babe: replace usage of SharedEpochChanges with internal RPC (#13883)

* babe: replace usage of SharedEpochChanges with internal RPC

* babe-rpc: fix tests

* babe: use SinkExt::send instead of Sender::try_send

SinkExt::send provides backpressure in case the channel is full

* Update client/consensus/babe/src/lib.rs

Co-authored-by: Bastian Köcher <git@kchr.de>

* babe: fix spawn

* babe: send handles backpressure

* babe: use testing::TaskExecutor

* babe-rpc: better error handling

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/Cargo.lock

@@ -5142,7 +5142,6 @@ dependencies = [
  "sc-client-api",
  "sc-consensus-babe",
  "sc-consensus-babe-rpc",
- "sc-consensus-epochs",
  "sc-consensus-grandpa",
  "sc-consensus-grandpa-rpc",
  "sc-rpc",

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

@@ -203,7 +203,7 @@ pub fn new_partial(
 	)?;
 
 	let slot_duration = babe_link.config().slot_duration();
-	let import_queue = sc_consensus_babe::import_queue(
+	let (import_queue, babe_worker_handle) = sc_consensus_babe::import_queue(
 		babe_link.clone(),
 		block_import.clone(),
 		Some(Box::new(justification_import)),
@@ -228,7 +228,7 @@ pub fn new_partial(
 	let import_setup = (block_import, grandpa_link, babe_link);
 
 	let (rpc_extensions_builder, rpc_setup) = {
-		let (_, grandpa_link, babe_link) = &import_setup;
+		let (_, grandpa_link, _) = &import_setup;
 
 		let justification_stream = grandpa_link.justification_stream();
 		let shared_authority_set = grandpa_link.shared_authority_set().clone();
@@ -240,9 +240,6 @@ pub fn new_partial(
 			Some(shared_authority_set.clone()),
 		);
 
-		let babe_config = babe_link.config().clone();
-		let shared_epoch_changes = babe_link.epoch_changes().clone();
-
 		let client = client.clone();
 		let pool = transaction_pool.clone();
 		let select_chain = select_chain.clone();
@@ -258,9 +255,8 @@ pub fn new_partial(
 				chain_spec: chain_spec.cloned_box(),
 				deny_unsafe,
 				babe: node_rpc::BabeDeps {
-					babe_config: babe_config.clone(),
-					shared_epoch_changes: shared_epoch_changes.clone(),
 					keystore: keystore.clone(),
+					babe_worker_handle: babe_worker_handle.clone(),
 				},
 				grandpa: node_rpc::GrandpaDeps {
 					shared_voter_state: shared_voter_state.clone(),

substrate/bin/node/rpc/Cargo.toml

@@ -21,7 +21,6 @@ sc-chain-spec = { version = "4.0.0-dev", path = "../../../client/chain-spec" }
 sc-client-api = { version = "4.0.0-dev", path = "../../../client/api" }
 sc-consensus-babe = { version = "0.10.0-dev", path = "../../../client/consensus/babe" }
 sc-consensus-babe-rpc = { version = "0.10.0-dev", path = "../../../client/consensus/babe/rpc" }
-sc-consensus-epochs = { version = "0.10.0-dev", path = "../../../client/consensus/epochs" }
 sc-consensus-grandpa = { version = "0.10.0-dev", path = "../../../client/consensus/grandpa" }
 sc-consensus-grandpa-rpc = { version = "0.10.0-dev", path = "../../../client/consensus/grandpa/rpc" }
 sc-rpc = { version = "4.0.0-dev", path = "../../../client/rpc" }

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

@@ -36,8 +36,7 @@ use std::sync::Arc;
 use jsonrpsee::RpcModule;
 use node_primitives::{AccountId, Balance, Block, BlockNumber, Hash, Index};
 use sc_client_api::AuxStore;
-use sc_consensus_babe::{BabeConfiguration, Epoch};
-use sc_consensus_epochs::SharedEpochChanges;
+use sc_consensus_babe::BabeWorkerHandle;
 use sc_consensus_grandpa::{
 	FinalityProofProvider, GrandpaJustificationStream, SharedAuthoritySet, SharedVoterState,
 };
@@ -53,10 +52,8 @@ use sp_keystore::KeystorePtr;
 
