Merge commit 'e5bed7ac380b6adb54b60a2a72a2a8f07f50d6c1' as 'bridges'

2026-05-31 02:51:01 +00:00 · 2021-04-21 11:56:23 -04:00
parent 86a376cd69 e5bed7ac38
commit 3f92e81541
339 changed files with 71658 additions and 0 deletions
@@ -0,0 +1,879 @@
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common 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.
+
+// Parity Bridges Common 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.
+
+//! Message delivery race delivers proof-of-messages from lane.source to lane.target.
+
+use crate::message_lane::{MessageLane, SourceHeaderIdOf, TargetHeaderIdOf};
+use crate::message_lane_loop::{
+	MessageDeliveryParams, MessageProofParameters, MessageWeightsMap, SourceClient as MessageLaneSourceClient,
+	SourceClientState, TargetClient as MessageLaneTargetClient, TargetClientState,
+};
+use crate::message_race_loop::{
+	MessageRace, NoncesRange, RaceState, RaceStrategy, SourceClient, SourceClientNonces, TargetClient,
+	TargetClientNonces,
+};
+use crate::message_race_strategy::BasicStrategy;
+use crate::metrics::MessageLaneLoopMetrics;
+
+use async_trait::async_trait;
+use bp_messages::{MessageNonce, UnrewardedRelayersState, Weight};
+use futures::stream::FusedStream;
+use relay_utils::FailedClient;
+use std::{
+	collections::{BTreeMap, VecDeque},
+	marker::PhantomData,
+	ops::RangeInclusive,
+	time::Duration,
+};
+
+/// Run message delivery race.
+pub async fn run<P: MessageLane>(
+	source_client: impl MessageLaneSourceClient<P>,
+	source_state_updates: impl FusedStream<Item = SourceClientState<P>>,
+	target_client: impl MessageLaneTargetClient<P>,
+	target_state_updates: impl FusedStream<Item = TargetClientState<P>>,
+	stall_timeout: Duration,
+	metrics_msg: Option<MessageLaneLoopMetrics>,
+	params: MessageDeliveryParams,
+) -> Result<(), FailedClient> {
+	crate::message_race_loop::run(
+		MessageDeliveryRaceSource {
+			client: source_client,
+			metrics_msg: metrics_msg.clone(),
+			_phantom: Default::default(),
+		},
+		source_state_updates,
+		MessageDeliveryRaceTarget {
+			client: target_client,
+			metrics_msg,
+			_phantom: Default::default(),
+		},
+		target_state_updates,
+		stall_timeout,
+		MessageDeliveryStrategy::<P> {
+			max_unrewarded_relayer_entries_at_target: params.max_unrewarded_relayer_entries_at_target,
+			max_unconfirmed_nonces_at_target: params.max_unconfirmed_nonces_at_target,
+			max_messages_in_single_batch: params.max_messages_in_single_batch,
+			max_messages_weight_in_single_batch: params.max_messages_weight_in_single_batch,
+			max_messages_size_in_single_batch: params.max_messages_size_in_single_batch,
+			latest_confirmed_nonces_at_source: VecDeque::new(),
+			target_nonces: None,
+			strategy: BasicStrategy::new(),
+		},
+	)
+	.await
+}
+
+/// Message delivery race.
+struct MessageDeliveryRace<P>(std::marker::PhantomData<P>);
+
+impl<P: MessageLane> MessageRace for MessageDeliveryRace<P> {
+	type SourceHeaderId = SourceHeaderIdOf<P>;
+	type TargetHeaderId = TargetHeaderIdOf<P>;
+
+	type MessageNonce = MessageNonce;
+	type Proof = P::MessagesProof;
+
+	fn source_name() -> String {
+		format!("{}::MessagesDelivery", P::SOURCE_NAME)
+	}
+
+	fn target_name() -> String {
+		format!("{}::MessagesDelivery", P::TARGET_NAME)
+	}
+}
+
+/// Message delivery race source, which is a source of the lane.
