Monolog GDPR Filter

Monolog GDPR Filter is a PHP library that provides a Monolog processor for GDPR compliance. It allows masking, removing, or replacing sensitive data in logs using regex patterns, field-level configuration, and custom callbacks. Designed for easy integration with Monolog and Laravel.

Features

• Regex-based masking for patterns like SSNs, credit cards, emails
• Field-level masking/removal/replacement using dot-notation paths
• Custom callbacks for advanced masking logic per field
• Audit logging for compliance tracking
• Easy integration with Monolog and Laravel

Installation

Install via Composer:

composer require ivuorinen/monolog-gdpr-filter

Usage

Basic Monolog Setup

use Monolog\Logger;
use Monolog\Handler\StreamHandler;
use Ivuorinen\MonologGdprFilter\GdprProcessor;
use Ivuorinen\MonologGdprFilter\FieldMaskConfig;

$patterns = GdprProcessor::getDefaultPatterns();
$fieldPaths = [
    'user.ssn' => GdprProcessor::removeField(),
    'payment.card' => GdprProcessor::replaceWith('[CC]'),
    'contact.email' => GdprProcessor::maskWithRegex(),
    'metadata.session' => GdprProcessor::replaceWith('[SESSION]'),
];

// Optional: custom callback for advanced masking
$customCallbacks = [
    'user.name' => fn($value) => strtoupper($value),
];

// Optional: audit logger for compliance
$auditLogger = function($path, $original, $masked) {
    error_log("GDPR mask: $path: $original => $masked");
};

$logger = new Logger('app');
$logger->pushHandler(new StreamHandler('path/to/your.log', Logger::WARNING));
$logger->pushProcessor(
    new GdprProcessor($patterns, $fieldPaths, $customCallbacks, $auditLogger)
);

$logger->warning('This is a warning message.', [
    'user' => ['ssn' => '123456-900T'],
    'contact' => ['email' => 'user@example.com'],
    'payment' => ['card' => '1234567812345678'],
]);

FieldMaskConfig Options

• GdprProcessor::maskWithRegex() — Mask field value using regex patterns
• GdprProcessor::removeField() — Remove field from context
• GdprProcessor::replaceWith($value) — Replace field value with static value

Custom Callbacks

Provide custom callbacks for specific fields:

$customCallbacks = [
    'user.name' => fn($value) => strtoupper($value),
];

Audit Logger

Optionally provide an audit logger callback to record masking actions:

$auditLogger = function($path, $original, $masked) {
    // Log or store audit info
};

Important

: Be mindful what you send to your audit log. Passing the original value might defeat the whole purpose of this project.

Laravel Integration

You can integrate the GDPR processor with Laravel logging in two ways:

1. Service Provider

// app/Providers/AppServiceProvider.php
use Illuminate\Support\ServiceProvider;
use Ivuorinen\MonologGdprFilter\GdprProcessor;

class AppServiceProvider extends ServiceProvider
{
    public function boot()
    {
        $patterns = GdprProcessor::getDefaultPatterns();
        $fieldPaths = [
            'user.ssn' => '[GDPR]',
            'payment.card' => '[CC]',
            'contact.email' => '', // empty string = regex mask
            'metadata.session' => '[SESSION]',
        ];
        $this->app['log']->getLogger()
            ->pushProcessor(new GdprProcessor($patterns, $fieldPaths));
    }
}

2. Tap Class (config/logging.php)

// app/Logging/GdprTap.php
namespace App\Logging;
use Monolog\Logger;
use Ivuorinen\MonologGdprFilter\GdprProcessor;

class GdprTap
{
    public function __invoke(Logger $logger)
    {
        $patterns = GdprProcessor::getDefaultPatterns();
        $fieldPaths = [
            'user.ssn' => '[GDPR]',
            'payment.card' => '[CC]',
            'contact.email' => '',
            'metadata.session' => '[SESSION]',
        ];
        $logger->pushProcessor(new GdprProcessor($patterns, $fieldPaths));
    }
}

