Candidate backing respects scheduled collator (#1613)

* extract collator assignment from cores

* check required collator

* test and fix checks

node/core/backing/src/lib.rs

@@ -32,7 +32,7 @@ use polkadot_primitives::v1::{
 	CommittedCandidateReceipt, BackedCandidate, Id as ParaId, ValidatorId,
 	ValidatorIndex, SigningContext, PoV,
 	CandidateDescriptor, AvailableData, ValidatorSignature, Hash, CandidateReceipt,
-	CandidateCommitments, CoreState, CoreIndex,
+	CandidateCommitments, CoreState, CoreIndex, CollatorId,
 };
 use polkadot_node_primitives::{
 	FromTableMisbehavior, Statement, SignedFullStatement, MisbehaviorReport,
@@ -91,8 +91,10 @@ struct CandidateBackingJob {
 	rx_to: mpsc::Receiver<ToJob>,
 	/// Outbound message channel sending part.
 	tx_from: mpsc::Sender<FromJob>,
-	/// The `ParaId`s assigned to this validator.
+	/// The `ParaId` assigned to this validator
 	assignment: ParaId,
+	/// The collator required to author the candidate, if any.
+	required_collator: Option<CollatorId>,
 	/// We issued `Valid` or `Invalid` statements on about these candidates.
 	issued_statements: HashSet<Hash>,
 	/// `Some(h)` if this job has already issues `Seconded` statemt for some candidate with `h` hash.
@@ -268,6 +270,14 @@ impl CandidateBackingJob {
 		candidate: &CandidateReceipt,
 		pov: PoV,
 	) -> Result<bool, Error> {
+		// Check that candidate is collated by the right collator.
+		if self.required_collator.as_ref()
+			.map_or(false, |c| c != &candidate.descriptor().collator)
+		{
+			self.issue_candidate_invalid_message(candidate.clone()).await?;
+			return Ok(false);
+		}
+
 		let valid = self.request_candidate_validation(
 			candidate.descriptor().clone(),
 			Arc::new(pov.clone()),
@@ -479,6 +489,19 @@ impl CandidateBackingJob {
 		let expected_commitments = candidate.commitments.clone();
 
 		let descriptor = candidate.descriptor().clone();
+
+		// Check that candidate is collated by the right collator.
+		if self.required_collator.as_ref()
+			.map_or(false, |c| c != &descriptor.collator)
+		{
+			// If not, we've got the statement in the table but we will
+			// not issue validation work for it.
+			//
+			// Act as though we've issued a statement.
+			self.issued_statements.insert(candidate_hash);
+			return Ok(());
+		}
+
 		let pov = self.request_pov_from_distribution(descriptor.clone()).await?;
 		let v = self.request_candidate_validation(descriptor, pov.clone()).await?;
 
@@ -721,30 +744,39 @@ impl util::JobTrait for CandidateBackingJob {
 			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 validator = match Validator::construct(
+				&validators,
+				signing_context,
+				keystore.clone(),
+			) {
+				Ok(v) => v,
+				Err(util::Error::NotAValidator) => { return Ok(()) },
+				Err(e) => {
+					log::warn!(
+						target: "candidate_backing",
+						"Cannot participate in candidate backing: {:?}",
+						e
+					);
+
+					return Ok(())
+				}
+			};
 
 			let mut groups = HashMap::new();
 
 			let n_cores = cores.len();
+
+			let mut assignment = None;
 			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());
-					}
-				}
+						if g.contains(&validator.index()) {
+							assignment = Some((scheduled.para_id, scheduled.collator));
 						}
-
-			let mut assignment = Default::default();
-
-			if let Some(idx) = validators.iter().position(|k| *k == validator.id()) {
-				let idx = idx as u32;
-				for (para_id, group) in groups.iter() {
-					if group.contains(&idx) {
-						assignment = *para_id;
-						break;
+						groups.insert(scheduled.para_id, g.clone());
 					}
 				}
 			}
@@ -756,11 +788,17 @@ impl util::JobTrait for CandidateBackingJob {
 				validator: Some(validator),
 			};
 
