pallet-mmr: generate historical proofs

bin/node/runtime/src/lib.rs

@@ -2010,10 +2010,7 @@ impl_runtime_apis! {
 		}
 	}
 
-	impl pallet_mmr::primitives::MmrApi<
-		Block,
-		mmr::Hash,
-	> for Runtime {
+	impl pallet_mmr::primitives::MmrApi<Block, mmr::Hash> for Runtime {
 		fn generate_proof(leaf_index: pallet_mmr::primitives::LeafIndex)
 			-> Result<(mmr::EncodableOpaqueLeaf, mmr::Proof<mmr::Hash>), mmr::Error>
 		{
@@ -2048,11 +2045,35 @@ impl_runtime_apis! {
 			Ok(Mmr::mmr_root())
 		}
 
-		fn generate_batch_proof(leaf_indices: Vec<pallet_mmr::primitives::LeafIndex>)
-			-> Result<(Vec<mmr::EncodableOpaqueLeaf>, mmr::BatchProof<mmr::Hash>), mmr::Error>
-		{
-			Mmr::generate_batch_proof(leaf_indices)
-				.map(|(leaves, proof)| (leaves.into_iter().map(|leaf| mmr::EncodableOpaqueLeaf::from_leaf(&leaf)).collect(), proof))
+		fn generate_batch_proof(
+			leaf_indices: Vec<pallet_mmr::primitives::LeafIndex>,
+		) -> Result<(Vec<mmr::EncodableOpaqueLeaf>, mmr::BatchProof<mmr::Hash>), mmr::Error> {
+			Mmr::generate_batch_proof(leaf_indices).map(|(leaves, proof)| {
+				(
+					leaves
+						.into_iter()
+						.map(|leaf| mmr::EncodableOpaqueLeaf::from_leaf(&leaf))
+						.collect(),
+					proof,
+				)
+			})
+		}
+
+		fn generate_historical_batch_proof(
+			leaf_indices: Vec<pallet_mmr::primitives::LeafIndex>,
+			leaves_count: pallet_mmr::primitives::LeafIndex,
+		) -> Result<(Vec<mmr::EncodableOpaqueLeaf>, mmr::BatchProof<mmr::Hash>), mmr::Error> {
+			Mmr::generate_historical_batch_proof(leaf_indices, leaves_count).map(
+				|(leaves, proof)| {
+					(
+						leaves
+							.into_iter()
+							.map(|leaf| mmr::EncodableOpaqueLeaf::from_leaf(&leaf))
+							.collect(),
+						proof,
+					)
+				},
+			)
 		}
 
 		fn verify_batch_proof(leaves: Vec<mmr::EncodableOpaqueLeaf>, proof: mmr::BatchProof<mmr::Hash>)

client/beefy/src/tests.rs

@@ -277,6 +277,13 @@ macro_rules! create_test_api {
 						unimplemented!()
 					}
 
+					fn generate_historical_batch_proof(
+						_leaf_indices: Vec<LeafIndex>,
+						_leaves_count: LeafIndex
+					) -> Result<(Vec<EncodableOpaqueLeaf>, BatchProof<MmrRootHash>), MmrError> {
+						unimplemented!()
+					}
+
 					fn verify_batch_proof(_leaves: Vec<EncodableOpaqueLeaf>, _proof: BatchProof<MmrRootHash>) -> Result<(), MmrError> {
 						unimplemented!()
 					}

