FinalityEngine in substrate relay (#1374)

* introduce FinalityEngine in relay code

* add FinalityEngine to relay

* spelling

* fix test compilation

* Update relays/lib-substrate-relay/src/finality/source.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

Co-authored-by: Adrian Catangiu <adrian@parity.io>

bridges/relays/bin-substrate/src/chains/kusama_headers_to_polkadot.rs

@@ -18,7 +18,10 @@
 
 use async_trait::async_trait;
 use relay_polkadot_client::Polkadot;
-use substrate_relay_helper::{finality_pipeline::SubstrateFinalitySyncPipeline, TransactionParams};
+use substrate_relay_helper::{
+	finality::{engine::Grandpa as GrandpaFinalityEngine, SubstrateFinalitySyncPipeline},
+	TransactionParams,
+};
 
 /// Maximal saturating difference between `balance(now)` and `balance(now-24h)` to treat
 /// relay as gone wild.
@@ -47,6 +50,7 @@ impl SubstrateFinalitySyncPipeline for KusamaFinalityToPolkadot {
 	type SourceChain = relay_kusama_client::Kusama;
 	type TargetChain = Polkadot;
 
+	type FinalityEngine = GrandpaFinalityEngine<Self::SourceChain>;
 	type SubmitFinalityProofCallBuilder = KusamaFinalityToPolkadotCallBuilder;
 	type TransactionSignScheme = Polkadot;
 
@@ -55,7 +59,7 @@ impl SubstrateFinalitySyncPipeline for KusamaFinalityToPolkadot {
 		transaction_params: &TransactionParams<sp_core::sr25519::Pair>,
 		enable_version_guard: bool,
 	) -> relay_substrate_client::Result<()> {
-		substrate_relay_helper::finality_guards::start::<Polkadot, Polkadot>(
+		substrate_relay_helper::finality::guards::start::<Polkadot, Polkadot>(
 			target_client,
 			transaction_params,
 			enable_version_guard,

bridges/relays/bin-substrate/src/chains/millau_headers_to_rialto.rs

@@ -16,8 +16,9 @@
 
 //! Millau-to-Rialto headers sync entrypoint.
 
-use substrate_relay_helper::finality_pipeline::{
-	DirectSubmitFinalityProofCallBuilder, SubstrateFinalitySyncPipeline,
+use substrate_relay_helper::finality::{
+	engine::Grandpa as GrandpaFinalityEngine, DirectSubmitGrandpaFinalityProofCallBuilder,
+	SubstrateFinalitySyncPipeline,
 };
 
 /// Description of Millau -> Rialto finalized headers bridge.
@@ -28,7 +29,8 @@ impl SubstrateFinalitySyncPipeline for MillauFinalityToRialto {
 	type SourceChain = relay_millau_client::Millau;
 	type TargetChain = relay_rialto_client::Rialto;
 
-	type SubmitFinalityProofCallBuilder = DirectSubmitFinalityProofCallBuilder<
+	type FinalityEngine = GrandpaFinalityEngine<Self::SourceChain>;
+	type SubmitFinalityProofCallBuilder = DirectSubmitGrandpaFinalityProofCallBuilder<
 		Self,
 		rialto_runtime::Runtime,
 		rialto_runtime::MillauGrandpaInstance,

bridges/relays/bin-substrate/src/chains/polkadot_headers_to_kusama.rs

@@ -18,7 +18,10 @@
 
 use async_trait::async_trait;
 use relay_kusama_client::Kusama;
-use substrate_relay_helper::{finality_pipeline::SubstrateFinalitySyncPipeline, TransactionParams};
+use substrate_relay_helper::{
+	finality::{engine::Grandpa as GrandpaFinalityEngine, SubstrateFinalitySyncPipeline},
+	TransactionParams,
+};
 
 /// Maximal saturating difference between `balance(now)` and `balance(now-24h)` to treat
 /// relay as gone wild.
@@ -47,6 +50,7 @@ impl SubstrateFinalitySyncPipeline for PolkadotFinalityToKusama {
 	type SourceChain = relay_polkadot_client::Polkadot;
 	type TargetChain = Kusama;
 
+	type FinalityEngine = GrandpaFinalityEngine<Self::SourceChain>;
 	type SubmitFinalityProofCallBuilder = PolkadotFinalityToKusamaCallBuilder;
 	type TransactionSignScheme = Kusama;
 
@@ -55,7 +59,7 @@ impl SubstrateFinalitySyncPipeline for PolkadotFinalityToKusama {
 		transaction_params: &TransactionParams<sp_core::sr25519::Pair>,
 		enable_version_guard: bool,
 	) -> relay_substrate_client::Result<()> {
-		substrate_relay_helper::finality_guards::start::<Kusama, Kusama>(
+		substrate_relay_helper::finality::guards::start::<Kusama, Kusama>(
 			target_client,
 			transaction_params,
 			enable_version_guard,

bridges/relays/bin-substrate/src/chains/rialto_headers_to_millau.rs

@@ -16,8 +16,9 @@
 
 //! Rialto-to-Millau headers sync entrypoint.
 
-use substrate_relay_helper::finality_pipeline::{
-	DirectSubmitFinalityProofCallBuilder, SubstrateFinalitySyncPipeline,
+use substrate_relay_helper::finality::{
+	engine::Grandpa as GrandpaFinalityEngine, DirectSubmitGrandpaFinalityProofCallBuilder,
+	SubstrateFinalitySyncPipeline,
 };
 
 /// Description of Millau -> Rialto finalized headers bridge.
@@ -28,7 +29,8 @@ impl SubstrateFinalitySyncPipeline for RialtoFinalityToMillau {
 	type SourceChain = relay_rialto_client::Rialto;
 	type TargetChain = relay_millau_client::Millau;
 
-	type SubmitFinalityProofCallBuilder = DirectSubmitFinalityProofCallBuilder<
+	type FinalityEngine = GrandpaFinalityEngine<Self::SourceChain>;
+	type SubmitFinalityProofCallBuilder = DirectSubmitGrandpaFinalityProofCallBuilder<
 		Self,
 		millau_runtime::Runtime,
 		millau_runtime::RialtoGrandpaInstance,

bridges/relays/bin-substrate/src/chains/rococo_headers_to_wococo.rs

@@ -20,7 +20,10 @@ use crate::chains::wococo_headers_to_rococo::MAXIMAL_BALANCE_DECREASE_PER_DAY;
 
 use async_trait::async_trait;
 use relay_wococo_client::Wococo;
-use substrate_relay_helper::{finality_pipeline::SubstrateFinalitySyncPipeline, TransactionParams};
+use substrate_relay_helper::{
+	finality::{engine::Grandpa as GrandpaFinalityEngine, SubstrateFinalitySyncPipeline},
+	TransactionParams,
+};
 
 /// Description of Rococo -> Wococo finalized headers bridge.
 #[derive(Clone, Debug)]
@@ -37,6 +40,7 @@ impl SubstrateFinalitySyncPipeline for RococoFinalityToWococo {
 	type SourceChain = relay_rococo_client::Rococo;
 	type TargetChain = Wococo;
 
+	type FinalityEngine = GrandpaFinalityEngine<Self::SourceChain>;
 	type SubmitFinalityProofCallBuilder = RococoFinalityToWococoCallBuilder;
 	type TransactionSignScheme = Wococo;
 
@@ -45,7 +49,7 @@ impl SubstrateFinalitySyncPipeline for RococoFinalityToWococo {
 		transaction_params: &TransactionParams<sp_core::sr25519::Pair>,
 		enable_version_guard: bool,
 	) -> relay_substrate_client::Result<()> {
-		substrate_relay_helper::finality_guards::start::<Wococo, Wococo>(
+		substrate_relay_helper::finality::guards::start::<Wococo, Wococo>(
 			target_client,
 			transaction_params,
 			enable_version_guard,

bridges/relays/bin-substrate/src/chains/westend_headers_to_millau.rs

@@ -16,8 +16,9 @@
 
 //! Westend-to-Millau headers sync entrypoint.
 
