Relay receiving + processing confirmations (#351)

* relay receiving + processing confirmations

* fmt && clippy

* removed message processing race

* remove more traces

* generic args names

bridges/relays/ethereum/src/main.rs

@@ -31,6 +31,7 @@ mod message_lane;
 mod message_lane_loop;
 mod message_race_delivery;
 mod message_race_loop;
+mod message_race_receiving;
 mod metrics;
 mod rpc;
 mod rpc_errors;

bridges/relays/ethereum/src/message_lane.rs

@@ -17,11 +17,11 @@
 //! One-way message lane types. Within single one-way lane we have three 'races' where we try to:
 //!
 //! 1) relay new messages from source to target node;
-//! 2) relay proof-of-receiving from target to source node;
+//! 2) relay proof-of-receiving from target to source node.
-//! 3) relay proof-of-processing from target no source node.
 
 use crate::utils::HeaderId;
 
+use num_traits::{One, Zero};
 use std::fmt::Debug;
 
 /// One-way message lane.
@@ -32,10 +32,20 @@ pub trait MessageLane {
 	const TARGET_NAME: &'static str;
 
 	/// Message nonce type.
-	type MessageNonce: Clone + Copy + Debug + Default + From<u32> + Ord + std::ops::Add<Output = Self::MessageNonce>;
+	type MessageNonce: Clone
+		+ Copy
+		+ Debug
+		+ Default
+		+ From<u32>
+		+ Ord
+		+ std::ops::Add<Output = Self::MessageNonce>
+		+ One
+		+ Zero;
 
 	/// Messages proof.
 	type MessagesProof: Clone;
+	/// Messages receiving proof.
+	type MessagesReceivingProof: Clone;
 
 	/// Number of the source header.
 	type SourceHeaderNumber: Clone + Debug + Default + Ord + PartialEq;

bridges/relays/ethereum/src/message_lane_loop.rs

@@ -29,6 +29,7 @@
 
 use crate::message_lane::{MessageLane, SourceHeaderIdOf, TargetHeaderIdOf};
 use crate::message_race_delivery::run as run_message_delivery_race;
+use crate::message_race_receiving::run as run_message_receiving_race;
 use crate::utils::{interval, process_future_result, retry_backoff, FailedClient, MaybeConnectionError};
 
 use async_trait::async_trait;
@@ -52,6 +53,11 @@ pub trait SourceClient<P: MessageLane>: Clone {
 		&self,
 		id: SourceHeaderIdOf<P>,
 	) -> Result<(SourceHeaderIdOf<P>, P::MessageNonce), Self::Error>;
+	/// Get nonce of the latest message, which receiving has been confirmed by the target chain.
+	async fn latest_confirmed_received_nonce(
+		&self,
+		id: SourceHeaderIdOf<P>,
+	) -> Result<(SourceHeaderIdOf<P>, P::MessageNonce), Self::Error>;
 
 	/// Prove messages in inclusive range [begin; end].
 	async fn prove_messages(
@@ -59,6 +65,13 @@ pub trait SourceClient<P: MessageLane>: Clone {
 		id: SourceHeaderIdOf<P>,
 		nonces: RangeInclusive<P::MessageNonce>,
 	) -> Result<(SourceHeaderIdOf<P>, RangeInclusive<P::MessageNonce>, P::MessagesProof), Self::Error>;
+
+	/// Submit messages receiving proof.
+	async fn submit_messages_receiving_proof(
+		&self,
+		generated_at_block: TargetHeaderIdOf<P>,
+		proof: P::MessagesReceivingProof,
+	) -> Result<RangeInclusive<P::MessageNonce>, Self::Error>;
 }
 
 /// Target client trait.
@@ -73,12 +86,18 @@ pub trait TargetClient<P: MessageLane>: Clone {
 	/// Returns state of the client.
 	async fn state(&self) -> Result<TargetClientState<P>, Self::Error>;
 
-	/// Get nonce of latest message, which receival has been confirmed.
+	/// Get nonce of latest received message.
 	async fn latest_received_nonce(
 		&self,
 		id: TargetHeaderIdOf<P>,
 	) -> Result<(TargetHeaderIdOf<P>, P::MessageNonce), Self::Error>;
 
