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>

templates/minimal/node/src/command.rs

@@ -119,7 +119,15 @@ pub fn run() -> sc_cli::Result<()> {
 		None => {
 			let runner = cli.create_runner(&cli.run)?;
 			runner.run_node_until_exit(|config| async move {
-				service::new_full(config, cli.consensus).map_err(sc_cli::Error::Service)
+				match config.network.network_backend {
+					sc_network::config::NetworkBackendType::Libp2p =>
+						service::new_full::<sc_network::NetworkWorker<_, _>>(config, cli.consensus)
+							.map_err(sc_cli::Error::Service),
+					sc_network::config::NetworkBackendType::Litep2p => service::new_full::<
+						sc_network::Litep2pNetworkBackend,
+					>(config, cli.consensus)
+					.map_err(sc_cli::Error::Service),
+				}
 			})
 		},
 	}

templates/minimal/node/src/service.rs

@@ -22,6 +22,7 @@ use sc_executor::WasmExecutor;
 use sc_service::{error::Error as ServiceError, Configuration, TaskManager};
 use sc_telemetry::{Telemetry, TelemetryWorker};
 use sc_transaction_pool_api::OffchainTransactionPoolFactory;
+use sp_runtime::traits::Block as BlockT;
 use std::sync::Arc;
 
 use crate::cli::Consensus;
@@ -104,7 +105,10 @@ pub fn new_partial(config: &Configuration) -> Result<Service, ServiceError> {
 }
 
 /// Builds a new service for a full client.
-pub fn new_full(config: Configuration, consensus: Consensus) -> Result<TaskManager, ServiceError> {
+pub fn new_full<Network: sc_network::NetworkBackend<Block, <Block as BlockT>::Hash>>(
+	config: Configuration,
+	consensus: Consensus,
+) -> Result<TaskManager, ServiceError> {
 	let sc_service::PartialComponents {
 		client,
 		backend,
@@ -116,7 +120,14 @@ pub fn new_full(config: Configuration, consensus: Consensus) -> Result<TaskManag
 		other: mut telemetry,
 	} = new_partial(&config)?;
 
-	let net_config = sc_network::config::FullNetworkConfiguration::new(&config.network);
+	let net_config = sc_network::config::FullNetworkConfiguration::<
+		Block,
+		<Block as BlockT>::Hash,
+		Network,
+	>::new(&config.network);
+	let metrics = Network::register_notification_metrics(
+		config.prometheus_config.as_ref().map(|cfg| &cfg.registry),
+	);
 
 	let (network, system_rpc_tx, tx_handler_controller, network_starter, sync_service) =
 		sc_service::build_network(sc_service::BuildNetworkParams {
@@ -129,6 +140,7 @@ pub fn new_full(config: Configuration, consensus: Consensus) -> Result<TaskManag
 			block_announce_validator_builder: None,
 			warp_sync_params: None,
 			block_relay: None,
+			metrics,
 		})?;
 
 	if config.offchain_worker.enabled {
@@ -143,7 +155,7 @@ pub fn new_full(config: Configuration, consensus: Consensus) -> Result<TaskManag
 				transaction_pool: Some(OffchainTransactionPoolFactory::new(
 					transaction_pool.clone(),
 				)),
-				network_provider: network.clone(),
+				network_provider: Arc::new(network.clone()),
 				enable_http_requests: true,
 				custom_extensions: |_| vec![],
 			})