Follow-up on #1068 (#1567)

* BestParaHead small changes

Signed-off-by: Serban Iorga <serban@parity.io>

* Renamings

Signed-off-by: Serban Iorga <serban@parity.io>

* Use ParaInfo in parachains loop

Signed-off-by: Serban Iorga <serban@parity.io>

* Define StorageMapKeyProvider

Signed-off-by: Serban Iorga <serban@parity.io>

* CR fixes

Signed-off-by: Serban Iorga <serban@parity.io>

bridges/modules/parachains/src/extension.rs

@@ -56,7 +56,7 @@ where
 			_ => return Ok(ValidTransaction::default()),
 		};
 
-		let maybe_stored_best_head = crate::BestParaHeads::<T, I>::get(parachain);
+		let maybe_stored_best_head = crate::ParasInfo::<T, I>::get(parachain);
 		Self::validate_updated_parachain_head(
 			parachain,
 			&maybe_stored_best_head,
@@ -72,8 +72,9 @@ mod tests {
 	use crate::{
 		extension::FilterCall,
 		mock::{run_test, Call, TestRuntime},
-		BestParaHead, BestParaHeads, RelayBlockNumber,
+		ParaInfo, ParasInfo, RelayBlockNumber,
 	};
+	use bp_parachains::BestParaHeadHash;
 	use bp_polkadot_core::parachains::{ParaHash, ParaHeadsProof, ParaId};
 
 	fn validate_submit_parachain_heads(
@@ -91,11 +92,13 @@ mod tests {
 	}
 
 	fn sync_to_relay_header_10() {
-		BestParaHeads::<TestRuntime, ()>::insert(
+		ParasInfo::<TestRuntime, ()>::insert(
 			ParaId(1),
-			BestParaHead {
+			ParaInfo {
-				at_relay_block_number: 10,
+				best_head_hash: BestParaHeadHash {
-				head_hash: [1u8; 32].into(),
+					at_relay_block_number: 10,
+					head_hash: [1u8; 32].into(),
+				},
 				next_imported_hash_position: 0,
 			},
 		);

bridges/modules/parachains/src/lib.rs

@@ -26,12 +26,10 @@
 pub use weights::WeightInfo;
 pub use weights_ext::WeightInfoExt;
 
-use bp_parachains::parachain_head_storage_key_at_source;
+use bp_parachains::{parachain_head_storage_key_at_source, ParaInfo};
 use bp_polkadot_core::parachains::{ParaHash, ParaHasher, ParaHead, ParaHeadsProof, ParaId};
 use bp_runtime::StorageProofError;
-use codec::{Decode, Encode};
+use frame_support::{traits::Contains, weights::PostDispatchInfo};
-use frame_support::{traits::Contains, weights::PostDispatchInfo, RuntimeDebug};
-use scale_info::TypeInfo;
 use sp_runtime::traits::Header as HeaderT;
 use sp_std::vec::Vec;
 
@@ -58,21 +56,10 @@ pub type RelayBlockNumber = bp_polkadot_core::BlockNumber;
 /// Hasher of the bridged relay chain.
 pub type RelayBlockHasher = bp_polkadot_core::Hasher;
 
-/// Best known parachain head as it is stored in the runtime storage.
-#[derive(Decode, Encode, PartialEq, RuntimeDebug, TypeInfo)]
-pub struct BestParaHead {
-	/// Number of relay block where this head has been updated.
-	pub at_relay_block_number: RelayBlockNumber,
-	/// Hash of parachain head.
-	pub head_hash: ParaHash,
-	/// Current ring buffer position for this parachain.
-	pub next_imported_hash_position: u32,
-}
-
 /// Artifacts of the parachains head update.
 struct UpdateParachainHeadArtifacts {
 	/// New best head of the parachain.
-	pub best_head: BestParaHead,
+	pub best_head: ParaInfo,
 	/// If `true`, some old parachain head has been pruned during update.
 	pub prune_happened: bool,
 }
@@ -80,8 +67,10 @@ struct UpdateParachainHeadArtifacts {
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
-	use bp_parachains::ImportedParaHeadsKeyProvider;
+	use bp_parachains::{BestParaHeadHash, ImportedParaHeadsKeyProvider, ParasInfoKeyProvider};
-	use bp_runtime::{BasicOperatingMode, OwnedBridgeModule, StorageDoubleMapKeyProvider};
+	use bp_runtime::{
+		BasicOperatingMode, OwnedBridgeModule, StorageDoubleMapKeyProvider, StorageMapKeyProvider,
+	};
 	use frame_support::pallet_prelude::*;
 	use frame_system::pallet_prelude::*;
 