-use substrate_relay_helper::finality_pipeline::{
-	DirectSubmitFinalityProofCallBuilder, SubstrateFinalitySyncPipeline,
+use substrate_relay_helper::finality::{
+	engine::Grandpa as GrandpaFinalityEngine, DirectSubmitGrandpaFinalityProofCallBuilder,
+	SubstrateFinalitySyncPipeline,
 };
 
 /// Description of Westend -> Millau finalized headers bridge.
@@ -28,7 +29,8 @@ impl SubstrateFinalitySyncPipeline for WestendFinalityToMillau {
 	type SourceChain = relay_westend_client::Westend;
 	type TargetChain = relay_millau_client::Millau;
 
-	type SubmitFinalityProofCallBuilder = DirectSubmitFinalityProofCallBuilder<
+	type FinalityEngine = GrandpaFinalityEngine<Self::SourceChain>;
+	type SubmitFinalityProofCallBuilder = DirectSubmitGrandpaFinalityProofCallBuilder<
 		Self,
 		millau_runtime::Runtime,
 		millau_runtime::WestendGrandpaInstance,

bridges/relays/bin-substrate/src/chains/wococo_headers_to_rococo.rs

@@ -18,7 +18,10 @@
 
 use async_trait::async_trait;
 use relay_rococo_client::Rococo;
-use substrate_relay_helper::{finality_pipeline::SubstrateFinalitySyncPipeline, TransactionParams};
+use substrate_relay_helper::{
+	finality::{engine::Grandpa as GrandpaFinalityEngine, SubstrateFinalitySyncPipeline},
+	TransactionParams,
+};
 
 /// Maximal saturating difference between `balance(now)` and `balance(now-24h)` to treat
 /// relay as gone wild.
@@ -42,6 +45,7 @@ impl SubstrateFinalitySyncPipeline for WococoFinalityToRococo {
 	type SourceChain = relay_wococo_client::Wococo;
 	type TargetChain = Rococo;
 
+	type FinalityEngine = GrandpaFinalityEngine<Self::SourceChain>;
 	type SubmitFinalityProofCallBuilder = WococoFinalityToRococoCallBuilder;
 	type TransactionSignScheme = Rococo;
 
@@ -50,7 +54,7 @@ impl SubstrateFinalitySyncPipeline for WococoFinalityToRococo {
 		transaction_params: &TransactionParams<sp_core::sr25519::Pair>,
 		enable_version_guard: bool,
 	) -> relay_substrate_client::Result<()> {
-		substrate_relay_helper::finality_guards::start::<Rococo, Rococo>(
+		substrate_relay_helper::finality::guards::start::<Rococo, Rococo>(
 			target_client,
 			transaction_params,
 			enable_version_guard,

bridges/relays/bin-substrate/src/cli/init_bridge.rs

@@ -22,6 +22,7 @@ use relay_substrate_client::{Chain, SignParam, TransactionSignScheme, UnsignedTr
 use sp_core::{Bytes, Pair};
 use structopt::StructOpt;
 use strum::{EnumString, EnumVariantNames, VariantNames};
+use substrate_relay_helper::finality::engine::Grandpa as GrandpaFinalityEngine;
 
 /// Initialize bridge pallet.
 #[derive(StructOpt)]
@@ -56,6 +57,7 @@ macro_rules! select_bridge {
 			InitBridgeName::MillauToRialto => {
 				type Source = relay_millau_client::Millau;
 				type Target = relay_rialto_client::Rialto;
+				type Engine = GrandpaFinalityEngine<Source>;
 
 				fn encode_init_bridge(
 					init_data: InitializationData<<Source as ChainBase>::Header>,
@@ -74,6 +76,7 @@ macro_rules! select_bridge {
 			InitBridgeName::RialtoToMillau => {
 				type Source = relay_rialto_client::Rialto;
 				type Target = relay_millau_client::Millau;
+				type Engine = GrandpaFinalityEngine<Source>;
 
 				fn encode_init_bridge(
 					init_data: InitializationData<<Source as ChainBase>::Header>,
@@ -92,6 +95,7 @@ macro_rules! select_bridge {
 			InitBridgeName::WestendToMillau => {
 				type Source = relay_westend_client::Westend;
 				type Target = relay_millau_client::Millau;
+				type Engine = GrandpaFinalityEngine<Source>;
 
 				fn encode_init_bridge(
 					init_data: InitializationData<<Source as ChainBase>::Header>,
@@ -114,6 +118,7 @@ macro_rules! select_bridge {
 			InitBridgeName::RococoToWococo => {
 				type Source = relay_rococo_client::Rococo;
 				type Target = relay_wococo_client::Wococo;
+				type Engine = GrandpaFinalityEngine<Source>;
 
 				fn encode_init_bridge(
 					init_data: InitializationData<<Source as ChainBase>::Header>,
@@ -130,6 +135,7 @@ macro_rules! select_bridge {
 			InitBridgeName::WococoToRococo => {
 				type Source = relay_wococo_client::Wococo;
 				type Target = relay_rococo_client::Rococo;
+				type Engine = GrandpaFinalityEngine<Source>;
 
 				fn encode_init_bridge(
 					init_data: InitializationData<<Source as ChainBase>::Header>,
@@ -146,6 +152,7 @@ macro_rules! select_bridge {
 			InitBridgeName::KusamaToPolkadot => {
 				type Source = relay_kusama_client::Kusama;
 				type Target = relay_polkadot_client::Polkadot;
+				type Engine = GrandpaFinalityEngine<Source>;
 
 				fn encode_init_bridge(
 					init_data: InitializationData<<Source as ChainBase>::Header>,
@@ -162,6 +169,7 @@ macro_rules! select_bridge {
 			InitBridgeName::PolkadotToKusama => {
 				type Source = relay_polkadot_client::Polkadot;
 				type Target = relay_kusama_client::Kusama;
+				type Engine = GrandpaFinalityEngine<Source>;
 
 				fn encode_init_bridge(
 					init_data: InitializationData<<Source as ChainBase>::Header>,
@@ -189,7 +197,7 @@ impl InitBridge {
 
 			let (spec_version, transaction_version) =
 				target_client.simple_runtime_version().await?;
-			substrate_relay_helper::headers_initialize::initialize(
+			substrate_relay_helper::finality::initialize::initialize::<Engine, _, _, _>(
 				source_client,
 				target_client.clone(),
 				target_sign.public().into(),

bridges/relays/bin-substrate/src/cli/reinit_bridge.rs

@@ -24,7 +24,6 @@ use crate::{
 		TargetConnectionParams, TargetSigningParams,
 	},
 };
-use bp_header_chain::justification::GrandpaJustification;
 use bp_runtime::Chain;
 use codec::Encode;
 use finality_relay::{SourceClient, SourceHeader};
@@ -40,8 +39,12 @@ use std::convert::{TryFrom, TryInto};
 use structopt::StructOpt;
 use strum::{EnumString, EnumVariantNames, VariantNames};
 use substrate_relay_helper::{
-	finality_pipeline::SubstrateFinalitySyncPipeline, finality_source::SubstrateFinalitySource,
-	finality_target::SubstrateFinalityTarget, messages_source::read_client_state,
+	finality::{
+		source::{SubstrateFinalityProof, SubstrateFinalitySource},
+		target::SubstrateFinalityTarget,
+		SubstrateFinalitySyncPipeline,
+	},
+	messages_source::read_client_state,
 	TransactionParams,
 };
 
