PHP Sessions

Proper management of user data is important for an enhanced user experience in any online application. PHP sessions are helpful for this purpose because they allow developers to store user data and access this information on multiple pages. This article will discuss in detail PHP sessions and their management, with a focus on user authentication. It will also list the best practices when using PHP sessions. If you are new to web development and want to learn and understand how to maintain user state and build secure login systems, this guide is for you.

Table of Contents:

• What Are PHP Sessions?
• PHP Sessions vs. Cookies: What’s the Difference?
• How PHP Session Management Works Internally?
• How to Use PHP Sessions
  • Step 1: Starting a PHP Session
  • Step 2: Storing Data in PHP Sessions
  • Step 3: Retrieving Session Data
  • Step 4: Checking if Session Variables Exist
  • Step 5: Destroying PHP Sessions
• Managing PHP Sessions
• Best Practices for Session Management
• Debugging Common PHP Session Issues
• Advantages of PHP Sessions
• PHP Session Cheatsheet
• Conclusion

What Are PHP Sessions?

When a user visits a website, they will interact with things such as forms, buttons, and links. Interacting with these elements can create sessions that keep track of user states as they navigate from item to item on the website. The PHP sessions are a server-side storage method of keeping track of user activity without having to continually be manually passing information between the client and the server.

PHP Sessions vs Cookies: What’s the Difference?

Before we proceed with our exploration of PHP sessions, we should clearly understand the distinction between sessions and cookies. PHP sessions, by design, are meant to alleviate the downsides of PHP cookies. Therefore, let’s take a closer look at the concept of cookies.

What are Cookies?

Cookies are small pieces of data stored on a client’s computer. Cookies can store different kinds of data, such as user preferences or session tokens or session identifiers. Cookies have limitations including size restrictions and security. Since cookies are written on the client-side, sensitive data should not be stored within cookies.

How Sessions Overcome Cookie Limitations

PHP sessions are a lot more secure than cookies because they store information server-side, along with a unique identifier that identifies the session of each user. Additionally, sessions do not expose sensitive information to any clients. Moreover, sessions can store much larger amounts of data than cookies. Sessions are ideal when you need to store large amounts of user data.

Why Use PHP Sessions?

Managing users effectively is crucial for any application that requires user authentication or personalization. It is the job of the developer to design a pipeline or a system that accurately segregates and stores each user’s information for a better user experience. For instance, online stores need to remember what items a user has added to their cart. Social media platforms must keep track of the information of the user who has just logged in. With the Session Management feature of PHP, developers can make better applications to improve both functionality and user experience. 

• Enhanced User Experience: Sessions improve the user experience by letting users maintain user states, which allows users to navigate more smoothly. In other words, users log in once and remain logged in without needing to reauthenticate on every page.
• Personalization: Using sessions, web applications can provide personalization in the form of user preference content. For example, if you are shopping on an e-commerce site, even after you navigate away from the shopping cart page, sessions will keep the items in your cart.
• Increased Security: When developers use PHP Sessions, they can create security features that prevent unauthorized access and session fixation, as well as create an automated session ending and message to the user when their session has expired or has to be restarted.

How PHP Session Management Works Internally?

Understanding how PHP sessions function under the hood is important for a beginner developer to effectively implement them in their applications. Sessions work by creating a unique identifier for each user and storing session data on the server.

Lifecycle of a PHP Session

The lifecycle of a PHP session consists of these major stages:

1. Creation: A new session is created when a user first accesses a website. 
2. Storage: Data associated with the user’s session is stored on the server.
3. Retrieval: Session data can be accessed on any page where the session is started.
4. Validation: You can check if certain session variables exist before using them to avoid errors.
5. Destruction: The session data is deleted when a user logs out or the session times out.

Each of these stages is important in ensuring smooth transitions and secure user interactions with the server on your website.

Various Session Storage Mechanisms

Server-Side Sessions PHP utilizes various methods for storing session data. This includes:

• Filesystem
• Databases
• In-memory storage systems (like Redis)

Choosing the right storage mechanism depends on the requirements of your application. It also depends on the amount of storage you have available on the server. You don’t want to deploy a method that causes too much memory overhead.

The Role of Session IDs

This is the most important component of a session. The whole mechanism of how session works is dependent on the Session IDs. Every session is assigned a unique session ID, typically generated when the session starts. The session ID is sent to the client as a cookie or via URL parameters. This ID is then used to retrieve the corresponding session data stored on the server. Session IDs are typically stored in a cookie named PHPSESSID by default.

