grandpa-rpc: use FinalityProofProvider to check finality for rpc (#6215)

* grandpa-rpc: use FinalityProofProvider to check finality for rpc

* grandpa-rpc: minor tidy

* grandpa-rpc: remove dyn FinalityProofProvider

* grandpa-rpc: remove unused dependencies

* node: move finality_proof_provider setup

* grandpa-rpc: print error reported by finality_proof_provider

* grandpa-rpc: add note about unnecessary encode/decode

* grandpa-rpc: dont encode/decode and use correct hash

* grandpa-rpc: set_id is optional

* grandpa-rpc: create test for prove_finality

* grandpa-rpc: set visibility back to how it was

* grandpa-rpc: remove unused dependency

* grandpa-rpc: minor tidy

* grandpa: doc strings

* grandpa-rpc: rename to prove_finality

* grandpa-rpc: use current set id if none is provided

* grandpa-rpc: remove unnecessary check in test

* node: group finality_proof_provider in rpc_setup

* grandpa: make prove_finality concrete in FinalityProofProvider

* grandpa-rpc: wrap finality output in struct and store as Bytes

* grandpa-rpc: exhaustive error codes and wrap

* grandpa-rpc: let prove_finality take a range instead of a starting point

* grandpa-rpc: fix test for changed API

* grandpa-rpc: fix line length

* grandpa: fix reviewer nits

* node/rpc: fix reviewer comments

substrate/Cargo.lock

@@ -3823,6 +3823,7 @@ dependencies = [
  "sp-blockchain",
  "sp-consensus",
  "sp-consensus-babe",
+ "sp-runtime",
  "sp-transaction-pool",
  "substrate-frame-rpc-system",
 ]
@@ -6821,6 +6822,7 @@ dependencies = [
  "log",
  "parity-scale-codec",
  "sc-block-builder",
+ "sc-client-api",
  "sc-finality-grandpa",
  "sc-network-test",
  "sc-rpc",

substrate/bin/node/cli/src/service.rs

@@ -58,7 +58,10 @@ pub fn new_partial(config: &Configuration) -> Result<sc_service::PartialComponen
 			grandpa::LinkHalf<Block, FullClient, FullSelectChain>,
 			sc_consensus_babe::BabeLink<Block>,
 		),
-		grandpa::SharedVoterState,
+		(
+			grandpa::SharedVoterState,
+			Arc<GrandpaFinalityProofProvider<FullBackend, Block>>,
+		),
 	)
 >, ServiceError> {
 	let (client, backend, keystore, task_manager) =
@@ -108,8 +111,10 @@ pub fn new_partial(config: &Configuration) -> Result<sc_service::PartialComponen
 		let justification_stream = grandpa_link.justification_stream();
 		let shared_authority_set = grandpa_link.shared_authority_set().clone();
 		let shared_voter_state = grandpa::SharedVoterState::empty();
+		let finality_proof_provider =
+			GrandpaFinalityProofProvider::new_for_service(backend.clone(), client.clone());
 
-		let rpc_setup = shared_voter_state.clone();
+		let rpc_setup = (shared_voter_state.clone(), finality_proof_provider.clone());
 
 		let babe_config = babe_link.config().clone();
 		let shared_epoch_changes = babe_link.epoch_changes().clone();
@@ -135,6 +140,7 @@ pub fn new_partial(config: &Configuration) -> Result<sc_service::PartialComponen
 					shared_authority_set: shared_authority_set.clone(),
 					justification_stream: justification_stream.clone(),
 					subscription_executor,
+					finality_provider: finality_proof_provider.clone(),
 				},
 			};
 
@@ -174,8 +180,7 @@ pub fn new_full_base(
 		other: (rpc_extensions_builder, import_setup, rpc_setup),
 	} = new_partial(&config)?;
 