@@ -299,7 +302,7 @@ impl ReinitBridge {
 /// Mandatory header and its finality proof.
 type HeaderAndProof<P> = (
 	SyncHeader<HeaderOf<<P as SubstrateFinalitySyncPipeline>::SourceChain>>,
-	GrandpaJustification<HeaderOf<<P as SubstrateFinalitySyncPipeline>::SourceChain>>,
+	SubstrateFinalityProof<P>,
 );
 /// Vector of mandatory headers and their finality proofs.
 type HeadersAndProofs<P> = Vec<HeaderAndProof<P>>;
@@ -425,6 +428,7 @@ fn make_mandatory_headers_batches<
 mod tests {
 	use super::*;
 	use crate::cli::{RuntimeVersionType, SourceRuntimeVersionParams, TargetRuntimeVersionParams};
+	use bp_header_chain::justification::GrandpaJustification;
 	use bp_test_utils::{make_default_justification, test_header};
 	use relay_polkadot_client::Polkadot;
 	use sp_runtime::{traits::Header as _, DigestItem};

bridges/relays/bin-substrate/src/cli/relay_headers.rs

@@ -18,7 +18,7 @@ use structopt::StructOpt;
 use strum::{EnumString, EnumVariantNames, VariantNames};
 
 use relay_utils::metrics::{GlobalMetrics, StandaloneMetric};
-use substrate_relay_helper::finality_pipeline::SubstrateFinalitySyncPipeline;
+use substrate_relay_helper::finality::SubstrateFinalitySyncPipeline;
 
 use crate::cli::{
 	PrometheusParams, SourceConnectionParams, TargetConnectionParams, TargetSigningParams,
@@ -136,7 +136,7 @@ impl RelayHeaders {
 			)
 			.await?;
 
-			substrate_relay_helper::finality_pipeline::run::<Finality>(
+			substrate_relay_helper::finality::run::<Finality>(
 				source_client,
 				target_client,
 				self.only_mandatory_headers,

bridges/relays/bin-substrate/src/cli/relay_headers_and_messages.rs

@@ -35,7 +35,7 @@ use relay_substrate_client::{
 use relay_utils::metrics::MetricsParams;
 use sp_core::{Bytes, Pair};
 use substrate_relay_helper::{
-	finality_pipeline::SubstrateFinalitySyncPipeline, messages_lane::MessagesRelayParams,
+	finality::SubstrateFinalitySyncPipeline, messages_lane::MessagesRelayParams,
 	on_demand_headers::OnDemandHeadersRelay, TransactionParams,
 };
 

bridges/relays/client-substrate/src/client.rs

@@ -704,8 +704,8 @@ impl<C: Chain> Client<C> {
 		.await
 	}
 
-	/// Return new justifications stream.
-	pub async fn subscribe_justifications(&self) -> Result<Subscription<Bytes>> {
+	/// Return new GRANDPA justifications stream.
+	pub async fn subscribe_grandpa_justifications(&self) -> Result<Subscription<Bytes>> {
 		let subscription = self
 			.jsonrpsee_execute(move |client| async move {
 				Ok(client

bridges/relays/client-substrate/src/error.rs

@@ -45,9 +45,9 @@ pub enum Error {
 	/// Account does not exist on the chain.
 	#[error("Account does not exist on the chain.")]
 	AccountDoesNotExist,
-	/// Runtime storage is missing mandatory ":code:" entry.
-	#[error("Mandatory :code: entry is missing from runtime storage.")]
-	MissingMandatoryCodeEntry,
+	/// Runtime storage is missing some mandatory value.
+	#[error("Mandatory storage value is missing from the runtime storage.")]
+	MissingMandatoryStorageValue,
 	/// The client we're connected to is not synced, so we can't rely on its state.
 	#[error("Substrate client is not synced {0}.")]
 	ClientNotSynced(Health),

bridges/relays/client-substrate/src/metrics/storage_proof_overhead.rs

@@ -72,7 +72,7 @@ impl<C: Chain> StorageProofOverheadMetric<C> {
 		let maybe_encoded_storage_value =
 			storage_value_reader.read_value(CODE).map_err(Error::StorageProofError)?;
 		let encoded_storage_value_size =
-			maybe_encoded_storage_value.ok_or(Error::MissingMandatoryCodeEntry)?.len();
+			maybe_encoded_storage_value.ok_or(Error::MissingMandatoryStorageValue)?.len();
 
