Integrate litep2p into Polkadot SDK (#2944)

[litep2p](https://github.com/altonen/litep2p) is a libp2p-compatible P2P
networking library. It supports all of the features of `rust-libp2p`
that are currently being utilized by Polkadot SDK.

Compared to `rust-libp2p`, `litep2p` has a quite different architecture
which is why the new `litep2p` network backend is only able to use a
little of the existing code in `sc-network`. The design has been mainly
influenced by how we'd wish to structure our networking-related code in
Polkadot SDK: independent higher-levels protocols directly communicating
with the network over links that support bidirectional backpressure. A
good example would be `NotificationHandle`/`RequestResponseHandle`
abstractions which allow, e.g., `SyncingEngine` to directly communicate
with peers to announce/request blocks.

I've tried running `polkadot --network-backend litep2p` with a few
different peer configurations and there is a noticeable reduction in
networking CPU usage. For high load (`--out-peers 200`), networking CPU
usage goes down from ~110% to ~30% (80 pp) and for normal load
(`--out-peers 40`), the usage goes down from ~55% to ~18% (37 pp).

These should not be taken as final numbers because:

a) there are still some low-hanging optimization fruits, such as
enabling [receive window
auto-tuning](https://github.com/libp2p/rust-yamux/pull/176), integrating
`Peerset` more closely with `litep2p` or improving memory usage of the
WebSocket transport
b) fixing bugs/instabilities that incorrectly cause `litep2p` to do less
work will increase the networking CPU usage
c) verification in a more diverse set of tests/conditions is needed

Nevertheless, these numbers should give an early estimate for CPU usage
of the new networking backend.

This PR consists of three separate changes:
* introduce a generic `PeerId` (wrapper around `Multihash`) so that we
don't have use `NetworkService::PeerId` in every part of the code that
uses a `PeerId`
* introduce `NetworkBackend` trait, implement it for the libp2p network
stack and make Polkadot SDK generic over `NetworkBackend`
  * implement `NetworkBackend` for litep2p

The new library should be considered experimental which is why
`rust-libp2p` will remain as the default option for the time being. This
PR currently depends on the master branch of `litep2p` but I'll cut a
new release for the library once all review comments have been
addresses.

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Dmitry Markin <dmitry@markin.tech>
Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>
Co-authored-by: Alexandru Vasile <alexandru.vasile@parity.io>

substrate/client/network/src/peer_store.rs

@@ -19,7 +19,8 @@
 //! [`PeerStore`] manages peer reputations and provides connection candidates to
 //! [`crate::protocol_controller::ProtocolController`].
 
-use libp2p::PeerId;
+use crate::{service::traits::PeerStore as PeerStoreT, PeerId};
+
 use log::trace;
 use parking_lot::Mutex;
 use partial_sort::PartialSort;
@@ -33,8 +34,6 @@ use std::{
 };
 use wasm_timer::Delay;
 
-use crate::protocol_controller::ProtocolHandle;
-
 /// Log target for this file.
 pub const LOG_TARGET: &str = "peerset";
 
@@ -52,31 +51,50 @@ const INVERSE_DECREMENT: i32 = 50;
 /// remove it, once the reputation value reaches 0.
 const FORGET_AFTER: Duration = Duration::from_secs(3600);
 
+/// Trait describing the required functionality from a `Peerset` handle.
+pub trait ProtocolHandle: Debug + Send + Sync {
+	/// Disconnect peer.
+	fn disconnect_peer(&self, peer_id: sc_network_types::PeerId);
+}
+
 /// Trait providing peer reputation management and connection candidates.
-pub trait PeerStoreProvider: Debug + Send {
+pub trait PeerStoreProvider: Debug + Send + Sync {
 	/// Check whether the peer is banned.
-	fn is_banned(&self, peer_id: &PeerId) -> bool;
+	fn is_banned(&self, peer_id: &sc_network_types::PeerId) -> bool;
 
