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/src/litep2p/discovery.rs

@@ -0,0 +1,528 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! libp2p-related discovery code for litep2p backend.
+
+use crate::{
+	config::{NetworkConfiguration, ProtocolId},
+	multiaddr::Protocol,
+	peer_store::PeerStoreProvider,
+	Multiaddr,
+};
+
+use array_bytes::bytes2hex;
+use futures::{FutureExt, Stream};
+use futures_timer::Delay;
+use ip_network::IpNetwork;
+use libp2p::kad::record::Key as KademliaKey;
+use litep2p::{
+	protocol::{
+		libp2p::{
+			identify::{Config as IdentifyConfig, IdentifyEvent},
+			kademlia::{
+				Config as KademliaConfig, ConfigBuilder as KademliaConfigBuilder, KademliaEvent,
+				KademliaHandle, QueryId, Quorum, Record, RecordKey,
+			},
+			ping::{Config as PingConfig, PingEvent},
+		},
+		mdns::{Config as MdnsConfig, MdnsEvent},
+	},
+	PeerId, ProtocolName,
+};
+use parking_lot::RwLock;
+use schnellru::{ByLength, LruMap};
+
+use std::{
+	cmp,
+	collections::{HashMap, HashSet, VecDeque},
+	pin::Pin,
+	sync::Arc,
+	task::{Context, Poll},
+	time::Duration,
+};
+
+/// Logging target for the file.
+const LOG_TARGET: &str = "sub-libp2p::discovery";
+
+/// Kademlia query interval.
+const KADEMLIA_QUERY_INTERVAL: Duration = Duration::from_secs(5);
+
+/// mDNS query interval.
+const MDNS_QUERY_INTERVAL: Duration = Duration::from_secs(30);
+
+/// Minimum number of confirmations received before an address is verified.
+const MIN_ADDRESS_CONFIRMATIONS: usize = 5;
+
+/// Discovery events.
+#[derive(Debug)]
+pub enum DiscoveryEvent {
+	/// Ping RTT measured for peer.
+	Ping {
+		/// Remote peer ID.
+		peer: PeerId,
+
+		/// Ping round-trip time.
+		rtt: Duration,
+	},
+
+	/// Peer identified over `/ipfs/identify/1.0.0` protocol.
+	Identified {
+		/// Peer ID.
+		peer: PeerId,
+
+		/// Identify protocol version.
+		protocol_version: Option<String>,
+
+		/// Identify user agent version.
+		user_agent: Option<String>,
+
+		/// Observed address.
+		observed_address: Multiaddr,
+
+		/// Listen addresses.
+		listen_addresses: Vec<Multiaddr>,
+
+		/// Supported protocols.
+		supported_protocols: HashSet<ProtocolName>,
+	},
+
+	/// One or more addresses discovered.
+	Discovered {
+		/// Discovered addresses.
+		addresses: Vec<Multiaddr>,
+	},
+
+	/// Routing table has been updated.
+	RoutingTableUpdate {
+		/// Peers that were added to routing table.
+		peers: HashSet<PeerId>,
+	},
+
+	/// New external address discovered.
+	ExternalAddressDiscovered {
+		/// Discovered addresses.
+		address: Multiaddr,
+	},
+
+	/// Record was found from the DHT.
+	GetRecordSuccess {
+		/// Query ID.
+		query_id: QueryId,
+
+		/// Record.
+		record: Record,
+	},
+
+	/// Record was successfully stored on the DHT.
+	PutRecordSuccess {
+		/// Query ID.
+		query_id: QueryId,
+	},
+
+	/// Query failed.
+	QueryFailed {
+		/// Query ID.
+		query_id: QueryId,
+	},
+}
+
+/// Discovery.
+pub struct Discovery {
+	/// Ping event stream.
+	ping_event_stream: Box<dyn Stream<Item = PingEvent> + Send + Unpin>,
+
+	/// Identify event stream.
+	identify_event_stream: Box<dyn Stream<Item = IdentifyEvent> + Send + Unpin>,
+
+	/// mDNS event stream, if enabled.
+	mdns_event_stream: Option<Box<dyn Stream<Item = MdnsEvent> + Send + Unpin>>,
+
+	/// Kademlia handle.
+	kademlia_handle: KademliaHandle,
+
+	/// `Peerstore` handle.
+	_peerstore_handle: Arc<dyn PeerStoreProvider>,
+
+	/// Next Kademlia query for a random peer ID.
+	///
+	/// If `None`, there is currently a query pending.
+	next_kad_query: Option<Delay>,
+
+	/// Active `FIND_NODE` query if it exists.
+	find_node_query_id: Option<QueryId>,
+
+	/// Pending events.
+	pending_events: VecDeque<DiscoveryEvent>,
+
+	/// Allow non-global addresses in the DHT.
+	allow_non_global_addresses: bool,
+
+	/// Protocols supported by the local node.
+	local_protocols: HashSet<ProtocolName>,
+
+	/// Public addresses.
+	public_addresses: HashSet<Multiaddr>,
+
+	/// Listen addresses.
+	listen_addresses: Arc<RwLock<HashSet<Multiaddr>>>,
+
+	/// External address confirmations.
+	address_confirmations: LruMap<Multiaddr, usize>,
+
+	/// Delay to next `FIND_NODE` query.
+	duration_to_next_find_query: Duration,
+}
+
+/// Legacy (fallback) Kademlia protocol name based on `protocol_id`.
+fn legacy_kademlia_protocol_name(id: &ProtocolId) -> ProtocolName {
+	ProtocolName::from(format!("/{}/kad", id.as_ref()))
+}
+
+/// Kademlia protocol name based on `genesis_hash` and `fork_id`.
+fn kademlia_protocol_name<Hash: AsRef<[u8]>>(
+	genesis_hash: Hash,
+	fork_id: Option<&str>,
+) -> ProtocolName {
+	let genesis_hash_hex = bytes2hex("", genesis_hash.as_ref());
+	let protocol = if let Some(fork_id) = fork_id {
+		format!("/{}/{}/kad", genesis_hash_hex, fork_id)
+	} else {
+		format!("/{}/kad", genesis_hash_hex)
+	};
+
+	ProtocolName::from(protocol)
+}
+
+impl Discovery {
+	/// Create new [`Discovery`].
+	///
+	/// Enables `/ipfs/ping/1.0.0` and `/ipfs/identify/1.0.0` by default and starts
+	/// the mDNS peer discovery if it was enabled.
+	pub fn new<Hash: AsRef<[u8]> + Clone>(
+		config: &NetworkConfiguration,
+		genesis_hash: Hash,
+		fork_id: Option<&str>,
+		protocol_id: &ProtocolId,
+		known_peers: HashMap<PeerId, Vec<Multiaddr>>,
+		listen_addresses: Arc<RwLock<HashSet<Multiaddr>>>,
+		_peerstore_handle: Arc<dyn PeerStoreProvider>,
+	) -> (Self, PingConfig, IdentifyConfig, KademliaConfig, Option<MdnsConfig>) {
+		let (ping_config, ping_event_stream) = PingConfig::default();
+		let user_agent = format!("{} ({})", config.client_version, config.node_name);
+		let (identify_config, identify_event_stream) = IdentifyConfig::new(
+			"/substrate/1.0".to_string(),
+			Some(user_agent),
+			config.public_addresses.clone(),
+		);
+
+		let (mdns_config, mdns_event_stream) = match config.transport {
+			crate::config::TransportConfig::Normal { enable_mdns, .. } => match enable_mdns {
+				true => {
+					let (mdns_config, mdns_event_stream) = MdnsConfig::new(MDNS_QUERY_INTERVAL);
+					(Some(mdns_config), Some(mdns_event_stream))
+				},
+				false => (None, None),
+			},
+			_ => panic!("memory transport not supported"),
+		};
+
+		let (kademlia_config, kademlia_handle) = {
+			let protocol_names = vec![
+				kademlia_protocol_name(genesis_hash.clone(), fork_id),
+				legacy_kademlia_protocol_name(protocol_id),
+			];
+
+			KademliaConfigBuilder::new()
+				.with_known_peers(known_peers)
+				.with_protocol_names(protocol_names)
+				.build()
+		};
+
+		(
+			Self {
+				ping_event_stream,
+				identify_event_stream,
+				mdns_event_stream,
+				kademlia_handle,
+				_peerstore_handle,
+				listen_addresses,
+				find_node_query_id: None,
+				pending_events: VecDeque::new(),
+				duration_to_next_find_query: Duration::from_secs(1),
+				address_confirmations: LruMap::new(ByLength::new(8)),
+				allow_non_global_addresses: config.allow_non_globals_in_dht,
+				public_addresses: config.public_addresses.iter().cloned().collect(),
+				next_kad_query: Some(Delay::new(KADEMLIA_QUERY_INTERVAL)),
+				local_protocols: HashSet::from_iter([
+					kademlia_protocol_name(genesis_hash, fork_id),
+					legacy_kademlia_protocol_name(protocol_id),
+				]),
+			},
+			ping_config,
+			identify_config,
+			kademlia_config,
+			mdns_config,
+		)
+	}
+
+	/// Add known peer to `Kademlia`.
+	#[allow(unused)]
+	pub async fn add_known_peer(&mut self, peer: PeerId, addresses: Vec<Multiaddr>) {
+		self.kademlia_handle.add_known_peer(peer, addresses).await;
+	}
+
+	/// Add self-reported addresses to routing table if `peer` supports
+	/// at least one of the locally supported DHT protocol.
+	pub async fn add_self_reported_address(
+		&mut self,
+		peer: PeerId,
+		supported_protocols: HashSet<ProtocolName>,
+		addresses: Vec<Multiaddr>,
+	) {
+		if self.local_protocols.is_disjoint(&supported_protocols) {
+			return
+		}
+
+		let addresses = addresses
+			.into_iter()
+			.filter_map(|address| {
+				if !self.allow_non_global_addresses && !Discovery::can_add_to_dht(&address) {
+					log::trace!(
+						target: LOG_TARGET,
+						"ignoring self-reported non-global address {address} from {peer}."
+					);
+
+					return None
+				}
+
+				Some(address)
+			})
+			.collect();
+
+		log::trace!(
+			target: LOG_TARGET,
+			"add self-reported addresses for {peer:?}: {addresses:?}",
+		);
+
+		self.kademlia_handle.add_known_peer(peer, addresses).await;
+	}
+
+	/// Start Kademlia `GET_VALUE` query for `key`.
+	pub async fn get_value(&mut self, key: KademliaKey) -> QueryId {
+		self.kademlia_handle
+			.get_record(RecordKey::new(&key.to_vec()), Quorum::One)
+			.await
+	}
+
+	/// Publish value on the DHT using Kademlia `PUT_VALUE`.
+	pub async fn put_value(&mut self, key: KademliaKey, value: Vec<u8>) -> QueryId {
+		self.kademlia_handle
+			.put_record(Record::new(RecordKey::new(&key.to_vec()), value))
+			.await
+	}
+
+	/// Check if the observed address is a known address.
+	fn is_known_address(known: &Multiaddr, observed: &Multiaddr) -> bool {
+		let mut known = known.iter();
+		let mut observed = observed.iter();
+
+		loop {
+			match (known.next(), observed.next()) {
+				(None, None) => return true,
+				(None, Some(Protocol::P2p(_))) => return true,
+				(Some(Protocol::P2p(_)), None) => return true,
+				(known, observed) if known != observed => return false,
+				_ => {},
+			}
+		}
+	}
+
+	/// Can `address` be added to DHT.
+	fn can_add_to_dht(address: &Multiaddr) -> bool {
+		let ip = match address.iter().next() {
+			Some(Protocol::Ip4(ip)) => IpNetwork::from(ip),
+			Some(Protocol::Ip6(ip)) => IpNetwork::from(ip),
+			Some(Protocol::Dns(_)) | Some(Protocol::Dns4(_)) | Some(Protocol::Dns6(_)) =>
+				return true,
+			_ => return false,
+		};
+
+		ip.is_global()
+	}
+
+	/// Check if `address` can be considered a new external address.
+	fn is_new_external_address(&mut self, address: &Multiaddr) -> bool {
+		log::trace!(target: LOG_TARGET, "verify new external address: {address}");
+
+		// is the address one of our known addresses
+		if self
+			.listen_addresses
+			.read()
+			.iter()
+			.chain(self.public_addresses.iter())
+			.any(|known_address| Discovery::is_known_address(&known_address, &address))
+		{
+			return true
+		}
+
+		match self.address_confirmations.get(address) {
+			Some(confirmations) => {
+				*confirmations += 1usize;
+
+				if *confirmations >= MIN_ADDRESS_CONFIRMATIONS {
+					return true
+				}
+			},
+			None => {
+				self.address_confirmations.insert(address.clone(), 1usize);
+			},
+		}
+
+		false
+	}
+}
+
+impl Stream for Discovery {
+	type Item = DiscoveryEvent;
+
+	fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+		let this = Pin::into_inner(self);
+
+		if let Some(event) = this.pending_events.pop_front() {
+			return Poll::Ready(Some(event))
+		}
+
+		if let Some(mut delay) = this.next_kad_query.take() {
+			match delay.poll_unpin(cx) {
+				Poll::Pending => {
+					this.next_kad_query = Some(delay);
+				},
+				Poll::Ready(()) => {
+					let peer = PeerId::random();
+
+					log::trace!(target: LOG_TARGET, "start next kademlia query for {peer:?}");
+
+					match this.kademlia_handle.try_find_node(peer) {
+						Ok(query_id) => {
+							this.find_node_query_id = Some(query_id);
+						},
+						Err(()) => {
+							this.duration_to_next_find_query = cmp::min(
+								this.duration_to_next_find_query * 2,
+								Duration::from_secs(60),
+							);
+							this.next_kad_query =
+								Some(Delay::new(this.duration_to_next_find_query));
+						},
+					}
+				},
+			}
+		}
+
+		match Pin::new(&mut this.kademlia_handle).poll_next(cx) {
+			Poll::Pending => {},
+			Poll::Ready(None) => return Poll::Ready(None),
+			Poll::Ready(Some(KademliaEvent::FindNodeSuccess { peers, .. })) => {
+				// the addresses are already inserted into the DHT and in `TransportManager` so
+				// there is no need to add them again. The found peers must be registered to
+				// `Peerstore` so other protocols are aware of them through `Peerset`.
+				log::trace!(target: LOG_TARGET, "dht random walk yielded {} peers", peers.len());
+
+				this.next_kad_query = Some(Delay::new(KADEMLIA_QUERY_INTERVAL));
+
+				return Poll::Ready(Some(DiscoveryEvent::RoutingTableUpdate {
+					peers: peers.into_iter().map(|(peer, _)| peer).collect(),
+				}))
+			},
+			Poll::Ready(Some(KademliaEvent::RoutingTableUpdate { peers })) => {
+				log::trace!(target: LOG_TARGET, "routing table update, discovered {} peers", peers.len());
+
+				return Poll::Ready(Some(DiscoveryEvent::RoutingTableUpdate {
+					peers: peers.into_iter().collect(),
+				}))
+			},
+			Poll::Ready(Some(KademliaEvent::GetRecordSuccess { query_id, record })) => {
+				log::trace!(
+					target: LOG_TARGET,
+					"`GET_RECORD` succeeded for {query_id:?}: {record:?}",
+				);
+
+				return Poll::Ready(Some(DiscoveryEvent::GetRecordSuccess { query_id, record }));
+			},
+			Poll::Ready(Some(KademliaEvent::PutRecordSucess { query_id, key: _ })) =>
+				return Poll::Ready(Some(DiscoveryEvent::PutRecordSuccess { query_id })),
+			Poll::Ready(Some(KademliaEvent::QueryFailed { query_id })) => {
+				match this.find_node_query_id == Some(query_id) {
+					true => {
+						this.find_node_query_id = None;
+						this.duration_to_next_find_query =
+							cmp::min(this.duration_to_next_find_query * 2, Duration::from_secs(60));
+						this.next_kad_query = Some(Delay::new(this.duration_to_next_find_query));
+					},
+					false => return Poll::Ready(Some(DiscoveryEvent::QueryFailed { query_id })),
+				}
+			},
+		}
+
+		match Pin::new(&mut this.identify_event_stream).poll_next(cx) {
+			Poll::Pending => {},
+			Poll::Ready(None) => return Poll::Ready(None),
+			Poll::Ready(Some(IdentifyEvent::PeerIdentified {
+				peer,
+				protocol_version,
+				user_agent,
+				listen_addresses,
+				supported_protocols,
+				observed_address,
+			})) => {
+				if this.is_new_external_address(&observed_address) {
+					this.pending_events.push_back(DiscoveryEvent::ExternalAddressDiscovered {
+						address: observed_address.clone(),
+					});
+				}
+
+				return Poll::Ready(Some(DiscoveryEvent::Identified {
+					peer,
+					protocol_version,
+					user_agent,
+					listen_addresses,
+					observed_address,
+					supported_protocols,
+				}));
+			},
+		}
+
+		match Pin::new(&mut this.ping_event_stream).poll_next(cx) {
+			Poll::Pending => {},
+			Poll::Ready(None) => return Poll::Ready(None),
+			Poll::Ready(Some(PingEvent::Ping { peer, ping })) =>
+				return Poll::Ready(Some(DiscoveryEvent::Ping { peer, rtt: ping })),
+		}
+
+		if let Some(ref mut mdns_event_stream) = &mut this.mdns_event_stream {
+			match Pin::new(mdns_event_stream).poll_next(cx) {
+				Poll::Pending => {},
+				Poll::Ready(None) => return Poll::Ready(None),
+				Poll::Ready(Some(MdnsEvent::Discovered(addresses))) =>
+					return Poll::Ready(Some(DiscoveryEvent::Discovered { addresses })),
+			}
+		}
+
+		Poll::Pending
+	}
+}

