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/consensus/beefy/src/communication/gossip.rs

@@ -18,8 +18,9 @@
 
 use std::{collections::BTreeSet, sync::Arc, time::Duration};
 
-use sc_network::{NetworkPeers, PeerId, ReputationChange};
+use sc_network::{NetworkPeers, ReputationChange};
 use sc_network_gossip::{MessageIntent, ValidationResult, Validator, ValidatorContext};
+use sc_network_types::PeerId;
 use sp_runtime::traits::{Block, Hash, Header, NumberFor};
 
 use codec::{Decode, DecodeAll, Encode};
@@ -506,6 +507,7 @@ pub(crate) mod tests {
 		}
 	}
 
+	#[async_trait::async_trait]
 	impl NetworkPeers for TestNetwork {
 		fn set_authorized_peers(&self, _: std::collections::HashSet<PeerId>) {
 			unimplemented!()
@@ -581,6 +583,10 @@ pub(crate) mod tests {
 		fn peer_role(&self, _: PeerId, _: Vec<u8>) -> Option<sc_network::ObservedRole> {
 			unimplemented!()
 		}
+
+		async fn reserved_peers(&self) -> Result<Vec<PeerId>, ()> {
+			unimplemented!();
+		}
 	}
 
 	struct TestContext;
@@ -591,11 +597,11 @@ pub(crate) mod tests {
 
 		fn broadcast_message(&mut self, _topic: B::Hash, _message: Vec<u8>, _force: bool) {}
 
-		fn send_message(&mut self, _who: &sc_network::PeerId, _message: Vec<u8>) {
+		fn send_message(&mut self, _who: &sc_network_types::PeerId, _message: Vec<u8>) {
 			unimplemented!()
 		}
 
-		fn send_topic(&mut self, _who: &sc_network::PeerId, _topic: B::Hash, _force: bool) {
+		fn send_topic(&mut self, _who: &sc_network_types::PeerId, _topic: B::Hash, _force: bool) {
 			unimplemented!()
 		}
 	}
@@ -772,7 +778,7 @@ pub(crate) mod tests {
 			Arc::new(TestNetwork::new().0),
 		);
 		gv.update_filter(GossipFilterCfg { start: 0, end: 10, validator_set: &validator_set });
-		let sender = sc_network::PeerId::random();
+		let sender = sc_network_types::PeerId::random();
 		let topic = Default::default();
 		let intent = MessageIntent::Broadcast;
 
@@ -852,7 +858,7 @@ pub(crate) mod tests {
 			Arc::new(TestNetwork::new().0),
 		);
 		gv.update_filter(GossipFilterCfg { start: 0, end: 10, validator_set: &validator_set });
-		let sender = sc_network::PeerId::random();
+		let sender = sc_network_types::PeerId::random();
 		let topic = Default::default();
 
 		let vote = dummy_vote(1);

substrate/client/consensus/beefy/src/communication/mod.rs

@@ -65,17 +65,28 @@ pub(crate) mod beefy_protocol_name {
 /// Returns the configuration value to put in
 /// [`sc_network::config::FullNetworkConfiguration`].
 /// For standard protocol name see [`beefy_protocol_name::gossip_protocol_name`].
-pub fn beefy_peers_set_config(
+pub fn beefy_peers_set_config<
+	B: sp_runtime::traits::Block,
+	N: sc_network::NetworkBackend<B, <B as sp_runtime::traits::Block>::Hash>,
+>(
 	gossip_protocol_name: sc_network::ProtocolName,
-) -> (sc_network::config::NonDefaultSetConfig, Box<dyn sc_network::NotificationService>) {
-	let (mut cfg, notification_service) = sc_network::config::NonDefaultSetConfig::new(
+	metrics: sc_network::service::NotificationMetrics,
+	peer_store_handle: std::sync::Arc<dyn sc_network::peer_store::PeerStoreProvider>,
+) -> (N::NotificationProtocolConfig, Box<dyn sc_network::NotificationService>) {
+	let (cfg, notification_service) = N::notification_config(
 		gossip_protocol_name,
 		Vec::new(),
 		1024 * 1024,
 		None,
-		Default::default(),
+		sc_network::config::SetConfig {
+			in_peers: 25,
+			out_peers: 25,
+			reserved_nodes: Vec::new(),
+			non_reserved_mode: sc_network::config::NonReservedPeerMode::Accept,
+		},
+		metrics,
+		peer_store_handle,
 	);
-	cfg.allow_non_reserved(25, 25);
 	(cfg, notification_service)
 }
 

substrate/client/consensus/beefy/src/communication/peers.rs

@@ -18,7 +18,8 @@
 
 //! Logic for keeping track of BEEFY peers.
 
