PSR-15 Middleware Implementation Guide

Master the art of HTTP middleware in XOOPS 4.0 with PSR-15 compliance.

PSR-15 defines standard interfaces for HTTP server request handlers and middleware. XOOPS 4.0 fully embraces this standard, providing a robust middleware pipeline for request processing.

Understanding PSR-15

The Standard Interfaces

<?php

namespace Psr\Http\Server;

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;

/**
 * Handles a server request and produces a response.
 */
interface RequestHandlerInterface
{
    public function handle(ServerRequestInterface $request): ResponseInterface;
}

/**
 * Participant in processing a server request and response.
 */
interface MiddlewareInterface
{
    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface;
}

How Middleware Works

flowchart LR
    subgraph Pipeline["Middleware Pipeline"]
        direction LR
        REQ[Request] --> M1[Middleware 1]
        M1 --> M2[Middleware 2]
        M2 --> M3[Middleware 3]
        M3 --> HANDLER[Handler]
        HANDLER --> M3R[Middleware 3]
        M3R --> M2R[Middleware 2]
        M2R --> M1R[Middleware 1]
        M1R --> RES[Response]
    end

    style M1 fill:#e3f2fd
    style M2 fill:#e3f2fd
    style M3 fill:#e3f2fd
    style HANDLER fill:#c8e6c9

Each middleware can:

Modify the request before passing it to the next middleware
Pass to the next handler in the pipeline
Modify the response before returning it
Short-circuit by returning a response directly

XOOPS 4.0 Middleware Stack

Default Pipeline

flowchart TB
    REQ[HTTP Request] --> STACK

    subgraph STACK["XOOPS Middleware Stack"]
        direction TB
        E[🛡️ Error Handler<br/><small>Catches all exceptions</small>]
        S[🔒 Security<br/><small>CSRF, Rate Limiting</small>]
        SS[📋 Session<br/><small>Session management</small>]
        A[👤 Authentication<br/><small>User identification</small>]
        R[🔀 Router<br/><small>Route matching</small>]
        M[📦 Module Loader<br/><small>Load module context</small>]
        P[🔐 Permission<br/><small>Access control</small>]
        C[🎯 Controller<br/><small>Request handler</small>]

        E --> S --> SS --> A --> R --> M --> P --> C
    end

    C --> RES[HTTP Response]

Pipeline Configuration

<?php
declare(strict_types=1);

return [
    // Global middleware (always executed)
    'global' => [
        \Xoops\Middleware\ErrorHandler::class,
        \Xoops\Middleware\Security::class,
        \Xoops\Middleware\Session::class,
        \Xoops\Middleware\Authentication::class,
    ],

    // Route-level middleware
    'route' => [
        \Xoops\Middleware\Router::class,
        \Xoops\Middleware\ModuleLoader::class,
        \Xoops\Middleware\Permission::class,
    ],

    // Named middleware (can be applied to routes)
    'named' => [
        'auth' => \Xoops\Middleware\RequireAuthentication::class,
        'admin' => \Xoops\Middleware\RequireAdmin::class,
        'api' => \Xoops\Middleware\ApiAuthentication::class,
        'throttle' => \Xoops\Middleware\RateLimiter::class,
        'cache' => \Xoops\Middleware\HttpCache::class,
    ],
];

Creating Custom Middleware

Basic Middleware Structure

<?php

declare(strict_types=1);

namespace MyModule\Middleware;

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\MiddlewareInterface;
use Psr\Http\Server\RequestHandlerInterface;

final class MyCustomMiddleware implements MiddlewareInterface
{
    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface {
        // Before: Modify request or perform pre-processing
        $request = $this->beforeHandle($request);

        // Delegate to the next handler
        $response = $handler->handle($request);