-	let finality_proof_provider =
+	let (shared_voter_state, finality_proof_provider) = rpc_setup;
-		GrandpaFinalityProofProvider::new_for_service(backend.clone(), client.clone());
 
 	let (network, network_status_sinks, system_rpc_tx, network_starter) =
 		sc_service::build_network(sc_service::BuildNetworkParams {
@@ -220,7 +225,6 @@ pub fn new_full_base(
 	})?;
 
 	let (block_import, grandpa_link, babe_link) = import_setup;
-	let shared_voter_state = rpc_setup;
 
 	(with_startup_data)(&block_import, &babe_link);
 

substrate/bin/node/rpc/Cargo.toml

@@ -30,5 +30,6 @@ sp-block-builder = { version = "2.0.0-rc6", path = "../../../primitives/block-bu
 sp-blockchain = { version = "2.0.0-rc6", path = "../../../primitives/blockchain" }
 sp-consensus = { version = "0.8.0-rc6", path = "../../../primitives/consensus/common" }
 sp-consensus-babe = { version = "0.8.0-rc6", path = "../../../primitives/consensus/babe" }
+sp-runtime = { version = "2.0.0-rc6", path = "../../../primitives/runtime" }
 sp-transaction-pool = { version = "2.0.0-rc6", path = "../../../primitives/transaction-pool" }
 substrate-frame-rpc-system = { version = "2.0.0-rc6", path = "../../../utils/frame/rpc/system" }

substrate/bin/node/rpc/src/lib.rs

@@ -36,7 +36,9 @@ use node_primitives::{Block, BlockNumber, AccountId, Index, Balance, Hash};
 use sc_consensus_babe::{Config, Epoch};
 use sc_consensus_babe_rpc::BabeRpcHandler;
 use sc_consensus_epochs::SharedEpochChanges;
-use sc_finality_grandpa::{SharedVoterState, SharedAuthoritySet, GrandpaJustificationStream};
+use sc_finality_grandpa::{
+	SharedVoterState, SharedAuthoritySet, FinalityProofProvider, GrandpaJustificationStream
+};
 use sc_finality_grandpa_rpc::GrandpaRpcHandler;
 use sc_keystore::KeyStorePtr;
 pub use sc_rpc_api::DenyUnsafe;
@@ -71,7 +73,7 @@ pub struct BabeDeps {
 }
 
 /// Extra dependencies for GRANDPA
-pub struct GrandpaDeps {
+pub struct GrandpaDeps<B> {
 	/// Voting round info.
 	pub shared_voter_state: SharedVoterState,
 	/// Authority set info.
@@ -80,10 +82,12 @@ pub struct GrandpaDeps {
 	pub justification_stream: GrandpaJustificationStream<Block>,
 	/// Executor to drive the subscription manager in the Grandpa RPC handler.
 	pub subscription_executor: SubscriptionTaskExecutor,
+	/// Finality proof provider.
+	pub finality_provider: Arc<FinalityProofProvider<B, Block>>,
 }
 
 /// Full client dependencies.
-pub struct FullDeps<C, P, SC> {
+pub struct FullDeps<C, P, SC, B> {
 	/// The client instance to use.
 	pub client: Arc<C>,
 	/// Transaction pool instance.
@@ -95,15 +99,15 @@ pub struct FullDeps<C, P, SC> {
 	/// BABE specific dependencies.
 	pub babe: BabeDeps,
 	/// GRANDPA specific dependencies.
-	pub grandpa: GrandpaDeps,
+	pub grandpa: GrandpaDeps<B>,
 }
 
 /// A IO handler that uses all Full RPC extensions.
 pub type IoHandler = jsonrpc_core::IoHandler<sc_rpc::Metadata>;
 
