README

A micro-framework built around one simple principle: everything should be explicit, replaceable, and safe to change.

Middle takes a different approach to web application architecture. Instead of magic and conventions, it provides clear interfaces and explicit composition. You can use it to build your organization's perfect framework, not be forced to fit into someone else's choices. Instead of hidden coupling, it enforces clean boundaries. Instead of "getting started quickly," it optimizes for "maintaining confidently."

Why Middle?

🔍 No Magic, No Surprises

Every dependency is explicit. Every behavior is visible. No hidden auto-wiring, no surprise side effects, no debugging mysterious framework behavior at 3 AM.

// You can see exactly what's happening
$app = new ApplicationStack(
    new ControllerRunner(),
    new RoutingMiddleware($router, $fallbackController),
    new SessionMiddleware($sessionProcessor),
    new ErrorHandlerMiddleware($logger, $errorController)
);

🔧 Everything is Replaceable

Don't like how routing works? Swap the router. Need custom session handling? Implement SessionProcessorInterface. Every component is designed to be replaced without touching anything else.

// Custom session implementation? No problem.
class RedisSessionProcessor implements SessionProcessorInterface 
{
    // Your implementation here
}

$app = $app->withMiddleware(
    new SessionMiddleware(new RedisSessionProcessor())
);

🛡️ Safe to Change and Extend

The architecture prevents accidental coupling. You can modify any part of your application with confidence that you're not breaking something unexpected elsewhere.

// Adding middleware is safe and predictable
$app = $app->withMiddleware(new AuthenticationMiddleware($authService));
$app = $app->withMiddleware(new CacheMiddleware($cache));
// Original $app is unchanged, no side effects

🧪 Built for Testing

Interface-driven design means every component can be easily mocked, tested in isolation, and verified independently. No complex test setup, no framework mocking libraries needed.

// Testing is straightforward
$mockRouter = $this->createMock(RouterInterface::class);
$mockController = $this->createMock(ControllerInterface::class);
$middleware = new RoutingMiddleware($mockRouter, $mockController);

How Middle Compares

Like other micro-frameworks, Middle is for composing applications. Unlike them, Middle nudges towards architectural boundaries through interfaces, making SOLID principles and domain-driven design the path of least resistance.

Choose Middle when: You want simplicity with architecture meant for SOLID and Domain Driven Development.
Choose Others when: You disagree with the philosophy or prefer configuration-driven development.

Core Philosophy

Explicitness over Convenience: Middle makes you write a bit more code upfront, but prevents the hidden complexity that accumulates in applications over time.

Objects over Arrays: Configuration, data, and behavior are represented by proper classes with clear contracts, not deeply nested arrays or magic properties.

Immutability by Default: Adding or removing middleware creates new application instances. No shared mutable state, no spooky action-at-a-distance.

Standards Compliance: Full PSR-1, PSR-2, PSR-3, PSR-4, PSR-7, PSR-15, and PSR-17 compliance. Not because we have to, but because standards represent solved problems.

Minimal Attack Surface: The framework core is tiny, reducing security vulnerabilities and update risks. Your chosen components update independently.

Security Through Architecture

🔒 Minimal Attack Surface

Middle Framework's core contains almost no security-sensitive code. The entire framework is essentially middleware orchestration—no input parsing, no template engines, no ORMs, no file handling. What can't be exploited, won't be exploited.

🛡️ Security by Delegation

Critical security functionality is handled by specialized, battle-tested libraries that you choose and control:

// Security-critical components are external and replaceable
$app = $app->withMiddleware(
    new RoutingMiddleware(
        new SymfonyRouter($baseUrl),          // Symfony's battle-tested routing
        $fallbackController
    )
);

$app = $app->withMiddleware(
    new SessionMiddleware(
        new LaminasSessionProcessor()         // Laminas's proven session handling
    )
);

🔄 Future-Proof Security Updates

When security vulnerabilities are discovered, updates happen in the concrete libraries—not the framework. Your application code remains unchanged:

Symfony Router vulnerability? → composer update symfony/routing
Session handling issue? → composer update laminas/laminas-session
Template engine exploit? → composer update twig/twig

No framework rewrites, no breaking changes, no security debt.

