Idempotency Handler Generator

Creates idempotency handling infrastructure for safe request deduplication.

When to Use

Scenario	Example
Payment processing	Prevent duplicate charges on retry
Order creation	Avoid duplicate orders from network retries
Webhook handling	Deduplicate incoming webhook deliveries
API mutations	Ensure POST/PUT/PATCH safety on retry

Component Characteristics

IdempotencyKey

• Value Object validating UUID v4 format
• Immutable, self-validating on construction
• Extracted from Idempotency-Key HTTP header

IdempotencyStorageInterface

• Storage contract for idempotency records
• Methods: exists(), store(), get(), remove()
• TTL-based expiration support

RedisIdempotencyStorage

• Redis SETNX implementation for atomic check-and-store
• Configurable TTL for automatic key expiration
• Stores serialized response for replay

IdempotencyMiddleware

• PSR-15 middleware intercepting requests
• Checks for existing idempotency key before processing
• Stores response after successful processing
• Returns cached response on duplicate request

IdempotencyException

• Thrown when duplicate request detected without stored response
• Contains the conflicting idempotency key

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Generation Process

Step 1: Generate Core Components

Path: src/Infrastructure/Idempotency/

1. IdempotencyKey.php — Value Object with UUID validation
2. IdempotencyException.php — Duplicate request exception
3. StoredResponse.php — Serializable response wrapper

Step 2: Generate Storage Layer

Path: src/Infrastructure/Idempotency/

1. IdempotencyStorageInterface.php — Storage contract
2. RedisIdempotencyStorage.php — Redis SETNX + TTL implementation

Step 3: Generate Middleware

Path: src/Infrastructure/Idempotency/

1. IdempotencyMiddleware.php — PSR-15 middleware

Step 4: Generate Tests

1. IdempotencyKeyTest.php — Value Object validation tests
2. IdempotencyMiddlewareTest.php — Middleware behavior tests

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File Placement

Component	Path
All Classes	src/Infrastructure/Idempotency/
Unit Tests	tests/Unit/Infrastructure/Idempotency/

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Naming Conventions

Component	Pattern	Example
Value Object	IdempotencyKey	IdempotencyKey
Storage Interface	IdempotencyStorageInterface	IdempotencyStorageInterface
Redis Storage	RedisIdempotencyStorage	RedisIdempotencyStorage
Middleware	IdempotencyMiddleware	IdempotencyMiddleware
Response VO	StoredResponse	StoredResponse
Exception	IdempotencyException	IdempotencyException
Test	{ClassName}Test	IdempotencyKeyTest

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Quick Template Reference

IdempotencyKey

final readonly class IdempotencyKey
{
    public function __construct(public string $value)
    {
        // Validates UUID v4 format
    }

    public static function fromHeader(string $headerValue): self;
    public function toString(): string;
}

IdempotencyStorageInterface

interface IdempotencyStorageInterface
{
    public function exists(IdempotencyKey $key): bool;
    public function store(IdempotencyKey $key, StoredResponse $response, int $ttl): void;
    public function get(IdempotencyKey $key): ?StoredResponse;
    public function remove(IdempotencyKey $key): void;
}

IdempotencyMiddleware

final readonly class IdempotencyMiddleware implements MiddlewareInterface
{
    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface;
}

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Usage Example

$middleware = new IdempotencyMiddleware(
    storage: $redisStorage,
    ttl: 86400,
    headerName: 'Idempotency-Key'
);

// Client sends: POST /orders with header Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000
// First request: processes and stores response
// Retry request: returns cached response immediately

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Request Flow

Request ──→ Extract Idempotency-Key header
                │
         Key exists in storage?
           │              │
          YES             NO
           │              │
    Return stored    Process request
     response           │
                   Store response
                        │
                   Return response

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Anti-patterns to Avoid

Anti-pattern	Problem	Solution
No TTL on keys	Storage grows unbounded	Set TTL (e.g., 24h)
In-memory storage	Lost on restart, no clustering	Use Redis or database
Idempotency on GET	GET is already idempotent	Only apply to mutations
Missing key validation	Accept invalid keys	Validate UUID format
No response caching	Cannot replay response	Store full response
Race conditions	Concurrent duplicates	Use SETNX atomic operation

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References

For complete PHP templates and examples, see:

• references/templates.md — IdempotencyKey, StorageInterface, RedisStorage, Middleware templates
• references/examples.md — API integration examples and tests