Backport: Implement basic equivocations detection loop (#2375)

* Implement basic equivocations detection loop (#2367)

* FinalityProofsBuf adjustments

- store a Vec<FinalityProof>
- transform prune `buf_limit` to Option

* FinalityProof: add target_header_hash()

* Target client: implement best_synced_header_hash()

* Implement first version of the equivocations detection loop

* Address code review comments

* Leftover

* polkadot-staging adjustments

bridges/relays/lib-substrate-relay/src/equivocation/target.rs

@@ -17,14 +17,16 @@
 //! Default generic implementation of equivocation source for basic Substrate client.
 
 use crate::{
-	equivocation::{EquivocationDetectionPipelineAdapter, SubstrateEquivocationDetectionPipeline},
-	finality_base::engine::Engine,
+	equivocation::{
+		EquivocationDetectionPipelineAdapter, FinalityProoffOf, FinalityVerificationContextfOf,
+		SubstrateEquivocationDetectionPipeline,
+	},
+	finality_base::{best_synced_header_id, engine::Engine},
 };
 
-use crate::equivocation::{FinalityProoffOf, FinalityVerificationContextfOf};
 use async_trait::async_trait;
 use bp_header_chain::HeaderFinalityInfo;
-use bp_runtime::BlockNumberOf;
+use bp_runtime::{BlockNumberOf, HashOf};
 use equivocation_detector::TargetClient;
 use relay_substrate_client::{Client, Error};
 use relay_utils::relay_loop::Client as RelayClient;
@@ -59,6 +61,24 @@ impl<P: SubstrateEquivocationDetectionPipeline> RelayClient for SubstrateEquivoc
 impl<P: SubstrateEquivocationDetectionPipeline>
 	TargetClient<EquivocationDetectionPipelineAdapter<P>> for SubstrateEquivocationTarget<P>
 {
+	async fn best_finalized_header_number(
+		&self,
+	) -> Result<BlockNumberOf<P::TargetChain>, Self::Error> {
+		self.client.best_finalized_header_number().await
+	}
+
+	async fn best_synced_header_hash(
+		&self,
+		at: BlockNumberOf<P::TargetChain>,
+	) -> Result<Option<HashOf<P::SourceChain>>, Self::Error> {
+		Ok(best_synced_header_id::<P::SourceChain, P::TargetChain>(
+			&self.client,
+			self.client.header_by_number(at).await?.hash(),
+		)
+		.await?
+		.map(|id| id.hash()))
+	}
+
 	async fn finality_verification_context(
 		&self,
 		at: BlockNumberOf<P::TargetChain>,

bridges/relays/lib-substrate-relay/src/finality/target.rs

@@ -20,7 +20,7 @@ use crate::{
 	finality::{
 		FinalitySyncPipelineAdapter, SubmitFinalityProofCallBuilder, SubstrateFinalitySyncPipeline,
 	},
-	finality_base::{engine::Engine, SubstrateFinalityProof},
+	finality_base::{best_synced_header_id, engine::Engine, SubstrateFinalityProof},
 	TransactionParams,
 };
 
@@ -31,6 +31,7 @@ use relay_substrate_client::{
 	TransactionTracker, UnsignedTransaction,
 };
 use relay_utils::relay_loop::Client as RelayClient;
+use sp_runtime::traits::Header;
 
 /// Substrate client as Substrate finality target.
 pub struct SubstrateFinalityTarget<P: SubstrateFinalitySyncPipeline> {
@@ -94,12 +95,11 @@ impl<P: SubstrateFinalitySyncPipeline> TargetClient<FinalitySyncPipelineAdapter<
 		// we can't relay finality if bridge pallet at target chain is halted
 		self.ensure_pallet_active().await?;
 
-		Ok(crate::messages_source::read_client_state::<P::TargetChain, P::SourceChain>(
+		Ok(best_synced_header_id::<P::SourceChain, P::TargetChain>(
 			&self.client,
-			None,
+			self.client.best_header().await?.hash(),
 		)
 		.await?
-		.best_finalized_peer_at_best_self
 		.ok_or(Error::BridgePalletIsNotInitialized)?)
 	}
 

bridges/relays/lib-substrate-relay/src/finality_base/engine.rs

@@ -36,7 +36,7 @@ use relay_substrate_client::{
 use sp_consensus_grandpa::{AuthorityList as GrandpaAuthoritiesSet, GRANDPA_ENGINE_ID};
 use sp_core::{storage::StorageKey, Bytes};
 use sp_runtime::{scale_info::TypeInfo, traits::Header, ConsensusEngineId};
-use std::marker::PhantomData;
+use std::{fmt::Debug, marker::PhantomData};
 