 /// Instantiate all Full RPC extensions.
-pub fn create_full<C, P, SC>(
+pub fn create_full<C, P, SC, B>(
-	deps: FullDeps<C, P, SC>,
+	deps: FullDeps<C, P, SC, B>,
 ) -> jsonrpc_core::IoHandler<sc_rpc_api::Metadata> where
 	C: ProvideRuntimeApi<Block>,
 	C: HeaderBackend<Block> + HeaderMetadata<Block, Error=BlockChainError> + 'static,
@@ -115,6 +119,8 @@ pub fn create_full<C, P, SC>(
 	C::Api: BlockBuilder<Block>,
 	P: TransactionPool + 'static,
 	SC: SelectChain<Block> +'static,
+	B: sc_client_api::Backend<Block> + Send + Sync + 'static,
+	B::State: sc_client_api::backend::StateBackend<sp_runtime::traits::HashFor<Block>>,
 {
 	use substrate_frame_rpc_system::{FullSystem, SystemApi};
 	use pallet_contracts_rpc::{Contracts, ContractsApi};
@@ -140,6 +146,7 @@ pub fn create_full<C, P, SC>(
 		shared_authority_set,
 		justification_stream,
 		subscription_executor,
+		finality_provider,
 	} = grandpa;
 
 	io.extend_with(
@@ -173,6 +180,7 @@ pub fn create_full<C, P, SC>(
 				shared_voter_state,
 				justification_stream,
 				subscription_executor,
+				finality_provider,
 			)
 		)
 	);

substrate/client/finality-grandpa/rpc/Cargo.toml

@@ -10,6 +10,7 @@ license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
 [dependencies]
 sc-finality-grandpa = { version = "0.8.0-rc6", path = "../" }
 sc-rpc = { version = "2.0.0-rc6", path = "../../rpc" }
+sp-blockchain = { version = "2.0.0-rc6", path = "../../../primitives/blockchain" }
 sp-core = { version = "2.0.0-rc6", path = "../../../primitives/core" }
 sp-runtime = { version = "2.0.0-rc6", path = "../../../primitives/runtime" }
 finality-grandpa = { version = "0.12.3", features = ["derive-codec"] }
@@ -23,12 +24,12 @@ serde_json = "1.0.50"
 log = "0.4.8"
 derive_more = "0.99.2"
 parity-scale-codec = { version = "1.3.0", features = ["derive"] }
+sc-client-api = { version = "2.0.0-rc6", path = "../../api" }
 
 [dev-dependencies]
 sc-block-builder = { version = "0.8.0-rc6", path = "../../block-builder" }
 sc-network-test = { version = "0.8.0-rc6", path = "../../network/test" }
 sc-rpc = { version = "2.0.0-rc6", path = "../../rpc", features = ["test-helpers"] }
-sp-blockchain = { version = "2.0.0-rc6", path = "../../../primitives/blockchain" }
 sp-consensus = { version = "0.8.0-rc6", path = "../../../primitives/consensus/common" }
 sp-core = { version = "2.0.0-rc6", path = "../../../primitives/core" }
 sp-finality-grandpa = { version = "2.0.0-rc6", path = "../../../primitives/finality-grandpa" }

substrate/client/finality-grandpa/rpc/src/error.rs

@@ -16,8 +16,6 @@
 // You should have received a copy of the GNU General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
-use crate::NOT_READY_ERROR_CODE;
-
 #[derive(derive_more::Display, derive_more::From)]
 /// Top-level error type for the RPC handler
 pub enum Error {
@@ -30,13 +28,41 @@ pub enum Error {
 	/// GRANDPA reports voter state with round id or weights larger than 32-bits.
 	#[display(fmt = "GRANDPA reports voter state as unreasonably large")]
 	VoterStateReportsUnreasonablyLargeNumbers,
+	/// GRANDPA prove finality failed.
+	#[display(fmt = "GRANDPA prove finality rpc failed: {}", _0)]
+	ProveFinalityFailed(sp_blockchain::Error),
+}
+
+/// The error codes returned by jsonrpc.
+pub enum ErrorCode {
+	/// Returned when Grandpa RPC endpoint is not ready.
+	NotReady = 1,
+	/// Authority set ID is larger than 32-bits.
+	AuthoritySetTooLarge,
+	/// Voter state with round id or weights larger than 32-bits.
+	VoterStateTooLarge,
+	/// Failed to prove finality.
+	ProveFinality,
+}
+
+impl From<Error> for ErrorCode {
+	fn from(error: Error) -> Self {
+		match error {
+			Error::EndpointNotReady => ErrorCode::NotReady,
+			Error::AuthoritySetIdReportedAsUnreasonablyLarge => ErrorCode::AuthoritySetTooLarge,
+			Error::VoterStateReportsUnreasonablyLargeNumbers => ErrorCode::VoterStateTooLarge,
+			Error::ProveFinalityFailed(_) => ErrorCode::ProveFinality,
+		}
+	}
 }
 