+struct MessageDeliveryRaceSource<P: MessageLane, C> {
+	client: C,
+	metrics_msg: Option<MessageLaneLoopMetrics>,
+	_phantom: PhantomData<P>,
+}
+
+#[async_trait]
+impl<P, C> SourceClient<MessageDeliveryRace<P>> for MessageDeliveryRaceSource<P, C>
+where
+	P: MessageLane,
+	C: MessageLaneSourceClient<P>,
+{
+	type Error = C::Error;
+	type NoncesRange = MessageWeightsMap;
+	type ProofParameters = MessageProofParameters;
+
+	async fn nonces(
+		&self,
+		at_block: SourceHeaderIdOf<P>,
+		prev_latest_nonce: MessageNonce,
+	) -> Result<(SourceHeaderIdOf<P>, SourceClientNonces<Self::NoncesRange>), Self::Error> {
+		let (at_block, latest_generated_nonce) = self.client.latest_generated_nonce(at_block).await?;
+		let (at_block, latest_confirmed_nonce) = self.client.latest_confirmed_received_nonce(at_block).await?;
+
+		if let Some(metrics_msg) = self.metrics_msg.as_ref() {
+			metrics_msg.update_source_latest_generated_nonce::<P>(latest_generated_nonce);
+			metrics_msg.update_source_latest_confirmed_nonce::<P>(latest_confirmed_nonce);
+		}
+
+		let new_nonces = if latest_generated_nonce > prev_latest_nonce {
+			self.client
+				.generated_messages_weights(at_block.clone(), prev_latest_nonce + 1..=latest_generated_nonce)
+				.await?
+		} else {
+			MessageWeightsMap::new()
+		};
+
+		Ok((
+			at_block,
+			SourceClientNonces {
+				new_nonces,
+				confirmed_nonce: Some(latest_confirmed_nonce),
+			},
+		))
+	}
+
+	async fn generate_proof(
+		&self,
+		at_block: SourceHeaderIdOf<P>,
+		nonces: RangeInclusive<MessageNonce>,
+		proof_parameters: Self::ProofParameters,
+	) -> Result<(SourceHeaderIdOf<P>, RangeInclusive<MessageNonce>, P::MessagesProof), Self::Error> {
+		self.client.prove_messages(at_block, nonces, proof_parameters).await
+	}
+}
+
+/// Message delivery race target, which is a target of the lane.
+struct MessageDeliveryRaceTarget<P: MessageLane, C> {
+	client: C,
+	metrics_msg: Option<MessageLaneLoopMetrics>,
+	_phantom: PhantomData<P>,
+}
+
+#[async_trait]
+impl<P, C> TargetClient<MessageDeliveryRace<P>> for MessageDeliveryRaceTarget<P, C>
+where
+	P: MessageLane,
+	C: MessageLaneTargetClient<P>,
+{
+	type Error = C::Error;
+	type TargetNoncesData = DeliveryRaceTargetNoncesData;
+
+	async fn require_source_header(&self, id: SourceHeaderIdOf<P>) {
+		self.client.require_source_header_on_target(id).await
+	}
+
+	async fn nonces(
+		&self,
+		at_block: TargetHeaderIdOf<P>,
+		update_metrics: bool,
+	) -> Result<(TargetHeaderIdOf<P>, TargetClientNonces<DeliveryRaceTargetNoncesData>), Self::Error> {
+		let (at_block, latest_received_nonce) = self.client.latest_received_nonce(at_block).await?;
+		let (at_block, latest_confirmed_nonce) = self.client.latest_confirmed_received_nonce(at_block).await?;
+		let (at_block, unrewarded_relayers) = self.client.unrewarded_relayers_state(at_block).await?;
+
+		if update_metrics {
+			if let Some(metrics_msg) = self.metrics_msg.as_ref() {
+				metrics_msg.update_target_latest_received_nonce::<P>(latest_received_nonce);
+				metrics_msg.update_target_latest_confirmed_nonce::<P>(latest_confirmed_nonce);
+			}
+		}
+
+		Ok((
+			at_block,
+			TargetClientNonces {
+				latest_nonce: latest_received_nonce,
+				nonces_data: DeliveryRaceTargetNoncesData {
+					confirmed_nonce: latest_confirmed_nonce,
+					unrewarded_relayers,
+				},
+			},
+		))
+	}
+
+	async fn submit_proof(
+		&self,
+		generated_at_block: SourceHeaderIdOf<P>,
+		nonces: RangeInclusive<MessageNonce>,
+		proof: P::MessagesProof,
+	) -> Result<RangeInclusive<MessageNonce>, Self::Error> {
+		self.client
+			.submit_messages_proof(generated_at_block, nonces, proof)
+			.await
+	}
+}
+
+/// Additional nonces data from the target client used by message delivery race.
