Ensure that we fetch another collation if the first collation was invalid (#3362)

* Ensure that we fetch another collation if the first collation was invalid

* Feedback

polkadot/node/network/collator-protocol/src/validator_side/mod.rs

@@ -480,12 +480,14 @@ type PendingCollationFetch = (
 );
 
 /// The status of the collations in [`CollationsPerRelayParent`].
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy)]
 enum CollationStatus {
 	/// We are waiting for a collation to be advertised to us.
 	Waiting,
 	/// We are currently fetching a collation.
 	Fetching,
+	/// We are waiting that a collation is being validated.
+	WaitingOnValidation,
 	/// We have seconded a collation.
 	Seconded,
 }
@@ -496,6 +498,16 @@ impl Default for CollationStatus {
 	}
 }
 
+impl CollationStatus {
+	/// Downgrades to `Waiting`, but only if `self != Seconded`.
+	fn back_to_waiting(&mut self) {
+		match self {
+			Self::Seconded => {},
+			_ => *self = Self::Waiting,
+		}
+	}
+}
+
 /// Information about collations per relay parent.
 #[derive(Default)]
 struct CollationsPerRelayParent {
@@ -505,6 +517,25 @@ struct CollationsPerRelayParent {
 	unfetched_collations: Vec<(PendingCollation, CollatorId)>,
 }
 
+impl CollationsPerRelayParent {
+	/// Returns the next collation to fetch from the `unfetched_collations`.
+	///
+	/// This will reset the status back to `Waiting` using [`CollationStatus::back_to_waiting`].
+	///
+	/// Returns `Some(_)` if there is any collation to fetch and the `status` is not `Seconded`.
+	pub fn get_next_collation_to_fetch(&mut self) -> Option<(PendingCollation, CollatorId)> {
+		self.status.back_to_waiting();
+
+		match self.status {
+			// We don't need to fetch any other collation when we already have seconded one.
+			CollationStatus::Seconded => None,
+			CollationStatus::Waiting => self.unfetched_collations.pop(),
+			CollationStatus::WaitingOnValidation | CollationStatus::Fetching =>
+				unreachable!("We have reset the status above!"),
+		}
+	}
+}
+
 /// All state relevant for the validator side of the protocol lives here.
 #[derive(Default)]
 struct State {
@@ -812,7 +843,7 @@ where
 					let collations = state.collations_per_relay_parent.entry(relay_parent).or_default();
 
 					match collations.status {
-						CollationStatus::Fetching =>
+						CollationStatus::Fetching | CollationStatus::WaitingOnValidation =>
 							collations.unfetched_collations.push((pending_collation, id)),
 						CollationStatus::Waiting => {
 							collations.status = CollationStatus::Fetching;
@@ -1024,14 +1055,28 @@ where
 			}
 		}
 		Invalid(parent, candidate_receipt) => {
-			if state.pending_candidates
-				.get(&parent)
-				.map(|e| e.1.commitments_hash == Some(candidate_receipt.commitments_hash))
-				.unwrap_or_default()
-			{
-				if let Some((id, _)) = state.pending_candidates.remove(&parent) {
-					report_collator(ctx, &state.peer_data, id).await;
+			let id = match state.pending_candidates.entry(parent) {
+				Entry::Occupied(entry)
+					if entry.get().1.commitments_hash == Some(candidate_receipt.commitments_hash) => entry.remove().0,
+				Entry::Occupied(_) => {
+					tracing::error!(
+						target: LOG_TARGET,
+						relay_parent = ?parent,
+						candidate = ?candidate_receipt.hash(),
+						"Reported invalid candidate for unknown `pending_candidate`!",
+					);
+					return
 				}
+				Entry::Vacant(_) => return,
+			};
+
+			report_collator(ctx, &state.peer_data, id).await;
+
+			if let Some((next, id)) = state.collations_per_relay_parent
+				.get_mut(&parent)
+				.and_then(|c| c.get_next_collation_to_fetch())
+			{
+				fetch_collation(ctx, state, next, id).await;
 			}
 		}
 	}
@@ -1139,30 +1184,21 @@ async fn handle_collation_fetched_result(
 				"Failed to fetch collation.",
 			);
 
