Expose GRANDPA round state through RPC (#5375)

* grandpa: wire up basic RPC call * grandpa: make it compile against GRANDPA with expose round state * grandpa: use shared voter state to expose RPC endpoint * grandpa: restructure into nested structs * grandpa: return background rounds too * grandpa: return error when endpoint not ready * grandpa: collect grandpa rpc deps * grandpa: decide to use concrete AuthorityId in finality-grandpa-rpc * grandpa: remove unncessary type annotation * grandpa: move error code to const * grandpa: remove unnecessary WIP comment * grandpa: remove Id type parameter for SharedVoterState * grandpa: update tests to add shared_voter_state in parameters * grandpa: remove old deprecated test * grandpa: fix getting the correct set_id * grandpa: make SharedVoterState a struct * grandpa: wrap shared_voter_state in rpc_setup * grandpa: replace spaces with tabs * grandpa: limit RwLock write attempt to 1 sec * grandpa: add missing doc comments and remove some pub * Apply suggestions from code review Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com> Co-Authored-By: Hernando Castano <HCastano@users.noreply.github.com> * grandpa: update function name call after change in finality-grandpa * grandpa: group pub use and only export voter::report * grandpa: add missing docs * grandpa: extract out structs used for json serialization * grandpa: stick to u32 for fields intended for js * grandpa: move Error type to its own file * grandpa: group pub use better * Apply code review suggestion Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com> * grandpa: use correct version of finality-granpda in rpc crate * grandpa: add back basic rpc unit test * grandpa: replace SharedVoterState::new() with empty() * node: cleanup grandpa::SharedVoterState usage in macro * grandpa: remove VoterState error variant * grandpa: enable missing futures compat feature * grandpa: fix typo in error variant * grandpa: remove test_utils * grandpa: allow mocking rpc handler components * grandpa: rename serialized to report in rpc module * grandpa: add proper test for RPC * grandpa: update to finality-grandpa v0.12.1 Co-authored-by: André Silva <andre.beat@gmail.com> Co-authored-by: Demi Obenour <demi@parity.io> Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com> Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com> Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
2026-06-09 20:11:09 +00:00 · 2020-05-04 21:37:22 +02:00
parent 8df33e50af
commit 1f7f8abb33
15 changed files with 552 additions and 19 deletions
@@ -1352,9 +1352,9 @@ dependencies = [

 [[package]]
 name = "finality-grandpa"
-version = "0.12.0"
+version = "0.12.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9d7907cc24468e29b5d3ea2097e78104492b6650c55f96af1f14e7915dc155ad"
+checksum = "5ab32971efbe776e46bfbc34d5b662d8e1de51fd14e26a2eba522c0f3470fc0f"
 dependencies = [
 "either",
 "futures 0.3.4",
@@ -3447,6 +3447,7 @@ dependencies = [
 "pallet-timestamp",
 "pallet-transaction-payment",
 "parity-scale-codec",
+ "parking_lot 0.10.2",
 "platforms",
 "rand 0.7.3",
 "regex",
@@ -3565,6 +3566,8 @@ dependencies = [
 "sc-consensus-babe",
 "sc-consensus-babe-rpc",
 "sc-consensus-epochs",
+ "sc-finality-grandpa",
+ "sc-finality-grandpa-rpc",
 "sc-keystore",
 "sp-api",
 "sp-blockchain",
@@ -3660,6 +3663,7 @@ dependencies = [
 "futures 0.3.4",
 "log",
 "node-template-runtime",
+ "parking_lot 0.10.2",
 "sc-basic-authorship",
 "sc-cli",
 "sc-client-api",
@@ -6400,6 +6404,23 @@ dependencies = [
 "tokio 0.2.18",
 ]

+[[package]]
+name = "sc-finality-grandpa-rpc"
+version = "0.8.0-dev"
+dependencies = [
+ "derive_more",
+ "finality-grandpa",
+ "futures 0.3.4",
+ "jsonrpc-core",
+ "jsonrpc-core-client",
+ "jsonrpc-derive",
+ "log",
+ "sc-finality-grandpa",
+ "serde",
+ "serde_json",
+ "sp-core",
+]
+
 [[package]]
 name = "sc-informant"
 version = "0.8.0-dev"
@@ -19,6 +19,7 @@ name = "node-template"
 futures = "0.3.4"
 log = "0.4.8"
 structopt = "0.3.8"
+parking_lot = "0.10.0"

 sc-cli = { version = "0.8.0-dev", path = "../../../client/cli" }
 sp-core = { version = "2.0.0-dev", path = "../../../primitives/core" }
@@ -10,7 +10,9 @@ use sp_inherents::InherentDataProviders;
 use sc_executor::native_executor_instance;
 pub use sc_executor::NativeExecutor;
 use sp_consensus_aura::sr25519::{AuthorityPair as AuraPair};
-use sc_finality_grandpa::{self, FinalityProofProvider as GrandpaFinalityProofProvider, StorageAndProofProvider};
+use sc_finality_grandpa::{
+	FinalityProofProvider as GrandpaFinalityProofProvider, StorageAndProofProvider, SharedVoterState,
+};