substrate/client/network/src/litep2p/mod.rs

@@ -0,0 +1,989 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! `NetworkBackend` implementation for `litep2p`.
+
+use crate::{
+	config::{
+		FullNetworkConfiguration, IncomingRequest, NodeKeyConfig, NotificationHandshake, Params,
+		SetConfig, TransportConfig,
+	},
+	error::Error,
+	event::{DhtEvent, Event},
+	litep2p::{
+		discovery::{Discovery, DiscoveryEvent},
+		peerstore::Peerstore,
+		service::{Litep2pNetworkService, NetworkServiceCommand},
+		shim::{
+			bitswap::BitswapServer,
+			notification::{
+				config::{NotificationProtocolConfig, ProtocolControlHandle},
+				peerset::PeersetCommand,
+			},
+			request_response::{RequestResponseConfig, RequestResponseProtocol},
+		},
+	},
+	multiaddr::{Multiaddr, Protocol},
+	peer_store::PeerStoreProvider,
+	protocol,
+	service::{
+		metrics::{register_without_sources, MetricSources, Metrics, NotificationMetrics},
+		out_events,
+		traits::{BandwidthSink, NetworkBackend, NetworkService},
+	},
+	NetworkStatus, NotificationService, ProtocolName,
+};
+
+use codec::Encode;
+use futures::StreamExt;
+use libp2p::kad::RecordKey;
+use litep2p::{
+	config::ConfigBuilder,
+	crypto::ed25519::{Keypair, SecretKey},
+	executor::Executor,
+	protocol::{
+		libp2p::{bitswap::Config as BitswapConfig, kademlia::QueryId},
+		request_response::ConfigBuilder as RequestResponseConfigBuilder,
+	},
+	transport::{
+		tcp::config::Config as TcpTransportConfig,
+		websocket::config::Config as WebSocketTransportConfig, Endpoint,
+	},
+	types::ConnectionId,
+	Error as Litep2pError, Litep2p, Litep2pEvent, ProtocolName as Litep2pProtocolName,
+};
+use parking_lot::RwLock;
+use prometheus_endpoint::Registry;
+
+use sc_client_api::BlockBackend;
+use sc_network_common::{role::Roles, ExHashT};
+use sc_network_types::PeerId;
+use sc_utils::mpsc::{tracing_unbounded, TracingUnboundedReceiver};
+use sp_runtime::traits::Block as BlockT;
+
+use std::{
+	cmp,
+	collections::{hash_map::Entry, HashMap, HashSet},
+	fs,
+	future::Future,
+	io, iter,
+	pin::Pin,
+	sync::{
+		atomic::{AtomicUsize, Ordering},
+		Arc,
+	},
+	time::{Duration, Instant},
+};
+
+mod discovery;
+mod peerstore;
+mod service;
+mod shim;
+
+/// Litep2p bandwidth sink.
+struct Litep2pBandwidthSink {
+	sink: litep2p::BandwidthSink,
+}
+
+impl BandwidthSink for Litep2pBandwidthSink {
+	fn total_inbound(&self) -> u64 {
+		self.sink.inbound() as u64
+	}
+
+	fn total_outbound(&self) -> u64 {
+		self.sink.outbound() as u64
+	}
+}
+
+/// Litep2p task executor.
+struct Litep2pExecutor {
+	/// Executor.
+	executor: Box<dyn Fn(Pin<Box<dyn Future<Output = ()> + Send>>) + Send + Sync>,
+}
+
+impl Executor for Litep2pExecutor {
+	fn run(&self, future: Pin<Box<dyn Future<Output = ()> + Send>>) {
+		(self.executor)(future)
+	}
+
+	fn run_with_name(&self, _: &'static str, future: Pin<Box<dyn Future<Output = ()> + Send>>) {
+		(self.executor)(future)
+	}
+}
+
+/// Logging target for the file.
+const LOG_TARGET: &str = "sub-libp2p";
+
+/// Peer context.
+struct ConnectionContext {
+	/// Peer endpoints.
+	endpoints: HashMap<ConnectionId, Endpoint>,
+
+	/// Number of active connections.
+	num_connections: usize,
+}
+
+/// Networking backend for `litep2p`.
+pub struct Litep2pNetworkBackend {
+	/// Main `litep2p` object.
+	litep2p: Litep2p,
+
+	/// `NetworkService` implementation for `Litep2pNetworkBackend`.
+	network_service: Arc<dyn NetworkService>,
+
+	/// RX channel for receiving commands from `Litep2pNetworkService`.
+	cmd_rx: TracingUnboundedReceiver<NetworkServiceCommand>,
+
+	/// `Peerset` handles to notification protocols.
+	peerset_handles: HashMap<ProtocolName, ProtocolControlHandle>,
+
+	/// Pending `GET_VALUE` queries.
+	pending_get_values: HashMap<QueryId, (RecordKey, Instant)>,
+
+	/// Pending `PUT_VALUE` queries.
+	pending_put_values: HashMap<QueryId, (RecordKey, Instant)>,
+
+	/// Discovery.
+	discovery: Discovery,
+
+	/// Number of connected peers.
+	num_connected: Arc<AtomicUsize>,
+
+	/// Connected peers.
+	peers: HashMap<litep2p::PeerId, ConnectionContext>,
+
+	/// Peerstore.
+	peerstore_handle: Arc<dyn PeerStoreProvider>,
+
+	/// Block announce protocol name.
+	block_announce_protocol: ProtocolName,
+
+	/// Sender for DHT events.
+	event_streams: out_events::OutChannels,
+
+	/// Prometheus metrics.
+	metrics: Option<Metrics>,
+
+	/// External addresses.
+	external_addresses: Arc<RwLock<HashSet<Multiaddr>>>,
+}
+
+impl Litep2pNetworkBackend {
+	/// From an iterator of multiaddress(es), parse and group all addresses of peers
+	/// so that litep2p can consume the information easily.
+	fn parse_addresses(
+		addresses: impl Iterator<Item = Multiaddr>,
+	) -> HashMap<PeerId, Vec<Multiaddr>> {
+		addresses
+			.into_iter()
+			.filter_map(|address| match address.iter().next() {
+				Some(
+					Protocol::Dns(_) |
+					Protocol::Dns4(_) |
+					Protocol::Dns6(_) |
+					Protocol::Ip6(_) |
+					Protocol::Ip4(_),
+				) => match address.iter().find(|protocol| std::matches!(protocol, Protocol::P2p(_)))
+				{
+					Some(Protocol::P2p(multihash)) => PeerId::from_multihash(multihash)
+						.map_or(None, |peer| Some((peer, Some(address)))),
+					_ => None,
+				},
+				Some(Protocol::P2p(multihash)) =>
+					PeerId::from_multihash(multihash).map_or(None, |peer| Some((peer, None))),
+				_ => None,
+			})
+			.fold(HashMap::new(), |mut acc, (peer, maybe_address)| {
+				let entry = acc.entry(peer).or_default();
+				maybe_address.map(|address| entry.push(address));
+
+				acc
+			})
+	}
+
+	/// Add new known addresses to `litep2p` and return the parsed peer IDs.
+	fn add_addresses(&mut self, peers: impl Iterator<Item = Multiaddr>) -> HashSet<PeerId> {
+		Self::parse_addresses(peers.into_iter())
+			.into_iter()
+			.filter_map(|(peer, addresses)| {
+				// `peers` contained multiaddress in the form `/p2p/<peer ID>`
+				if addresses.is_empty() {
+					return Some(peer)
+				}
+
+				if self.litep2p.add_known_address(peer.into(), addresses.clone().into_iter()) == 0 {
+					log::warn!(
+						target: LOG_TARGET,
+						"couldn't add any addresses for {peer:?} and it won't be added as reserved peer",
+					);
+					return None
+				}
+
+				self.peerstore_handle.add_known_peer(peer);
+				Some(peer)
+			})
+			.collect()
+	}
+}
+
+impl Litep2pNetworkBackend {
+	/// Get `litep2p` keypair from `NodeKeyConfig`.
+	fn get_keypair(node_key: &NodeKeyConfig) -> Result<(Keypair, litep2p::PeerId), Error> {
+		let secret = libp2p::identity::Keypair::try_into_ed25519(node_key.clone().into_keypair()?)
+			.map_err(|error| {
+				log::error!(target: LOG_TARGET, "failed to convert to ed25519: {error:?}");
+				Error::Io(io::ErrorKind::InvalidInput.into())
+			})?
+			.secret();
+
+		let mut secret = secret.as_ref().iter().cloned().collect::<Vec<_>>();
+		let secret = SecretKey::from_bytes(&mut secret)
+			.map_err(|_| Error::Io(io::ErrorKind::InvalidInput.into()))?;
+		let local_identity = Keypair::from(secret);
+		let local_public = local_identity.public();
+		let local_peer_id = local_public.to_peer_id();
+
+		Ok((local_identity, local_peer_id))
+	}
+
+	/// Configure transport protocols for `Litep2pNetworkBackend`.
+	fn configure_transport<B: BlockT + 'static, H: ExHashT>(
+		config: &FullNetworkConfiguration<B, H, Self>,
+	) -> ConfigBuilder {
+		let _ = match config.network_config.transport {
+			TransportConfig::MemoryOnly => panic!("memory transport not supported"),
+			TransportConfig::Normal { .. } => false,
+		};
+		let config_builder = ConfigBuilder::new();
+
+		// The yamux buffer size limit is configured to be equal to the maximum frame size
+		// of all protocols. 10 bytes are added to each limit for the length prefix that
+		// is not included in the upper layer protocols limit but is still present in the
+		// yamux buffer. These 10 bytes correspond to the maximum size required to encode
+		// a variable-length-encoding 64bits number. In other words, we make the
+		// assumption that no notification larger than 2^64 will ever be sent.
+		let yamux_maximum_buffer_size = {
+			let requests_max = config
+				.request_response_protocols
+				.iter()
+				.map(|cfg| usize::try_from(cfg.max_request_size).unwrap_or(usize::MAX));
+			let responses_max = config
+				.request_response_protocols
+				.iter()
+				.map(|cfg| usize::try_from(cfg.max_response_size).unwrap_or(usize::MAX));
+			let notifs_max = config
+				.notification_protocols
+				.iter()
+				.map(|cfg| usize::try_from(cfg.max_notification_size()).unwrap_or(usize::MAX));
+
+			// A "default" max is added to cover all the other protocols: ping, identify,
+			// kademlia, block announces, and transactions.
+			let default_max = cmp::max(
+				1024 * 1024,
+				usize::try_from(protocol::BLOCK_ANNOUNCES_TRANSACTIONS_SUBSTREAM_SIZE)
+					.unwrap_or(usize::MAX),
+			);
+
+			iter::once(default_max)
+				.chain(requests_max)
+				.chain(responses_max)
+				.chain(notifs_max)
+				.max()
+				.expect("iterator known to always yield at least one element; qed")
+				.saturating_add(10)
+		};
+
+		let yamux_config = {
+			let mut yamux_config = litep2p::yamux::Config::default();
+			// Enable proper flow-control: window updates are only sent when
+			// buffered data has been consumed.
+			yamux_config.set_window_update_mode(litep2p::yamux::WindowUpdateMode::OnRead);
+			yamux_config.set_max_buffer_size(yamux_maximum_buffer_size);
+
+			if let Some(yamux_window_size) = config.network_config.yamux_window_size {
+				yamux_config.set_receive_window(yamux_window_size);
+			}
+
+			yamux_config
+		};
+
+		let (tcp, websocket): (Vec<Option<_>>, Vec<Option<_>>) = config
+			.network_config
+			.listen_addresses
+			.iter()
+			.filter_map(|address| {
+				let mut iter = address.iter();
+
+				match iter.next() {
+					Some(Protocol::Ip4(_) | Protocol::Ip6(_)) => {},
+					protocol => {
+						log::error!(
+							target: LOG_TARGET,
+							"unknown protocol {protocol:?}, ignoring {address:?}",
+						);
+
+						return None
+					},
+				}
+
+				match iter.next() {
+					Some(Protocol::Tcp(_)) => match iter.next() {
+						Some(Protocol::Ws(_) | Protocol::Wss(_)) =>
+							Some((None, Some(address.clone()))),
+						Some(Protocol::P2p(_)) | None => Some((Some(address.clone()), None)),
+						protocol => {
+							log::error!(
+								target: LOG_TARGET,
+								"unknown protocol {protocol:?}, ignoring {address:?}",
+							);
+							None
+						},
+					},
+					protocol => {
+						log::error!(
+							target: LOG_TARGET,
+							"unknown protocol {protocol:?}, ignoring {address:?}",
+						);
+						None
+					},
+				}
+			})
+			.unzip();
+
+		config_builder
+			.with_websocket(WebSocketTransportConfig {
+				listen_addresses: websocket.into_iter().flatten().collect(),
+				yamux_config: yamux_config.clone(),
+				..Default::default()
+			})
+			.with_tcp(TcpTransportConfig {
+				listen_addresses: tcp.into_iter().flatten().collect(),
+				yamux_config,
+				..Default::default()
+			})
+	}
+}
+
+#[async_trait::async_trait]
+impl<B: BlockT + 'static, H: ExHashT> NetworkBackend<B, H> for Litep2pNetworkBackend {
+	type NotificationProtocolConfig = NotificationProtocolConfig;
+	type RequestResponseProtocolConfig = RequestResponseConfig;
+	type NetworkService<Block, Hash> = Arc<Litep2pNetworkService>;
+	type PeerStore = Peerstore;
+	type BitswapConfig = BitswapConfig;
+
+	fn new(mut params: Params<B, H, Self>) -> Result<Self, Error>
+	where
+		Self: Sized,
+	{
+		let (keypair, local_peer_id) =
+			Self::get_keypair(&params.network_config.network_config.node_key)?;
+		let (cmd_tx, cmd_rx) = tracing_unbounded("mpsc_network_worker", 100_000);
+
+		params.network_config.network_config.boot_nodes = params
+			.network_config
+			.network_config
+			.boot_nodes
+			.into_iter()
+			.filter(|boot_node| boot_node.peer_id != local_peer_id.into())
+			.collect();
+		params.network_config.network_config.default_peers_set.reserved_nodes = params
+			.network_config
+			.network_config
+			.default_peers_set
+			.reserved_nodes
+			.into_iter()
+			.filter(|reserved_node| {
+				if reserved_node.peer_id == local_peer_id.into() {
+					log::warn!(
+						target: LOG_TARGET,
+						"Local peer ID used in reserved node, ignoring: {reserved_node}",
+					);
+					false
+				} else {
+					true
+				}
+			})
+			.collect();
+
+		if let Some(path) = &params.network_config.network_config.net_config_path {
+			fs::create_dir_all(path)?;
+		}
+
+		log::info!(target: LOG_TARGET, "Local node identity is: {local_peer_id}");
+		log::info!(target: LOG_TARGET, "Running litep2p network backend");
+
+		params.network_config.sanity_check_addresses()?;
+		params.network_config.sanity_check_bootnodes()?;
+
+		let mut config_builder =
+			Self::configure_transport(&params.network_config).with_keypair(keypair.clone());
+		let known_addresses = params.network_config.known_addresses();
+		let peer_store_handle = params.network_config.peer_store_handle();
+		let executor = Arc::new(Litep2pExecutor { executor: params.executor });
+
+		let FullNetworkConfiguration {
+			notification_protocols,
+			request_response_protocols,
+			network_config,
+			..
+		} = params.network_config;
+
+		// initialize notification protocols
+		//
+		// pass the protocol configuration to `Litep2pConfigBuilder` and save the TX channel
+		// to the protocol's `Peerset` together with the protocol name to allow other subsystems
+		// of Polkadot SDK to control connectivity of the notification protocol
+		let block_announce_protocol = params.block_announce_config.protocol_name().clone();
+		let mut notif_protocols = HashMap::from_iter([(
+			params.block_announce_config.protocol_name().clone(),
+			params.block_announce_config.handle,
+		)]);
+
+		// handshake for all but the syncing protocol is set to node role
+		config_builder = notification_protocols
+			.into_iter()
+			.fold(config_builder, |config_builder, mut config| {
+				config.config.set_handshake(Roles::from(&params.role).encode());
+				notif_protocols.insert(config.protocol_name, config.handle);
+
+				config_builder.with_notification_protocol(config.config)
+			})
+			.with_notification_protocol(params.block_announce_config.config);
+
+		// initialize request-response protocols
+		let metrics = match &params.metrics_registry {
+			Some(registry) => Some(register_without_sources(registry)?),
+			None => None,
+		};
+
+		// create channels that are used to send request before initializing protocols so the
+		// senders can be passed onto all request-response protocols
+		//
+		// all protocols must have each others' senders so they can send the fallback request in
+		// case the main protocol is not supported by the remote peer and user specified a fallback
+		let (mut request_response_receivers, request_response_senders): (
+			HashMap<_, _>,
+			HashMap<_, _>,
+		) = request_response_protocols
+			.iter()
+			.map(|config| {
+				let (tx, rx) = tracing_unbounded("outbound-requests", 10_000);
+				((config.protocol_name.clone(), rx), (config.protocol_name.clone(), tx))
+			})
+			.unzip();
+
+		config_builder = request_response_protocols.into_iter().fold(
+			config_builder,
+			|config_builder, config| {
+				let (protocol_config, handle) = RequestResponseConfigBuilder::new(
+					Litep2pProtocolName::from(config.protocol_name.clone()),
+				)
+				.with_max_size(cmp::max(config.max_request_size, config.max_response_size) as usize)
+				.with_fallback_names(config.fallback_names.into_iter().map(From::from).collect())
+				.with_timeout(config.request_timeout)
+				.build();
+
+				let protocol = RequestResponseProtocol::new(
+					config.protocol_name.clone(),
+					handle,
+					Arc::clone(&peer_store_handle),
+					config.inbound_queue,
+					request_response_receivers
+						.remove(&config.protocol_name)
+						.expect("receiver exists as it was just added and there are no duplicate protocols; qed"),
+					request_response_senders.clone(),
+					metrics.clone(),
+				);
+
+				executor.run(Box::pin(async move {
+					protocol.run().await;
+				}));
+
+				config_builder.with_request_response_protocol(protocol_config)
+			},
+		);
+
+		// collect known addresses
+		let known_addresses: HashMap<litep2p::PeerId, Vec<Multiaddr>> =
+			known_addresses.into_iter().fold(HashMap::new(), |mut acc, (peer, address)| {
+				let address = match address.iter().last() {
+					Some(Protocol::Ws(_) | Protocol::Wss(_) | Protocol::Tcp(_)) =>
+						address.with(Protocol::P2p(peer.into())),
+					Some(Protocol::P2p(_)) => address,
+					_ => return acc,
+				};
+
+				acc.entry(peer.into()).or_default().push(address);
+				peer_store_handle.add_known_peer(peer);
+
+				acc
+			});
+
+		// enable ipfs ping, identify and kademlia, and potentially mdns if user enabled it
+		let listen_addresses = Arc::new(Default::default());
+		let (discovery, ping_config, identify_config, kademlia_config, maybe_mdns_config) =
+			Discovery::new(
+				&network_config,
+				params.genesis_hash,
+				params.fork_id.as_deref(),
+				&params.protocol_id,
+				known_addresses.clone(),
+				Arc::clone(&listen_addresses),
+				Arc::clone(&peer_store_handle),
+			);
+
+		config_builder = config_builder
+			.with_known_addresses(known_addresses.clone().into_iter())
+			.with_libp2p_ping(ping_config)
+			.with_libp2p_identify(identify_config)
+			.with_libp2p_kademlia(kademlia_config)
+			.with_executor(executor);
+
+		if let Some(config) = maybe_mdns_config {
+			config_builder = config_builder.with_mdns(config);
+		}
+
+		if let Some(config) = params.bitswap_config {
+			config_builder = config_builder.with_libp2p_bitswap(config);
+		}
+
+		let litep2p =
+			Litep2p::new(config_builder.build()).map_err(|error| Error::Litep2p(error))?;
+
+		let external_addresses: Arc<RwLock<HashSet<Multiaddr>>> = Arc::new(RwLock::new(
+			HashSet::from_iter(network_config.public_addresses.iter().cloned()),
+		));
+		litep2p.listen_addresses().for_each(|address| {
+			log::debug!(target: LOG_TARGET, "listening on: {address}");
+
+			listen_addresses.write().insert(address.clone());
+		});
+
+		let network_service = Arc::new(Litep2pNetworkService::new(
+			local_peer_id,
+			keypair.clone(),
+			cmd_tx,
+			Arc::clone(&peer_store_handle),
+			notif_protocols.clone(),
+			block_announce_protocol.clone(),
+			request_response_senders,
+			Arc::clone(&listen_addresses),
+			Arc::clone(&external_addresses),
+		));
+
+		// register rest of the metrics now that `Litep2p` has been created
+		let num_connected = Arc::new(Default::default());
+		let bandwidth: Arc<dyn BandwidthSink> =
+			Arc::new(Litep2pBandwidthSink { sink: litep2p.bandwidth_sink() });
+
+		if let Some(registry) = &params.metrics_registry {
+			MetricSources::register(registry, bandwidth, Arc::clone(&num_connected))?;
+		}
+
+		Ok(Self {
+			network_service,
+			cmd_rx,
+			metrics,
+			peerset_handles: notif_protocols,
+			num_connected,
+			discovery,
+			pending_put_values: HashMap::new(),
+			pending_get_values: HashMap::new(),
+			peerstore_handle: peer_store_handle,
+			block_announce_protocol,
+			event_streams: out_events::OutChannels::new(None)?,
+			peers: HashMap::new(),
+			litep2p,
+			external_addresses,
+		})
+	}
+
+	fn network_service(&self) -> Arc<dyn NetworkService> {
+		Arc::clone(&self.network_service)
+	}
+
+	fn peer_store(bootnodes: Vec<sc_network_types::PeerId>) -> Self::PeerStore {
+		Peerstore::new(bootnodes)
+	}
+
+	fn register_notification_metrics(registry: Option<&Registry>) -> NotificationMetrics {
+		NotificationMetrics::new(registry)
+	}
+
+	/// Create Bitswap server.
+	fn bitswap_server(
+		client: Arc<dyn BlockBackend<B> + Send + Sync>,
+	) -> (Pin<Box<dyn Future<Output = ()> + Send>>, Self::BitswapConfig) {
+		BitswapServer::new(client)
+	}
+
+	/// Create notification protocol configuration for `protocol`.
+	fn notification_config(
+		protocol_name: ProtocolName,
+		fallback_names: Vec<ProtocolName>,
+		max_notification_size: u64,
+		handshake: Option<NotificationHandshake>,
+		set_config: SetConfig,
+		metrics: NotificationMetrics,
+		peerstore_handle: Arc<dyn PeerStoreProvider>,
+	) -> (Self::NotificationProtocolConfig, Box<dyn NotificationService>) {
+		Self::NotificationProtocolConfig::new(
+			protocol_name,
+			fallback_names,
+			max_notification_size as usize,
+			handshake,
+			set_config,
+			metrics,
+			peerstore_handle,
+		)
+	}
+
+	/// Create request-response protocol configuration.
+	fn request_response_config(
+		protocol_name: ProtocolName,
+		fallback_names: Vec<ProtocolName>,
+		max_request_size: u64,
+		max_response_size: u64,
+		request_timeout: Duration,
+		inbound_queue: Option<async_channel::Sender<IncomingRequest>>,
+	) -> Self::RequestResponseProtocolConfig {
+		Self::RequestResponseProtocolConfig::new(
+			protocol_name,
+			fallback_names,
+			max_request_size,
+			max_response_size,
+			request_timeout,
+			inbound_queue,
+		)
+	}
+
+	/// Start [`Litep2pNetworkBackend`] event loop.
+	async fn run(mut self) {
+		log::debug!(target: LOG_TARGET, "starting litep2p network backend");
+
+		loop {
+			let num_connected_peers = self
+				.peerset_handles
+				.get(&self.block_announce_protocol)
+				.map_or(0usize, |handle| handle.connected_peers.load(Ordering::Relaxed));
+			self.num_connected.store(num_connected_peers, Ordering::Relaxed);
+
+			tokio::select! {
+				command = self.cmd_rx.next() => match command {
+					None => return,
+					Some(command) => match command {
+						NetworkServiceCommand::GetValue{ key } => {
+							let query_id = self.discovery.get_value(key.clone()).await;
+							self.pending_get_values.insert(query_id, (key, Instant::now()));
+						}
+						NetworkServiceCommand::PutValue { key, value } => {
+							let query_id = self.discovery.put_value(key.clone(), value).await;
+							self.pending_put_values.insert(query_id, (key, Instant::now()));
+						}
+						NetworkServiceCommand::EventStream { tx } => {
+							self.event_streams.push(tx);
+						}
+						NetworkServiceCommand::Status { tx } => {
+							let _ = tx.send(NetworkStatus {
+								num_connected_peers: self
+									.peerset_handles
+									.get(&self.block_announce_protocol)
+									.map_or(0usize, |handle| handle.connected_peers.load(Ordering::Relaxed)),
+								total_bytes_inbound: self.litep2p.bandwidth_sink().inbound() as u64,
+								total_bytes_outbound: self.litep2p.bandwidth_sink().outbound() as u64,
+							});
+						}
+						NetworkServiceCommand::AddPeersToReservedSet {
+							protocol,
+							peers,
+						} => {
+							let peers = self.add_addresses(peers.into_iter());
+
+							match self.peerset_handles.get(&protocol) {
+								Some(handle) => {
+									let _ = handle.tx.unbounded_send(PeersetCommand::AddReservedPeers { peers });
+								}
+								None => log::warn!(target: LOG_TARGET, "protocol {protocol} doens't exist"),
+							};
+						}
+						NetworkServiceCommand::AddKnownAddress { peer, mut address } => {
+							if !address.iter().any(|protocol| std::matches!(protocol, Protocol::P2p(_))) {
+								address.push(Protocol::P2p(peer.into()));
+							}
+
+							if self.litep2p.add_known_address(peer.into(), iter::once(address.clone())) == 0usize {
+								log::warn!(
+									target: LOG_TARGET,
+									"couldn't add known address ({address}) for {peer:?}, unsupported transport"
+								);
+							}
+						},
+						NetworkServiceCommand::SetReservedPeers { protocol, peers } => {
+							let peers = self.add_addresses(peers.into_iter());
+
+							match self.peerset_handles.get(&protocol) {
+								Some(handle) => {
+									let _ = handle.tx.unbounded_send(PeersetCommand::SetReservedPeers { peers });
+								}
+								None => log::warn!(target: LOG_TARGET, "protocol {protocol} doens't exist"),
+							}
+
+						},
+						NetworkServiceCommand::DisconnectPeer {
+							protocol,
+							peer,
+						} => {
+							let Some(handle) = self.peerset_handles.get(&protocol) else {
+								log::warn!(target: LOG_TARGET, "protocol {protocol} doens't exist");
+								continue
+							};
+
+							let _ = handle.tx.unbounded_send(PeersetCommand::DisconnectPeer { peer });
+						}
+						NetworkServiceCommand::SetReservedOnly {
+							protocol,
+							reserved_only,
+						} => {
+							let Some(handle) = self.peerset_handles.get(&protocol) else {
+								log::warn!(target: LOG_TARGET, "protocol {protocol} doens't exist");
+								continue
+							};
+
+							let _ = handle.tx.unbounded_send(PeersetCommand::SetReservedOnly { reserved_only });
+						}
+						NetworkServiceCommand::RemoveReservedPeers {
+							protocol,
+							peers,
+						} => {
+							let Some(handle) = self.peerset_handles.get(&protocol) else {
+								log::warn!(target: LOG_TARGET, "protocol {protocol} doens't exist");
+								continue
+							};
+
+							let _ = handle.tx.unbounded_send(PeersetCommand::RemoveReservedPeers { peers });
+						}
+					}
+				},
+				event = self.discovery.next() => match event {
+					None => return,
+					Some(DiscoveryEvent::Discovered { addresses }) => {
+						// if at least one address was added for the peer, report the peer to `Peerstore`
+						for (peer, addresses) in Litep2pNetworkBackend::parse_addresses(addresses.into_iter()) {
+							if self.litep2p.add_known_address(peer.into(), addresses.clone().into_iter()) > 0 {
+								self.peerstore_handle.add_known_peer(peer);
+							}
+						}
+					}
+					Some(DiscoveryEvent::RoutingTableUpdate { peers }) => {
+						for peer in peers {
+							self.peerstore_handle.add_known_peer(peer.into());
+						}
+					}
+					Some(DiscoveryEvent::GetRecordSuccess { query_id, record }) => {
+						match self.pending_get_values.remove(&query_id) {
+							None => log::warn!(
+								target: LOG_TARGET,
+								"`GET_VALUE` succeeded for a non-existent query",
+							),
+							Some((_key, started)) => {
+								log::trace!(
+									target: LOG_TARGET,
+									"`GET_VALUE` for {:?} ({query_id:?}) succeeded",
+									record.key,
+								);
+
+								self.event_streams.send(Event::Dht(
+									DhtEvent::ValueFound(vec![
+										(libp2p::kad::RecordKey::new(&record.key), record.value)
+									])
+								));
+
+								if let Some(ref metrics) = self.metrics {
+									metrics
+										.kademlia_query_duration
+										.with_label_values(&["value-get"])
+										.observe(started.elapsed().as_secs_f64());
+								}
+							}
+						}
+					}
+					Some(DiscoveryEvent::PutRecordSuccess { query_id }) => {
+						match self.pending_put_values.remove(&query_id) {
+							None => log::warn!(
+								target: LOG_TARGET,
+								"`PUT_VALUE` succeeded for a non-existent query",
+							),
+							Some((key, started)) => {
+								log::trace!(
+									target: LOG_TARGET,
+									"`PUT_VALUE` for {key:?} ({query_id:?}) succeeded",
+								);
+
+								if let Some(ref metrics) = self.metrics {
+									metrics
+										.kademlia_query_duration
+										.with_label_values(&["value-put"])
+										.observe(started.elapsed().as_secs_f64());
+								}
+							}
+						}
+					}
+					Some(DiscoveryEvent::QueryFailed { query_id }) => {
+						match self.pending_get_values.remove(&query_id) {
+							None => match self.pending_put_values.remove(&query_id) {
+								None => log::warn!(
+									target: LOG_TARGET,
+									"non-existent query failed ({query_id:?})",
+								),
+								Some((key, started)) => {
+									log::debug!(
+										target: LOG_TARGET,
+										"`PUT_VALUE` ({query_id:?}) failed for key {key:?}",
+									);
+
+									self.event_streams.send(Event::Dht(
+										DhtEvent::ValuePutFailed(libp2p::kad::RecordKey::new(&key))
+									));
+
+									if let Some(ref metrics) = self.metrics {
+										metrics
+											.kademlia_query_duration
+											.with_label_values(&["value-put-failed"])
+											.observe(started.elapsed().as_secs_f64());
+									}
+								}
+							}
+							Some((key, started)) => {
+								log::debug!(
+									target: LOG_TARGET,
+									"`GET_VALUE` ({query_id:?}) failed for key {key:?}",
+								);
+
+								self.event_streams.send(Event::Dht(
+									DhtEvent::ValueNotFound(libp2p::kad::RecordKey::new(&key))
+								));
+
+								if let Some(ref metrics) = self.metrics {
+									metrics
+										.kademlia_query_duration
+										.with_label_values(&["value-get-failed"])
+										.observe(started.elapsed().as_secs_f64());
+								}
+							}
+						}
+					}
+					Some(DiscoveryEvent::Identified { peer, listen_addresses, supported_protocols, .. }) => {
+						self.discovery.add_self_reported_address(peer, supported_protocols, listen_addresses).await;
+					}
+					Some(DiscoveryEvent::ExternalAddressDiscovered { address }) => {
+						let mut addresses = self.external_addresses.write();
+
+						if addresses.insert(address.clone()) {
+							log::info!(target: LOG_TARGET, "discovered new external address for our node: {address}");
+						}
+					}
+					Some(DiscoveryEvent::Ping { peer, rtt }) => {
+						log::trace!(
+							target: LOG_TARGET,
+							"ping time with {peer:?}: {rtt:?}",
+						);
+					}
+				},
+				event = self.litep2p.next_event() => match event {
+					Some(Litep2pEvent::ConnectionEstablished { peer, endpoint }) => {
+						let Some(metrics) = &self.metrics else {
+							continue;
+						};
+
+						let direction = match endpoint {
+							Endpoint::Dialer { .. } => "out",
+							Endpoint::Listener { .. } => "in",
+						};
+						metrics.connections_opened_total.with_label_values(&[direction]).inc();
+
+						match self.peers.entry(peer) {
+							Entry::Vacant(entry) => {
+								entry.insert(ConnectionContext {
+									endpoints: HashMap::from_iter([(endpoint.connection_id(), endpoint)]),
+									num_connections: 1usize,
+								});
+								metrics.distinct_peers_connections_opened_total.inc();
+							}
+							Entry::Occupied(entry) => {
+								let entry = entry.into_mut();
+								entry.num_connections += 1;
+								entry.endpoints.insert(endpoint.connection_id(), endpoint);
+							}
+						}
+					}
+					Some(Litep2pEvent::ConnectionClosed { peer, connection_id }) => {
+						let Some(metrics) = &self.metrics else {
+							continue;
+						};
+
+						let Some(context) = self.peers.get_mut(&peer) else {
+							log::debug!(target: LOG_TARGET, "unknown peer disconnected: {peer:?} ({connection_id:?})");
+							continue
+						};
+
+						let direction = match context.endpoints.remove(&connection_id) {
+							None => {
+								log::debug!(target: LOG_TARGET, "connection {connection_id:?} doesn't exist for {peer:?} ");
+								continue
+							}
+							Some(endpoint) => {
+								context.num_connections -= 1;
+
+								match endpoint {
+									Endpoint::Dialer { .. } => "out",
+									Endpoint::Listener { .. } => "in",
+								}
+							}
+						};
+
+						metrics.connections_closed_total.with_label_values(&[direction, "actively-closed"]).inc();
+
+						if context.num_connections == 0 {
+							self.peers.remove(&peer);
+							metrics.distinct_peers_connections_closed_total.inc();
+						}
+					}
+					Some(Litep2pEvent::DialFailure { address, error }) => {
+						log::trace!(
+							target: LOG_TARGET,
+							"failed to dial peer at {address:?}: {error:?}",
+						);
+
+						let reason = match error {
+							Litep2pError::PeerIdMismatch(_, _) => "invalid-peer-id",
+							Litep2pError::Timeout | Litep2pError::TransportError(_) |
+							Litep2pError::IoError(_) | Litep2pError::WebSocket(_) => "transport-error",
+							_ => "other",
+						};
+
+						if let Some(metrics) = &self.metrics {
+							metrics.pending_connections_errors_total.with_label_values(&[reason]).inc();
+						}
+					}
+					_ => {}
+				},
+			}
+		}
+	}
+}

