Add missing fields to the light sync state (#7225)

* Initial draft * Add an iterator that helps us get most items * Revert changes to grandpa * Change fields to just be the grandpa authority set and babe epoch changes * Only use the fields we need from the shared authority set * Switch to RPC call * Revert "Only use the fields we need from the shared authority set" This reverts commit 6ede87b0c5fe53f251d7cb45951006a7dc8f9b83. * Add babe_finalized_block_weight from `ashley-improve-sync-state-WIP-loading` * Fix rpc test * Move sync state rpc stuff into sc-sync-state-rpc * Remove as_json_value and remove unwraps from sc-sync-state-rpc * Add clone_inner to SharedAuthoritySet
2026-05-08 04:18:01 +00:00 · 2020-10-15 12:10:43 +02:00
parent a297e447f2
commit d1ef8507d7
22 changed files with 263 additions and 195 deletions
@@ -3826,6 +3826,7 @@ dependencies = [
 "node-runtime",
 "pallet-contracts-rpc",
 "pallet-transaction-payment-rpc",
+ "sc-chain-spec",
 "sc-client-api",
 "sc-consensus-babe",
 "sc-consensus-babe-rpc",
@@ -3835,6 +3836,7 @@ dependencies = [
 "sc-keystore",
 "sc-rpc",
 "sc-rpc-api",
+ "sc-sync-state-rpc",
 "sp-api",
 "sp-block-builder",
 "sp-blockchain",
@@ -6315,11 +6317,15 @@ dependencies = [
 "impl-trait-for-tuples",
 "parity-scale-codec",
 "sc-chain-spec-derive",
+ "sc-consensus-babe",
+ "sc-consensus-epochs",
+ "sc-finality-grandpa",
 "sc-network",
 "sc-telemetry",
 "serde",
 "serde_json",
 "sp-chain-spec",
+ "sp-consensus-babe",
 "sp-core",
 "sp-runtime",
 ]
@@ -6357,6 +6363,9 @@ dependencies = [
 "regex",
 "rpassword",
 "sc-client-api",
+ "sc-consensus-babe",
+ "sc-consensus-epochs",
+ "sc-finality-grandpa",
 "sc-informant",
 "sc-keystore",
 "sc-network",
@@ -7284,6 +7293,24 @@ dependencies = [
 "sp-core",
 ]

+[[package]]
+name = "sc-sync-state-rpc"
+version = "0.8.0"
+dependencies = [
+ "jsonrpc-core",
+ "jsonrpc-core-client",
+ "jsonrpc-derive",
+ "sc-chain-spec",
+ "sc-client-api",
+ "sc-consensus-babe",
+ "sc-consensus-epochs",
+ "sc-finality-grandpa",
+ "sc-rpc-api",
+ "serde_json",
+ "sp-blockchain",
+ "sp-runtime",
+]
+
 [[package]]
 name = "sc-telemetry"
 version = "2.0.0"
@@ -7570,9 +7597,9 @@ dependencies = [

 [[package]]
 name = "serde_json"
-version = "1.0.56"
+version = "1.0.58"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3433e879a558dde8b5e8feb2a04899cf34fdde1fafb894687e52105fc1162ac3"
+checksum = "a230ea9107ca2220eea9d46de97eddcb04cd00e92d13dda78e478dd33fa82bd4"
 dependencies = [
 "itoa",
 "ryu",
@@ -53,6 +53,7 @@ members = [
 	"client/service",
 	"client/service/test",
 	"client/state-db",
+	"client/sync-state-rpc",
 	"client/telemetry",
 	"client/transaction-pool",
 	"client/transaction-pool/graph",
@@ -59,9 +59,6 @@ pub enum Subcommand {
 	/// Build a chain specification.
 	BuildSpec(sc_cli::BuildSpecCmd),

-	/// Build a chain specification with a light client sync state.
-	BuildSyncSpec(sc_cli::BuildSyncSpecCmd),
-
 	/// Validate blocks.
 	CheckBlock(sc_cli::CheckBlockCmd),