 impl From<Error> for jsonrpc_core::Error {
 	fn from(error: Error) -> Self {
+		let message = format!("{}", error);
+		let code = ErrorCode::from(error);
 		jsonrpc_core::Error {
-			message: format!("{}", error),
+			message,
-			code: jsonrpc_core::ErrorCode::ServerError(NOT_READY_ERROR_CODE),
+			code: jsonrpc_core::ErrorCode::ServerError(code as i64),
 			data: None,
 		}
 	}

substrate/client/finality-grandpa/rpc/src/finality.rs

@@ -0,0 +1,54 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2020 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program 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.
+
+// This program 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 this program. If not, see <https://www.gnu.org/licenses/>.
+
+use serde::{Serialize, Deserialize};
+
+use sc_finality_grandpa::FinalityProofProvider;
+use sp_runtime::traits::{Block as BlockT, NumberFor};
+
+#[derive(Serialize, Deserialize)]
+pub struct EncodedFinalityProofs(pub sp_core::Bytes);
+
+/// Local trait mainly to allow mocking in tests.
+pub trait RpcFinalityProofProvider<Block: BlockT> {
+	/// Return finality proofs for the given authorities set id, if it is provided, otherwise the
+	/// current one will be used.
+	fn rpc_prove_finality(
+		&self,
+		begin: Block::Hash,
+		end: Block::Hash,
+		authorities_set_id: u64,
+	) -> Result<Option<EncodedFinalityProofs>, sp_blockchain::Error>;
+}
+
+impl<B, Block> RpcFinalityProofProvider<Block> for FinalityProofProvider<B, Block>
+where
+	Block: BlockT,
+	NumberFor<Block>: finality_grandpa::BlockNumberOps,
+	B: sc_client_api::backend::Backend<Block> + Send + Sync + 'static,
+{
+	fn rpc_prove_finality(
+		&self,
+		begin: Block::Hash,
+		end: Block::Hash,
+		authorities_set_id: u64,
+	) -> Result<Option<EncodedFinalityProofs>, sp_blockchain::Error> {
+		self.prove_finality(begin, end, authorities_set_id)
+			.map(|x| x.map(|y| EncodedFinalityProofs(y.into())))
+	}
+}

substrate/client/finality-grandpa/rpc/src/lib.rs

@@ -32,24 +32,23 @@ use jsonrpc_core::futures::{
 };
 
 mod error;
+mod finality;
 mod notification;
 mod report;
 
 use sc_finality_grandpa::GrandpaJustificationStream;
 use sp_runtime::traits::Block as BlockT;
 
+use finality::{EncodedFinalityProofs, RpcFinalityProofProvider};
 use report::{ReportAuthoritySet, ReportVoterState, ReportedRoundStates};
 use notification::JustificationNotification;
 
-/// Returned when Grandpa RPC endpoint is not ready.
-pub const NOT_READY_ERROR_CODE: i64 = 1;
-
 type FutureResult<T> =
 	Box<dyn jsonrpc_core::futures::Future<Item = T, Error = jsonrpc_core::Error> + Send>;
 
 /// Provides RPC methods for interacting with GRANDPA.
 #[rpc]
-pub trait GrandpaApi<Notification> {
+pub trait GrandpaApi<Notification, Hash> {
 	/// RPC Metadata
 	type Metadata;
 