substrate/client/network/src/litep2p/peerstore.rs

@@ -0,0 +1,391 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! `Peerstore` implementation for `litep2p`.
+//!
+//! `Peerstore` is responsible for storing information about remote peers
+//! such as their addresses, reputations, supported protocols etc.
+
+use crate::{
+	peer_store::{PeerStoreProvider, ProtocolHandle},
+	service::traits::PeerStore,
+	ObservedRole, ReputationChange,
+};
+
+use parking_lot::Mutex;
+use wasm_timer::Delay;
+
+use sc_network_types::PeerId;
+
+use std::{
+	collections::{HashMap, HashSet},
+	sync::Arc,
+	time::{Duration, Instant},
+};
+
+/// Logging target for the file.
+const LOG_TARGET: &str = "sub-libp2p::peerstore";
+
+/// We don't accept nodes whose reputation is under this value.
+pub const BANNED_THRESHOLD: i32 = 82 * (i32::MIN / 100);
+
+/// Relative decrement of a reputation value that is applied every second. I.e., for inverse
+/// decrement of 50 we decrease absolute value of the reputation by 1/50. This corresponds to a
+/// factor of `k = 0.98`. It takes ~ `ln(0.5) / ln(k)` seconds to reduce the reputation by half,
+/// or 34.3 seconds for the values above. In this setup the maximum allowed absolute value of
+/// `i32::MAX` becomes 0 in ~1100 seconds (actually less due to integer arithmetic).
+const INVERSE_DECREMENT: i32 = 50;
+
+/// Amount of time between the moment we last updated the [`PeerStore`] entry and the moment we
+/// remove it, once the reputation value reaches 0.
+const FORGET_AFTER: Duration = Duration::from_secs(3600);
+
+/// Peer information.
+#[derive(Debug, Clone, Copy)]
+struct PeerInfo {
+	/// Reputation of the peer.
+	reputation: i32,
+
+	/// Instant when the peer was last updated.
+	last_updated: Instant,
+
+	/// Role of the peer, if known.
+	role: Option<ObservedRole>,
+}
+
+impl Default for PeerInfo {
+	fn default() -> Self {
+		Self { reputation: 0i32, last_updated: Instant::now(), role: None }
+	}
+}
+
+impl PeerInfo {
+	fn is_banned(&self) -> bool {
+		self.reputation < BANNED_THRESHOLD
+	}
+
+	fn decay_reputation(&mut self, seconds_passed: u64) {
+		// Note that decaying the reputation value happens "on its own",
+		// so we don't do `bump_last_updated()`.
+		for _ in 0..seconds_passed {
+			let mut diff = self.reputation / INVERSE_DECREMENT;
+			if diff == 0 && self.reputation < 0 {
+				diff = -1;
+			} else if diff == 0 && self.reputation > 0 {
+				diff = 1;
+			}
+
+			self.reputation = self.reputation.saturating_sub(diff);
+
+			if self.reputation == 0 {
+				break
+			}
+		}
+	}
+}
+
+#[derive(Debug, Default)]
+pub struct PeerstoreHandleInner {
+	peers: HashMap<PeerId, PeerInfo>,
+	protocols: Vec<Arc<dyn ProtocolHandle>>,
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct PeerstoreHandle(Arc<Mutex<PeerstoreHandleInner>>);
+
+impl PeerstoreHandle {
+	/// Add known peer to [`Peerstore`].
+	pub fn add_known_peer(&self, peer: PeerId) {
+		self.0
+			.lock()
+			.peers
+			.insert(peer, PeerInfo { reputation: 0i32, last_updated: Instant::now(), role: None });
+	}
+
+	pub fn peer_count(&self) -> usize {
+		self.0.lock().peers.len()
+	}
+
+	fn progress_time(&self, seconds_passed: u64) {
+		if seconds_passed == 0 {
+			return
+		}
+
+		let mut lock = self.0.lock();
+
+		// Drive reputation values towards 0.
+		lock.peers
+			.iter_mut()
+			.for_each(|(_, info)| info.decay_reputation(seconds_passed));
+
+		// Retain only entries with non-zero reputation values or not expired ones.
+		let now = Instant::now();
+		lock.peers
+			.retain(|_, info| info.reputation != 0 || info.last_updated + FORGET_AFTER > now);
+	}
+}
+
+impl PeerStoreProvider for PeerstoreHandle {
+	fn is_banned(&self, peer: &PeerId) -> bool {
+		self.0.lock().peers.get(peer).map_or(false, |info| info.is_banned())
+	}
+
+	/// Register a protocol handle to disconnect peers whose reputation drops below the threshold.
+	fn register_protocol(&self, protocol_handle: Arc<dyn ProtocolHandle>) {
+		self.0.lock().protocols.push(protocol_handle);
+	}
+
+	/// Report peer disconnection for reputation adjustment.
+	fn report_disconnect(&self, _peer: PeerId) {
+		unimplemented!();
+	}
+
+	/// Adjust peer reputation.
+	fn report_peer(&self, peer: PeerId, reputation_change: ReputationChange) {
+		let mut lock = self.0.lock();
+
+		log::trace!(target: LOG_TARGET, "report peer {reputation_change:?}");
+
+		match lock.peers.get_mut(&peer) {
+			Some(info) => {
+				info.reputation = info.reputation.saturating_add(reputation_change.value);
+			},
+			None => {
+				lock.peers.insert(
+					peer,
+					PeerInfo {
+						reputation: reputation_change.value,
+						last_updated: Instant::now(),
+						role: None,
+					},
+				);
+			},
+		}
+
+		if lock
+			.peers
+			.get(&peer)
+			.expect("peer exist since it was just modified; qed")
+			.is_banned()
+		{
+			log::warn!(target: LOG_TARGET, "{peer:?} banned, disconnecting, reason: {}", reputation_change.reason);
+
+			for sender in &lock.protocols {
+				sender.disconnect_peer(peer);
+			}
+		}
+	}
+
+	/// Set peer role.
+	fn set_peer_role(&self, peer: &PeerId, role: ObservedRole) {
+		self.0.lock().peers.entry(*peer).or_default().role = Some(role);
+	}
+
+	/// Get peer reputation.
+	fn peer_reputation(&self, peer: &PeerId) -> i32 {
+		self.0.lock().peers.get(peer).map_or(0i32, |info| info.reputation)
+	}
+
+	/// Get peer role, if available.
+	fn peer_role(&self, peer: &PeerId) -> Option<ObservedRole> {
+		self.0.lock().peers.get(peer).and_then(|info| info.role)
+	}
+
+	/// Get candidates with highest reputations for initiating outgoing connections.
+	fn outgoing_candidates(&self, count: usize, ignored: HashSet<PeerId>) -> Vec<PeerId> {
+		let handle = self.0.lock();
+
+		let mut candidates = handle
+			.peers
+			.iter()
+			.filter_map(|(peer, info)| {
+				(!ignored.contains(&peer) && !info.is_banned()).then_some((*peer, info.reputation))
+			})
+			.collect::<Vec<(PeerId, _)>>();
+		candidates.sort_by(|(_, a), (_, b)| b.cmp(a));
+		candidates
+			.into_iter()
+			.take(count)
+			.map(|(peer, _score)| peer)
+			.collect::<Vec<_>>()
+	}
+
+	/// Get the number of known peers.
+	///
+	/// This number might not include some connected peers in rare cases when their reputation
+	/// was not updated for one hour, because their entries in [`PeerStore`] were dropped.
+	fn num_known_peers(&self) -> usize {
+		self.0.lock().peers.len()
+	}
+
+	/// Add known peer.
+	fn add_known_peer(&self, peer: PeerId) {
+		self.0.lock().peers.entry(peer).or_default().last_updated = Instant::now();
+	}
+}
+
+/// `Peerstore` handle for testing.
+///
+/// This instance of `Peerstore` is not shared between protocols.
+#[cfg(test)]
+pub fn peerstore_handle_test() -> PeerstoreHandle {
+	PeerstoreHandle(Arc::new(Mutex::new(Default::default())))
+}
+
+/// Peerstore implementation.
+pub struct Peerstore {
+	/// Handle to `Peerstore`.
+	peerstore_handle: PeerstoreHandle,
+}
+
+impl Peerstore {
+	/// Create new [`Peerstore`].
+	pub fn new(bootnodes: Vec<PeerId>) -> Self {
+		let peerstore_handle = PeerstoreHandle(Arc::new(Mutex::new(Default::default())));
+
+		for bootnode in bootnodes {
+			peerstore_handle.add_known_peer(bootnode);
+		}
+
+		Self { peerstore_handle }
+	}
+
+	/// Create new [`Peerstore`] from a [`PeerstoreHandle`].
+	pub fn from_handle(peerstore_handle: PeerstoreHandle, bootnodes: Vec<PeerId>) -> Self {
+		for bootnode in bootnodes {
+			peerstore_handle.add_known_peer(bootnode);
+		}
+
+		Self { peerstore_handle }
+	}
+
+	/// Get mutable reference to the underlying [`PeerstoreHandle`].
+	pub fn handle(&mut self) -> &mut PeerstoreHandle {
+		&mut self.peerstore_handle
+	}
+
+	/// Add known peer to [`Peerstore`].
+	pub fn add_known_peer(&mut self, peer: PeerId) {
+		self.peerstore_handle.add_known_peer(peer);
+	}
+
+	/// Start [`Peerstore`] event loop.
+	async fn run(self) {
+		let started = Instant::now();
+		let mut latest_time_update = started;
+
+		loop {
+			let now = Instant::now();
+			// We basically do `(now - self.latest_update).as_secs()`, except that by the way we do
+			// it we know that we're not going to miss seconds because of rounding to integers.
+			let seconds_passed = {
+				let elapsed_latest = latest_time_update - started;
+				let elapsed_now = now - started;
+				latest_time_update = now;
+				elapsed_now.as_secs() - elapsed_latest.as_secs()
+			};
+
+			self.peerstore_handle.progress_time(seconds_passed);
+			let _ = Delay::new(Duration::from_secs(1)).await;
+		}
+	}
+}
+
+#[async_trait::async_trait]
+impl PeerStore for Peerstore {
+	/// Get handle to `PeerStore`.
+	fn handle(&self) -> Arc<dyn PeerStoreProvider> {
+		Arc::new(self.peerstore_handle.clone())
+	}
+
+	/// Start running `PeerStore` event loop.
+	async fn run(self) {
+		self.run().await;
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::PeerInfo;
+
+	#[test]
+	fn decaying_zero_reputation_yields_zero() {
+		let mut peer_info = PeerInfo::default();
+		assert_eq!(peer_info.reputation, 0);
+
+		peer_info.decay_reputation(1);
+		assert_eq!(peer_info.reputation, 0);
+
+		peer_info.decay_reputation(100_000);
+		assert_eq!(peer_info.reputation, 0);
+	}
+
+	#[test]
+	fn decaying_positive_reputation_decreases_it() {
+		const INITIAL_REPUTATION: i32 = 100;
+
+		let mut peer_info = PeerInfo::default();
+		peer_info.reputation = INITIAL_REPUTATION;
+
+		peer_info.decay_reputation(1);
+		assert!(peer_info.reputation >= 0);
+		assert!(peer_info.reputation < INITIAL_REPUTATION);
+	}
+
+	#[test]
+	fn decaying_negative_reputation_increases_it() {
+		const INITIAL_REPUTATION: i32 = -100;
+
+		let mut peer_info = PeerInfo::default();
+		peer_info.reputation = INITIAL_REPUTATION;
+
+		peer_info.decay_reputation(1);
+		assert!(peer_info.reputation <= 0);
+		assert!(peer_info.reputation > INITIAL_REPUTATION);
+	}
+
+	#[test]
+	fn decaying_max_reputation_finally_yields_zero() {
+		const INITIAL_REPUTATION: i32 = i32::MAX;
+		const SECONDS: u64 = 1000;
+
+		let mut peer_info = PeerInfo::default();
+		peer_info.reputation = INITIAL_REPUTATION;
+
+		peer_info.decay_reputation(SECONDS / 2);
+		assert!(peer_info.reputation > 0);
+
+		peer_info.decay_reputation(SECONDS / 2);
+		assert_eq!(peer_info.reputation, 0);
+	}
+
+	#[test]
+	fn decaying_min_reputation_finally_yields_zero() {
+		const INITIAL_REPUTATION: i32 = i32::MIN;
+		const SECONDS: u64 = 1000;
+
+		let mut peer_info = PeerInfo::default();
+		peer_info.reputation = INITIAL_REPUTATION;
+
+		peer_info.decay_reputation(SECONDS / 2);
+		assert!(peer_info.reputation < 0);
+
+		peer_info.decay_reputation(SECONDS / 2);
+		assert_eq!(peer_info.reputation, 0);
+	}
+}