@@ -21,7 +21,7 @@ use node_executor::Executor;
 use node_runtime::{Block, RuntimeApi};
 use sc_cli::{Result, SubstrateCli, RuntimeVersion, Role, ChainSpec};
 use sc_service::PartialComponents;
-use crate::service::{new_partial, new_full_base, NewFullBase};
+use crate::service::new_partial;

 impl SubstrateCli for Cli {
 	fn impl_name() -> String {
@@ -102,17 +102,6 @@ pub fn run() -> Result<()> {
 			let runner = cli.create_runner(cmd)?;
 			runner.sync_run(|config| cmd.run(config.chain_spec, config.network))
 		},
-		Some(Subcommand::BuildSyncSpec(cmd)) => {
-			let runner = cli.create_runner(cmd)?;
-			runner.async_run(|config| {
-				let chain_spec = config.chain_spec.cloned_box();
-				let network_config = config.network.clone();
-				let NewFullBase { task_manager, client, network_status_sinks, .. }
-					= new_full_base(config, |_, _| ())?;
-
-				Ok((cmd.run(chain_spec, network_config, client, network_status_sinks), task_manager))
-			})
-		},
 		Some(Subcommand::CheckBlock(cmd)) => {
 			let runner = cli.create_runner(cmd)?;
 			runner.async_run(|config| {
@@ -122,12 +122,14 @@ pub fn new_partial(config: &Configuration) -> Result<sc_service::PartialComponen
 		let pool = transaction_pool.clone();
 		let select_chain = select_chain.clone();
 		let keystore = keystore_container.sync_keystore();
+		let chain_spec = config.chain_spec.cloned_box();

 		let rpc_extensions_builder = move |deny_unsafe, subscription_executor| {
 			let deps = node_rpc::FullDeps {
 				client: client.clone(),
 				pool: pool.clone(),
 				select_chain: select_chain.clone(),
+				chain_spec: chain_spec.cloned_box(),
 				deny_unsafe,
 				babe: node_rpc::BabeDeps {
 					babe_config: babe_config.clone(),
@@ -20,11 +20,13 @@ sc-client-api = { version = "2.0.0", path = "../../../client/api" }
 sc-consensus-babe = { version = "0.8.0", path = "../../../client/consensus/babe" }
 sc-consensus-babe-rpc = { version = "0.8.0", path = "../../../client/consensus/babe/rpc" }
 sc-consensus-epochs = { version = "0.8.0", path = "../../../client/consensus/epochs" }
+sc-chain-spec = { version = "2.0.0", path = "../../../client/chain-spec" }
 sc-finality-grandpa = { version = "0.8.0", path = "../../../client/finality-grandpa" }
 sc-finality-grandpa-rpc = { version = "0.8.0", path = "../../../client/finality-grandpa/rpc" }
 sc-keystore = { version = "2.0.0", path = "../../../client/keystore" }
 sc-rpc-api = { version = "0.8.0", path = "../../../client/rpc-api" }
 sc-rpc = { version = "2.0.0", path = "../../../client/rpc" }
+sc-sync-state-rpc = { version = "0.8.0", path = "../../../client/sync-state-rpc" }
 sp-api = { version = "2.0.0", path = "../../../primitives/api" }
 sp-block-builder = { version = "2.0.0", path = "../../../primitives/block-builder" }
 sp-blockchain = { version = "2.0.0", path = "../../../primitives/blockchain" }
@@ -49,6 +49,7 @@ use sp_consensus::SelectChain;
 use sp_consensus_babe::BabeApi;
 use sc_rpc::SubscriptionTaskExecutor;
 use sp_transaction_pool::TransactionPool;
+use sc_client_api::AuxStore;

