`ServerInterceptor.intercept_service` return type doesn't match continuation return type

[bkeryan]

`ServerInterceptor.intercept_service` return type doesn't match continuation return type

[bkeryan]

Hi @macro1,

Thanks for the heads up.

According to the linked documentation, intercept_service is allowed to return None. It is not required to raise an exception when the intercepted service returns None.

The return type in the example was copied from grpc-stubs. At the time I filed this issue, grpc-stubs annotated intercept_service with a return type of grpc.RpcMethodHandler[grpc.TRequest, grpc.TResponse]. It has since been fixed by #43, which added typing.Optional to the return type.

[macro1]

hi @bkeryan. the issue isn't the library in this case.

the return type you have defined for continuation is typing.Optional[grpc.RpcMethodHandler[grpc.TRequest, grpc.TResponse]], which means returning it directly would violate the return type you've defined for intercept_service()

one way to demonstrate this is to raise an exception when the value is None, this will cause the typing to work out:

class NullServerInterceptor(grpc.ServerInterceptor[grpc.TRequest, grpc.TResponse]):
    def intercept_service(
        self,
        continuation: Callable[
            [grpc.HandlerCallDetails],
            Optional[grpc.RpcMethodHandler[grpc.TRequest, grpc.TResponse]]
        ],
        handler_call_details: grpc.HandlerCallDetails,
    ) -> grpc.RpcMethodHandler[grpc.TRequest, grpc.TResponse]:
        response = continuation(handler_call_details)
        if response is None:
            raise NotImplementedError
        return response