Function actix_service::apply_fn

pub fn apply_fn<T, F, In, Out, U>(service: U, f: F) -> Apply<T, F, In, Out> where
    T: Service,
    F: FnMut(In, &mut T) -> Out,
    Out: IntoFuture,
    Out::Error: From<T::Error>,
    U: IntoService<T>, 

Apply tranform function to a service