 /// Light client extra dependencies.
 pub struct LightDeps<C, F, P> {
@@ -94,6 +95,8 @@ pub struct FullDeps<C, P, SC, B> {
 	pub pool: Arc<P>,
 	/// The SelectChain Strategy
 	pub select_chain: SC,
+	/// A copy of the chain spec.
+	pub chain_spec: Box<dyn sc_chain_spec::ChainSpec>,
 	/// Whether to deny unsafe calls
 	pub deny_unsafe: DenyUnsafe,
 	/// BABE specific dependencies.
@@ -109,9 +112,8 @@ pub type IoHandler = jsonrpc_core::IoHandler<sc_rpc::Metadata>;
 pub fn create_full<C, P, SC, B>(
 	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,
-	C: Send + Sync + 'static,
+	C: ProvideRuntimeApi<Block> + HeaderBackend<Block> + AuxStore +
+		HeaderMetadata<Block, Error=BlockChainError> + Sync + Send + 'static,
 	C::Api: substrate_frame_rpc_system::AccountNonceApi<Block, AccountId, Index>,
 	C::Api: pallet_contracts_rpc::ContractsRuntimeApi<Block, AccountId, Balance, BlockNumber>,
 	C::Api: pallet_transaction_payment_rpc::TransactionPaymentRuntimeApi<Block, Balance>,
@@ -131,6 +133,7 @@ pub fn create_full<C, P, SC, B>(
 		client,
 		pool,
 		select_chain,
+		chain_spec,
 		deny_unsafe,
 		babe,
 		grandpa,
@@ -164,8 +167,8 @@ pub fn create_full<C, P, SC, B>(
 	io.extend_with(
 		sc_consensus_babe_rpc::BabeApi::to_delegate(
 			BabeRpcHandler::new(
-				client,
-				shared_epoch_changes,
+				client.clone(),
+				shared_epoch_changes.clone(),
 				keystore,
 				babe_config,
 				select_chain,
@@ -176,7 +179,7 @@ pub fn create_full<C, P, SC, B>(
 	io.extend_with(
 		sc_finality_grandpa_rpc::GrandpaApi::to_delegate(
 			GrandpaRpcHandler::new(
-				shared_authority_set,
+				shared_authority_set.clone(),
 				shared_voter_state,
 				justification_stream,
 				subscription_executor,
@@ -185,6 +188,18 @@ pub fn create_full<C, P, SC, B>(
 		)
 	);

+	io.extend_with(
+		sc_sync_state_rpc::SyncStateRpcApi::to_delegate(
+			sc_sync_state_rpc::SyncStateRpcHandler::new(
+				chain_spec,
+				client,
+				shared_authority_set,
+				shared_epoch_changes,
+				deny_unsafe,
+			)
+		)
+	);
+
 	io
 }

@@ -23,3 +23,7 @@ sp-runtime = { version = "2.0.0", path = "../../primitives/runtime" }
 sp-chain-spec = { version = "2.0.0", path = "../../primitives/chain-spec" }
 sc-telemetry = { version = "2.0.0", path = "../telemetry" }
 codec = { package = "parity-scale-codec", version = "1.3.4" }
+sc-consensus-babe = { version = "0.8.0-rc6", path = "../consensus/babe" }
+sp-consensus-babe = { version = "0.8.0-rc6", path = "../../primitives/consensus/babe" }
+sc-consensus-epochs = { version = "0.8.0-rc6", path = "../consensus/epochs" }
+sc-finality-grandpa = { version = "0.8.0-rc6", path = "../finality-grandpa" }
@@ -27,7 +27,7 @@ use serde_json as json;
 use crate::{RuntimeGenesis, ChainType, extension::GetExtension, Properties};
 use sc_network::config::MultiaddrWithPeerId;
 use sc_telemetry::TelemetryEndpoints;
-use sp_runtime::traits::Block as BlockT;
+use sp_runtime::traits::{Block as BlockT, NumberFor};

 enum GenesisSource<G> {
 	File(PathBuf),
@@ -264,7 +264,7 @@ impl<G, E> ChainSpec<G, E> {

 	/// Hardcode infomation to allow light clients to sync quickly into the chain spec.
 	fn set_light_sync_state(&mut self, light_sync_state: SerializableLightSyncState) {
-		self.client_spec.light_sync_state = Some(light_sync_state);	
+		self.client_spec.light_sync_state = Some(light_sync_state);
 	}
 }