A Framework You'll Never Replace for Security

Traditional frameworks become security liabilities over time—their monolithic nature means security updates can break your application. Middle's architectural approach eliminates this problem entirely. Security is handled by focused libraries that update independently, while your business logic remains protected behind stable interfaces.

The result: A framework with virtually no inherent security vulnerabilities and a security posture that improves over time as underlying libraries mature.

Composition Over Framework Lock-in

Middle doesn't compete with mature frameworks - it lets you compose their proven components on your terms. Instead of accepting a framework's architectural decisions, you define your own interfaces and adapt battle-tested libraries to fit your domain.

// Your domain interface - exactly what your application needs
interface UserRepositoryInterface 
{
    public function findByEmail(string $email): ?User;
    public function save(User $user): void;
    public function findActiveUsers(): array;
}

// Adapter that wraps Doctrine behind your interface
class DoctrineUserRepository implements UserRepositoryInterface 
{
    public function __construct(private EntityManagerInterface $em) {}
    
    public function findByEmail(string $email): ?User 
    {
        return $this->em->getRepository(User::class)->findOneBy(['email' => $email]);
    }
    
    public function save(User $user): void 
    {
        $this->em->persist($user);
        $this->em->flush();
    }
    
    public function findActiveUsers(): array 
    {
        return $this->em->createQuery('SELECT u FROM User u WHERE u.active = true')
                         ->getResult();
    }
}

// Your controllers depend on YOUR interface, not Doctrine's
class UserController implements ControllerInterface 
{
    public function __construct(private UserRepositoryInterface $repository) {}
    
    public function execute(ServerRequestInterface $request): ResponseInterface 
    {
        // Clean, domain-focused code
        $users = $this->repository->findActiveUsers();
        // ...
    }
}

This approach delivers:

Library Independence: Replace Doctrine with another ORM by implementing your interface
Domain Clarity: Your interfaces reflect business needs, not library abstractions
Future-Proof Evolution: Library updates only require adapter changes, not application rewrites
Focused Testing: Mock exactly what your application needs, not complex library interfaces

You get mature, battle-tested components (Symfony Routing, Laminas Diactoros) with complete architectural control.

How It Works

Middle is built around the middleware pipeline pattern. Your application is a stack of middleware that processes requests in LIFO (last in, first out) order:

$app = new ApplicationStack(
    new ControllerRunner()              // Executes the matched controller
);

$app = $app->withMiddleware(
    new RoutingMiddleware($router, $fallback)  // Matches routes, adds controller to request
);

$app = $app->withMiddleware(
    new SessionMiddleware($sessionProcessor)   // Adds session to request
);

$app = $app->withMiddleware(
    new ErrorHandlerMiddleware($logger, $errorHandler)  // Catches exceptions
);

Each middleware gets a chance to:

Modify the incoming request
Pass control to the next middleware
Modify the outgoing response

Getting Started

Check out the Middle skeleton application for a complete example setup.

Minimal Setup

<?php
use jschreuder\Middle;

// Create a router with fallback for unmatched routes
$router = new Middle\Router\SymfonyRouter('http://localhost');
$fallbackController = Middle\Controller\CallableController::fromCallable(
    function () {
        return new Laminas\Diactoros\Response\JsonResponse(['error' => 'Not found'], 404);
    }
);

// Build the application stack
$app = new Middle\ApplicationStack(
    new Middle\Controller\ControllerRunner(),
    new Middle\ServerMiddleware\RoutingMiddleware($router, $fallbackController)
);

// Add a route
$router->get('home', '/', 
    Middle\Controller\CallableController::factoryFromCallable(function () {
        return new Laminas\Diactoros\Response\JsonResponse([
            'message' => 'Welcome to Middle Framework'
        ]);
    })
);

// Process requests
$request = Laminas\Diactoros\ServerRequestFactory::fromGlobals();
$response = $app->process($request);
(new Laminas\Diactoros\Response\SapiEmitter())->emit($response);

Processing Requests

At its heart, Middle's ApplicationStackInterface takes a PSR-7 ServerRequestInterface and returns a ResponseInterface. Running your application follows this simple pattern:

<?php
// Create PSR-7 request from globals ($_GET, $_POST, $_SERVER, etc.)
$request = Laminas\Diactoros\ServerRequestFactory::fromGlobals();

// Process the request through your middleware stack
$response = $app->process($request);

// Send the response to the browser
(new Laminas\Diactoros\Response\SapiEmitter())->emit($response);

This separation makes testing trivial and allows you to process requests from any source (CLI, queue workers, etc.).