 // Our native executor instance.
 native_executor_instance!(
@@ -157,7 +159,8 @@ pub fn new_full(config: Configuration) -> Result<impl AbstractService, ServiceEr
 			inherent_data_providers: inherent_data_providers.clone(),
 			telemetry_on_connect: Some(service.telemetry_on_connect_stream()),
 			voting_rule: sc_finality_grandpa::VotingRulesBuilder::default().build(),
-			prometheus_registry: service.prometheus_registry()
+			prometheus_registry: service.prometheus_registry(),
+			shared_voter_state: SharedVoterState::empty(),
 		};

 		// the GRANDPA voter task is considered infallible, i.e.
@@ -43,6 +43,7 @@ log = "0.4.8"
 rand = "0.7.2"
 structopt = { version = "0.3.8", optional = true }
 tracing = "0.1.10"
+parking_lot = "0.10.0"

 # primitives
 sp-authority-discovery = { version = "2.0.0-dev",  path = "../../../primitives/authority-discovery" }
@@ -21,7 +21,9 @@
 use std::sync::Arc;

 use sc_consensus_babe;
-use grandpa::{self, FinalityProofProvider as GrandpaFinalityProofProvider, StorageAndProofProvider};
+use grandpa::{
+	self, FinalityProofProvider as GrandpaFinalityProofProvider, StorageAndProofProvider,
+};
 use node_executor;
 use node_primitives::Block;
 use node_runtime::RuntimeApi;
@@ -38,8 +40,10 @@ use sc_consensus::LongestChain;
 macro_rules! new_full_start {
 	($config:expr) => {{
 		use std::sync::Arc;
+
 		type RpcExtension = jsonrpc_core::IoHandler<sc_rpc::Metadata>;
 		let mut import_setup = None;
+		let mut rpc_setup = None;
 		let inherent_data_providers = sp_inherents::InherentDataProviders::new();

 		let builder = sc_service::ServiceBuilder::new_full::<
@@ -88,6 +92,10 @@ macro_rules! new_full_start {
 			.with_rpc_extensions(|builder| -> std::result::Result<RpcExtension, _> {
 				let babe_link = import_setup.as_ref().map(|s| &s.2)
 					.expect("BabeLink is present for full services or set up failed; qed.");
+				let grandpa_link = import_setup.as_ref().map(|s| &s.1)
+					.expect("GRANDPA LinkHalf is present for full services or set up failed; qed.");
+				let shared_authority_set = grandpa_link.shared_authority_set();
+				let shared_voter_state = grandpa::SharedVoterState::empty();
 				let deps = node_rpc::FullDeps {
 					client: builder.client().clone(),
 					pool: builder.pool(),
@@ -97,12 +105,17 @@ macro_rules! new_full_start {
 						keystore: builder.keystore(),
 						babe_config: sc_consensus_babe::BabeLink::config(babe_link).clone(),
 						shared_epoch_changes: sc_consensus_babe::BabeLink::epoch_changes(babe_link).clone()
-					}
+					},
+					grandpa: node_rpc::GrandpaDeps {
+						shared_voter_state: shared_voter_state.clone(),
+						shared_authority_set: shared_authority_set.clone(),
+					},
 				};
+				rpc_setup = Some((shared_voter_state));
 				Ok(node_rpc::create_full(deps))
 			})?;

-		(builder, import_setup, inherent_data_providers)
+		(builder, import_setup, inherent_data_providers, rpc_setup)
 	}}
 }

@@ -128,7 +141,8 @@ macro_rules! new_full {
 			$config.disable_grandpa,
 		);

-		let (builder, mut import_setup, inherent_data_providers) = new_full_start!($config);
+		let (builder, mut import_setup, inherent_data_providers, mut rpc_setup) =
+			new_full_start!($config);

 		let service = builder
 			.with_finality_proof_provider(|client, backend| {
@@ -139,7 +153,10 @@ macro_rules! new_full {
 			.build()?;

 		let (block_import, grandpa_link, babe_link) = import_setup.take()
-				.expect("Link Half and Block Import are present for Full Services or setup failed before. qed");
+			.expect("Link Half and Block Import are present for Full Services or setup failed before. qed");
+
+		let shared_voter_state = rpc_setup.take()
+			.expect("The SharedVoterState is present for Full Services or setup failed before. qed");