@@ -338,7 +338,7 @@ impl<G: RuntimeGenesis, E: serde::Serialize + Clone + 'static> ChainSpec<G, E> {
 impl<G, E> crate::ChainSpec for ChainSpec<G, E>
 where
 	G: RuntimeGenesis + 'static,
-	E: GetExtension + serde::Serialize + Clone + Send + 'static,
+	E: GetExtension + serde::Serialize + Clone + Send + Sync + 'static,
 {
 	fn boot_nodes(&self) -> &[MultiaddrWithPeerId] {
 		ChainSpec::boot_nodes(self)
@@ -400,7 +400,13 @@ where
 /// Hardcoded infomation that allows light clients to sync quickly.
 pub struct LightSyncState<Block: BlockT> {
 	/// The header of the best finalized block.
-	pub header: <Block as BlockT>::Header,
+	pub finalized_block_header: <Block as BlockT>::Header,
+	/// The epoch changes tree for babe.
+	pub babe_epoch_changes: sc_consensus_epochs::EpochChangesFor<Block, sc_consensus_babe::Epoch>,
+	/// The babe weight of the finalized block.
+	pub babe_finalized_block_weight: sp_consensus_babe::BabeBlockWeight,
+	/// The authority set for grandpa.
+	pub grandpa_authority_set: sc_finality_grandpa::AuthoritySet<<Block as BlockT>::Hash, NumberFor<Block>>,
 }

 impl<Block: BlockT> LightSyncState<Block> {
@@ -409,14 +415,26 @@ impl<Block: BlockT> LightSyncState<Block> {
 		use codec::Encode;

 		SerializableLightSyncState {
-			header: StorageData(self.header.encode()),
+			finalized_block_header: StorageData(self.finalized_block_header.encode()),
+			babe_epoch_changes:
+				StorageData(self.babe_epoch_changes.encode()),
+			babe_finalized_block_weight:
+				self.babe_finalized_block_weight,
+			grandpa_authority_set:
+				StorageData(self.grandpa_authority_set.encode()),
 		}
 	}

 	/// Convert from a `SerializableLightSyncState`.
 	pub fn from_serializable(serialized: &SerializableLightSyncState) -> Result<Self, codec::Error> {
 		Ok(Self {
-			header: codec::Decode::decode(&mut &serialized.header.0[..])?,
+			finalized_block_header: codec::Decode::decode(&mut &serialized.finalized_block_header.0[..])?,
+			babe_epoch_changes:
+				codec::Decode::decode(&mut &serialized.babe_epoch_changes.0[..])?,
+			babe_finalized_block_weight:
+				serialized.babe_finalized_block_weight,
+			grandpa_authority_set:
+				codec::Decode::decode(&mut &serialized.grandpa_authority_set.0[..])?,
 		})
 	}
 }
@@ -426,7 +444,10 @@ impl<Block: BlockT> LightSyncState<Block> {
 #[serde(rename_all = "camelCase")]
 #[serde(deny_unknown_fields)]
 pub struct SerializableLightSyncState {
-	header: StorageData,
+	finalized_block_header: StorageData,
+	babe_epoch_changes: StorageData,
+	babe_finalized_block_weight: sp_consensus_babe::BabeBlockWeight,
+	grandpa_authority_set: StorageData,
 }

 #[cfg(test)]
@@ -126,7 +126,7 @@ pub trait RuntimeGenesis: Serialize + DeserializeOwned + BuildStorage {}
 impl<T: Serialize + DeserializeOwned + BuildStorage> RuntimeGenesis for T {}

