Add new Runtime API messages and make runtime API request fallible (#1485)

* polkadot-subsystem: update runtime API message types

* update all networking subsystems to use fallible runtime APIs

* fix bitfield-signing and make it use new runtime APIs

* port candidate-backing to handle runtime API errors and new types

* remove old runtime API messages

* remove unused imports

* fix grumbles

* fix backing tests

polkadot/Cargo.lock

@@ -4606,6 +4606,7 @@ dependencies = [
  "bitvec",
  "derive_more 0.99.9",
  "futures 0.3.5",
+ "log 0.4.8",
  "polkadot-erasure-coding",
  "polkadot-node-primitives",
  "polkadot-node-subsystem",

polkadot/node/core/backing/Cargo.toml

@@ -17,6 +17,7 @@ erasure-coding = { package = "polkadot-erasure-coding", path = "../../../erasure
 statement-table = { package = "polkadot-statement-table", path = "../../../statement-table" }
 derive_more = "0.99.9"
 bitvec = { version = "0.17.4", default-features = false, features = ["alloc"] }
+log = "0.4.8"
 
 [dev-dependencies]
 sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }

polkadot/node/core/backing/src/lib.rs

@@ -32,7 +32,7 @@ use polkadot_primitives::v1::{
 	CommittedCandidateReceipt, BackedCandidate, Id as ParaId, ValidatorId,
 	ValidatorIndex, SigningContext, PoV, OmittedValidationData,
 	CandidateDescriptor, AvailableData, ValidatorSignature, Hash, CandidateReceipt,
-	CandidateCommitments,
+	CandidateCommitments, CoreState, CoreIndex,
 };
 use polkadot_node_primitives::{
 	FromTableMisbehavior, Statement, SignedFullStatement, MisbehaviorReport,
@@ -44,12 +44,14 @@ use polkadot_subsystem::{
 		AllMessages, AvailabilityStoreMessage, CandidateBackingMessage, CandidateSelectionMessage,
 		CandidateValidationMessage, NewBackedCandidate, PoVDistributionMessage, ProvisionableData,
 		ProvisionerMessage, RuntimeApiMessage, StatementDistributionMessage, ValidationFailed,
+		RuntimeApiRequest,
 	},
 	util::{
 		self,
-		request_signing_context,
+		request_session_index_for_child,
 		request_validator_groups,
 		request_validators,
+		request_from_runtime,
 		Validator,
 	},
 };
@@ -680,19 +682,56 @@ impl util::JobTrait for CandidateBackingJob {
 		mut tx_from: mpsc::Sender<Self::FromJob>,
 	) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>> {
 		async move {
-			let (validators, roster, signing_context) = futures::try_join!(
+			macro_rules! try_runtime_api {
+				($x: expr) => {
+					match $x {
+						Ok(x) => x,
+						Err(e) => {
+							log::warn!(
+								target: "candidate_backing",
+								"Failed to fetch runtime API data for job: {:?}",
+								e,
+							);
+
+							// We can't do candidate validation work if we don't have the
+							// requisite runtime API data. But these errors should not take
+							// down the node.
+							return Ok(());
+						}
+					}
+				}
+			}
+
+			let (validators, groups, session_index, cores) = futures::try_join!(
 				request_validators(parent, &mut tx_from).await?,
 				request_validator_groups(parent, &mut tx_from).await?,
-				request_signing_context(parent, &mut tx_from).await?,
+				request_session_index_for_child(parent, &mut tx_from).await?,
+				request_from_runtime(
+					parent,
+					&mut tx_from,
+					|tx| RuntimeApiRequest::AvailabilityCores(tx),
+				).await?,
 			)?;
 
+			let validators = try_runtime_api!(validators);
+			let (validator_groups, group_rotation_info) = try_runtime_api!(groups);
+			let session_index = try_runtime_api!(session_index);
+			let cores = try_runtime_api!(cores);
+
+			let signing_context = SigningContext { parent_hash: parent, session_index };
 			let validator = Validator::construct(&validators, signing_context, keystore.clone())?;
 
 			let mut groups = HashMap::new();
 
