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/authority-discovery/src/worker/addr_cache.rs

@@ -16,10 +16,8 @@
 // You should have received a copy of the GNU General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
-use libp2p::{
-	core::multiaddr::{Multiaddr, Protocol},
-	PeerId,
-};
+use sc_network::{multiaddr::Protocol, Multiaddr};
+use sc_network_types::PeerId;
 use sp_authority_discovery::AuthorityId;
 use std::collections::{hash_map::Entry, HashMap, HashSet};
 
@@ -178,7 +176,7 @@ fn addresses_to_peer_ids(addresses: &HashSet<Multiaddr>) -> HashSet<PeerId> {
 mod tests {
 	use super::*;
 
-	use libp2p::multihash::{self, Multihash};
+	use multihash::{self, Multihash};
 	use quickcheck::{Arbitrary, Gen, QuickCheck, TestResult};
 
 	use sp_authority_discovery::{AuthorityId, AuthorityPair};

substrate/client/authority-discovery/src/worker/schema/tests.rs

@@ -21,8 +21,9 @@ mod schema_v1 {
 }
 
 use super::*;
-use libp2p::{identity::Keypair, multiaddr::Multiaddr, PeerId};
+use libp2p::identity::Keypair;
 use prost::Message;
+use sc_network::{Multiaddr, PeerId};
 
 #[test]
 fn v2_decodes_v1() {

substrate/client/authority-discovery/src/worker/tests.rs

@@ -29,16 +29,11 @@ use futures::{
 	sink::SinkExt,
 	task::LocalSpawn,
 };
-use libp2p::{
-	core::multiaddr,
-	identity::{Keypair, SigningError},
-	kad::record::Key as KademliaKey,
-	PeerId,
-};
+use libp2p::{core::multiaddr, identity::SigningError, kad::record::Key as KademliaKey, PeerId};
 use prometheus_endpoint::prometheus::default_registry;
 
 use sc_client_api::HeaderBackend;
-use sc_network::Signature;
+use sc_network::{service::signature::Keypair, Signature};
 use sp_api::{ApiRef, ProvideRuntimeApi};
 use sp_keystore::{testing::MemoryKeystore, Keystore};
 use sp_runtime::traits::{Block as BlockT, NumberFor, Zero};
@@ -122,7 +117,7 @@ pub enum TestNetworkEvent {
 }
 
 pub struct TestNetwork {
-	peer_id: PeerId,
+	peer_id: sc_network_types::PeerId,
 	identity: Keypair,
 	external_addresses: Vec<Multiaddr>,
 	// Whenever functions on `TestNetwork` are called, the function arguments are added to the
@@ -158,10 +153,25 @@ impl Default for TestNetwork {
 impl NetworkSigner for TestNetwork {
 	fn sign_with_local_identity(
 		&self,
-		msg: impl AsRef<[u8]>,
+		msg: Vec<u8>,
 	) -> std::result::Result<Signature, SigningError> {
 		Signature::sign_message(msg, &self.identity)
 	}
+
+	fn verify(
+		&self,
+		peer_id: sc_network_types::PeerId,
+		public_key: &Vec<u8>,
+		signature: &Vec<u8>,
+		message: &Vec<u8>,
+	) -> std::result::Result<bool, String> {
+		let public_key = libp2p::identity::PublicKey::try_decode_protobuf(&public_key)
+			.map_err(|error| error.to_string())?;
+		let peer_id: PeerId = peer_id.into();
+		let remote: libp2p::PeerId = public_key.to_peer_id();
+
+		Ok(peer_id == remote && public_key.verify(message, signature))
+	}
 }
 
 impl NetworkDHTProvider for TestNetwork {
@@ -182,8 +192,8 @@ impl NetworkDHTProvider for TestNetwork {
 }
 
 impl NetworkStateInfo for TestNetwork {
-	fn local_peer_id(&self) -> PeerId {
-		self.peer_id
+	fn local_peer_id(&self) -> sc_network_types::PeerId {
+		self.peer_id.into()
 	}
 
 	fn external_addresses(&self) -> Vec<Multiaddr> {
@@ -202,10 +212,20 @@ struct TestSigner<'a> {
 impl<'a> NetworkSigner for TestSigner<'a> {
 	fn sign_with_local_identity(
 		&self,
-		msg: impl AsRef<[u8]>,
+		msg: Vec<u8>,
 	) -> std::result::Result<Signature, SigningError> {
 		Signature::sign_message(msg, self.keypair)
 	}
+
+	fn verify(
+		&self,
+		_: sc_network_types::PeerId,
+		_: &Vec<u8>,
+		_: &Vec<u8>,
+		_: &Vec<u8>,
+	) -> std::result::Result<bool, String> {
+		unimplemented!();
+	}
 }
 
 fn build_dht_event<Signer: NetworkSigner>(
@@ -500,7 +520,6 @@ struct DhtValueFoundTester {
 	pub local_worker: Option<
 		Worker<
 			TestApi,
-			TestNetwork,
 			sp_runtime::generic::Block<
 				sp_runtime::generic::Header<u64, sp_runtime::traits::BlakeTwo256>,
 				substrate_test_runtime_client::runtime::Extrinsic,