 		Ok(storage_proof_size - encoded_storage_value_size)
 	}

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

@@ -0,0 +1,226 @@
+// 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.
+
+// 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/>.
+
+//! Support of different finality engines, available in Substrate.
+
+use crate::error::Error;
+use async_trait::async_trait;
+use bp_header_chain::{
+	find_grandpa_authorities_scheduled_change,
+	justification::{verify_justification, GrandpaJustification},
+	FinalityProof,
+};
+use codec::{Decode, Encode};
+use finality_grandpa::voter_set::VoterSet;
+use num_traits::{One, Zero};
+use relay_substrate_client::{
+	BlockNumberOf, Chain, ChainWithGrandpa, Client, Error as SubstrateError, HashOf, HeaderOf,
+	Subscription,
+};
+use sp_core::{storage::StorageKey, Bytes};
+use sp_finality_grandpa::AuthorityList as GrandpaAuthoritiesSet;
+use sp_runtime::{traits::Header, ConsensusEngineId};
+use std::marker::PhantomData;
+
+/// Finality enfine, used by the Substrate chain.
+#[async_trait]
+pub trait Engine<C: Chain> {
+	/// Unique consensus engine identifier.
+	const ID: ConsensusEngineId;
+	/// Type of finality proofs, used by consensus engine.
+	type FinalityProof: FinalityProof<BlockNumberOf<C>> + Decode + Encode;
+	/// Type of bridge pallet initialization data.
+	type InitializationData: std::fmt::Debug + Send + Sync + 'static;
+
+	/// Returns storage key at the bridged (target) chain that corresponds to the `bool` value,
+	/// which is true when the bridge pallet is halted.
+	fn is_halted_key() -> StorageKey;
+	/// Returns storage at the bridged (target) chain that corresponds to some value that is
+	/// missing from the storage until bridge pallet is initialized.
+	///
+	/// Note that we don't care about type of the value - just if it present or not.
+	fn is_initialized_key() -> StorageKey;
+	/// A method to subscribe to encoded finality proofs, given source client.
+	async fn finality_proofs(client: Client<C>) -> Result<Subscription<Bytes>, SubstrateError>;
+	/// Prepare initialization data for the finality bridge pallet.
+	async fn prepare_initialization_data(
+		client: Client<C>,
+	) -> Result<Self::InitializationData, Error<HashOf<C>, BlockNumberOf<C>>>;
+}
+
+/// GRANDPA finality engine.
+pub struct Grandpa<C>(PhantomData<C>);
+
+impl<C: ChainWithGrandpa> Grandpa<C> {
+	/// Read header by hash from the source client.
+	async fn source_header(
+		source_client: &Client<C>,
+		header_hash: C::Hash,
+	) -> Result<C::Header, Error<HashOf<C>, BlockNumberOf<C>>> {
+		source_client
+			.header_by_hash(header_hash)
+			.await
+			.map_err(|err| Error::RetrieveHeader(C::NAME, header_hash, err))
+	}
+
+	/// Read GRANDPA authorities set at given header.
+	async fn source_authorities_set(
+		source_client: &Client<C>,
+		header_hash: C::Hash,
+	) -> Result<GrandpaAuthoritiesSet, Error<HashOf<C>, BlockNumberOf<C>>> {
+		let raw_authorities_set = source_client
+			.grandpa_authorities_set(header_hash)
+			.await
+			.map_err(|err| Error::RetrieveAuthorities(C::NAME, header_hash, err))?;
+		GrandpaAuthoritiesSet::decode(&mut &raw_authorities_set[..])
+			.map_err(|err| Error::DecodeAuthorities(C::NAME, header_hash, err))
+	}
+}
+
+#[async_trait]
+impl<C: ChainWithGrandpa> Engine<C> for Grandpa<C> {
+	const ID: ConsensusEngineId = sp_finality_grandpa::GRANDPA_ENGINE_ID;
+	type FinalityProof = GrandpaJustification<HeaderOf<C>>;
+	type InitializationData = bp_header_chain::InitializationData<C::Header>;
+
+	fn is_halted_key() -> StorageKey {
+		bp_header_chain::storage_keys::is_halted_key(C::WITH_CHAIN_GRANDPA_PALLET_NAME)
+	}
+
+	fn is_initialized_key() -> StorageKey {
+		bp_header_chain::storage_keys::best_finalized_hash_key(C::WITH_CHAIN_GRANDPA_PALLET_NAME)
+	}
+
+	async fn finality_proofs(client: Client<C>) -> Result<Subscription<Bytes>, SubstrateError> {
+		client.subscribe_grandpa_justifications().await
+	}
+
+	/// Prepare initialization data for the GRANDPA verifier pallet.
+	async fn prepare_initialization_data(
+		source_client: Client<C>,
+	) -> Result<Self::InitializationData, Error<HashOf<C>, BlockNumberOf<C>>> {
+		// In ideal world we just need to get best finalized header and then to read GRANDPA
+		// authorities set (`pallet_grandpa::CurrentSetId` + `GrandpaApi::grandpa_authorities()`) at
+		// this header.
+		//
+		// But now there are problems with this approach - `CurrentSetId` may return invalid value.
+		// So here we're waiting for the next justification, read the authorities set and then try
+		// to figure out the set id with bruteforce.
+		let justifications = source_client
+			.subscribe_grandpa_justifications()
+			.await
+			.map_err(|err| Error::Subscribe(C::NAME, err))?;
+		// Read next justification - the header that it finalizes will be used as initial header.
+		let justification = justifications
+			.next()
+			.await
+			.map_err(|e| Error::ReadJustification(C::NAME, e))
+			.and_then(|justification| {
+				justification.ok_or(Error::ReadJustificationStreamEnded(C::NAME))
+			})?;
+
+		// Read initial header.
+		let justification: GrandpaJustification<C::Header> =
+			Decode::decode(&mut &justification.0[..])
+				.map_err(|err| Error::DecodeJustification(C::NAME, err))?;
+
+		let (initial_header_hash, initial_header_number) =
+			(justification.commit.target_hash, justification.commit.target_number);
+
+		let initial_header = Self::source_header(&source_client, initial_header_hash).await?;
+		log::trace!(target: "bridge", "Selected {} initial header: {}/{}",
+			C::NAME,
+			initial_header_number,
+			initial_header_hash,
+		);
+
+		// Read GRANDPA authorities set at initial header.
+		let initial_authorities_set =
+			Self::source_authorities_set(&source_client, initial_header_hash).await?;
+		log::trace!(target: "bridge", "Selected {} initial authorities set: {:?}",
+			C::NAME,
+			initial_authorities_set,
+		);
+
+		// If initial header changes the GRANDPA authorities set, then we need previous authorities
+		// to verify justification.
+		let mut authorities_for_verification = initial_authorities_set.clone();
+		let scheduled_change = find_grandpa_authorities_scheduled_change(&initial_header);
+		assert!(
+			scheduled_change.as_ref().map(|c| c.delay.is_zero()).unwrap_or(true),
+			"GRANDPA authorities change at {} scheduled to happen in {:?} blocks. We expect\
+			regular hange to have zero delay",
+			initial_header_hash,
+			scheduled_change.as_ref().map(|c| c.delay),
+		);
+		let schedules_change = scheduled_change.is_some();
+		if schedules_change {
+			authorities_for_verification =
+				Self::source_authorities_set(&source_client, *initial_header.parent_hash()).await?;
+			log::trace!(
+				target: "bridge",
+				"Selected {} header is scheduling GRANDPA authorities set changes. Using previous set: {:?}",
+				C::NAME,
+				authorities_for_verification,
+			);
+		}
+
+		// Now let's try to guess authorities set id by verifying justification.
+		let mut initial_authorities_set_id = 0;
+		let mut min_possible_block_number = C::BlockNumber::zero();
+		let authorities_for_verification = VoterSet::new(authorities_for_verification.clone())
+			.ok_or(Error::ReadInvalidAuthorities(C::NAME, authorities_for_verification))?;
+		loop {
+			log::trace!(
+				target: "bridge", "Trying {} GRANDPA authorities set id: {}",
+				C::NAME,
+				initial_authorities_set_id,
+			);
+
+			let is_valid_set_id = verify_justification::<C::Header>(
+				(initial_header_hash, initial_header_number),
+				initial_authorities_set_id,
+				&authorities_for_verification,
+				&justification,
+			)
+			.is_ok();
+
+			if is_valid_set_id {
+				break
+			}
+
+			initial_authorities_set_id += 1;
+			min_possible_block_number += One::one();
+			if min_possible_block_number > initial_header_number {
+				// there can't be more authorities set changes than headers => if we have reached
+				// `initial_block_number` and still have not found correct value of
+				// `initial_authorities_set_id`, then something else is broken => fail
+				return Err(Error::GuessInitialAuthorities(C::NAME, initial_header_number))
+			}
+		}
+
+		Ok(bp_header_chain::InitializationData {
+			header: Box::new(initial_header),
+			authority_list: initial_authorities_set,
+			set_id: if schedules_change {
+				initial_authorities_set_id + 1
+			} else {
+				initial_authorities_set_id
+			},
+			is_halted: false,
+		})
+	}
+}

