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/equivocation/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "equivocation-detector"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2021"
+license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
+description = "Equivocation detector"
+
+[dependencies]
+async-trait = "0.1"
+bp-header-chain = { path = "../../primitives/header-chain" }
+finality-relay = { path = "../finality" }
+relay-utils = { path = "../utils" }

bridges/relays/equivocation/src/lib.rs

@@ -0,0 +1,70 @@
+// 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/>.
+
+use async_trait::async_trait;
+use bp_header_chain::{FindEquivocations, HeaderFinalityInfo};
+use finality_relay::{FinalityPipeline, SourceClientBase};
+use relay_utils::{relay_loop::Client as RelayClient, TransactionTracker};
+
+pub trait EquivocationDetectionPipeline: FinalityPipeline {
+	/// Block number of the target chain.
+	type TargetNumber: relay_utils::BlockNumberBase;
+	/// The context needed for validating finality proofs.
+	type FinalityVerificationContext;
+	/// The type of the equivocation proof.
+	type EquivocationProof;
+	/// The equivocations finder.
+	type EquivocationsFinder: FindEquivocations<
+		Self::FinalityProof,
+		Self::FinalityVerificationContext,
+		Self::EquivocationProof,
+	>;
+}
+
+/// Source client used in equivocation detection loop.
+#[async_trait]
+pub trait SourceClient<P: EquivocationDetectionPipeline>: SourceClientBase<P> {
+	/// Transaction tracker to track submitted transactions.
+	type TransactionTracker: TransactionTracker;
+
+	/// Report equivocation.
+	async fn report_equivocation(
+		&self,
+		at: P::Hash,
+		equivocation: P::EquivocationProof,
+	) -> Result<Self::TransactionTracker, Self::Error>;
+}
+
+/// Target client used in equivocation detection loop.
+#[async_trait]
+pub trait TargetClient<P: EquivocationDetectionPipeline>: RelayClient {
+	/// Get the data stored by the target at the specified block for validating source finality
+	/// proofs.
+	async fn finality_verification_context(
+		&self,
+		at: P::TargetNumber,
+	) -> Result<P::FinalityVerificationContext, Self::Error>;
+
+	/// Get the finality info associated to the source headers synced with the target chain at the
+	/// specified block.
+	async fn synced_headers_finality_info(
+		&self,
+		at: P::TargetNumber,
+	) -> Result<
+		Vec<HeaderFinalityInfo<P::FinalityProof, P::FinalityVerificationContext>>,
+		Self::Error,
+	>;
+}