 		($with_startup_data)(&block_import, &babe_link);

@@ -240,6 +257,7 @@ macro_rules! new_full {
 				telemetry_on_connect: Some(service.telemetry_on_connect_stream()),
 				voting_rule: grandpa::VotingRulesBuilder::default().build(),
 				prometheus_registry: service.prometheus_registry(),
+				shared_voter_state,
 			};

 			// the GRANDPA voter task is considered infallible, i.e.
@@ -28,3 +28,5 @@ sc-keystore = { version = "2.0.0-dev", path = "../../../client/keystore" }
 sc-consensus-epochs = { version = "0.8.0-dev", path = "../../../client/consensus/epochs" }
 sp-consensus = { version = "0.8.0-dev", path = "../../../primitives/consensus/common" }
 sp-blockchain = { version = "2.0.0-dev", path = "../../../primitives/blockchain" }
+sc-finality-grandpa = { version = "0.8.0-dev", path = "../../../client/finality-grandpa" }
+sc-finality-grandpa-rpc = { version = "0.8.0-dev", path = "../../../client/finality-grandpa/rpc" }
@@ -31,7 +31,7 @@

 use std::{sync::Arc, fmt};

-use node_primitives::{Block, BlockNumber, AccountId, Index, Balance};
+use node_primitives::{Block, BlockNumber, AccountId, Index, Balance, Hash};
 use node_runtime::UncheckedExtrinsic;
 use sp_api::ProvideRuntimeApi;
 use sp_transaction_pool::TransactionPool;
@@ -42,6 +42,8 @@ use sp_consensus_babe::BabeApi;
 use sc_consensus_epochs::SharedEpochChanges;
 use sc_consensus_babe::{Config, Epoch};
 use sc_consensus_babe_rpc::BabeRPCHandler;
+use sc_finality_grandpa::{SharedVoterState, SharedAuthoritySet};
+use sc_finality_grandpa_rpc::GrandpaRpcHandler;

 /// Light client extra dependencies.
 pub struct LightDeps<C, F, P> {
@@ -65,6 +67,14 @@ pub struct BabeDeps {
 	pub keystore: KeyStorePtr,
 }

+/// Extra dependencies for GRANDPA
+pub struct GrandpaDeps {
+	/// Voting round info.
+	pub shared_voter_state: SharedVoterState,
+	/// Authority set info.
+	pub shared_authority_set: SharedAuthoritySet<Hash, BlockNumber>,
+}
+
 /// Full client dependencies.
 pub struct FullDeps<C, P, SC> {
 	/// The client instance to use.
@@ -75,6 +85,8 @@ pub struct FullDeps<C, P, SC> {
 	pub select_chain: SC,
 	/// BABE specific dependencies.
 	pub babe: BabeDeps,
+	/// GRANDPA specific dependencies.
+	pub grandpa: GrandpaDeps,
 }

 /// Instantiate all Full RPC extensions.
@@ -102,13 +114,18 @@ pub fn create_full<C, P, M, SC>(
 		client,
 		pool,
 		select_chain,
-		babe
+		babe,
+		grandpa,
 	} = deps;
 	let BabeDeps {
 		keystore,
 		babe_config,
 		shared_epoch_changes,
 	} = babe;
+	let GrandpaDeps {
+		shared_voter_state,
+		shared_authority_set,
+	} = grandpa;

 	io.extend_with(
 		SystemApi::to_delegate(FullSystem::new(client.clone(), pool))
@@ -127,6 +144,11 @@ pub fn create_full<C, P, M, SC>(
 			BabeRPCHandler::new(client, shared_epoch_changes, keystore, babe_config, select_chain)
 		)
 	);
+	io.extend_with(
+		sc_finality_grandpa_rpc::GrandpaApi::to_delegate(
+			GrandpaRpcHandler::new(shared_authority_set, shared_voter_state)
+		)
+	);

 	io
 }
@@ -42,11 +42,11 @@ sp-finality-tracker = { version = "2.0.0-dev", path = "../../primitives/finality
 sp-finality-grandpa = { version = "2.0.0-dev", path = "../../primitives/finality-grandpa" }
 prometheus-endpoint = { package = "substrate-prometheus-endpoint", path = "../../utils/prometheus", version = "0.8.0-dev"}
 sc-block-builder = { version = "0.8.0-dev", path = "../block-builder" }
-finality-grandpa = { version = "0.12.0", features = ["derive-codec"] }
+finality-grandpa = { version = "0.12.1", features = ["derive-codec"] }
 pin-project = "0.4.6"

