HTTP allows the website to be replicated across many servers for load balancing purposes. A major drawback is that while browsing from one page to another, the website does not remember the State of the browsing session. This make interactivity almost impossible.

In order to increase interactivity, the developer can use the session handling features of PHP to augment the features of HTTP in order to remember the State of the browsing session. The are basically 2 ways PHP does this:

1. Using cookies
2. Using Sessions

The next installment discusses how to manage sessions using cookies...

Installment 2

Cookies

Cookies are used to store State-information in the browser. Browsers are allowed to keep up to 20 cookies for each domain and the values stored in the cookie cannot exceed 4 KB. If more than 20 cookies are created by the website, only the latest 20 are stored. Cookies are only suitable in instances that do not require complex session communications and are not favoured by some developers because of privacy issues. Furthermore, some users disable support for cookies at their browsers.

The following is a typical server-browser sequence of events that occur when a cookie is used:

1. The server knows that it needs to remember the State of browsing session

2. The server creates a cookie and uses the Set-Cookie header field in the HTTP response to pass the cookie to the browser

3. The browser reads the cookie field in the HTTP response and stores the cookie

4. This cookie information is passed along future browser-server communications and can be used in the PHP scripts as a variable

PHP provides a function called setcookie() to allow easy creation of cookies. The syntax for setcookie is: int setcookie(string name, [string val], [int expiration_date], [string path], string domain, [int secure])

The parameters are:

1. name - this is a mandatory parameter and is used subsequently to identify the cookie

2. value - the value of the cookie - e.g. if the cookie is used to store the name of the user, the value parameter will store the actual name - e.g. John

3. expiration_date - the lifetime of the cookie. After this date, the cookie expires and is unusable

4. path - the path refers to the URL from which the cookie is valid and allowed

5. domain - the domain the created the cookie and is allowed to read the contents of the cookie

6. secure - specifies if the cookie can be sent only through a secure connection - e.g. SSL enable sessions

The following is an example that displays to the user how many times a specific web page has been displayed to the user. Copy the code below (both the php and the html) into a file with the .php extension and test it out.

[?php //check if the $count variable has been associated with the count cookie if (!isset($count)) {

$count = 0; } else {

$count++; } setcookie("count", $count, time()+600, "/", "", 0); ?]

[html]

[head]

[title]Session Handling Using Cookies[/title]

[/head]

[body]

This page has been displayed: [?=$count ?] times.

[/body] [/html]

The next installment discusses how to manage sessions using PHP session handling functions with cookies enabled...

Installment 3

PHP Session Handling - Cookies Enabled

Instead of storing session information at the browser through the use of cookies, the information can instead be stored at the server in session files. One session file is created and maintained for each user session. For example, if there are three concurrent users browsing the website, three session files will be created and maintained - one for each user. The session files are deleted if the session is explicitly closed by the PHP script or by a daemon garbage collection process provided by PHP. Good programming practice would call for sessions to be closed explicitly in the script.

The following is a typical server-browser sequence of events that occur when a PHP session handling is used:

1. The server knows that it needs to remember the State of browsing session

2. PHP generates a sssion ID and creates a session file to store future information as required by subsequent pages

3. A cookie is generated wih the session ID at the browser

4. This cookie that stores the session ID is transparently and automatically sent to the server for all subsequent requests to the server

The following PHP session-handling example accomplishes the same outcome as the previous cookie example. Copy the code below (both the php and the html) into a file with the .php extension and test it out.

[?php //starts a session session_start();

//informs PHP that count information needs to be remembered in the session file if (!session_is_registered("count")) {

session_register("count");

$count = 0; } else {

$count++; }

$session_id = session_id(); ?]

[html]

[head]

[title]PHP Session Handling - Cookie-Enabled[/title]

[/head]

[body]

The current session id is: [?=$session_id ?]

This page has been displayed: [?=$count ?] times.

[/body] [/html]

A summary of the functions that PHP provides for session handling are:

1. boolean start_session() - initializes a session

2. string session_id([string id]) - either returns the current session id or specify the session id to be used when the session is created

3. boolean session_register(mixed name [, mixed ...]) - registers variables to be stored in the session file. Each parameter passed in the function is a separate variable

4. boolean session_is_registered(string variable_name) - checks if a variable has been previously registered to be stored in the session file

5. session_unregister(string varriable_name) - unregisters a variable from the session file. Unregistered variables are no longer valid for reference in the session.

6. session_unset() - unsets all session variables. It is important to note that all the variables remain registered.

