Define StorageDoubleMapKeyProvider

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

bridges/primitives/parachains/src/lib.rs

@@ -19,9 +19,10 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 use bp_polkadot_core::{
-	parachains::{ParaHash, ParaId},
+	parachains::{ParaHash, ParaHead, ParaId},
 	BlockNumber as RelayBlockNumber,
 };
+use bp_runtime::StorageDoubleMapKeyProvider;
 use codec::{Decode, Encode};
 use frame_support::{Blake2_128Concat, RuntimeDebug, Twox64Concat};
 use scale_info::TypeInfo;
@@ -67,18 +68,16 @@ pub fn best_parachain_head_hash_storage_key_at_target(
 	)
 }
 
-/// Returns runtime storage key of the parachain head with given hash at the target chain.
+/// Can be use to access the runtime storage key of the parachain head at the target chain.
 ///
 /// The head is stored by the `pallet-bridge-parachains` pallet in the `ImportedParaHeads` map.
-pub fn imported_parachain_head_storage_key_at_target(
-	bridge_parachains_pallet_name: &str,
-	para_id: ParaId,
-	head_hash: ParaHash,
-) -> StorageKey {
-	bp_runtime::storage_double_map_final_key::<Blake2_128Concat, Blake2_128Concat>(
-		bridge_parachains_pallet_name,
-		"ImportedParaHeads",
-		&para_id.encode(),
-		&head_hash.encode(),
-	)
+pub struct ImportedParaHeadsKeyProvider;
+impl StorageDoubleMapKeyProvider for ImportedParaHeadsKeyProvider {
+	const MAP_NAME: &'static str = "ImportedParaHeads";
+
+	type Hasher1 = Blake2_128Concat;
+	type Key1 = ParaId;
+	type Hasher2 = Blake2_128Concat;
+	type Key2 = ParaHash;
+	type Value = ParaHead;
 }

bridges/primitives/runtime/src/lib.rs

@@ -246,38 +246,6 @@ pub fn storage_map_final_key<H: StorageHasher>(
 	StorageKey(final_key)
 }
 
-/// This is a copy of the
-/// `frame_support::storage::generator::StorageDoubleMap::storage_double_map_final_key` for maps
-/// based on selected hashers.
-///
-/// We're using it because to call `storage_double_map_final_key` directly, we need access to the
-/// runtime and pallet instance, which (sometimes) is impossible.
-pub fn storage_double_map_final_key<H1: StorageHasher, H2: StorageHasher>(
-	pallet_prefix: &str,
-	map_name: &str,
-	key1: &[u8],
-	key2: &[u8],
-) -> StorageKey {
-	let key1_hashed = H1::hash(key1);
-	let key2_hashed = H2::hash(key2);
-	let pallet_prefix_hashed = frame_support::Twox128::hash(pallet_prefix.as_bytes());
-	let storage_prefix_hashed = frame_support::Twox128::hash(map_name.as_bytes());
-
-	let mut final_key = Vec::with_capacity(
-		pallet_prefix_hashed.len() +
-			storage_prefix_hashed.len() +
-			key1_hashed.as_ref().len() +
-			key2_hashed.as_ref().len(),
-	);
-
-	final_key.extend_from_slice(&pallet_prefix_hashed[..]);
-	final_key.extend_from_slice(&storage_prefix_hashed[..]);
-	final_key.extend_from_slice(key1_hashed.as_ref());
-	final_key.extend_from_slice(key2_hashed.as_ref());
-
-	StorageKey(final_key)
-}
-
 /// This is how a storage key of storage parameter (`parameter_types! { storage Param: bool = false;
 /// }`) is computed.
 ///
@@ -304,6 +272,49 @@ 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`.
+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`
+	type Key1: FullCodec;
+	// The same as `StorageDoubleMap::Hasher2`
+	type Hasher2: StorageHasher;
+	// The same as `StorageDoubleMap::Key2`
+	type Key2: FullCodec;
+	// The same as `StorageDoubleMap::Value`
+	type Value: FullCodec;
+
+	/// This is a copy of the
+	/// `frame_support::storage::generator::StorageDoubleMap::storage_double_map_final_key`.
+	///
+	/// We're using it because to call `storage_double_map_final_key` directly, we need access
+	/// to the runtime and pallet instance, which (sometimes) is impossible.
+	fn final_key(pallet_prefix: &str, key1: &Self::Key1, key2: &Self::Key2) -> StorageKey {
+		let key1_hashed = Self::Hasher1::hash(&key1.encode());
+		let key2_hashed = Self::Hasher2::hash(&key2.encode());
+		let pallet_prefix_hashed = frame_support::Twox128::hash(pallet_prefix.as_bytes());
+		let storage_prefix_hashed = frame_support::Twox128::hash(Self::MAP_NAME.as_bytes());
+
+		let mut final_key = Vec::with_capacity(
+			pallet_prefix_hashed.len() +
+				storage_prefix_hashed.len() +
+				key1_hashed.as_ref().len() +
+				key2_hashed.as_ref().len(),
+		);
+
+		final_key.extend_from_slice(&pallet_prefix_hashed[..]);
+		final_key.extend_from_slice(&storage_prefix_hashed[..]);
+		final_key.extend_from_slice(key1_hashed.as_ref());
+		final_key.extend_from_slice(key2_hashed.as_ref());
+
+		StorageKey(final_key)
+	}
+}
+
 /// Error generated by the `OwnedBridgeModule` trait.
 #[derive(Encode, Decode, TypeInfo, PalletError)]
 pub enum OwnedBridgeModuleError {