 [dev-dependencies]
-finality-grandpa = { version = "0.12.0", features = ["derive-codec", "test-helpers"] }
+finality-grandpa = { version = "0.12.1", features = ["derive-codec", "test-helpers"] }
 sc-network = { version = "0.8.0-dev", path = "../network" }
 sc-network-test = { version = "0.8.0-dev", path = "../network/test" }
 sp-keyring = { version = "2.0.0-dev", path = "../../primitives/keyring" }
@@ -0,0 +1,22 @@
+[package]
+name = "sc-finality-grandpa-rpc"
+version = "0.8.0-dev"
+authors = ["Parity Technologies <admin@parity.io>"]
+description = "RPC extensions for the GRANDPA finality gadget"
+edition = "2018"
+license = "GPL-3.0"
+
+[dependencies]
+sc-finality-grandpa = { version = "0.8.0-dev", path = "../" }
+finality-grandpa = { version = "0.12.1", features = ["derive-codec"] }
+jsonrpc-core = "14.0.3"
+jsonrpc-core-client = "14.0.3"
+jsonrpc-derive = "14.0.3"
+futures = { version = "0.3.4", features = ["compat"] }
+serde = { version = "1.0.105", features = ["derive"] }
+serde_json = "1.0.50"
+log = "0.4.8"
+derive_more = "0.99.2"
+
+[dev-dependencies]
+sp-core = { version = "2.0.0-dev", path = "../../../primitives/core" }
@@ -0,0 +1,47 @@
+// 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 crate::NOT_READY_ERROR_CODE;
+
+#[derive(derive_more::Display, derive_more::From)]
+/// Top-level error type for the RPC handler
+pub enum Error {
+	/// The GRANDPA RPC endpoint is not ready.
+	#[display(fmt = "GRANDPA RPC endpoint not ready")]
+	EndpointNotReady,
+	/// GRANDPA reports the authority set id to be larger than 32-bits.
+	#[display(fmt = "GRANDPA reports authority set id unreasonably large")]
+	AuthoritySetIdReportedAsUnreasonablyLarge,
+	/// GRANDPA reports voter state with round id or weights larger than 32-bits.
+	#[display(fmt = "GRANDPA reports voter state as unreasonably large")]
+	VoterStateReportsUnreasonablyLargeNumbers,
+}
+
+impl From<Error> for jsonrpc_core::Error {
+	fn from(error: Error) -> Self {
+		jsonrpc_core::Error {
+			message: format!("{}", error).into(),
+			code: jsonrpc_core::ErrorCode::ServerError(NOT_READY_ERROR_CODE),
+			data: None,
+		}
+	}
+}
+
+impl From<std::num::TryFromIntError> for Error {
+	fn from(_error: std::num::TryFromIntError) -> Self {
+		Error::VoterStateReportsUnreasonablyLargeNumbers
+	}
+}
@@ -0,0 +1,169 @@
+// 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/>.
+
+//! RPC API for GRANDPA.
+#![warn(missing_docs)]
+
+use futures::{FutureExt, TryFutureExt};
+use jsonrpc_derive::rpc;
+
+mod error;
+mod report;
+
+use report::{ReportAuthoritySet, ReportVoterState, ReportedRoundStates};
+
+/// 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 {
+	/// Returns the state of the current best round state as well as the
+	/// ongoing background rounds.
+	#[rpc(name = "grandpa_roundState")]
+	fn round_state(&self) -> FutureResult<ReportedRoundStates>;
+}
+
+/// Implements the GrandpaApi RPC trait for interacting with GRANDPA.
+pub struct GrandpaRpcHandler<AuthoritySet, VoterState> {
+	authority_set: AuthoritySet,
+	voter_state: VoterState,
+}
+
+impl<AuthoritySet, VoterState> GrandpaRpcHandler<AuthoritySet, VoterState> {
+	/// Creates a new GrandpaRpcHander instance.
+	pub fn new(authority_set: AuthoritySet, voter_state: VoterState) -> Self {
+		Self {
+			authority_set,
+			voter_state,
+		}
+	}
+}
+
+impl<AuthoritySet, VoterState> GrandpaApi for GrandpaRpcHandler<AuthoritySet, VoterState>
+where
+	VoterState: ReportVoterState + Send + Sync + 'static,
+	AuthoritySet: ReportAuthoritySet + Send + Sync + 'static,
+{
+	fn round_state(&self) -> FutureResult<ReportedRoundStates> {
