Cookie Breakdown: Fixing Special Character Issues in Web Apps

Cookies are the unsung heroes of the web, quietly managing user sessions, preferences, and other data while we browse, shop, and log in. But when you start dealing with special characters—spaces, accents, symbols, and more—cookie handling can quickly descend into a chaos of miscommunication between browsers and web servers.

Let’s take a look at the special character handling in cookies and how to avoid the pitfalls through real-world examples and best practices. Buckle up, as we journey through a history of cookie blunders, browser quirks, and clever solutions.

A Comedy of Errors: The Challenges of Special Characters

Let’s start with the classic case of special characters: spaces. Different browsers handle spaces in cookies inconsistently, causing a range of issues that developers have to troubleshoot:

• Chrome and Firefox encode spaces as %20.
• Internet Explorer and older versions of Edge encode spaces as +.

This leads to scenarios where the same cookie, containing a user’s language preference, could be interpreted differently depending on the browser.

Example: Language Dropdown Gone Wrong

Suppose you’re managing a multilingual website with a dropdown for language selection. The user chooses "French Canadian", which, of course, includes a space. Depending on the browser:

• Chrome/Firefox would store this as French%20Canadian.
• IE/Edge would store it as French+Canadian.

Without careful handling, this simple space could break your app when users switch between browsers, leading to incorrect data display or even bugs.

Here’s a PHP snippet to store and retrieve this cookie correctly:

// Storing a language preference in a cookie
$language = rawurlencode("French Canadian"); 

// Encoding space as %20 
setcookie('preferredLanguage', $language, time() + 3600, "/");

// Retrieving and decoding the language cookie 
if (isset($_COOKIE['preferredLanguage'])) { 
    $decodedLanguage = rawurldecode($_COOKIE['preferredLanguage']); 
    echo "User's Language: $decodedLanguage"; 
}        

Handling Special Characters: %20 vs. + (A High-Priority Bug)

Let’s dig deeper into the specific issue of encoding spaces. In URL encoding, spaces can either be represented as %20 or +. This is where the comedy really begins.

• %20 is the official encoding in URLs (per RFC 3986).
• + is a legacy encoding, often used in application/x-www-form-urlencoded data (typically in forms).

The Bug: Why is This a Problem? When a cookie stores a space as + in one browser and %20 in another, retrieving the cookie without proper decoding can lead to different behaviors across browsers. For example:

• A user’s selected language might display as "French+Canadian" in some browsers, causing confusion and potential display issues.

To prevent this, you should always encode spaces as %20 for consistency across browsers.

// Avoid using + for spaces, ensure %20 is used 
$language = rawurlencode("French Canadian"); // Encodes space as %20        

Key takeaway: Prioritize encoding spaces as %20 and avoid using + to eliminate potential bugs when cookies are shared across browsers.

Other Special Characters: It Gets Trickier

While spaces might seem like a small hiccup, handling other special characters such as ampersands (&), semicolons (;), or accented characters (é, ?) can create more complex issues. These characters, if not properly encoded, can cause cookie values to truncate or behave unexpectedly.

Key Examples:

• Ampersands (&): If not properly encoded, they might break the cookie string, resulting in incomplete data.
• Semicolons (;): These can terminate the cookie prematurely, causing parts of your cookie value to be lost.
• Accented characters (é, ?): Browsers handle non-ASCII characters differently, so it’s important to use UTF-8 encoding.

Here’s a comprehensive example of how to store and retrieve cookies containing special characters:

// Store cookie with special characters
$language = rawurlencode("Café au lait; Fran?ais canadien & 中国"); setcookie('userLanguageAndPreference', $language, time() + 3600, "/"); 

// Retrieve and decode the special characters correctly 
if (isset($_COOKIE['userLanguageAndPreference'])) { 
    $decodedValue = rawurldecode($_COOKIE['userLanguageAndPreference']); 
    echo "Your selection: $decodedValue"; 
}        

Output:

Your selection: Café au lait; Fran?ais canadien & 中国        

Notice how we handle multiple special characters, ensuring they are correctly encoded and decoded.

The Shortcomings of URL Encoding

While URL encoding is a reliable method to handle special characters in cookies, it’s not without its downsides:

• Increased Data Size: Special characters like %20 take up more space than their original counterparts. This can quickly eat into the cookie size limit (typically 4096 bytes).
• Double Encoding Issues: If a string is URL-encoded twice, it can become corrupted (%25 for %, for instance), leading to data integrity problems.
• Limited Readability: When debugging cookies, reading URL-encoded data isn’t as intuitive. A string like Fran%C3%A7ais%20canadien isn’t as easy to interpret as "Fran?ais canadien."

Recommendations: Keep It Consistent

Given the complexity of handling cookies across browsers, the best practices for managing special characters are:

1. Always encode spaces as %20: This ensures consistency across all browsers and avoids the + issue.
2. Use rawurlencode() and rawurldecode(): These functions handle special characters like semicolons, ampersands, and non-Latin characters properly.
3. Sanitize all cookie inputs: Before storing any data in cookies, make sure it’s sanitized to prevent injection attacks or malformed data.
4. Avoid double encoding: Ensure your data is only encoded once, and test to avoid any double encoding scenarios.

Conclusion: Avoiding the Cookie Chaos

Handling special characters in cookies might feel like navigating a comedy of errors, but with the right approach, you can avoid the pitfalls and ensure consistency across platforms. From spaces to accented characters, proper encoding is essential to delivering a smooth user experience.

Always test your cookies across multiple browsers, ensure you're using the correct encoding method, and don’t forget to decode them when retrieving the data. By following these practices, you'll sidestep the famous cookie-related bugs of the past and deliver seamless web experiences.