 /// Finality engine, used by the Substrate chain.
 #[async_trait]
@@ -48,11 +48,11 @@ pub trait Engine<C: Chain>: Send {
 	/// Type of Finality RPC client used by this engine.
 	type FinalityClient: SubstrateFinalityClient<C>;
 	/// Type of finality proofs, used by consensus engine.
-	type FinalityProof: FinalityProof<BlockNumberOf<C>> + Decode + Encode;
+	type FinalityProof: FinalityProof<HashOf<C>, BlockNumberOf<C>> + Decode + Encode;
 	/// The context needed for verifying finality proofs.
-	type FinalityVerificationContext;
+	type FinalityVerificationContext: Send;
 	/// The type of the equivocation proof used by the consensus engine.
-	type EquivocationProof: Send + Sync;
+	type EquivocationProof: Clone + Debug + Send + Sync;
 	/// The equivocations finder.
 	type EquivocationsFinder: FindEquivocations<
 		Self::FinalityProof,
@@ -62,7 +62,7 @@ pub trait Engine<C: Chain>: Send {
 	/// The type of the key owner proof used by the consensus engine.
 	type KeyOwnerProof: Send;
 	/// Type of bridge pallet initialization data.
-	type InitializationData: std::fmt::Debug + Send + Sync + 'static;
+	type InitializationData: Debug + Send + Sync + 'static;
 	/// Type of bridge pallet operating mode.
 	type OperatingMode: OperatingMode + 'static;
 

bridges/relays/lib-substrate-relay/src/finality_base/mod.rs

@@ -20,7 +20,9 @@
 pub mod engine;
 
 use crate::finality_base::engine::Engine;
+
 use async_trait::async_trait;
+use bp_runtime::{HashOf, HeaderIdOf};
 use codec::Decode;
 use futures::{stream::unfold, Stream, StreamExt};
 use relay_substrate_client::{Chain, Client, Error};
@@ -85,3 +87,21 @@ pub async fn finality_proofs<P: SubstrateFinalityPipeline>(
 	)
 	.boxed())
 }
+
+/// Get the id of the best `SourceChain` header known to the `TargetChain` at the provided
+/// target block using the exposed runtime API method.
+///
+/// The runtime API method should be `<TargetChain>FinalityApi::best_finalized()`.
+pub async fn best_synced_header_id<SourceChain, TargetChain>(
+	target_client: &Client<TargetChain>,
+	at: HashOf<TargetChain>,
+) -> Result<Option<HeaderIdOf<SourceChain>>, Error>
+where
+	SourceChain: Chain,
+	TargetChain: Chain,
+{
+	// now let's read id of best finalized peer header at our best finalized block
+	target_client
+		.typed_state_call(SourceChain::BEST_FINALIZED_HEADER_ID_METHOD.into(), (), Some(at))
+		.await
+}

bridges/relays/lib-substrate-relay/src/messages_source.rs

@@ -19,6 +19,7 @@
 //! `<BridgedName>` chain.
 
 use crate::{
+	finality_base::best_synced_header_id,
 	messages_lane::{
 		BatchProofTransaction, MessageLaneAdapter, ReceiveMessagesDeliveryProofCallBuilder,
 		SubstrateMessageLane,
@@ -428,11 +429,7 @@ where
 
 	// now let's read id of best finalized peer header at our best finalized block
 	let peer_on_self_best_finalized_id =
-		best_finalized_peer_header_at_self::<SelfChain, PeerChain>(
-			self_client,
-			self_best_id.hash(),
-		)
-		.await?;
+		best_synced_header_id::<PeerChain, SelfChain>(self_client, self_best_id.hash()).await?;
 
 	// read actual header, matching the `peer_on_self_best_finalized_id` from the peer chain
 	let actual_peer_on_self_best_finalized_id =