+	/// Prove messages receiving at given block.
+	async fn prove_messages_receiving(
+		&self,
+		id: TargetHeaderIdOf<P>,
+	) -> Result<(TargetHeaderIdOf<P>, P::MessagesReceivingProof), Self::Error>;
+
 	/// Submit messages proof.
 	async fn submit_messages_proof(
 		&self,
@@ -196,6 +215,19 @@ async fn run_until_connection_lost<P: MessageLane, SC: SourceClient<P>, TC: Targ
 	)
 	.fuse();
 
+	let (
+		(receiving_source_state_sender, receiving_source_state_receiver),
+		(receiving_target_state_sender, receiving_target_state_receiver),
+	) = (unbounded(), unbounded());
+	let receiving_race_loop = run_message_receiving_race(
+		source_client.clone(),
+		receiving_source_state_receiver,
+		target_client.clone(),
+		receiving_target_state_receiver,
+		stall_timeout,
+	)
+	.fuse();
+
 	let exit_signal = exit_signal.fuse();
 
 	futures::pin_mut!(
@@ -206,6 +238,7 @@ async fn run_until_connection_lost<P: MessageLane, SC: SourceClient<P>, TC: Targ
 		target_go_offline_future,
 		target_tick_stream,
 		delivery_race_loop,
+		receiving_race_loop,
 		exit_signal
 	);
 
@@ -224,7 +257,8 @@ async fn run_until_connection_lost<P: MessageLane, SC: SourceClient<P>, TC: Targ
 							P::SOURCE_NAME,
 							new_source_state,
 						);
-						let _ = delivery_source_state_sender.unbounded_send(new_source_state);
+						let _ = delivery_source_state_sender.unbounded_send(new_source_state.clone());
+						let _ = receiving_source_state_sender.unbounded_send(new_source_state.clone());
 					},
 					&mut source_go_offline_future,
 					|delay| async_std::task::sleep(delay),
@@ -250,7 +284,8 @@ async fn run_until_connection_lost<P: MessageLane, SC: SourceClient<P>, TC: Targ
 							P::TARGET_NAME,
 							new_target_state,
 						);
-						let _ = delivery_target_state_sender.unbounded_send(new_target_state);
+						let _ = delivery_target_state_sender.unbounded_send(new_target_state.clone());
+						let _ = receiving_target_state_sender.unbounded_send(new_target_state.clone());
 					},
 					&mut target_go_offline_future,
 					|delay| async_std::task::sleep(delay),
@@ -270,6 +305,12 @@ async fn run_until_connection_lost<P: MessageLane, SC: SourceClient<P>, TC: Targ
 					Err(err) => return Err(err),
 				}
 			},
+			receiving_error = receiving_race_loop => {
+				match receiving_error {
+					Ok(_) => unreachable!("only ends with error; qed"),
+					Err(err) => return Err(err),
+				}
+			},
 
 			() = exit_signal => {
 				return Ok(());
@@ -304,6 +345,7 @@ pub(crate) mod tests {
 
 	pub type TestMessageNonce = u64;
 	pub type TestMessagesProof = RangeInclusive<TestMessageNonce>;
+	pub type TestMessagesReceivingProof = TestMessageNonce;
 
 	pub type TestSourceHeaderNumber = u64;
 	pub type TestSourceHeaderHash = u64;
@@ -333,7 +375,9 @@ pub(crate) mod tests {
 		const TARGET_NAME: &'static str = "TestTarget";
 
 		type MessageNonce = TestMessageNonce;
+
 		type MessagesProof = TestMessagesProof;
+		type MessagesReceivingProof = TestMessagesReceivingProof;
 
 		type SourceHeaderNumber = TestSourceHeaderNumber;
 		type SourceHeaderHash = TestSourceHeaderHash;
@@ -348,6 +392,8 @@ pub(crate) mod tests {
 		is_source_reconnected: bool,
 		source_state: SourceClientState<TestMessageLane>,
 		source_latest_generated_nonce: TestMessageNonce,
+		source_latest_confirmed_received_nonce: TestMessageNonce,
+		submitted_messages_receiving_proofs: Vec<TestMessagesReceivingProof>,
 		is_target_fails: bool,
 		is_target_reconnected: bool,
 		target_state: SourceClientState<TestMessageLane>,
@@ -383,7 +429,6 @@ pub(crate) mod tests {
 			Ok(data.source_state.clone())
 		}
 