@@ -82,23 +81,37 @@ pub trait GrandpaApi<Notification> {
 		metadata: Option<Self::Metadata>,
 		id: SubscriptionId
 	) -> jsonrpc_core::Result<bool>;
+
+	/// Prove finality for the range (begin; end] hash. Returns None if there are no finalized blocks
+	/// unknown in the range. If no authorities set is provided, the current one will be attempted.
+	#[rpc(name = "grandpa_proveFinality")]
+	fn prove_finality(
+		&self,
+		begin: Hash,
+		end: Hash,
+		authorities_set_id: Option<u64>,
+	) -> FutureResult<Option<EncodedFinalityProofs>>;
 }
 
 /// Implements the GrandpaApi RPC trait for interacting with GRANDPA.
-pub struct GrandpaRpcHandler<AuthoritySet, VoterState, Block: BlockT> {
+pub struct GrandpaRpcHandler<AuthoritySet, VoterState, Block: BlockT, ProofProvider> {
 	authority_set: AuthoritySet,
 	voter_state: VoterState,
 	justification_stream: GrandpaJustificationStream<Block>,
 	manager: SubscriptionManager,
+	finality_proof_provider: Arc<ProofProvider>,
 }
 
-impl<AuthoritySet, VoterState, Block: BlockT> GrandpaRpcHandler<AuthoritySet, VoterState, Block> {
+impl<AuthoritySet, VoterState, Block: BlockT, ProofProvider>
+	GrandpaRpcHandler<AuthoritySet, VoterState, Block, ProofProvider>
+{
 	/// Creates a new GrandpaRpcHandler instance.
 	pub fn new<E>(
 		authority_set: AuthoritySet,
 		voter_state: VoterState,
 		justification_stream: GrandpaJustificationStream<Block>,
 		executor: E,
+		finality_proof_provider: Arc<ProofProvider>,
 	) -> Self
 	where
 		E: Executor01<Box<dyn Future01<Item = (), Error = ()> + Send>> + Send + Sync + 'static,
@@ -109,16 +122,18 @@ impl<AuthoritySet, VoterState, Block: BlockT> GrandpaRpcHandler<AuthoritySet, Vo
 			voter_state,
 			justification_stream,
 			manager,
+			finality_proof_provider,
 		}
 	}
 }
 
-impl<AuthoritySet, VoterState, Block> GrandpaApi<JustificationNotification>
+impl<AuthoritySet, VoterState, Block, ProofProvider> GrandpaApi<JustificationNotification, Block::Hash>
-	for GrandpaRpcHandler<AuthoritySet, VoterState, Block>
+	for GrandpaRpcHandler<AuthoritySet, VoterState, Block, ProofProvider>
 where
 	VoterState: ReportVoterState + Send + Sync + 'static,
 	AuthoritySet: ReportAuthoritySet + Send + Sync + 'static,
 	Block: BlockT,
+	ProofProvider: RpcFinalityProofProvider<Block> + Send + Sync + 'static,
 {
 	type Metadata = sc_rpc::Metadata;
 
@@ -153,6 +168,30 @@ where
 	) -> jsonrpc_core::Result<bool> {
 		Ok(self.manager.cancel(id))
 	}
+
+	fn prove_finality(
+		&self,
+		begin: Block::Hash,
+		end: Block::Hash,
+		authorities_set_id: Option<u64>,
+	) -> FutureResult<Option<EncodedFinalityProofs>> {
+		// If we are not provided a set_id, try with the current one.
+		let authorities_set_id = authorities_set_id
+			.unwrap_or_else(|| self.authority_set.get().0);
+		let result = self
+			.finality_proof_provider
+			.rpc_prove_finality(begin, end, authorities_set_id);
+		let future = async move { result }.boxed();
+		Box::new(
+			future
+				.map_err(|e| {
+					warn!("Error proving finality: {}", e);
+					error::Error::ProveFinalityFailed(e)
+				})
+				.map_err(jsonrpc_core::Error::from)
+				.compat()
+		)
+	}
 }
 