 /// Common interface of a chain specification.
-pub trait ChainSpec: BuildStorage + Send {
+pub trait ChainSpec: BuildStorage + Send + Sync {
 	/// Spec name.
 	fn name(&self) -> &str;
 	/// Spec id.
@@ -45,6 +45,9 @@ sp-state-machine = { version = "0.8.0", path = "../../primitives/state-machine"
 sc-telemetry = { version = "2.0.0", path = "../telemetry" }
 substrate-prometheus-endpoint = { path = "../../utils/prometheus" , version = "0.8.0"}
 sp-keyring = { version = "2.0.0", path = "../../primitives/keyring" }
+sc-consensus-babe = { version = "0.8.0", path = "../consensus/babe" }
+sc-consensus-epochs = { version = "0.8.0", path = "../consensus/epochs" }
+sc-finality-grandpa = { version = "0.8.0", path = "../finality-grandpa" }
 names = "0.11.0"
 structopt = "0.3.8"
 sc-tracing = { version = "2.0.0", path = "../tracing" }
@@ -1,113 +0,0 @@
-// This file is part of Substrate.
-
-// Copyright (C) 2018-2020 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 crate::error;
-use crate::params::{SharedParams, NetworkParams};
-use crate::CliConfiguration;
-use log::info;
-use sc_network::config::build_multiaddr;
-use sc_service::{config::{MultiaddrWithPeerId, NetworkConfiguration}, ChainSpec};
-use structopt::StructOpt;
-use std::io::Write;
-use std::sync::Arc;
-use sp_runtime::traits::Block as BlockT;
-use sc_service::chain_ops::build_light_sync_state;
-use sc_service::NetworkStatusSinks;
-use futures::{FutureExt, StreamExt};
-use futures::future::ready;
-
-/// The `build-sync-spec` command used to build a chain spec that contains a light client state
-/// so that light clients can sync faster.
-#[derive(Debug, StructOpt)]
-pub struct BuildSyncSpecCmd {
-	/// Force raw genesis storage output.
-	#[structopt(long = "raw")]
-	pub raw: bool,
-
-	/// Sync the chain using a full client first.
-	#[structopt(long)]
-	pub sync_first: bool,
-
-	/// Disable adding the default bootnode to the specification.
-	///
-	/// By default the `/ip4/127.0.0.1/tcp/30333/p2p/NODE_PEER_ID` bootnode is added to the
-	/// specification when no bootnode exists.
-	#[structopt(long = "disable-default-bootnode")]
-	pub disable_default_bootnode: bool,
-
-	#[allow(missing_docs)]
-	#[structopt(flatten)]
-	pub shared_params: SharedParams,
-
-	#[allow(missing_docs)]
-	#[structopt(flatten)]
-	pub network_params: NetworkParams,
-}
-
-impl BuildSyncSpecCmd {
-	/// Run the build-sync-spec command
-	pub async fn run<B, CL>(
-		&self,
-		mut spec: Box<dyn ChainSpec>,
-		network_config: NetworkConfiguration,
-		client: Arc<CL>,
-		network_status_sinks: NetworkStatusSinks<B>,
-	) -> error::Result<()>
-		where
-			B: BlockT,
-			CL: sp_blockchain::HeaderBackend<B>,
-	{
-        if self.sync_first {
-            network_status_sinks.status_stream(std::time::Duration::from_secs(1)).filter(|status| {
-                ready(status.sync_state == sc_network::SyncState::Idle && status.num_sync_peers > 0)
-            }).into_future().map(drop).await;
-        }
-
-        let light_sync_state = build_light_sync_state(client)?;
-        spec.set_light_sync_state(light_sync_state.to_serializable());
-
-		info!("Building chain spec");
-		let raw_output = self.raw;
-
-		if spec.boot_nodes().is_empty() && !self.disable_default_bootnode {
-			let keys = network_config.node_key.into_keypair()?;
-			let peer_id = keys.public().into_peer_id();
-			let addr = MultiaddrWithPeerId {
-				multiaddr: build_multiaddr![Ip4([127, 0, 0, 1]), Tcp(30333u16)],
-				peer_id,
-			};
-			spec.add_boot_node(addr)
-		}
-
-		let json = sc_service::chain_ops::build_spec(&*spec, raw_output)?;
-		if std::io::stdout().write_all(json.as_bytes()).is_err() {
-			let _ = std::io::stderr().write_all(b"Error writing to stdout\n");
-		}
-		Ok(())
-	}
-}
-
-impl CliConfiguration for BuildSyncSpecCmd {
-	fn shared_params(&self) -> &SharedParams {
-		&self.shared_params
-	}
-
-	fn network_params(&self) -> Option<&NetworkParams> {
-		Some(&self.network_params)
-	}
-}
@@ -16,7 +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/>.
 mod build_spec_cmd;
-mod build_sync_spec_cmd;
 mod check_block_cmd;
 mod export_blocks_cmd;
 mod export_state_cmd;
@@ -37,7 +36,6 @@ pub mod utils;

 pub use self::{
 	build_spec_cmd::BuildSpecCmd,
-	build_sync_spec_cmd::BuildSyncSpecCmd,
 	check_block_cmd::CheckBlockCmd,
 	export_blocks_cmd::ExportBlocksCmd,
 	export_state_cmd::ExportStateCmd,
@@ -126,7 +126,7 @@ pub(crate) fn write_block_weight<H: Encode, F, R>(
 }