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

@@ -0,0 +1,121 @@
+// 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.
+
+// 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/>.
+
+//! Initialize Substrate -> Substrate finality bridge.
+//!
+//! Initialization is a transaction that calls `initialize()` function of the
+//! finality pallet (GRANDPA/BEEFY/...). This transaction brings initial header
+//! and authorities set from source to target chain. The finality sync starts
+//! with this header.
+
+use crate::{error::Error, finality::engine::Engine};
+
+use relay_substrate_client::{BlockNumberOf, Chain, Client, Error as SubstrateError, HashOf};
+use sp_core::Bytes;
+use sp_runtime::traits::Header as HeaderT;
+
+/// Submit headers-bridge initialization transaction.
+pub async fn initialize<E: Engine<SourceChain>, SourceChain: Chain, TargetChain: Chain, F>(
+	source_client: Client<SourceChain>,
+	target_client: Client<TargetChain>,
+	target_transactions_signer: TargetChain::AccountId,
+	prepare_initialize_transaction: F,
+) where
+	F: FnOnce(TargetChain::Index, E::InitializationData) -> Result<Bytes, SubstrateError>
+		+ Send
+		+ 'static,
+{
+	let result = do_initialize::<E, _, _, _>(
+		source_client,
+		target_client,
+		target_transactions_signer,
+		prepare_initialize_transaction,
+	)
+	.await;
+
+	match result {
+		Ok(Some(tx_hash)) => log::info!(
+			target: "bridge",
+			"Successfully submitted {}-headers bridge initialization transaction to {}: {:?}",
+			SourceChain::NAME,
+			TargetChain::NAME,
+			tx_hash,
+		),
+		Ok(None) => (),
+		Err(err) => log::error!(
+			target: "bridge",
+			"Failed to submit {}-headers bridge initialization transaction to {}: {:?}",
+			SourceChain::NAME,
+			TargetChain::NAME,
+			err,
+		),
+	}
+}
+
+/// Craft and submit initialization transaction, returning any error that may occur.
+async fn do_initialize<E: Engine<SourceChain>, SourceChain: Chain, TargetChain: Chain, F>(
+	source_client: Client<SourceChain>,
+	target_client: Client<TargetChain>,
+	target_transactions_signer: TargetChain::AccountId,
+	prepare_initialize_transaction: F,
+) -> Result<
+	Option<TargetChain::Hash>,
+	Error<SourceChain::Hash, <SourceChain::Header as HeaderT>::Number>,
+>
+where
+	F: FnOnce(TargetChain::Index, E::InitializationData) -> Result<Bytes, SubstrateError>
+		+ Send
+		+ 'static,
+{
+	let is_initialized = is_initialized::<E, SourceChain, TargetChain>(&target_client).await?;
+	if is_initialized {
+		log::info!(
+			target: "bridge",
+			"{}-headers bridge at {} is already initialized. Skipping",
+			SourceChain::NAME,
+			TargetChain::NAME,
+		);
+		return Ok(None)
+	}
+
+	let initialization_data = E::prepare_initialization_data(source_client).await?;
+	log::info!(
+		target: "bridge",
+		"Prepared initialization data for {}-headers bridge at {}: {:?}",
+		SourceChain::NAME,
+		TargetChain::NAME,
+		initialization_data,
+	);
+
+	let initialization_tx_hash = target_client
+		.submit_signed_extrinsic(target_transactions_signer, move |_, transaction_nonce| {
+			prepare_initialize_transaction(transaction_nonce, initialization_data)
+		})
+		.await
+		.map_err(|err| Error::SubmitTransaction(TargetChain::NAME, err))?;
+	Ok(Some(initialization_tx_hash))
+}
+
+/// Returns `Ok(true)` if bridge has already been initialized.
+async fn is_initialized<E: Engine<SourceChain>, SourceChain: Chain, TargetChain: Chain>(
+	target_client: &Client<TargetChain>,
+) -> Result<bool, Error<HashOf<SourceChain>, BlockNumberOf<SourceChain>>> {
+	Ok(target_client
+		.raw_storage_value(E::is_initialized_key(), None)
+		.await
+		.map_err(|err| Error::RetrieveBestFinalizedHeaderHash(SourceChain::NAME, err))?
+		.is_some())
+}

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

@@ -18,7 +18,11 @@
 //! finality proofs synchronization pipelines.
 
 use crate::{
-	finality_source::SubstrateFinalitySource, finality_target::SubstrateFinalityTarget,
+	finality::{
+		engine::Engine,
+		source::{SubstrateFinalityProof, SubstrateFinalitySource},
+		target::SubstrateFinalityTarget,
+	},
 	TransactionParams,
 };
 
@@ -27,13 +31,19 @@ use bp_header_chain::justification::GrandpaJustification;
 use finality_relay::FinalitySyncPipeline;
 use pallet_bridge_grandpa::{Call as BridgeGrandpaCall, Config as BridgeGrandpaConfig};
 use relay_substrate_client::{
-	transaction_stall_timeout, AccountIdOf, AccountKeyPairOf, BlockNumberOf, CallOf, Chain,
-	ChainWithGrandpa, Client, HashOf, HeaderOf, SyncHeader, TransactionSignScheme,
+	transaction_stall_timeout, AccountIdOf, AccountKeyPairOf, BlockNumberOf, CallOf, Chain, Client,
+	HashOf, HeaderOf, SyncHeader, TransactionSignScheme,
 };
 use relay_utils::metrics::MetricsParams;
 use sp_core::Pair;
 use std::{fmt::Debug, marker::PhantomData};
 
+pub mod engine;
+pub mod guards;
+pub mod initialize;
+pub mod source;
+pub mod target;
+
 /// Default limit of recent finality proofs.
 ///
 /// Finality delay of 4096 blocks is unlikely to happen in practice in
@@ -44,10 +54,12 @@ pub(crate) const RECENT_FINALITY_PROOFS_LIMIT: usize = 4096;
 #[async_trait]
 pub trait SubstrateFinalitySyncPipeline: 'static + Clone + Debug + Send + Sync {
 	/// Headers of this chain are submitted to the `TargetChain`.
-	type SourceChain: ChainWithGrandpa;
+	type SourceChain: Chain;
 	/// Headers of the `SourceChain` are submitted to this chain.
 	type TargetChain: Chain;
 
+	/// Finality engine.
+	type FinalityEngine: Engine<Self::SourceChain>;
 	/// How submit finality proof call is built?
 	type SubmitFinalityProofCallBuilder: SubmitFinalityProofCallBuilder<Self>;
 	/// Scheme used to sign target chain transactions.
@@ -76,7 +88,7 @@ impl<P: SubstrateFinalitySyncPipeline> FinalitySyncPipeline for FinalitySyncPipe
 	type Hash = HashOf<P::SourceChain>;
 	type Number = BlockNumberOf<P::SourceChain>;
 	type Header = relay_substrate_client::SyncHeader<HeaderOf<P::SourceChain>>;
-	type FinalityProof = GrandpaJustification<HeaderOf<P::SourceChain>>;
+	type FinalityProof = SubstrateFinalityProof<P>;
 }
 
