Function fn_service_st 

pub fn fn_service_st<F, St, Req, Res, Err>(
    f: F,
) -> FnServiceSt<F, St, Req, Res, Err>
where
    F: AsyncFn(&St, Req) -> Result<Res, Err>,

Converts a state-aware asynchronous function into a Service.

This service accesses the pipeline state via the first &St parameter.