 /// Load the cumulative chain-weight associated with a block.
-pub(crate) fn load_block_weight<H: Encode, B: AuxStore>(
+pub fn load_block_weight<H: Encode, B: AuxStore>(
 	backend: &B,
 	block_hash: H,
 ) -> ClientResult<Option<BabeBlockWeight>> {
@@ -81,6 +81,11 @@ where N: Add<Output=N> + Ord + Clone + Debug,
 			 qed.",
 		)
 	}
+
+	/// Clone the inner `AuthoritySet`.
+	pub fn clone_inner(&self) -> AuthoritySet<H, N> {
+		self.inner.read().clone()
+	}
 }

 impl<H, N> From<AuthoritySet<H, N>> for SharedAuthoritySet<H, N> {
@@ -101,7 +106,7 @@ pub(crate) struct Status<H, N> {

 /// A set of authorities.
 #[derive(Debug, Clone, Encode, Decode, PartialEq)]
-pub(crate) struct AuthoritySet<H, N> {
+pub struct AuthoritySet<H, N> {
 	/// The current active authorities.
 	pub(crate) current_authorities: AuthorityList,
 	/// The current set id.
@@ -494,7 +499,7 @@ where

 /// Kinds of delays for pending changes.
 #[derive(Debug, Clone, Encode, Decode, PartialEq)]
-pub(crate) enum DelayKind<N> {
+pub enum DelayKind<N> {
 	/// Depth in finalized chain.
 	Finalized,
 	/// Depth in best chain. The median last finalized block is calculated at the time the
@@ -507,7 +512,7 @@ pub(crate) enum DelayKind<N> {
 /// This will be applied when the announcing block is at some depth within
 /// the finalized or unfinalized chain.
 #[derive(Debug, Clone, Encode, PartialEq)]
-pub(crate) struct PendingChange<H, N> {
+pub struct PendingChange<H, N> {
 	/// The new authorities and weights to apply.
 	pub(crate) next_authorities: AuthorityList,
 	/// How deep in the chain the announcing block must be
@@ -124,7 +124,7 @@ mod observer;
 mod until_imported;
 mod voting_rule;

-pub use authorities::SharedAuthoritySet;
+pub use authorities::{SharedAuthoritySet, AuthoritySet};
 pub use finality_proof::{FinalityProofFragment, FinalityProofProvider, StorageAndProofProvider};
 pub use notification::{GrandpaJustificationSender, GrandpaJustificationStream};
 pub use import::GrandpaBlockImport;
@@ -1,36 +0,0 @@
-// Copyright 2020 Parity Technologies (UK) Ltd.
-// This file is part of Substrate.
-
-// Substrate 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.
-
-// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
-
-use sp_runtime::traits::Block as BlockT;
-use sp_blockchain::HeaderBackend;
-use std::sync::Arc;
-use sp_runtime::generic::BlockId;
-
-/// Build a `LightSyncState` from the CHT roots stored in a backend.
-pub fn build_light_sync_state<TBl, TCl>(
-	client: Arc<TCl>,
-) -> Result<sc_chain_spec::LightSyncState<TBl>, sp_blockchain::Error>
-	where
-		TBl: BlockT,
-		TCl: HeaderBackend<TBl>,
-{
-	let finalized_hash = client.info().finalized_hash;
-	let header = client.header(BlockId::Hash(finalized_hash))?.unwrap();
-
-	Ok(sc_chain_spec::LightSyncState {
-		header
-	})
-}
@@ -21,11 +21,9 @@ mod export_blocks;
 mod export_raw_state;
 mod import_blocks;
 mod revert_chain;
-mod build_sync_spec;

 pub use check_block::*;
 pub use export_blocks::*;
 pub use export_raw_state::*;
 pub use import_blocks::*;
 pub use revert_chain::*;
-pub use build_sync_spec::*;
@@ -194,7 +194,7 @@ where F: Clone + Send + 'static, L: Clone + Send +'static, U: Clone + Send + 'st
 	}
 }

