pub trait DirectService<Request> {
    /// Responses given by the service.
    type Response;

    /// Errors produced by servicing a request.
    type ResponseError;

    /// Errors produced during attempts to drive the service.
    type ServiceError;

    /// The future response value.
    type Future: Future<Item = Self::Response, Error = Self::ResponseError>;

    fn poll_ready(&mut self) -> Poll<(), Self::ServiceError>;

    fn poll_service(&mut self) -> Poll<(), Self::ServiceError>;

    fn poll_close(&mut self) -> Poll<(), Self::ServiceError>;

    fn call(&mut self, req: Request) -> Self::Future;
}