 /// Extra dependencies for BABE.
 pub struct BabeDeps {
-	/// BABE protocol config.
-	pub babe_config: BabeConfiguration,
-	/// BABE pending epoch changes.
-	pub shared_epoch_changes: SharedEpochChanges<Block, Epoch>,
+	/// A handle to the BABE worker for issuing requests.
+	pub babe_worker_handle: BabeWorkerHandle<Block>,
 	/// The keystore that manages the keys of the node.
 	pub keystore: KeystorePtr,
 }
@@ -130,7 +127,7 @@ where
 	let mut io = RpcModule::new(());
 	let FullDeps { client, pool, select_chain, chain_spec, deny_unsafe, babe, grandpa } = deps;
 
-	let BabeDeps { keystore, babe_config, shared_epoch_changes } = babe;
+	let BabeDeps { keystore, babe_worker_handle } = babe;
 	let GrandpaDeps {
 		shared_voter_state,
 		shared_authority_set,
@@ -151,15 +148,8 @@ where
 	io.merge(Mmr::new(client.clone()).into_rpc())?;
 	io.merge(TransactionPayment::new(client.clone()).into_rpc())?;
 	io.merge(
-		Babe::new(
-			client.clone(),
-			shared_epoch_changes.clone(),
-			keystore,
-			babe_config,
-			select_chain,
-			deny_unsafe,
-		)
-		.into_rpc(),
+		Babe::new(client.clone(), babe_worker_handle.clone(), keystore, select_chain, deny_unsafe)
+			.into_rpc(),
 	)?;
 	io.merge(
 		Grandpa::new(
@@ -173,7 +163,7 @@ where
 	)?;
 
 	io.merge(
-		SyncState::new(chain_spec, client.clone(), shared_authority_set, shared_epoch_changes)?
+		SyncState::new(chain_spec, client.clone(), shared_authority_set, babe_worker_handle)?
 			.into_rpc(),
 	)?;
 

substrate/client/consensus/babe/rpc/src/lib.rs

@@ -18,28 +18,29 @@
 
 //! RPC api for babe.
 
+use std::{collections::HashMap, sync::Arc};
+
 use futures::TryFutureExt;
 use jsonrpsee::{
 	core::{async_trait, Error as JsonRpseeError, RpcResult},
 	proc_macros::rpc,
 	types::{error::CallError, ErrorObject},
 };
-
-use sc_consensus_babe::{authorship, Epoch};
-use sc_consensus_epochs::{descendent_query, Epoch as EpochT, SharedEpochChanges};
-use sc_rpc_api::DenyUnsafe;
 use serde::{Deserialize, Serialize};
+
+use sc_consensus_babe::{authorship, BabeWorkerHandle};
+use sc_consensus_epochs::Epoch as EpochT;
+use sc_rpc_api::DenyUnsafe;
 use sp_api::ProvideRuntimeApi;
 use sp_application_crypto::AppCrypto;
 use sp_blockchain::{Error as BlockChainError, HeaderBackend, HeaderMetadata};
 use sp_consensus::{Error as ConsensusError, SelectChain};
-use sp_consensus_babe::{
-	digests::PreDigest, AuthorityId, BabeApi as BabeRuntimeApi, BabeConfiguration,
-};
+use sp_consensus_babe::{digests::PreDigest, AuthorityId, BabeApi as BabeRuntimeApi};
 use sp_core::crypto::ByteArray;
 use sp_keystore::KeystorePtr;
 use sp_runtime::traits::{Block as BlockT, Header as _};
-use std::{collections::HashMap, sync::Arc};
+
+const BABE_ERROR: i32 = 9000;
 
 /// Provides rpc methods for interacting with Babe.
 #[rpc(client, server)]
@@ -54,12 +55,10 @@ pub trait BabeApi {
 pub struct Babe<B: BlockT, C, SC> {
 	/// shared reference to the client.
 	client: Arc<C>,
-	/// shared reference to EpochChanges
-	shared_epoch_changes: SharedEpochChanges<B, Epoch>,
+	/// A handle to the BABE worker for issuing requests.
+	babe_worker_handle: BabeWorkerHandle<B>,
 	/// shared reference to the Keystore
 	keystore: KeystorePtr,
-	/// config (actually holds the slot duration)
-	babe_config: BabeConfiguration,
 	/// The SelectChain strategy
 	select_chain: SC,
 	/// Whether to deny unsafe calls
@@ -70,13 +69,12 @@ impl<B: BlockT, C, SC> Babe<B, C, SC> {
 	/// Creates a new instance of the Babe Rpc handler.
 	pub fn new(
 		client: Arc<C>,
-		shared_epoch_changes: SharedEpochChanges<B, Epoch>,
+		babe_worker_handle: BabeWorkerHandle<B>,
 		keystore: KeystorePtr,
-		babe_config: BabeConfiguration,
 		select_chain: SC,
 		deny_unsafe: DenyUnsafe,
 	) -> Self {
-		Self { client, shared_epoch_changes, keystore, babe_config, select_chain, deny_unsafe }
+		Self { client, babe_worker_handle, keystore, select_chain, deny_unsafe }
 	}
 }
 