@@ -159,10 +148,18 @@ pub mod pallet {
 	pub type PalletOperatingMode<T: Config<I>, I: 'static = ()> =
 		StorageValue<_, BasicOperatingMode, ValueQuery>;
 
-	/// Best parachain heads.
+	/// Parachains info.
+	///
+	/// Contains the following info:
+	/// - best parachain head hash
+	/// - the head of the `ImportedParaHashes` ring buffer
 	#[pallet::storage]
-	pub type BestParaHeads<T: Config<I>, I: 'static = ()> =
+	pub type ParasInfo<T: Config<I>, I: 'static = ()> = StorageMap<
-		StorageMap<_, Blake2_128Concat, ParaId, BestParaHead>;
+		_,
+		<ParasInfoKeyProvider as StorageMapKeyProvider>::Hasher,
+		<ParasInfoKeyProvider as StorageMapKeyProvider>::Key,
+		<ParasInfoKeyProvider as StorageMapKeyProvider>::Value,
+	>;
 
 	/// Parachain heads which have been imported into the pallet.
 	#[pallet::storage]
@@ -261,7 +258,7 @@ pub mod pallet {
 									target: LOG_TARGET,
 									"The head of parachain {:?} is None. {}",
 									parachain,
-									if BestParaHeads::<T, I>::contains_key(&parachain) {
+									if ParasInfo::<T, I>::contains_key(&parachain) {
 										"Looks like it is not yet registered at the source relay chain"
 									} else {
 										"Looks like it has been deregistered from the source relay chain"
@@ -294,7 +291,7 @@ pub mod pallet {
 							continue;
 						}
 
-						let update_result: Result<_, ()> = BestParaHeads::<T, I>::try_mutate(parachain, |stored_best_head| {
+						let update_result: Result<_, ()> = ParasInfo::<T, I>::try_mutate(parachain, |stored_best_head| {
 							let artifacts = Pallet::<T, I>::update_parachain_head(
 								parachain,
 								stored_best_head.take(),
@@ -348,7 +345,7 @@ pub mod pallet {
 	impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		/// Get best finalized header of the given parachain.
 		pub fn best_parachain_head(parachain: ParaId) -> Option<ParaHead> {
-			let best_para_head_hash = BestParaHeads::<T, I>::get(parachain)?.head_hash;
+			let best_para_head_hash = ParasInfo::<T, I>::get(parachain)?.best_head_hash.head_hash;
 			ImportedParaHeads::<T, I>::get(parachain, best_para_head_hash)
 		}
 
@@ -392,7 +389,7 @@ pub mod pallet {
 		/// Without this check, we may import heads in random order.
 		pub fn validate_updated_parachain_head(
 			parachain: ParaId,
-			maybe_stored_best_head: &Option<BestParaHead>,
+			maybe_stored_best_head: &Option<ParaInfo>,
 			updated_at_relay_block_number: RelayBlockNumber,
 			updated_head_hash: ParaHash,
 			err_log_prefix: &str,
@@ -402,26 +399,28 @@ pub mod pallet {
 				None => return Ok(ValidTransaction::default()),
 			};
 
-			if stored_best_head.at_relay_block_number >= updated_at_relay_block_number {
+			if stored_best_head.best_head_hash.at_relay_block_number >=
+				updated_at_relay_block_number
+			{
 				log::trace!(
 					target: LOG_TARGET,
 					"{}. The parachain head for {:?} was already updated at better relay chain block {} >= {}.",
 					err_log_prefix,
 					parachain,
-					stored_best_head.at_relay_block_number,
+					stored_best_head.best_head_hash.at_relay_block_number,
 					updated_at_relay_block_number
 				);
 				return InvalidTransaction::Stale.into()
 			}
 