7. boolean session_destroy() - destroys the session. This is opposite of the start_session function.

The next installment discusses how to manage sessions using PHP session handling functions when cookies are disabled...

Installment 4

PHP Session Handling - Without Cookies

If cookies are disabled at the browser, the above example cannot work. This is because although the session file that stores all the variables is kept at the server, a cookie is still needed at the browser to store the session ID that is used to identify the session and its associated session file. The most common way around this would be to explicitly pass the session ID back to the server from the browser as a query parameter in the URL.

For example, the PHP script generates requests subsequent to the start_session call in the following format: http://www.yourhost.com/yourphpfile.php?PHPSESSID=[actual session ID]

The following are excerpts that illustrate the discussion:

Manually building the URL:
$url = "http://www.yoursite.com/yourphppage.php?PHPSESSID=" . session_id(); [a href="[?=$url ?]"]Anchor Text[/a]

Building the URL using SID:
[a href="http://www.yoursite.com/yourphppage.php?[?=SID ?]"]Anchor Text[/a]

Used with the author's permission.

This article is written by John L.
John L is the Webmaster of Designer Banners (http://www.designerbanners.com).

---

Beyond Web Usability: Web Credibility

If you've been developing websites on Mars for the past... Read More

Making The Business Case For Web Standards

Through the explosive growth of the Web, companies have realized... Read More

Study Your Sites Performance Via Hit Tracking

Knowledge is power.And undoubtedly, it is the key to making... Read More

Get Your Business on the Web

I can't think of any business alive today that couldn't... Read More

How to Create a Professional Web Site in 24 Hours

While creating a Web site may seem like... Read More

Thinking Of Taking Money Online? Whats Best For Merchants? PayPal, WorldPay or Something Else?

It's now easier than ever to take payments on the... Read More

The Dos and Donts of Launching a Small Business Website

Launching a new small business website is often a long... Read More

The Power Is In The Pipes: How To Get Maximum Leverage From Your Website

What is the most important part of your online business?Many... Read More

Content Management ? The New Standard in Web Design

The evolution of web development parallels the model of technology... Read More

CPanel Fantastico - Features and Benefits

Fantastico is a 3rd-party cPanel add-on and can be purchased... Read More

Abandonment - Why Visitors Don?t Turn Into Customers

Every good Internet business understands the value of conversions versus... Read More

Ten Ways NOT to Set Up a Website-based Service Business

1. As the first step, "Hire a web designer."First create... Read More

Building eCommerce Websites that Work - Part 2

Succeeding with an eCommerce website is a dream for many... Read More

Beware the Software Siren

I've heard several prominent web marketers mention in their classes... Read More

Why Should Your Business Go O.N.L.I.N.E.

Optimize your time. How much time each day must you... Read More

Tell me what your website does!

You know exactly what your organisation does and what your... Read More

WYSIWYG Versus Coding: HTML With A Purpose

After years of working with entrepreneurs who developed their first... Read More

The Power Of CPanel

cPanel is a control panel for your website and allows... Read More

How to Get a Knock Out Website!

The first step in setting up an online business...Starting an... Read More

Running An Effective Website

Running an effective website is a continuous process. I have... Read More

Making the Most of Your Website: Start with the Basics

One of my most salient memories from when I sold... Read More

Tips for Building a Great Business Website

A website is lifeline of internet home business. In order... Read More

Link Trades That Waste Your Time

Never has competition been so difficult in the Internet world.... Read More

Introductory PHP For Non-Programmers

When you started reading this sentence you assumed lo acabaría... Read More

FREE Amber Alert Tickers for Your Website

Project Safekids provides webmasters a valuable tool which could save... Read More

The Number One Reason Most Websites Fail

Failure, just like success, is measured differently by each and... Read More

The 5 Biggest Mistakes Almost All Web Designers Make

Huge Mistake #1: Creating a Website with Flash -- Did... Read More

Your Website Should Be Selling

It may come as some surprise to a traditionally off-line... Read More

Five Essential Questions to Answer Before Creating Your First (or second...or third) Website

Right after the thought, "I need a website," people usually... Read More

Be Creative Before You Purchase Or Create A Website

Before you jump into spending coutnless hours on designing and... Read More

The Web: Your Window of Opportunity

Thinking about starting up a business? The web is the... Read More

Build or Buy a CMS?

Creating a content management system either from scratch,... Read More

The Two Most Common Mistakes That Scare Away Web Visitors

Can you imagine the hypocrisy of spending thousands of dollars,... Read More