 #[cfg(test)]
@@ -161,16 +200,19 @@ mod tests {
 	use std::{collections::HashSet, convert::TryInto, sync::Arc};
 	use jsonrpc_core::{Notification, Output, types::Params};
 
-	use parity_scale_codec::Decode;
+	use parity_scale_codec::{Encode, Decode};
 	use sc_block_builder::BlockBuilder;
-	use sc_finality_grandpa::{report, AuthorityId, GrandpaJustificationSender, GrandpaJustification};
+	use sc_finality_grandpa::{
+		report, AuthorityId, GrandpaJustificationSender, GrandpaJustification,
+		FinalityProofFragment,
+	};
 	use sp_blockchain::HeaderBackend;
 	use sp_consensus::RecordProof;
 	use sp_core::crypto::Public;
 	use sp_keyring::Ed25519Keyring;
-	use sp_runtime::traits::Header as HeaderT;
+	use sp_runtime::traits::{Block as BlockT, Header as HeaderT};
 	use substrate_test_runtime_client::{
-		runtime::Block,
+		runtime::{Block, Header, H256},
 		DefaultTestClientBuilderExt,
 		TestClientBuilderExt,
 		TestClientBuilder,
@@ -180,6 +222,10 @@ mod tests {
 	struct TestVoterState;
 	struct EmptyVoterState;
 
+	struct TestFinalityProofProvider {
+		finality_proofs: Vec<FinalityProofFragment<Header>>,
+	}
+
 	fn voters() -> HashSet<AuthorityId> {
 		let voter_id_1 = AuthorityId::from_slice(&[1; 32]);
 		let voter_id_2 = AuthorityId::from_slice(&[2; 32]);
@@ -199,6 +245,31 @@ mod tests {
 		}
 	}
 
+	fn header(number: u64) -> Header {
+		let parent_hash = match number {
+			0 => Default::default(),
+			_ => header(number - 1).hash(),
+		};
+		Header::new(
+			number,
+			H256::from_low_u64_be(0),
+			H256::from_low_u64_be(0),
+			parent_hash,
+			Default::default(),
+		)
+	}
+
+	impl<Block: BlockT> RpcFinalityProofProvider<Block> for TestFinalityProofProvider {
+		fn rpc_prove_finality(
+			&self,
+			_begin: Block::Hash,
+			_end: Block::Hash,
+			_authoritites_set_id: u64,
+		) -> Result<Option<EncodedFinalityProofs>, sp_blockchain::Error> {
+			Ok(Some(EncodedFinalityProofs(self.finality_proofs.encode().into())))
+		}
+	}
+
 	impl ReportVoterState for TestVoterState {
 		fn get(&self) -> Option<report::VoterState<AuthorityId>> {
 			let voter_id_1 = AuthorityId::from_slice(&[1; 32]);
@@ -236,14 +307,28 @@ mod tests {
 		GrandpaJustificationSender<Block>,
 	) where
 		VoterState: ReportVoterState + Send + Sync + 'static,
+	{
+		setup_io_handler_with_finality_proofs(voter_state, Default::default())
+	}
+
+	fn setup_io_handler_with_finality_proofs<VoterState>(
+		voter_state: VoterState,
+		finality_proofs: Vec<FinalityProofFragment<Header>>,
+	) -> (
+		jsonrpc_core::MetaIoHandler<sc_rpc::Metadata>,
+		GrandpaJustificationSender<Block>,
+	) where
+		VoterState: ReportVoterState + Send + Sync + 'static,
 	{
 		let (justification_sender, justification_stream) = GrandpaJustificationStream::channel();
+		let finality_proof_provider = Arc::new(TestFinalityProofProvider { finality_proofs });
 
 		let handler = GrandpaRpcHandler::new(
 			TestAuthoritySet,
 			voter_state,
 			justification_stream,
 			sc_rpc::testing::TaskExecutor,
+			finality_proof_provider,
 		);
 