-			if stored_best_head.head_hash == updated_head_hash {
+			if stored_best_head.best_head_hash.head_hash == updated_head_hash {
 				log::trace!(
 					target: LOG_TARGET,
 					"{}. The parachain head hash for {:?} was already updated to {} at block {} < {}.",
 					err_log_prefix,
 					parachain,
 					updated_head_hash,
-					stored_best_head.at_relay_block_number,
+					stored_best_head.best_head_hash.at_relay_block_number,
 					updated_at_relay_block_number
 				);
 				return InvalidTransaction::Stale.into()
@@ -433,7 +432,7 @@ pub mod pallet {
 		/// Try to update parachain head.
 		pub(super) fn update_parachain_head(
 			parachain: ParaId,
-			stored_best_head: Option<BestParaHead>,
+			stored_best_head: Option<ParaInfo>,
 			updated_at_relay_block_number: RelayBlockNumber,
 			updated_head: ParaHead,
 			updated_head_hash: ParaHash,
@@ -454,9 +453,11 @@ pub mod pallet {
 			// insert updated best parachain head
 			let head_hash_to_prune =
 				ImportedParaHashes::<T, I>::try_get(parachain, next_imported_hash_position);
-			let updated_best_para_head = BestParaHead {
+			let updated_best_para_head = ParaInfo {
-				at_relay_block_number: updated_at_relay_block_number,
+				best_head_hash: BestParaHeadHash {
-				head_hash: updated_head_hash,
+					at_relay_block_number: updated_at_relay_block_number,
+					head_hash: updated_head_hash,
+				},
 				next_imported_hash_position: (next_imported_hash_position + 1) %
 					T::HeadsToKeep::get(),
 			};
@@ -527,9 +528,13 @@ mod tests {
 	use crate::mock::{
 		run_test, test_relay_header, Origin, TestRuntime, PARAS_PALLET_NAME, UNTRACKED_PARACHAIN_ID,
 	};
+	use codec::Encode;
 
-	use bp_parachains::ImportedParaHeadsKeyProvider;
+	use bp_parachains::{BestParaHeadHash, ImportedParaHeadsKeyProvider, ParasInfoKeyProvider};
-	use bp_runtime::{BasicOperatingMode, OwnedBridgeModuleError, StorageDoubleMapKeyProvider};
+	use bp_runtime::{
+		BasicOperatingMode, OwnedBridgeModuleError, StorageDoubleMapKeyProvider,
+		StorageMapKeyProvider,
+	};
 	use bp_test_utils::{
 		authority_list, generate_owned_bridge_module_tests, make_default_justification,
 	};
@@ -606,10 +611,12 @@ mod tests {
 		(root, ParaHeadsProof(storage_proof), parachains)
 	}
 
-	fn initial_best_head(parachain: u32) -> BestParaHead {
+	fn initial_best_head(parachain: u32) -> ParaInfo {
-		BestParaHead {
+		ParaInfo {
-			at_relay_block_number: 0,
+			best_head_hash: BestParaHeadHash {
-			head_hash: head_data(parachain, 0).hash(),
+				at_relay_block_number: 0,
+				head_hash: head_data(parachain, 0).hash(),
+			},
 			next_imported_hash_position: 1,
 		}
 	}
@@ -697,23 +704,31 @@ mod tests {
 			assert_eq!(result.expect("checked above").actual_weight, Some(expected_weight));
 
 			// but only 1 and 2 are updated, because proof is missing head of parachain#2
-			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
+			assert_eq!(ParasInfo::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
-			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(2)), None);
+			assert_eq!(ParasInfo::<TestRuntime>::get(ParaId(2)), None);
 			assert_eq!(
-				BestParaHeads::<TestRuntime>::get(ParaId(3)),
+				ParasInfo::<TestRuntime>::get(ParaId(3)),
-				Some(BestParaHead {
+				Some(ParaInfo {
-					at_relay_block_number: 0,
+					best_head_hash: BestParaHeadHash {
-					head_hash: head_data(3, 10).hash(),
+						at_relay_block_number: 0,
+						head_hash: head_data(3, 10).hash()
+					},
 					next_imported_hash_position: 1,
 				})
 			);
 