+#[derive(Debug, Clone)]
+struct DeliveryRaceTargetNoncesData {
+	/// Latest nonce that we know: (1) has been delivered to us (2) has been confirmed
+	/// back to the source node (by confirmations race) and (3) relayer has received
+	/// reward for (and this has been confirmed by the message delivery race).
+	confirmed_nonce: MessageNonce,
+	/// State of the unrewarded relayers set at the target node.
+	unrewarded_relayers: UnrewardedRelayersState,
+}
+
+/// Messages delivery strategy.
+struct MessageDeliveryStrategy<P: MessageLane> {
+	/// Maximal unrewarded relayer entries at target client.
+	max_unrewarded_relayer_entries_at_target: MessageNonce,
+	/// Maximal unconfirmed nonces at target client.
+	max_unconfirmed_nonces_at_target: MessageNonce,
+	/// Maximal number of messages in the single delivery transaction.
+	max_messages_in_single_batch: MessageNonce,
+	/// Maximal cumulative messages weight in the single delivery transaction.
+	max_messages_weight_in_single_batch: Weight,
+	/// Maximal messages size in the single delivery transaction.
+	max_messages_size_in_single_batch: usize,
+	/// Latest confirmed nonces at the source client + the header id where we have first met this nonce.
+	latest_confirmed_nonces_at_source: VecDeque<(SourceHeaderIdOf<P>, MessageNonce)>,
+	/// Target nonces from the source client.
+	target_nonces: Option<TargetClientNonces<DeliveryRaceTargetNoncesData>>,
+	/// Basic delivery strategy.
+	strategy: MessageDeliveryStrategyBase<P>,
+}
+
+type MessageDeliveryStrategyBase<P> = BasicStrategy<
+	<P as MessageLane>::SourceHeaderNumber,
+	<P as MessageLane>::SourceHeaderHash,
+	<P as MessageLane>::TargetHeaderNumber,
+	<P as MessageLane>::TargetHeaderHash,
+	MessageWeightsMap,
+	<P as MessageLane>::MessagesProof,
+>;
+
+impl<P: MessageLane> std::fmt::Debug for MessageDeliveryStrategy<P> {
+	fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+		fmt.debug_struct("MessageDeliveryStrategy")
+			.field(
+				"max_unrewarded_relayer_entries_at_target",
+				&self.max_unrewarded_relayer_entries_at_target,
+			)
+			.field(
+				"max_unconfirmed_nonces_at_target",
+				&self.max_unconfirmed_nonces_at_target,
+			)
+			.field("max_messages_in_single_batch", &self.max_messages_in_single_batch)
+			.field(
+				"max_messages_weight_in_single_batch",
+				&self.max_messages_weight_in_single_batch,
+			)
+			.field(
+				"max_messages_size_in_single_batch",
+				&self.max_messages_size_in_single_batch,
+			)
+			.field(
+				"latest_confirmed_nonces_at_source",
+				&self.latest_confirmed_nonces_at_source,
+			)
+			.field("target_nonces", &self.target_nonces)
+			.field("strategy", &self.strategy)
+			.finish()
+	}
+}
+
+impl<P: MessageLane> RaceStrategy<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::MessagesProof>
+	for MessageDeliveryStrategy<P>
+{
+	type SourceNoncesRange = MessageWeightsMap;
+	type ProofParameters = MessageProofParameters;
+	type TargetNoncesData = DeliveryRaceTargetNoncesData;
+
+	fn is_empty(&self) -> bool {
+		self.strategy.is_empty()
+	}
+
+	fn required_source_header_at_target(&self, current_best: &SourceHeaderIdOf<P>) -> Option<SourceHeaderIdOf<P>> {
+		self.strategy.required_source_header_at_target(current_best)
+	}
+
+	fn best_at_source(&self) -> Option<MessageNonce> {
+		self.strategy.best_at_source()
+	}
+
+	fn best_at_target(&self) -> Option<MessageNonce> {
+		self.strategy.best_at_target()
+	}
+
+	fn source_nonces_updated(
+		&mut self,
+		at_block: SourceHeaderIdOf<P>,
+		nonces: SourceClientNonces<Self::SourceNoncesRange>,
+	) {
+		if let Some(confirmed_nonce) = nonces.confirmed_nonce {
+			let is_confirmed_nonce_updated = self
+				.latest_confirmed_nonces_at_source
+				.back()
+				.map(|(_, prev_nonce)| *prev_nonce != confirmed_nonce)
+				.unwrap_or(true);
+			if is_confirmed_nonce_updated {
+				self.latest_confirmed_nonces_at_source