+		let round_states = ReportedRoundStates::from(&self.authority_set, &self.voter_state);
+		let future = async move { round_states }.boxed();
+		Box::new(future.map_err(jsonrpc_core::Error::from).compat())
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use jsonrpc_core::IoHandler;
+	use sc_finality_grandpa::{report, AuthorityId};
+	use sp_core::crypto::Public;
+	use std::{collections::HashSet, convert::TryInto};
+
+	struct TestAuthoritySet;
+	struct TestVoterState;
+	struct EmptyVoterState;
+
+	fn voters() -> HashSet<AuthorityId> {
+		let voter_id_1 = AuthorityId::from_slice(&[1; 32]);
+		let voter_id_2 = AuthorityId::from_slice(&[2; 32]);
+
+		vec![voter_id_1, voter_id_2].into_iter().collect()
+	}
+
+	impl ReportAuthoritySet for TestAuthoritySet {
+		fn get(&self) -> (u64, HashSet<AuthorityId>) {
+			(1, voters())
+		}
+	}
+
+	impl ReportVoterState for EmptyVoterState {
+		fn get(&self) -> Option<report::VoterState<AuthorityId>> {
+			None
+		}
+	}
+
+	impl ReportVoterState for TestVoterState {
+		fn get(&self) -> Option<report::VoterState<AuthorityId>> {
+			let voter_id_1 = AuthorityId::from_slice(&[1; 32]);
+			let voters_best: HashSet<_> = vec![voter_id_1].into_iter().collect();
+
+			let best_round_state = report::RoundState {
+				total_weight: 100_u64.try_into().unwrap(),
+				threshold_weight: 67_u64.try_into().unwrap(),
+				prevote_current_weight: 50.into(),
+				prevote_ids: voters_best,
+				precommit_current_weight: 0.into(),
+				precommit_ids: HashSet::new(),
+			};
+
+			let past_round_state = report::RoundState {
+				total_weight: 100_u64.try_into().unwrap(),
+				threshold_weight: 67_u64.try_into().unwrap(),
+				prevote_current_weight: 100.into(),
+				prevote_ids: voters(),
+				precommit_current_weight: 100.into(),
+				precommit_ids: voters(),
+			};
+
+			let background_rounds = vec![(1, past_round_state)].into_iter().collect();
+
+			Some(report::VoterState {
+				background_rounds,
+				best_round: (2, best_round_state),
+			})
+		}
+	}
+
+	#[test]
+	fn uninitialized_rpc_handler() {
+		let handler = GrandpaRpcHandler::new(TestAuthoritySet, EmptyVoterState);
+		let mut io = IoHandler::new();
+		io.extend_with(GrandpaApi::to_delegate(handler));
+
+		let request = r#"{"jsonrpc":"2.0","method":"grandpa_roundState","params":[],"id":1}"#;
+		let response = r#"{"jsonrpc":"2.0","error":{"code":1,"message":"GRANDPA RPC endpoint not ready"},"id":1}"#;
+
+		assert_eq!(Some(response.into()), io.handle_request_sync(request));
+	}
+
+	#[test]
+	fn working_rpc_handler() {
+		let handler = GrandpaRpcHandler::new(TestAuthoritySet, TestVoterState);
+		let mut io = IoHandler::new();
+		io.extend_with(GrandpaApi::to_delegate(handler));
+
+		let request = r#"{"jsonrpc":"2.0","method":"grandpa_roundState","params":[],"id":1}"#;
+		let response = "{\"jsonrpc\":\"2.0\",\"result\":{\
+			\"background\":[{\
+				\"precommits\":{\"currentWeight\":100,\"missing\":[]},\
+				\"prevotes\":{\"currentWeight\":100,\"missing\":[]},\
+				\"round\":1,\"thresholdWeight\":67,\"totalWeight\":100\
+			}],\
+			\"best\":{\
+				\"precommits\":{\"currentWeight\":0,\"missing\":[\"5C62Ck4UrFPiBtoCmeSrgF7x9yv9mn38446dhCpsi2mLHiFT\",\"5C7LYpP2ZH3tpKbvVvwiVe54AapxErdPBbvkYhe6y9ZBkqWt\"]},\
+				\"prevotes\":{\"currentWeight\":50,\"missing\":[\"5C7LYpP2ZH3tpKbvVvwiVe54AapxErdPBbvkYhe6y9ZBkqWt\"]},\
+				\"round\":2,\"thresholdWeight\":67,\"totalWeight\":100\
+			},\
+			\"setId\":1\
+		},\"id\":1}";
+
+		assert_eq!(io.handle_request_sync(request), Some(response.into()));
+	}
+}
@@ -0,0 +1,159 @@
+// 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 std::{