 			assert_eq!(
-				ImportedParaHeads::<TestRuntime>::get(ParaId(1), initial_best_head(1).head_hash),
+				ImportedParaHeads::<TestRuntime>::get(
+					ParaId(1),
+					initial_best_head(1).best_head_hash.head_hash
+				),
 				Some(head_data(1, 0))
 			);
 			assert_eq!(
-				ImportedParaHeads::<TestRuntime>::get(ParaId(2), initial_best_head(2).head_hash),
+				ImportedParaHeads::<TestRuntime>::get(
+					ParaId(2),
+					initial_best_head(2).best_head_hash.head_hash
+				),
 				None
 			);
 			assert_eq!(
@@ -734,10 +749,12 @@ mod tests {
 			initialize(state_root_5);
 			assert_ok!(import_parachain_1_head(0, state_root_5, parachains_5, proof_5));
 			assert_eq!(
-				BestParaHeads::<TestRuntime>::get(ParaId(1)),
+				ParasInfo::<TestRuntime>::get(ParaId(1)),
-				Some(BestParaHead {
+				Some(ParaInfo {
-					at_relay_block_number: 0,
+					best_head_hash: BestParaHeadHash {
-					head_hash: head_data(1, 5).hash(),
+						at_relay_block_number: 0,
+						head_hash: head_data(1, 5).hash()
+					},
 					next_imported_hash_position: 1,
 				})
 			);
@@ -754,10 +771,12 @@ mod tests {
 			proceed(1, state_root_10);
 			assert_ok!(import_parachain_1_head(1, state_root_10, parachains_10, proof_10));
 			assert_eq!(
-				BestParaHeads::<TestRuntime>::get(ParaId(1)),
+				ParasInfo::<TestRuntime>::get(ParaId(1)),
-				Some(BestParaHead {
+				Some(ParaInfo {
-					at_relay_block_number: 1,
+					best_head_hash: BestParaHeadHash {
-					head_hash: head_data(1, 10).hash(),
+						at_relay_block_number: 1,
+						head_hash: head_data(1, 10).hash()
+					},
 					next_imported_hash_position: 2,
 				})
 			);
@@ -797,19 +816,23 @@ mod tests {
 			assert_ok!(result);
 			assert_eq!(result.expect("checked above").actual_weight, Some(expected_weight));
 			assert_eq!(
-				BestParaHeads::<TestRuntime>::get(ParaId(1)),
+				ParasInfo::<TestRuntime>::get(ParaId(1)),
-				Some(BestParaHead {
+				Some(ParaInfo {
-					at_relay_block_number: 0,
+					best_head_hash: BestParaHeadHash {
-					head_hash: head_data(1, 5).hash(),
+						at_relay_block_number: 0,
+						head_hash: head_data(1, 5).hash()
+					},
 					next_imported_hash_position: 1,
 				})
 			);
-			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(UNTRACKED_PARACHAIN_ID)), None,);
+			assert_eq!(ParasInfo::<TestRuntime>::get(ParaId(UNTRACKED_PARACHAIN_ID)), None,);
 			assert_eq!(
-				BestParaHeads::<TestRuntime>::get(ParaId(2)),
+				ParasInfo::<TestRuntime>::get(ParaId(2)),
-				Some(BestParaHead {
+				Some(ParaInfo {
-					at_relay_block_number: 0,
+					best_head_hash: BestParaHeadHash {
-					head_hash: head_data(1, 5).hash(),
+						at_relay_block_number: 0,
+						head_hash: head_data(1, 5).hash()
+					},
 					next_imported_hash_position: 1,
 				})
 			);
@@ -824,13 +847,13 @@ mod tests {
 			// import head#0 of parachain#1 at relay block#0
 			initialize(state_root);
 			assert_ok!(import_parachain_1_head(0, state_root, parachains.clone(), proof.clone()));
-			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
+			assert_eq!(ParasInfo::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
 
 			// try to import head#0 of parachain#1 at relay block#1
 			// => call succeeds, but nothing is changed
 			proceed(1, state_root);
 			assert_ok!(import_parachain_1_head(1, state_root, parachains, proof));
-			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
+			assert_eq!(ParasInfo::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
 		});
 	}
 
@@ -848,10 +871,12 @@ mod tests {
 			proceed(1, state_root_10);
 			assert_ok!(import_parachain_1_head(1, state_root_10, parachains_10, proof_10));
 			assert_eq!(
-				BestParaHeads::<TestRuntime>::get(ParaId(1)),
+				ParasInfo::<TestRuntime>::get(ParaId(1)),
-				Some(BestParaHead {
+				Some(ParaInfo {
-					at_relay_block_number: 1,
+					best_head_hash: BestParaHeadHash {
-					head_hash: head_data(1, 10).hash(),
+						at_relay_block_number: 1,
+						head_hash: head_data(1, 10).hash()
+					},
 					next_imported_hash_position: 1,
 				})
 			);
@@ -860,10 +885,12 @@ mod tests {
 			// => nothing is changed, because better head has already been imported
 			assert_ok!(import_parachain_1_head(0, state_root_5, parachains_5, proof_5));
 			assert_eq!(
-				BestParaHeads::<TestRuntime>::get(ParaId(1)),
+				ParasInfo::<TestRuntime>::get(ParaId(1)),
-				Some(BestParaHead {
+				Some(ParaInfo {
-					at_relay_block_number: 1,
+					best_head_hash: BestParaHeadHash {
-					head_hash: head_data(1, 10).hash(),
+						at_relay_block_number: 1,
+						head_hash: head_data(1, 10).hash()
+					},
 					next_imported_hash_position: 1,
 				})
 			);
@@ -1003,9 +1030,8 @@ mod tests {
 	#[test]
 	fn storage_keys_computed_properly() {
 		assert_eq!(
-			BestParaHeads::<TestRuntime>::storage_map_final_key(ParaId(42)).to_vec(),
+			ParasInfo::<TestRuntime>::storage_map_final_key(ParaId(42)).to_vec(),
-			bp_parachains::best_parachain_head_hash_storage_key_at_target("Parachains", ParaId(42))
+			ParasInfoKeyProvider::final_key("Parachains", &ParaId(42)).0
-				.0,
 		);
 