-			for assignment in roster.scheduled {
-				if let Some(g) = roster.validator_groups.get(assignment.group_idx.0 as usize) {
-					groups.insert(assignment.para_id, g.clone());
+			let n_cores = cores.len();
+			for (idx, core) in cores.into_iter().enumerate() {
+				// Ignore prospective assignments on occupied cores for the time being.
+				if let CoreState::Scheduled(scheduled) = core {
+					let core_index = CoreIndex(idx as _);
+					let group_index = group_rotation_info.group_for_core(core_index, n_cores);
+					if let Some(g) = validator_groups.get(group_index.0 as usize) {
+						groups.insert(scheduled.para_id, g.clone());
+					}
 				}
 			}
 
@@ -779,12 +818,12 @@ mod tests {
 	use assert_matches::assert_matches;
 	use futures::{executor, future, Future};
 	use polkadot_primitives::v1::{
-		AssignmentKind, BlockData, CandidateCommitments, CollatorId, CoreAssignment, CoreIndex,
-		LocalValidationData, GlobalValidationData, GroupIndex, HeadData,
-		ValidatorPair, ValidityAttestation,
+		ScheduledCore, BlockData, CandidateCommitments, CollatorId,
+		LocalValidationData, GlobalValidationData, HeadData,
+		ValidatorPair, ValidityAttestation, GroupRotationInfo,
 	};
 	use polkadot_subsystem::{
-		messages::{RuntimeApiRequest, SchedulerRoster},
+		messages::RuntimeApiRequest,
 		ActiveLeavesUpdate, FromOverseer, OverseerSignal,
 	};
 	use sp_keyring::Sr25519Keyring;
@@ -801,7 +840,8 @@ mod tests {
 		validator_public: Vec<ValidatorId>,
 		global_validation_data: GlobalValidationData,
 		local_validation_data: LocalValidationData,
-		roster: SchedulerRoster,
+		validator_groups: (Vec<Vec<ValidatorIndex>>, GroupRotationInfo),
+		availability_cores: Vec<CoreState>,
 		head_data: HashMap<ParaId, HeadData>,
 		signing_context: SigningContext,
 		relay_parent: Hash,
@@ -830,53 +870,39 @@ mod tests {
 
 			let validator_public = validator_pubkeys(&validators);
 
-			let chain_a_assignment = CoreAssignment {
-				core: CoreIndex::from(0),
-				para_id: chain_a,
-				kind: AssignmentKind::Parachain,
-				group_idx: GroupIndex::from(0),
-			};
-
-			let chain_b_assignment = CoreAssignment {
-				core: CoreIndex::from(1),
-				para_id: chain_b,
-				kind: AssignmentKind::Parachain,
-				group_idx: GroupIndex::from(1),
+			let validator_groups = vec![vec![2, 0, 3], vec![1], vec![4]];
+			let group_rotation_info = GroupRotationInfo {
+				session_start_block: 0,
+				group_rotation_frequency: 100,
+				now: 1,
 			};
 
 			let thread_collator: CollatorId = Sr25519Keyring::Two.public().into();
-
-			let thread_a_assignment = CoreAssignment {
-				core: CoreIndex::from(2),
-				para_id: thread_a,
-				kind: AssignmentKind::Parathread(thread_collator.clone(), 0),
-				group_idx: GroupIndex::from(2),
-			};
-
-			let validator_groups = vec![vec![2, 0, 3], vec![1], vec![4]];
-
-			let parent_hash_1 = [1; 32].into();
-
-			let roster = SchedulerRoster {
-				validator_groups,
-				scheduled: vec![
-					chain_a_assignment,
-					chain_b_assignment,
-					thread_a_assignment,
-				],
-				upcoming: vec![],
-				availability_cores: vec![],
-			};
-			let signing_context = SigningContext {
-				session_index: 1,
-				parent_hash: parent_hash_1,
-			};
+			let availability_cores = vec![
+				CoreState::Scheduled(ScheduledCore {
+					para_id: chain_a,
+					collator: None,
+				}),
+				CoreState::Scheduled(ScheduledCore {
+					para_id: chain_b,
+					collator: None,
+				}),
+				CoreState::Scheduled(ScheduledCore {
+					para_id: thread_a,
+					collator: Some(thread_collator.clone()),
+				}),
+			];
 
 			let mut head_data = HashMap::new();
 			head_data.insert(chain_a, HeadData(vec![4, 5, 6]));
 
 			let relay_parent = Hash::from([5; 32]);
 