+	collections::{BTreeSet, HashSet},
+	fmt::Debug,
+	ops::Add,
+};
+
+use serde::{Deserialize, Serialize};
+
+use sc_finality_grandpa::{report, AuthorityId, SharedAuthoritySet, SharedVoterState};
+
+use crate::error::Error;
+
+/// Utility trait to get reporting data for the current GRANDPA authority set.
+pub trait ReportAuthoritySet {
+	fn get(&self) -> (u64, HashSet<AuthorityId>);
+}
+
+/// Utility trait to get reporting data for the current GRANDPA voter state.
+pub trait ReportVoterState {
+	fn get(&self) -> Option<report::VoterState<AuthorityId>>;
+}
+
+impl<H, N> ReportAuthoritySet for SharedAuthoritySet<H, N>
+where
+	N: Add<Output = N> + Ord + Clone + Debug,
+	H: Clone + Debug + Eq,
+{
+	fn get(&self) -> (u64, HashSet<AuthorityId>) {
+		let current_voters: HashSet<AuthorityId> = self
+			.current_authorities()
+			.iter()
+			.map(|p| p.0.clone())
+			.collect();
+
+		(self.set_id(), current_voters)
+	}
+}
+
+impl ReportVoterState for SharedVoterState {
+	fn get(&self) -> Option<report::VoterState<AuthorityId>> {
+		self.voter_state()
+	}
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct Prevotes {
+	current_weight: u32,
+	missing: BTreeSet<AuthorityId>,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct Precommits {
+	current_weight: u32,
+	missing: BTreeSet<AuthorityId>,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct RoundState {
+	round: u32,
+	total_weight: u32,
+	threshold_weight: u32,
+	prevotes: Prevotes,
+	precommits: Precommits,
+}
+
+impl RoundState {
+	fn from(
+		round: u64,
+		round_state: &report::RoundState<AuthorityId>,
+		voters: &HashSet<AuthorityId>,
+	) -> Result<Self, Error> {
+		use std::convert::TryInto;
+
+		let prevotes = &round_state.prevote_ids;
+		let missing_prevotes = voters.difference(&prevotes).cloned().collect();
+
+		let precommits = &round_state.precommit_ids;
+		let missing_precommits = voters.difference(&precommits).cloned().collect();
+
+		Ok(Self {
+			round: round.try_into()?,
+			total_weight: round_state.total_weight.get().try_into()?,
+			threshold_weight: round_state.threshold_weight.get().try_into()?,
+			prevotes: Prevotes {
+				current_weight: round_state.prevote_current_weight.0.try_into()?,
+				missing: missing_prevotes,
+			},
+			precommits: Precommits {
+				current_weight: round_state.precommit_current_weight.0.try_into()?,
+				missing: missing_precommits,
+			},
+		})
+	}
+}
+
+/// The state of the current best round, as well as the background rounds in a
+/// form suitable for serialization.
+#[derive(Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ReportedRoundStates {
+	set_id: u32,
+	best: RoundState,
+	background: Vec<RoundState>,
+}
+
+impl ReportedRoundStates {
+	pub fn from<AuthoritySet, VoterState>(
+		authority_set: &AuthoritySet,
+		voter_state: &VoterState,
+	) -> Result<Self, Error>
+	where
+		AuthoritySet: ReportAuthoritySet,
+		VoterState: ReportVoterState,
+	{
+		use std::convert::TryFrom;
+
+		let voter_state = voter_state.get().ok_or(Error::EndpointNotReady)?;
+
+		let (set_id, current_voters) = authority_set.get();
+		let set_id =
+			u32::try_from(set_id).map_err(|_| Error::AuthoritySetIdReportedAsUnreasonablyLarge)?;
+
+		let best = {
+			let (round, round_state) = voter_state.best_round;
+			RoundState::from(round, &round_state, &current_voters)?
+		};
+
+		let background = voter_state
+			.background_rounds
+			.iter()
+			.map(|(round, round_state)| RoundState::from(*round, round_state, &current_voters))
+			.collect::<Result<Vec<_>, Error>>()?;
+
+		Ok(Self {
+			set_id,
+			best,
+			background,
+		})
+	}
+}
@@ -39,7 +39,7 @@ pub enum Error<E> {
 }