-use sc_network::{PeerId, ReputationChange};
+use sc_network::ReputationChange;
+use sc_network_types::PeerId;
 use sp_runtime::traits::{Block, NumberFor, Zero};
 use std::collections::{HashMap, VecDeque};
 

substrate/client/consensus/beefy/src/communication/request_response/incoming_requests_handler.rs

@@ -21,9 +21,10 @@ use futures::{channel::oneshot, StreamExt};
 use log::{debug, trace};
 use sc_client_api::BlockBackend;
 use sc_network::{
-	config as netconfig, config::RequestResponseConfig, types::ProtocolName, PeerId,
-	ReputationChange,
+	config as netconfig, service::traits::RequestResponseConfig, types::ProtocolName,
+	NetworkBackend, ReputationChange,
 };
+use sc_network_types::PeerId;
 use sp_consensus_beefy::BEEFY_ENGINE_ID;
 use sp_runtime::traits::Block;
 use std::{marker::PhantomData, sync::Arc};
@@ -139,15 +140,15 @@ where
 	Client: BlockBackend<B> + Send + Sync,
 {
 	/// Create a new [`BeefyJustifsRequestHandler`].
-	pub fn new<Hash: AsRef<[u8]>>(
+	pub fn new<Hash: AsRef<[u8]>, Network: NetworkBackend<B, <B as Block>::Hash>>(
 		genesis_hash: Hash,
 		fork_id: Option<&str>,
 		client: Arc<Client>,
 		prometheus_registry: Option<prometheus::Registry>,
-	) -> (Self, RequestResponseConfig) {
-		let (request_receiver, config) =
-			on_demand_justifications_protocol_config(genesis_hash, fork_id);
-		let justif_protocol_name = config.name.clone();
+	) -> (Self, Network::RequestResponseProtocolConfig) {
+		let (request_receiver, config): (_, Network::RequestResponseProtocolConfig) =
+			on_demand_justifications_protocol_config::<_, _, Network>(genesis_hash, fork_id);
+		let justif_protocol_name = config.protocol_name().clone();
 		let metrics = register_metrics(prometheus_registry);
 		(
 			Self { request_receiver, justif_protocol_name, client, metrics, _block: PhantomData },

substrate/client/consensus/beefy/src/communication/request_response/mod.rs

@@ -26,7 +26,8 @@ pub use incoming_requests_handler::BeefyJustifsRequestHandler;
 use std::time::Duration;
 
 use codec::{Decode, Encode, Error as CodecError};
-use sc_network::{config::RequestResponseConfig, PeerId};
+use sc_network::NetworkBackend;
+use sc_network_types::PeerId;
 use sp_runtime::traits::{Block, NumberFor};
 
 use crate::communication::{beefy_protocol_name::justifications_protocol_name, peers::PeerReport};
@@ -47,23 +48,27 @@ const BEEFY_SYNC_LOG_TARGET: &str = "beefy::sync";
 /// `ProtocolConfig`.
 ///
 /// Consider using [`BeefyJustifsRequestHandler`] instead of this low-level function.
-pub(crate) fn on_demand_justifications_protocol_config<Hash: AsRef<[u8]>>(
+pub(crate) fn on_demand_justifications_protocol_config<
+	Hash: AsRef<[u8]>,
+	B: Block,
+	Network: NetworkBackend<B, <B as Block>::Hash>,
+>(
 	genesis_hash: Hash,
 	fork_id: Option<&str>,
-) -> (IncomingRequestReceiver, RequestResponseConfig) {
+) -> (IncomingRequestReceiver, Network::RequestResponseProtocolConfig) {
 	let name = justifications_protocol_name(genesis_hash, fork_id);
 	let fallback_names = vec![];
 	let (tx, rx) = async_channel::bounded(JUSTIF_CHANNEL_SIZE);
 	let rx = IncomingRequestReceiver::new(rx);
-	let cfg = RequestResponseConfig {
+	let cfg = Network::request_response_config(
 		name,
 		fallback_names,
-		max_request_size: 32,
-		max_response_size: MAX_RESPONSE_SIZE,
+		32,
+		MAX_RESPONSE_SIZE,
 		// We are connected to all validators:
-		request_timeout: JUSTIF_REQUEST_TIMEOUT,
-		inbound_queue: Some(tx),
-	};
+		JUSTIF_REQUEST_TIMEOUT,
+		Some(tx),
+	);
 	(rx, cfg)
 }
 

substrate/client/consensus/beefy/src/communication/request_response/outgoing_requests_engine.rs

@@ -24,8 +24,9 @@ use log::{debug, warn};
 use parking_lot::Mutex;
 use sc_network::{
 	request_responses::{IfDisconnected, RequestFailure},
-	NetworkRequest, PeerId, ProtocolName,
+	NetworkRequest, ProtocolName,
 };
+use sc_network_types::PeerId;
 use sp_consensus_beefy::{ecdsa_crypto::AuthorityId, ValidatorSet};
 use sp_runtime::traits::{Block, NumberFor};
 use std::{collections::VecDeque, result::Result, sync::Arc};