+			let signing_context = SigningContext {
+				session_index: 1,
+				parent_hash: relay_parent,
+			};
+
 			let local_validation_data = LocalValidationData {
 				parent_head: HeadData(vec![7, 8, 9]),
 				balance: Default::default(),
@@ -895,7 +921,8 @@ mod tests {
 				keystore,
 				validators,
 				validator_public,
-				roster,
+				validator_groups: (validator_groups, group_rotation_info),
+				availability_cores,
 				head_data,
 				local_validation_data,
 				global_validation_data,
@@ -984,7 +1011,7 @@ mod tests {
 			AllMessages::RuntimeApi(
 				RuntimeApiMessage::Request(parent, RuntimeApiRequest::Validators(tx))
 			) if parent == test_state.relay_parent => {
-				tx.send(test_state.validator_public.clone()).unwrap();
+				tx.send(Ok(test_state.validator_public.clone())).unwrap();
 			}
 		);
 
@@ -994,19 +1021,29 @@ mod tests {
 			AllMessages::RuntimeApi(
 				RuntimeApiMessage::Request(parent, RuntimeApiRequest::ValidatorGroups(tx))
 			) if parent == test_state.relay_parent => {
-				tx.send(test_state.roster.clone()).unwrap();
+				tx.send(Ok(test_state.validator_groups.clone())).unwrap();
 			}
 		);
 
-		// Check that subsystem job issues a request for the signing context.
+		// Check that subsystem job issues a request for the session index for child.
 		assert_matches!(
 			virtual_overseer.recv().await,
 			AllMessages::RuntimeApi(
-				RuntimeApiMessage::Request(parent, RuntimeApiRequest::SigningContext(tx))
+				RuntimeApiMessage::Request(parent, RuntimeApiRequest::SessionIndexForChild(tx))
 			) if parent == test_state.relay_parent => {
-				tx.send(test_state.signing_context.clone()).unwrap();
+				tx.send(Ok(test_state.signing_context.session_index)).unwrap();
 			}
 		);
+
+			// Check that subsystem job issues a request for the availability cores.
+			assert_matches!(
+				virtual_overseer.recv().await,
+				AllMessages::RuntimeApi(
+					RuntimeApiMessage::Request(parent, RuntimeApiRequest::AvailabilityCores(tx))
+				) if parent == test_state.relay_parent => {
+					tx.send(Ok(test_state.availability_cores.clone())).unwrap();
+				}
+			);
 	}
 
 	// Test that a `CandidateBackingMessage::Second` issues validation work

polkadot/node/core/bitfield-signing/src/lib.rs

@@ -30,7 +30,7 @@ use polkadot_node_subsystem::{
 	},
 	util::{self, JobManager, JobTrait, ToJobTrait, Validator},
 };
-use polkadot_primitives::v1::{AvailabilityBitfield, CoreOccupied, Hash};
+use polkadot_primitives::v1::{AvailabilityBitfield, CoreState, Hash};
 use std::{convert::TryFrom, pin::Pin, time::Duration};
 use wasm_timer::{Delay, Instant};
 
@@ -130,8 +130,7 @@ pub enum Error {
 // this function exists mainly to collect a bunch of potential error points into one.
 async fn get_core_availability(
 	relay_parent: Hash,
-	idx: usize,
-	core: Option<CoreOccupied>,
+	core: CoreState,
 	sender: &mpsc::Sender<FromJob>,
 ) -> Result<bool, Error> {
 	use messages::{
@@ -144,18 +143,23 @@ async fn get_core_availability(
 	// we have to (cheaply) clone this sender so we can mutate it to actually send anything
 	let mut sender = sender.clone();
 