+			let (assignment, required_collator) = match assignment {
+				None => return Ok(()), // no need to work.
+				Some((a, r)) => (a, r),
+			};
+
 			let job = CandidateBackingJob {
 				parent,
 				rx_to,
 				tx_from,
 				assignment,
+				required_collator,
 				issued_statements: HashSet::new(),
 				seconded: None,
 				reported_misbehavior_for: HashSet::new(),
@@ -829,7 +867,7 @@ mod tests {
 	use assert_matches::assert_matches;
 	use futures::{executor, future, Future};
 	use polkadot_primitives::v1::{
-		ScheduledCore, BlockData, CandidateCommitments, CollatorId,
+		ScheduledCore, BlockData, CandidateCommitments,
 		PersistedValidationData, ValidationData, TransientValidationData, HeadData,
 		ValidatorPair, ValidityAttestation, GroupRotationInfo,
 	};
@@ -1747,4 +1785,108 @@ mod tests {
 			assert_eq!(rx.await.unwrap().len(), 0);
 		});
 	}
+
+	// Test that a `CandidateBackingMessage::Second` issues validation work
+	// and in case validation is successful issues a `StatementDistributionMessage`.
+	#[test]
+	fn backing_doesnt_second_wrong_collator() {
+		let mut test_state = TestState::default();
+		test_state.availability_cores[0] = CoreState::Scheduled(ScheduledCore {
+			para_id: ParaId::from(1),
+			collator: Some(Sr25519Keyring::Bob.public().into()),
+		});
+
+		test_harness(test_state.keystore.clone(), |test_harness| async move {
+			let TestHarness { mut virtual_overseer } = test_harness;
+
+			test_startup(&mut virtual_overseer, &test_state).await;
+
+			let pov = PoV {
+				block_data: BlockData(vec![42, 43, 44]),
+			};
+
+			let expected_head_data = test_state.head_data.get(&test_state.chain_ids[0]).unwrap();
+
+			let pov_hash = pov.hash();
+			let candidate = TestCandidateBuilder {
+				para_id: test_state.chain_ids[0],
+				relay_parent: test_state.relay_parent,
+				pov_hash,
+				head_data: expected_head_data.clone(),
+				erasure_root: make_erasure_root(&test_state, pov.clone()),
+				..Default::default()
+			}.build();
+
+			let second = CandidateBackingMessage::Second(
+				test_state.relay_parent,
+				candidate.to_plain(),
+				pov.clone(),
+			);
+
+			virtual_overseer.send(FromOverseer::Communication{ msg: second }).await;
+
+			assert_matches!(
+				virtual_overseer.recv().await,
+				AllMessages::CandidateSelection(
+					CandidateSelectionMessage::Invalid(parent, c)
+				) if parent == test_state.relay_parent && c == candidate.to_plain() => {
+				}
+			);
+
+			virtual_overseer.send(FromOverseer::Signal(
+				OverseerSignal::ActiveLeaves(ActiveLeavesUpdate::stop_work(test_state.relay_parent)))
+			).await;
+		});
+	}
+
+	#[test]
+	fn validation_work_ignores_wrong_collator() {
+		let mut test_state = TestState::default();
+		test_state.availability_cores[0] = CoreState::Scheduled(ScheduledCore {
+			para_id: ParaId::from(1),
+			collator: Some(Sr25519Keyring::Bob.public().into()),
+		});
+
+		test_harness(test_state.keystore.clone(), |test_harness| async move {
+			let TestHarness { mut virtual_overseer } = test_harness;
+
+			test_startup(&mut virtual_overseer, &test_state).await;
+
+			let pov = PoV {
+				block_data: BlockData(vec![1, 2, 3]),
+			};
+
+			let pov_hash = pov.hash();
+
+			let expected_head_data = test_state.head_data.get(&test_state.chain_ids[0]).unwrap();
+
+			let candidate_a = TestCandidateBuilder {
+				para_id: test_state.chain_ids[0],
+				relay_parent: test_state.relay_parent,
+				pov_hash,
+				head_data: expected_head_data.clone(),
+				erasure_root: make_erasure_root(&test_state, pov.clone()),
+				..Default::default()
+			}.build();
+
+			let seconding = SignedFullStatement::sign(
+				Statement::Seconded(candidate_a.clone()),
+				&test_state.signing_context,
+				2,
+				&test_state.validators[2].pair().into(),
+			);
+
+			let statement = CandidateBackingMessage::Statement(
+				test_state.relay_parent,
+				seconding.clone(),
+			);
+
+			virtual_overseer.send(FromOverseer::Communication{ msg: statement }).await;
+
+			// The statement will be ignored because it has the wrong collator.
+			virtual_overseer.send(FromOverseer::Signal(
+				OverseerSignal::ActiveLeaves(ActiveLeavesUpdate::stop_work(test_state.relay_parent)))
+			).await;
+		});
+	}
 }