 /// A shared authority set.
-pub(crate) struct SharedAuthoritySet<H, N> {
+pub struct SharedAuthoritySet<H, N> {
 	inner: Arc<RwLock<AuthoritySet<H, N>>>,
 }

@@ -67,12 +67,12 @@ where N: Add<Output=N> + Ord + Clone + Debug,
 	}

 	/// Get the current set ID. This is incremented every time the set changes.
-	pub(crate) fn set_id(&self) -> u64 {
+	pub fn set_id(&self) -> u64 {
 		self.inner.read().set_id
 	}

 	/// Get the current authorities and their weights (for the current set ID).
-	pub(crate) fn current_authorities(&self) -> VoterSet<AuthorityId> {
+	pub fn current_authorities(&self) -> VoterSet<AuthorityId> {
 		VoterSet::new(self.inner.read().current_authorities.iter().cloned()).expect(
 			"current_authorities is non-empty and weights are non-zero; \
 			 constructor and all mutating operations on `AuthoritySet` ensure this; \
@@ -52,6 +52,8 @@
 //! or prune any signaled changes based on whether the signaling block is
 //! included in the newly-finalized chain.

+#![warn(missing_docs)]
+
 use futures::prelude::*;
 use futures::StreamExt;
 use log::{debug, info};
@@ -72,6 +74,7 @@ use sp_core::Pair;
 use sp_utils::mpsc::{tracing_unbounded, TracingUnboundedReceiver};
 use sc_telemetry::{telemetry, CONSENSUS_INFO, CONSENSUS_DEBUG};
 use serde_json;
+use parking_lot::RwLock;

 use sp_finality_tracker;

@@ -114,12 +117,14 @@ mod observer;
 mod until_imported;
 mod voting_rule;

+pub use authorities::SharedAuthoritySet;
 pub use finality_proof::{FinalityProofProvider, StorageAndProofProvider};
 pub use justification::GrandpaJustification;
 pub use light_import::light_block_import;
 pub use voting_rule::{
 	BeforeBestBlockBy, ThreeQuartersOfTheUnfinalizedChain, VotingRule, VotingRulesBuilder
 };
+pub use finality_grandpa::voter::report;

 use aux_schema::PersistentData;
 use environment::{Environment, VoterSetState};
@@ -203,7 +208,44 @@ type CommunicationOutH<Block, H> = finality_grandpa::voter::CommunicationOut<
 	AuthorityId,
 >;

-/// Configuration for the GRANDPA service.
+/// Shared voter state for querying.
+pub struct SharedVoterState {
+	inner: Arc<RwLock<Option<Box<dyn voter::VoterState<AuthorityId> + Sync + Send>>>>,
+}
+
+impl SharedVoterState {
+	/// Create a new empty `SharedVoterState` instance.
+	pub fn empty() -> Self {
+		Self {
+			inner: Arc::new(RwLock::new(None)),
+		}
+	}
+
+	fn reset(
+		&self,
+		voter_state: Box<dyn voter::VoterState<AuthorityId> + Sync + Send>,
+	) -> Option<()> {
+		let mut shared_voter_state = self
+			.inner
+			.try_write_for(Duration::from_secs(1))?;
+
+		*shared_voter_state = Some(voter_state);
+		Some(())
+	}
+
+	/// Get the inner `VoterState` instance.
+	pub fn voter_state(&self) -> Option<voter::report::VoterState<AuthorityId>> {
+		self.inner.read().as_ref().map(|vs| vs.get())
+	}
+}
+
+impl Clone for SharedVoterState {
+	fn clone(&self) -> Self {
+		SharedVoterState { inner: self.inner.clone() }
+	}
+}
+
+/// Configuration for the GRANDPA service
 #[derive(Clone)]
 pub struct Config {
 	/// The expected duration for a message to be gossiped across the network.
@@ -392,6 +434,7 @@ impl<H, N> fmt::Display for CommandOrError<H, N> {
 	}
 }

+/// Link between the block importer and the background voter.
 pub struct LinkHalf<Block: BlockT, C, SC> {
 	client: Arc<C>,
 	select_chain: SC,
@@ -399,6 +442,13 @@ pub struct LinkHalf<Block: BlockT, C, SC> {
 	voter_commands_rx: TracingUnboundedReceiver<VoterCommand<Block::Hash, NumberFor<Block>>>,
 }

+impl<Block: BlockT, C, SC> LinkHalf<Block, C, SC> {
+	/// Get the shared authority set.
+	pub fn shared_authority_set(&self) -> &SharedAuthoritySet<Block::Hash, NumberFor<Block>> {
+		&self.persistent_data.authority_set
+	}
+}
+
 /// Provider for the Grandpa authority set configured on the genesis block.
 pub trait GenesisAuthoritySetProvider<Block: BlockT> {
 	/// Get the authority set at the genesis block.
@@ -620,6 +670,8 @@ pub struct GrandpaParams<Block: BlockT, C, N, SC, VR> {
 	pub voting_rule: VR,
 	/// The prometheus metrics registry.
 	pub prometheus_registry: Option<prometheus_endpoint::Registry>,
+	/// The voter state is exposed at an RPC endpoint.
+	pub shared_voter_state: SharedVoterState,
 }

