What is an Interceptor?

An Interceptor is a component that sits between the incoming request/message and the controller where it is applied. They allow you to read, modify, and process incoming requests.

Why use Interceptors?

Interceptors are useful for:

• Authentication and authorization
• Request logging and monitoring
• Request validation

The three variants

Sword provides three types of interceptors:

Traditional

The most common variant. They are declared as structs that derive the Interceptor trait and implement traits such as OnRequest, OnRequestStream, or OnConnect, depending on the controller type. Under the hood they are Components, so they can have dependencies without requiring a defined constructor.

With configuration

They behave like the traditional ones, but add an extra T parameter to the signature of the interception method (OnRequestWithConfig, OnConnectWithConfig, etc.). That parameter lets you pass additional configuration to the interceptor.

Tower layers

Sword integrates with the Tower ecosystem. You can apply local layers in web controllers using the #[interceptor(TowerLayer::example())] attribute.

Application by controller type

Each variant is applied differently depending on the controller type. The full examples live in the practical guides:

• Web Controllers → Interceptors in web controllers
• Socket.IO Controllers → Interceptors in Socket.IO controllers
• gRPC Controllers → Interceptors in gRPC controllers