-			let (next_try, id) = if let Some(collations) = state.collations_per_relay_parent.get_mut(&relay_parent) {
-				if let Some(next_try) = collations.unfetched_collations.pop() {
-					next_try
-				} else if matches!(collations.status, CollationStatus::Fetching) {
-					collations.status = CollationStatus::Waiting;
-					return
-				} else {
-					tracing::error!(
-						target: LOG_TARGET,
-						status = ?collations.status,
-						"Expected status `CollationStatus::Fetching` but got unexpected status."
-					);
-					return
-				}
-			} else {
-				return
-			};
-
-			fetch_collation(ctx, state, next_try, id).await;
+			if let Some((next, id)) = state.collations_per_relay_parent
+				.get_mut(&relay_parent)
+				.and_then(|c| c.get_next_collation_to_fetch())
+			{
+				fetch_collation(ctx, state, next, id).await;
+			}
 
 			return
 		},
 	};
 
+	if let Some(collations) = state.collations_per_relay_parent.get_mut(&relay_parent) {
+		collations.status = CollationStatus::WaitingOnValidation;
+	}
+
 	if let Entry::Vacant(entry) = state.pending_candidates.entry(relay_parent) {
 		collation_event.1.commitments_hash = Some(candidate_receipt.commitments_hash);
 		ctx.send_message(
@@ -1174,6 +1210,13 @@ async fn handle_collation_fetched_result(
 		).await;
 
 		entry.insert(collation_event);
+	} else {
+		tracing::error!(
+			target: LOG_TARGET,
+			?relay_parent,
+			candidate = ?candidate_receipt.hash(),
+			"Trying to insert a pending candidate failed, because there is already one!",
+		)
 	}
 }
 

polkadot/node/network/collator-protocol/src/validator_side/tests.rs

@@ -36,7 +36,7 @@ use polkadot_node_network_protocol::{
 	our_view, ObservedRole, request_response::{Requests, ResponseSender},
 };
 
-const ACTIVITY_TIMEOUT: Duration = Duration::from_millis(50);
+const ACTIVITY_TIMEOUT: Duration = Duration::from_millis(500);
 const DECLARE_TIMEOUT: Duration = Duration::from_millis(25);
 
 #[derive(Clone)]
@@ -262,7 +262,7 @@ async fn assert_candidate_backing_second(
 	expected_relay_parent: Hash,
 	expected_para_id: ParaId,
 	expected_pov: &PoV,
-) {
+) -> CandidateReceipt {
 	assert_matches!(
 		overseer_recv(virtual_overseer).await,
 		AllMessages::CandidateBacking(CandidateBackingMessage::Second(relay_parent, candidate_receipt, incoming_pov)
@@ -270,7 +270,8 @@ async fn assert_candidate_backing_second(
 		assert_eq!(expected_relay_parent, relay_parent);
 		assert_eq!(expected_para_id, candidate_receipt.descriptor.para_id);
 		assert_eq!(*expected_pov, incoming_pov);
-	});
+		candidate_receipt
+	})
 }
 
 /// Assert that a collator got disconnected.
@@ -290,25 +291,6 @@ async fn assert_collator_disconnect(
 	);
 }
 
-/// Assert that the given collators got disconnected.
-async fn assert_collators_disconnect(
-	virtual_overseer: &mut VirtualOverseer,
-	expected_peers: &[PeerId],
-) {
-	for _ in expected_peers {
-		assert_matches!(
-			overseer_recv(virtual_overseer).await,
-			AllMessages::NetworkBridge(NetworkBridgeMessage::DisconnectPeer(
-				peer,
-				peer_set,
-			)) => {
-				assert!(expected_peers.contains(&peer), "Unexpected collator disconnected: {:?}", peer);
-				assert_eq!(PeerSet::Collation, peer_set);
-			}
-		);
-	}
-}
-
 /// Assert that a fetch collation request was send.
 async fn assert_fetch_collation_request(
 	virtual_overseer: &mut VirtualOverseer,
@@ -603,8 +585,6 @@ fn fetch_collations_works() {
 			&pov,
 		).await;
 
