Infrastructure improvements (#2897)

* Factor out runtime module into utils.

* Add maybe_authority information to `PeerConnected` event.

We already gather this information in authority discovery, so we might
as well share it with others.

This opens up an easy path to trigger validators differently from normal
nodes, e.g. for prioritization. This change has become more important
now, that we just connect to all validators and therefore just have a
long peer list without any information about those nodes.

* Test fix.

polkadot/node/subsystem-util/src/runtime/error.rs

@@ -0,0 +1,52 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+//! Error handling related code and Error/Result definitions.
+
+use thiserror::Error;
+use futures::channel::oneshot;
+
+use polkadot_node_subsystem::errors::RuntimeApiError;
+use polkadot_primitives::v1::SessionIndex;
+
+pub type Result<T> = std::result::Result<T, Error>;
+
+/// Errors for fetching of runtime information.
+#[derive(Debug, Error)]
+pub enum Error {
+	/// Runtime API subsystem is down, which means we're shutting down.
+	#[error("Runtime request canceled")]
+	RuntimeRequestCanceled(oneshot::Canceled),
+
+	/// Some request to the runtime failed.
+	/// For example if we prune a block we're requesting info about.
+	#[error("Runtime API error")]
+	RuntimeRequest(RuntimeApiError),
+
+	/// We tried fetching a session info which was not available.
+	#[error("There was no session with the given index")]
+	NoSuchSession(SessionIndex),
+}
+
+/// Receive a response from a runtime request and convert errors.
+pub(crate) async fn recv_runtime<V>(
+	r: oneshot::Receiver<std::result::Result<V, RuntimeApiError>>,
+) -> std::result::Result<V, Error> {
+	r.await
+		.map_err(Error::RuntimeRequestCanceled)?
+		.map_err(Error::RuntimeRequest)
+}