How to Use PHP Sessions?

Now that we are familiar with the fundamentals, let us delve into the practical aspects of using PHP sessions in your applications. In this section, you will understand each stage of the Session Lifecycle and the beginner-level implementation of them. This will help you add this functionality to your web application and create a better user experience.

Step 1: Starting a PHP Session

To initiate a session in PHP, use the session_start() function. This function either initializes a new session or continues a previously started session based on the session ID sent from the client.

Remember: Make sure that you must call session_start() at the beginning of your script before any output is sent to the browser.  If you do not, you will have errors and possibly broken functionality.

Code:

<?php
session_start();

$_SESSION['username'] = 'Aarav';

echo "Session started. Username is: " . $_SESSION['username'];
?>

Output: 

Explanation:

This code starts a session and stores the name “Aarav” in a session variable called username. It then prints the stored username to the screen.

This output appears in the browser when you run the PHP file on a server (like XAMPP, WAMP, or a live server).

Step 2: Storing Data in PHP Sessions

We encountered a session variable in the example above by the name of username. Once a session is started, you can store data using the $_SESSION array. This data remains available throughout the user’s interaction with the site.

Code:

<?php
session_start();

$_SESSION['username'] = 'Aarav';
$_SESSION['user_id'] = 101;

echo "User " . $_SESSION['username'] . " with ID " . $_SESSION['user_id'] . " is logged in.";
?>

Output:

Explanation: 

Here, we store both a username and a user ID into session variables. This information can now be accessed on any page where session_start() is called.

Note: If you are running this code on a browser, the ‘n’ character won’t work. It will instead show as plain text. Use the <br> HTML tag to create a new line or line break. 

Step 3: Retrieving Session Data

When you store this information, you can then call this data at some point and utilize it elsewhere on your website.

Code:

<?php
session_start();

echo "Welcome back, " . $_SESSION['username'] . "!";
?>

Output:

Explanation: The code above retrieves the session variable username that we stored in the ‘storing session data’ example. This demonstrates how session data allows for continuity between pages.

Step 4: Checking if Session Variables Exist

Whenever you are going to use session variables, it is best practice to check for existence with the isset() function to avoid PHP undefined index errors.

Code:

<?php
session_start();

if (isset($_SESSION['username'])) {
    echo "Welcome, " . $_SESSION['username'];
} else {
    echo "Please log in.";
}
?>

Output:

Explanation: This conditional check is helpful because it checks for existence of the session variable before using it, and if it is not set, it gives the user a reason to log in.

Step 5: Destroying PHP Sessions

Once the session is over or the time specified for the session has expired, you, as the developer, must make sure that it gets destroyed by itself. To destroy a session, you will need to make use of session_destroy().  session_destroy() deletes session data on the server, but it does not remove session variables already stored in the $_SESSION array in the current script. To fully clear session data, also use session_unset() in addition to session_destroy().

Code: 

<?php
session_start();

$_SESSION['username'] = 'Aarav';
session_destroy();

echo "Session destroyed.";
?>

Output:

Explanation: We start the session and assign a value to $_SESSION[‘username’]. Then we call session_destroy(), which will remove all session data but won’t unset variables in the current script.

Managing PHP Sessions

There are a few other actions you can do with your PHP sessions that helps you enhance user experience.

Unsetting Session Variables

If you want to remove a specific session variable, you can use the unset() function. This function allows you flexibility in managing session data. This contributes to the overall efficiency and performance of your web application.

Code: 

<?php
session_start();

$_SESSION['username'] = 'Aarav';
unset($_SESSION['username']);

echo isset($_SESSION['username']) ? "Username exists." : "Username is unset.";
?>

Output:

Explanation: In this code example, we set a session variable username, then unset it using unset(). After unsetting, we check its existence and display the result.

Unsetting Session Data

This is different from unsetting variables in concept but uses the same function, unset(). You may sometimes wish to unset specific data without terminating the entire session.

Code: 

<?php
session_start();

$_SESSION['user_id'] = 101;
unset($_SESSION['user_id']);

echo isset($_SESSION['user_id']) ? "User ID exists." : "User ID is unset.";
?>

Output:

Explanation: Here, we set and then unset the user_id session variable. We confirm its removal by checking if it is still set. You can ignore the warning.

