Agent Skills: PHP HTTP — PSR-7 / 15 / 17 / 18

Includes guidance on reference implementations (nyholm/psr7, guzzlehttp/psr7, laminas-diactoros) and how to choose between them, plus a complete middleware-pipeline template.

Do NOT use this skill for Laravel's own HTTP layer (route to laravel-expert instead) or for Symfony's HttpFoundation component, which is a different, non-PSR-7 HTTP model — bridge the two via symfony/psr-http-message-bridge when needed (see references/implementations.md). </objective>

PHP HTTP — PSR-7 / 15 / 17 / 18

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Detect the PSR-7 implementation already in use (composer.json)
2. fuse-ai-pilot:research-expert - Verify current interface versions on php-fig.org + Packagist
3. mcp__context7__query-docs - Check the chosen implementation's factory API

After implementation, run fuse-ai-pilot:sniper for validation.

Overview

These four PSR standards let libraries handle HTTP without coupling to any framework. Code depends on interfaces (Psr\Http\*); a concrete implementation is injected.

| Standard | Package | Provides | |----------|---------|----------| | PSR-7 | psr/http-message | Immutable HTTP messages: MessageInterface, RequestInterface, ResponseInterface, ServerRequestInterface, StreamInterface, UriInterface, UploadedFileInterface | | PSR-15 | psr/http-server-handler + psr/http-server-middleware | RequestHandlerInterface, MiddlewareInterface — the middleware pipeline | | PSR-17 | psr/http-factory | Factories that create PSR-7 objects without naming a concrete class | | PSR-18 | psr/http-client | ClientInterface::sendRequest() — send a PSR-7 request, get a PSR-7 response |

Critical Rules

1. Messages are immutable - Every with*() returns a NEW instance; the original is unchanged. $r->withHeader(...) alone is a no-op — reassign.
2. Depend on interfaces, not classes - Type-hint ResponseInterface, inject a ResponseFactoryInterface. NEVER new Response() inside reusable code.
3. Streams are NOT immutable - StreamInterface wraps a real resource; use read-only streams for requests/responses.
4. PSR-18 4xx/5xx are NOT errors - A client MUST return them as normal responses; it throws only on transport failure (NetworkExceptionInterface) or malformed requests (RequestExceptionInterface).
5. Headers are case-insensitive - getHeaderLine('foo') == getHeaderLine('FOO'); original case is preserved in getHeaders().

Architecture

src/
├── Http/
│   ├── Middleware/          # implements Psr\Http\Server\MiddlewareInterface
│   │   ├── ErrorHandlerMiddleware.php
│   │   └── AuthMiddleware.php
│   ├── Handler/             # implements Psr\Http\Server\RequestHandlerInterface
│   │   └── Dispatcher.php   # the pipeline runner
│   └── Client/              # wraps a Psr\Http\Client\ClientInterface
└── interfaces/              # your own contracts (SOLID)

→ See middleware-pipeline.md for a complete runnable pipeline

Reference Guide

Concepts

| Topic | Reference | When to Consult | |-------|-----------|-----------------| | Messages | psr7-messages.md | Reading/building requests, responses, streams, URIs | | Middleware | psr15-middleware.md | Building a middleware + handler pipeline | | Factories | psr17-factories.md | Creating PSR-7 objects implementation-agnostically | | HTTP Client | psr18-client.md | Sending outbound requests, exception handling | | Implementations | implementations.md | Choosing nyholm / guzzle / laminas + PSR-18 clients |

Templates

| Template | When to Use | |----------|-------------| | middleware-pipeline.md | Building a PSR-15 dispatcher with middleware queue |

Quick Reference

Immutable update (reassign!)

$response = $response
    ->withStatus(201)
    ->withHeader('Content-Type', 'application/json');

Minimal middleware

final class AuthMiddleware implements MiddlewareInterface
{
    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
    {
        if (!$request->hasHeader('Authorization')) {
            return $this->responseFactory->createResponse(401);
        }
        return $handler->handle($request);
    }
}

PSR-17 factory (no concrete class named)

$request = $requestFactory->createRequest('GET', 'https://api.example.com');
$request = $request->withBody($streamFactory->createStream('{"ping":true}'));

→ See psr17-factories.md for all six factory interfaces

Best Practices

DO

• Inject a ResponseFactoryInterface so middleware never names a concrete class
• Put an exception-catching middleware FIRST in the queue (PSR-15 recommendation)
• Use nyholm/psr7 when you want a lightweight, strict PSR-7 + PSR-17 in one package
• Reassign the result of every with*() call

DON'T

• Mutate a message in place — with*() returns a new object
• Treat a 404/500 response from a PSR-18 client as an exception
• Confuse Symfony HttpFoundation with PSR-7 — they are different; bridge via symfony/psr-http-message-bridge
• Hardcode new GuzzleHttp\Psr7\Response() in library code — depend on the factory