-	// REVIEW: is it safe to ignore parathreads here, or do they also figure in the availability mapping?
-	if let Some(CoreOccupied::Parachain) = core {
+	if let CoreState::Occupied(core) = core {
 		let (tx, rx) = oneshot::channel();
 		sender
 			.send(RuntimeApi(Request(
 				relay_parent,
-				CandidatePendingAvailability(idx.into(), tx),
+				CandidatePendingAvailability(core.para_id, tx),
 			)))
 			.await?;
+
 		let committed_candidate_receipt = match rx.await? {
-			Some(ccr) => ccr,
-			None => return Ok(false),
+			Ok(Some(ccr)) => ccr,
+			Ok(None) => return Ok(false),
+			Err(e) => {
+				// Don't take down the node on runtime API errors.
+				log::warn!(target: "bitfield_signing", "Encountered a runtime API error: {:?}", e);
+				return Ok(false);
+			}
 		};
 		let (tx, rx) = oneshot::channel();
 		sender
@@ -171,35 +175,41 @@ async fn get_core_availability(
 
 // the way this function works is not intuitive:
 //
-// - get the scheduler roster so we have a list of cores, in order.
+// - get the availability cores so we have a list of cores, in order.
 // - for each occupied core, fetch `candidate_pending_availability` from runtime
 // - from there, we can get the `CandidateDescriptor`
 // - from there, we can send a `AvailabilityStore::QueryPoV` and set the indexed bit to 1 if it returns Some(_)
 async fn construct_availability_bitfield(
 	relay_parent: Hash,
 	sender: &mut mpsc::Sender<FromJob>,
-) -> Result<AvailabilityBitfield, Error> {
+) -> Result<Option<AvailabilityBitfield>, Error> {
 	use futures::lock::Mutex;
 
-	use messages::RuntimeApiRequest::ValidatorGroups;
+	use messages::RuntimeApiRequest::AvailabilityCores;
 	use FromJob::RuntimeApi;
 	use RuntimeApiMessage::Request;
 
-	// request the validator groups so we can get the scheduler roster
+	// request the availability cores metadata from runtime.
 	let (tx, rx) = oneshot::channel();
 	sender
-		.send(RuntimeApi(Request(relay_parent, ValidatorGroups(tx))))
+		.send(RuntimeApi(Request(relay_parent, AvailabilityCores(tx))))
 		.await?;
 
 	// we now need sender to be immutable so we can copy the reference to multiple concurrent closures
 	let sender = &*sender;
 
-	// wait for the scheduler roster
-	let scheduler_roster = rx.await?;
+	// wait for the cores
+	let availability_cores = match rx.await? {
+		Ok(a) => a,
+		Err(e) => {
+			log::warn!(target: "bitfield_signing", "Encountered a runtime API error: {:?}", e);
+			return Ok(None);
+		}
+	};
 
 	// prepare outputs
 	let out =
-		Mutex::new(bitvec!(bitvec::order::Lsb0, u8; 0; scheduler_roster.availability_cores.len()));
+		Mutex::new(bitvec!(bitvec::order::Lsb0, u8; 0; availability_cores.len()));
 	// in principle, we know that we never want concurrent access to the _same_ bit within the vec;
 	// we could `let out_ref = out.as_mut_ptr();` here instead, and manually assign bits, avoiding
 	// any need to ever wait to lock this mutex.
@@ -213,9 +223,9 @@ async fn construct_availability_bitfield(
 	//
 	// In principle, this work is all concurrent, not parallel. In practice, we can't guarantee it, which is why
 	// we need the mutexes and explicit references above.
-	stream::iter(scheduler_roster.availability_cores.into_iter().enumerate())
+	stream::iter(availability_cores.into_iter().enumerate())
 		.for_each_concurrent(None, |(idx, core)| async move {
-			let availability = match get_core_availability(relay_parent, idx, core, sender).await {
+			let availability = match get_core_availability(relay_parent, core, sender).await {
 				Ok(availability) => availability,
 				Err(err) => {
 					errs_ref.lock().await.push(err);
@@ -228,7 +238,7 @@ async fn construct_availability_bitfield(
 
 	let errs = errs.into_inner();
 	if errs.is_empty() {
-		Ok(out.into_inner().into())
+		Ok(Some(out.into_inner().into()))
 	} else {
 		Err(errs.into())
 	}
@@ -264,7 +274,13 @@ impl JobTrait for BitfieldSigningJob {
 			// wait a bit before doing anything else
 			Delay::new_at(wait_until).await?;
 