-		assert_collators_disconnect(&mut virtual_overseer, &[peer_b.clone(), peer_c.clone()]).await;
-
 		overseer_send(
 			&mut virtual_overseer,
 			CollatorProtocolMessage::NetworkBridgeUpdateV1(NetworkBridgeEvent::PeerDisconnected(peer_b.clone())),
@@ -681,6 +661,97 @@ fn fetch_collations_works() {
 	});
 }
 
+// Ensure that we fetch a second collation, after the first checked collation was found to be invalid.
+#[test]
+fn fetch_next_collation_on_invalid_collation() {
+	let test_state = TestState::default();
+
+	test_harness(|test_harness| async move {
+		let TestHarness {
+			mut virtual_overseer,
+		} = test_harness;
+
+		let second = Hash::random();
+
+		overseer_send(
+			&mut virtual_overseer,
+			CollatorProtocolMessage::NetworkBridgeUpdateV1(
+				NetworkBridgeEvent::OurViewChange(our_view![test_state.relay_parent, second])
+			),
+		).await;
+
+		respond_to_core_info_queries(&mut virtual_overseer, &test_state).await;
+		respond_to_core_info_queries(&mut virtual_overseer, &test_state).await;
+
+		let peer_b = PeerId::random();
+		let peer_c = PeerId::random();
+
+		connect_and_declare_collator(
+			&mut virtual_overseer,
+			peer_b.clone(),
+			test_state.collators[0].clone(),
+			test_state.chain_ids[0].clone(),
+		).await;
+
+		connect_and_declare_collator(
+			&mut virtual_overseer,
+			peer_c.clone(),
+			test_state.collators[1].clone(),
+			test_state.chain_ids[0].clone(),
+		).await;
+
+		advertise_collation(&mut virtual_overseer, peer_b.clone(), test_state.relay_parent).await;
+		advertise_collation(&mut virtual_overseer, peer_c.clone(), test_state.relay_parent).await;
+
+		let response_channel = assert_fetch_collation_request(
+			&mut virtual_overseer,
+			test_state.relay_parent,
+			test_state.chain_ids[0],
+		).await;
+
+		let pov = PoV { block_data: BlockData(vec![]) };
+		let mut candidate_a = CandidateReceipt::default();
+		candidate_a.descriptor.para_id = test_state.chain_ids[0];
+		candidate_a.descriptor.relay_parent = test_state.relay_parent;
+		response_channel.send(Ok(
+			CollationFetchingResponse::Collation(
+				candidate_a.clone(),
+				pov.clone(),
+			).encode()
+		)).expect("Sending response should succeed");
+
+		let receipt = assert_candidate_backing_second(
+			&mut virtual_overseer,
+			test_state.relay_parent,
+			test_state.chain_ids[0],
+			&pov,
+		).await;
+
+		// Inform that the candidate was invalid.
+		overseer_send(&mut virtual_overseer, CollatorProtocolMessage::Invalid(test_state.relay_parent, receipt)).await;
+
+		assert_matches!(
+			overseer_recv(&mut virtual_overseer).await,
+			AllMessages::NetworkBridge(NetworkBridgeMessage::ReportPeer(
+				peer,
+				rep,
+			)) => {
+				assert_eq!(peer, peer_b);
+				assert_eq!(rep, COST_REPORT_BAD);
+			}
+		);
+
+		// We should see a request for another collation.
+		assert_fetch_collation_request(
+			&mut virtual_overseer,
+			test_state.relay_parent,
+			test_state.chain_ids[0],
+		).await;
+
+		virtual_overseer
+	});
+}
+
 #[test]
 fn inactive_disconnected() {
 	let test_state = TestState::default();