Function relay_split 

pub async fn relay_split<'a, LR, LW, RR, RW>(
    lr: &'a mut LR,
    lw: &'a mut LW,
    rr: &'a mut RR,
    rw: &'a mut RW,
) -> Result<(u64, u64)>
where
    LR: AsyncRead + Unpin + ?Sized,
    LW: AsyncWrite + Unpin + ?Sized,
    RR: AsyncRead + Unpin + ?Sized,
    RW: AsyncWrite + Unpin + ?Sized,