-fn node_config<G: RuntimeGenesis + 'static, E: ChainSpecExtension + Clone + 'static + Send> (
+fn node_config<G: RuntimeGenesis + 'static, E: ChainSpecExtension + Clone + 'static + Send + Sync> (
 	index: usize,
 	spec: &GenericChainSpec<G, E>,
 	role: Role,
@@ -275,7 +275,7 @@ fn node_config<G: RuntimeGenesis + 'static, E: ChainSpecExtension + Clone + 'sta
 impl<G, E, F, L, U> TestNet<G, E, F, L, U> where
 	F: TestNetNode,
 	L: TestNetNode,
-	E: ChainSpecExtension + Clone + 'static + Send,
+	E: ChainSpecExtension + Clone + 'static + Send + Sync,
 	G: RuntimeGenesis + 'static,
 {
 	fn new(
@@ -389,7 +389,7 @@ pub fn connectivity<G, E, Fb, F, Lb, L>(
 	full_builder: Fb,
 	light_builder: Lb,
 ) where
-	E: ChainSpecExtension + Clone + 'static + Send,
+	E: ChainSpecExtension + Clone + 'static + Send + Sync,
 	G: RuntimeGenesis + 'static,
 	Fb: Fn(Configuration) -> Result<F, Error>,
 	F: TestNetNode,
@@ -509,7 +509,7 @@ pub fn sync<G, E, Fb, F, Lb, L, B, ExF, U>(
 	B: FnMut(&F, &mut U),
 	ExF: FnMut(&F, &U) -> <F::Block as BlockT>::Extrinsic,
 	U: Clone + Send + 'static,
-	E: ChainSpecExtension + Clone + 'static + Send,
+	E: ChainSpecExtension + Clone + 'static + Send + Sync,
 	G: RuntimeGenesis + 'static,
 {
 	const NUM_FULL_NODES: usize = 10;
@@ -584,7 +584,7 @@ pub fn consensus<G, E, Fb, F, Lb, L>(
 	F: TestNetNode,
 	Lb: Fn(Configuration) -> Result<L, Error>,
 	L: TestNetNode,
-	E: ChainSpecExtension + Clone + 'static + Send,
+	E: ChainSpecExtension + Clone + 'static + Send + Sync,
 	G: RuntimeGenesis + 'static,
 {
 	const NUM_FULL_NODES: usize = 10;
@@ -0,0 +1,27 @@
+[package]
+name = "sc-sync-state-rpc"
+version = "0.8.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+description = "A RPC handler to create sync states for light clients."
+edition = "2018"
+license = "Apache-2.0"
+homepage = "https://substrate.dev"
+repository = "https://github.com/paritytech/substrate/"
+readme = "README.md"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+jsonrpc-core = "15.0"
+jsonrpc-core-client = "15.0"
+jsonrpc-derive = "15.0"
+sc-chain-spec = { version = "2.0.0", path = "../chain-spec" }
+sc-client-api = { version = "2.0.0", path = "../api" }
+sc-consensus-babe = { version = "0.8.0", path = "../consensus/babe" }
+sc-consensus-epochs = { version = "0.8.0", path = "../consensus/epochs" }
+sc-finality-grandpa = { version = "0.8.0", path = "../finality-grandpa" }
+sc-rpc-api = { version = "0.8.0", path = "../rpc-api" }
+serde_json = "1.0.58"
+sp-blockchain = { version = "2.0.0", path = "../../primitives/blockchain" }
+sp-runtime = { version = "2.0.0", path = "../../primitives/runtime" }
@@ -0,0 +1,128 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! A RPC handler to create sync states for light clients.
+//! Currently only usable with BABE + GRANDPA.
+
+use sp_runtime::traits::{Block as BlockT, NumberFor};
+use sp_blockchain::HeaderBackend;
+use std::sync::Arc;
+use sp_runtime::generic::BlockId;
+
+use jsonrpc_derive::rpc;
+
+type SharedAuthoritySet<TBl> =
+	sc_finality_grandpa::SharedAuthoritySet<<TBl as BlockT>::Hash, NumberFor<TBl>>;
+type SharedEpochChanges<TBl> = sc_consensus_epochs::SharedEpochChanges<TBl, sc_consensus_babe::Epoch>;
+
+struct Error(sp_blockchain::Error);
+
+impl From<Error> for jsonrpc_core::Error {
+	fn from(error: Error) -> Self {