 /// Different ways of building `submit_finality_proof` calls.
@@ -85,23 +97,26 @@ pub trait SubmitFinalityProofCallBuilder<P: SubstrateFinalitySyncPipeline> {
 	/// function of bridge GRANDPA module at the target chain.
 	fn build_submit_finality_proof_call(
 		header: SyncHeader<HeaderOf<P::SourceChain>>,
-		proof: GrandpaJustification<HeaderOf<P::SourceChain>>,
+		proof: SubstrateFinalityProof<P>,
 	) -> CallOf<P::TargetChain>;
 }
 
 /// Building `submit_finality_proof` call when you have direct access to the target
 /// chain runtime.
-pub struct DirectSubmitFinalityProofCallBuilder<P, R, I> {
+pub struct DirectSubmitGrandpaFinalityProofCallBuilder<P, R, I> {
 	_phantom: PhantomData<(P, R, I)>,
 }
 
-impl<P, R, I> SubmitFinalityProofCallBuilder<P> for DirectSubmitFinalityProofCallBuilder<P, R, I>
+impl<P, R, I> SubmitFinalityProofCallBuilder<P>
+	for DirectSubmitGrandpaFinalityProofCallBuilder<P, R, I>
 where
 	P: SubstrateFinalitySyncPipeline,
 	R: BridgeGrandpaConfig<I>,
 	I: 'static,
 	R::BridgedChain: bp_runtime::Chain<Header = HeaderOf<P::SourceChain>>,
 	CallOf<P::TargetChain>: From<BridgeGrandpaCall<R, I>>,
+	P::FinalityEngine:
+		Engine<P::SourceChain, FinalityProof = GrandpaJustification<HeaderOf<P::SourceChain>>>,
 {
 	fn build_submit_finality_proof_call(
 		header: SyncHeader<HeaderOf<P::SourceChain>>,
@@ -125,22 +140,22 @@ macro_rules! generate_mocked_submit_finality_proof_call_builder {
 	($pipeline:ident, $mocked_builder:ident, $bridge_grandpa:path, $submit_finality_proof:path) => {
 		pub struct $mocked_builder;
 
-		impl $crate::finality_pipeline::SubmitFinalityProofCallBuilder<$pipeline>
+		impl $crate::finality::SubmitFinalityProofCallBuilder<$pipeline>
 			for $mocked_builder
 		{
 			fn build_submit_finality_proof_call(
 				header: relay_substrate_client::SyncHeader<
 					relay_substrate_client::HeaderOf<
-						<$pipeline as $crate::finality_pipeline::SubstrateFinalitySyncPipeline>::SourceChain
+						<$pipeline as $crate::finality::SubstrateFinalitySyncPipeline>::SourceChain
 					>
 				>,
 				proof: bp_header_chain::justification::GrandpaJustification<
 					relay_substrate_client::HeaderOf<
-						<$pipeline as $crate::finality_pipeline::SubstrateFinalitySyncPipeline>::SourceChain
+						<$pipeline as $crate::finality::SubstrateFinalitySyncPipeline>::SourceChain
 					>
 				>,
 			) -> relay_substrate_client::CallOf<
-				<$pipeline as $crate::finality_pipeline::SubstrateFinalitySyncPipeline>::TargetChain
+				<$pipeline as $crate::finality::SubstrateFinalitySyncPipeline>::TargetChain
 			> {
 				$bridge_grandpa($submit_finality_proof(Box::new(header.into_inner()), proof))
 			}

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

@@ -16,11 +16,10 @@
 
 //! Default generic implementation of finality source for basic Substrate client.
 
-use crate::finality_pipeline::{FinalitySyncPipelineAdapter, SubstrateFinalitySyncPipeline};
+use crate::finality::{engine::Engine, FinalitySyncPipelineAdapter, SubstrateFinalitySyncPipeline};
 
 use async_std::sync::{Arc, Mutex};
 use async_trait::async_trait;
-use bp_header_chain::justification::GrandpaJustification;
 use codec::Decode;
 use finality_relay::SourceClient;
 use futures::stream::{unfold, Stream, StreamExt};
@@ -38,13 +37,19 @@ pub type RequiredHeaderNumberRef<C> = Arc<Mutex<<C as bp_runtime::Chain>::BlockN
 pub type SubstrateFinalityProofsStream<P> = Pin<
 	Box<
 		dyn Stream<
-				Item = GrandpaJustification<
-					HeaderOf<<P as SubstrateFinalitySyncPipeline>::SourceChain>,
-				>,
+				Item = <<P as SubstrateFinalitySyncPipeline>::FinalityEngine as Engine<
+					<P as SubstrateFinalitySyncPipeline>::SourceChain,
+				>>::FinalityProof,
 			> + Send,
 	>,
 >;
 
+/// Substrate finality proof. Specific to the used `FinalityEngine`.
+pub type SubstrateFinalityProof<P> =
+	<<P as SubstrateFinalitySyncPipeline>::FinalityEngine as Engine<
+		<P as SubstrateFinalitySyncPipeline>::SourceChain,
+	>>::FinalityProof;
+
 /// Substrate node as finality source.
 pub struct SubstrateFinalitySource<P: SubstrateFinalitySyncPipeline> {
 	client: Client<P::SourceChain>,
@@ -120,7 +125,7 @@ impl<P: SubstrateFinalitySyncPipeline> SourceClient<FinalitySyncPipelineAdapter<
 	) -> Result<
 		(
 			relay_substrate_client::SyncHeader<HeaderOf<P::SourceChain>>,
-			Option<GrandpaJustification<HeaderOf<P::SourceChain>>>,
+			Option<SubstrateFinalityProof<P>>,
 		),
 		Error,
 	> {
@@ -130,9 +135,7 @@ impl<P: SubstrateFinalitySyncPipeline> SourceClient<FinalitySyncPipelineAdapter<
 		let justification = signed_block
 			.justification()
 			.map(|raw_justification| {
-				GrandpaJustification::<HeaderOf<P::SourceChain>>::decode(
-					&mut raw_justification.as_slice(),
-				)
+				SubstrateFinalityProof::<P>::decode(&mut raw_justification.as_slice())
 			})
 			.transpose()
 			.map_err(Error::ResponseParseFailed)?;
@@ -142,7 +145,7 @@ impl<P: SubstrateFinalitySyncPipeline> SourceClient<FinalitySyncPipelineAdapter<
 
 	async fn finality_proofs(&self) -> Result<Self::FinalityProofsStream, Error> {
 		Ok(unfold(
-			self.client.clone().subscribe_justifications().await?,
+			P::FinalityEngine::finality_proofs(self.client.clone()).await?,
 			move |subscription| async move {
 				loop {
 					let log_error = |err| {
@@ -161,7 +164,7 @@ impl<P: SubstrateFinalitySyncPipeline> SourceClient<FinalitySyncPipelineAdapter<
 						.ok()??;
 
 					let decoded_justification =
-						GrandpaJustification::<HeaderOf<P::SourceChain>>::decode(
+						<P::FinalityEngine as Engine<P::SourceChain>>::FinalityProof::decode(
 							&mut &next_justification[..],
 						);
 

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

@@ -14,24 +14,22 @@
 // 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/>.
 
