README

PSR-15 HTTP caching middleware with ETag support and RFC 7234 compliance

Automatic HTTP caching for PSR-15 applications with ETag generation, 304 Not Modified responses, and Cache-Control header management. Zero configuration, production-ready.

✨ Features

• 🏷️ Automatic ETag Generation - MD5/SHA256/custom algorithm support
• 🚀 304 Not Modified - Automatic conditional request handling
• 📋 Cache-Control Builder - Fluent interface for RFC 7234 directives
• ✅ RFC Compliant - RFC 7234 (caching) & RFC 7232 (conditional requests)
• 🎯 Conditional Requests - If-None-Match, wildcard support
• 💪 Strong & Weak ETags - Full support for both ETag types
• 🔧 Zero Configuration - Sensible defaults, works out-of-the-box
• 🎨 Highly Customizable - Control caching behavior per-route
• 📦 Framework Agnostic - Works with any PSR-15 application

📦 Installation

composer require methorz/http-cache-middleware

🚀 Quick Start

Basic Usage

use MethorZ\HttpCache\Middleware\CacheMiddleware;

// Add to middleware pipeline
$app->pipe(new CacheMiddleware());

That's it! All GET and HEAD requests will now have:

• Automatic ETag generation
• 304 Not Modified responses
• Proper caching headers

📖 Detailed Usage

With Cache-Control Directives

use MethorZ\HttpCache\Middleware\CacheMiddleware;
use MethorZ\HttpCache\Directive\CacheControlDirective;

$cacheControl = CacheControlDirective::create()
    ->public()
    ->maxAge(3600)
    ->mustRevalidate();

$middleware = new CacheMiddleware(cacheControl: $cacheControl);

Generated Headers:

ETag: "5d41402abc4b2a76b9719d911017c592"
Cache-Control: public, max-age=3600, must-revalidate

Configuration Options

$middleware = new CacheMiddleware(
    enabled: true,                  // Enable/disable caching
    cacheControl: $directive,       // Cache-Control directive
    useWeakEtag: false,            // Use weak ETags (W/)
    etagAlgorithm: 'md5',          // Hash algorithm (md5, sha256, etc.)
    cacheableMethods: ['GET', 'HEAD'], // Cacheable HTTP methods
    cacheableStatuses: [200, 203], // Cacheable status codes
);

Development Mode (Disable Caching)

For development, you want fresh data on every request. Simply disable the middleware:

// Option 1: Conditionally add middleware based on environment
if (getenv('APP_ENV') !== 'development') {
    $app->pipe(new CacheMiddleware());
}

// Option 2: Disable via constructor parameter
$middleware = new CacheMiddleware(
    enabled: getenv('APP_ENV') !== 'development'
);

// Option 3: Don't add middleware to pipeline in development
// (recommended - cleanest approach)

Recommended approach: Only add CacheMiddleware to your production pipeline configuration, not in development.

🎯 Cache-Control Directive Builder

Fluent interface for building Cache-Control headers:

Common Patterns

Public, cacheable for 1 hour:

CacheControlDirective::create()
    ->public()
    ->maxAge(3600)
    ->mustRevalidate();
// Output: "public, max-age=3600, must-revalidate"

Private, no caching:

CacheControlDirective::create()
    ->private()
    ->noCache();
// Output: "private, no-cache"

Immutable assets (images, CSS, JS):

CacheControlDirective::create()
    ->public()
    ->maxAge(31536000) // 1 year
    ->immutable();
// Output: "public, max-age=31536000, immutable"

API responses with shared cache:

CacheControlDirective::create()
    ->public()
    ->maxAge(300)      // Browser cache: 5 minutes
    ->sMaxAge(3600)    // CDN cache: 1 hour
    ->staleWhileRevalidate(60);
// Output: "public, max-age=300, s-maxage=3600, stale-while-revalidate=60"

All Directives

Method	Description	Example
public()	Cache may be stored by any cache	public
private()	Cache only for single user	private
noCache()	Must revalidate before use	no-cache
noStore()	Must not be stored anywhere	no-store
maxAge(int)	Maximum freshness time	max-age=3600
sMaxAge(int)	Shared cache max age	s-maxage=7200
mustRevalidate()	Must revalidate when stale	must-revalidate
proxyRevalidate()	Proxy must revalidate	proxy-revalidate
noTransform()	Cache must not transform response	no-transform
staleWhileRevalidate(int)	Serve stale while fetching fresh	stale-while-revalidate=60
staleIfError(int)	Serve stale if origin errors	stale-if-error=120
immutable()	Response will never change	immutable

🏷️ ETag Generation

Automatic ETag Generation

use MethorZ\HttpCache\Generator\ETagGenerator;

// Strong ETag (exact match required)
$etag = ETagGenerator::generate($response);
// Output: "5d41402abc4b2a76b9719d911017c592"

// Weak ETag (semantic equality)
$weakEtag = ETagGenerator::generateWeak($response);
// Output: W/"5d41402abc4b2a76b9719d911017c592"

// Custom algorithm
$sha256Etag = ETagGenerator::generateWithAlgorithm($response, 'sha256');

ETag Utilities

// Check if ETag is weak
ETagGenerator::isWeak('W/"abc"'); // true
ETagGenerator::isWeak('"abc"');   // false

// Extract hash value
ETagGenerator::extractHash('"abc123"');   // "abc123"
ETagGenerator::extractHash('W/"abc123"'); // "abc123"

// Compare ETags
ETagGenerator::matches('"abc"', 'W/"abc"', weakComparison: true);  // true
ETagGenerator::matches('"abc"', 'W/"abc"', weakComparison: false); // false