        // After: Modify response or perform post-processing
        return $this->afterHandle($response);
    }

    private function beforeHandle(ServerRequestInterface $request): ServerRequestInterface
    {
        // Add custom attribute
        return $request->withAttribute('my_timestamp', microtime(true));
    }

    private function afterHandle(ResponseInterface $response): ResponseInterface
    {
        // Add custom header
        return $response->withHeader('X-Processed-By', 'MyModule');
    }
}

Middleware with Dependencies

<?php

declare(strict_types=1);

namespace MyModule\Middleware;

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\MiddlewareInterface;
use Psr\Http\Server\RequestHandlerInterface;
use Psr\Log\LoggerInterface;
use Xoops\Security\TokenValidator;

final class CsrfProtection implements MiddlewareInterface
{
    public function __construct(
        private readonly TokenValidator $tokenValidator,
        private readonly LoggerInterface $logger,
        private readonly ResponseFactory $responseFactory,
    ) {}

    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface {
        // Skip for safe methods
        if (in_array($request->getMethod(), ['GET', 'HEAD', 'OPTIONS'])) {
            return $handler->handle($request);
        }

        // Validate CSRF token
        $token = $this->extractToken($request);

        if (!$this->tokenValidator->validate($token)) {
            $this->logger->warning('CSRF validation failed', [
                'ip' => $request->getServerParams()['REMOTE_ADDR'] ?? 'unknown',
                'uri' => (string) $request->getUri(),
            ]);

            return $this->responseFactory->forbidden('Invalid CSRF token');
        }

        return $handler->handle($request);
    }

    private function extractToken(ServerRequestInterface $request): ?string
    {
        // Check header first
        $token = $request->getHeaderLine('X-CSRF-Token');
        if ($token !== '') {
            return $token;
        }

        // Check body
        $body = $request->getParsedBody();
        return $body['_token'] ?? null;
    }
}

Common Middleware Patterns

1. Authentication Middleware

<?php

declare(strict_types=1);

namespace Xoops\Middleware;

final class Authentication implements MiddlewareInterface
{
    public function __construct(
        private readonly SessionManager $session,
        private readonly UserRepository $users,
    ) {}

    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface {
        $user = null;

        // Check session for user ID
        $userId = $this->session->get('user_id');
        if ($userId !== null) {
            $user = $this->users->find($userId);
        }

        // Check for API token
        if ($user === null) {
            $user = $this->authenticateViaToken($request);
        }

        // Add user to request attributes
        $request = $request->withAttribute('user', $user);
        $request = $request->withAttribute('is_authenticated', $user !== null);

        return $handler->handle($request);
    }

    private function authenticateViaToken(ServerRequestInterface $request): ?User
    {
        $authHeader = $request->getHeaderLine('Authorization');
        if (str_starts_with($authHeader, 'Bearer ')) {
            $token = substr($authHeader, 7);
            return $this->users->findByApiToken($token);
        }
        return null;
    }
}

2. Rate Limiting Middleware

<?php

declare(strict_types=1);

namespace Xoops\Middleware;

final class RateLimiter implements MiddlewareInterface
{
    public function __construct(
        private readonly RateLimiterFactory $limiterFactory,
        private readonly ResponseFactory $responseFactory,
        private readonly int $maxAttempts = 60,
        private readonly int $decaySeconds = 60,
    ) {}

    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface {
        $key = $this->resolveRequestSignature($request);
        $limiter = $this->limiterFactory->create($key, $this->maxAttempts, $this->decaySeconds);

        if ($limiter->tooManyAttempts()) {
            return $this->buildTooManyAttemptsResponse($limiter);
        }

        $limiter->hit();