Regenerating Session IDs

Regenerating session IDs is a security best practice, especially during critical actions like logging in. You can regenerate a session ID using the session_regenerate_id() function. Regenerating session IDs prevents session fixation attacks, especially during login or other critical actions.

Code: 

<?php
session_start();

session_regenerate_id(true);
echo "Session ID regenerated.";
?>

Output:

Explanation: To generate a new session ID, you give the true parameter to the session_regenerate_id() function. It will generate a new session ID.

How to Enable Auto Session Start in PHP via php.ini

By default, you have to manually start a session in PHP using the start_session() function. However, PHP allows you to auto-start sessions whenever a user accesses the site. You can do this by making adjustments in the php.ini file. In the file, set the session.auto_start directive to 1. For the change to take effect on your website, restart the web server. 

session.auto_start = 1

Best Practice: 

In most real-world applications, it is better to call session_start() manually. This gives you more control and avoids unexpected behaviors, especially in REST APIs or when returning non-HTML content.

Caution:

• No need to call session_start() in your scripts if session.auto_start is enabled.
• session.auto_start can interfere with frameworks or output buffering in some setups.

Best Practices for Session Management

By adopting best practices in session management, you can optimize performance and security. Adopting best practices can help protect user data and enable a safer browsing experience. Below are a few tactics you should implement for improved session management.

• Always validate user input when retrieving session data.
• When performing important actions, regenerate session IDs when re-establishing sessions.
• Utilize HTTPS to encrypt session data in transit.

Debugging Common PHP Session Issues

Issue 1:  Session_start() Doesn’t Work

This is often the result of output being sent to the browser before the session_start() function is called. Always put session_start() at the very beginning of your PHP script.

Issue 2: Session Data Is Not Saving

If your session data is not saving, check if session_start() is not called. It must be called at the beginning of each script that uses the $_SESSION variable, or the data will not be saved.

Issue 3:  $_SESSION Array Empty

This can happen if cookies are disabled in your browser. PHP sessionsuse cookies to identify users, so verify that your browser accepts them. This is why each website has a ‘necessary cookies’ option that the user must accept.

Issue 4:  Session Variables Disappear

Your session is probably timing out, and the variables are disappearing unexpectedly. To avoid this, you must increase the duration of the session/or increase the session.gc_maxlifetime value in your php.ini file.

Issue 5:  Session_destroy() does not clear Everything

When you call session_destroy(), you are ending the session, but you do not unset the session variables for the currently running script. To remove all the session data, you must also unset the $_SESSION variable by giving it the value of array(). This way, everything is new and destroyed.

Issue 6: Too Many Session ID Changes

It is a good security measure to change the session IDs, but calling session_regenerate_id() too many times can lead to confused and unintended results. Use this function with caution, and better to use it right after you log in.

Issue 7: Data Not Present Across Pages

In the event that your session data appears to be missing when you navigate to one of the pages, please ensure you call session_start() at the start of all .php files that utilize the session variables.

Advantages of PHP Sessions

1. Better Security for User Data
   Since the data is stored server-side, it’s less likely to be manipulated or modified. Unlike cookies, users can’t view or edit session data directly, which helps protect sensitive information like login states or preferences.
2. Server-Side Storage for Sensitive Information
   Sessions keep the sensitive information safely on the server
3. Persistence Across Multiple Pages
   Sessions allow information to be passed across multiple pages without requiring them to log in or reselect the options again and again. This saves a lot of time and enhances user experience.
4. Minimal Client-Side Storage
   Only the session ID is stored in the user’s browser (via a cookie or URL). This drastically reduces the amount of data exposed on the client-side and contributes to information safety
5. Unique Session IDs for Tracking
   Each session gets a unique ID, which makes it easy to track user interactions and personalize experiences without needing to constantly query a database.

PHP Session Cheatsheet

This table contains all the basic functions related to a session in PHP. You can use it to take a glance or as a checklist when setting up the mechanism for a session in your web application.

Conclusion

PHP sessions and cookies have made it possible to personalize every user’s web browsing experience. They make it possible for the browsers to start from where the user last left off. By understanding their importance, lifespan, and use cases, developers can implement PHP sessions to improve their user experience, along with ensuring the integrity and security of their data. As a web developer, you must understand how PHP sessions work and add them to your web application. PHP sessions can provide a great deal of benefits for your web application. 

To learn more about PHP, how to become a PHP developer, and gain hands-on experience. Also, prepare for job interviews with PHP interview questions prepared by industry experts.

PHP Sessions – FAQs