substrate/client/network/src/litep2p/service.rs

@@ -0,0 +1,469 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! `NetworkService` implementation for `litep2p`.
+
+use crate::{
+	config::MultiaddrWithPeerId,
+	litep2p::shim::{
+		notification::{config::ProtocolControlHandle, peerset::PeersetCommand},
+		request_response::OutboundRequest,
+	},
+	multiaddr::Protocol,
+	network_state::NetworkState,
+	peer_store::PeerStoreProvider,
+	service::out_events,
+	Event, IfDisconnected, NetworkDHTProvider, NetworkEventStream, NetworkPeers, NetworkRequest,
+	NetworkSigner, NetworkStateInfo, NetworkStatus, NetworkStatusProvider, ProtocolName,
+	RequestFailure, Signature,
+};
+
+use codec::DecodeAll;
+use futures::{channel::oneshot, stream::BoxStream};
+use libp2p::{identity::SigningError, kad::record::Key as KademliaKey, Multiaddr};
+use litep2p::crypto::ed25519::Keypair;
+use parking_lot::RwLock;
+
+use sc_network_common::{
+	role::{ObservedRole, Roles},
+	types::ReputationChange,
+};
+use sc_network_types::PeerId;
+use sc_utils::mpsc::TracingUnboundedSender;
+
+use std::{
+	collections::{HashMap, HashSet},
+	sync::{atomic::Ordering, Arc},
+};
+
+/// Logging target for the file.
+const LOG_TARGET: &str = "sub-libp2p";
+
+/// Commands sent by [`Litep2pNetworkService`] to
+/// [`Litep2pNetworkBackend`](super::Litep2pNetworkBackend).
+#[derive(Debug)]
+pub enum NetworkServiceCommand {
+	/// Get value from DHT.
+	GetValue {
+		/// Record key.
+		key: KademliaKey,
+	},
+
+	/// Put value to DHT.
+	PutValue {
+		/// Record key.
+		key: KademliaKey,
+
+		/// Record value.
+		value: Vec<u8>,
+	},
+
+	/// Query network status.
+	Status {
+		/// `oneshot::Sender` for sending the status.
+		tx: oneshot::Sender<NetworkStatus>,
+	},
+
+	/// Add `peers` to `protocol`'s reserved set.
+	AddPeersToReservedSet {
+		/// Protocol.
+		protocol: ProtocolName,
+
+		/// Reserved peers.
+		peers: HashSet<Multiaddr>,
+	},
+
+	/// Add known address for peer.
+	AddKnownAddress {
+		/// Peer ID.
+		peer: PeerId,
+
+		/// Address.
+		address: Multiaddr,
+	},
+
+	/// Set reserved peers for `protocol`.
+	SetReservedPeers {
+		/// Protocol.
+		protocol: ProtocolName,
+
+		/// Reserved peers.
+		peers: HashSet<Multiaddr>,
+	},
+
+	/// Disconnect peer from protocol.
+	DisconnectPeer {
+		/// Protocol.
+		protocol: ProtocolName,
+
+		/// Peer ID.
+		peer: PeerId,
+	},
+
+	/// Set protocol to reserved only (true/false) mode.
+	SetReservedOnly {
+		/// Protocol.
+		protocol: ProtocolName,
+
+		/// Reserved only?
+		reserved_only: bool,
+	},
+
+	/// Remove reserved peers from protocol.
+	RemoveReservedPeers {
+		/// Protocol.
+		protocol: ProtocolName,
+
+		/// Peers to remove from the reserved set.
+		peers: HashSet<PeerId>,
+	},
+
+	/// Create event stream for DHT events.
+	EventStream {
+		/// Sender for the events.
+		tx: out_events::Sender,
+	},
+}
+
+/// `NetworkService` implementation for `litep2p`.
+#[derive(Debug, Clone)]
+pub struct Litep2pNetworkService {
+	/// Local peer ID.
+	local_peer_id: litep2p::PeerId,
+
+	/// The `KeyPair` that defines the `PeerId` of the local node.
+	keypair: Keypair,
+
+	/// TX channel for sending commands to [`Litep2pNetworkBackend`](super::Litep2pNetworkBackend).
+	cmd_tx: TracingUnboundedSender<NetworkServiceCommand>,
+
+	/// Handle to `PeerStore`.
+	peer_store_handle: Arc<dyn PeerStoreProvider>,
+
+	/// Peerset handles.
+	peerset_handles: HashMap<ProtocolName, ProtocolControlHandle>,
+
+	/// Name for the block announce protocol.
+	block_announce_protocol: ProtocolName,
+
+	/// Installed request-response protocols.
+	request_response_protocols: HashMap<ProtocolName, TracingUnboundedSender<OutboundRequest>>,
+
+	/// Listen addresses.
+	listen_addresses: Arc<RwLock<HashSet<Multiaddr>>>,
+
+	/// External addresses.
+	external_addresses: Arc<RwLock<HashSet<Multiaddr>>>,
+}
+
+impl Litep2pNetworkService {
+	/// Create new [`Litep2pNetworkService`].
+	pub fn new(
+		local_peer_id: litep2p::PeerId,
+		keypair: Keypair,
+		cmd_tx: TracingUnboundedSender<NetworkServiceCommand>,
+		peer_store_handle: Arc<dyn PeerStoreProvider>,
+		peerset_handles: HashMap<ProtocolName, ProtocolControlHandle>,
+		block_announce_protocol: ProtocolName,
+		request_response_protocols: HashMap<ProtocolName, TracingUnboundedSender<OutboundRequest>>,
+		listen_addresses: Arc<RwLock<HashSet<Multiaddr>>>,
+		external_addresses: Arc<RwLock<HashSet<Multiaddr>>>,
+	) -> Self {
+		Self {
+			local_peer_id,
+			keypair,
+			cmd_tx,
+			peer_store_handle,
+			peerset_handles,
+			block_announce_protocol,
+			request_response_protocols,
+			listen_addresses,
+			external_addresses,
+		}
+	}
+}
+
+impl NetworkSigner for Litep2pNetworkService {
+	fn sign_with_local_identity(&self, msg: Vec<u8>) -> Result<Signature, SigningError> {
+		let public_key = self.keypair.public();
+		let bytes = self.keypair.sign(msg.as_ref());
+
+		Ok(Signature {
+			public_key: crate::service::signature::PublicKey::Litep2p(
+				litep2p::crypto::PublicKey::Ed25519(public_key),
+			),
+			bytes,
+		})
+	}
+
+	fn verify(
+		&self,
+		peer: PeerId,
+		public_key: &Vec<u8>,
+		signature: &Vec<u8>,
+		message: &Vec<u8>,
+	) -> Result<bool, String> {
+		let public_key = litep2p::crypto::PublicKey::from_protobuf_encoding(&public_key)
+			.map_err(|error| error.to_string())?;
+		let peer: litep2p::PeerId = peer.into();
+
+		Ok(peer == public_key.to_peer_id() && public_key.verify(message, signature))
+	}
+}
+
+impl NetworkDHTProvider for Litep2pNetworkService {
+	fn get_value(&self, key: &KademliaKey) {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::GetValue { key: key.clone() });
+	}
+
+	fn put_value(&self, key: KademliaKey, value: Vec<u8>) {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::PutValue { key, value });
+	}
+}
+
+#[async_trait::async_trait]
+impl NetworkStatusProvider for Litep2pNetworkService {
+	async fn status(&self) -> Result<NetworkStatus, ()> {
+		let (tx, rx) = oneshot::channel();
+		self.cmd_tx
+			.unbounded_send(NetworkServiceCommand::Status { tx })
+			.map_err(|_| ())?;
+
+		rx.await.map_err(|_| ())
+	}
+
+	async fn network_state(&self) -> Result<NetworkState, ()> {
+		Ok(NetworkState {
+			peer_id: self.local_peer_id.to_base58(),
+			listened_addresses: self.listen_addresses.read().iter().cloned().collect(),
+			external_addresses: self.external_addresses.read().iter().cloned().collect(),
+			connected_peers: HashMap::new(),
+			not_connected_peers: HashMap::new(),
+			// TODO: Check what info we can include here.
+			//       Issue reference: https://github.com/paritytech/substrate/issues/14160.
+			peerset: serde_json::json!(
+				"Unimplemented. See https://github.com/paritytech/substrate/issues/14160."
+			),
+		})
+	}
+}
+
+// Manual implementation to avoid extra boxing here
+// TODO: functions modifying peerset state could be modified to call peerset directly if the
+// `Multiaddr` only contains a `PeerId`
+#[async_trait::async_trait]
+impl NetworkPeers for Litep2pNetworkService {
+	fn set_authorized_peers(&self, peers: HashSet<PeerId>) {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::SetReservedPeers {
+			protocol: self.block_announce_protocol.clone(),
+			peers: peers
+				.into_iter()
+				.map(|peer| Multiaddr::empty().with(Protocol::P2p(peer.into())))
+				.collect(),
+		});
+	}
+
+	fn set_authorized_only(&self, reserved_only: bool) {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::SetReservedOnly {
+			protocol: self.block_announce_protocol.clone(),
+			reserved_only,
+		});
+	}
+
+	fn add_known_address(&self, peer: PeerId, address: Multiaddr) {
+		let _ = self
+			.cmd_tx
+			.unbounded_send(NetworkServiceCommand::AddKnownAddress { peer, address });
+	}
+
+	fn peer_reputation(&self, peer_id: &PeerId) -> i32 {
+		self.peer_store_handle.peer_reputation(peer_id)
+	}
+
+	fn report_peer(&self, peer: PeerId, cost_benefit: ReputationChange) {
+		self.peer_store_handle.report_peer(peer, cost_benefit);
+	}
+
+	fn disconnect_peer(&self, peer: PeerId, protocol: ProtocolName) {
+		let _ = self
+			.cmd_tx
+			.unbounded_send(NetworkServiceCommand::DisconnectPeer { protocol, peer });
+	}
+
+	fn accept_unreserved_peers(&self) {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::SetReservedOnly {
+			protocol: self.block_announce_protocol.clone(),
+			reserved_only: false,
+		});
+	}
+
+	fn deny_unreserved_peers(&self) {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::SetReservedOnly {
+			protocol: self.block_announce_protocol.clone(),
+			reserved_only: true,
+		});
+	}
+
+	fn add_reserved_peer(&self, peer: MultiaddrWithPeerId) -> Result<(), String> {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::AddPeersToReservedSet {
+			protocol: self.block_announce_protocol.clone(),
+			peers: HashSet::from_iter([peer.concat()]),
+		});
+
+		Ok(())
+	}
+
+	fn remove_reserved_peer(&self, peer: PeerId) {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::RemoveReservedPeers {
+			protocol: self.block_announce_protocol.clone(),
+			peers: HashSet::from_iter([peer]),
+		});
+	}
+
+	fn set_reserved_peers(
+		&self,
+		protocol: ProtocolName,
+		peers: HashSet<Multiaddr>,
+	) -> Result<(), String> {
+		let _ = self
+			.cmd_tx
+			.unbounded_send(NetworkServiceCommand::SetReservedPeers { protocol, peers });
+		Ok(())
+	}
+
+	fn add_peers_to_reserved_set(
+		&self,
+		protocol: ProtocolName,
+		peers: HashSet<Multiaddr>,
+	) -> Result<(), String> {
+		let _ = self
+			.cmd_tx
+			.unbounded_send(NetworkServiceCommand::AddPeersToReservedSet { protocol, peers });
+		Ok(())
+	}
+
+	fn remove_peers_from_reserved_set(
+		&self,
+		protocol: ProtocolName,
+		peers: Vec<PeerId>,
+	) -> Result<(), String> {
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::RemoveReservedPeers {
+			protocol,
+			peers: peers.into_iter().map(From::from).collect(),
+		});
+
+		Ok(())
+	}
+
+	fn sync_num_connected(&self) -> usize {
+		self.peerset_handles
+			.get(&self.block_announce_protocol)
+			.map_or(0usize, |handle| handle.connected_peers.load(Ordering::Relaxed))
+	}
+
+	fn peer_role(&self, peer: PeerId, handshake: Vec<u8>) -> Option<ObservedRole> {
+		match Roles::decode_all(&mut &handshake[..]) {
+			Ok(role) => Some(role.into()),
+			Err(_) => {
+				log::debug!(target: LOG_TARGET, "handshake doesn't contain peer role: {handshake:?}");
+				self.peer_store_handle.peer_role(&(peer.into()))
+			},
+		}
+	}
+
+	/// Get the list of reserved peers.
+	///
+	/// Returns an error if the `NetworkWorker` is no longer running.
+	async fn reserved_peers(&self) -> Result<Vec<PeerId>, ()> {
+		let Some(handle) = self.peerset_handles.get(&self.block_announce_protocol) else {
+			return Err(())
+		};
+		let (tx, rx) = oneshot::channel();
+
+		handle
+			.tx
+			.unbounded_send(PeersetCommand::GetReservedPeers { tx })
+			.map_err(|_| ())?;
+
+		// the channel can only be closed if `Peerset` no longer exists
+		rx.await.map_err(|_| ())
+	}
+}
+
+impl NetworkEventStream for Litep2pNetworkService {
+	fn event_stream(&self, stream_name: &'static str) -> BoxStream<'static, Event> {
+		let (tx, rx) = out_events::channel(stream_name, 100_000);
+		let _ = self.cmd_tx.unbounded_send(NetworkServiceCommand::EventStream { tx });
+		Box::pin(rx)
+	}
+}
+
+impl NetworkStateInfo for Litep2pNetworkService {
+	fn external_addresses(&self) -> Vec<Multiaddr> {
+		self.external_addresses.read().iter().cloned().collect()
+	}
+
+	fn listen_addresses(&self) -> Vec<Multiaddr> {
+		self.listen_addresses.read().iter().cloned().collect()
+	}
+
+	fn local_peer_id(&self) -> PeerId {
+		self.local_peer_id.into()
+	}
+}
+
+// Manual implementation to avoid extra boxing here
+#[async_trait::async_trait]
+impl NetworkRequest for Litep2pNetworkService {
+	async fn request(
+		&self,
+		_target: PeerId,
+		_protocol: ProtocolName,
+		_request: Vec<u8>,
+		_fallback_request: Option<(Vec<u8>, ProtocolName)>,
+		_connect: IfDisconnected,
+	) -> Result<(Vec<u8>, ProtocolName), RequestFailure> {
+		unimplemented!();
+	}
+
+	fn start_request(
+		&self,
+		peer: PeerId,
+		protocol: ProtocolName,
+		request: Vec<u8>,
+		fallback_request: Option<(Vec<u8>, ProtocolName)>,
+		sender: oneshot::Sender<Result<(Vec<u8>, ProtocolName), RequestFailure>>,
+		connect: IfDisconnected,
+	) {
+		match self.request_response_protocols.get(&protocol) {
+			Some(tx) => {
+				let _ = tx.unbounded_send(OutboundRequest::new(
+					peer,
+					request,
+					sender,
+					fallback_request,
+					connect,
+				));
+			},
+			None => log::warn!(
+				target: LOG_TARGET,
+				"{protocol} doesn't exist, cannot send request to {peer:?}"
+			),
+		}
+	}
+}

substrate/client/network/src/litep2p/shim/bitswap.rs

@@ -0,0 +1,104 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! Shim for litep2p's Bitswap implementation to make it work with `sc-network`.
+
+use futures::StreamExt;
+use litep2p::protocol::libp2p::bitswap::{
+	BitswapEvent, BitswapHandle, BlockPresenceType, Config, ResponseType, WantType,
+};
+
+use sc_client_api::BlockBackend;
+use sp_runtime::traits::Block as BlockT;
+
+use std::{future::Future, pin::Pin, sync::Arc};
+
+/// Logging target for the file.
+const LOG_TARGET: &str = "sub-libp2p::bitswap";
+
+pub struct BitswapServer<Block: BlockT> {
+	/// Bitswap handle.
+	handle: BitswapHandle,
+
+	/// Blockchain client.
+	client: Arc<dyn BlockBackend<Block> + Send + Sync>,
+}
+
+impl<Block: BlockT> BitswapServer<Block> {
+	/// Create new [`BitswapServer`].
+	pub fn new(
+		client: Arc<dyn BlockBackend<Block> + Send + Sync>,
+	) -> (Pin<Box<dyn Future<Output = ()> + Send>>, Config) {
+		let (config, handle) = Config::new();
+		let bitswap = Self { client, handle };
+
+		(Box::pin(async move { bitswap.run().await }), config)
+	}
+
+	async fn run(mut self) {
+		log::debug!(target: LOG_TARGET, "starting bitswap server");
+
+		while let Some(event) = self.handle.next().await {
+			match event {
+				BitswapEvent::Request { peer, cids } => {
+					log::debug!(target: LOG_TARGET, "handle bitswap request from {peer:?} for {cids:?}");
+
+					let response: Vec<ResponseType> = cids
+						.into_iter()
+						.map(|(cid, want_type)| {
+							let mut hash = Block::Hash::default();
+							hash.as_mut().copy_from_slice(&cid.hash().digest()[0..32]);
+							let transaction = match self.client.indexed_transaction(hash) {
+								Ok(ex) => ex,
+								Err(error) => {
+									log::error!(target: LOG_TARGET, "error retrieving transaction {hash}: {error}");
+									None
+								},
+							};
+
+							match transaction {
+								Some(transaction) => {
+									log::trace!(target: LOG_TARGET, "found cid {cid:?}, hash {hash:?}");
+
+									match want_type {
+										WantType::Block =>
+											ResponseType::Block { cid, block: transaction },
+										_ => ResponseType::Presence {
+											cid,
+											presence: BlockPresenceType::Have,
+										},
+									}
+								},
+								None => {
+									log::trace!(target: LOG_TARGET, "missing cid {cid:?}, hash {hash:?}");
+
+									ResponseType::Presence {
+										cid,
+										presence: BlockPresenceType::DontHave,
+									}
+								},
+							}
+						})
+						.collect();
+
+					self.handle.send_response(peer, response).await;
+				},
+			}
+		}
+	}
+}

substrate/client/network/src/litep2p/shim/mod.rs

@@ -0,0 +1,23 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! Shims for fitting `litep2p` APIs to `sc-network` APIs.
+
+pub(crate) mod bitswap;
+pub(crate) mod notification;
+pub(crate) mod request_response;

substrate/client/network/src/litep2p/shim/notification/config.rs

@@ -0,0 +1,168 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! `litep2p` notification protocol configuration.
+
+use crate::{
+	config::{MultiaddrWithPeerId, NonReservedPeerMode, NotificationHandshake, SetConfig},
+	litep2p::shim::notification::{
+		peerset::{Peerset, PeersetCommand},
+		NotificationProtocol,
+	},
+	peer_store::PeerStoreProvider,
+	service::{metrics::NotificationMetrics, traits::NotificationConfig},
+	NotificationService, ProtocolName,
+};
+
+use litep2p::protocol::notification::{Config, ConfigBuilder};
+
+use sc_utils::mpsc::TracingUnboundedSender;
+
+use std::sync::{atomic::AtomicUsize, Arc};
+
+/// Handle for controlling the notification protocol.
+#[derive(Debug, Clone)]
+pub struct ProtocolControlHandle {
+	/// TX channel for sending commands to `Peerset` of the notification protocol.
+	pub tx: TracingUnboundedSender<PeersetCommand>,
+
+	/// Peers currently connected to this protocol.
+	pub connected_peers: Arc<AtomicUsize>,
+}
+
+impl ProtocolControlHandle {
+	/// Create new [`ProtocolControlHandle`].
+	pub fn new(
+		tx: TracingUnboundedSender<PeersetCommand>,
+		connected_peers: Arc<AtomicUsize>,
+	) -> Self {
+		Self { tx, connected_peers }
+	}
+}
+
+/// Configuration for the notification protocol.
+#[derive(Debug)]
+pub struct NotificationProtocolConfig {
+	/// Name of the notifications protocols of this set. A substream on this set will be
+	/// considered established once this protocol is open.
+	pub protocol_name: ProtocolName,
+
+	/// Maximum allowed size of single notifications.
+	max_notification_size: usize,
+
+	/// Base configuration.
+	set_config: SetConfig,
+
+	/// `litep2p` notification config.
+	pub config: Config,
+
+	/// Handle for controlling the notification protocol.
+	pub handle: ProtocolControlHandle,
+}
+
+impl NotificationProtocolConfig {
+	// Create new [`NotificationProtocolConfig`].
+	pub fn new(
+		protocol_name: ProtocolName,
+		fallback_names: Vec<ProtocolName>,
+		max_notification_size: usize,
+		handshake: Option<NotificationHandshake>,
+		set_config: SetConfig,
+		metrics: NotificationMetrics,
+		peerstore_handle: Arc<dyn PeerStoreProvider>,
+	) -> (Self, Box<dyn NotificationService>) {
+		// create `Peerset`/`Peerstore` handle for the protocol
+		let connected_peers = Arc::new(Default::default());
+		let (peerset, peerset_tx) = Peerset::new(
+			protocol_name.clone(),
+			set_config.out_peers as usize,
+			set_config.in_peers as usize,
+			set_config.non_reserved_mode == NonReservedPeerMode::Deny,
+			set_config.reserved_nodes.iter().map(|address| address.peer_id).collect(),
+			Arc::clone(&connected_peers),
+			peerstore_handle,
+		);
+
+		// create `litep2p` notification protocol configuration for the protocol
+		//
+		// NOTE: currently only dummy value is given as the handshake as protocols (apart from
+		// syncing) are not configuring their own handshake and instead default to role being the
+		// handshake. As the time of writing this, most protocols are not aware of the role and
+		// that should be refactored in the future.
+		let (config, handle) = ConfigBuilder::new(protocol_name.clone().into())
+			.with_handshake(handshake.map_or(vec![1], |handshake| (*handshake).to_vec()))
+			.with_max_size(max_notification_size as usize)
+			.with_auto_accept_inbound(true)
+			.with_fallback_names(fallback_names.into_iter().map(From::from).collect())
+			.build();
+
+		// initialize the actual object implementing `NotificationService` and combine the
+		// `litep2p::NotificationHandle` with `Peerset` to implement a full and independent
+		// notification protocol runner
+		let protocol = NotificationProtocol::new(protocol_name.clone(), handle, peerset, metrics);
+
+		(
+			Self {
+				protocol_name,
+				max_notification_size,
+				set_config,
+				config,
+				handle: ProtocolControlHandle::new(peerset_tx, connected_peers),
+			},
+			Box::new(protocol),
+		)
+	}
+
+	/// Get reference to protocol name.
+	pub fn protocol_name(&self) -> &ProtocolName {
+		&self.protocol_name
+	}
+
+	/// Get reference to `SetConfig`.
+	pub fn set_config(&self) -> &SetConfig {
+		&self.set_config
+	}
+
+	/// Modifies the configuration to allow non-reserved nodes.
+	pub fn allow_non_reserved(&mut self, in_peers: u32, out_peers: u32) {
+		self.set_config.in_peers = in_peers;
+		self.set_config.out_peers = out_peers;
+		self.set_config.non_reserved_mode = NonReservedPeerMode::Accept;
+	}
+
+	/// Add a node to the list of reserved nodes.
+	pub fn add_reserved(&mut self, peer: MultiaddrWithPeerId) {
+		self.set_config.reserved_nodes.push(peer);
+	}
+
+	/// Get maximum notification size.
+	pub fn max_notification_size(&self) -> usize {
+		self.max_notification_size
+	}
+}
+
+impl NotificationConfig for NotificationProtocolConfig {
+	fn set_config(&self) -> &SetConfig {
+		&self.set_config
+	}
+
+	/// Get reference to protocol name.
+	fn protocol_name(&self) -> &ProtocolName {
+		&self.protocol_name
+	}
+}

