Correlation Context Generator

Creates Correlation ID propagation infrastructure for distributed PHP applications.

When to Use

• Need to trace requests across multiple services or layers
• Log entries from different components must be linked together
• Async flows (RabbitMQ, Symfony Messenger) lose request context
• Debugging distributed systems requires end-to-end tracing
• Implementing observability and distributed tracing

Generated Components

Component	Layer	Path	Purpose
CorrelationId	Domain/Shared	src/Domain/Shared/Correlation/CorrelationId.php	UUID-based Value Object
CorrelationContext	Domain/Shared	src/Domain/Shared/Correlation/CorrelationContext.php	Immutable context holder
CorrelationContextMiddleware	Presentation	src/Presentation/Middleware/CorrelationContextMiddleware.php	PSR-15 middleware
CorrelationLogProcessor	Infrastructure	src/Infrastructure/Logging/CorrelationLogProcessor.php	Monolog processor
CorrelationMessageStamp	Infrastructure	src/Infrastructure/Messaging/CorrelationMessageStamp.php	Message bus stamp
Unit tests	Tests	tests/Unit/...	Tests for all components

Component Characteristics

CorrelationId Value Object

• Immutable, final readonly class in Domain layer
• UUID v4 based with factory method generate()
• Constructor accepts existing string UUID
• Implements Stringable and JsonSerializable
• Equality comparison via equals() method

CorrelationContext

• Immutable context holder with correlationId, causationId, optional userId
• Factory method create() generates new correlation ID
• Factory method fromRequest() extracts from PSR-7 request headers
• Wither methods: withCausationId(), withUserId()

CorrelationContextMiddleware (PSR-15)

• Extracts X-Correlation-ID header from incoming request (or generates new UUID)
• Also reads X-Causation-ID if present
• Stores CorrelationContext as request attribute
• Adds X-Correlation-ID to response headers
• Thread-safe via request attribute passing (no global state)

CorrelationLogProcessor (Monolog)

• Implements Monolog ProcessorInterface
• Adds correlation_id, causation_id to every log record extra field
• Reads context from a CorrelationContextHolder (request-scoped)

CorrelationMessageStamp

• Implements Symfony Messenger StampInterface (or custom stamp interface)
• Carries correlationId and causationId through message bus
• Used by middleware to propagate context into async handlers
• AMQP header mapping for RabbitMQ interoperability

---

Generation Process

Step 1: Generate Domain Layer

Path: src/Domain/Shared/Correlation/

1. CorrelationId.php -- UUID-based Value Object
2. CorrelationContext.php -- Immutable context holder

Use templates from references/templates.md (Domain section).

Step 2: Generate Presentation Layer

Path: src/Presentation/Middleware/

1. CorrelationContextMiddleware.php -- PSR-15 middleware

Use templates from references/templates.md (Presentation section).

Step 3: Generate Infrastructure Layer

Path: src/Infrastructure/Logging/ and src/Infrastructure/Messaging/

1. CorrelationLogProcessor.php -- Monolog processor
2. CorrelationMessageStamp.php -- Message bus stamp

Use templates from references/templates.md (Infrastructure section).

Step 4: Generate Tests

Path: tests/Unit/Domain/Shared/Correlation/ and tests/Unit/Presentation/Middleware/ and tests/Unit/Infrastructure/

1. CorrelationIdTest.php
2. CorrelationContextTest.php
3. CorrelationContextMiddlewareTest.php
4. CorrelationLogProcessorTest.php

Use templates from references/templates.md (Tests section).

---

File Placement

Component	Default Path
CorrelationId	src/Domain/Shared/Correlation/CorrelationId.php
CorrelationContext	src/Domain/Shared/Correlation/CorrelationContext.php
Middleware	src/Presentation/Middleware/CorrelationContextMiddleware.php
Log Processor	src/Infrastructure/Logging/CorrelationLogProcessor.php
Message Stamp	src/Infrastructure/Messaging/CorrelationMessageStamp.php
Tests	tests/Unit/{layer}/...Test.php

Adapt paths to match existing project structure detected via:

Glob: src/Domain/**/*.php
Glob: src/Presentation/**/*.php
Glob: src/Infrastructure/**/*.php

---

Quick Template Reference

CorrelationId (Value Object)

final readonly class CorrelationId implements \Stringable, \JsonSerializable
{
    public function __construct(public string $value) {}
    public static function generate(): self { /* UUID v4 */ }
    public function equals(self $other): bool { /* comparison */ }
}

CorrelationContext (Context Holder)

final readonly class CorrelationContext
{
    public function __construct(
        public CorrelationId $correlationId,
        public ?string $causationId = null,
        public ?string $userId = null,
    ) {}
    public static function create(): self { /* new with generated ID */ }
    public static function fromRequest(ServerRequestInterface $request): self { /* extract headers */ }
}

Middleware (PSR-15)

final readonly class CorrelationContextMiddleware implements MiddlewareInterface
{
    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
    {
        $context = CorrelationContext::fromRequest($request);
        $request = $request->withAttribute(CorrelationContext::class, $context);
        $response = $handler->handle($request);
        return $response->withHeader('X-Correlation-ID', $context->correlationId->value);
    }
}

See references/templates.md for complete implementations and references/examples.md for integration examples.

---

Usage Example

Middleware Registration (Slim/Mezzio)

$app->add(new CorrelationContextMiddleware());

DI Configuration

return [
    CorrelationContextMiddleware::class => autowire(),
    CorrelationLogProcessor::class => autowire(),
];

Reading Context in Handler

$context = $request->getAttribute(CorrelationContext::class);
$this->logger->info('Processing order', ['orderId' => $orderId]);
// Log automatically includes correlation_id via processor

See references/examples.md for Symfony, Laravel, and message bus integration.