 /// Run a GRANDPA voter as a task. Provide configuration and a link to a
@@ -644,6 +696,7 @@ pub fn run_grandpa_voter<Block: BlockT, BE: 'static, C, N, SC, VR>(
 		telemetry_on_connect,
 		voting_rule,
 		prometheus_registry,
+		shared_voter_state,
 	} = grandpa_params;

 	// NOTE: we have recently removed `run_grandpa_observer` from the public
@@ -704,6 +757,7 @@ pub fn run_grandpa_voter<Block: BlockT, BE: 'static, C, N, SC, VR>(
 		persistent_data,
 		voter_commands_rx,
 		prometheus_registry,
+		shared_voter_state,
 	);

 	let voter_work = voter_work
@@ -734,6 +788,7 @@ impl Metrics {
 #[must_use]
 struct VoterWork<B, Block: BlockT, C, N: NetworkT<Block>, SC, VR> {
 	voter: Pin<Box<dyn Future<Output = Result<(), CommandOrError<Block::Hash, NumberFor<Block>>>> + Send>>,
+	shared_voter_state: SharedVoterState,
 	env: Arc<Environment<B, Block, C, N, SC, VR>>,
 	voter_commands_rx: TracingUnboundedReceiver<VoterCommand<Block::Hash, NumberFor<Block>>>,
 	network: NetworkBridge<Block, N>,
@@ -761,6 +816,7 @@ where
 		persistent_data: PersistentData<Block>,
 		voter_commands_rx: TracingUnboundedReceiver<VoterCommand<Block::Hash, NumberFor<Block>>>,
 		prometheus_registry: Option<prometheus_endpoint::Registry>,
+		shared_voter_state: SharedVoterState,
 	) -> Self {
 		let metrics = match prometheus_registry.as_ref().map(Metrics::register) {
 			Some(Ok(metrics)) => Some(metrics),
@@ -791,6 +847,7 @@ where
 			// `voter` is set to a temporary value and replaced below when
 			// calling `rebuild_voter`.
 			voter: Box::pin(future::pending()),
+			shared_voter_state,
 			env,
 			voter_commands_rx,
 			network,
@@ -858,6 +915,14 @@ where
 					last_finalized,
 				);

+				// Repoint shared_voter_state so that the RPC endpoint can query the state
+				if let None = self.shared_voter_state.reset(voter.voter_state()) {
+					info!(target: "afg",
+						"Timed out trying to update shared GRANDPA voter state. \
+						RPC endpoints may return stale data."
+					);
+				}
+
 				self.voter = Box::pin(voter);
 			},
 			VoterSetState::Paused { .. } =>
@@ -295,8 +295,6 @@ fn run_to_completion_with<F>(
 ) -> u64 where
 	F: FnOnce(Handle) -> Option<Pin<Box<dyn Future<Output = ()>>>>
 {
-	use parking_lot::RwLock;
-
 	let mut wait_for = Vec::new();

 	let highest_finalized = Arc::new(RwLock::new(0));
@@ -354,6 +352,7 @@ fn run_to_completion_with<F>(
 			telemetry_on_connect: None,
 			voting_rule: (),
 			prometheus_registry: None,
+			shared_voter_state: SharedVoterState::empty(),
 		};
 		let voter = run_grandpa_voter(grandpa_params).expect("all in order with client and network");

@@ -485,6 +484,7 @@ fn finalize_3_voters_1_full_observer() {
 			telemetry_on_connect: None,
 			voting_rule: (),
 			prometheus_registry: None,
+			shared_voter_state: SharedVoterState::empty(),
 		};

 		voters.push(run_grandpa_voter(grandpa_params).expect("all in order with client and network"));
@@ -648,6 +648,7 @@ fn transition_3_voters_twice_1_full_observer() {
 			telemetry_on_connect: None,
 			voting_rule: (),
 			prometheus_registry: None,
+			shared_voter_state: SharedVoterState::empty(),
 		};
 		let voter = run_grandpa_voter(grandpa_params).expect("all in order with client and network");

@@ -1072,6 +1073,7 @@ fn voter_persists_its_votes() {
 							telemetry_on_connect: None,
 							voting_rule: VotingRulesBuilder::default().build(),
 							prometheus_registry: None,
+							shared_voter_state: SharedVoterState::empty(),
 						};

 						let voter = run_grandpa_voter(grandpa_params)
@@ -1417,6 +1419,7 @@ fn voter_catches_up_to_latest_round_when_behind() {
 			telemetry_on_connect: None,
 			voting_rule: (),
 			prometheus_registry: None,
+			shared_voter_state: SharedVoterState::empty(),
 		};

 		Box::pin(run_grandpa_voter(grandpa_params).expect("all in order with client and network"))