-//! Substrate client as Substrate finality proof target. The chain we connect to should have
-//! bridge GRANDPA pallet deployed and provide `<BridgedChainName>FinalityApi` to allow bridging
-//! with <BridgedName> chain.
+//! Substrate client as Substrate finality proof target.
 
 use crate::{
-	finality_pipeline::{
-		FinalitySyncPipelineAdapter, SubmitFinalityProofCallBuilder, SubstrateFinalitySyncPipeline,
+	finality::{
+		engine::Engine, source::SubstrateFinalityProof, FinalitySyncPipelineAdapter,
+		SubmitFinalityProofCallBuilder, SubstrateFinalitySyncPipeline,
 	},
 	TransactionParams,
 };
 
 use async_trait::async_trait;
-use bp_header_chain::{justification::GrandpaJustification, storage_keys::is_halted_key};
 use codec::Encode;
 use finality_relay::TargetClient;
 use relay_substrate_client::{
-	AccountIdOf, AccountKeyPairOf, Chain, ChainWithGrandpa, Client, Error, HeaderIdOf, HeaderOf,
-	SignParam, SyncHeader, TransactionEra, TransactionSignScheme, UnsignedTransaction,
+	AccountIdOf, AccountKeyPairOf, Chain, Client, Error, HeaderIdOf, HeaderOf, SignParam,
+	SyncHeader, TransactionEra, TransactionSignScheme, UnsignedTransaction,
 };
 use relay_utils::relay_loop::Client as RelayClient;
 use sp_core::{Bytes, Pair};
@@ -51,12 +49,9 @@ impl<P: SubstrateFinalitySyncPipeline> SubstrateFinalityTarget<P> {
 		SubstrateFinalityTarget { client, transaction_params }
 	}
 
-	/// Ensure that the GRANDPA pallet at target chain is active.
+	/// Ensure that the bridge pallet at target chain is active.
 	pub async fn ensure_pallet_active(&self) -> Result<(), Error> {
-		let is_halted = self
-			.client
-			.storage_value(is_halted_key(P::SourceChain::WITH_CHAIN_GRANDPA_PALLET_NAME), None)
-			.await?;
+		let is_halted = self.client.storage_value(P::FinalityEngine::is_halted_key(), None).await?;
 		if is_halted.unwrap_or(false) {
 			Err(Error::BridgePalletIsHalted)
 		} else {
@@ -94,7 +89,7 @@ where
 		// we can't continue to relay finality if target node is out of sync, because
 		// it may have already received (some of) headers that we're going to relay
 		self.client.ensure_synced().await?;
-		// we can't relay finality if GRANDPA pallet at target chain is halted
+		// 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>(
@@ -109,7 +104,7 @@ where
 	async fn submit_finality_proof(
 		&self,
 		header: SyncHeader<HeaderOf<P::SourceChain>>,
-		proof: GrandpaJustification<HeaderOf<P::SourceChain>>,
+		proof: SubstrateFinalityProof<P>,
 	) -> Result<(), Error> {
 		let genesis_hash = *self.client.genesis_hash();
 		let transaction_params = self.transaction_params.clone();