Adding Routes

Routes are added directly to the router instance using HTTP method helpers:

// Simple routes with closures
$router->get('home', '/', 
    Middle\Controller\CallableController::factoryFromCallable(function () {
        return new Laminas\Diactoros\Response\JsonResponse(['message' => 'Hello World']);
    })
);

// Routes with parameters and requirements
$router->get('user.profile', '/users/{id}',
    Middle\Controller\CallableController::factoryFromCallable(function ($request) {
        $userId = $request->getAttribute('id');
        return new Laminas\Diactoros\Response\JsonResponse(['user_id' => $userId]);
    }),
    [], // defaults
    ['id' => '\d+'] // requirements - id must be numeric
);

// Routes can use any HTTP method
$router->post('api.users.create', '/api/users', $createUserControllerFactory);
$router->put('api.users.update', '/api/users/{id}', $updateUserControllerFactory);
$router->delete('api.users.delete', '/api/users/{id}', $deleteUserControllerFactory);

Adding Functionality

Middle grows by composition. Need sessions? Add session middleware:

$app = $app->withMiddleware(
    new Middle\ServerMiddleware\SessionMiddleware(
        new Middle\Session\LaminasSessionProcessor()
    )
);

Need error handling? Add error middleware:

$errorController = Middle\Controller\CallableController::fromCallable(function ($request) {
    $error = $request->getAttribute('error');
    return new Laminas\Diactoros\Response\JsonResponse([
        'error' => 'Something went wrong'
    ], 500);
});

$app = $app->withMiddleware(
    new Middle\ServerMiddleware\ErrorHandlerMiddleware($logger, $errorController)
);

Advanced Features

Request Validation and Filtering

Controllers can implement RequestFilterInterface and RequestValidatorInterface to handle input filtering and validation automatically:

class CreateUserController implements ControllerInterface, RequestFilterInterface, RequestValidatorInterface 
{
    public function filterRequest(ServerRequestInterface $request): ServerRequestInterface 
    {
        $data = $request->getParsedBody();
        if (is_array($data)) {
            $data['textfield'] = strip_tags(trim(data['textfield']));
            $request = $request->withParsedBody($data);
        }
        
        return $request;
    }
    
    public function validateRequest(ServerRequestInterface $request): void 
    {
        $data = $request->getParsedBody();
        if (empty($data['email'])) {
            throw new ValidationFailedException(['email' => 'Email is required']);
        }
        if (!filter_var($data['email'], FILTER_VALIDATE_EMAIL)) {
            throw new ValidationFailedException(['email' => 'Invalid email format']);
        }
    }
    
    public function execute(ServerRequestInterface $request): ResponseInterface 
    {
        // Request is guaranteed to be filtered and valid
        $data = $request->getParsedBody();
        // $data['name'] has been stripped of HTML tags
        // $data['email'] has been validated
        // ... create user
    }
}

The processing order is: Filter → Validate → Execute. This ensures validation always runs on clean data.

Templating with Views

Middle provides a clean abstraction for rendering responses:

// Setup Twig renderer
$renderer = new Middle\View\TwigRenderer($twig, $responseFactory);

// For redirects, decorate with redirect capability
$renderer = new Middle\View\RedirectRendererMiddleware($renderer, $responseFactory);

// Controllers return View objects
$router->get('profile', '/profile/{id}',
    Middle\Controller\CallableController::factoryFromCallable(
        function ($request) use ($renderer) {
            $userId = $request->getAttribute('id');
            return $renderer->render($request, new Middle\View\View('profile.twig', [
                'user' => $userRepository->find($userId)
            ]));
        }
    )
);

// Redirects are views too - RedirectRendererMiddleware handles status codes 300-399
return $renderer->render($request, new Middle\View\RedirectView('/dashboard', 302));