-		/// Get nonce of instance of latest generated message.
 		async fn latest_generated_nonce(
 			&self,
 			id: SourceHeaderIdOf<TestMessageLane>,
@@ -396,6 +441,15 @@ pub(crate) mod tests {
 			Ok((id, data.source_latest_generated_nonce))
 		}
 
+		async fn latest_confirmed_received_nonce(
+			&self,
+			id: SourceHeaderIdOf<TestMessageLane>,
+		) -> Result<(SourceHeaderIdOf<TestMessageLane>, TestMessageNonce), Self::Error> {
+			let mut data = self.data.lock();
+			(self.tick)(&mut *data);
+			Ok((id, data.source_latest_confirmed_received_nonce))
+		}
+
 		async fn prove_messages(
 			&self,
 			id: SourceHeaderIdOf<TestMessageLane>,
@@ -410,6 +464,18 @@ pub(crate) mod tests {
 		> {
 			Ok((id, nonces.clone(), nonces))
 		}
+
+		async fn submit_messages_receiving_proof(
+			&self,
+			_generated_at_block: TargetHeaderIdOf<TestMessageLane>,
+			proof: TestMessagesReceivingProof,
+		) -> Result<RangeInclusive<TestMessageNonce>, Self::Error> {
+			let mut data = self.data.lock();
+			(self.tick)(&mut *data);
+			data.submitted_messages_receiving_proofs.push(proof);
+			data.source_latest_confirmed_received_nonce = proof;
+			Ok(proof..=proof)
+		}
 	}
 
 	#[derive(Clone)]
@@ -452,7 +518,13 @@ pub(crate) mod tests {
 			Ok((id, data.target_latest_received_nonce))
 		}
 
-		/// Submit messages proof.
+		async fn prove_messages_receiving(
+			&self,
+			id: TargetHeaderIdOf<TestMessageLane>,
+		) -> Result<(TargetHeaderIdOf<TestMessageLane>, TestMessagesReceivingProof), Self::Error> {
+			Ok((id, self.data.lock().target_latest_received_nonce))
+		}
+
 		async fn submit_messages_proof(
 			&self,
 			_generated_at_header: SourceHeaderIdOf<TestMessageLane>,
@@ -570,16 +642,22 @@ pub(crate) mod tests {
 			},
 			Arc::new(|_: &mut TestClientData| {}),
 			Arc::new(move |data: &mut TestClientData| {
-				if data.target_state.best_peer.0 < 10 {
+				// syncing source headers -> target chain (by one)
+				if data.target_state.best_peer.0 < data.source_state.best_self.0 {
 					data.target_state.best_peer =
 						HeaderId(data.target_state.best_peer.0 + 1, data.target_state.best_peer.0 + 1);
 				}
-				if data
+				// syncing source headers -> target chain (all at once)
-					.submitted_messages_proofs
+				if data.source_state.best_peer.0 < data.target_state.best_self.0 {
-					.last()
+					data.source_state.best_peer = data.target_state.best_self;
-					.map(|last| *last.end() == 10)
+				}
-					.unwrap_or(false)
+				// if target has received all messages => increase target block so that confirmations may be sent
-				{
+				if data.target_latest_received_nonce == 10 {
+					data.target_state.best_self =
+						HeaderId(data.source_state.best_self.0 + 1, data.source_state.best_self.0 + 1);
+				}
+				// if source has received all messages receiving confirmations => increase source block so that confirmations may be sent
+				if data.source_latest_confirmed_received_nonce == 10 {
 					exit_sender.unbounded_send(()).unwrap();
 				}
 			}),
@@ -587,5 +665,6 @@ pub(crate) mod tests {
 		);
 
 		assert_eq!(result.submitted_messages_proofs, vec![1..=4, 5..=8, 9..=10],);
+		assert!(!result.submitted_messages_receiving_proofs.is_empty());
 	}
 }

bridges/relays/ethereum/src/message_race_delivery.rs

@@ -19,10 +19,11 @@ use crate::message_lane_loop::{
 	TargetClientState,
 };
 use crate::message_race_loop::{MessageRace, RaceState, RaceStrategy, SourceClient, TargetClient};
-use crate::utils::FailedClient;
+use crate::utils::{FailedClient, HeaderId};
 
 use async_trait::async_trait;
 use futures::stream::FusedStream;
+use num_traits::{One, Zero};
 use std::{collections::VecDeque, marker::PhantomData, ops::RangeInclusive, time::Duration};
 