substrate/client/network/src/litep2p/shim/notification/mod.rs

@@ -0,0 +1,374 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! Shim for `litep2p::NotificationHandle` to combine `Peerset`-like behavior
+//! with `NotificationService`.
+
+use crate::{
+	error::Error,
+	litep2p::shim::notification::peerset::{OpenResult, Peerset, PeersetNotificationCommand},
+	service::{
+		metrics::NotificationMetrics,
+		traits::{NotificationEvent as SubstrateNotificationEvent, ValidationResult},
+	},
+	MessageSink, NotificationService, ProtocolName,
+};
+
+use futures::{future::BoxFuture, stream::FuturesUnordered, StreamExt};
+use litep2p::protocol::notification::{
+	NotificationEvent, NotificationHandle, NotificationSink,
+	ValidationResult as Litep2pValidationResult,
+};
+use tokio::sync::oneshot;
+
+use sc_network_types::PeerId;
+
+use std::{collections::HashSet, fmt};
+
+pub mod config;
+pub mod peerset;
+
+#[cfg(test)]
+mod tests;
+
+/// Logging target for the file.
+const LOG_TARGET: &str = "sub-libp2p::notification";
+
+/// Wrapper over `litep2p`'s notification sink.
+pub struct Litep2pMessageSink {
+	/// Protocol.
+	protocol: ProtocolName,
+
+	/// Remote peer ID.
+	peer: PeerId,
+
+	/// Notification sink.
+	sink: NotificationSink,
+
+	/// Notification metrics.
+	metrics: NotificationMetrics,
+}
+
+impl Litep2pMessageSink {
+	/// Create new [`Litep2pMessageSink`].
+	fn new(
+		peer: PeerId,
+		protocol: ProtocolName,
+		sink: NotificationSink,
+		metrics: NotificationMetrics,
+	) -> Self {
+		Self { protocol, peer, sink, metrics }
+	}
+}
+
+#[async_trait::async_trait]
+impl MessageSink for Litep2pMessageSink {
+	/// Send synchronous `notification` to the peer associated with this [`MessageSink`].
+	fn send_sync_notification(&self, notification: Vec<u8>) {
+		let size = notification.len();
+
+		match self.sink.send_sync_notification(notification) {
+			Ok(_) => self.metrics.register_notification_sent(&self.protocol, size),
+			Err(error) => log::trace!(
+				target: LOG_TARGET,
+				"{}: failed to send sync notification to {:?}: {error:?}",
+				self.protocol,
+				self.peer,
+			),
+		}
+	}
+
+	/// Send an asynchronous `notification` to to the peer associated with this [`MessageSink`],
+	/// allowing sender to exercise backpressure.
+	///
+	/// Returns an error if the peer does not exist.
+	async fn send_async_notification(&self, notification: Vec<u8>) -> Result<(), Error> {
+		let size = notification.len();
+
+		match self.sink.send_async_notification(notification).await {
+			Ok(_) => {
+				self.metrics.register_notification_sent(&self.protocol, size);
+				Ok(())
+			},
+			Err(error) => {
+				log::trace!(
+					target: LOG_TARGET,
+					"{}: failed to send async notification to {:?}: {error:?}",
+					self.protocol,
+					self.peer,
+				);
+
+				Err(Error::Litep2p(error))
+			},
+		}
+	}
+}
+
+/// Notification protocol implementation.
+pub struct NotificationProtocol {
+	/// Protocol name.
+	protocol: ProtocolName,
+
+	/// `litep2p` notification handle.
+	handle: NotificationHandle,
+
+	/// Peerset for the notification protocol.
+	///
+	/// Listens to peering-related events and either opens or closes substreams to remote peers.
+	peerset: Peerset,
+
+	/// Pending validations for inbound substreams.
+	pending_validations: FuturesUnordered<
+		BoxFuture<'static, (PeerId, Result<ValidationResult, oneshot::error::RecvError>)>,
+	>,
+
+	/// Pending cancels.
+	pending_cancels: HashSet<litep2p::PeerId>,
+
+	/// Notification metrics.
+	metrics: NotificationMetrics,
+}
+
+impl fmt::Debug for NotificationProtocol {
+	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+		f.debug_struct("NotificationProtocol")
+			.field("protocol", &self.protocol)
+			.field("handle", &self.handle)
+			.finish()
+	}
+}
+
+impl NotificationProtocol {
+	/// Create new [`NotificationProtocol`].
+	pub fn new(
+		protocol: ProtocolName,
+		handle: NotificationHandle,
+		peerset: Peerset,
+		metrics: NotificationMetrics,
+	) -> Self {
+		Self {
+			protocol,
+			handle,
+			peerset,
+			metrics,
+			pending_cancels: HashSet::new(),
+			pending_validations: FuturesUnordered::new(),
+		}
+	}
+
+	/// Handle `Peerset` command.
+	async fn on_peerset_command(&mut self, command: PeersetNotificationCommand) {
+		match command {
+			PeersetNotificationCommand::OpenSubstream { peers } => {
+				log::debug!(target: LOG_TARGET, "{}: open substreams to {peers:?}", self.protocol);
+
+				let _ = self.handle.open_substream_batch(peers.into_iter().map(From::from)).await;
+			},
+			PeersetNotificationCommand::CloseSubstream { peers } => {
+				log::debug!(target: LOG_TARGET, "{}: close substreams to {peers:?}", self.protocol);
+
+				self.handle.close_substream_batch(peers.into_iter().map(From::from)).await;
+			},
+		}
+	}
+}
+
+#[async_trait::async_trait]
+impl NotificationService for NotificationProtocol {
+	async fn open_substream(&mut self, _peer: PeerId) -> Result<(), ()> {
+		unimplemented!();
+	}
+
+	async fn close_substream(&mut self, _peer: PeerId) -> Result<(), ()> {
+		unimplemented!();
+	}
+
+	fn send_sync_notification(&mut self, peer: &PeerId, notification: Vec<u8>) {
+		let size = notification.len();
+
+		if let Ok(_) = self.handle.send_sync_notification(peer.into(), notification) {
+			self.metrics.register_notification_sent(&self.protocol, size);
+		}
+	}
+
+	async fn send_async_notification(
+		&mut self,
+		peer: &PeerId,
+		notification: Vec<u8>,
+	) -> Result<(), Error> {
+		let size = notification.len();
+
+		match self.handle.send_async_notification(peer.into(), notification).await {
+			Ok(_) => {
+				self.metrics.register_notification_sent(&self.protocol, size);
+				Ok(())
+			},
+			Err(_) => Err(Error::ChannelClosed),
+		}
+	}
+
+	/// Set handshake for the notification protocol replacing the old handshake.
+	async fn set_handshake(&mut self, handshake: Vec<u8>) -> Result<(), ()> {
+		self.handle.set_handshake(handshake);
+
+		Ok(())
+	}
+
+	/// Set handshake for the notification protocol replacing the old handshake.
+	///
+	/// For `litep2p` this is identical to `NotificationService::set_handshake()` since `litep2p`
+	/// allows updating the handshake synchronously.
+	fn try_set_handshake(&mut self, handshake: Vec<u8>) -> Result<(), ()> {
+		self.handle.set_handshake(handshake);
+
+		Ok(())
+	}
+
+	/// Make a copy of the object so it can be shared between protocol components
+	/// who wish to have access to the same underlying notification protocol.
+	fn clone(&mut self) -> Result<Box<dyn NotificationService>, ()> {
+		unimplemented!("clonable `NotificationService` not supported by `litep2p`");
+	}
+
+	/// Get protocol name of the `NotificationService`.
+	fn protocol(&self) -> &ProtocolName {
+		&self.protocol
+	}
+
+	/// Get message sink of the peer.
+	fn message_sink(&self, peer: &PeerId) -> Option<Box<dyn MessageSink>> {
+		self.handle.notification_sink(peer.into()).map(|sink| {
+			let sink: Box<dyn MessageSink> = Box::new(Litep2pMessageSink::new(
+				*peer,
+				self.protocol.clone(),
+				sink,
+				self.metrics.clone(),
+			));
+			sink
+		})
+	}
+
+	/// Get next event from the `Notifications` event stream.
+	async fn next_event(&mut self) -> Option<SubstrateNotificationEvent> {
+		loop {
+			tokio::select! {
+				biased;
+
+				event = self.handle.next() => match event? {
+					NotificationEvent::ValidateSubstream { peer, handshake, .. } => {
+						if let ValidationResult::Reject = self.peerset.report_inbound_substream(peer.into()) {
+							self.handle.send_validation_result(peer, Litep2pValidationResult::Reject);
+							continue;
+						}
+
+						let (tx, rx) = oneshot::channel();
+						self.pending_validations.push(Box::pin(async move { (peer.into(), rx.await) }));
+
+						log::trace!(target: LOG_TARGET, "{}: validate substream for {peer:?}", self.protocol);
+
+						return Some(SubstrateNotificationEvent::ValidateInboundSubstream {
+							peer: peer.into(),
+							handshake,
+							result_tx: tx,
+						});
+					}
+					NotificationEvent::NotificationStreamOpened {
+						peer,
+						fallback,
+						handshake,
+						direction,
+						..
+					} => {
+						self.metrics.register_substream_opened(&self.protocol);
+
+						match self.peerset.report_substream_opened(peer.into(), direction.into()) {
+							OpenResult::Reject => {
+								let _ = self.handle.close_substream_batch(vec![peer].into_iter().map(From::from)).await;
+								self.pending_cancels.insert(peer);
+
+								continue
+							}
+							OpenResult::Accept { direction } => {
+								log::trace!(target: LOG_TARGET, "{}: substream opened for {peer:?}", self.protocol);
+
+								return Some(SubstrateNotificationEvent::NotificationStreamOpened {
+									peer: peer.into(),
+									handshake,
+									direction,
+									negotiated_fallback: fallback.map(From::from),
+								});
+							}
+						}
+					}
+					NotificationEvent::NotificationStreamClosed {
+						peer,
+					} => {
+						log::trace!(target: LOG_TARGET, "{}: substream closed for {peer:?}", self.protocol);
+
+						self.metrics.register_substream_closed(&self.protocol);
+						self.peerset.report_substream_closed(peer.into());
+
+						if self.pending_cancels.remove(&peer) {
+							log::debug!(
+								target: LOG_TARGET,
+								"{}: substream closed to canceled peer ({peer:?})",
+								self.protocol
+							);
+							continue
+						}
+
+						return Some(SubstrateNotificationEvent::NotificationStreamClosed { peer: peer.into() })
+					}
+					NotificationEvent::NotificationStreamOpenFailure {
+						peer,
+						error,
+					} => {
+						log::trace!(target: LOG_TARGET, "{}: open failure for {peer:?}", self.protocol);
+						self.peerset.report_substream_open_failure(peer.into(), error);
+					}
+					NotificationEvent::NotificationReceived {
+						peer,
+						notification,
+					} => {
+						self.metrics.register_notification_received(&self.protocol, notification.len());
+
+						if !self.pending_cancels.contains(&peer) {
+							return Some(SubstrateNotificationEvent::NotificationReceived {
+								peer: peer.into(),
+								notification: notification.to_vec(),
+							});
+						}
+					}
+				},
+				result = self.pending_validations.next(), if !self.pending_validations.is_empty() => {
+					let (peer, result) = result?;
+					let validation_result = match result {
+						Ok(ValidationResult::Accept) => Litep2pValidationResult::Accept,
+						_ => {
+							self.peerset.report_substream_rejected(peer);
+							Litep2pValidationResult::Reject
+						}
+					};
+
+					self.handle.send_validation_result(peer.into(), validation_result);
+				}
+				command = self.peerset.next() => self.on_peerset_command(command?).await,
+			}
+		}
+	}
+}

substrate/client/network/src/litep2p/shim/notification/tests/fuzz.rs

@@ -0,0 +1,384 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! Fuzz test emulates network events and peer connection handling by `Peerset`
+//! and `PeerStore` to discover possible inconsistencies in peer management.
+
+use crate::{
+	litep2p::{
+		peerstore::Peerstore,
+		shim::notification::peerset::{
+			OpenResult, Peerset, PeersetCommand, PeersetNotificationCommand,
+		},
+	},
+	service::traits::{Direction, PeerStore, ValidationResult},
+	ProtocolName,
+};
+
+use futures::{FutureExt, StreamExt};
+use litep2p::protocol::notification::NotificationError;
+use rand::{
+	distributions::{Distribution, Uniform, WeightedIndex},
+	seq::IteratorRandom,
+};
+
+use sc_network_common::types::ReputationChange;
+use sc_network_types::PeerId;
+
+use std::{
+	collections::{HashMap, HashSet},
+	sync::Arc,
+};
+
+#[tokio::test]
+#[cfg(debug_assertions)]
+async fn run() {
+	sp_tracing::try_init_simple();
+
+	for _ in 0..50 {
+		test_once().await;
+	}
+}
+
+#[cfg(debug_assertions)]
+async fn test_once() {
+	// PRNG to use.
+	let mut rng = rand::thread_rng();
+
+	// peers that the peerset knows about.
+	let mut known_peers = HashSet::<PeerId>::new();
+
+	// peers that we have reserved. Always a subset of `known_peers`.
+	let mut reserved_peers = HashSet::<PeerId>::new();
+
+	// reserved only mode
+	let mut reserved_only = Uniform::new_inclusive(0, 10).sample(&mut rng) == 0;
+
+	// Bootnodes for `PeerStore` initialization.
+	let bootnodes = (0..Uniform::new_inclusive(0, 4).sample(&mut rng))
+		.map(|_| {
+			let id = PeerId::random();
+			known_peers.insert(id);
+			id
+		})
+		.collect();
+
+	let peerstore = Peerstore::new(bootnodes);
+	let peer_store_handle = peerstore.handle();
+
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		Uniform::new_inclusive(0, 25).sample(&mut rng),
+		Uniform::new_inclusive(0, 25).sample(&mut rng),
+		reserved_only,
+		(0..Uniform::new_inclusive(0, 2).sample(&mut rng))
+			.map(|_| {
+				let id = PeerId::random();
+				known_peers.insert(id);
+				reserved_peers.insert(id);
+				id
+			})
+			.collect(),
+		Default::default(),
+		Arc::clone(&peer_store_handle),
+	);
+
+	tokio::spawn(peerstore.run());
+
+	// opening substreams
+	let mut opening = HashMap::<PeerId, Direction>::new();
+
+	// open substreams
+	let mut open = HashMap::<PeerId, Direction>::new();
+
+	// closing substreams
+	let mut closing = HashSet::<PeerId>::new();
+
+	// closed substreams
+	let mut closed = HashSet::<PeerId>::new();
+
+	// perform a certain number of actions while checking that the state is consistent.
+	//
+	// if we reach the end of the loop, the run has succeeded
+	let _ = tokio::task::spawn_blocking(move || {
+		// PRNG to use in `spawn_blocking` context.
+		let mut rng = rand::thread_rng();
+
+		for _ in 0..2500 {
+			// each of these weights corresponds to an action that we may perform
+			let action_weights =
+				[300, 110, 110, 110, 110, 90, 70, 30, 110, 110, 110, 110, 20, 110, 50, 110];
+
+			match WeightedIndex::new(&action_weights).unwrap().sample(&mut rng) {
+				0 => match peerset.next().now_or_never() {
+					// open substreams to `peers`
+					Some(Some(PeersetNotificationCommand::OpenSubstream { peers })) =>
+						for peer in peers {
+							opening.insert(peer, Direction::Outbound);
+							closed.remove(&peer);
+
+							assert!(!closing.contains(&peer));
+							assert!(!open.contains_key(&peer));
+						},
+					// close substreams to `peers`
+					Some(Some(PeersetNotificationCommand::CloseSubstream { peers })) =>
+						for peer in peers {
+							assert!(closing.insert(peer));
+							assert!(open.remove(&peer).is_some());
+							assert!(!opening.contains_key(&peer));
+						},
+					Some(None) => panic!("peerset exited"),
+					None => {},
+				},
+				// get inbound connection from an unknown peer
+				1 => {
+					let new_peer = PeerId::random();
+					peer_store_handle.add_known_peer(new_peer);
+
+					match peerset.report_inbound_substream(new_peer) {
+						ValidationResult::Accept => {
+							opening.insert(new_peer, Direction::Inbound);
+						},
+						ValidationResult::Reject => {},
+					}
+				},
+				// substream opened successfully
+				//
+				// remove peer from `opening` (which contains its direction), report the open
+				// substream to `Peerset` and move peer state to `open`.
+				//
+				// if the substream was canceled while it was opening, move peer to `closing`
+				2 =>
+					if let Some(peer) = opening.keys().choose(&mut rng).copied() {
+						let direction = opening.remove(&peer).unwrap();
+						match peerset.report_substream_opened(peer, direction) {
+							OpenResult::Accept { .. } => {
+								assert!(open.insert(peer, direction).is_none());
+							},
+							OpenResult::Reject => {
+								assert!(closing.insert(peer));
+							},
+						}
+					},
+				// substream failed to open
+				3 =>
+					if let Some(peer) = opening.keys().choose(&mut rng).copied() {
+						let _ = opening.remove(&peer).unwrap();
+						peerset.report_substream_open_failure(peer, NotificationError::Rejected);
+					},
+				// substream was closed by remote peer
+				4 =>
+					if let Some(peer) = open.keys().choose(&mut rng).copied() {
+						let _ = open.remove(&peer).unwrap();
+						peerset.report_substream_closed(peer);
+						assert!(closed.insert(peer));
+					},
+				// substream was closed by local node
+				5 =>
+					if let Some(peer) = closing.iter().choose(&mut rng).copied() {
+						assert!(closing.remove(&peer));
+						assert!(closed.insert(peer));
+						peerset.report_substream_closed(peer);
+					},
+				// random connected peer was disconnected by the protocol
+				6 =>
+					if let Some(peer) = open.keys().choose(&mut rng).copied() {
+						to_peerset.unbounded_send(PeersetCommand::DisconnectPeer { peer }).unwrap();
+					},
+				// ban random peer
+				7 =>
+					if let Some(peer) = known_peers.iter().choose(&mut rng).copied() {
+						peer_store_handle.report_peer(peer, ReputationChange::new_fatal(""));
+					},
+				// inbound substream is received for a peer that was considered
+				// outbound
+				8 => {
+					let outbound_peers = opening
+						.iter()
+						.filter_map(|(peer, direction)| {
+							std::matches!(direction, Direction::Outbound).then_some(*peer)
+						})
+						.collect::<HashSet<_>>();
+
+					if let Some(peer) = outbound_peers.iter().choose(&mut rng).copied() {
+						match peerset.report_inbound_substream(peer) {
+							ValidationResult::Accept => {
+								opening.insert(peer, Direction::Inbound);
+							},
+							ValidationResult::Reject => {},
+						}
+					}
+				},
+				// set reserved peers
+				//
+				// choose peers from all available sets (open, opening, closing, closed) + some new
+				// peers
+				9 => {
+					let num_open = Uniform::new_inclusive(0, open.len()).sample(&mut rng);
+					let num_opening = Uniform::new_inclusive(0, opening.len()).sample(&mut rng);
+					let num_closing = Uniform::new_inclusive(0, closing.len()).sample(&mut rng);
+					let num_closed = Uniform::new_inclusive(0, closed.len()).sample(&mut rng);
+
+					let peers = open
+						.keys()
+						.copied()
+						.choose_multiple(&mut rng, num_open)
+						.into_iter()
+						.chain(
+							opening
+								.keys()
+								.copied()
+								.choose_multiple(&mut rng, num_opening)
+								.into_iter(),
+						)
+						.chain(
+							closing
+								.iter()
+								.copied()
+								.choose_multiple(&mut rng, num_closing)
+								.into_iter(),
+						)
+						.chain(
+							closed
+								.iter()
+								.copied()
+								.choose_multiple(&mut rng, num_closed)
+								.into_iter(),
+						)
+						.chain((0..5).map(|_| {
+							let peer = PeerId::random();
+							known_peers.insert(peer);
+							peer_store_handle.add_known_peer(peer);
+							peer
+						}))
+						.filter(|peer| !reserved_peers.contains(peer))
+						.collect::<HashSet<_>>();
+
+					reserved_peers.extend(peers.clone().into_iter());
+					to_peerset.unbounded_send(PeersetCommand::SetReservedPeers { peers }).unwrap();
+				},
+				// add reserved peers
+				10 => {
+					let num_open = Uniform::new_inclusive(0, open.len()).sample(&mut rng);
+					let num_opening = Uniform::new_inclusive(0, opening.len()).sample(&mut rng);
+					let num_closing = Uniform::new_inclusive(0, closing.len()).sample(&mut rng);
+					let num_closed = Uniform::new_inclusive(0, closed.len()).sample(&mut rng);
+
+					let peers = open
+						.keys()
+						.copied()
+						.choose_multiple(&mut rng, num_open)
+						.into_iter()
+						.chain(
+							opening
+								.keys()
+								.copied()
+								.choose_multiple(&mut rng, num_opening)
+								.into_iter(),
+						)
+						.chain(
+							closing
+								.iter()
+								.copied()
+								.choose_multiple(&mut rng, num_closing)
+								.into_iter(),
+						)
+						.chain(
+							closed
+								.iter()
+								.copied()
+								.choose_multiple(&mut rng, num_closed)
+								.into_iter(),
+						)
+						.chain((0..5).map(|_| {
+							let peer = PeerId::random();
+							known_peers.insert(peer);
+							peer_store_handle.add_known_peer(peer);
+							peer
+						}))
+						.filter(|peer| !reserved_peers.contains(peer))
+						.collect::<HashSet<_>>();
+
+					reserved_peers.extend(peers.clone().into_iter());
+					to_peerset.unbounded_send(PeersetCommand::AddReservedPeers { peers }).unwrap();
+				},
+				// remove reserved peers
+				11 => {
+					let num_to_remove =
+						Uniform::new_inclusive(0, reserved_peers.len()).sample(&mut rng);
+					let peers = reserved_peers
+						.iter()
+						.copied()
+						.choose_multiple(&mut rng, num_to_remove)
+						.into_iter()
+						.collect::<HashSet<_>>();
+
+					peers.iter().for_each(|peer| {
+						assert!(reserved_peers.remove(peer));
+					});
+
+					to_peerset
+						.unbounded_send(PeersetCommand::RemoveReservedPeers { peers })
+						.unwrap();
+				},
+				// set reserved only
+				12 => {
+					reserved_only = !reserved_only;
+
+					let _ = to_peerset
+						.unbounded_send(PeersetCommand::SetReservedOnly { reserved_only });
+				},
+				//
+				// discover a new node.
+				13 => {
+					let new_peer = PeerId::random();
+					known_peers.insert(new_peer);
+					peer_store_handle.add_known_peer(new_peer);
+				},
+				// protocol rejected a substream that was accepted by `Peerset`
+				14 => {
+					let inbound_peers = opening
+						.iter()
+						.filter_map(|(peer, direction)| {
+							std::matches!(direction, Direction::Inbound).then_some(*peer)
+						})
+						.collect::<HashSet<_>>();
+
+					if let Some(peer) = inbound_peers.iter().choose(&mut rng).copied() {
+						peerset.report_substream_rejected(peer);
+						opening.remove(&peer);
+					}
+				},
+				// inbound substream received for a peer in `closed`
+				15 =>
+					if let Some(peer) = closed.iter().choose(&mut rng).copied() {
+						match peerset.report_inbound_substream(peer) {
+							ValidationResult::Accept => {
+								assert!(closed.remove(&peer));
+								opening.insert(peer, Direction::Inbound);
+							},
+							ValidationResult::Reject => {},
+						}
+					},
+				_ => unreachable!(),
+			}
+		}
+	})
+	.await
+	.unwrap();
+}