 		assert_eq!(

bridges/primitives/parachains/src/lib.rs

@@ -22,7 +22,7 @@ use bp_polkadot_core::{
 	parachains::{ParaHash, ParaHead, ParaId},
 	BlockNumber as RelayBlockNumber,
 };
-use bp_runtime::StorageDoubleMapKeyProvider;
+use bp_runtime::{StorageDoubleMapKeyProvider, StorageMapKeyProvider};
 use codec::{Decode, Encode};
 use frame_support::{Blake2_128Concat, RuntimeDebug, Twox64Concat};
 use scale_info::TypeInfo;
@@ -44,6 +44,15 @@ pub struct BestParaHeadHash {
 	pub head_hash: ParaHash,
 }
 
+/// Best known parachain head as it is stored in the runtime storage.
+#[derive(Decode, Encode, PartialEq, RuntimeDebug, TypeInfo)]
+pub struct ParaInfo {
+	/// Best known parachain head hash.
+	pub best_head_hash: BestParaHeadHash,
+	/// Current ring buffer position for this parachain.
+	pub next_imported_hash_position: u32,
+}
+
 /// Returns runtime storage key of given parachain head at the source chain.
 ///
 /// The head is stored by the `paras` pallet in the `Heads` map.
@@ -54,18 +63,16 @@ pub fn parachain_head_storage_key_at_source(
 	bp_runtime::storage_map_final_key::<Twox64Concat>(paras_pallet_name, "Heads", &para_id.encode())
 }
 
-/// Returns runtime storage key of best known parachain head at the target chain.
+/// Can be use to access the runtime storage key of the parachains info at the target chain.
 ///
-/// The head is stored by the `pallet-bridge-parachains` pallet in the `BestParaHeads` map.
+/// The info is stored by the `pallet-bridge-parachains` pallet in the `ParasInfo` map.
-pub fn best_parachain_head_hash_storage_key_at_target(
+pub struct ParasInfoKeyProvider;
-	bridge_parachains_pallet_name: &str,
+impl StorageMapKeyProvider for ParasInfoKeyProvider {
-	para_id: ParaId,
+	const MAP_NAME: &'static str = "ParasInfo";
-) -> StorageKey {
+
-	bp_runtime::storage_map_final_key::<Blake2_128Concat>(
+	type Hasher = Blake2_128Concat;
-		bridge_parachains_pallet_name,
+	type Key = ParaId;
-		"BestParaHeads",
+	type Value = ParaInfo;
-		&para_id.encode(),
-	)
 }
 
 /// Can be use to access the runtime storage key of the parachain head at the target chain.

bridges/primitives/runtime/src/lib.rs

@@ -285,20 +285,42 @@ pub fn storage_value_key(pallet_prefix: &str, value_name: &str) -> StorageKey {
 	StorageKey(final_key)
 }
 
-/// Can be use to access the runtime storage key of a `StorageDoubleMap`.
+/// Can be use to access the runtime storage key of a `StorageMap`.
-pub trait StorageDoubleMapKeyProvider {
+pub trait StorageMapKeyProvider {
-	// The name of the variable that holds the `StorageDoubleMap`
+	/// The name of the variable that holds the `StorageMap`.
 	const MAP_NAME: &'static str;
 