-			let bitfield = construct_availability_bitfield(relay_parent, &mut sender).await?;
+			let bitfield =
+				match construct_availability_bitfield(relay_parent, &mut sender).await?
+			{
+				None => return Ok(()),
+				Some(b) => b,
+			};
+
 			let signed_bitfield = validator.sign(bitfield);
 
 			// make an anonymous scope to contain some use statements to simplify creating the outbound message

polkadot/node/network/bitfield-distribution/src/lib.rs

@@ -161,17 +161,23 @@ impl BitfieldDistribution {
 					for relay_parent in activated {
 						trace!(target: "bitd", "Start {:?}", relay_parent);
 						// query basic system parameters once
-						let (validator_set, signing_context) =
-							query_basics(&mut ctx, relay_parent).await?;
-
-						let _ = state.per_relay_parent.insert(
-							relay_parent,
-							PerRelayParentData {
-								signing_context,
-								validator_set,
-								..Default::default()
-							},
-						);
+						if let Some((validator_set, signing_context)) =
+							query_basics(&mut ctx, relay_parent).await?
+						{
+							// If our runtime API fails, we don't take down the node,
+							// but we might alter peers' reputations erroneously as a result
+							// of not having the correct bookkeeping. If we have lost a race
+							// with state pruning, it is unlikely that peers will be sending
+							// us anything to do with this relay-parent anyway.
+							let _ = state.per_relay_parent.insert(
+								relay_parent,
+								PerRelayParentData {
+									signing_context,
+									validator_set,
+									..Default::default()
+								},
+							);
+						}
 					}
 
 					for relay_parent in deactivated {
@@ -562,12 +568,12 @@ where
 async fn query_basics<Context>(
 	ctx: &mut Context,
 	relay_parent: Hash,
-) -> SubsystemResult<(Vec<ValidatorId>, SigningContext)>
+) -> SubsystemResult<Option<(Vec<ValidatorId>, SigningContext)>>
 where
 	Context: SubsystemContext<Message = BitfieldDistributionMessage>,
 {
 	let (validators_tx, validators_rx) = oneshot::channel();
-	let (signing_tx, signing_rx) = oneshot::channel();
+	let (session_tx, session_rx) = oneshot::channel();
 
 	let query_validators = AllMessages::RuntimeApi(RuntimeApiMessage::Request(
 		relay_parent.clone(),
@@ -576,13 +582,22 @@ where
 
 	let query_signing = AllMessages::RuntimeApi(RuntimeApiMessage::Request(
 		relay_parent.clone(),
-		RuntimeApiRequest::SigningContext(signing_tx),
+		RuntimeApiRequest::SessionIndexForChild(session_tx),
 	));
 
 	ctx.send_messages(std::iter::once(query_validators).chain(std::iter::once(query_signing)))
 		.await?;
 
-	Ok((validators_rx.await?, signing_rx.await?))
+	match (validators_rx.await?, session_rx.await?) {
+		(Ok(v), Ok(s)) => Ok(Some((
+			v,
+			SigningContext { parent_hash: relay_parent, session_index: s },
+		))),
+		(Err(e), _) | (_, Err(e)) => {
+			warn!(target: "bitd", "Failed to fetch basics from runtime API: {:?}", e);
+			Ok(None)
+		}
+	}
 }
 
 #[cfg(test)]

polkadot/node/network/pov-distribution/src/lib.rs

@@ -115,10 +115,27 @@ async fn handle_signal(
 					RuntimeApiRequest::Validators(vals_tx),
 				))).await?;
 