Reference in config/logging.php:

'channels' => [
    'stack' => [
        'driver' => 'stack',
        'channels' => ['single'],
        'tap' => [App\Logging\GdprTap::class],
    ],
    // ...
],

Configuration

You can configure the processor to filter out sensitive data by specifying:

• Regex patterns: Used for masking values in messages and context
• Field paths: Dot-notation paths for masking/removal/replacement
• Custom callbacks: For advanced per-field masking
• Audit logger: For compliance tracking

Testing & Quality

This project uses PHPUnit for testing, Psalm and PHPStan for static analysis, and PHP_CodeSniffer for code style checks.

Running Tests

To run the test suite:

composer test

To generate a code coverage report (HTML output in the coverage/ directory):

composer test:coverage

Linting & Static Analysis

To run all linters and static analysis:

composer lint

To automatically fix code style and static analysis issues:

composer lint:fix

Performance Considerations

Pattern Optimization

The library processes patterns sequentially, so pattern order can affect performance:

// Good: More specific patterns first
$patterns = [
    '/\b\d{3}-\d{2}-\d{4}\b/' => '***SSN***',     // Specific format
    '/\b\d+\b/' => '***NUMBER***',                // Generic pattern last
];

// Avoid: Too many broad patterns
$patterns = [
    '/.*sensitive.*/' => '***MASKED***',          // Too broad, may be slow
];

Large Dataset Handling

For applications processing large volumes of logs:

// Consider pattern count vs. performance
$processor = new GdprProcessor(
    $patterns,        // Keep to essential patterns only
    $fieldPaths,      // More efficient than regex for known fields
    $callbacks        // Most efficient for complex logic
);

Memory Usage

• Regex Compilation: Patterns are compiled on each use. Consider caching for high-volume applications.
• Deep Nesting: The recursiveMask() method processes nested arrays. Very deep structures may impact memory.
• Audit Logging: Be mindful of audit logger memory usage in high-volume scenarios.

Benchmarking

Test performance with your actual data patterns:

$start = microtime(true);
$processor = new GdprProcessor($patterns);
$result = $processor->regExpMessage($yourLogMessage);
$time = microtime(true) - $start;
echo "Processing time: " . ($time * 1000) . "ms\n";

Troubleshooting

Common Issues

Pattern Not Matching

Problem: Custom regex pattern isn't masking expected data.

Solutions:

// 1. Test pattern in isolation
$testPattern = '/your-pattern/';
if (preg_match($testPattern, $testString)) {
    echo "Pattern matches!";
} else {
    echo "Pattern doesn't match.";
}

// 2. Validate pattern safety
try {
    GdprProcessor::validatePatterns([
        '/your-pattern/' => '***MASKED***'
    ]);
    echo "Pattern is valid and safe.";
} catch (InvalidArgumentException $e) {
    echo "Pattern error: " . $e->getMessage();
}

// 3. Enable audit logging to see what's happening
$auditLogger = function ($path, $original, $masked) {
    error_log("GDPR Debug: {$path} - Original type: " . gettype($original));
};

Performance Issues

Problem: Slow log processing with many patterns.

Solutions:

// 1. Reduce pattern count
$essentialPatterns = [
    '/\b\d{3}-\d{2}-\d{4}\b/' => '***SSN***',
    '/\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b/' => '***EMAIL***',
];

// 2. Use field-specific masking instead of global patterns
$fieldPaths = [
    'user.email' => GdprProcessor::maskWithRegex(), // Only for specific fields
    'user.ssn' => GdprProcessor::replaceWith('***SSN***'),
];

// 3. Profile pattern performance
$start = microtime(true);
// ... processing
$duration = microtime(true) - $start;
if ($duration > 0.1) { // 100ms threshold
    error_log("Slow GDPR processing: {$duration}s");
}

Audit Logging Issues

Problem: Audit logger not being called or logging sensitive data.

