Strict server

The strict server is generated with --strict-responders. Instead of every handler returning a generic middleware.Responder — which lets you hand back any response, including ones the spec never declared — each operation gets its own responder interface. The compiler then enforces that a handler can only return responses declared for that operation.

The generated responder interface

For each operation, the generator emits a marker interface embedding middleware.Responder. Only the response types declared for addOne implement AddOneResponder, so nothing else can be returned:

type AddOneResponder interface {
	middleware.Responder
	AddOneResponder()
}

Full source: todo-list-strict/restapi/operations/todos/add_one_responses.go

Every generated response for the operation — AddOneCreated, AddOneDefault, AddOneNotImplemented — carries a no-op AddOneResponder() method, which is what admits it to the interface. A FindDefault value, for instance, simply won’t compile inside an addOne handler.

The handler signature

Compare with the default todo-list server, where the handler returns middleware.Responder. Here the return type is the operation-specific todos.AddOneResponder:

if api.TodosAddOneHandler == nil {
	api.TodosAddOneHandler = todos.AddOneHandlerFunc(func(params todos.AddOneParams, principal any) todos.AddOneResponder {
		_ = params
		_ = principal

		return todos.AddOneNotImplemented()
	})
}

Full source: todo-list-strict/restapi/configure_simple_to_do_list_api.go

The scaffold guards each assignment with if … == nil, so you can wire a handler from elsewhere and leave the rest returning NotImplemented. You replace the body with real logic, returning one of the operation’s typed responders.

When to use it

Reach for strict responders when you want the type system to guarantee your handlers stay in sync with the contract — you can’t accidentally return a response shape the spec doesn’t describe. The cost is a little more generated surface (one interface per operation) and slightly more verbose returns.

Related

• Todo list server — the default (non-strict) responder style.
• Custom error handling — returning errors from handlers.