HTML Purifier is a standards-compliant HTML filter library written in PHP. It removes malicious code (such as cross-site scripting) from user-submitted HTML, ensuring that the output is safe to display on a web page.

Pros

• Comprehensive Security: HTML Purifier is designed to thoroughly sanitize HTML input, protecting against a wide range of security vulnerabilities, including cross-site scripting (XSS), SQL injection, and more.
• Flexible Configuration: The library provides a highly customizable configuration system, allowing developers to tailor the sanitization process to their specific needs.
• Standards Compliance: HTML Purifier adheres to web standards, ensuring that the output is compatible with modern browsers and web technologies.
• Active Development and Community: The project is actively maintained, with regular updates and a supportive community of contributors.

Cons

• Performance Overhead: Depending on the complexity of the input and the level of sanitization required, HTML Purifier may introduce some performance overhead, which could be a concern for high-traffic websites.
• Complexity: The library's comprehensive feature set and configurability can make it more complex to set up and integrate into a project, especially for developers new to the library.
• Dependency on PHP: As a PHP-based library, HTML Purifier is limited to projects that are built using the PHP programming language.
• Potential Compatibility Issues: While the library aims to be standards-compliant, there may be instances where the sanitized output does not perfectly match the original input, which could cause compatibility issues with certain web applications.

Code Examples

Here are a few examples of how to use HTML Purifier in your PHP code:

1. Basic HTML Sanitization:

require_once 'vendor/autoload.php';

$config = HTMLPurifier_Config::createDefault();
$purifier = new HTMLPurifier($config);

$dirtyHTML = '<script>alert("XSS attack!");</script><p>This is some safe HTML.</p>';
$cleanHTML = $purifier->purify($dirtyHTML);

echo $cleanHTML;

2. Customizing the Purifier Configuration:

$config = HTMLPurifier_Config::createDefault();
$config->set('HTML.Allowed', 'p,a[href],img[src]');
$config->set('HTML.MaxImgLength', '500');

$purifier = new HTMLPurifier($config);
$cleanHTML = $purifier->purify($dirtyHTML);

3. Caching for Performance:

$config = HTMLPurifier_Config::createDefault();
$config->set('Cache.SerializerPath', '/path/to/cache/directory');

$purifier = new HTMLPurifier($config);
$cleanHTML = $purifier->purify($dirtyHTML);

4. Handling User-Uploaded Files:

$config = HTMLPurifier_Config::createDefault();
$config->set('URI.AllowedSchemes', array(
    'http' => true,
    'https' => true,
    'mailto' => true,
    'ftp' => true,
    'urn' => true,
));

$purifier = new HTMLPurifier($config);
$cleanHTML = $purifier->purify(file_get_contents('/path/to/uploaded/file.html'));

Getting Started

To get started with HTML Purifier, follow these steps:

1. Install the library using Composer:

composer require ezyang/htmlpurifier

2. Require the Composer autoloader in your PHP script:

require_once 'vendor/autoload.php';

3. Create a new HTMLPurifier instance with the default configuration:

$config = HTMLPurifier_Config::createDefault();
$purifier = new HTMLPurifier($config);

4. Use the purify() method to sanitize your HTML input:

$dirtyHTML = '<script>alert("XSS attack!");</script><p>This is some safe HTML.</p>';
$cleanHTML = $purifier->purify($dirtyHTML);

echo $cleanHTML;