Solutions:

// 1. Verify audit logger is callable
$auditLogger = function ($path, $original, $masked) {
    // SECURITY: Never log original sensitive data!
    $safeLog = [
        'path' => $path,
        'original_type' => gettype($original),
        'was_masked' => $original !== $masked,
        'timestamp' => date('c'),
    ];
    error_log('GDPR Audit: ' . json_encode($safeLog));
};

// 2. Test audit logger independently  
$processor = new GdprProcessor($patterns, [], [], $auditLogger);
$processor->regExpMessage('test@example.com'); // Should trigger audit log

// 3. Check if masking actually occurred
if ($original === $masked) {
    // No masking happened - check your patterns
}

Laravel Integration Issues

Problem: GDPR processor not working in Laravel.

Solutions:

// 1. Verify processor is registered
Log::info('Test message with email@example.com');
// Check logs to see if masking occurred

// 2. Check logging channel configuration
// In config/logging.php, ensure tap is properly configured
'single' => [
    'driver' => 'single',
    'path' => storage_path('logs/laravel.log'),
    'level' => 'debug',
    'tap' => [App\Logging\GdprTap::class], // Ensure this line exists
],

// 3. Debug in service provider
class AppServiceProvider extends ServiceProvider
{
    public function boot()
    {
        $logger = Log::getLogger();
        $processor = new GdprProcessor($patterns, $fieldPaths);
        $logger->pushProcessor($processor);

        // Test immediately
        Log::info('GDPR test: email@example.com should be masked');
    }
}

Error Messages

"Invalid regex pattern"

• Cause: Pattern fails validation due to syntax error or security risk
• Solution: Check pattern syntax and avoid nested quantifiers

"Compilation failed"

• Cause: PHP regex compilation error
• Solution: Test pattern with preg_match() in isolation

"Unknown modifier"

• Cause: Invalid regex modifiers or malformed pattern
• Solution: Use standard modifiers like /pattern/i for case-insensitive

Debugging Tips

1. Enable Error Logging:

   error_reporting(E_ALL);
   ini_set('display_errors', 1);
   

2. Test Patterns Separately:

   foreach ($patterns as $pattern => $replacement) {
       echo "Testing: {$pattern}\n";
       $result = preg_replace($pattern, $replacement, 'test string');
       if ($result === null) {
           echo "Error in pattern: {$pattern}\n";
       }
   }
   

3. Monitor Performance:

   $processor = new GdprProcessor($patterns, $fieldPaths, [], function($path, $orig, $masked) {
       if (microtime(true) - $_SERVER['REQUEST_TIME_FLOAT'] > 1.0) {
           error_log("Slow GDPR processing detected");
       }
   });
   

Getting Help

• Documentation: Check CONTRIBUTING.md for development setup
• Security Issues: See SECURITY.md for responsible disclosure
• Bug Reports: Create an issue on GitHub with minimal reproduction example
• Performance Issues: Include profiling data and pattern counts

Notable Implementation Details

• If a regex replacement in regExpMessage results in an empty string or the string "0", the original message is returned. This is covered by dedicated PHPUnit tests.
• If a regex pattern is invalid, the audit logger (if set) is called, and the original message is returned.
• All patterns are validated for security before use to prevent regex injection attacks.
• The library includes ReDoS (Regular Expression Denial of Service) protection.

Directory Structure

• src/ — Main library source code
• tests/ — PHPUnit tests
• coverage/ — Code coverage reports
• vendor/ — Composer dependencies

Legal Disclaimer

Caution

: This library helps mask/filter sensitive data for GDPR compliance, but it is your responsibility to ensure your application fully complies with all legal requirements. Review your logging and data handling policies regularly.

Contributing

If you would like to contribute to this project, please fork the repository and submit a pull request.

License

This project is licensed under the MIT License. See the LICENSE file for more details.