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/sync/src/service/mock.rs

@@ -17,17 +17,16 @@
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 use futures::channel::oneshot;
-use libp2p::{Multiaddr, PeerId};
 
 use sc_consensus::{BlockImportError, BlockImportStatus};
 use sc_network::{
 	config::MultiaddrWithPeerId,
 	request_responses::{IfDisconnected, RequestFailure},
 	types::ProtocolName,
-	NetworkNotification, NetworkPeers, NetworkRequest, NetworkSyncForkRequest,
-	NotificationSenderError, NotificationSenderT, ReputationChange,
+	Multiaddr, NetworkPeers, NetworkRequest, NetworkSyncForkRequest, ReputationChange,
 };
 use sc_network_common::role::ObservedRole;
+use sc_network_types::PeerId;
 use sp_runtime::traits::{Block as BlockT, NumberFor};
 
 use std::collections::HashSet;
@@ -80,6 +79,7 @@ mockall::mock! {
 mockall::mock! {
 	pub Network {}
 
+	#[async_trait::async_trait]
 	impl NetworkPeers for Network {
 		fn set_authorized_peers(&self, peers: HashSet<PeerId>);
 		fn set_authorized_only(&self, reserved_only: bool);
@@ -108,6 +108,7 @@ mockall::mock! {
 		) -> Result<(), String>;
 		fn sync_num_connected(&self) -> usize;
 		fn peer_role(&self, peer_id: PeerId, handshake: Vec<u8>) -> Option<ObservedRole>;
+		async fn reserved_peers(&self) -> Result<Vec<sc_network_types::PeerId>, ()>;
 	}
 
 	#[async_trait::async_trait]
@@ -130,14 +131,4 @@ mockall::mock! {
 			connect: IfDisconnected,
 		);
 	}
-
-	impl NetworkNotification for Network {
-		fn write_notification(&self, target: PeerId, protocol: ProtocolName, message: Vec<u8>);
-		fn notification_sender(
-			&self,
-			target: PeerId,
-			protocol: ProtocolName,
-		) -> Result<Box<dyn NotificationSenderT>, NotificationSenderError>;
-		fn set_notification_handshake(&self, protocol: ProtocolName, handshake: Vec<u8>);
-	}
 }

substrate/client/network/sync/src/service/network.rs

@@ -17,21 +17,21 @@
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 use futures::{channel::oneshot, StreamExt};
-use libp2p::PeerId;
+use sc_network_types::PeerId;
 
 use sc_network::{
 	request_responses::{IfDisconnected, RequestFailure},
 	types::ProtocolName,
-	NetworkNotification, NetworkPeers, NetworkRequest, ReputationChange,
+	NetworkPeers, NetworkRequest, ReputationChange,
 };
 use sc_utils::mpsc::{tracing_unbounded, TracingUnboundedReceiver, TracingUnboundedSender};
 
 use std::sync::Arc;
 
 /// Network-related services required by `sc-network-sync`
-pub trait Network: NetworkPeers + NetworkRequest + NetworkNotification {}
+pub trait Network: NetworkPeers + NetworkRequest {}
 
-impl<T> Network for T where T: NetworkPeers + NetworkRequest + NetworkNotification {}
+impl<T> Network for T where T: NetworkPeers + NetworkRequest {}
 
 /// Network service provider for `ChainSync`
 ///
@@ -57,12 +57,6 @@ pub enum ToServiceCommand {
 		oneshot::Sender<Result<(Vec<u8>, ProtocolName), RequestFailure>>,
 		IfDisconnected,
 	),
-
-	/// Call `NetworkNotification::write_notification()`
-	WriteNotification(PeerId, ProtocolName, Vec<u8>),
-
-	/// Call `NetworkNotification::set_notification_handshake()`
-	SetNotificationHandshake(ProtocolName, Vec<u8>),
 }
 
 /// Handle that is (temporarily) passed to `ChainSync` so it can
@@ -101,20 +95,6 @@ impl NetworkServiceHandle {
 			.tx
 			.unbounded_send(ToServiceCommand::StartRequest(who, protocol, request, tx, connect));
 	}
-
-	/// Send notification to peer
-	pub fn write_notification(&self, who: PeerId, protocol: ProtocolName, message: Vec<u8>) {
-		let _ = self
-			.tx
-			.unbounded_send(ToServiceCommand::WriteNotification(who, protocol, message));
-	}
-
-	/// Set handshake for the notification protocol.
-	pub fn set_notification_handshake(&self, protocol: ProtocolName, handshake: Vec<u8>) {
-		let _ = self
-			.tx
-			.unbounded_send(ToServiceCommand::SetNotificationHandshake(protocol, handshake));
-	}
 }
 
 impl NetworkServiceProvider {
@@ -135,10 +115,6 @@ impl NetworkServiceProvider {
 					service.report_peer(peer, reputation_change),
 				ToServiceCommand::StartRequest(peer, protocol, request, tx, connect) =>
 					service.start_request(peer, protocol, request, None, tx, connect),
-				ToServiceCommand::WriteNotification(peer, protocol, message) =>
-					service.write_notification(peer, protocol, message),
-				ToServiceCommand::SetNotificationHandshake(protocol, handshake) =>
-					service.set_notification_handshake(protocol, handshake),
 			}
 		}
 	}

substrate/client/network/sync/src/service/syncing_service.rs

@@ -19,7 +19,7 @@
 use crate::types::{ExtendedPeerInfo, SyncEvent, SyncEventStream, SyncStatus, SyncStatusProvider};
 
 use futures::{channel::oneshot, Stream};
-use libp2p::PeerId;
+use sc_network_types::PeerId;
 
 use sc_consensus::{BlockImportError, BlockImportStatus, JustificationSyncLink, Link};
 use sc_network::{NetworkBlock, NetworkSyncForkRequest};