 /// Maximal number of messages to relay in single transaction.
@@ -48,7 +49,7 @@ pub async fn run<P: MessageLane>(
 		},
 		target_state_updates,
 		stall_timeout,
-		MessageDeliveryStrategy::<P>::default(),
+		MessageDeliveryStrategy::<P>::new(MAX_MESSAGES_TO_RELAY_IN_SINGLE_TX.into()),
 	)
 	.await
 }
@@ -135,34 +136,60 @@ where
 	}
 }
 
-/// Message delivery strategy.
+/// Messages delivery strategy.
-struct MessageDeliveryStrategy<P: MessageLane> {
+type MessageDeliveryStrategy<P> = DeliveryStrategy<
+	<P as MessageLane>::SourceHeaderNumber,
+	<P as MessageLane>::SourceHeaderHash,
+	<P as MessageLane>::TargetHeaderNumber,
+	<P as MessageLane>::TargetHeaderHash,
+	<P as MessageLane>::MessageNonce,
+	<P as MessageLane>::MessagesProof,
+>;
+
+/// Nonces delivery strategy.
+#[derive(Debug)]
+pub struct DeliveryStrategy<SourceHeaderNumber, SourceHeaderHash, TargetHeaderNumber, TargetHeaderHash, Nonce, Proof> {
 	/// All queued nonces.
-	source_queue: VecDeque<(SourceHeaderIdOf<P>, P::MessageNonce)>,
+	source_queue: VecDeque<(HeaderId<SourceHeaderHash, SourceHeaderNumber>, Nonce)>,
 	/// Best nonce known to target node.
-	target_nonce: P::MessageNonce,
+	target_nonce: Nonce,
+	/// Max nonces to relay in single transaction.
+	max_nonces_to_relay_in_single_tx: Nonce,
 	/// Unused generic types dump.
-	_phantom: PhantomData<P>,
+	_phantom: PhantomData<(TargetHeaderNumber, TargetHeaderHash, Proof)>,
 }
 
-impl<P: MessageLane> Default for MessageDeliveryStrategy<P> {
+impl<SourceHeaderNumber, SourceHeaderHash, TargetHeaderNumber, TargetHeaderHash, Nonce: Default, Proof>
-	fn default() -> Self {
+	DeliveryStrategy<SourceHeaderNumber, SourceHeaderHash, TargetHeaderNumber, TargetHeaderHash, Nonce, Proof>
-		MessageDeliveryStrategy {
+{
+	/// Create new delivery strategy.
+	pub fn new(max_nonces_to_relay_in_single_tx: Nonce) -> Self {
+		DeliveryStrategy {
 			source_queue: VecDeque::new(),
 			target_nonce: Default::default(),
+			max_nonces_to_relay_in_single_tx,
 			_phantom: Default::default(),
 		}
 	}
 }
 
-impl<P: MessageLane> RaceStrategy<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::MessageNonce, P::MessagesProof>
+impl<SourceHeaderNumber, SourceHeaderHash, TargetHeaderNumber, TargetHeaderHash, Nonce, Proof>
-	for MessageDeliveryStrategy<P>
+	RaceStrategy<
+		HeaderId<SourceHeaderHash, SourceHeaderNumber>,
+		HeaderId<TargetHeaderHash, TargetHeaderNumber>,
+		Nonce,
+		Proof,
+	> for DeliveryStrategy<SourceHeaderNumber, SourceHeaderHash, TargetHeaderNumber, TargetHeaderHash, Nonce, Proof>
+where
+	SourceHeaderHash: Clone,
+	SourceHeaderNumber: Clone + Ord,
+	Nonce: Clone + Copy + From<u32> + Ord + std::ops::Add<Output = Nonce> + One + Zero,
 {
 	fn is_empty(&self) -> bool {
 		self.source_queue.is_empty()
 	}
 