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

@@ -1,282 +0,0 @@
-// 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.
-
-// 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/>.
-
-//! Initialize Substrate -> Substrate headers bridge.
-//!
-//! Initialization is a transaction that calls `initialize()` function of the
-//! `pallet-bridge-grandpa` pallet. This transaction brings initial header
-//! and authorities set from source to target chain. The headers sync starts
-//! with this header.
-
-use crate::error::Error;
-
-use bp_header_chain::{
-	find_grandpa_authorities_scheduled_change,
-	justification::{verify_justification, GrandpaJustification},
-	InitializationData,
-};
-use codec::Decode;
-use finality_grandpa::voter_set::VoterSet;
-use num_traits::{One, Zero};
-use relay_substrate_client::{
-	BlockNumberOf, Chain, ChainWithGrandpa, Client, Error as SubstrateError, HashOf,
-};
-use sp_core::Bytes;
-use sp_finality_grandpa::AuthorityList as GrandpaAuthoritiesSet;
-use sp_runtime::traits::Header as HeaderT;
-
-/// Submit headers-bridge initialization transaction.
-pub async fn initialize<SourceChain: ChainWithGrandpa, TargetChain: Chain>(
-	source_client: Client<SourceChain>,
-	target_client: Client<TargetChain>,
-	target_transactions_signer: TargetChain::AccountId,
-	prepare_initialize_transaction: impl FnOnce(
-			TargetChain::Index,
-			InitializationData<SourceChain::Header>,
-		) -> Result<Bytes, SubstrateError>
-		+ Send
-		+ 'static,
-) {
-	let result = do_initialize(
-		source_client,
-		target_client,
-		target_transactions_signer,
-		prepare_initialize_transaction,
-	)
-	.await;
-
-	match result {
-		Ok(Some(tx_hash)) => log::info!(
-			target: "bridge",
-			"Successfully submitted {}-headers bridge initialization transaction to {}: {:?}",
-			SourceChain::NAME,
-			TargetChain::NAME,
-			tx_hash,
-		),
-		Ok(None) => (),
-		Err(err) => log::error!(
-			target: "bridge",
-			"Failed to submit {}-headers bridge initialization transaction to {}: {:?}",
-			SourceChain::NAME,
-			TargetChain::NAME,
-			err,
-		),
-	}
-}
-
-/// Craft and submit initialization transaction, returning any error that may occur.
-async fn do_initialize<SourceChain: ChainWithGrandpa, TargetChain: Chain>(
-	source_client: Client<SourceChain>,
-	target_client: Client<TargetChain>,
-	target_transactions_signer: TargetChain::AccountId,
-	prepare_initialize_transaction: impl FnOnce(
-			TargetChain::Index,
-			InitializationData<SourceChain::Header>,
-		) -> Result<Bytes, SubstrateError>
-		+ Send
-		+ 'static,
-) -> Result<
-	Option<TargetChain::Hash>,
-	Error<SourceChain::Hash, <SourceChain::Header as HeaderT>::Number>,
-> {
-	let is_initialized = is_initialized::<SourceChain, TargetChain>(&target_client).await?;
-	if is_initialized {
-		log::info!(
-			target: "bridge",
-			"{}-headers bridge at {} is already initialized. Skipping",
-			SourceChain::NAME,
-			TargetChain::NAME,
-		);
-		return Ok(None)
-	}
-
-	let initialization_data = prepare_initialization_data(source_client).await?;
-	log::info!(
-		target: "bridge",
-		"Prepared initialization data for {}-headers bridge at {}: {:?}",
-		SourceChain::NAME,
-		TargetChain::NAME,
-		initialization_data,
-	);
-
-	let initialization_tx_hash = target_client
-		.submit_signed_extrinsic(target_transactions_signer, move |_, transaction_nonce| {
-			prepare_initialize_transaction(transaction_nonce, initialization_data)
-		})
-		.await
-		.map_err(|err| Error::SubmitTransaction(TargetChain::NAME, err))?;
-	Ok(Some(initialization_tx_hash))
-}
-
-/// Returns `Ok(true)` if bridge has already been initialized.
-async fn is_initialized<SourceChain: ChainWithGrandpa, TargetChain: Chain>(
-	target_client: &Client<TargetChain>,
-) -> Result<bool, Error<HashOf<SourceChain>, BlockNumberOf<SourceChain>>> {
-	Ok(target_client
-		.raw_storage_value(
-			bp_header_chain::storage_keys::best_finalized_hash_key(
-				SourceChain::WITH_CHAIN_GRANDPA_PALLET_NAME,
-			),
-			None,
-		)
-		.await
-		.map_err(|err| Error::RetrieveBestFinalizedHeaderHash(SourceChain::NAME, err))?
-		.is_some())
-}
-
-/// Prepare initialization data for the GRANDPA verifier pallet.
-async fn prepare_initialization_data<SourceChain: Chain>(
-	source_client: Client<SourceChain>,
-) -> Result<
-	InitializationData<SourceChain::Header>,
-	Error<SourceChain::Hash, <SourceChain::Header as HeaderT>::Number>,
-> {
-	// In ideal world we just need to get best finalized header and then to read GRANDPA authorities
-	// set (`pallet_grandpa::CurrentSetId` + `GrandpaApi::grandpa_authorities()`) at this header.
-	//
-	// But now there are problems with this approach - `CurrentSetId` may return invalid value. So
-	// here we're waiting for the next justification, read the authorities set and then try to
-	// figure out the set id with bruteforce.
-	let justifications = source_client
-		.subscribe_justifications()
-		.await
-		.map_err(|err| Error::Subscribe(SourceChain::NAME, err))?;
-	// Read next justification - the header that it finalizes will be used as initial header.
-	let justification = justifications
-		.next()
-		.await
-		.map_err(|e| Error::ReadJustification(SourceChain::NAME, e))
-		.and_then(|justification| {
-			justification.ok_or(Error::ReadJustificationStreamEnded(SourceChain::NAME))
-		})?;
-
-	// Read initial header.
-	let justification: GrandpaJustification<SourceChain::Header> =
-		Decode::decode(&mut &justification.0[..])
-			.map_err(|err| Error::DecodeJustification(SourceChain::NAME, err))?;
-
-	let (initial_header_hash, initial_header_number) =
-		(justification.commit.target_hash, justification.commit.target_number);
-
-	let initial_header = source_header(&source_client, initial_header_hash).await?;
-	log::trace!(target: "bridge", "Selected {} initial header: {}/{}",
-		SourceChain::NAME,
-		initial_header_number,
-		initial_header_hash,
-	);
-
-	// Read GRANDPA authorities set at initial header.
-	let initial_authorities_set =
-		source_authorities_set(&source_client, initial_header_hash).await?;
-	log::trace!(target: "bridge", "Selected {} initial authorities set: {:?}",
-		SourceChain::NAME,
-		initial_authorities_set,
-	);
-
-	// If initial header changes the GRANDPA authorities set, then we need previous authorities
-	// to verify justification.
-	let mut authorities_for_verification = initial_authorities_set.clone();
-	let scheduled_change = find_grandpa_authorities_scheduled_change(&initial_header);
-	assert!(
-		scheduled_change.as_ref().map(|c| c.delay.is_zero()).unwrap_or(true),
-		"GRANDPA authorities change at {} scheduled to happen in {:?} blocks. We expect\
-		regular hange to have zero delay",
-		initial_header_hash,
-		scheduled_change.as_ref().map(|c| c.delay),
-	);
-	let schedules_change = scheduled_change.is_some();
-	if schedules_change {
-		authorities_for_verification =
-			source_authorities_set(&source_client, *initial_header.parent_hash()).await?;
-		log::trace!(
-			target: "bridge",
-			"Selected {} header is scheduling GRANDPA authorities set changes. Using previous set: {:?}",
-			SourceChain::NAME,
-			authorities_for_verification,
-		);
-	}
-
-	// Now let's try to guess authorities set id by verifying justification.
-	let mut initial_authorities_set_id = 0;
-	let mut min_possible_block_number = SourceChain::BlockNumber::zero();
-	let authorities_for_verification = VoterSet::new(authorities_for_verification.clone())
-		.ok_or(Error::ReadInvalidAuthorities(SourceChain::NAME, authorities_for_verification))?;
-	loop {
-		log::trace!(
-			target: "bridge", "Trying {} GRANDPA authorities set id: {}",
-			SourceChain::NAME,
-			initial_authorities_set_id,
-		);
-
-		let is_valid_set_id = verify_justification::<SourceChain::Header>(
-			(initial_header_hash, initial_header_number),
-			initial_authorities_set_id,
-			&authorities_for_verification,
-			&justification,
-		)
-		.is_ok();
-
-		if is_valid_set_id {
-			break
-		}
-
-		initial_authorities_set_id += 1;
-		min_possible_block_number += One::one();
-		if min_possible_block_number > initial_header_number {
-			// there can't be more authorities set changes than headers => if we have reached
-			// `initial_block_number` and still have not found correct value of
-			// `initial_authorities_set_id`, then something else is broken => fail
-			return Err(Error::GuessInitialAuthorities(SourceChain::NAME, initial_header_number))
-		}
-	}
-
-	Ok(InitializationData {
-		header: Box::new(initial_header),
-		authority_list: initial_authorities_set,
-		set_id: if schedules_change {
-			initial_authorities_set_id + 1
-		} else {
-			initial_authorities_set_id
-		},
-		is_halted: false,
-	})
-}
-
-/// Read header by hash from the source client.
-async fn source_header<SourceChain: Chain>(
-	source_client: &Client<SourceChain>,
-	header_hash: SourceChain::Hash,
-) -> Result<SourceChain::Header, Error<SourceChain::Hash, <SourceChain::Header as HeaderT>::Number>>
-{
-	source_client
-		.header_by_hash(header_hash)
-		.await
-		.map_err(|err| Error::RetrieveHeader(SourceChain::NAME, header_hash, err))
-}
-
-/// Read GRANDPA authorities set at given header.
-async fn source_authorities_set<SourceChain: Chain>(
-	source_client: &Client<SourceChain>,
-	header_hash: SourceChain::Hash,
-) -> Result<GrandpaAuthoritiesSet, Error<SourceChain::Hash, <SourceChain::Header as HeaderT>::Number>>
-{
-	let raw_authorities_set = source_client
-		.grandpa_authorities_set(header_hash)
-		.await
-		.map_err(|err| Error::RetrieveAuthorities(SourceChain::NAME, header_hash, err))?;
-	GrandpaAuthoritiesSet::decode(&mut &raw_authorities_set[..])
-		.map_err(|err| Error::DecodeAuthorities(SourceChain::NAME, header_hash, err))
-}

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

@@ -22,11 +22,7 @@ use std::time::Duration;
 
 pub mod conversion_rate_update;
 pub mod error;
-pub mod finality_guards;
-pub mod finality_pipeline;
-pub mod finality_source;
-pub mod finality_target;
-pub mod headers_initialize;
+pub mod finality;
 pub mod helpers;
 pub mod messages_lane;
 pub mod messages_metrics;

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

@@ -30,9 +30,11 @@ use relay_utils::{
 };
 
 use crate::{
-	finality_pipeline::{SubstrateFinalitySyncPipeline, RECENT_FINALITY_PROOFS_LIMIT},
-	finality_source::{RequiredHeaderNumberRef, SubstrateFinalitySource},
-	finality_target::SubstrateFinalityTarget,
+	finality::{
+		source::{RequiredHeaderNumberRef, SubstrateFinalitySource},
+		target::SubstrateFinalityTarget,
+		SubstrateFinalitySyncPipeline, RECENT_FINALITY_PROOFS_LIMIT,
+	},
 	TransactionParams, STALL_TIMEOUT,
 };