+					.push_back((at_block.clone(), confirmed_nonce));
+			}
+		}
+		self.strategy.source_nonces_updated(at_block, nonces)
+	}
+
+	fn best_target_nonces_updated(
+		&mut self,
+		nonces: TargetClientNonces<DeliveryRaceTargetNoncesData>,
+		race_state: &mut RaceState<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::MessagesProof>,
+	) {
+		// best target nonces must always be ge than finalized target nonces
+		let mut target_nonces = self.target_nonces.take().unwrap_or_else(|| nonces.clone());
+		target_nonces.nonces_data = nonces.nonces_data.clone();
+		target_nonces.latest_nonce = std::cmp::max(target_nonces.latest_nonce, nonces.latest_nonce);
+		self.target_nonces = Some(target_nonces);
+
+		self.strategy.best_target_nonces_updated(
+			TargetClientNonces {
+				latest_nonce: nonces.latest_nonce,
+				nonces_data: (),
+			},
+			race_state,
+		)
+	}
+
+	fn finalized_target_nonces_updated(
+		&mut self,
+		nonces: TargetClientNonces<DeliveryRaceTargetNoncesData>,
+		race_state: &mut RaceState<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::MessagesProof>,
+	) {
+		if let Some(ref best_finalized_source_header_id_at_best_target) =
+			race_state.best_finalized_source_header_id_at_best_target
+		{
+			let oldest_header_number_to_keep = best_finalized_source_header_id_at_best_target.0;
+			while self
+				.latest_confirmed_nonces_at_source
+				.front()
+				.map(|(id, _)| id.0 < oldest_header_number_to_keep)
+				.unwrap_or(false)
+			{
+				self.latest_confirmed_nonces_at_source.pop_front();
+			}
+		}
+
+		if let Some(ref mut target_nonces) = self.target_nonces {
+			target_nonces.latest_nonce = std::cmp::max(target_nonces.latest_nonce, nonces.latest_nonce);
+		}
+
+		self.strategy.finalized_target_nonces_updated(
+			TargetClientNonces {
+				latest_nonce: nonces.latest_nonce,
+				nonces_data: (),
+			},
+			race_state,
+		)
+	}
+
+	fn select_nonces_to_deliver(
+		&mut self,
+		race_state: &RaceState<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::MessagesProof>,
+	) -> Option<(RangeInclusive<MessageNonce>, Self::ProofParameters)> {
+		let best_finalized_source_header_id_at_best_target =
+			race_state.best_finalized_source_header_id_at_best_target.clone()?;
+		let latest_confirmed_nonce_at_source = self
+			.latest_confirmed_nonces_at_source
+			.iter()
+			.take_while(|(id, _)| id.0 <= best_finalized_source_header_id_at_best_target.0)
+			.last()
+			.map(|(_, nonce)| *nonce)?;
+		let target_nonces = self.target_nonces.as_ref()?;
+
+		// There's additional condition in the message delivery race: target would reject messages
+		// if there are too much unconfirmed messages at the inbound lane.
+
+		// The receiving race is responsible to deliver confirmations back to the source chain. So if
+		// there's a lot of unconfirmed messages, let's wait until it'll be able to do its job.
+		let latest_received_nonce_at_target = target_nonces.latest_nonce;
+		let confirmations_missing = latest_received_nonce_at_target.checked_sub(latest_confirmed_nonce_at_source);
+		match confirmations_missing {
+			Some(confirmations_missing) if confirmations_missing >= self.max_unconfirmed_nonces_at_target => {
+				log::debug!(
+					target: "bridge",
+					"Cannot deliver any more messages from {} to {}. Too many unconfirmed nonces \
+					at target: target.latest_received={:?}, source.latest_confirmed={:?}, max={:?}",
+					MessageDeliveryRace::<P>::source_name(),
+					MessageDeliveryRace::<P>::target_name(),
+					latest_received_nonce_at_target,
+					latest_confirmed_nonce_at_source,
+					self.max_unconfirmed_nonces_at_target,
+				);
+
+				return None;
+			}
+			_ => (),
+		}
+
+		// Ok - we may have new nonces to deliver. But target may still reject new messages, because we haven't
+		// notified it that (some) messages have been confirmed. So we may want to include updated
+		// `source.latest_confirmed` in the proof.