+		jsonrpc_core::Error {
+			message: error.0.to_string(),
+			code:  jsonrpc_core::ErrorCode::ServerError(1),
+			data: None,
+		}
+	}
+}
+
+/// An api for sync state RPC calls.
+#[rpc]
+pub trait SyncStateRpcApi {
+	/// Returns the json-serialized chainspec running the node, with a sync state.
+	#[rpc(name = "sync_state_genSyncSpec", returns = "jsonrpc_core::Value")]
+	fn system_gen_sync_spec(&self, raw: bool)
+		-> jsonrpc_core::Result<jsonrpc_core::Value>;
+}
+
+/// The handler for sync state RPC calls.
+pub struct SyncStateRpcHandler<TBl: BlockT, TCl> {
+	chain_spec: Box<dyn sc_chain_spec::ChainSpec>,
+	client: Arc<TCl>,
+	shared_authority_set: SharedAuthoritySet<TBl>,
+	shared_epoch_changes: SharedEpochChanges<TBl>,
+	deny_unsafe: sc_rpc_api::DenyUnsafe,
+}
+
+impl<TBl, TCl> SyncStateRpcHandler<TBl, TCl>
+	where
+		TBl: BlockT,
+		TCl: HeaderBackend<TBl> + sc_client_api::AuxStore + 'static,
+{
+	/// Create a new handler.
+	pub fn new(
+		chain_spec: Box<dyn sc_chain_spec::ChainSpec>,
+		client: Arc<TCl>,
+		shared_authority_set: SharedAuthoritySet<TBl>,
+		shared_epoch_changes: SharedEpochChanges<TBl>,
+		deny_unsafe: sc_rpc_api::DenyUnsafe,
+	) -> Self {
+		Self {
+			chain_spec, client, shared_authority_set, shared_epoch_changes, deny_unsafe,
+		}
+	}
+	
+	fn build_sync_state(&self) -> Result<sc_chain_spec::LightSyncState<TBl>, sp_blockchain::Error> {
+		let finalized_hash = self.client.info().finalized_hash;
+		let finalized_header = self.client.header(BlockId::Hash(finalized_hash))?
+			.ok_or_else(|| sp_blockchain::Error::Msg(
+				format!("Failed to get the header for block {:?}", finalized_hash)
+			))?;
+
+		let finalized_block_weight = sc_consensus_babe::aux_schema::load_block_weight(
+			&*self.client,
+			finalized_hash,
+		)?
+			.ok_or_else(|| sp_blockchain::Error::Msg(
+				format!("Failed to load the block weight for block {:?}", finalized_hash)
+			))?;
+
+		Ok(sc_chain_spec::LightSyncState {
+			finalized_block_header: finalized_header,
+			babe_epoch_changes: self.shared_epoch_changes.lock().clone(),
+			babe_finalized_block_weight: finalized_block_weight,
+			grandpa_authority_set: self.shared_authority_set.clone_inner(),
+		})
+	}
+}
+
+impl<TBl, TCl> SyncStateRpcApi for SyncStateRpcHandler<TBl, TCl>
+	where
+		TBl: BlockT,
+		TCl: HeaderBackend<TBl> + sc_client_api::AuxStore + 'static,
+{
+	fn system_gen_sync_spec(&self, raw: bool)
+		-> jsonrpc_core::Result<jsonrpc_core::Value>
+	{
+		if let Err(err) = self.deny_unsafe.check_if_safe() {
+			return Err(err.into());
+		}
+
+		let mut chain_spec = self.chain_spec.cloned_box();
+
+		let sync_state = self.build_sync_state().map_err(Error)?;
+
+		chain_spec.set_light_sync_state(sync_state.to_serializable());
+		let string = chain_spec.as_json(raw).map_err(map_error)?;
+
+		serde_json::from_str(&string).map_err(|err| map_error(err.to_string()))
+	}
+}
+
+fn map_error(error: String) -> jsonrpc_core::Error {
+	Error(sp_blockchain::Error::Msg(error)).into()
+}
@@ -41,7 +41,7 @@ pub async fn browser_configuration<G, E>(chain_spec: GenericChainSpec<G, E>)
 	-> Result<Configuration, Box<dyn std::error::Error>>
 where
 	G: RuntimeGenesis + 'static,
-	E: Extension + 'static + Send,
+	E: Extension + 'static + Send + Sync,
 {
 	let name = chain_spec.name().to_string();