 	/// Register a protocol handle to disconnect peers whose reputation drops below the threshold.
-	fn register_protocol(&self, protocol_handle: ProtocolHandle);
+	fn register_protocol(&self, protocol_handle: Arc<dyn ProtocolHandle>);
 
 	/// Report peer disconnection for reputation adjustment.
-	fn report_disconnect(&mut self, peer_id: PeerId);
+	fn report_disconnect(&self, peer_id: sc_network_types::PeerId);
 
 	/// Adjust peer reputation.
-	fn report_peer(&mut self, peer_id: PeerId, change: ReputationChange);
+	fn report_peer(&self, peer_id: sc_network_types::PeerId, change: ReputationChange);
 
 	/// Set peer role.
-	fn set_peer_role(&mut self, peer_id: &PeerId, role: ObservedRole);
+	fn set_peer_role(&self, peer_id: &sc_network_types::PeerId, role: ObservedRole);
 
 	/// Get peer reputation.
-	fn peer_reputation(&self, peer_id: &PeerId) -> i32;
+	fn peer_reputation(&self, peer_id: &sc_network_types::PeerId) -> i32;
 
 	/// Get peer role, if available.
-	fn peer_role(&self, peer_id: &PeerId) -> Option<ObservedRole>;
+	fn peer_role(&self, peer_id: &sc_network_types::PeerId) -> Option<ObservedRole>;
 
 	/// Get candidates with highest reputations for initiating outgoing connections.
-	fn outgoing_candidates(&self, count: usize, ignored: HashSet<&PeerId>) -> Vec<PeerId>;
+	fn outgoing_candidates(
+		&self,
+		count: usize,
+		ignored: HashSet<sc_network_types::PeerId>,
+	) -> Vec<sc_network_types::PeerId>;
+
+	/// Get the number of known peers.
+	///
+	/// This number might not include some connected peers in rare cases when their reputation
+	/// was not updated for one hour, because their entries in [`PeerStore`] were dropped.
+	fn num_known_peers(&self) -> usize;
+
+	/// Add known peer.
+	fn add_known_peer(&self, peer_id: sc_network_types::PeerId);
 }
 
 /// Actual implementation of peer reputations and connection candidates provider.
@@ -86,51 +104,56 @@ pub struct PeerStoreHandle {
 }
 
 impl PeerStoreProvider for PeerStoreHandle {
-	fn is_banned(&self, peer_id: &PeerId) -> bool {
-		self.inner.lock().is_banned(peer_id)
+	fn is_banned(&self, peer_id: &sc_network_types::PeerId) -> bool {
+		self.inner.lock().is_banned(&peer_id.into())
 	}
 
-	fn register_protocol(&self, protocol_handle: ProtocolHandle) {
+	fn register_protocol(&self, protocol_handle: Arc<dyn ProtocolHandle>) {
 		self.inner.lock().register_protocol(protocol_handle);
 	}
 
-	fn report_disconnect(&mut self, peer_id: PeerId) {
-		self.inner.lock().report_disconnect(peer_id)
+	fn report_disconnect(&self, peer_id: sc_network_types::PeerId) {
+		let mut inner = self.inner.lock();
+		inner.report_disconnect(peer_id.into())
 	}
 
-	fn report_peer(&mut self, peer_id: PeerId, change: ReputationChange) {
-		self.inner.lock().report_peer(peer_id, change)
+	fn report_peer(&self, peer_id: sc_network_types::PeerId, change: ReputationChange) {
+		let mut inner = self.inner.lock();
+		inner.report_peer(peer_id.into(), change)
 	}
 
-	fn set_peer_role(&mut self, peer_id: &PeerId, role: ObservedRole) {
-		self.inner.lock().set_peer_role(peer_id, role)
+	fn set_peer_role(&self, peer_id: &sc_network_types::PeerId, role: ObservedRole) {
+		let mut inner = self.inner.lock();
+		inner.set_peer_role(&peer_id.into(), role)
 	}
 