+				let n_validators = match vals_rx.await? {
+					Ok(v) => v.len(),
+					Err(e) => {
+						log::warn!(target: "pov_distribution",
+							"Error fetching validators from runtime API for active leaf: {:?}",
+							e
+						);
+
+						// Not adding bookkeeping here might make us behave funny, but we
+						// shouldn't take down the node on spurious runtime API errors.
+						//
+						// and this is "behave funny" as in be bad at our job, but not in any
+						// slashable or security-related way.
+						continue;
+					}
+				};
+
 				state.relay_parent_state.insert(relay_parent, BlockBasedState {
 					known: HashMap::new(),
 					fetching: HashMap::new(),
-					n_validators: vals_rx.await?.len(),
+					n_validators: n_validators,
 				});
 			}
 

polkadot/node/network/statement-distribution/src/lib.rs

@@ -847,17 +847,37 @@ async fn run(
 						let (session_tx, session_rx) = oneshot::channel();
 
 						let val_message = AllMessages::RuntimeApi(
-							RuntimeApiMessage::Request(relay_parent, RuntimeApiRequest::Validators(val_tx)),
+							RuntimeApiMessage::Request(
+								relay_parent,
+								RuntimeApiRequest::Validators(val_tx),
+							),
 						);
 						let session_message = AllMessages::RuntimeApi(
-							RuntimeApiMessage::Request(relay_parent, RuntimeApiRequest::SigningContext(session_tx)),
+							RuntimeApiMessage::Request(
+								relay_parent,
+								RuntimeApiRequest::SessionIndexForChild(session_tx),
+							),
 						);
 
 						ctx.send_messages(
 							std::iter::once(val_message).chain(std::iter::once(session_message))
 						).await?;
 
-						(val_rx.await?, session_rx.await?.session_index)
+						match (val_rx.await?, session_rx.await?) {
+							(Ok(v), Ok(s)) => (v, s),
+							(Err(e), _) | (_, Err(e)) => {
+								log::warn!(
+									target: "statement_distribution",
+									"Failed to fetch runtime API data for active leaf: {:?}",
+									e,
+								);
+
+								// Lacking this bookkeeping might make us behave funny, although
+								// not in any slashable way. But we shouldn't take down the node
+								// on what are likely spurious runtime API errors.
+								continue;
+							}
+						}
 					};
 
 					active_heads.entry(relay_parent)

polkadot/node/subsystem/src/messages.rs

@@ -25,11 +25,13 @@
 use futures::channel::{mpsc, oneshot};
 
 use polkadot_primitives::v1::{
-	BlockNumber, Hash, CommittedCandidateReceipt,
+	Hash, CommittedCandidateReceipt,
 	CandidateReceipt, PoV, ErasureChunk, BackedCandidate, Id as ParaId,
-	SignedAvailabilityBitfield, SigningContext, ValidatorId, ValidationCode, ValidatorIndex,
-	CoreAssignment, CoreOccupied, HeadData, CandidateDescriptor,
-	ValidatorSignature, OmittedValidationData, AvailableData,
+	SignedAvailabilityBitfield, ValidatorId, ValidationCode, ValidatorIndex,
+	CoreAssignment, CoreOccupied, CandidateDescriptor,
+	ValidatorSignature, OmittedValidationData, AvailableData, GroupRotationInfo,
+	CoreState, LocalValidationData, GlobalValidationData, OccupiedCoreAssumption,
+	CandidateEvent, SessionIndex,
 };
 use polkadot_node_primitives::{
 	MisbehaviorReport, SignedFullStatement, View, ProtocolId, ValidationResult,
@@ -286,23 +288,39 @@ pub struct SchedulerRoster {
 	pub availability_cores: Vec<Option<CoreOccupied>>,
 }
 