substrate/client/network/src/litep2p/shim/notification/tests/mod.rs

@@ -0,0 +1,22 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+#[cfg(test)]
+mod fuzz;
+#[cfg(test)]
+mod peerset;

substrate/client/network/src/litep2p/shim/notification/tests/peerset.rs

@@ -0,0 +1,891 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// 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 crate::{
+	litep2p::{
+		peerstore::peerstore_handle_test,
+		shim::notification::peerset::{
+			Direction, OpenResult, PeerState, Peerset, PeersetCommand, PeersetNotificationCommand,
+			Reserved,
+		},
+	},
+	service::traits::{self, ValidationResult},
+	ProtocolName,
+};
+
+use futures::prelude::*;
+use litep2p::protocol::notification::NotificationError;
+
+use sc_network_types::PeerId;
+
+use std::{
+	collections::HashSet,
+	sync::{atomic::Ordering, Arc},
+	task::Poll,
+};
+
+// outbound substream was initiated for a peer but an inbound substream from that same peer
+// was receied while the `Peerset` was waiting for the outbound substream to be opened
+//
+// verify that the peer state is updated correctly
+#[tokio::test]
+async fn inbound_substream_for_outbound_peer() {
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let peers = (0..3)
+		.map(|_| {
+			let peer = PeerId::random();
+			peerstore_handle.add_known_peer(peer);
+			peer
+		})
+		.collect::<Vec<_>>();
+	let inbound_peer = *peers.iter().next().unwrap();
+
+	let (mut peerset, _to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		false,
+		Default::default(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(out_peers.len(), 3usize);
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 3usize);
+			assert_eq!(
+				peerset.peers().get(&inbound_peer),
+				Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::No) })
+			);
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// inbound substream was received from peer who was marked outbound
+	//
+	// verify that the peer state and inbound/outbound counts are updated correctly
+	assert_eq!(peerset.report_inbound_substream(inbound_peer), ValidationResult::Accept);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 3usize);
+	assert_eq!(
+		peerset.peers().get(&inbound_peer),
+		Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::No) })
+	);
+}
+
+// substream was opening to peer but then it was canceled and before the substream
+// was fully closed, the peer got banned
+#[tokio::test]
+async fn canceled_peer_gets_banned() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let peers = HashSet::from_iter([PeerId::random(), PeerId::random(), PeerId::random()]);
+
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		0,
+		0,
+		true,
+		peers.clone(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 0usize);
+
+			for outbound_peer in &out_peers {
+				assert!(peers.contains(outbound_peer));
+				assert_eq!(
+					peerset.peers().get(&outbound_peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) })
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// remove all reserved peers
+	to_peerset
+		.unbounded_send(PeersetCommand::RemoveReservedPeers { peers: peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::CloseSubstream { peers: out_peers }) => {
+			assert!(out_peers.is_empty());
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// verify all reserved peers are canceled
+	for (_, state) in peerset.peers() {
+		assert_eq!(state, &PeerState::Canceled { direction: Direction::Outbound(Reserved::Yes) });
+	}
+}
+
+#[tokio::test]
+async fn peer_added_and_removed_from_peerset() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		0,
+		0,
+		true,
+		Default::default(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	// add peers to reserved set
+	let peers = HashSet::from_iter([PeerId::random(), PeerId::random(), PeerId::random()]);
+	to_peerset
+		.unbounded_send(PeersetCommand::AddReservedPeers { peers: peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 0usize);
+
+			for outbound_peer in &out_peers {
+				assert!(peers.contains(outbound_peer));
+				assert!(peerset.reserved_peers().contains(outbound_peer));
+				assert_eq!(
+					peerset.peers().get(&outbound_peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) })
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// report that all substreams were opened
+	for peer in &peers {
+		assert!(std::matches!(
+			peerset.report_substream_opened(*peer, traits::Direction::Outbound),
+			OpenResult::Accept { .. }
+		));
+		assert_eq!(
+			peerset.peers().get(peer),
+			Some(&PeerState::Connected { direction: Direction::Outbound(Reserved::Yes) })
+		);
+	}
+
+	// remove all reserved peers
+	to_peerset
+		.unbounded_send(PeersetCommand::RemoveReservedPeers { peers: peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::CloseSubstream { peers: out_peers }) => {
+			assert!(!out_peers.is_empty());
+
+			for peer in &out_peers {
+				assert!(peers.contains(peer));
+				assert!(!peerset.reserved_peers().contains(peer));
+				assert_eq!(
+					peerset.peers().get(peer),
+					Some(&PeerState::Closing { direction: Direction::Outbound(Reserved::Yes) }),
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// add the peers again and verify that the command is ignored because the substreams are closing
+	to_peerset
+		.unbounded_send(PeersetCommand::AddReservedPeers { peers: peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert!(out_peers.is_empty());
+
+			for peer in &peers {
+				assert!(peerset.reserved_peers().contains(peer));
+				assert_eq!(
+					peerset.peers().get(peer),
+					Some(&PeerState::Closing { direction: Direction::Outbound(Reserved::Yes) }),
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// remove the peers again and verify the state remains as `Closing`
+	to_peerset
+		.unbounded_send(PeersetCommand::RemoveReservedPeers { peers: peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::CloseSubstream { peers: out_peers }) => {
+			assert!(out_peers.is_empty());
+
+			for peer in &peers {
+				assert!(!peerset.reserved_peers().contains(peer));
+				assert_eq!(
+					peerset.peers().get(peer),
+					Some(&PeerState::Closing { direction: Direction::Outbound(Reserved::Yes) }),
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}
+
+#[tokio::test]
+async fn set_reserved_peers() {
+	sp_tracing::try_init_simple();
+
+	let reserved = HashSet::from_iter([PeerId::random(), PeerId::random(), PeerId::random()]);
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		true,
+		reserved.clone(),
+		Default::default(),
+		Arc::new(peerstore_handle_test()),
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 0usize);
+
+			for outbound_peer in &out_peers {
+				assert!(reserved.contains(outbound_peer));
+				assert!(peerset.reserved_peers().contains(outbound_peer));
+				assert_eq!(
+					peerset.peers().get(&outbound_peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) })
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// report that all substreams were opened
+	for peer in &reserved {
+		assert!(std::matches!(
+			peerset.report_substream_opened(*peer, traits::Direction::Outbound),
+			OpenResult::Accept { .. }
+		));
+		assert_eq!(
+			peerset.peers().get(peer),
+			Some(&PeerState::Connected { direction: Direction::Outbound(Reserved::Yes) })
+		);
+	}
+
+	// add a totally new set of reserved peers
+	let new_reserved_peers =
+		HashSet::from_iter([PeerId::random(), PeerId::random(), PeerId::random()]);
+	to_peerset
+		.unbounded_send(PeersetCommand::SetReservedPeers { peers: new_reserved_peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::CloseSubstream { peers: out_peers }) => {
+			assert!(!out_peers.is_empty());
+			assert_eq!(out_peers.len(), 3);
+
+			for peer in &out_peers {
+				assert!(reserved.contains(peer));
+				assert!(!peerset.reserved_peers().contains(peer));
+				assert_eq!(
+					peerset.peers().get(peer),
+					Some(&PeerState::Closing { direction: Direction::Outbound(Reserved::Yes) }),
+				);
+			}
+
+			for peer in &new_reserved_peers {
+				assert!(peerset.reserved_peers().contains(peer));
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert!(!out_peers.is_empty());
+			assert_eq!(out_peers.len(), 3);
+
+			for peer in &new_reserved_peers {
+				assert!(peerset.reserved_peers().contains(peer));
+				assert_eq!(
+					peerset.peers().get(peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) }),
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}
+
+#[tokio::test]
+async fn set_reserved_peers_one_peer_already_in_the_set() {
+	sp_tracing::try_init_simple();
+
+	let reserved = HashSet::from_iter([PeerId::random(), PeerId::random(), PeerId::random()]);
+	let common_peer = *reserved.iter().next().unwrap();
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		true,
+		reserved.clone(),
+		Default::default(),
+		Arc::new(peerstore_handle_test()),
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 0usize);
+
+			for outbound_peer in &out_peers {
+				assert!(reserved.contains(outbound_peer));
+				assert!(peerset.reserved_peers().contains(outbound_peer));
+				assert_eq!(
+					peerset.peers().get(&outbound_peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) })
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// report that all substreams were opened
+	for peer in &reserved {
+		assert!(std::matches!(
+			peerset.report_substream_opened(*peer, traits::Direction::Outbound),
+			OpenResult::Accept { .. }
+		));
+		assert_eq!(
+			peerset.peers().get(peer),
+			Some(&PeerState::Connected { direction: Direction::Outbound(Reserved::Yes) })
+		);
+	}
+
+	// add a new set of reserved peers with one peer from the original set
+	let new_reserved_peers = HashSet::from_iter([PeerId::random(), PeerId::random(), common_peer]);
+	to_peerset
+		.unbounded_send(PeersetCommand::SetReservedPeers { peers: new_reserved_peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::CloseSubstream { peers: out_peers }) => {
+			assert_eq!(out_peers.len(), 2);
+
+			for peer in &out_peers {
+				assert!(reserved.contains(peer));
+
+				if peer != &common_peer {
+					assert!(!peerset.reserved_peers().contains(peer));
+					assert_eq!(
+						peerset.peers().get(peer),
+						Some(&PeerState::Closing { direction: Direction::Outbound(Reserved::Yes) }),
+					);
+				} else {
+					panic!("common peer disconnected");
+				}
+			}
+
+			for peer in &new_reserved_peers {
+				assert!(peerset.reserved_peers().contains(peer));
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// verify the `common_peer` peer between the reserved sets is still in the state `Open`
+	assert_eq!(
+		peerset.peers().get(&common_peer),
+		Some(&PeerState::Connected { direction: Direction::Outbound(Reserved::Yes) })
+	);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert!(!out_peers.is_empty());
+			assert_eq!(out_peers.len(), 2);
+
+			for peer in &new_reserved_peers {
+				assert!(peerset.reserved_peers().contains(peer));
+
+				if peer != &common_peer {
+					assert_eq!(
+						peerset.peers().get(peer),
+						Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) }),
+					);
+				}
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}
+
+#[tokio::test]
+async fn add_reserved_peers_one_peer_already_in_the_set() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let reserved = (0..3)
+		.map(|_| {
+			let peer = PeerId::random();
+			peerstore_handle.add_known_peer(peer);
+			peer
+		})
+		.collect::<Vec<_>>();
+	let common_peer = *reserved.iter().next().unwrap();
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		true,
+		reserved.iter().cloned().collect(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 0usize);
+			assert_eq!(out_peers.len(), 3);
+
+			for outbound_peer in &out_peers {
+				assert!(reserved.contains(outbound_peer));
+				assert!(peerset.reserved_peers().contains(outbound_peer));
+				assert_eq!(
+					peerset.peers().get(&outbound_peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) })
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// report that all substreams were opened
+	for peer in &reserved {
+		assert!(std::matches!(
+			peerset.report_substream_opened(*peer, traits::Direction::Outbound),
+			OpenResult::Accept { .. }
+		));
+		assert_eq!(
+			peerset.peers().get(peer),
+			Some(&PeerState::Connected { direction: Direction::Outbound(Reserved::Yes) })
+		);
+	}
+
+	// add a new set of reserved peers with one peer from the original set
+	let new_reserved_peers = HashSet::from_iter([PeerId::random(), PeerId::random(), common_peer]);
+	to_peerset
+		.unbounded_send(PeersetCommand::AddReservedPeers { peers: new_reserved_peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(out_peers.len(), 2);
+			assert!(!out_peers.iter().any(|peer| peer == &common_peer));
+
+			for peer in &out_peers {
+				assert!(!reserved.contains(peer));
+
+				if peer != &common_peer {
+					assert!(peerset.reserved_peers().contains(peer));
+					assert_eq!(
+						peerset.peers().get(peer),
+						Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) }),
+					);
+				}
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// verify the `common_peer` peer between the reserved sets is still in the state `Open`
+	assert_eq!(
+		peerset.peers().get(&common_peer),
+		Some(&PeerState::Connected { direction: Direction::Outbound(Reserved::Yes) })
+	);
+}
+
+#[tokio::test]
+async fn opening_peer_gets_canceled_and_disconnected() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let _known_peers = (0..1)
+		.map(|_| {
+			let peer = PeerId::random();
+			peerstore_handle.add_known_peer(peer);
+			peer
+		})
+		.collect::<Vec<_>>();
+	let num_connected = Arc::new(Default::default());
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		false,
+		Default::default(),
+		Arc::clone(&num_connected),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0);
+	assert_eq!(peerset.num_out(), 0);
+
+	let peer = match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0);
+			assert_eq!(peerset.num_out(), 1);
+			assert_eq!(out_peers.len(), 1);
+
+			for peer in &out_peers {
+				assert_eq!(
+					peerset.peers().get(&peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::No) })
+				);
+			}
+
+			out_peers[0]
+		},
+		event => panic!("invalid event: {event:?}"),
+	};
+
+	// disconnect the now-opening peer
+	to_peerset.unbounded_send(PeersetCommand::DisconnectPeer { peer }).unwrap();
+
+	// poll `Peerset` to register the command and verify the peer is now in state `Canceled`
+	futures::future::poll_fn(|cx| match peerset.poll_next_unpin(cx) {
+		Poll::Pending => Poll::Ready(()),
+		_ => panic!("unexpected event"),
+	})
+	.await;
+
+	assert_eq!(
+		peerset.peers().get(&peer),
+		Some(&PeerState::Canceled { direction: Direction::Outbound(Reserved::No) })
+	);
+	assert_eq!(peerset.num_out(), 1);
+
+	// report to `Peerset` that the substream was opened, verify that it gets closed
+	assert!(std::matches!(
+		peerset.report_substream_opened(peer, traits::Direction::Outbound),
+		OpenResult::Reject { .. }
+	));
+	assert_eq!(
+		peerset.peers().get(&peer),
+		Some(&PeerState::Closing { direction: Direction::Outbound(Reserved::No) })
+	);
+	assert_eq!(num_connected.load(Ordering::SeqCst), 1);
+	assert_eq!(peerset.num_out(), 1);
+
+	// report close event to `Peerset` and verify state
+	peerset.report_substream_closed(peer);
+	assert_eq!(peerset.num_out(), 0);
+	assert_eq!(num_connected.load(Ordering::SeqCst), 0);
+	assert_eq!(peerset.peers().get(&peer), Some(&PeerState::Backoff));
+}
+
+#[tokio::test]
+async fn open_failure_for_canceled_peer() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let _known_peers = (0..1)
+		.map(|_| {
+			let peer = PeerId::random();
+			peerstore_handle.add_known_peer(peer);
+			peer
+		})
+		.collect::<Vec<_>>();
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		false,
+		Default::default(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	let peer = match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 1usize);
+			assert_eq!(out_peers.len(), 1);
+
+			for peer in &out_peers {
+				assert_eq!(
+					peerset.peers().get(&peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::No) })
+				);
+			}
+
+			out_peers[0]
+		},
+		event => panic!("invalid event: {event:?}"),
+	};
+
+	// disconnect the now-opening peer
+	to_peerset.unbounded_send(PeersetCommand::DisconnectPeer { peer }).unwrap();
+
+	// poll `Peerset` to register the command and verify the peer is now in state `Canceled`
+	futures::future::poll_fn(|cx| match peerset.poll_next_unpin(cx) {
+		Poll::Pending => Poll::Ready(()),
+		_ => panic!("unexpected event"),
+	})
+	.await;
+
+	assert_eq!(
+		peerset.peers().get(&peer),
+		Some(&PeerState::Canceled { direction: Direction::Outbound(Reserved::No) })
+	);
+
+	// the substream failed to open, verify that peer state is now `Backoff`
+	// and that `Peerset` doesn't emit any events
+	peerset.report_substream_open_failure(peer, NotificationError::NoConnection);
+	assert_eq!(peerset.peers().get(&peer), Some(&PeerState::Backoff));
+
+	futures::future::poll_fn(|cx| match peerset.poll_next_unpin(cx) {
+		Poll::Pending => Poll::Ready(()),
+		_ => panic!("unexpected event"),
+	})
+	.await;
+}
+
+#[tokio::test]
+async fn peer_disconnected_when_being_validated_then_rejected() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let (mut peerset, _to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		false,
+		Default::default(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	// inbound substream received
+	let peer = PeerId::random();
+	assert_eq!(peerset.report_inbound_substream(peer), ValidationResult::Accept);
+
+	// substream failed to open while it was being validated by the protocol
+	peerset.report_substream_open_failure(peer, NotificationError::NoConnection);
+	assert_eq!(peerset.peers().get(&peer), Some(&PeerState::Backoff));
+
+	// protocol rejected substream, verify
+	peerset.report_substream_rejected(peer);
+	assert_eq!(peerset.peers().get(&peer), Some(&PeerState::Backoff));
+}
+
+#[tokio::test]
+async fn removed_reserved_peer_kept_due_to_free_slots() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let peers = HashSet::from_iter([PeerId::random(), PeerId::random(), PeerId::random()]);
+
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		true,
+		peers.clone(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(peerset.num_in(), 0usize);
+			assert_eq!(peerset.num_out(), 0usize);
+
+			for outbound_peer in &out_peers {
+				assert!(peers.contains(outbound_peer));
+				assert_eq!(
+					peerset.peers().get(&outbound_peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) })
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// remove all reserved peers
+	to_peerset
+		.unbounded_send(PeersetCommand::RemoveReservedPeers { peers: peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::CloseSubstream { peers: out_peers }) => {
+			assert!(out_peers.is_empty());
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// verify all reserved peers are canceled
+	for (_, state) in peerset.peers() {
+		assert_eq!(state, &PeerState::Opening { direction: Direction::Outbound(Reserved::No) });
+	}
+
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 3usize);
+}
+
+#[tokio::test]
+async fn set_reserved_peers_but_available_slots() {
+	sp_tracing::try_init_simple();
+
+	let peerstore_handle = Arc::new(peerstore_handle_test());
+	let known_peers = (0..3)
+		.map(|_| {
+			let peer = PeerId::random();
+			peerstore_handle.add_known_peer(peer);
+			peer
+		})
+		.collect::<Vec<_>>();
+
+	// one peer is common across operations meaning an outbound substream will be opened to them
+	// when `Peerset` is polled (along with two random peers) and later on `SetReservedPeers`
+	// is called with the common peer and with two new random peers
+	let common_peer = *known_peers.iter().next().unwrap();
+	let disconnected_peers = known_peers.iter().skip(1).copied().collect::<HashSet<_>>();
+	assert_eq!(disconnected_peers.len(), 2);
+
+	let (mut peerset, to_peerset) = Peerset::new(
+		ProtocolName::from("/notif/1"),
+		25,
+		25,
+		false,
+		Default::default(),
+		Default::default(),
+		peerstore_handle,
+	);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 0usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers: out_peers }) => {
+			assert_eq!(out_peers.len(), 3);
+
+			for peer in &out_peers {
+				assert_eq!(
+					peerset.peers().get(&peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::No) })
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// verify all three peers are counted as outbound peers
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 3usize);
+
+	// report that all substreams were opened
+	for peer in &known_peers {
+		assert!(std::matches!(
+			peerset.report_substream_opened(*peer, traits::Direction::Outbound),
+			OpenResult::Accept { .. }
+		));
+		assert_eq!(
+			peerset.peers().get(peer),
+			Some(&PeerState::Connected { direction: Direction::Outbound(Reserved::No) })
+		);
+	}
+
+	// set reserved peers with `common_peer` being one of them
+	let reserved_peers = HashSet::from_iter([common_peer, PeerId::random(), PeerId::random()]);
+	to_peerset
+		.unbounded_send(PeersetCommand::SetReservedPeers { peers: reserved_peers.clone() })
+		.unwrap();
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::CloseSubstream { peers: out_peers }) => {
+			assert_eq!(out_peers.len(), 2);
+
+			for peer in &out_peers {
+				assert!(disconnected_peers.contains(peer));
+				assert_eq!(
+					peerset.peers().get(peer),
+					Some(&PeerState::Closing { direction: Direction::Outbound(Reserved::No) }),
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	// verify that `Peerset` is aware of five peers, with two of them as outbound
+	// (the two disconnected peers)
+	assert_eq!(peerset.peers().len(), 5);
+	assert_eq!(peerset.num_in(), 0usize);
+	assert_eq!(peerset.num_out(), 2usize);
+
+	match peerset.next().await {
+		Some(PeersetNotificationCommand::OpenSubstream { peers }) => {
+			assert_eq!(peers.len(), 2);
+			assert!(!peers.contains(&common_peer));
+
+			for peer in &peers {
+				assert!(reserved_peers.contains(peer));
+				assert!(peerset.reserved_peers().contains(peer));
+				assert_eq!(
+					peerset.peers().get(peer),
+					Some(&PeerState::Opening { direction: Direction::Outbound(Reserved::Yes) }),
+				);
+			}
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	assert_eq!(peerset.peers().len(), 5);
+	assert_eq!(peerset.num_in(), 0usize);
+
+	// two substreams are closing still closing
+	assert_eq!(peerset.num_out(), 2usize);
+}

substrate/client/network/src/litep2p/shim/request_response/metrics.rs

@@ -0,0 +1,78 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! Metrics for [`RequestResponseProtocol`](super::RequestResponseProtocol).
+
+use crate::{service::metrics::Metrics, types::ProtocolName};
+
+use std::time::Duration;
+
+/// Request-response metrics.
+pub struct RequestResponseMetrics {
+	/// Metrics.
+	metrics: Option<Metrics>,
+
+	/// Protocol name.
+	protocol: ProtocolName,
+}
+
+impl RequestResponseMetrics {
+	pub fn new(metrics: Option<Metrics>, protocol: ProtocolName) -> Self {
+		Self { metrics, protocol }
+	}
+
+	/// Register inbound request failure to Prometheus
+	pub fn register_inbound_request_failure(&self, reason: &str) {
+		if let Some(metrics) = &self.metrics {
+			metrics
+				.requests_in_failure_total
+				.with_label_values(&[&self.protocol, reason])
+				.inc();
+		}
+	}
+
+	/// Register inbound request success to Prometheus
+	pub fn register_inbound_request_success(&self, serve_time: Duration) {
+		if let Some(metrics) = &self.metrics {
+			metrics
+				.requests_in_success_total
+				.with_label_values(&[&self.protocol])
+				.observe(serve_time.as_secs_f64());
+		}
+	}
+
+	/// Register inbound request failure to Prometheus
+	pub fn register_outbound_request_failure(&self, reason: &str) {
+		if let Some(metrics) = &self.metrics {
+			metrics
+				.requests_out_failure_total
+				.with_label_values(&[&self.protocol, reason])
+				.inc();
+		}
+	}
+
+	/// Register inbound request success to Prometheus
+	pub fn register_outbound_request_success(&self, duration: Duration) {
+		if let Some(metrics) = &self.metrics {
+			metrics
+				.requests_out_success_total
+				.with_label_values(&[&self.protocol])
+				.observe(duration.as_secs_f64());
+		}
+	}
+}