        $response = $handler->handle($request);

        return $this->addRateLimitHeaders($response, $limiter);
    }

    private function resolveRequestSignature(ServerRequestInterface $request): string
    {
        $user = $request->getAttribute('user');
        if ($user !== null) {
            return 'user:' . $user->id;
        }
        return 'ip:' . ($request->getServerParams()['REMOTE_ADDR'] ?? 'unknown');
    }

    private function buildTooManyAttemptsResponse(Limiter $limiter): ResponseInterface
    {
        return $this->responseFactory->json([
            'error' => 'Too many requests',
            'retry_after' => $limiter->availableIn(),
        ], 429)->withHeader('Retry-After', (string) $limiter->availableIn());
    }

    private function addRateLimitHeaders(ResponseInterface $response, Limiter $limiter): ResponseInterface
    {
        return $response
            ->withHeader('X-RateLimit-Limit', (string) $this->maxAttempts)
            ->withHeader('X-RateLimit-Remaining', (string) $limiter->remaining())
            ->withHeader('X-RateLimit-Reset', (string) $limiter->resetTime());
    }
}

3. Caching Middleware

<?php

declare(strict_types=1);

namespace Xoops\Middleware;

final class HttpCache implements MiddlewareInterface
{
    public function __construct(
        private readonly CacheInterface $cache,
        private readonly int $ttl = 3600,
    ) {}

    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface {
        // Only cache GET requests
        if ($request->getMethod() !== 'GET') {
            return $handler->handle($request);
        }

        // Skip for authenticated users
        if ($request->getAttribute('is_authenticated')) {
            return $handler->handle($request);
        }

        $cacheKey = $this->buildCacheKey($request);

        // Try to get from cache
        $cached = $this->cache->get($cacheKey);
        if ($cached !== null) {
            return $this->hydrateResponse($cached)
                ->withHeader('X-Cache', 'HIT');
        }

        // Generate response
        $response = $handler->handle($request);

        // Cache successful responses
        if ($response->getStatusCode() === 200) {
            $this->cache->set($cacheKey, $this->dehydrateResponse($response), $this->ttl);
        }

        return $response->withHeader('X-Cache', 'MISS');
    }

    private function buildCacheKey(ServerRequestInterface $request): string
    {
        return 'http:' . md5((string) $request->getUri());
    }
}

4. Logging Middleware

<?php

declare(strict_types=1);

namespace Xoops\Middleware;

final class RequestLogger implements MiddlewareInterface
{
    public function __construct(
        private readonly LoggerInterface $logger,
    ) {}

    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface {
        $startTime = microtime(true);
        $requestId = bin2hex(random_bytes(8));

        // Add request ID to request
        $request = $request->withAttribute('request_id', $requestId);

        $this->logger->info('Request started', [
            'request_id' => $requestId,
            'method' => $request->getMethod(),
            'uri' => (string) $request->getUri(),
            'ip' => $request->getServerParams()['REMOTE_ADDR'] ?? 'unknown',
        ]);

        try {
            $response = $handler->handle($request);

            $this->logger->info('Request completed', [
                'request_id' => $requestId,
                'status' => $response->getStatusCode(),
                'duration_ms' => round((microtime(true) - $startTime) * 1000, 2),
            ]);

            return $response->withHeader('X-Request-Id', $requestId);
        } catch (\Throwable $e) {
            $this->logger->error('Request failed', [
                'request_id' => $requestId,
                'exception' => $e::class,
                'message' => $e->getMessage(),
                'duration_ms' => round((microtime(true) - $startTime) * 1000, 2),
            ]);

            throw $e;
        }
    }
}

Middleware Flow Visualization

Request Lifecycle

sequenceDiagram
    participant Client
    participant ErrorHandler
    participant Security
    participant Session
    participant Auth
    participant Router
    participant Module
    participant Controller

    Client->>ErrorHandler: HTTP Request
    ErrorHandler->>Security: process()
    Security->>Session: process()
    Session->>Auth: process()
    Auth->>Router: process()
    Router->>Module: process()
    Module->>Controller: handle()
    Controller-->>Module: Response
    Module-->>Router: Response
    Router-->>Auth: Response
    Auth-->>Session: Response
    Session-->>Security: Response
    Security-->>ErrorHandler: Response
    ErrorHandler-->>Client: HTTP Response