@@ -93,21 +91,21 @@ where
 {
 	async fn epoch_authorship(&self) -> RpcResult<HashMap<AuthorityId, EpochAuthorship>> {
 		self.deny_unsafe.check_if_safe()?;
-		let header = self.select_chain.best_chain().map_err(Error::Consensus).await?;
+
+		let best_header = self.select_chain.best_chain().map_err(Error::SelectChain).await?;
+
 		let epoch_start = self
 			.client
 			.runtime_api()
-			.current_epoch_start(header.hash())
-			.map_err(|err| Error::StringError(format!("{:?}", err)))?;
+			.current_epoch_start(best_header.hash())
+			.map_err(|_| Error::FetchEpoch)?;
+
+		let epoch = self
+			.babe_worker_handle
+			.epoch_data_for_child_of(best_header.hash(), *best_header.number(), epoch_start)
+			.await
+			.map_err(|_| Error::FetchEpoch)?;
 
-		let epoch = epoch_data(
-			&self.shared_epoch_changes,
-			&self.client,
-			&self.babe_config,
-			*epoch_start,
-			&self.select_chain,
-		)
-		.await?;
 		let (epoch_start, epoch_end) = (epoch.start_slot(), epoch.end_slot());
 		let mut claims: HashMap<AuthorityId, EpochAuthorship> = HashMap::new();
 
@@ -159,59 +157,37 @@ pub struct EpochAuthorship {
 	secondary_vrf: Vec<u64>,
 }
 
-/// Errors encountered by the RPC
+/// Top-level error type for the RPC handler.
 #[derive(Debug, thiserror::Error)]
 pub enum Error {
-	/// Consensus error
-	#[error(transparent)]
-	Consensus(#[from] ConsensusError),
-	/// Errors that can be formatted as a String
-	#[error("{0}")]
-	StringError(String),
+	/// Failed to fetch the current best header.
+	#[error("Failed to fetch the current best header: {0}")]
+	SelectChain(ConsensusError),
+	/// Failed to fetch epoch data.
+	#[error("Failed to fetch epoch data")]
+	FetchEpoch,
 }
 
 impl From<Error> for JsonRpseeError {
 	fn from(error: Error) -> Self {
+		let error_code = match error {
+			Error::SelectChain(_) => 1,
+			Error::FetchEpoch => 2,
+		};
+
 		JsonRpseeError::Call(CallError::Custom(ErrorObject::owned(
-			1234,
+			BABE_ERROR + error_code,
 			error.to_string(),
-			None::<()>,
+			Some(format!("{:?}", error)),
 		)))
 	}
 }
 
-/// Fetches the epoch data for a given slot.
-async fn epoch_data<B, C, SC>(
-	epoch_changes: &SharedEpochChanges<B, Epoch>,
-	client: &Arc<C>,
-	babe_config: &BabeConfiguration,
-	slot: u64,
-	select_chain: &SC,
-) -> Result<Epoch, Error>
-where
-	B: BlockT,
-	C: HeaderBackend<B> + HeaderMetadata<B, Error = BlockChainError> + 'static,
-	SC: SelectChain<B>,
-{
-	let parent = select_chain.best_chain().await?;
-	epoch_changes
-		.shared_data()
-		.epoch_data_for_child_of(
-			descendent_query(&**client),
-			&parent.hash(),
-			*parent.number(),
-			slot.into(),
-			|slot| Epoch::genesis(babe_config, slot),
-		)
-		.map_err(|e| Error::Consensus(ConsensusError::ChainLookup(e.to_string())))?
-		.ok_or(Error::Consensus(ConsensusError::InvalidAuthoritiesSet))
-}
-
 #[cfg(test)]
 mod tests {
 	use super::*;
-	use sc_consensus_babe::block_import;
-	use sp_core::crypto::key_types::BABE;
+	use sp_consensus_babe::inherents::InherentDataProvider;
+	use sp_core::{crypto::key_types::BABE, testing::TaskExecutor};
 	use sp_keyring::Sr25519Keyring;
 	use sp_keystore::{testing::MemoryKeystore, Keystore};
 	use substrate_test_runtime_client::{
@@ -233,14 +209,35 @@ mod tests {
 		let builder = TestClientBuilder::new();
 		let (client, longest_chain) = builder.build_with_longest_chain();
 		let client = Arc::new(client);
-		let config = sc_consensus_babe::configuration(&*client).expect("config available");
-		let (_, link) = block_import(config.clone(), client.clone(), client.clone())
-			.expect("can initialize block-import");
-
-		let epoch_changes = link.epoch_changes().clone();
+		let task_executor = TaskExecutor::new();
 		let keystore = create_keystore(Sr25519Keyring::Alice);
 