-	fn peer_reputation(&self, peer_id: &PeerId) -> i32 {
-		self.inner.lock().peer_reputation(peer_id)
+	fn peer_reputation(&self, peer_id: &sc_network_types::PeerId) -> i32 {
+		self.inner.lock().peer_reputation(&peer_id.into())
 	}
 
-	fn peer_role(&self, peer_id: &PeerId) -> Option<ObservedRole> {
-		self.inner.lock().peer_role(peer_id)
+	fn peer_role(&self, peer_id: &sc_network_types::PeerId) -> Option<ObservedRole> {
+		self.inner.lock().peer_role(&peer_id.into())
 	}
 
-	fn outgoing_candidates(&self, count: usize, ignored: HashSet<&PeerId>) -> Vec<PeerId> {
-		self.inner.lock().outgoing_candidates(count, ignored)
+	fn outgoing_candidates(
+		&self,
+		count: usize,
+		ignored: HashSet<sc_network_types::PeerId>,
+	) -> Vec<sc_network_types::PeerId> {
+		self.inner
+			.lock()
+			.outgoing_candidates(count, ignored.iter().map(|peer_id| (*peer_id).into()).collect())
+			.iter()
+			.map(|peer_id| peer_id.into())
+			.collect()
 	}
-}
 
-impl PeerStoreHandle {
-	/// Get the number of known peers.
-	///
-	/// This number might not include some connected peers in rare cases when their reputation
-	/// was not updated for one hour, because their entries in [`PeerStore`] were dropped.
-	pub fn num_known_peers(&self) -> usize {
+	fn num_known_peers(&self) -> usize {
 		self.inner.lock().peers.len()
 	}
 
-	/// Add known peer.
-	pub fn add_known_peer(&mut self, peer_id: PeerId) {
-		self.inner.lock().add_known_peer(peer_id);
+	fn add_known_peer(&self, peer_id: sc_network_types::PeerId) {
+		self.inner.lock().add_known_peer(peer_id.into());
 	}
 }
 
@@ -210,7 +233,7 @@ impl PeerInfo {
 #[derive(Debug)]
 struct PeerStoreInner {
 	peers: HashMap<PeerId, PeerInfo>,
-	protocols: Vec<ProtocolHandle>,
+	protocols: Vec<Arc<dyn ProtocolHandle>>,
 }
 
 impl PeerStoreInner {
@@ -218,7 +241,7 @@ impl PeerStoreInner {
 		self.peers.get(peer_id).map_or(false, |info| info.is_banned())
 	}
 
-	fn register_protocol(&mut self, protocol_handle: ProtocolHandle) {
+	fn register_protocol(&mut self, protocol_handle: Arc<dyn ProtocolHandle>) {
 		self.protocols.push(protocol_handle);
 	}
 
@@ -240,7 +263,7 @@ impl PeerStoreInner {
 		peer_info.add_reputation(change.value);
 
 		if peer_info.reputation < BANNED_THRESHOLD {
-			self.protocols.iter().for_each(|handle| handle.disconnect_peer(peer_id));
+			self.protocols.iter().for_each(|handle| handle.disconnect_peer(peer_id.into()));
 
 			log::warn!(
 				target: LOG_TARGET,
@@ -283,7 +306,7 @@ impl PeerStoreInner {
 		self.peers.get(peer_id).map_or(None, |info| info.role)
 	}
 
-	fn outgoing_candidates(&self, count: usize, ignored: HashSet<&PeerId>) -> Vec<PeerId> {
+	fn outgoing_candidates(&self, count: usize, ignored: HashSet<PeerId>) -> Vec<PeerId> {
 		let mut candidates = self
 			.peers
 			.iter()
@@ -378,6 +401,17 @@ impl PeerStore {
 	}
 }
 
+#[async_trait::async_trait]
+impl PeerStoreT for PeerStore {
+	fn handle(&self) -> Arc<dyn PeerStoreProvider> {
+		Arc::new(self.handle())
+	}
+
+	async fn run(self) {
+		self.run().await;
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::PeerInfo;