+		//
+		// Important note: we're including outbound state lane proof whenever there are unconfirmed nonces
+		// on the target chain. Other strategy is to include it only if it's absolutely necessary.
+		let latest_confirmed_nonce_at_target = target_nonces.nonces_data.confirmed_nonce;
+		let outbound_state_proof_required = latest_confirmed_nonce_at_target < latest_confirmed_nonce_at_source;
+
+		// The target node would also reject messages if there are too many entries in the
+		// "unrewarded relayers" set. If we are unable to prove new rewards to the target node, then
+		// we should wait for confirmations race.
+		let unrewarded_relayer_entries_limit_reached =
+			target_nonces.nonces_data.unrewarded_relayers.unrewarded_relayer_entries
+				>= self.max_unrewarded_relayer_entries_at_target;
+		if unrewarded_relayer_entries_limit_reached {
+			// so there are already too many unrewarded relayer entries in the set
+			//
+			// => check if we can prove enough rewards. If not, we should wait for more rewards to be paid
+			let number_of_rewards_being_proved =
+				latest_confirmed_nonce_at_source.saturating_sub(latest_confirmed_nonce_at_target);
+			let enough_rewards_being_proved = number_of_rewards_being_proved
+				>= target_nonces.nonces_data.unrewarded_relayers.messages_in_oldest_entry;
+			if !enough_rewards_being_proved {
+				return None;
+			}
+		}
+
+		// If we're here, then the confirmations race did its job && sending side now knows that messages
+		// have been delivered. Now let's select nonces that we want to deliver.
+		//
+		// We may deliver at most:
+		//
+		// max_unconfirmed_nonces_at_target - (latest_received_nonce_at_target - latest_confirmed_nonce_at_target)
+		//
+		// messages in the batch. But since we're including outbound state proof in the batch, then it
+		// may be increased to:
+		//
+		// max_unconfirmed_nonces_at_target - (latest_received_nonce_at_target - latest_confirmed_nonce_at_source)
+		let future_confirmed_nonce_at_target = if outbound_state_proof_required {
+			latest_confirmed_nonce_at_source
+		} else {
+			latest_confirmed_nonce_at_target
+		};
+		let max_nonces = latest_received_nonce_at_target
+			.checked_sub(future_confirmed_nonce_at_target)
+			.and_then(|diff| self.max_unconfirmed_nonces_at_target.checked_sub(diff))
+			.unwrap_or_default();
+		let max_nonces = std::cmp::min(max_nonces, self.max_messages_in_single_batch);
+		let max_messages_weight_in_single_batch = self.max_messages_weight_in_single_batch;
+		let max_messages_size_in_single_batch = self.max_messages_size_in_single_batch;
+		let mut selected_weight: Weight = 0;
+		let mut selected_size: usize = 0;
+		let mut selected_count: MessageNonce = 0;
+
+		let selected_nonces = self
+			.strategy
+			.select_nonces_to_deliver_with_selector(race_state, |range| {
+				let to_requeue = range
+					.into_iter()
+					.skip_while(|(_, weight)| {
+						// Since we (hopefully) have some reserves in `max_messages_weight_in_single_batch`
+						// and `max_messages_size_in_single_batch`, we may still try to submit transaction
+						// with single message if message overflows these limits. The worst case would be if
+						// transaction will be rejected by the target runtime, but at least we have tried.
