Collator protocol subsystem (#1659)

* WIP

* The initial implementation of the collator side.

* Improve comments

* Multiple collation requests

* Add more tests and comments to validator side

* Add comments, remove dead code

* Apply suggestions from code review

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* Fix build after suggested changes

* Also connect to the next validator group

* Remove a Future impl and move TimeoutExt to util

* Minor nits

* Fix build

* Change FetchCollations back to FetchCollation

* Try this

* Final fixes

* Fix build

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

polkadot/node/network/collator-protocol/src/lib.rs

@@ -0,0 +1,136 @@
+// Copyright 2020 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/>.
+
+//! The Collator Protocol allows collators and validators talk to each other.
+//! This subsystem implements both sides of the collator protocol.
+
+#![deny(missing_docs)]
+
+use std::time::Duration;
+use futures::{channel::oneshot, FutureExt};
+use log::trace;
+
+use polkadot_subsystem::{
+	Subsystem, SubsystemContext, SubsystemError, SpawnedSubsystem,
+	errors::RuntimeApiError,
+	metrics::{self, prometheus},
+	messages::{
+		AllMessages, CollatorProtocolMessage, NetworkBridgeMessage,
+	},
+};
+use polkadot_node_network_protocol::{
+	PeerId, ReputationChange as Rep,
+};
+use polkadot_primitives::v1::CollatorId;
+use polkadot_node_subsystem_util as util;
+
+mod collator_side;
+mod validator_side;
+
+const TARGET: &'static str = "colp";
+const REQUEST_TIMEOUT: Duration = Duration::from_secs(1);
+
+#[derive(Debug, derive_more::From)]
+enum Error {
+	#[from]
+	Subsystem(SubsystemError),
+	#[from]
+	Oneshot(oneshot::Canceled),
+	#[from]
+	RuntimeApi(RuntimeApiError),
+	#[from]
+	UtilError(util::Error),
+}
+
+type Result<T> = std::result::Result<T, Error>;
+
+enum ProtocolSide {
+	Validator,
+	Collator(CollatorId),
+}
+
+/// The collator protocol subsystem.
+pub struct CollatorProtocolSubsystem {
+	protocol_side: ProtocolSide, 
+}
+
+impl CollatorProtocolSubsystem {
+	/// Start the collator protocol.
+	/// If `id` is `Some` this is a collator side of the protocol.
+	/// If `id` is `None` this is a validator side of the protocol. 
+	pub fn new(id: Option<CollatorId>) -> Self {
+		let protocol_side = match id {
+			Some(id) => ProtocolSide::Collator(id),
+			None => ProtocolSide::Validator,
+		};
+
+		Self {
+			protocol_side,
+		}
+	}
+
+	async fn run<Context>(self, ctx: Context) -> Result<()>
+	where
+		Context: SubsystemContext<Message = CollatorProtocolMessage>,
+	{
+		match self.protocol_side {
+		    ProtocolSide::Validator => validator_side::run(ctx, REQUEST_TIMEOUT).await,
+		    ProtocolSide::Collator(id) => collator_side::run(ctx, id).await,
+		}
+	}
+}
+
+/// Collator protocol metrics.
+#[derive(Default, Clone)]
+pub struct Metrics;
+
+impl metrics::Metrics for Metrics {
+	fn try_register(_registry: &prometheus::Registry) 
+		-> std::result::Result<Self, prometheus::PrometheusError> {
+		Ok(Metrics)
+	}
+}
+
+impl<Context> Subsystem<Context> for CollatorProtocolSubsystem
+where
+	Context: SubsystemContext<Message = CollatorProtocolMessage> + Sync + Send,
+{
+	type Metrics = Metrics;
+
+	fn start(self, ctx: Context) -> SpawnedSubsystem {
+		SpawnedSubsystem {
+			name: "collator-protocol-subsystem",
+			future: Box::pin(async move { self.run(ctx) }.map(|_| ())),
+		}
+	}
+}
+
+/// Modify the reputation of a peer based on its behavior.
+async fn modify_reputation<Context>(ctx: &mut Context, peer: PeerId, rep: Rep) -> Result<()>
+where
+	Context: SubsystemContext<Message = CollatorProtocolMessage>,
+{
+	trace!(
+		target: TARGET,
+		"Reputation change of {:?} for peer {:?}", rep, peer,
+	);
+
+	ctx.send_message(AllMessages::NetworkBridge(
+		NetworkBridgeMessage::ReportPeer(peer, rep),
+	)).await?;
+
+	Ok(())
+}