-		Babe::new(client.clone(), epoch_changes, keystore, config, longest_chain, deny_unsafe)
+		let config = sc_consensus_babe::configuration(&*client).expect("config available");
+		let slot_duration = config.slot_duration();
+
+		let (block_import, link) =
+			sc_consensus_babe::block_import(config.clone(), client.clone(), client.clone())
+				.expect("can initialize block-import");
+
+		let (_, babe_worker_handle) = sc_consensus_babe::import_queue(
+			link.clone(),
+			block_import.clone(),
+			None,
+			client.clone(),
+			longest_chain.clone(),
+			move |_, _| async move {
+				Ok((InherentDataProvider::from_timestamp_and_slot_duration(
+					0.into(),
+					slot_duration,
+				),))
+			},
+			&task_executor,
+			None,
+			None,
+		)
+		.unwrap();
+
+		Babe::new(client.clone(), babe_worker_handle, keystore, longest_chain, deny_unsafe)
 	}
 
 	#[tokio::test]

substrate/client/consensus/babe/src/lib.rs

@@ -89,8 +89,8 @@ use prometheus_endpoint::Registry;
 use schnorrkel::SignatureError;
 
 use sc_client_api::{
-	backend::AuxStore, AuxDataOperations, Backend as BackendT, BlockchainEvents,
-	FinalityNotification, PreCommitActions, ProvideUncles, UsageProvider,
+	backend::AuxStore, AuxDataOperations, Backend as BackendT, FinalityNotification,
+	PreCommitActions, UsageProvider,
 };
 use sc_consensus::{
 	block_import::{
@@ -338,6 +338,9 @@ pub enum Error<B: BlockT> {
 	/// Create inherents error.
 	#[error("Creating inherents failed: {0}")]
 	CreateInherents(sp_inherents::Error),
+	/// Background worker is not running and therefore requests cannot be answered.
+	#[error("Background worker is not running")]
+	BackgroundWorkerTerminated,
 	/// Client error
 	#[error(transparent)]
 	Client(sp_blockchain::Error),
@@ -475,9 +478,6 @@ pub fn start_babe<B, C, SC, E, I, SO, CIDP, BS, L, Error>(
 where
 	B: BlockT,
 	C: ProvideRuntimeApi<B>
-		+ ProvideUncles<B>
-		+ BlockchainEvents<B>
-		+ PreCommitActions<B>
 		+ HeaderBackend<B>
 		+ HeaderMetadata<B, Error = ClientError>
 		+ Send
@@ -498,8 +498,6 @@ where
 	BS: BackoffAuthoringBlocksStrategy<NumberFor<B>> + Send + Sync + 'static,
 	Error: std::error::Error + Send + From<ConsensusError> + From<I::Error> + 'static,
 {
-	const HANDLE_BUFFER_SIZE: usize = 1024;
-
 	let slot_notification_sinks = Arc::new(Mutex::new(Vec::new()));
 
 	let worker = BabeSlotWorker {
@@ -529,17 +527,7 @@ where
 		create_inherent_data_providers,
 	);
 
-	let (worker_tx, worker_rx) = channel(HANDLE_BUFFER_SIZE);
-
-	let answer_requests =
-		answer_requests(worker_rx, babe_link.config, client, babe_link.epoch_changes);
-
-	let inner = future::select(Box::pin(slot_worker), Box::pin(answer_requests));
-	Ok(BabeWorker {
-		inner: Box::pin(inner.map(|_| ())),
-		slot_notification_sinks,
-		handle: BabeWorkerHandle(worker_tx),
-	})
+	Ok(BabeWorker { inner: Box::pin(slot_worker), slot_notification_sinks })
 }
 