 		let mut io = jsonrpc_core::MetaIoHandler::default();
@@ -432,4 +517,32 @@ mod tests {
 		assert_eq!(recv_sub_id, sub_id);
 		assert_eq!(recv_justification, justification);
 	}
+
+	#[test]
+	fn prove_finality_with_test_finality_proof_provider() {
+		let finality_proofs = vec![FinalityProofFragment {
+			block: header(42).hash(),
+			justification: create_justification().encode(),
+			unknown_headers: vec![header(2)],
+			authorities_proof: None,
+		}];
+		let (io,  _) = setup_io_handler_with_finality_proofs(
+			TestVoterState,
+			finality_proofs.clone(),
+		);
+
+		let request = "{\"jsonrpc\":\"2.0\",\"method\":\"grandpa_proveFinality\",\"params\":[\
+			\"0x0000000000000000000000000000000000000000000000000000000000000000\",\
+			\"0x0000000000000000000000000000000000000000000000000000000000000001\",\
+			42\
+		],\"id\":1}";
+
+		let meta = sc_rpc::Metadata::default();
+		let resp = io.handle_request_sync(request, meta);
+		let mut resp: serde_json::Value = serde_json::from_str(&resp.unwrap()).unwrap();
+		let result: sp_core::Bytes = serde_json::from_value(resp["result"].take()).unwrap();
+		let fragments: Vec<FinalityProofFragment<Header>> =
+			Decode::decode(&mut &result[..]).unwrap();
+		assert_eq!(fragments, finality_proofs);
+	}
 }

substrate/client/finality-grandpa/src/finality_proof.rs

@@ -180,7 +180,30 @@ impl<B, Block: BlockT> FinalityProofProvider<B, Block>
 	) -> Arc<Self> {
 		Arc::new(Self::new(backend, storage_and_proof_provider))
 	}
+}
 
+impl<B, Block> FinalityProofProvider<B, Block>
+	where
+		Block: BlockT,
+		NumberFor<Block>: BlockNumberOps,
+		B: Backend<Block> + Send + Sync + 'static,
+{
+	/// Prove finality for the range (begin; end] hash. Returns None if there are no finalized blocks
+	/// unknown in the range.
+	pub fn prove_finality(
+		&self,
+		begin: Block::Hash,
+		end: Block::Hash,
+		authorities_set_id: u64,
+	) -> Result<Option<Vec<u8>>, ClientError> {
+		prove_finality::<_, _, GrandpaJustification<Block>>(
+			&*self.backend.blockchain(),
+			&*self.authority_provider,
+			authorities_set_id,
+			begin,
+			end,
+		)
+	}
 }
 
 impl<B, Block> sc_network::config::FinalityProofProvider<Block> for FinalityProofProvider<B, Block>
@@ -232,8 +255,8 @@ pub struct FinalityEffects<Header: HeaderT> {
 /// 1) the justification for the descendant block F;
 /// 2) headers sub-chain (B; F] if B != F;
 /// 3) proof of GRANDPA::authorities() if the set changes at block F.
-#[derive(Debug, PartialEq, Encode, Decode)]
+#[derive(Debug, PartialEq, Encode, Decode, Clone)]
-pub(crate) struct FinalityProofFragment<Header: HeaderT> {
+pub struct FinalityProofFragment<Header: HeaderT> {
 	/// The hash of block F for which justification is provided.
 	pub block: Header::Hash,
 	/// Justification of the block F.

substrate/client/finality-grandpa/src/lib.rs

@@ -125,7 +125,7 @@ mod until_imported;
 mod voting_rule;
 
 pub use authorities::SharedAuthoritySet;
-pub use finality_proof::{FinalityProofProvider, StorageAndProofProvider};
+pub use finality_proof::{FinalityProofFragment, FinalityProofProvider, StorageAndProofProvider};
 pub use notification::{GrandpaJustificationSender, GrandpaJustificationStream};
 pub use import::GrandpaBlockImport;
 pub use justification::GrandpaJustification;