Function handle 

pub async fn handle<B>(
    engine: Arc<ArcSwap<Engine>>,
    addr: Option<SocketAddr>,
    req: Request<B>,
) -> Result<Response<BoxBody<Bytes, Box<dyn Error + Send + Sync>>>, Box<dyn Error + Send + Sync>>
where
    B: Body + Unpin + Send + 'static,
    B::Data: Into<Bytes> + Clone + Send,
    B::Error: Into<Box<dyn Error + Send + Sync>> + Send,