+/// A description of an error causing the runtime API request to be unservable.
+#[derive(Debug, Clone)]
+pub struct RuntimeApiError(String);
+
+/// A sender for the result of a runtime API request.
+pub type RuntimeApiSender<T> = oneshot::Sender<Result<T, RuntimeApiError>>;
+
 /// A request to the Runtime API subsystem.
 #[derive(Debug)]
 pub enum RuntimeApiRequest {
 	/// Get the current validator set.
-	Validators(oneshot::Sender<Vec<ValidatorId>>),
-	/// Get the assignments of validators to cores.
-	ValidatorGroups(oneshot::Sender<SchedulerRoster>),
-	/// Get a signing context for bitfields and statements.
-	SigningContext(oneshot::Sender<SigningContext>),
-	/// Get the validation code for a specific para, assuming execution under given block number, and
-	/// an optional block number representing an intermediate parablock executed in the context of
-	/// that block.
-	ValidationCode(ParaId, BlockNumber, Option<BlockNumber>, oneshot::Sender<ValidationCode>),
-	/// Get head data for a specific para.
-	HeadData(ParaId, oneshot::Sender<HeadData>),
+	Validators(RuntimeApiSender<Vec<ValidatorId>>),
+	/// Get the validator groups and group rotation info.
+	ValidatorGroups(RuntimeApiSender<(Vec<Vec<ValidatorIndex>>, GroupRotationInfo)>),
+	/// Get information on all availability cores.
+	AvailabilityCores(RuntimeApiSender<Vec<CoreState>>),
+	/// Get the global validation data.
+	GlobalValidationData(RuntimeApiSender<GlobalValidationData>),
+	/// Get the local validation data for a particular para, taking the given
+	/// `OccupiedCoreAssumption`, which will inform on how the validation data should be computed
+	/// if the para currently occupies a core.
+	LocalValidationData(
+		ParaId,
+		OccupiedCoreAssumption,
+		RuntimeApiSender<Option<LocalValidationData>>,
+	),
+	/// Get the session index that a child of the block will have.
+	SessionIndexForChild(RuntimeApiSender<SessionIndex>),
 	/// Get a the candidate pending availability for a particular parachain by parachain / core index
-	CandidatePendingAvailability(ParaId, oneshot::Sender<Option<CommittedCandidateReceipt>>),
+	CandidatePendingAvailability(ParaId, RuntimeApiSender<Option<CommittedCandidateReceipt>>),
+	/// Get all events concerning candidates (backing, inclusion, time-out) in the parent of
+	/// the block in whose state this request is executed.
+	CandidateEvents(RuntimeApiSender<Vec<CandidateEvent>>),
 }
 
 /// A message to the Runtime API subsystem.

polkadot/node/subsystem/src/util.rs

@@ -21,7 +21,9 @@
 //! this module.
 
 use crate::{
-	messages::{AllMessages, RuntimeApiMessage, RuntimeApiRequest, SchedulerRoster},
+	messages::{
+		AllMessages, RuntimeApiError, RuntimeApiMessage, RuntimeApiRequest, RuntimeApiSender,
+	},
 	FromOverseer, SpawnedSubsystem, Subsystem, SubsystemContext, SubsystemError, SubsystemResult,
 };
 use futures::{
@@ -37,8 +39,8 @@ use keystore::KeyStorePtr;
 use parity_scale_codec::Encode;
 use pin_project::{pin_project, pinned_drop};
 use polkadot_primitives::v1::{
-	EncodeAs, Hash, HeadData, Id as ParaId, Signed, SigningContext,
-	ValidatorId, ValidatorIndex, ValidatorPair,
+	EncodeAs, Hash, Signed, SigningContext, SessionIndex,
+	ValidatorId, ValidatorIndex, ValidatorPair, GroupRotationInfo,
 };
 use sp_core::{
 	Pair,
@@ -70,6 +72,9 @@ pub enum Error {
 	/// A subsystem error
 	#[from]
 	Subsystem(SubsystemError),
+	/// An error in the runtime API.
+	#[from]
+	RuntimeApi(RuntimeApiError),
 	/// The type system wants this even though it doesn't make sense
 	#[from]
 	Infallible(std::convert::Infallible),
@@ -83,14 +88,17 @@ pub enum Error {
 	AlreadyForwarding,
 }
 