Error Handling Flow

flowchart TB
    subgraph Normal["Normal Flow"]
        R[Request] --> M1[Middleware 1]
        M1 --> M2[Middleware 2]
        M2 --> H[Handler]
        H --> RES[Response]
    end

    subgraph Error["Error Flow"]
        EX[Exception Thrown] --> EH[Error Handler]
        EH --> ERR[Error Response]
    end

    M2 -.->|throws| EX
    H -.->|throws| EX

Registering Middleware

Global Middleware

<?php
return [
    'global' => [
        \App\Middleware\RequestLogger::class,
        \Xoops\Middleware\ErrorHandler::class,
        // ... more middleware
    ],
];

Route-Level Middleware

<?php
use Xoops\Routing\Router;

return static function (Router $router): void {
    // Apply middleware to a single route
    $router->get('/api/articles', ArticleController::class)
        ->middleware('throttle:100,60');

    // Apply middleware to a group
    $router->group(['middleware' => ['auth', 'admin']], function (Router $router) {
        $router->get('/admin/dashboard', AdminController::class);
        $router->get('/admin/users', UserController::class);
    });

    // API routes with multiple middleware
    $router->group([
        'prefix' => '/api/v1',
        'middleware' => ['api', 'throttle'],
    ], function (Router $router) {
        $router->resource('articles', ArticleApiController::class);
    });
};

Module Middleware

<?php
return [
    // Middleware specific to this module
    'module' => [
        \MyModule\Middleware\AuditLog::class,
        \MyModule\Middleware\FeatureFlags::class,
    ],

    // Middleware for admin routes only
    'admin' => [
        \MyModule\Middleware\AdminAccess::class,
    ],
];

Testing Middleware

Unit Testing

<?php

declare(strict_types=1);

namespace Tests\Unit\Middleware;

use PHPUnit\Framework\TestCase;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\RequestHandlerInterface;

final class RateLimiterTest extends TestCase
{
    public function testAllowsRequestUnderLimit(): void
    {
        $limiterFactory = $this->createMock(RateLimiterFactory::class);
        $limiter = $this->createMock(Limiter::class);
        $limiter->method('tooManyAttempts')->willReturn(false);
        $limiter->method('remaining')->willReturn(59);
        $limiterFactory->method('create')->willReturn($limiter);

        $middleware = new RateLimiter($limiterFactory, new ResponseFactory());

        $request = $this->createMock(ServerRequestInterface::class);
        $handler = $this->createMock(RequestHandlerInterface::class);
        $handler->expects($this->once())->method('handle');

        $middleware->process($request, $handler);
    }

    public function testBlocksRequestOverLimit(): void
    {
        $limiterFactory = $this->createMock(RateLimiterFactory::class);
        $limiter = $this->createMock(Limiter::class);
        $limiter->method('tooManyAttempts')->willReturn(true);
        $limiter->method('availableIn')->willReturn(30);
        $limiterFactory->method('create')->willReturn($limiter);

        $middleware = new RateLimiter($limiterFactory, new ResponseFactory());

        $request = $this->createMock(ServerRequestInterface::class);
        $handler = $this->createMock(RequestHandlerInterface::class);
        $handler->expects($this->never())->method('handle');

        $response = $middleware->process($request, $handler);

        $this->assertSame(429, $response->getStatusCode());
    }
}

Best Practices

Do’s

Keep middleware focused - One responsibility per middleware
Use dependency injection - Don’t create dependencies inside middleware
Handle exceptions gracefully - Let the error handler catch them
Add appropriate headers - Security headers, cache headers, etc.
Log important events - Request/response logging for debugging

Don’ts

Don’t modify request body - PSR-7 requests are immutable
Don’t share state between requests - Use request attributes
Don’t catch all exceptions - Let them bubble to error handler
Don’t do heavy processing - Middleware should be fast
Don’t bypass the pipeline - Always call $handler->handle()

Architecture Vision
PSR Standards
Security Best Practices
Vision 2026 Architecture

#psr-15 #middleware #http #xoops-4.0 #implementation