-	fn source_nonce_updated(&mut self, at_block: SourceHeaderIdOf<P>, nonce: P::MessageNonce) {
+	fn source_nonce_updated(&mut self, at_block: HeaderId<SourceHeaderHash, SourceHeaderNumber>, nonce: Nonce) {
 		if nonce <= self.target_nonce {
 			return;
 		}
@@ -178,8 +205,13 @@ impl<P: MessageLane> RaceStrategy<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::M
 
 	fn target_nonce_updated(
 		&mut self,
-		nonce: P::MessageNonce,
+		nonce: Nonce,
-		race_state: &mut RaceState<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::MessageNonce, P::MessagesProof>,
+		race_state: &mut RaceState<
+			HeaderId<SourceHeaderHash, SourceHeaderNumber>,
+			HeaderId<TargetHeaderHash, TargetHeaderNumber>,
+			Nonce,
+			Proof,
+		>,
 	) {
 		if nonce < self.target_nonce {
 			return;
@@ -216,8 +248,13 @@ impl<P: MessageLane> RaceStrategy<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::M
 
 	fn select_nonces_to_deliver(
 		&mut self,
-		race_state: &RaceState<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::MessageNonce, P::MessagesProof>,
+		race_state: &RaceState<
-	) -> Option<RangeInclusive<P::MessageNonce>> {
+			HeaderId<SourceHeaderHash, SourceHeaderNumber>,
+			HeaderId<TargetHeaderHash, TargetHeaderNumber>,
+			Nonce,
+			Proof,
+		>,
+	) -> Option<RangeInclusive<Nonce>> {
 		// if we have already selected nonces that we want to submit, do nothing
 		if race_state.nonces_to_submit.is_some() {
 			return None;
@@ -229,18 +266,19 @@ impl<P: MessageLane> RaceStrategy<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::M
 		}
 
 		// 1) we want to deliver all nonces, starting from `target_nonce + 1`
-		// 2) we want to deliver at most `MAX_MESSAGES_TO_RELAY_IN_SINGLE_TX` nonces in this batch
+		// 2) we want to deliver at most `self.max_nonces_to_relay_in_single_tx` nonces in this batch
 		// 3) we can't deliver new nonce until header, that has emitted this nonce, is finalized
 		// by target client
 		let nonces_begin = self.target_nonce + 1.into();
 		let best_header_at_target = &race_state.target_state.as_ref()?.best_peer;
 		let mut nonces_end = None;
-		for i in 0..MAX_MESSAGES_TO_RELAY_IN_SINGLE_TX {
+		let mut i = Zero::zero();
-			let nonce = nonces_begin + i.into();
+		while i < self.max_nonces_to_relay_in_single_tx {
+			let nonce = nonces_begin + i;
 
 			// if queue is empty, we don't need to prove anything
 			let (first_queued_at, first_queued_nonce) = match self.source_queue.front() {
-				Some((first_queued_at, first_queued_nonce)) => (first_queued_at.clone(), *first_queued_nonce),
+				Some((first_queued_at, first_queued_nonce)) => ((*first_queued_at).clone(), *first_queued_nonce),
 				None => break,
 			};
 
@@ -257,6 +295,8 @@ impl<P: MessageLane> RaceStrategy<SourceHeaderIdOf<P>, TargetHeaderIdOf<P>, P::M
 			if nonce == first_queued_nonce {
 				self.source_queue.pop_front();
 			}
+
+			i = i + One::one();
 		}
 
 		nonces_end.map(|nonces_end| RangeInclusive::new(nonces_begin, nonces_end))
@@ -273,7 +313,7 @@ mod tests {
 
 	#[test]
 	fn strategy_is_empty_works() {
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		assert_eq!(strategy.is_empty(), true);
 		strategy.source_nonce_updated(header_id(1), 1);
 		assert_eq!(strategy.is_empty(), false);
@@ -281,7 +321,7 @@ mod tests {
 