 // Remove obsolete block's weight data by leveraging finality notifications.
@@ -593,42 +581,26 @@ async fn answer_requests<B: BlockT, C>(
 	client: Arc<C>,
 	epoch_changes: SharedEpochChanges<B, Epoch>,
 ) where
-	C: ProvideRuntimeApi<B>
-		+ ProvideUncles<B>
-		+ BlockchainEvents<B>
-		+ HeaderBackend<B>
-		+ HeaderMetadata<B, Error = ClientError>
-		+ Send
-		+ Sync
-		+ 'static,
+	C: HeaderBackend<B> + HeaderMetadata<B, Error = ClientError>,
 {
 	while let Some(request) = request_rx.next().await {
 		match request {
-			BabeRequest::EpochForChild(parent_hash, parent_number, slot_number, response) => {
+			BabeRequest::EpochData(response) => {
+				let _ = response.send(epoch_changes.shared_data().clone());
+			},
+			BabeRequest::EpochDataForChildOf(parent_hash, parent_number, slot, response) => {
 				let lookup = || {
 					let epoch_changes = epoch_changes.shared_data();
-					let epoch_descriptor = epoch_changes
-						.epoch_descriptor_for_child_of(
+					epoch_changes
+						.epoch_data_for_child_of(
 							descendent_query(&*client),
 							&parent_hash,
 							parent_number,
-							slot_number,
+							slot,
+							|slot| Epoch::genesis(&config, slot),
 						)
 						.map_err(|e| Error::<B>::ForkTree(Box::new(e)))?
-						.ok_or(Error::<B>::FetchEpoch(parent_hash))?;
-
-					let viable_epoch = epoch_changes
-						.viable_epoch(&epoch_descriptor, |slot| Epoch::genesis(&config, slot))
-						.ok_or(Error::<B>::FetchEpoch(parent_hash))?;
-
-					Ok(sp_consensus_babe::Epoch {
-						epoch_index: viable_epoch.as_ref().epoch_index,
-						start_slot: viable_epoch.as_ref().start_slot,
-						duration: viable_epoch.as_ref().duration,
-						authorities: viable_epoch.as_ref().authorities.clone(),
-						randomness: viable_epoch.as_ref().randomness,
-						config: viable_epoch.as_ref().config.clone(),
-					})
+						.ok_or(Error::<B>::FetchEpoch(parent_hash))
 				};
 
 				let _ = response.send(lookup());
@@ -638,17 +610,13 @@ async fn answer_requests<B: BlockT, C>(
 }
 
 /// Requests to the BABE service.
-#[non_exhaustive]
-pub enum BabeRequest<B: BlockT> {
+enum BabeRequest<B: BlockT> {
+	/// Request all available epoch data.
+	EpochData(oneshot::Sender<EpochChangesFor<B, Epoch>>),
 	/// Request the epoch that a child of the given block, with the given slot number would have.
 	///
 	/// The parent block is identified by its hash and number.
-	EpochForChild(
-		B::Hash,
-		NumberFor<B>,
-		Slot,
-		oneshot::Sender<Result<sp_consensus_babe::Epoch, Error<B>>>,
-	),
+	EpochDataForChildOf(B::Hash, NumberFor<B>, Slot, oneshot::Sender<Result<Epoch, Error<B>>>),
 }
 
 /// A handle to the BABE worker for issuing requests.
@@ -656,11 +624,41 @@ pub enum BabeRequest<B: BlockT> {
 pub struct BabeWorkerHandle<B: BlockT>(Sender<BabeRequest<B>>);
 