substrate/client/network/src/litep2p/shim/request_response/mod.rs

@@ -0,0 +1,529 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! Shim for litep2p's request-response implementation to make it work with `sc_network`'s
+//! request-response API.
+
+use crate::{
+	litep2p::shim::request_response::metrics::RequestResponseMetrics,
+	peer_store::PeerStoreProvider,
+	request_responses::{IncomingRequest, OutgoingResponse},
+	service::{metrics::Metrics, traits::RequestResponseConfig as RequestResponseConfigT},
+	IfDisconnected, ProtocolName, RequestFailure,
+};
+
+use futures::{channel::oneshot, future::BoxFuture, stream::FuturesUnordered, StreamExt};
+use litep2p::{
+	protocol::request_response::{
+		DialOptions, RequestResponseError, RequestResponseEvent, RequestResponseHandle,
+	},
+	types::RequestId,
+};
+
+use sc_network_types::PeerId;
+use sc_utils::mpsc::{TracingUnboundedReceiver, TracingUnboundedSender};
+
+use std::{
+	collections::HashMap,
+	sync::Arc,
+	time::{Duration, Instant},
+};
+
+mod metrics;
+
+#[cfg(test)]
+mod tests;
+
+/// Logging target for the file.
+const LOG_TARGET: &str = "sub-libp2p::request-response";
+
+/// Type containing information related to an outbound request.
+#[derive(Debug)]
+pub struct OutboundRequest {
+	/// Peer ID.
+	peer: PeerId,
+
+	/// Request.
+	request: Vec<u8>,
+
+	/// Fallback request, if provided.
+	fallback_request: Option<(Vec<u8>, ProtocolName)>,
+
+	/// `oneshot::Sender` for sending the received response, or failure.
+	sender: oneshot::Sender<Result<(Vec<u8>, ProtocolName), RequestFailure>>,
+
+	/// What should the node do if `peer` is disconnected.
+	dial_behavior: IfDisconnected,
+}
+
+impl OutboundRequest {
+	/// Create new [`OutboundRequest`].
+	pub fn new(
+		peer: PeerId,
+		request: Vec<u8>,
+		sender: oneshot::Sender<Result<(Vec<u8>, ProtocolName), RequestFailure>>,
+		fallback_request: Option<(Vec<u8>, ProtocolName)>,
+		dial_behavior: IfDisconnected,
+	) -> Self {
+		OutboundRequest { peer, request, sender, fallback_request, dial_behavior }
+	}
+}
+
+/// Pending request.
+struct PendingRequest {
+	tx: oneshot::Sender<Result<(Vec<u8>, ProtocolName), RequestFailure>>,
+	started: Instant,
+	fallback_request: Option<(Vec<u8>, ProtocolName)>,
+}
+
+impl PendingRequest {
+	/// Create new [`PendingRequest`].
+	fn new(
+		tx: oneshot::Sender<Result<(Vec<u8>, ProtocolName), RequestFailure>>,
+		started: Instant,
+		fallback_request: Option<(Vec<u8>, ProtocolName)>,
+	) -> Self {
+		Self { tx, started, fallback_request }
+	}
+}
+
+/// Request-response protocol configuration.
+///
+/// See [`RequestResponseConfiguration`](crate::request_response::ProtocolConfig) for more details.
+#[derive(Debug)]
+pub struct RequestResponseConfig {
+	/// Name of the protocol on the wire. Should be something like `/foo/bar`.
+	pub protocol_name: ProtocolName,
+
+	/// Fallback on the wire protocol names to support.
+	pub fallback_names: Vec<ProtocolName>,
+
+	/// Maximum allowed size, in bytes, of a request.
+	pub max_request_size: u64,
+
+	/// Maximum allowed size, in bytes, of a response.
+	pub max_response_size: u64,
+
+	/// Duration after which emitted requests are considered timed out.
+	pub request_timeout: Duration,
+
+	/// Channel on which the networking service will send incoming requests.
+	pub inbound_queue: Option<async_channel::Sender<IncomingRequest>>,
+}
+
+impl RequestResponseConfig {
+	/// Create new [`RequestResponseConfig`].
+	pub(crate) fn new(
+		protocol_name: ProtocolName,
+		fallback_names: Vec<ProtocolName>,
+		max_request_size: u64,
+		max_response_size: u64,
+		request_timeout: Duration,
+		inbound_queue: Option<async_channel::Sender<IncomingRequest>>,
+	) -> Self {
+		Self {
+			protocol_name,
+			fallback_names,
+			max_request_size,
+			max_response_size,
+			request_timeout,
+			inbound_queue,
+		}
+	}
+}
+
+impl RequestResponseConfigT for RequestResponseConfig {
+	fn protocol_name(&self) -> &ProtocolName {
+		&self.protocol_name
+	}
+}
+
+/// Request-response protocol.
+///
+/// This is slightly different from the `RequestResponsesBehaviour` in that it is protocol-specific,
+/// meaning there is an instance of `RequestResponseProtocol` for each installed request-response
+/// protocol and that instance deals only with the requests and responses of that protocol, nothing
+/// else. It also differs from the other implementation by combining both inbound and outbound
+/// requests under one instance so all request-response-related behavior of any given protocol is
+/// handled through one instance of `RequestResponseProtocol`.
+pub struct RequestResponseProtocol {
+	/// Protocol name.
+	protocol: ProtocolName,
+
+	/// Handle to request-response protocol.
+	handle: RequestResponseHandle,
+
+	/// Inbound queue for sending received requests to protocol implementation in Polkadot SDK.
+	inbound_queue: Option<async_channel::Sender<IncomingRequest>>,
+
+	/// Handle to `Peerstore`.
+	peerstore_handle: Arc<dyn PeerStoreProvider>,
+
+	/// Pending responses.
+	pending_inbound_responses: HashMap<RequestId, PendingRequest>,
+
+	/// Pending outbound responses.
+	pending_outbound_responses: FuturesUnordered<
+		BoxFuture<'static, (litep2p::PeerId, RequestId, Result<OutgoingResponse, ()>, Instant)>,
+	>,
+
+	/// RX channel for receiving info for outbound requests.
+	request_rx: TracingUnboundedReceiver<OutboundRequest>,
+
+	/// Map of supported request-response protocols which are used to support fallback requests.
+	///
+	/// If negotiation for the main protocol fails and the request was sent with a fallback,
+	/// [`RequestResponseProtocol`] queries this map and sends the request that protocol for
+	/// processing.
+	request_tx: HashMap<ProtocolName, TracingUnboundedSender<OutboundRequest>>,
+
+	/// Metrics, if enabled.
+	metrics: RequestResponseMetrics,
+}
+
+impl RequestResponseProtocol {
+	/// Create new [`RequestResponseProtocol`].
+	pub fn new(
+		protocol: ProtocolName,
+		handle: RequestResponseHandle,
+		peerstore_handle: Arc<dyn PeerStoreProvider>,
+		inbound_queue: Option<async_channel::Sender<IncomingRequest>>,
+		request_rx: TracingUnboundedReceiver<OutboundRequest>,
+		request_tx: HashMap<ProtocolName, TracingUnboundedSender<OutboundRequest>>,
+		metrics: Option<Metrics>,
+	) -> Self {
+		Self {
+			handle,
+			request_rx,
+			request_tx,
+			inbound_queue,
+			peerstore_handle,
+			protocol: protocol.clone(),
+			pending_inbound_responses: HashMap::new(),
+			pending_outbound_responses: FuturesUnordered::new(),
+			metrics: RequestResponseMetrics::new(metrics, protocol),
+		}
+	}
+
+	/// Send `request` to `peer`.
+	async fn on_send_request(
+		&mut self,
+		peer: PeerId,
+		request: Vec<u8>,
+		fallback_request: Option<(Vec<u8>, ProtocolName)>,
+		tx: oneshot::Sender<Result<(Vec<u8>, ProtocolName), RequestFailure>>,
+		connect: IfDisconnected,
+	) {
+		let dial_options = match connect {
+			IfDisconnected::TryConnect => DialOptions::Dial,
+			IfDisconnected::ImmediateError => DialOptions::Reject,
+		};
+
+		log::trace!(
+			target: LOG_TARGET,
+			"{}: send request to {:?} (fallback {:?}) (dial options: {:?})",
+			self.protocol,
+			peer,
+			fallback_request,
+			dial_options,
+		);
+
+		match self.handle.try_send_request(peer.into(), request, dial_options) {
+			Ok(request_id) => {
+				self.pending_inbound_responses
+					.insert(request_id, PendingRequest::new(tx, Instant::now(), fallback_request));
+			},
+			Err(error) => {
+				log::warn!(
+					target: LOG_TARGET,
+					"{}: failed to send request to {peer:?}: {error:?}",
+					self.protocol,
+				);
+
+				let _ = tx.send(Err(RequestFailure::Refused));
+				self.metrics.register_inbound_request_failure(error.to_string().as_ref());
+			},
+		}
+	}
+
+	/// Handle inbound request from `peer`
+	///
+	/// If the protocol is configured outbound only, reject the request immediately.
+	fn on_inbound_request(
+		&mut self,
+		peer: litep2p::PeerId,
+		fallback: Option<litep2p::ProtocolName>,
+		request_id: RequestId,
+		request: Vec<u8>,
+	) {
+		let Some(inbound_queue) = &self.inbound_queue else {
+			log::trace!(
+				target: LOG_TARGET,
+				"{}: rejecting inbound request from {peer:?}, protocol configured as outbound only",
+				self.protocol,
+			);
+
+			self.handle.reject_request(request_id);
+			return;
+		};
+
+		log::trace!(
+			target: LOG_TARGET,
+			"{}: request received from {peer:?} ({fallback:?} {request_id:?}), request size {:?}",
+			self.protocol,
+			request.len(),
+		);
+		let (tx, rx) = oneshot::channel();
+
+		match inbound_queue.try_send(IncomingRequest {
+			peer: peer.into(),
+			payload: request,
+			pending_response: tx,
+		}) {
+			Ok(_) => {
+				self.pending_outbound_responses.push(Box::pin(async move {
+					(peer, request_id, rx.await.map_err(|_| ()), Instant::now())
+				}));
+			},
+			Err(error) => {
+				log::trace!(
+					target: LOG_TARGET,
+					"{:?}: dropping request from {peer:?} ({request_id:?}), inbound queue full",
+					self.protocol,
+				);
+
+				self.handle.reject_request(request_id);
+				self.metrics.register_inbound_request_failure(error.to_string().as_ref());
+			},
+		}
+	}
+
+	/// Handle received inbound response.
+	fn on_inbound_response(
+		&mut self,
+		peer: litep2p::PeerId,
+		request_id: RequestId,
+		fallback: Option<litep2p::ProtocolName>,
+		response: Vec<u8>,
+	) {
+		match self.pending_inbound_responses.remove(&request_id) {
+			None => log::warn!(
+				target: LOG_TARGET,
+				"{:?}: response received for {peer:?} but {request_id:?} doesn't exist",
+				self.protocol,
+			),
+			Some(PendingRequest { tx, started, .. }) => {
+				log::trace!(
+					target: LOG_TARGET,
+					"{:?}: response received for {peer:?} ({request_id:?}), response size {:?}",
+					self.protocol,
+					response.len(),
+				);
+
+				let _ = tx.send(Ok((
+					response,
+					fallback.map_or_else(|| self.protocol.clone(), Into::into),
+				)));
+				self.metrics.register_outbound_request_success(started.elapsed());
+			},
+		}
+	}
+
+	/// Handle failed outbound request.
+	fn on_request_failed(
+		&mut self,
+		peer: litep2p::PeerId,
+		request_id: RequestId,
+		error: RequestResponseError,
+	) {
+		log::debug!(
+			target: LOG_TARGET,
+			"{:?}: request failed for {peer:?} ({request_id:?}): {error:?}",
+			self.protocol
+		);
+
+		let Some(PendingRequest { tx, fallback_request, .. }) =
+			self.pending_inbound_responses.remove(&request_id)
+		else {
+			log::warn!(
+				target: LOG_TARGET,
+				"{:?}: request failed for peer {peer:?} but {request_id:?} doesn't exist",
+				self.protocol,
+			);
+
+			return
+		};
+
+		let error = match error {
+			RequestResponseError::NotConnected => Some(RequestFailure::NotConnected),
+			RequestResponseError::Rejected | RequestResponseError::Timeout =>
+				Some(RequestFailure::Refused),
+			RequestResponseError::Canceled => {
+				log::debug!(
+					target: LOG_TARGET,
+					"{}: request canceled by local node to {peer:?} ({request_id:?})",
+					self.protocol,
+				);
+				None
+			},
+			RequestResponseError::TooLargePayload => {
+				log::warn!(
+					target: LOG_TARGET,
+					"{}: tried to send too large request to {peer:?} ({request_id:?})",
+					self.protocol,
+				);
+				Some(RequestFailure::Refused)
+			},
+			RequestResponseError::UnsupportedProtocol => match fallback_request {
+				Some((request, protocol)) => match self.request_tx.get(&protocol) {
+					Some(sender) => {
+						log::debug!(
+							target: LOG_TARGET,
+							"{}: failed to negotiate protocol with {:?}, try fallback request: ({})",
+							self.protocol,
+							peer,
+							protocol,
+						);
+
+						let outbound_request = OutboundRequest::new(
+							peer.into(),
+							request,
+							tx,
+							None,
+							IfDisconnected::ImmediateError,
+						);
+
+						// since remote peer doesn't support the main protocol (`self.protocol`),
+						// try to send the request over a fallback protocol by creating a new
+						// `OutboundRequest` from the original data, now with the fallback request
+						// payload, and send it over to the (fallback) request handler like it was
+						// a normal request.
+						let _ = sender.unbounded_send(outbound_request);
+
+						return;
+					},
+					None => {
+						log::warn!(
+							target: LOG_TARGET,
+							"{}: fallback request provided but protocol ({}) doesn't exist (peer {:?})",
+							self.protocol,
+							protocol,
+							peer,
+						);
+
+						Some(RequestFailure::Refused)
+					},
+				},
+				None => Some(RequestFailure::Refused),
+			},
+		};
+
+		if let Some(error) = error {
+			self.metrics.register_outbound_request_failure(error.to_string().as_ref());
+			let _ = tx.send(Err(error));
+		}
+	}
+
+	/// Handle outbound response.
+	fn on_outbound_response(
+		&mut self,
+		peer: litep2p::PeerId,
+		request_id: RequestId,
+		response: OutgoingResponse,
+		started: Instant,
+	) {
+		let OutgoingResponse { result, reputation_changes, sent_feedback } = response;
+
+		for change in reputation_changes {
+			log::trace!(target: LOG_TARGET, "{}: report {peer:?}: {change:?}", self.protocol);
+			self.peerstore_handle.report_peer(peer.into(), change);
+		}
+
+		match result {
+			Err(()) => {
+				log::debug!(
+					target: LOG_TARGET,
+					"{}: response rejected ({request_id:?}) for {peer:?}",
+					self.protocol,
+				);
+
+				self.handle.reject_request(request_id);
+				self.metrics.register_inbound_request_failure("rejected");
+			},
+			Ok(response) => {
+				log::trace!(
+					target: LOG_TARGET,
+					"{}: send response ({request_id:?}) to {peer:?}, response size {}",
+					self.protocol,
+					response.len(),
+				);
+
+				match sent_feedback {
+					None => self.handle.send_response(request_id, response),
+					Some(feedback) =>
+						self.handle.send_response_with_feedback(request_id, response, feedback),
+				}
+
+				self.metrics.register_inbound_request_success(started.elapsed());
+			},
+		}
+	}
+
+	/// Start running event loop of the request-response protocol.
+	pub async fn run(mut self) {
+		loop {
+			tokio::select! {
+				event = self.handle.next() => match event {
+					None => return,
+					Some(RequestResponseEvent::RequestReceived {
+						peer,
+						fallback,
+						request_id,
+						request,
+					}) => self.on_inbound_request(peer, fallback, request_id, request),
+					Some(RequestResponseEvent::ResponseReceived { peer, request_id, fallback, response }) => {
+						self.on_inbound_response(peer, request_id, fallback, response);
+					},
+					Some(RequestResponseEvent::RequestFailed { peer, request_id, error }) => {
+						self.on_request_failed(peer, request_id, error);
+					},
+				},
+				event = self.pending_outbound_responses.next(), if !self.pending_outbound_responses.is_empty() => match event {
+					None => return,
+					Some((peer, request_id, Err(()), _)) => {
+						log::debug!(target: LOG_TARGET, "{}: reject request ({request_id:?}) from {peer:?}", self.protocol);
+
+						self.handle.reject_request(request_id);
+						self.metrics.register_inbound_request_failure("rejected");
+					}
+					Some((peer, request_id, Ok(response), started)) => {
+						self.on_outbound_response(peer, request_id, response, started);
+					}
+				},
+				event = self.request_rx.next() => match event {
+					None => return,
+					Some(outbound_request) => {
+						let OutboundRequest { peer, request, sender, dial_behavior, fallback_request } = outbound_request;
+
+						self.on_send_request(peer, request, fallback_request, sender, dial_behavior).await;
+					}
+				}
+			}
+		}
+	}
+}

