Function actix_service::transform_fn

pub fn transform_fn<F, S, In, Out, Err>(
    f: F
) -> impl Transform<S, Request = In, Response = Out::Item, Error = Out::Error, InitError = Err> where
    S: Service,
    F: FnMut(In, &mut S) -> Out + Clone,
    Out: IntoFuture,
    Out::Error: From<S::Error>, 

Use function as transform service