 	#[test]
 	fn source_nonce_is_never_lower_than_known_target_nonce() {
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		strategy.target_nonce_updated(10, &mut Default::default());
 		strategy.source_nonce_updated(header_id(1), 5);
 		assert_eq!(strategy.source_queue, vec![]);
@@ -289,7 +329,7 @@ mod tests {
 
 	#[test]
 	fn source_nonce_is_never_lower_than_latest_known_source_nonce() {
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		strategy.source_nonce_updated(header_id(1), 5);
 		strategy.source_nonce_updated(header_id(2), 3);
 		strategy.source_nonce_updated(header_id(2), 5);
@@ -298,7 +338,7 @@ mod tests {
 
 	#[test]
 	fn target_nonce_is_never_lower_than_latest_known_target_nonce() {
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		strategy.target_nonce_updated(10, &mut Default::default());
 		strategy.target_nonce_updated(5, &mut Default::default());
 		assert_eq!(strategy.target_nonce, 10);
@@ -306,7 +346,7 @@ mod tests {
 
 	#[test]
 	fn updated_target_nonce_removes_queued_entries() {
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		strategy.source_nonce_updated(header_id(1), 5);
 		strategy.source_nonce_updated(header_id(2), 10);
 		strategy.source_nonce_updated(header_id(3), 15);
@@ -318,7 +358,7 @@ mod tests {
 	#[test]
 	fn selected_nonces_are_dropped_on_target_nonce_update() {
 		let mut state = RaceState::default();
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		state.nonces_to_submit = Some((header_id(1), 5..=10, 5..=10));
 		strategy.target_nonce_updated(7, &mut state);
 		assert!(state.nonces_to_submit.is_some());
@@ -329,7 +369,7 @@ mod tests {
 	#[test]
 	fn submitted_nonces_are_dropped_on_target_nonce_update() {
 		let mut state = RaceState::default();
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		state.nonces_submitted = Some(5..=10);
 		strategy.target_nonce_updated(7, &mut state);
 		assert!(state.nonces_submitted.is_some());
@@ -340,7 +380,7 @@ mod tests {
 	#[test]
 	fn nothing_is_selected_if_something_is_already_selected() {
 		let mut state = RaceState::default();
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		state.nonces_to_submit = Some((header_id(1), 1..=10, 1..=10));
 		strategy.source_nonce_updated(header_id(1), 10);
 		assert_eq!(strategy.select_nonces_to_deliver(&state), None);
@@ -349,7 +389,7 @@ mod tests {
 	#[test]
 	fn nothing_is_selected_if_something_is_already_submitted() {
 		let mut state = RaceState::default();
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		state.nonces_submitted = Some(1..=10);
 		strategy.source_nonce_updated(header_id(1), 10);
 		assert_eq!(strategy.select_nonces_to_deliver(&state), None);
@@ -358,7 +398,7 @@ mod tests {
 	#[test]
 	fn select_nonces_to_deliver_works() {
 		let mut state = RaceState::<_, _, TestMessageNonce, TestMessagesProof>::default();
-		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::default();
+		let mut strategy = MessageDeliveryStrategy::<TestMessageLane>::new(4);
 		strategy.source_nonce_updated(header_id(1), 1);
 		strategy.source_nonce_updated(header_id(2), 2);
 		strategy.source_nonce_updated(header_id(3), 6);