+/// A type alias for Runtime API receivers.
+pub type RuntimeApiReceiver<T> = oneshot::Receiver<Result<T, RuntimeApiError>>;
+
 /// Request some data from the `RuntimeApi`.
 pub async fn request_from_runtime<RequestBuilder, Response, FromJob>(
 	parent: Hash,
 	sender: &mut mpsc::Sender<FromJob>,
 	request_builder: RequestBuilder,
-) -> Result<oneshot::Receiver<Response>, Error>
+) -> Result<RuntimeApiReceiver<Response>, Error>
 where
-	RequestBuilder: FnOnce(oneshot::Sender<Response>) -> RuntimeApiRequest,
+	RequestBuilder: FnOnce(RuntimeApiSender<Response>) -> RuntimeApiRequest,
 	FromJob: TryFrom<AllMessages>,
 	<FromJob as TryFrom<AllMessages>>::Error: std::fmt::Debug,
 {
@@ -111,7 +119,7 @@ where
 pub async fn request_validators<FromJob>(
 	parent: Hash,
 	s: &mut mpsc::Sender<FromJob>,
-) -> Result<oneshot::Receiver<Vec<ValidatorId>>, Error>
+) -> Result<RuntimeApiReceiver<Vec<ValidatorId>>, Error>
 where
 	FromJob: TryFrom<AllMessages>,
 	<FromJob as TryFrom<AllMessages>>::Error: std::fmt::Debug,
@@ -119,11 +127,11 @@ where
 	request_from_runtime(parent, s, |tx| RuntimeApiRequest::Validators(tx)).await
 }
 
-/// Request the scheduler roster from `RuntimeApi`.
+/// Request the validator groups.
 pub async fn request_validator_groups<FromJob>(
 	parent: Hash,
 	s: &mut mpsc::Sender<FromJob>,
-) -> Result<oneshot::Receiver<SchedulerRoster>, Error>
+) -> Result<RuntimeApiReceiver<(Vec<Vec<ValidatorIndex>>, GroupRotationInfo)>, Error>
 where
 	FromJob: TryFrom<AllMessages>,
 	<FromJob as TryFrom<AllMessages>>::Error: std::fmt::Debug,
@@ -131,29 +139,18 @@ where
 	request_from_runtime(parent, s, |tx| RuntimeApiRequest::ValidatorGroups(tx)).await
 }
 
-/// Request a `SigningContext` from the `RuntimeApi`.
-pub async fn request_signing_context<FromJob>(
+/// Request the session index of the child block.
+pub async fn request_session_index_for_child<FromJob>(
 	parent: Hash,
 	s: &mut mpsc::Sender<FromJob>,
-) -> Result<oneshot::Receiver<SigningContext>, Error>
+) -> Result<RuntimeApiReceiver<SessionIndex>, Error>
 where
 	FromJob: TryFrom<AllMessages>,
 	<FromJob as TryFrom<AllMessages>>::Error: std::fmt::Debug,
 {
-	request_from_runtime(parent, s, |tx| RuntimeApiRequest::SigningContext(tx)).await
-}
-
-/// Request `HeadData` for some `ParaId` from `RuntimeApi`.
-pub async fn request_head_data<FromJob>(
-	parent: Hash,
-	s: &mut mpsc::Sender<FromJob>,
-	id: ParaId,
-) -> Result<oneshot::Receiver<HeadData>, Error>
-where
-	FromJob: TryFrom<AllMessages>,
-	<FromJob as TryFrom<AllMessages>>::Error: std::fmt::Debug,
-{
-	request_from_runtime(parent, s, |tx| RuntimeApiRequest::HeadData(id, tx)).await
+	request_from_runtime(parent, s, |tx| {
+		RuntimeApiRequest::SessionIndexForChild(tx)
+	}).await
 }
 
 /// From the given set of validators, find the first key we can sign with, if any.
@@ -185,14 +182,21 @@ impl Validator {
 		FromJob: TryFrom<AllMessages>,
 		<FromJob as TryFrom<AllMessages>>::Error: std::fmt::Debug,
 	{
-		// Note: request_validators and request_signing_context do not and cannot run concurrently: they both
-		// have a mutable handle to the same sender.
+		// Note: request_validators and request_session_index_for_child do not and cannot
+		// run concurrently: they both have a mutable handle to the same sender.
 		// However, each of them returns a oneshot::Receiver, and those are resolved concurrently.
-		let (validators, signing_context) = futures::try_join!(
+		let (validators, session_index) = futures::try_join!(
 			request_validators(parent, &mut sender).await?,
-			request_signing_context(parent, &mut sender).await?,
+			request_session_index_for_child(parent, &mut sender).await?,
 		)?;
 
+		let signing_context = SigningContext {
+			session_index: session_index?,
+			parent_hash: parent,
+		};
+
+		let validators = validators?;
+
 		Self::construct(&validators, signing_context, keystore)
 	}