frame/merkle-mountain-range/rpc/src/lib.rs

@@ -128,6 +128,31 @@ pub trait MmrApi<BlockHash> {
 		leaf_indices: Vec<LeafIndex>,
 		at: Option<BlockHash>,
 	) -> RpcResult<LeafBatchProof<BlockHash>>;
+
+	/// Generate a MMR proof for the given `leaf_indices` of the MMR that had `leaves_count` leaves.
+	///
+	/// This method calls into a runtime with MMR pallet included and attempts to generate
+	/// a MMR proof for the set of leaves at the given `leaf_indices` with MMR fixed to the state
+	/// with exactly `leaves_count` leaves. `leaves_count` must be larger than the `leaf_index` for
+	/// the function to succeed.
+	///
+	/// Optionally, a block hash at which the runtime should be queried can be specified.
+	/// Note that specifying the block hash isn't super-useful here, unless you're generating
+	/// proof using non-finalized blocks where there are several competing forks. That's because
+	/// MMR state will be fixed to the state with `leaves_count`, which already points to some
+	/// historical block.
+	///
+	/// Returns the leaves and a proof for these leaves (compact encoding, i.e. hash of
+	/// the leaves). Both parameters are SCALE-encoded.
+	/// The order of entries in the `leaves` field of the returned struct
+	/// is the same as the order of the entries in `leaf_indices` supplied
+	#[method(name = "mmr_generateHistoricalBatchProof")]
+	fn generate_historical_batch_proof(
+		&self,
+		leaf_indices: Vec<LeafIndex>,
+		leaves_count: LeafIndex,
+		at: Option<BlockHash>,
+	) -> RpcResult<LeafBatchProof<BlockHash>>;
 }
 
 /// MMR RPC methods.
@@ -192,6 +217,30 @@ where
 
 		Ok(LeafBatchProof::new(block_hash, leaves, proof))
 	}
+
+	fn generate_historical_batch_proof(
+		&self,
+		leaf_indices: Vec<LeafIndex>,
+		leaves_count: LeafIndex,
+		at: Option<<Block as BlockT>::Hash>,
+	) -> RpcResult<LeafBatchProof<<Block as BlockT>::Hash>> {
+		let api = self.client.runtime_api();
+		let block_hash = at.unwrap_or_else(||
+			// If the block hash is not supplied assume the best block.
+			self.client.info().best_hash);
+
+		let (leaves, proof) = api
+			.generate_historical_batch_proof_with_context(
+				&BlockId::hash(block_hash),
+				sp_core::ExecutionContext::OffchainCall(None),
+				leaf_indices,
+				leaves_count,
+			)
+			.map_err(runtime_error_into_rpc_error)?
+			.map_err(mmr_error_into_rpc_error)?;
+
+		Ok(LeafBatchProof::new(block_hash, leaves, proof))
+	}
 }
 
 /// Converts a mmr-specific error into a [`CallError`].

frame/merkle-mountain-range/src/lib.rs

@@ -330,7 +330,27 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		(Vec<LeafOf<T, I>>, primitives::BatchProof<<T as Config<I>>::Hash>),
 		primitives::Error,
 	> {
-		let mmr: ModuleMmr<mmr::storage::OffchainStorage, T, I> = mmr::Mmr::new(Self::mmr_leaves());
+		Self::generate_historical_batch_proof(leaf_indices, Self::mmr_leaves())
+	}
+
+	/// Generate a MMR proof for the given `leaf_indices` of the MMR that had `leaves_count` leaves.
+	///
+	/// Note this method can only be used from an off-chain context
+	/// (Offchain Worker or Runtime API call), since it requires
+	/// all the leaves to be present.
+	/// It may return an error or panic if used incorrectly.
+	pub fn generate_historical_batch_proof(
+		leaf_indices: Vec<LeafIndex>,
+		leaves_count: LeafIndex,
+	) -> Result<
+		(Vec<LeafOf<T, I>>, primitives::BatchProof<<T as Config<I>>::Hash>),
+		primitives::Error,
+	> {
+		if leaves_count > Self::mmr_leaves() {
+			return Err(Error::InvalidLeavesCount)
+		}
+
+		let mmr: ModuleMmr<mmr::storage::OffchainStorage, T, I> = mmr::Mmr::new(leaves_count);
 		mmr.generate_batch_proof(leaf_indices)
 	}