How to handle error from tower middleware

I would like to return error from tower middleware and tonic.

But I don't know how to do that. I tried to return Err, like a Result Returning Ok work

I do

#[derive(Debug, Clone)]
struct MyMiddleware<S> {
    inner: S,
}

type BoxFuture<'a, T> = Pin<Box<dyn std::future::Future<Output = T> + Send + 'a>>;

impl<S> Service<hyper::Request<BoxBody>> for MyMiddleware<S>
where
    S: Service<hyper::Request<BoxBody>, Response = hyper::Response<BoxBody>>
        + Clone
        + Send
        + 'static,
    S::Future: Send + 'static,
{
    type Response = S::Response;
    type Error = S::Error;
    type Future = BoxFuture<'static, Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, req: hyper::Request<BoxBody>) -> Self::Future {
        // This is necessary because tonic internally uses `tower::buffer::Buffer`.
        // See https://github.com/tower-rs/tower/issues/547#issuecomment-767629149
        // for details on why this is necessary
        let clone = self.inner.clone();
        let mut inner = std::mem::replace(&mut self.inner, clone);

        Box::pin(async move {
            // Do extra async work here...
           if condition {
            let response = inner.call(req).await?;

            Ok(response) //work
         } else {
            return Err(Status::internal("foo")) ; //issue is here
        } 
        })
    }
}

So how to return Err?

Thanks

Source: View source