🔄 How It Works

1. First Request (Cache Miss)

Client → GET /api/items
Server → 200 OK
         ETag: "abc123"
         Cache-Control: public, max-age=3600
         Body: {...}

Client caches response with ETag

2. Subsequent Request (Cache Validation)

Client → GET /api/items
         If-None-Match: "abc123"
Server → 304 Not Modified
         ETag: "abc123"
         Cache-Control: public, max-age=3600
         (empty body)

Benefits:

• ⚡ Faster: No body transmission (~95% bandwidth reduction)
• 💰 Cheaper: Reduced server CPU & network costs
• 🌍 Better UX: Instant responses for unchanged resources

🎯 Use Cases

1. Static Asset Caching

// For images, CSS, JS with content hashing in filename
$middleware = new CacheMiddleware(
    cacheControl: CacheControlDirective::create()
        ->public()
        ->maxAge(31536000) // 1 year
        ->immutable(),
);

2. API Response Caching

// Cache API responses for 5 minutes
$middleware = new CacheMiddleware(
    cacheControl: CacheControlDirective::create()
        ->public()
        ->maxAge(300)
        ->mustRevalidate(),
);

3. Dynamic Content with Validation

// Always validate with server, but use weak ETags
$middleware = new CacheMiddleware(
    useWeakEtag: true,
    cacheControl: CacheControlDirective::create()
        ->public()
        ->noCache() // Always revalidate
        ->maxAge(0),
);

4. Private User Data

// Cache in browser only, not in shared caches
$middleware = new CacheMiddleware(
    cacheControl: CacheControlDirective::create()
        ->private()
        ->maxAge(300),
);

5. CDN Integration

// Different cache times for browser vs CDN
$middleware = new CacheMiddleware(
    cacheControl: CacheControlDirective::create()
        ->public()
        ->maxAge(300)      // Browser: 5 minutes
        ->sMaxAge(3600)    // CDN: 1 hour
        ->staleWhileRevalidate(60),
);

🔧 Configuration Examples

Mezzio / Laminas

// config/autoload/middleware.global.php
use MethorZ\HttpCache\Middleware\CacheMiddleware;
use MethorZ\HttpCache\Directive\CacheControlDirective;

return [
    'dependencies' => [
        'factories' => [
            CacheMiddleware::class => function (): CacheMiddleware {
                return new CacheMiddleware(
                    cacheControl: CacheControlDirective::create()
                        ->public()
                        ->maxAge(3600),
                );
            },
        ],
    ],
];

// config/pipeline.php
$app->pipe(CacheMiddleware::class);

Per-Route Configuration

// Apply different caching strategies per route
$publicCaching = new CacheMiddleware(
    cacheControl: CacheControlDirective::create()->public()->maxAge(3600),
);

$privateCaching = new CacheMiddleware(
    cacheControl: CacheControlDirective::create()->private()->maxAge(300),
);

$app->get('/api/public', [$publicCaching, PublicHandler::class]);
$app->get('/api/user/profile', [$privateCaching, ProfileHandler::class]);

📊 HTTP Headers Reference

Request Headers (Client → Server)

Header	Description	Example
If-None-Match	Conditional request with ETag	"abc123" or W/"abc123" or *
If-Modified-Since	Conditional request with date	Wed, 21 Oct 2015 07:28:00 GMT

Response Headers (Server → Client)

Header	Description	Example
ETag	Entity tag for resource version	"abc123" or W/"abc123"
Cache-Control	Caching directives	public, max-age=3600
Expires	Absolute expiration time	Wed, 21 Oct 2025 07:28:00 GMT
Last-Modified	Resource modification time	Wed, 21 Oct 2024 07:28:00 GMT

🧪 Testing

# Run tests
composer test

# Static analysis
composer analyze

# Code style
composer cs-check
composer cs-fix

Test Coverage: 37 tests, 57 assertions, 100% passing

⚡ Performance Impact

Bandwidth Savings

Without caching:
GET /api/items → 200 OK (10 KB body) → 10 KB transferred

With caching (subsequent requests):
GET /api/items (If-None-Match: "abc123") → 304 Not Modified → ~500 bytes transferred

Savings: ~95% bandwidth reduction

Server Load Reduction

• ✅ 304 responses skip expensive body serialization
• ✅ ETag comparison is instant (simple hash check)
• ✅ Reduces database queries when responses haven't changed
• ✅ Lower CPU usage for repeated identical requests

🔒 Security Considerations

Private vs Public

// ❌ Don't cache sensitive user data publicly
CacheControlDirective::create()->public(); // Bad for /api/user/profile

// ✅ Use private for user-specific data
CacheControlDirective::create()->private(); // Good for /api/user/profile

Cache Invalidation

This middleware handles validation (304 responses), not invalidation. For cache invalidation:

• Change resource content → new ETag → cache miss → fresh response
• Use no-cache directive → always revalidate with server
• Use CDN purge APIs for immediate invalidation

📚 Resources

• RFC 7234: HTTP Caching
• RFC 7232: Conditional Requests
• MDN: HTTP Caching
• MDN: Cache-Control

🔗 Related Packages

This package is part of the MethorZ HTTP middleware ecosystem:

Package	Description
methorz/http-dto	Automatic HTTP ↔ DTO conversion with validation
methorz/http-problem-details	RFC 7807 error handling middleware
methorz/http-cache-middleware	HTTP caching with ETag support (this package)
methorz/http-request-logger	Structured logging with request tracking
methorz/openapi-generator	Automatic OpenAPI spec generation

These packages work together seamlessly in PSR-15 applications.

📄 License

MIT License. See LICENSE for details.

🤝 Contributing

Contributions welcome! See CONTRIBUTING.md for guidelines.

🔗 Links

• Changelog
• Contributing
• Security
• Issues