-	// The same as `StorageDoubleMap::Hasher1`
+	/// The same as `StorageMap::Hasher1`.
+	type Hasher: StorageHasher;
+	/// The same as `StorageMap::Key1`.
+	type Key: FullCodec;
+	/// The same as `StorageMap::Value`.
+	type Value: FullCodec;
+
+	/// This is a copy of the
+	/// `frame_support::storage::generator::StorageMap::storage_map_final_key`.
+	///
+	/// We're using it because to call `storage_map_final_key` directly, we need access
+	/// to the runtime and pallet instance, which (sometimes) is impossible.
+	fn final_key(pallet_prefix: &str, key: &Self::Key) -> StorageKey {
+		storage_map_final_key::<Self::Hasher>(pallet_prefix, Self::MAP_NAME, &key.encode())
+	}
+}
+
+/// Can be use to access the runtime storage key of a `StorageDoubleMap`.
+pub trait StorageDoubleMapKeyProvider {
+	/// The name of the variable that holds the `StorageDoubleMap`.
+	const MAP_NAME: &'static str;
+
+	/// The same as `StorageDoubleMap::Hasher1`.
 	type Hasher1: StorageHasher;
-	// The same as `StorageDoubleMap::Key1`
+	/// The same as `StorageDoubleMap::Key1`.
 	type Key1: FullCodec;
-	// The same as `StorageDoubleMap::Hasher2`
+	/// The same as `StorageDoubleMap::Hasher2`.
 	type Hasher2: StorageHasher;
-	// The same as `StorageDoubleMap::Key2`
+	/// The same as `StorageDoubleMap::Key2`.
 	type Key2: FullCodec;
-	// The same as `StorageDoubleMap::Value`
+	/// The same as `StorageDoubleMap::Value`.
 	type Value: FullCodec;
 
 	/// This is a copy of the

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

@@ -29,7 +29,7 @@ use crate::{
 
 use async_std::sync::{Arc, Mutex};
 use async_trait::async_trait;
-use bp_runtime::{HeaderIdProvider, StorageDoubleMapKeyProvider};
+use bp_runtime::{HeaderIdProvider, StorageDoubleMapKeyProvider, StorageMapKeyProvider};
 use codec::{Decode, Encode};
 use frame_system::AccountInfo;
 use futures::{SinkExt, StreamExt};
@@ -320,6 +320,23 @@ impl<C: Chain> Client<C> {
 			.transpose()
 	}
 
+	/// Read `MapStorage` value from runtime storage.
+	pub async fn storage_map_value<T: StorageMapKeyProvider>(
+		&self,
+		pallet_prefix: &str,
+		key: &T::Key,
+		block_hash: Option<C::Hash>,
+	) -> Result<Option<T::Value>> {
+		let storage_key = T::final_key(pallet_prefix, key);
+
+		self.raw_storage_value(storage_key, block_hash)
+			.await?
+			.map(|encoded_value| {
+				T::Value::decode(&mut &encoded_value.0[..]).map_err(Error::ResponseParseFailed)
+			})
+			.transpose()
+	}
+
 	/// Read `DoubleMapStorage` value from runtime storage.
 	pub async fn storage_double_map_value<T: StorageDoubleMapKeyProvider>(
 		&self,

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

@@ -24,9 +24,7 @@ use crate::{
 };
 
 use async_trait::async_trait;
-use bp_parachains::{
+use bp_parachains::{BestParaHeadHash, ImportedParaHeadsKeyProvider, ParasInfoKeyProvider};
-	best_parachain_head_hash_storage_key_at_target, BestParaHeadHash, ImportedParaHeadsKeyProvider,
-};
 use bp_polkadot_core::parachains::{ParaHash, ParaHeadsProof, ParaId};
 use bp_runtime::HeaderIdProvider;
 use codec::Decode;
@@ -122,12 +120,16 @@ where
 		metrics: Option<&ParachainsLoopMetrics>,
 		para_id: ParaId,
 	) -> Result<Option<BestParaHeadHash>, Self::Error> {
-		let best_para_head_hash_key = best_parachain_head_hash_storage_key_at_target(
+		let best_para_head_hash: Option<BestParaHeadHash> = self
-			P::SourceRelayChain::PARACHAINS_FINALITY_PALLET_NAME,
+			.client
-			para_id,
+			.storage_map_value::<ParasInfoKeyProvider>(
-		);
+				P::SourceRelayChain::PARACHAINS_FINALITY_PALLET_NAME,
-		let best_para_head_hash: Option<BestParaHeadHash> =
+				&para_id,
-			self.client.storage_value(best_para_head_hash_key, Some(at_block.1)).await?;
+				Some(at_block.1),
+			)
+			.await?
+			.map(|para_info| para_info.best_head_hash);
+
 		if let (Some(metrics), &Some(ref best_para_head_hash)) = (metrics, &best_para_head_hash) {
 			let imported_para_head = self
 				.client