+
+						// limit messages in the batch by weight
+						let new_selected_weight = match selected_weight.checked_add(weight.weight) {
+							Some(new_selected_weight) if new_selected_weight <= max_messages_weight_in_single_batch => {
+								new_selected_weight
+							}
+							new_selected_weight if selected_count == 0 => {
+								log::warn!(
+									target: "bridge",
+									"Going to submit message delivery transaction with declared dispatch \
+									weight {:?} that overflows maximal configured weight {}",
+									new_selected_weight,
+									max_messages_weight_in_single_batch,
+								);
+								new_selected_weight.unwrap_or(Weight::MAX)
+							}
+							_ => return false,
+						};
+
+						// limit messages in the batch by size
+						let new_selected_size = match selected_size.checked_add(weight.size) {
+							Some(new_selected_size) if new_selected_size <= max_messages_size_in_single_batch => {
+								new_selected_size
+							}
+							new_selected_size if selected_count == 0 => {
+								log::warn!(
+									target: "bridge",
+									"Going to submit message delivery transaction with message \
+									size {:?} that overflows maximal configured size {}",
+									new_selected_size,
+									max_messages_size_in_single_batch,
+								);
+								new_selected_size.unwrap_or(usize::MAX)
+							}
+							_ => return false,
+						};
+
+						// limit number of messages in the batch
+						let new_selected_count = selected_count + 1;
+						if new_selected_count > max_nonces {
+							return false;
+						}
+
+						selected_weight = new_selected_weight;
+						selected_size = new_selected_size;
+						selected_count = new_selected_count;
+						true
+					})
+					.collect::<BTreeMap<_, _>>();
+				if to_requeue.is_empty() {
+					None
+				} else {
+					Some(to_requeue)
+				}
+			})?;
+
+		Some((
+			selected_nonces,
+			MessageProofParameters {
+				outbound_state_proof_required,
+				dispatch_weight: selected_weight,
+			},
+		))
+	}
+}
+
+impl NoncesRange for MessageWeightsMap {
+	fn begin(&self) -> MessageNonce {
+		self.keys().next().cloned().unwrap_or_default()
+	}
+
+	fn end(&self) -> MessageNonce {
+		self.keys().next_back().cloned().unwrap_or_default()
+	}
+
+	fn greater_than(mut self, nonce: MessageNonce) -> Option<Self> {
+		let gte = self.split_off(&(nonce + 1));
+		if gte.is_empty() {
+			None
+		} else {
+			Some(gte)
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use crate::message_lane_loop::{
+		tests::{header_id, TestMessageLane, TestMessagesProof, TestSourceHeaderId, TestTargetHeaderId},
+		MessageWeights,
+	};
+
+	type TestRaceState = RaceState<TestSourceHeaderId, TestTargetHeaderId, TestMessagesProof>;
+	type TestStrategy = MessageDeliveryStrategy<TestMessageLane>;
+
+	fn prepare_strategy() -> (TestRaceState, TestStrategy) {
+		let mut race_state = RaceState {
+			best_finalized_source_header_id_at_source: Some(header_id(1)),
+			best_finalized_source_header_id_at_best_target: Some(header_id(1)),
+			best_target_header_id: Some(header_id(1)),
+			best_finalized_target_header_id: Some(header_id(1)),
+			nonces_to_submit: None,
+			nonces_submitted: None,
+		};
+
+		let mut race_strategy = TestStrategy {
+			max_unrewarded_relayer_entries_at_target: 4,
+			max_unconfirmed_nonces_at_target: 4,
+			max_messages_in_single_batch: 4,
+			max_messages_weight_in_single_batch: 4,
+			max_messages_size_in_single_batch: 4,
+			latest_confirmed_nonces_at_source: vec![(header_id(1), 19)].into_iter().collect(),
+			target_nonces: Some(TargetClientNonces {
+				latest_nonce: 19,
+				nonces_data: DeliveryRaceTargetNoncesData {
+					confirmed_nonce: 19,
+					unrewarded_relayers: UnrewardedRelayersState {
+						unrewarded_relayer_entries: 0,
+						messages_in_oldest_entry: 0,
+						total_messages: 0,
+					},
+				},
+			}),
+			strategy: BasicStrategy::new(),
+		};
+
+		race_strategy.strategy.source_nonces_updated(
+			header_id(1),
+			SourceClientNonces {
+				new_nonces: vec![
+					(20, MessageWeights { weight: 1, size: 1 }),
+					(21, MessageWeights { weight: 1, size: 1 }),
+					(22, MessageWeights { weight: 1, size: 1 }),
+					(23, MessageWeights { weight: 1, size: 1 }),
+				]
+				.into_iter()
+				.collect(),
+				confirmed_nonce: Some(19),
+			},
+		);
+
+		let target_nonces = TargetClientNonces {
+			latest_nonce: 19,
+			nonces_data: (),
+		};
+		race_strategy
+			.strategy
+			.best_target_nonces_updated(target_nonces.clone(), &mut race_state);
+		race_strategy
+			.strategy
+			.finalized_target_nonces_updated(target_nonces, &mut race_state);
+
+		(race_state, race_strategy)
+	}
+
+	fn proof_parameters(state_required: bool, weight: Weight) -> MessageProofParameters {