 impl<B: BlockT> BabeWorkerHandle<B> {
-	/// Send a request to the BABE service.
-	pub async fn send(&mut self, request: BabeRequest<B>) {
-		// Failure to send means that the service is down.
-		// This will manifest as the receiver of the request being dropped.
-		let _ = self.0.send(request).await;
+	async fn send_request(&self, request: BabeRequest<B>) -> Result<(), Error<B>> {
+		match self.0.clone().send(request).await {
+			Err(err) if err.is_disconnected() => return Err(Error::BackgroundWorkerTerminated),
+			Err(err) => warn!(
+				target: LOG_TARGET,
+				"Unhandled error when sending request to worker: {:?}", err
+			),
+			_ => {},
+		}
+
+		Ok(())
+	}
+
+	/// Fetch all available epoch data.
+	pub async fn epoch_data(&self) -> Result<EpochChangesFor<B, Epoch>, Error<B>> {
+		let (tx, rx) = oneshot::channel();
+		self.send_request(BabeRequest::EpochData(tx)).await?;
+
+		rx.await.or(Err(Error::BackgroundWorkerTerminated))
+	}
+
+	/// Fetch the epoch that a child of the given block, with the given slot number would have.
+	///
+	/// The parent block is identified by its hash and number.
+	pub async fn epoch_data_for_child_of(
+		&self,
+		parent_hash: B::Hash,
+		parent_number: NumberFor<B>,
+		slot: Slot,
+	) -> Result<Epoch, Error<B>> {
+		let (tx, rx) = oneshot::channel();
+		self.send_request(BabeRequest::EpochDataForChildOf(parent_hash, parent_number, slot, tx))
+			.await?;
+
+		rx.await.or(Err(Error::BackgroundWorkerTerminated))?
 	}
 }
 
@@ -669,7 +667,6 @@ impl<B: BlockT> BabeWorkerHandle<B> {
 pub struct BabeWorker<B: BlockT> {
 	inner: Pin<Box<dyn Future<Output = ()> + Send + 'static>>,
 	slot_notification_sinks: SlotNotificationSinks<B>,
-	handle: BabeWorkerHandle<B>,
 }
 
 impl<B: BlockT> BabeWorker<B> {
@@ -684,11 +681,6 @@ impl<B: BlockT> BabeWorker<B> {
 		self.slot_notification_sinks.lock().push(sink);
 		stream
 	}
-
-	/// Get a handle to the worker.
-	pub fn handle(&self) -> BabeWorkerHandle<B> {
-		self.handle.clone()
-	}
 }
 
 impl<B: BlockT> Future for BabeWorker<B> {
@@ -1790,7 +1782,7 @@ pub fn import_queue<Block: BlockT, Client, SelectChain, Inner, CIDP>(
 	spawner: &impl sp_core::traits::SpawnEssentialNamed,
 	registry: Option<&Registry>,
 	telemetry: Option<TelemetryHandle>,
-) -> ClientResult<DefaultImportQueue<Block, Client>>
+) -> ClientResult<(DefaultImportQueue<Block, Client>, BabeWorkerHandle<Block>)>
 where
 	Inner: BlockImport<
 			Block,
@@ -1811,16 +1803,28 @@ where
 	CIDP: CreateInherentDataProviders<Block, ()> + Send + Sync + 'static,
 	CIDP::InherentDataProviders: InherentDataProviderExt + Send + Sync,
 {
+	const HANDLE_BUFFER_SIZE: usize = 1024;
+
 	let verifier = BabeVerifier {
 		select_chain,
 		create_inherent_data_providers,
-		config: babe_link.config,
-		epoch_changes: babe_link.epoch_changes,
+		config: babe_link.config.clone(),
+		epoch_changes: babe_link.epoch_changes.clone(),
 		telemetry,
-		client,
+		client: client.clone(),
 	};
 
-	Ok(BasicQueue::new(verifier, Box::new(block_import), justification_import, spawner, registry))
+	let (worker_tx, worker_rx) = channel(HANDLE_BUFFER_SIZE);
+
+	let answer_requests =
+		answer_requests(worker_rx, babe_link.config, client, babe_link.epoch_changes);
+
+	spawner.spawn_essential("babe-worker", Some("babe"), answer_requests.boxed());
+
+	Ok((
+		BasicQueue::new(verifier, Box::new(block_import), justification_import, spawner, registry),
+		BabeWorkerHandle(worker_tx),
+	))
 }
 
 /// Reverts protocol aux data to at most the last finalized block.

substrate/client/sync-state-rpc/src/lib.rs

@@ -41,20 +41,21 @@
 
 #![deny(unused_crate_dependencies)]
 
+use std::sync::Arc;
+
 use jsonrpsee::{
-	core::{Error as JsonRpseeError, RpcResult},
+	core::{async_trait, Error as JsonRpseeError, RpcResult},
 	proc_macros::rpc,
 	types::{error::CallError, ErrorObject},
 };
+
 use sc_client_api::StorageData;
+use sc_consensus_babe::{BabeWorkerHandle, Error as BabeError};
 use sp_blockchain::HeaderBackend;
 use sp_runtime::traits::{Block as BlockT, NumberFor};
-use std::sync::Arc;
 
 type SharedAuthoritySet<TBl> =
 	sc_consensus_grandpa::SharedAuthoritySet<<TBl as BlockT>::Hash, NumberFor<TBl>>;
-type SharedEpochChanges<TBl> =
-	sc_consensus_epochs::SharedEpochChanges<TBl, sc_consensus_babe::Epoch>;
 
