Add equivocation detector crate and implement clients (#2348) (#2353)

* Split FinalitySyncPipeline and SourceClient

* Move some logic to finality_base

* Add empty equivocation detection clients

* Add equivocation reporting logic to the source client

* Use convenience trait for SubstrateFinalitySyncPipeline

* Define JustificationVerificationContext for GRANDPA

* Equivocation source client: finality_verification_context()

* Equivocation source client: synced_headers_finality_info()

* reuse HeaderFinalityInfo

* Define EquivocationsFinder

* Fix spellcheck

* Address review comments

* Avoid equivocations lookup errors

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

@@ -0,0 +1,86 @@
+// Copyright 2019-2023 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.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Default generic implementation of equivocation source for basic Substrate client.
+
+use crate::{
+	equivocation::{EquivocationDetectionPipelineAdapter, SubstrateEquivocationDetectionPipeline},
+	finality_base::engine::Engine,
+};
+
+use crate::equivocation::{FinalityProoffOf, FinalityVerificationContextfOf};
+use async_trait::async_trait;
+use bp_header_chain::HeaderFinalityInfo;
+use bp_runtime::BlockNumberOf;
+use equivocation_detector::TargetClient;
+use relay_substrate_client::{Client, Error};
+use relay_utils::relay_loop::Client as RelayClient;
+use sp_runtime::traits::Header;
+use std::marker::PhantomData;
+
+/// Substrate node as equivocation source.
+pub struct SubstrateEquivocationTarget<P: SubstrateEquivocationDetectionPipeline> {
+	client: Client<P::TargetChain>,
+
+	_phantom: PhantomData<P>,
+}
+
+impl<P: SubstrateEquivocationDetectionPipeline> SubstrateEquivocationTarget<P> {}
+
+impl<P: SubstrateEquivocationDetectionPipeline> Clone for SubstrateEquivocationTarget<P> {
+	fn clone(&self) -> Self {
+		Self { client: self.client.clone(), _phantom: Default::default() }
+	}
+}
+
+#[async_trait]
+impl<P: SubstrateEquivocationDetectionPipeline> RelayClient for SubstrateEquivocationTarget<P> {
+	type Error = Error;
+
+	async fn reconnect(&mut self) -> Result<(), Error> {
+		self.client.reconnect().await
+	}
+}
+
+#[async_trait]
+impl<P: SubstrateEquivocationDetectionPipeline>
+	TargetClient<EquivocationDetectionPipelineAdapter<P>> for SubstrateEquivocationTarget<P>
+{
+	async fn finality_verification_context(
+		&self,
+		at: BlockNumberOf<P::TargetChain>,
+	) -> Result<FinalityVerificationContextfOf<P>, Self::Error> {
+		P::FinalityEngine::finality_verification_context(
+			&self.client,
+			self.client.header_by_number(at).await?.hash(),
+		)
+		.await
+	}
+
+	async fn synced_headers_finality_info(
+		&self,
+		at: BlockNumberOf<P::TargetChain>,
+	) -> Result<
+		Vec<HeaderFinalityInfo<FinalityProoffOf<P>, FinalityVerificationContextfOf<P>>>,
+		Self::Error,
+	> {
+		P::FinalityEngine::synced_headers_finality_info(
+			&self.client,
+			self.client.header_by_number(at).await?.hash(),
+		)
+		.await
+	}
+}