bridges/relays/ethereum/src/message_race_receiving.rs

@@ -0,0 +1,152 @@
+// Copyright 2019-2020 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.
+
+use crate::message_lane::{MessageLane, SourceHeaderIdOf, TargetHeaderIdOf};
+use crate::message_lane_loop::{
+	SourceClient as MessageLaneSourceClient, SourceClientState, TargetClient as MessageLaneTargetClient,
+	TargetClientState,
+};
+use crate::message_race_delivery::DeliveryStrategy;
+use crate::message_race_loop::{MessageRace, SourceClient, TargetClient};
+use crate::utils::FailedClient;
+
+use async_trait::async_trait;
+use futures::stream::FusedStream;
+use std::{marker::PhantomData, ops::RangeInclusive, time::Duration};
+
+/// Message receiving confirmations delivery strategy.
+type ReceivingConfirmationsDeliveryStrategy<P> = DeliveryStrategy<
+	<P as MessageLane>::TargetHeaderNumber,
+	<P as MessageLane>::TargetHeaderHash,
+	<P as MessageLane>::SourceHeaderNumber,
+	<P as MessageLane>::SourceHeaderHash,
+	<P as MessageLane>::MessageNonce,
+	<P as MessageLane>::MessagesReceivingProof,
+>;
+
+/// Run receiving confirmations 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,
+) -> Result<(), FailedClient> {
+	crate::message_race_loop::run(
+		ReceivingConfirmationsRaceSource {
+			client: target_client,
+			_phantom: Default::default(),
+		},
+		target_state_updates,
+		ReceivingConfirmationsRaceTarget {
+			client: source_client,
+			_phantom: Default::default(),
+		},
+		source_state_updates,
+		stall_timeout,
+		ReceivingConfirmationsDeliveryStrategy::<P>::new(std::u32::MAX.into()),
+	)
+	.await
+}
+
+/// Messages receiving confirmations race.
+struct ReceivingConfirmationsRace<P>(std::marker::PhantomData<P>);
+
+impl<P: MessageLane> MessageRace for ReceivingConfirmationsRace<P> {
+	type SourceHeaderId = TargetHeaderIdOf<P>;
+	type TargetHeaderId = SourceHeaderIdOf<P>;
+
+	type MessageNonce = P::MessageNonce;
+	type Proof = P::MessagesReceivingProof;
+
+	fn source_name() -> String {
+		format!("{}::ReceivingConfirmationsDelivery", P::SOURCE_NAME)
+	}
+
+	fn target_name() -> String {
+		format!("{}::ReceivingConfirmationsDelivery", P::TARGET_NAME)
+	}
+}
+
+/// Message receiving confirmations race source, which is a target of the lane.
+struct ReceivingConfirmationsRaceSource<P: MessageLane, C> {
+	client: C,
+	_phantom: PhantomData<P>,
+}
+
+#[async_trait(?Send)]
+impl<P, C> SourceClient<ReceivingConfirmationsRace<P>> for ReceivingConfirmationsRaceSource<P, C>
+where
+	P: MessageLane,
+	C: MessageLaneTargetClient<P>,
+{
+	type Error = C::Error;
+
+	async fn latest_nonce(
+		&self,
+		at_block: TargetHeaderIdOf<P>,
+	) -> Result<(TargetHeaderIdOf<P>, P::MessageNonce), Self::Error> {
+		self.client.latest_received_nonce(at_block).await
+	}
+
+	async fn generate_proof(
+		&self,
+		at_block: TargetHeaderIdOf<P>,
+		nonces: RangeInclusive<P::MessageNonce>,
+	) -> Result<
+		(
+			TargetHeaderIdOf<P>,
+			RangeInclusive<P::MessageNonce>,
+			P::MessagesReceivingProof,
+		),
+		Self::Error,
+	> {
+		self.client
+			.prove_messages_receiving(at_block)
+			.await
+			.map(|(at_block, proof)| (at_block, nonces, proof))
+	}
+}
+
+/// Message receiving confirmations race target, which is a source of the lane.
+struct ReceivingConfirmationsRaceTarget<P: MessageLane, C> {
+	client: C,
+	_phantom: PhantomData<P>,
+}
+
+#[async_trait(?Send)]
+impl<P, C> TargetClient<ReceivingConfirmationsRace<P>> for ReceivingConfirmationsRaceTarget<P, C>
+where
+	P: MessageLane,
+	C: MessageLaneSourceClient<P>,
+{
+	type Error = C::Error;
+
+	async fn latest_nonce(
+		&self,
+		at_block: SourceHeaderIdOf<P>,
+	) -> Result<(SourceHeaderIdOf<P>, P::MessageNonce), Self::Error> {
+		self.client.latest_confirmed_received_nonce(at_block).await
+	}
+
+	async fn submit_proof(
+		&self,
+		generated_at_block: TargetHeaderIdOf<P>,
+		_nonces: RangeInclusive<P::MessageNonce>,
+		proof: P::MessagesReceivingProof,
+	) -> Result<RangeInclusive<P::MessageNonce>, Self::Error> {
+		self.client
+			.submit_messages_receiving_proof(generated_at_block, proof)
+			.await
+	}
+}