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>

polkadot/node/network/bridge/src/network.rs

@@ -25,9 +25,8 @@ use parking_lot::Mutex;
 use parity_scale_codec::Encode;
 
 use sc_network::{
-	config::parse_addr, multiaddr::Multiaddr, types::ProtocolName, IfDisconnected, MessageSink,
-	NetworkPeers, NetworkRequest, NetworkService, OutboundFailure, ReputationChange,
-	RequestFailure,
+	config::parse_addr, multiaddr::Multiaddr, service::traits::NetworkService, types::ProtocolName,
+	IfDisconnected, MessageSink, OutboundFailure, ReputationChange, RequestFailure,
 };
 
 use polkadot_node_network_protocol::{
@@ -35,7 +34,7 @@ use polkadot_node_network_protocol::{
 	request_response::{OutgoingRequest, Recipient, ReqProtocolNames, Requests},
 	v1 as protocol_v1, v2 as protocol_v2, v3 as protocol_v3, PeerId,
 };
-use polkadot_primitives::{AuthorityDiscoveryId, Block, Hash};
+use polkadot_primitives::AuthorityDiscoveryId;
 
 use crate::{metrics::Metrics, validator_discovery::AuthorityDiscovery, WireMessage};
 
@@ -232,13 +231,13 @@ pub trait Network: Clone + Send + 'static {
 }
 
 #[async_trait]
-impl Network for Arc<NetworkService<Block, Hash>> {
+impl Network for Arc<dyn NetworkService> {
 	async fn set_reserved_peers(
 		&mut self,
 		protocol: ProtocolName,
 		multiaddresses: HashSet<Multiaddr>,
 	) -> Result<(), String> {
-		NetworkService::set_reserved_peers(&**self, protocol, multiaddresses)
+		<dyn NetworkService>::set_reserved_peers(&**self, protocol, multiaddresses)
 	}
 
 	async fn remove_from_peers_set(
@@ -246,15 +245,15 @@ impl Network for Arc<NetworkService<Block, Hash>> {
 		protocol: ProtocolName,
 		peers: Vec<PeerId>,
 	) -> Result<(), String> {
-		NetworkService::remove_peers_from_reserved_set(&**self, protocol, peers)
+		<dyn NetworkService>::remove_peers_from_reserved_set(&**self, protocol, peers)
 	}
 
 	fn report_peer(&self, who: PeerId, rep: ReputationChange) {
-		NetworkService::report_peer(&**self, who, rep);
+		<dyn NetworkService>::report_peer(&**self, who, rep);
 	}
 
 	fn disconnect_peer(&self, who: PeerId, protocol: ProtocolName) {
-		NetworkService::disconnect_peer(&**self, who, protocol);
+		<dyn NetworkService>::disconnect_peer(&**self, who, protocol);
 	}
 
 	async fn start_request<AD: AuthorityDiscovery>(
@@ -289,7 +288,7 @@ impl Network for Arc<NetworkService<Block, Hash>> {
 						Ok(v) => v,
 						Err(_) => continue,
 					};
-					NetworkService::add_known_address(self, peer_id, addr);
+					<dyn NetworkService>::add_known_address(&**self, peer_id, addr);
 					found_peer_id = Some(peer_id);
 				}
 				found_peer_id
@@ -321,8 +320,8 @@ impl Network for Arc<NetworkService<Block, Hash>> {
 			"Starting request",
 		);
 
-		NetworkService::start_request(
-			self,
+		<dyn NetworkService>::start_request(
+			&**self,
 			peer_id,
 			req_protocol_names.get_name(protocol),
 			payload,
@@ -333,7 +332,7 @@ impl Network for Arc<NetworkService<Block, Hash>> {
 	}
 
 	fn peer_role(&self, who: PeerId, handshake: Vec<u8>) -> Option<sc_network::ObservedRole> {
-		NetworkService::peer_role(self, who, handshake)
+		<dyn NetworkService>::peer_role(&**self, who, handshake)
 	}
 }
 

polkadot/node/network/bridge/src/rx/tests.rs

@@ -366,13 +366,13 @@ impl NotificationService for TestNotificationService {
 	}
 
 	/// Send synchronous `notification` to `peer`.
-	fn send_sync_notification(&self, _peer: &PeerId, _notification: Vec<u8>) {
+	fn send_sync_notification(&mut self, _peer: &PeerId, _notification: Vec<u8>) {
 		unimplemented!();
 	}
 
 	/// Send asynchronous `notification` to `peer`, allowing sender to exercise backpressure.
 	async fn send_async_notification(
-		&self,
+		&mut self,
 		_peer: &PeerId,
 		_notification: Vec<u8>,
 	) -> Result<(), sc_network::error::Error> {