server: wrapping jsonrpsee:TowerService is a new type pattern is not possible

[niklasad1]

So after upgrading hyper to v1.0 users may run into rust-lang/rust#102211 where the error type can't be deduced to Box<std::error::Error + Send Sync + 'static

For instance when using the tower::service_fn such as:

    let svc = tower::service_fn(move |req| {
        let stop_handle = stop_handle2.clone();
        let svc_builder = svc_builder2.clone();
        let methods = methods2.clone();

        let mut svc = svc_builder.build(methods, stop_handle.clone());

        // It's not possible to know whether the websocket upgrade handshake failed or not here.
        let is_websocket = ws::is_upgrade_request(&req);

        if is_websocket {
            println!("websocket")
        } else {
            println!("http")
        }
        
        // This won't work without converting the error to a concrete error....
        async move { svc.call(req).await.map_err(|e| anyhow::anyhow!("{:?}", e)) }
    });

This tower:service_fn is recommended because dealing with the trait bounds for the service itself is hard and tricky
but it's also possible to wrap the TowerService/TowerServiceBuilder in a new type with code like this:

#[derive(Clone)]
struct Svc<RpcMiddleware, HttpMiddleware> {
	svc_builder: TowerServiceBuilder<RpcMiddleware, HttpMiddleware>,
	methods: Methods,
	stop_handle: StopHandle,
	metrics: Metrics,
}

impl<RpcMiddleware, HttpMiddleware, B> tower::Service<HttpRequest<B>> for Svc<RpcMiddleware, HttpMiddleware>
where
	RpcMiddleware: for<'a> tower::Layer<RpcService> Send + Clone,
	<RpcMiddleware as tower::Layer<RpcService>>::Service: Send + Sync + 'static,
	for<'a> <RpcMiddleware as tower::Layer<RpcService>>::Service: RpcServiceT<'a>,
	HttpMiddleware: tower::Layer<TowerServiceNoHttp<RpcMiddleware>> + Send + 'static + Clone,
	<HttpMiddleware as tower::Layer<TowerServiceNoHttp<RpcMiddleware>>>::Service:
		Send + tower::Service<HttpRequest<B>, Response = HttpResponse, Error = BoxError>,
	<<HttpMiddleware as tower::Layer<TowerServiceNoHttp<RpcMiddleware>>>::Service as tower::Service<HttpRequest<B>>>::Future:
		Send + 'static,
	B: http_body::Body<Data = hyper::body::Bytes> + Send + 'static,
	B::Error: Into<BoxError>,
{
	type Error = BoxError;
	type Response = HttpResponse;
	type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;

	fn call(&mut self, req: HttpRequest<B>) -> Self::Future {
		let is_websocket = jsonrpsee::server::ws::is_upgrade_request(&req);
		let transport_label = if is_websocket { "ws" } else { "http" };

		let metrics = self.metrics.clone();


		let mut svc = self.svc_builder.clone().build(self.methods.clone(), self.stop_handle.clone());

		if is_websocket {
			// Utilize the session close future to know when the actual WebSocket
			// session was closed.
			let session_close = svc.on_session_closed();

			// A little bit weird API but the response to HTTP request must be returned below
			// and we spawn a task to register when the session is closed.
			tokio::spawn(async move {
				session_close.await;
				tracing::info!("Closed WebSocket connection");
				metrics.closed_ws_connections.fetch_add(1, Ordering::Relaxed);
			});

			async move {
				tracing::info!("Opened WebSocket connection");
				metrics.opened_ws_connections.fetch_add(1, Ordering::Relaxed);
				svc.call(req).await
			}
			.boxed()
		} else {
			// HTTP.
			async move {
				tracing::info!("Opened HTTP connection");
				metrics.http_calls.fetch_add(1, Ordering::Relaxed);
				let rp = svc.call(req).await;

				if rp.is_ok() {
					metrics.success_http_calls.fetch_add(1, Ordering::Relaxed);
				}

				tracing::info!("Closed HTTP connection");
				rp
			}
			.boxed()
		}
	}

	fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> std::task::Poll<Result<(), Self::Error>> {
		Poll::Ready(Ok(()))
	}
}

So, the question is really if we should re-export TowerNoHttpService and add an example with this mess?
Maybe it's possible to simplify the trait bounds somehow?

//cc @jsdw @lexnv