+		MessageProofParameters {
+			outbound_state_proof_required: state_required,
+			dispatch_weight: weight,
+		}
+	}
+
+	#[test]
+	fn weights_map_works_as_nonces_range() {
+		fn build_map(range: RangeInclusive<MessageNonce>) -> MessageWeightsMap {
+			range
+				.map(|idx| {
+					(
+						idx,
+						MessageWeights {
+							weight: idx,
+							size: idx as _,
+						},
+					)
+				})
+				.collect()
+		}
+
+		let map = build_map(20..=30);
+
+		assert_eq!(map.begin(), 20);
+		assert_eq!(map.end(), 30);
+		assert_eq!(map.clone().greater_than(10), Some(build_map(20..=30)));
+		assert_eq!(map.clone().greater_than(19), Some(build_map(20..=30)));
+		assert_eq!(map.clone().greater_than(20), Some(build_map(21..=30)));
+		assert_eq!(map.clone().greater_than(25), Some(build_map(26..=30)));
+		assert_eq!(map.clone().greater_than(29), Some(build_map(30..=30)));
+		assert_eq!(map.greater_than(30), None);
+	}
+
+	#[test]
+	fn message_delivery_strategy_selects_messages_to_deliver() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// both sides are ready to relay new messages
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=23), proof_parameters(false, 4)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_selects_nothing_if_too_many_confirmations_missing() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// if there are already `max_unconfirmed_nonces_at_target` messages on target,
+		// we need to wait until confirmations will be delivered by receiving race
+		strategy.latest_confirmed_nonces_at_source = vec![(
+			header_id(1),
+			strategy.target_nonces.as_ref().unwrap().latest_nonce - strategy.max_unconfirmed_nonces_at_target,
+		)]
+		.into_iter()
+		.collect();
+		assert_eq!(strategy.select_nonces_to_deliver(&state), None);
+	}
+
+	#[test]
+	fn message_delivery_strategy_includes_outbound_state_proof_when_new_nonces_are_available() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// if there are new confirmed nonces on source, we want to relay this information
+		// to target to prune rewards queue
+		let prev_confirmed_nonce_at_source = strategy.latest_confirmed_nonces_at_source.back().unwrap().1;
+		strategy.target_nonces.as_mut().unwrap().nonces_data.confirmed_nonce = prev_confirmed_nonce_at_source - 1;
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=23), proof_parameters(true, 4)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_selects_nothing_if_there_are_too_many_unrewarded_relayers() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// if there are already `max_unrewarded_relayer_entries_at_target` entries at target,
+		// we need to wait until rewards will be paid
+		{
+			let mut unrewarded_relayers = &mut strategy.target_nonces.as_mut().unwrap().nonces_data.unrewarded_relayers;
+			unrewarded_relayers.unrewarded_relayer_entries = strategy.max_unrewarded_relayer_entries_at_target;
+			unrewarded_relayers.messages_in_oldest_entry = 4;
+		}
+		assert_eq!(strategy.select_nonces_to_deliver(&state), None);
+	}
+
+	#[test]
+	fn message_delivery_strategy_selects_nothing_if_proved_rewards_is_not_enough_to_remove_oldest_unrewarded_entry() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// if there are already `max_unrewarded_relayer_entries_at_target` entries at target,
+		// we need to prove at least `messages_in_oldest_entry` rewards
+		let prev_confirmed_nonce_at_source = strategy.latest_confirmed_nonces_at_source.back().unwrap().1;
+		{
+			let mut nonces_data = &mut strategy.target_nonces.as_mut().unwrap().nonces_data;
+			nonces_data.confirmed_nonce = prev_confirmed_nonce_at_source - 1;
+			let mut unrewarded_relayers = &mut nonces_data.unrewarded_relayers;
+			unrewarded_relayers.unrewarded_relayer_entries = strategy.max_unrewarded_relayer_entries_at_target;
+			unrewarded_relayers.messages_in_oldest_entry = 4;
+		}
+		assert_eq!(strategy.select_nonces_to_deliver(&state), None);
+	}
+
+	#[test]
+	fn message_delivery_strategy_includes_outbound_state_proof_if_proved_rewards_is_enough() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// if there are already `max_unrewarded_relayer_entries_at_target` entries at target,
+		// we need to prove at least `messages_in_oldest_entry` rewards
+		let prev_confirmed_nonce_at_source = strategy.latest_confirmed_nonces_at_source.back().unwrap().1;
+		{
+			let mut nonces_data = &mut strategy.target_nonces.as_mut().unwrap().nonces_data;
+			nonces_data.confirmed_nonce = prev_confirmed_nonce_at_source - 3;
+			let mut unrewarded_relayers = &mut nonces_data.unrewarded_relayers;
+			unrewarded_relayers.unrewarded_relayer_entries = strategy.max_unrewarded_relayer_entries_at_target;
+			unrewarded_relayers.messages_in_oldest_entry = 3;
+		}
