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/transactions/src/lib.rs

@@ -30,20 +30,24 @@ use crate::config::*;
 
 use codec::{Decode, Encode};
 use futures::{prelude::*, stream::FuturesUnordered};
-use libp2p::{multiaddr, PeerId};
 use log::{debug, trace, warn};
 
 use prometheus_endpoint::{register, Counter, PrometheusError, Registry, U64};
 use sc_network::{
-	config::{NonDefaultSetConfig, NonReservedPeerMode, ProtocolId, SetConfig},
-	error,
-	service::traits::{NotificationEvent, NotificationService, ValidationResult},
+	config::{NonReservedPeerMode, ProtocolId, SetConfig},
+	error, multiaddr,
+	peer_store::PeerStoreProvider,
+	service::{
+		traits::{NotificationEvent, NotificationService, ValidationResult},
+		NotificationMetrics,
+	},
 	types::ProtocolName,
 	utils::{interval, LruHashSet},
-	NetworkEventStream, NetworkNotification, NetworkPeers,
+	NetworkBackend, NetworkEventStream, NetworkPeers,
 };
 use sc_network_common::{role::ObservedRole, ExHashT};
 use sc_network_sync::{SyncEvent, SyncEventStream};
+use sc_network_types::PeerId;
 use sc_utils::mpsc::{tracing_unbounded, TracingUnboundedReceiver, TracingUnboundedSender};
 use sp_runtime::traits::Block as BlockT;
 
@@ -61,6 +65,9 @@ pub mod config;
 /// A set of transactions.
 pub type Transactions<E> = Vec<E>;
 
+/// Logging target for the file.
+const LOG_TARGET: &str = "sync";
+
 mod rep {
 	use sc_network::ReputationChange as Rep;
 	/// Reputation change when a peer sends us any transaction.
@@ -124,11 +131,17 @@ pub struct TransactionsHandlerPrototype {
 
 impl TransactionsHandlerPrototype {
 	/// Create a new instance.
-	pub fn new<Hash: AsRef<[u8]>>(
+	pub fn new<
+		Hash: AsRef<[u8]>,
+		Block: BlockT,
+		Net: NetworkBackend<Block, <Block as BlockT>::Hash>,
+	>(
 		protocol_id: ProtocolId,
 		genesis_hash: Hash,
 		fork_id: Option<&str>,
-	) -> (Self, NonDefaultSetConfig) {
+		metrics: NotificationMetrics,
+		peer_store_handle: Arc<dyn PeerStoreProvider>,
+	) -> (Self, Net::NotificationProtocolConfig) {
 		let genesis_hash = genesis_hash.as_ref();
 		let protocol_name: ProtocolName = if let Some(fork_id) = fork_id {
 			format!("/{}/{}/transactions/1", array_bytes::bytes2hex("", genesis_hash), fork_id)
@@ -136,7 +149,7 @@ impl TransactionsHandlerPrototype {
 			format!("/{}/transactions/1", array_bytes::bytes2hex("", genesis_hash))
 		}
 		.into();
-		let (config, notification_service) = NonDefaultSetConfig::new(
+		let (config, notification_service) = Net::notification_config(
 			protocol_name.clone(),
 			vec![format!("/{}/transactions/1", protocol_id.as_ref()).into()],
 			MAX_TRANSACTIONS_SIZE,
@@ -147,6 +160,8 @@ impl TransactionsHandlerPrototype {
 				reserved_nodes: Vec::new(),
 				non_reserved_mode: NonReservedPeerMode::Deny,
 			},
+			metrics,
+			peer_store_handle,
 		);
 
 		(Self { protocol_name, notification_service }, config)
@@ -160,7 +175,7 @@ impl TransactionsHandlerPrototype {
 	pub fn build<
 		B: BlockT + 'static,
 		H: ExHashT,
-		N: NetworkPeers + NetworkEventStream + NetworkNotification,
+		N: NetworkPeers + NetworkEventStream,
 		S: SyncEventStream + sp_consensus::SyncOracle,
 	>(
 		self,
@@ -231,7 +246,7 @@ enum ToHandler<H: ExHashT> {
 pub struct TransactionsHandler<
 	B: BlockT + 'static,
 	H: ExHashT,
-	N: NetworkPeers + NetworkEventStream + NetworkNotification,
+	N: NetworkPeers + NetworkEventStream,
 	S: SyncEventStream + sp_consensus::SyncOracle,
 > {
 	protocol_name: ProtocolName,
@@ -272,7 +287,7 @@ impl<B, H, N, S> TransactionsHandler<B, H, N, S>
 where
 	B: BlockT + 'static,
 	H: ExHashT,
-	N: NetworkPeers + NetworkEventStream + NetworkNotification,
+	N: NetworkPeers + NetworkEventStream,
 	S: SyncEventStream + sp_consensus::SyncOracle,
 {
 	/// Turns the [`TransactionsHandler`] into a future that should run forever and not be
@@ -369,7 +384,7 @@ where
 					iter::once(addr).collect(),
 				);
 				if let Err(err) = result {
-					log::error!(target: "sync", "Add reserved peer failed: {}", err);
+					log::error!(target: LOG_TARGET, "Add reserved peer failed: {}", err);
 				}
 			},
 			SyncEvent::PeerDisconnected(remote) => {
@@ -378,7 +393,7 @@ where
 					iter::once(remote).collect(),
 				);
 				if let Err(err) = result {
-					log::error!(target: "sync", "Remove reserved peer failed: {}", err);
+					log::error!(target: LOG_TARGET, "Remove reserved peer failed: {}", err);
 				}
 			},
 		}
@@ -388,16 +403,16 @@ where
 	fn on_transactions(&mut self, who: PeerId, transactions: Transactions<B::Extrinsic>) {
 		// Accept transactions only when node is not major syncing
 		if self.sync.is_major_syncing() {
-			trace!(target: "sync", "{} Ignoring transactions while major syncing", who);
+			trace!(target: LOG_TARGET, "{} Ignoring transactions while major syncing", who);
 			return
 		}
 
-		trace!(target: "sync", "Received {} transactions from {}", transactions.len(), who);
+		trace!(target: LOG_TARGET, "Received {} transactions from {}", transactions.len(), who);
 		if let Some(ref mut peer) = self.peers.get_mut(&who) {
 			for t in transactions {
 				if self.pending_transactions.len() > MAX_PENDING_TRANSACTIONS {
 					debug!(
-						target: "sync",
+						target: LOG_TARGET,
 						"Ignoring any further transactions that exceed `MAX_PENDING_TRANSACTIONS`({}) limit",
 						MAX_PENDING_TRANSACTIONS,
 					);
@@ -442,7 +457,7 @@ where
 			return
 		}
 
-		debug!(target: "sync", "Propagating transaction [{:?}]", hash);
+		debug!(target: LOG_TARGET, "Propagating transaction [{:?}]", hash);
 		if let Some(transaction) = self.transaction_pool.transaction(hash) {
 			let propagated_to = self.do_propagate_transactions(&[(hash.clone(), transaction)]);
 			self.transaction_pool.on_broadcasted(propagated_to);
@@ -506,7 +521,7 @@ where
 			return
 		}
 
-		debug!(target: "sync", "Propagating transactions");
+		debug!(target: LOG_TARGET, "Propagating transactions");
 		let transactions = self.transaction_pool.transactions();
 		let propagated_to = self.do_propagate_transactions(&transactions);
 		self.transaction_pool.on_broadcasted(propagated_to);