Custom Exception Handling

Middle includes HTTP-aware exceptions that map to proper response codes:

throw new Middle\Exception\NotFoundException('User not found');        // 404
throw new Middle\Exception\AuthenticationException('Login required');  // 401
throw new Middle\Exception\AuthorizationException('Access denied');    // 403
throw new Middle\Exception\ValidationFailedException($errors);         // 400

Core Components

Middle provides several key interfaces and implementations that handle common application needs:

Session Management

The SessionProcessorInterface provides a clean abstraction for session handling:

// Use Laminas Session (default)
$sessionProcessor = new Middle\Session\LaminasSessionProcessor();

// Or implement your own (Redis, database, etc.)
class RedisSessionProcessor implements SessionProcessorInterface {
    public function processRequest(ServerRequestInterface $request): ServerRequestInterface {
        // Add session to request attributes
    }
    
    public function processResponse(ServerRequestInterface $request, ResponseInterface $response): ResponseInterface {
        // Handle session persistence, cookies, etc.
    }
}

The session processor adds a SessionInterface instance to the request's 'session' attribute:

function someController(ServerRequestInterface $request): ResponseInterface {
    $session = $request->getAttribute('session');
    $session->set('user_id', 123);
    $session->setFlash('message', 'Welcome back!');
    // ...
}

Routing

The RouterInterface abstracts routing logic and provides reverse URL generation:

$router = new Middle\Router\SymfonyRouter('http://localhost');

// The router supports all HTTP methods
$router->get('home', '/', $controllerFactory);
$router->post('api.users', '/api/users', $controllerFactory);
$router->put('api.user', '/api/users/{id}', $controllerFactory, [], ['id' => '\d+']);
$router->delete('api.user.delete', '/api/users/{id}', $controllerFactory);

// Generate URLs in your application
$urlGenerator = $router->getGenerator();
$userUrl = $urlGenerator->generatePath('api.user', ['id' => 123]); // '/api/users/123'
$fullUrl = $urlGenerator->generateUrl('home', []); // 'http://localhost/'

You can organize routes using RoutingProviderInterface:

class ApiRoutingProvider implements RoutingProviderInterface {
    public function registerRoutes(RouterInterface $router): void {
        $router->get('api.status', '/api/status', $this->statusControllerFactory());
        $router->post('api.users', '/api/users', $this->createUserControllerFactory());
        // ... more routes
    }
}

$router->registerRoutes(new ApiRoutingProvider());

Request Processing Middleware

Middle includes several middleware for common request processing needs:

// Parse JSON request bodies automatically
$app = $app->withMiddleware(
    new Middle\ServerMiddleware\JsonRequestParserMiddleware()
);

// Automatically validate requests if controller implements RequestValidatorInterface
$app = $app->withMiddleware(
    new Middle\ServerMiddleware\RequestValidatorMiddleware($validationErrorHandler)
);

// Automatically filter requests if controller implements RequestFilterInterface  
$app = $app->withMiddleware(
    new Middle\ServerMiddleware\RequestFilterMiddleware()
);

These middleware automatically detect when controllers implement the corresponding interfaces and apply the appropriate processing.

Dependency Injection Integration

Middle works excellently with DI containers. Here's an example with Pimple:

$container = new Pimple\Container();

$container['app'] = function ($c) {
    return new Middle\ApplicationStack(
        new Middle\Controller\ControllerRunner()
    );
};

// Add middleware through container extension
$container->extend('app', function ($app, $c) {
    return $app->withMiddleware(
        new Middle\ServerMiddleware\RoutingMiddleware(
            $c['router'], $c['fallbackController']
        )
    );
});

When to Choose Middle

Middle is ideal when you:

Value long-term maintainability over short-term convenience
Want to build your team's standard architecture
Want explicit, traceable request flow
Need confidence when refactoring or extending functionality
Prefer composition over inheritance
Want every component to be easily testable
Are building applications that will be maintained by teams over time

Middle might not be for you if:

You need to prototype very quickly
You prefer convention over configuration
You want a large ecosystem of plug-and-play components
You're building simple, short-lived applications

Requirements

PHP 8.3+
PSR-7 implementation (like Laminas Diactoros)
Symfony Routing component (for the included router)

Note: All examples use Laminas Diactoros, but any PSR-7 compatible library will work.

Middle Framework: Explicit. Replaceable. Safe.

jschreuder / middle

Maintainers

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