Gateway Pattern

Also Known As

TL;DR

Explanation

A Gateway (Martin Fowler, PoEAA) isolates external dependencies behind an interface. PaymentGateway, EmailGateway, SMSGateway — each wraps one external system. Benefits: the application code never calls the HTTP client or SDK directly; the gateway can be mocked in tests; switching providers means only changing the gateway implementation. Similar to Adapter but typically wraps external systems rather than incompatible interfaces. Distinguished from Repository (data storage) by focusing on external service calls.

Common Misconception

Why It Matters

Common Mistakes

• Gateway that leaks provider-specific exceptions — wrap them in domain exceptions.
• Fat gateway with too much logic — gateways translate calls, not implement business rules.
• Not defining a gateway interface — without an interface, mocking in tests requires more work.
• One giant ExternalServiceGateway — one gateway per external system.

Code Examples

// No gateway — Stripe SDK scattered everywhere:
class OrderService {
    public function charge(Order $order): void {
        $stripe = new \Stripe\StripeClient(getenv('STRIPE_KEY'));
        $charge = $stripe->charges->create([
            'amount'   => $order->total->cents(),
            'currency' => 'gbp',
            'source'   => $order->paymentToken,
        ]);
        // Stripe-specific code in domain service
    }
}

// Gateway isolates the provider:
interface PaymentGateway {
    public function charge(Money $amount, string $token): PaymentResult;
}

class StripeGateway implements PaymentGateway {
    public function charge(Money $amount, string $token): PaymentResult {
        $charge = $this->stripe->charges->create([...]);
        return new PaymentResult($charge->id, $charge->status);
    }
}

// Domain service depends on interface:
class OrderService {
    public function __construct(private PaymentGateway $payments) {}
    public function charge(Order $order): void {
        $result = $this->payments->charge($order->total, $order->token);
    }
}

References

• ↗ https://www.martinfowler.com/eaaCatalog/gateway.html

Tags

Related Terms