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=23), proof_parameters(true, 4)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_limits_batch_by_messages_weight() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// not all queued messages may fit in the batch, because batch has max weight
+		strategy.max_messages_weight_in_single_batch = 3;
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=22), proof_parameters(false, 3)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_accepts_single_message_even_if_its_weight_overflows_maximal_weight() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// first message doesn't fit in the batch, because it has weight (10) that overflows max weight (4)
+		strategy.strategy.source_queue_mut()[0].1.get_mut(&20).unwrap().weight = 10;
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=20), proof_parameters(false, 10)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_limits_batch_by_messages_size() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// not all queued messages may fit in the batch, because batch has max weight
+		strategy.max_messages_size_in_single_batch = 3;
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=22), proof_parameters(false, 3)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_accepts_single_message_even_if_its_weight_overflows_maximal_size() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// first message doesn't fit in the batch, because it has weight (10) that overflows max weight (4)
+		strategy.strategy.source_queue_mut()[0].1.get_mut(&20).unwrap().size = 10;
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=20), proof_parameters(false, 1)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_limits_batch_by_messages_count_when_there_is_upper_limit() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// not all queued messages may fit in the batch, because batch has max number of messages limit
+		strategy.max_messages_in_single_batch = 3;
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=22), proof_parameters(false, 3)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_limits_batch_by_messages_count_when_there_are_unconfirmed_nonces() {
+		let (state, mut strategy) = prepare_strategy();
+
+		// 1 delivery confirmation from target to source is still missing, so we may only
+		// relay 3 new messages
+		let prev_confirmed_nonce_at_source = strategy.latest_confirmed_nonces_at_source.back().unwrap().1;
+		strategy.latest_confirmed_nonces_at_source = vec![(header_id(1), prev_confirmed_nonce_at_source - 1)]
+			.into_iter()
+			.collect();
+		strategy.target_nonces.as_mut().unwrap().nonces_data.confirmed_nonce = prev_confirmed_nonce_at_source - 1;
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=22), proof_parameters(false, 3)))
+		);
+	}
+
+	#[test]
+	fn message_delivery_strategy_waits_for_confirmed_nonce_header_to_appear_on_target() {
+		// 1 delivery confirmation from target to source is still missing, so we may deliver
+		// reward confirmation with our message delivery transaction. But the problem is that
+		// the reward has been paid at header 2 && this header is still unknown to target node.
+		//
+		// => so we can't deliver more than 3 messages
+		let (mut state, mut strategy) = prepare_strategy();
+		let prev_confirmed_nonce_at_source = strategy.latest_confirmed_nonces_at_source.back().unwrap().1;
+		strategy.latest_confirmed_nonces_at_source = vec![
+			(header_id(1), prev_confirmed_nonce_at_source - 1),
+			(header_id(2), prev_confirmed_nonce_at_source),
+		]
+		.into_iter()
+		.collect();
+		strategy.target_nonces.as_mut().unwrap().nonces_data.confirmed_nonce = prev_confirmed_nonce_at_source - 1;
+		state.best_finalized_source_header_id_at_best_target = Some(header_id(1));
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=22), proof_parameters(false, 3)))
+		);
+
+		// the same situation, but the header 2 is known to the target node, so we may deliver reward confirmation
+		let (mut state, mut strategy) = prepare_strategy();
+		let prev_confirmed_nonce_at_source = strategy.latest_confirmed_nonces_at_source.back().unwrap().1;
+		strategy.latest_confirmed_nonces_at_source = vec![
+			(header_id(1), prev_confirmed_nonce_at_source - 1),
+			(header_id(2), prev_confirmed_nonce_at_source),
+		]
+		.into_iter()
+		.collect();
+		strategy.target_nonces.as_mut().unwrap().nonces_data.confirmed_nonce = prev_confirmed_nonce_at_source - 1;
+		state.best_finalized_source_header_id_at_source = Some(header_id(2));
+		state.best_finalized_source_header_id_at_best_target = Some(header_id(2));
+		assert_eq!(
+			strategy.select_nonces_to_deliver(&state),
+			Some(((20..=23), proof_parameters(true, 4)))
+		);
+	}
+}