substrate/client/network/src/litep2p/shim/request_response/tests.rs

@@ -0,0 +1,901 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// 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 crate::{
+	litep2p::{
+		peerstore::peerstore_handle_test,
+		shim::request_response::{OutboundRequest, RequestResponseProtocol},
+	},
+	request_responses::{IfDisconnected, IncomingRequest, OutgoingResponse},
+	ProtocolName, RequestFailure,
+};
+
+use futures::{channel::oneshot, StreamExt};
+use litep2p::{
+	config::ConfigBuilder as Litep2pConfigBuilder,
+	protocol::request_response::{
+		ConfigBuilder, DialOptions, RequestResponseError, RequestResponseEvent,
+		RequestResponseHandle,
+	},
+	transport::tcp::config::Config as TcpConfig,
+	Litep2p, Litep2pEvent,
+};
+
+use sc_network_types::PeerId;
+use sc_utils::mpsc::tracing_unbounded;
+
+use std::{collections::HashMap, sync::Arc, task::Poll};
+
+/// Create `litep2p` for testing.
+async fn make_litep2p() -> (Litep2p, RequestResponseHandle) {
+	let (config, handle) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+		.with_max_size(1024)
+		.build();
+
+	(
+		Litep2p::new(
+			Litep2pConfigBuilder::new()
+				.with_request_response_protocol(config)
+				.with_tcp(TcpConfig {
+					listen_addresses: vec![
+						"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+						"/ip6/::/tcp/0".parse().unwrap(),
+					],
+					..Default::default()
+				})
+				.build(),
+		)
+		.unwrap(),
+		handle,
+	)
+}
+
+// connect two `litep2p` instances together
+async fn connect_peers(litep2p1: &mut Litep2p, litep2p2: &mut Litep2p) {
+	let address = litep2p2.listen_addresses().next().unwrap().clone();
+	litep2p1.dial_address(address).await.unwrap();
+
+	let mut litep2p1_connected = false;
+	let mut litep2p2_connected = false;
+
+	loop {
+		tokio::select! {
+			event = litep2p1.next_event() => match event.unwrap() {
+				Litep2pEvent::ConnectionEstablished { .. } => {
+					litep2p1_connected = true;
+				}
+				_ => {},
+			},
+			event = litep2p2.next_event() => match event.unwrap() {
+				Litep2pEvent::ConnectionEstablished { .. } => {
+					litep2p2_connected = true;
+				}
+				_ => {},
+			}
+		}
+
+		if litep2p1_connected && litep2p2_connected {
+			break
+		}
+	}
+}
+
+#[tokio::test]
+async fn dial_failure() {
+	let (mut litep2p, handle) = make_litep2p().await;
+	let (tx, _rx) = async_channel::bounded(64);
+	let (outbound_tx, outbound_rx) = tracing_unbounded("outbound-request", 1000);
+	let senders = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx.clone())]);
+
+	let protocol = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle,
+		Arc::new(peerstore_handle_test()),
+		Some(tx),
+		outbound_rx,
+		senders,
+		None,
+	);
+
+	tokio::spawn(protocol.run());
+	tokio::spawn(async move { while let Some(_) = litep2p.next_event().await {} });
+
+	let peer = PeerId::random();
+	let (result_tx, result_rx) = oneshot::channel();
+
+	outbound_tx
+		.unbounded_send(OutboundRequest {
+			peer,
+			request: vec![1, 2, 3, 4],
+			sender: result_tx,
+			fallback_request: None,
+			dial_behavior: IfDisconnected::TryConnect,
+		})
+		.unwrap();
+
+	assert!(std::matches!(result_rx.await, Ok(Err(RequestFailure::Refused))));
+}
+
+#[tokio::test]
+async fn send_request_to_disconnected_peer() {
+	let (mut litep2p, handle) = make_litep2p().await;
+	let (tx, _rx) = async_channel::bounded(64);
+	let (outbound_tx, outbound_rx) = tracing_unbounded("outbound-request", 1000);
+	let senders = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx.clone())]);
+
+	let protocol = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle,
+		Arc::new(peerstore_handle_test()),
+		Some(tx),
+		outbound_rx,
+		senders,
+		None,
+	);
+
+	tokio::spawn(protocol.run());
+	tokio::spawn(async move { while let Some(_) = litep2p.next_event().await {} });
+
+	let peer = PeerId::random();
+	let (result_tx, result_rx) = oneshot::channel();
+
+	outbound_tx
+		.unbounded_send(OutboundRequest {
+			peer,
+			request: vec![1, 2, 3, 4],
+			sender: result_tx,
+			fallback_request: None,
+			dial_behavior: IfDisconnected::ImmediateError,
+		})
+		.unwrap();
+
+	assert!(std::matches!(result_rx.await, Ok(Err(RequestFailure::NotConnected))));
+}
+
+#[tokio::test]
+async fn send_request_to_disconnected_peer_and_dial() {
+	let (mut litep2p1, handle1) = make_litep2p().await;
+	let (mut litep2p2, handle2) = make_litep2p().await;
+
+	let peer1 = *litep2p1.local_peer_id();
+	let peer2 = *litep2p2.local_peer_id();
+
+	litep2p1.add_known_address(
+		peer2,
+		std::iter::once(litep2p2.listen_addresses().next().expect("listen address").clone()),
+	);
+
+	let (outbound_tx1, outbound_rx1) = tracing_unbounded("outbound-request", 1000);
+	let senders = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx1.clone())]);
+	let (tx1, _rx1) = async_channel::bounded(64);
+
+	let protocol1 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle1,
+		Arc::new(peerstore_handle_test()),
+		Some(tx1),
+		outbound_rx1,
+		senders,
+		None,
+	);
+
+	let (outbound_tx2, outbound_rx2) = tracing_unbounded("outbound-request", 1000);
+	let senders = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx2)]);
+	let (tx2, rx2) = async_channel::bounded(64);
+
+	let protocol2 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx2),
+		outbound_rx2,
+		senders,
+		None,
+	);
+
+	tokio::spawn(protocol1.run());
+	tokio::spawn(protocol2.run());
+	tokio::spawn(async move { while let Some(_) = litep2p1.next_event().await {} });
+	tokio::spawn(async move { while let Some(_) = litep2p2.next_event().await {} });
+
+	let (result_tx, _result_rx) = oneshot::channel();
+	outbound_tx1
+		.unbounded_send(OutboundRequest {
+			peer: peer2.into(),
+			request: vec![1, 2, 3, 4],
+			sender: result_tx,
+			fallback_request: None,
+			dial_behavior: IfDisconnected::TryConnect,
+		})
+		.unwrap();
+
+	match rx2.recv().await {
+		Ok(IncomingRequest { peer, payload, .. }) => {
+			assert_eq!(peer, Into::<PeerId>::into(peer1));
+			assert_eq!(payload, vec![1, 2, 3, 4]);
+		},
+		Err(error) => panic!("unexpected error: {error:?}"),
+	}
+}
+
+#[tokio::test]
+async fn too_many_inbound_requests() {
+	let (mut litep2p1, handle1) = make_litep2p().await;
+	let (mut litep2p2, mut handle2) = make_litep2p().await;
+	let peer1 = *litep2p1.local_peer_id();
+
+	connect_peers(&mut litep2p1, &mut litep2p2).await;
+
+	let (outbound_tx, outbound_rx) = tracing_unbounded("outbound-request", 1000);
+	let senders = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx)]);
+	let (tx, _rx) = async_channel::bounded(4);
+
+	let protocol = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle1,
+		Arc::new(peerstore_handle_test()),
+		Some(tx),
+		outbound_rx,
+		senders,
+		None,
+	);
+
+	tokio::spawn(protocol.run());
+	tokio::spawn(async move { while let Some(_) = litep2p1.next_event().await {} });
+	tokio::spawn(async move { while let Some(_) = litep2p2.next_event().await {} });
+
+	// send 5 request and verify that one of the requests will fail
+	for _ in 0..5 {
+		handle2
+			.send_request(peer1, vec![1, 2, 3, 4], DialOptions::Reject)
+			.await
+			.unwrap();
+	}
+
+	// verify that one of the requests is rejected
+	match handle2.next().await {
+		Some(RequestResponseEvent::RequestFailed { peer, error, .. }) => {
+			assert_eq!(peer, peer1);
+			assert_eq!(error, RequestResponseError::Rejected);
+		},
+		event => panic!("inavlid event: {event:?}"),
+	}
+
+	// verify that no other events are read from the handle
+	futures::future::poll_fn(|cx| match handle2.poll_next_unpin(cx) {
+		Poll::Pending => Poll::Ready(()),
+		event => panic!("invalid event: {event:?}"),
+	})
+	.await;
+}
+
+#[tokio::test]
+async fn feedback_works() {
+	let (mut litep2p1, handle1) = make_litep2p().await;
+	let (mut litep2p2, mut handle2) = make_litep2p().await;
+
+	let peer1 = *litep2p1.local_peer_id();
+	let peer2 = *litep2p2.local_peer_id();
+
+	connect_peers(&mut litep2p1, &mut litep2p2).await;
+
+	let (outbound_tx, outbound_rx) = tracing_unbounded("outbound-request", 1000);
+	let senders = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx)]);
+	let (tx, rx) = async_channel::bounded(4);
+
+	let protocol = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle1,
+		Arc::new(peerstore_handle_test()),
+		Some(tx),
+		outbound_rx,
+		senders,
+		None,
+	);
+
+	tokio::spawn(protocol.run());
+	tokio::spawn(async move { while let Some(_) = litep2p1.next_event().await {} });
+	tokio::spawn(async move { while let Some(_) = litep2p2.next_event().await {} });
+
+	let request_id = handle2
+		.send_request(peer1, vec![1, 2, 3, 4], DialOptions::Reject)
+		.await
+		.unwrap();
+
+	let rx = match rx.recv().await {
+		Ok(IncomingRequest { peer, payload, pending_response }) => {
+			assert_eq!(peer, peer2.into());
+			assert_eq!(payload, vec![1, 2, 3, 4]);
+
+			let (tx, rx) = oneshot::channel();
+			pending_response
+				.send(OutgoingResponse {
+					result: Ok(vec![5, 6, 7, 8]),
+					reputation_changes: Vec::new(),
+					sent_feedback: Some(tx),
+				})
+				.unwrap();
+			rx
+		},
+		event => panic!("invalid event: {event:?}"),
+	};
+
+	match handle2.next().await {
+		Some(RequestResponseEvent::ResponseReceived {
+			peer,
+			request_id: received_id,
+			response,
+			..
+		}) => {
+			assert_eq!(peer, peer1);
+			assert_eq!(request_id, received_id);
+			assert_eq!(response, vec![5, 6, 7, 8]);
+			assert!(rx.await.is_ok());
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}
+
+#[tokio::test]
+async fn fallback_request_compatible_peers() {
+	// `litep2p1` supports both the new and the old protocol
+	let (mut litep2p1, handle1_1, handle1_2) = {
+		let (config1, handle1) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/2"))
+			.with_max_size(1024)
+			.build();
+
+		let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+			.with_max_size(1024)
+			.build();
+		(
+			Litep2p::new(
+				Litep2pConfigBuilder::new()
+					.with_request_response_protocol(config1)
+					.with_request_response_protocol(config2)
+					.with_tcp(TcpConfig {
+						listen_addresses: vec![
+							"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+							"/ip6/::/tcp/0".parse().unwrap(),
+						],
+						..Default::default()
+					})
+					.build(),
+			)
+			.unwrap(),
+			handle1,
+			handle2,
+		)
+	};
+
+	// `litep2p2` supports only the new protocol
+	let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/2"))
+		.with_max_size(1024)
+		.build();
+
+	let mut litep2p2 = Litep2p::new(
+		Litep2pConfigBuilder::new()
+			.with_request_response_protocol(config2)
+			.with_tcp(TcpConfig {
+				listen_addresses: vec![
+					"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+					"/ip6/::/tcp/0".parse().unwrap(),
+				],
+				..Default::default()
+			})
+			.build(),
+	)
+	.unwrap();
+
+	let peer1 = *litep2p1.local_peer_id();
+	let peer2 = *litep2p2.local_peer_id();
+
+	connect_peers(&mut litep2p1, &mut litep2p2).await;
+
+	let (outbound_tx1, outbound_rx1) = tracing_unbounded("outbound-request", 1000);
+	let (outbound_tx_fallback, outbound_rx_fallback) = tracing_unbounded("outbound-request", 1000);
+
+	let senders1 = HashMap::from_iter([
+		(ProtocolName::from("/protocol/2"), outbound_tx1.clone()),
+		(ProtocolName::from("/protocol/1"), outbound_tx_fallback),
+	]);
+
+	let (tx1, _rx1) = async_channel::bounded(4);
+	let protocol1 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/2"),
+		handle1_1,
+		Arc::new(peerstore_handle_test()),
+		Some(tx1),
+		outbound_rx1,
+		senders1.clone(),
+		None,
+	);
+
+	let (tx_fallback, _rx_fallback) = async_channel::bounded(4);
+	let protocol_fallback = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle1_2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx_fallback),
+		outbound_rx_fallback,
+		senders1,
+		None,
+	);
+
+	let (outbound_tx2, outbound_rx2) = tracing_unbounded("outbound-request", 1000);
+	let senders2 = HashMap::from_iter([(ProtocolName::from("/protocol/2"), outbound_tx2)]);
+
+	let (tx2, rx2) = async_channel::bounded(4);
+	let protocol2 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/2"),
+		handle2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx2),
+		outbound_rx2,
+		senders2,
+		None,
+	);
+
+	tokio::spawn(protocol1.run());
+	tokio::spawn(protocol2.run());
+	tokio::spawn(protocol_fallback.run());
+	tokio::spawn(async move { while let Some(_) = litep2p1.next_event().await {} });
+	tokio::spawn(async move { while let Some(_) = litep2p2.next_event().await {} });
+
+	let (result_tx, result_rx) = oneshot::channel();
+	outbound_tx1
+		.unbounded_send(OutboundRequest {
+			peer: peer2.into(),
+			request: vec![1, 2, 3, 4],
+			sender: result_tx,
+			fallback_request: Some((vec![1, 3, 3, 7], ProtocolName::from("/protocol/1"))),
+			dial_behavior: IfDisconnected::ImmediateError,
+		})
+		.unwrap();
+
+	match rx2.recv().await {
+		Ok(IncomingRequest { peer, payload, pending_response }) => {
+			assert_eq!(peer, peer1.into());
+			assert_eq!(payload, vec![1, 2, 3, 4]);
+			pending_response
+				.send(OutgoingResponse {
+					result: Ok(vec![5, 6, 7, 8]),
+					reputation_changes: Vec::new(),
+					sent_feedback: None,
+				})
+				.unwrap();
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	match result_rx.await {
+		Ok(Ok((response, protocol))) => {
+			assert_eq!(response, vec![5, 6, 7, 8]);
+			assert_eq!(protocol, ProtocolName::from("/protocol/2"));
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}
+
+#[tokio::test]
+async fn fallback_request_old_peer_receives() {
+	sp_tracing::try_init_simple();
+
+	// `litep2p1` supports both the new and the old protocol
+	let (mut litep2p1, handle1_1, handle1_2) = {
+		let (config1, handle1) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/2"))
+			.with_max_size(1024)
+			.build();
+
+		let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+			.with_max_size(1024)
+			.build();
+		(
+			Litep2p::new(
+				Litep2pConfigBuilder::new()
+					.with_request_response_protocol(config1)
+					.with_request_response_protocol(config2)
+					.with_tcp(TcpConfig {
+						listen_addresses: vec![
+							"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+							"/ip6/::/tcp/0".parse().unwrap(),
+						],
+						..Default::default()
+					})
+					.build(),
+			)
+			.unwrap(),
+			handle1,
+			handle2,
+		)
+	};
+
+	// `litep2p2` supports only the new protocol
+	let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+		.with_max_size(1024)
+		.build();
+
+	let mut litep2p2 = Litep2p::new(
+		Litep2pConfigBuilder::new()
+			.with_request_response_protocol(config2)
+			.with_tcp(TcpConfig {
+				listen_addresses: vec![
+					"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+					"/ip6/::/tcp/0".parse().unwrap(),
+				],
+				..Default::default()
+			})
+			.build(),
+	)
+	.unwrap();
+
+	let peer1 = *litep2p1.local_peer_id();
+	let peer2 = *litep2p2.local_peer_id();
+
+	connect_peers(&mut litep2p1, &mut litep2p2).await;
+
+	let (outbound_tx1, outbound_rx1) = tracing_unbounded("outbound-request", 1000);
+	let (outbound_tx_fallback, outbound_rx_fallback) = tracing_unbounded("outbound-request", 1000);
+
+	let senders1 = HashMap::from_iter([
+		(ProtocolName::from("/protocol/2"), outbound_tx1.clone()),
+		(ProtocolName::from("/protocol/1"), outbound_tx_fallback),
+	]);
+
+	let (tx1, _rx1) = async_channel::bounded(4);
+	let protocol1 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/2"),
+		handle1_1,
+		Arc::new(peerstore_handle_test()),
+		Some(tx1),
+		outbound_rx1,
+		senders1.clone(),
+		None,
+	);
+
+	let (tx_fallback, _rx_fallback) = async_channel::bounded(4);
+	let protocol_fallback = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle1_2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx_fallback),
+		outbound_rx_fallback,
+		senders1,
+		None,
+	);
+
+	let (outbound_tx2, outbound_rx2) = tracing_unbounded("outbound-request", 1000);
+	let senders2 = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx2)]);
+
+	let (tx2, rx2) = async_channel::bounded(4);
+	let protocol2 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx2),
+		outbound_rx2,
+		senders2,
+		None,
+	);
+
+	tokio::spawn(protocol1.run());
+	tokio::spawn(protocol2.run());
+	tokio::spawn(protocol_fallback.run());
+	tokio::spawn(async move { while let Some(_) = litep2p1.next_event().await {} });
+	tokio::spawn(async move { while let Some(_) = litep2p2.next_event().await {} });
+
+	let (result_tx, result_rx) = oneshot::channel();
+	outbound_tx1
+		.unbounded_send(OutboundRequest {
+			peer: peer2.into(),
+			request: vec![1, 2, 3, 4],
+			sender: result_tx,
+			fallback_request: Some((vec![1, 3, 3, 7], ProtocolName::from("/protocol/1"))),
+			dial_behavior: IfDisconnected::ImmediateError,
+		})
+		.unwrap();
+
+	match rx2.recv().await {
+		Ok(IncomingRequest { peer, payload, pending_response }) => {
+			assert_eq!(peer, peer1.into());
+			assert_eq!(payload, vec![1, 3, 3, 7]);
+			pending_response
+				.send(OutgoingResponse {
+					result: Ok(vec![1, 3, 3, 8]),
+					reputation_changes: Vec::new(),
+					sent_feedback: None,
+				})
+				.unwrap();
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	match result_rx.await {
+		Ok(Ok((response, protocol))) => {
+			assert_eq!(response, vec![1, 3, 3, 8]);
+			assert_eq!(protocol, ProtocolName::from("/protocol/1"));
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}
+
+#[tokio::test]
+async fn fallback_request_old_peer_sends() {
+	sp_tracing::try_init_simple();
+
+	// `litep2p1` supports both the new and the old protocol
+	let (mut litep2p1, handle1_1, handle1_2) = {
+		let (config1, handle1) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/2"))
+			.with_max_size(1024)
+			.build();
+
+		let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+			.with_max_size(1024)
+			.build();
+		(
+			Litep2p::new(
+				Litep2pConfigBuilder::new()
+					.with_request_response_protocol(config1)
+					.with_request_response_protocol(config2)
+					.with_tcp(TcpConfig {
+						listen_addresses: vec![
+							"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+							"/ip6/::/tcp/0".parse().unwrap(),
+						],
+						..Default::default()
+					})
+					.build(),
+			)
+			.unwrap(),
+			handle1,
+			handle2,
+		)
+	};
+
+	// `litep2p2` supports only the new protocol
+	let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+		.with_max_size(1024)
+		.build();
+
+	let mut litep2p2 = Litep2p::new(
+		Litep2pConfigBuilder::new()
+			.with_request_response_protocol(config2)
+			.with_tcp(TcpConfig {
+				listen_addresses: vec![
+					"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+					"/ip6/::/tcp/0".parse().unwrap(),
+				],
+				..Default::default()
+			})
+			.build(),
+	)
+	.unwrap();
+
+	let peer1 = *litep2p1.local_peer_id();
+	let peer2 = *litep2p2.local_peer_id();
+
+	connect_peers(&mut litep2p1, &mut litep2p2).await;
+
+	let (outbound_tx1, outbound_rx1) = tracing_unbounded("outbound-request", 1000);
+	let (outbound_tx_fallback, outbound_rx_fallback) = tracing_unbounded("outbound-request", 1000);
+
+	let senders1 = HashMap::from_iter([
+		(ProtocolName::from("/protocol/2"), outbound_tx1.clone()),
+		(ProtocolName::from("/protocol/1"), outbound_tx_fallback),
+	]);
+
+	let (tx1, _rx1) = async_channel::bounded(4);
+	let protocol1 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/2"),
+		handle1_1,
+		Arc::new(peerstore_handle_test()),
+		Some(tx1),
+		outbound_rx1,
+		senders1.clone(),
+		None,
+	);
+
+	let (tx_fallback, rx_fallback) = async_channel::bounded(4);
+	let protocol_fallback = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle1_2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx_fallback),
+		outbound_rx_fallback,
+		senders1,
+		None,
+	);
+
+	let (outbound_tx2, outbound_rx2) = tracing_unbounded("outbound-request", 1000);
+	let senders2 = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx2.clone())]);
+
+	let (tx2, _rx2) = async_channel::bounded(4);
+	let protocol2 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx2),
+		outbound_rx2,
+		senders2,
+		None,
+	);
+
+	tokio::spawn(protocol1.run());
+	tokio::spawn(protocol2.run());
+	tokio::spawn(protocol_fallback.run());
+	tokio::spawn(async move { while let Some(_) = litep2p1.next_event().await {} });
+	tokio::spawn(async move { while let Some(_) = litep2p2.next_event().await {} });
+
+	let (result_tx, result_rx) = oneshot::channel();
+	outbound_tx2
+		.unbounded_send(OutboundRequest {
+			peer: peer1.into(),
+			request: vec![1, 2, 3, 4],
+			sender: result_tx,
+			fallback_request: None,
+			dial_behavior: IfDisconnected::ImmediateError,
+		})
+		.unwrap();
+
+	match rx_fallback.recv().await {
+		Ok(IncomingRequest { peer, payload, pending_response }) => {
+			assert_eq!(peer, peer2.into());
+			assert_eq!(payload, vec![1, 2, 3, 4]);
+			pending_response
+				.send(OutgoingResponse {
+					result: Ok(vec![1, 3, 3, 8]),
+					reputation_changes: Vec::new(),
+					sent_feedback: None,
+				})
+				.unwrap();
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+
+	match result_rx.await {
+		Ok(Ok((response, protocol))) => {
+			assert_eq!(response, vec![1, 3, 3, 8]);
+			assert_eq!(protocol, ProtocolName::from("/protocol/1"));
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}
+
+#[tokio::test]
+async fn old_protocol_supported_but_no_fallback_provided() {
+	sp_tracing::try_init_simple();
+
+	// `litep2p1` supports both the new and the old protocol
+	let (mut litep2p1, handle1_1, handle1_2) = {
+		let (config1, handle1) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/2"))
+			.with_max_size(1024)
+			.build();
+
+		let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+			.with_max_size(1024)
+			.build();
+		(
+			Litep2p::new(
+				Litep2pConfigBuilder::new()
+					.with_request_response_protocol(config1)
+					.with_request_response_protocol(config2)
+					.with_tcp(TcpConfig {
+						listen_addresses: vec![
+							"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+							"/ip6/::/tcp/0".parse().unwrap(),
+						],
+						..Default::default()
+					})
+					.build(),
+			)
+			.unwrap(),
+			handle1,
+			handle2,
+		)
+	};
+
+	// `litep2p2` supports only the old protocol
+	let (config2, handle2) = ConfigBuilder::new(litep2p::ProtocolName::from("/protocol/1"))
+		.with_max_size(1024)
+		.build();
+
+	let mut litep2p2 = Litep2p::new(
+		Litep2pConfigBuilder::new()
+			.with_request_response_protocol(config2)
+			.with_tcp(TcpConfig {
+				listen_addresses: vec![
+					"/ip4/0.0.0.0/tcp/0".parse().unwrap(),
+					"/ip6/::/tcp/0".parse().unwrap(),
+				],
+				..Default::default()
+			})
+			.build(),
+	)
+	.unwrap();
+
+	let peer2 = *litep2p2.local_peer_id();
+
+	connect_peers(&mut litep2p1, &mut litep2p2).await;
+
+	let (outbound_tx1, outbound_rx1) = tracing_unbounded("outbound-request", 1000);
+	let (outbound_tx_fallback, outbound_rx_fallback) = tracing_unbounded("outbound-request", 1000);
+
+	let senders1 = HashMap::from_iter([
+		(ProtocolName::from("/protocol/2"), outbound_tx1.clone()),
+		(ProtocolName::from("/protocol/1"), outbound_tx_fallback),
+	]);
+
+	let (tx1, _rx1) = async_channel::bounded(4);
+	let protocol1 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/2"),
+		handle1_1,
+		Arc::new(peerstore_handle_test()),
+		Some(tx1),
+		outbound_rx1,
+		senders1.clone(),
+		None,
+	);
+
+	let (tx_fallback, _rx_fallback) = async_channel::bounded(4);
+	let protocol_fallback = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle1_2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx_fallback),
+		outbound_rx_fallback,
+		senders1,
+		None,
+	);
+
+	let (outbound_tx2, outbound_rx2) = tracing_unbounded("outbound-request", 1000);
+	let senders2 = HashMap::from_iter([(ProtocolName::from("/protocol/1"), outbound_tx2)]);
+
+	let (tx2, _rx2) = async_channel::bounded(4);
+	let protocol2 = RequestResponseProtocol::new(
+		ProtocolName::from("/protocol/1"),
+		handle2,
+		Arc::new(peerstore_handle_test()),
+		Some(tx2),
+		outbound_rx2,
+		senders2,
+		None,
+	);
+
+	tokio::spawn(protocol1.run());
+	tokio::spawn(protocol2.run());
+	tokio::spawn(protocol_fallback.run());
+	tokio::spawn(async move { while let Some(_) = litep2p1.next_event().await {} });
+	tokio::spawn(async move { while let Some(_) = litep2p2.next_event().await {} });
+
+	let (result_tx, result_rx) = oneshot::channel();
+	outbound_tx1
+		.unbounded_send(OutboundRequest {
+			peer: peer2.into(),
+			request: vec![1, 2, 3, 4],
+			sender: result_tx,
+			fallback_request: None,
+			dial_behavior: IfDisconnected::ImmediateError,
+		})
+		.unwrap();
+
+	match result_rx.await {
+		Ok(Err(error)) => {
+			assert!(std::matches!(error, RequestFailure::Refused));
+		},
+		event => panic!("invalid event: {event:?}"),
+	}
+}