 /// Error type used by this crate.
 #[derive(Debug, thiserror::Error)]
@@ -66,6 +67,9 @@ pub enum Error<Block: BlockT> {
 	#[error("Failed to load the block weight for block {0:?}")]
 	LoadingBlockWeightFailed(Block::Hash),
 
+	#[error("Failed to load the BABE epoch data: {0}")]
+	LoadingEpochDataFailed(BabeError<Block>),
+
 	#[error("JsonRpc error: {0}")]
 	JsonRpc(String),
 
@@ -125,7 +129,7 @@ pub struct LightSyncState<Block: BlockT> {
 pub trait SyncStateApi {
 	/// Returns the JSON serialized chainspec running the node, with a sync state.
 	#[method(name = "sync_state_genSyncSpec")]
-	fn system_gen_sync_spec(&self, raw: bool) -> RpcResult<serde_json::Value>;
+	async fn system_gen_sync_spec(&self, raw: bool) -> RpcResult<serde_json::Value>;
 }
 
 /// An api for sync state RPC calls.
@@ -133,7 +137,7 @@ pub struct SyncState<Block: BlockT, Client> {
 	chain_spec: Box<dyn sc_chain_spec::ChainSpec>,
 	client: Arc<Client>,
 	shared_authority_set: SharedAuthoritySet<Block>,
-	shared_epoch_changes: SharedEpochChanges<Block>,
+	babe_worker_handle: BabeWorkerHandle<Block>,
 }
 
 impl<Block, Client> SyncState<Block, Client>
@@ -146,18 +150,24 @@ where
 		chain_spec: Box<dyn sc_chain_spec::ChainSpec>,
 		client: Arc<Client>,
 		shared_authority_set: SharedAuthoritySet<Block>,
-		shared_epoch_changes: SharedEpochChanges<Block>,
+		babe_worker_handle: BabeWorkerHandle<Block>,
 	) -> Result<Self, Error<Block>> {
 		if sc_chain_spec::get_extension::<LightSyncStateExtension>(chain_spec.extensions())
 			.is_some()
 		{
-			Ok(Self { chain_spec, client, shared_authority_set, shared_epoch_changes })
+			Ok(Self { chain_spec, client, shared_authority_set, babe_worker_handle })
 		} else {
 			Err(Error::<Block>::LightSyncStateExtensionNotFound)
 		}
 	}
 
-	fn build_sync_state(&self) -> Result<LightSyncState<Block>, Error<Block>> {
+	async fn build_sync_state(&self) -> Result<LightSyncState<Block>, Error<Block>> {
+		let epoch_changes = self
+			.babe_worker_handle
+			.epoch_data()
+			.await
+			.map_err(Error::LoadingEpochDataFailed)?;
+
 		let finalized_hash = self.client.info().finalized_hash;
 		let finalized_header = self
 			.client
@@ -170,20 +180,21 @@ where
 
 		Ok(LightSyncState {
 			finalized_block_header: finalized_header,
-			babe_epoch_changes: self.shared_epoch_changes.shared_data().clone(),
+			babe_epoch_changes: epoch_changes,
 			babe_finalized_block_weight: finalized_block_weight,
 			grandpa_authority_set: self.shared_authority_set.clone_inner(),
 		})
 	}
 }
 
+#[async_trait]
 impl<Block, Backend> SyncStateApiServer for SyncState<Block, Backend>
 where
 	Block: BlockT,
 	Backend: HeaderBackend<Block> + sc_client_api::AuxStore + 'static,
 {
-	fn system_gen_sync_spec(&self, raw: bool) -> RpcResult<serde_json::Value> {
-		let current_sync_state = self.build_sync_state()?;
+	async fn system_gen_sync_spec(&self, raw: bool) -> RpcResult<serde_json::Value> {
+		let current_sync_state = self.build_sync_state().await?;
 		let mut chain_spec = self.chain_spec.cloned_box();
 
 		let extension = sc_chain_spec::get_extension_mut::<LightSyncStateExtension>(