refactor View to include finalized_number (#2128)

* refactor View to include finalized_number

* guide: update the NetworkBridge on BlockFinalized

* av-store: fix the tests

* actually fix tests

* grumbles

* ignore macro doctest

* use Hash::repeat_bytes more consistently

* broadcast empty leaves updates as well

* fix issuing view updates on empty leaves updates

polkadot/node/collation-generation/src/lib.rs

@@ -145,7 +145,7 @@ impl CollationGenerationSubsystem {
 				}
 				false
 			}
-			Ok(Signal(BlockFinalized(_))) => false,
+			Ok(Signal(BlockFinalized(..))) => false,
 			Err(err) => {
 				tracing::error!(
 					target: LOG_TARGET,

polkadot/node/core/av-store/src/lib.rs

@@ -538,8 +538,8 @@ where
 						process_block_activated(ctx, &subsystem.inner, activated, &subsystem.metrics).await?;
 					}
 				}
-				FromOverseer::Signal(OverseerSignal::BlockFinalized(hash)) => {
-					process_block_finalized(subsystem, ctx, &subsystem.inner, hash).await?;
+				FromOverseer::Signal(OverseerSignal::BlockFinalized(_hash, number)) => {
+					process_block_finalized(subsystem, &subsystem.inner, number).await?;
 				}
 				FromOverseer::Communication { msg } => {
 					process_message(subsystem, ctx, msg).await?;
@@ -564,20 +564,14 @@ where
 /// The state of data has to be changed from
 /// `CandidateState::Included` to `CandidateState::Finalized` and their pruning times have
 /// to be updated to `now` + keep_finalized_{block, chunk}_for`.
-#[tracing::instrument(level = "trace", skip(subsystem, ctx, db), fields(subsystem = LOG_TARGET))]
-async fn process_block_finalized<Context>(
+#[tracing::instrument(level = "trace", skip(subsystem, db), fields(subsystem = LOG_TARGET))]
+async fn process_block_finalized(
 	subsystem: &AvailabilityStoreSubsystem,
-	ctx: &mut Context,
 	db: &Arc<dyn KeyValueDB>,
-	hash: Hash,
-) -> Result<(), Error>
-where
-	Context: SubsystemContext<Message=AvailabilityStoreMessage>
-{
+	block_number: BlockNumber,
+) -> Result<(), Error> {
 	let _timer = subsystem.metrics.time_process_block_finalized();
 
-	let block_number = get_block_number(ctx, hash).await?;
-
 	if let Some(mut pov_pruning) = pov_pruning(db) {
 		// Since the records are sorted by time in which they need to be pruned and not by block
 		// numbers we have to iterate through the whole collection here.

polkadot/node/core/av-store/src/tests.rs

@@ -274,7 +274,7 @@ fn store_block_works() {
 	let test_state = TestState::default();
 	test_harness(test_state.pruning_config.clone(), store.clone(), |test_harness| async move {
 		let TestHarness { mut virtual_overseer } = test_harness;
-		let candidate_hash = CandidateHash(Hash::from([1; 32]));
+		let candidate_hash = CandidateHash(Hash::repeat_byte(1));
 		let validator_index = 5;
 		let n_validators = 10;
 
@@ -328,7 +328,7 @@ fn store_pov_and_query_chunk_works() {
 
 	test_harness(test_state.pruning_config.clone(), store.clone(), |test_harness| async move {
 		let TestHarness { mut virtual_overseer } = test_harness;
-		let candidate_hash = CandidateHash(Hash::from([1; 32]));
+		let candidate_hash = CandidateHash(Hash::repeat_byte(1));
 		let n_validators = 10;
 
 		let pov = PoV {
@@ -543,20 +543,9 @@ fn stored_data_kept_until_finalized() {
 
 		overseer_signal(
 			&mut virtual_overseer,
-			OverseerSignal::BlockFinalized(new_leaf)
+			OverseerSignal::BlockFinalized(new_leaf, 10)
 		).await;
 
-		assert_matches!(
-			overseer_recv(&mut virtual_overseer).await,
-			AllMessages::ChainApi(ChainApiMessage::BlockNumber(
-				hash,
-				tx,
-			)) => {
-				assert_eq!(hash, new_leaf);
-				tx.send(Ok(Some(10))).unwrap();
-			}
-		);
-
 		// Wait for a half of the time finalized data should be available for
 		Delay::new(test_state.pruning_config.keep_finalized_block_for / 2).await;
 
@@ -658,20 +647,9 @@ fn stored_chunk_kept_until_finalized() {
 
 		overseer_signal(
 			&mut virtual_overseer,
-			OverseerSignal::BlockFinalized(new_leaf)
+			OverseerSignal::BlockFinalized(new_leaf, 10)
 		).await;
 
-		assert_matches!(
-			overseer_recv(&mut virtual_overseer).await,
-			AllMessages::ChainApi(ChainApiMessage::BlockNumber(
-				hash,
-				tx,
-			)) => {
-				assert_eq!(hash, new_leaf);
-				tx.send(Ok(Some(10))).unwrap();
-			}
-		);
-
 		// Wait for a half of the time finalized data should be available for
 		Delay::new(test_state.pruning_config.keep_finalized_block_for / 2).await;
 
@@ -812,21 +790,9 @@ fn forkfullness_works() {
 
 		overseer_signal(
 			&mut virtual_overseer,
-			OverseerSignal::BlockFinalized(new_leaf_1)
+			OverseerSignal::BlockFinalized(new_leaf_1, 5)
 		).await;
 
-		assert_matches!(
-			overseer_recv(&mut virtual_overseer).await,
-			AllMessages::ChainApi(ChainApiMessage::BlockNumber(
-				hash,
-				tx,
-			)) => {
-				assert_eq!(hash, new_leaf_1);
-				tx.send(Ok(Some(5))).unwrap();
-			}
-		);
-
-
 		// Data of both candidates should be still present in the DB.
 		assert_eq!(
 			query_available_data(&mut virtual_overseer, candidate_1_hash).await.unwrap(),

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

@@ -1157,7 +1157,7 @@ mod tests {
 			let mut head_data = HashMap::new();
 			head_data.insert(chain_a, HeadData(vec![4, 5, 6]));
 
-			let relay_parent = Hash::from([5; 32]);
+			let relay_parent = Hash::repeat_byte(5);
 
 			let signing_context = SigningContext {
 				session_index: 1,

polkadot/node/core/candidate-validation/src/lib.rs

@@ -95,7 +95,7 @@ async fn run(
 	loop {
 		match ctx.recv().await? {
 			FromOverseer::Signal(OverseerSignal::ActiveLeaves(_)) => {}
-			FromOverseer::Signal(OverseerSignal::BlockFinalized(_)) => {}
+			FromOverseer::Signal(OverseerSignal::BlockFinalized(..)) => {}
 			FromOverseer::Signal(OverseerSignal::Conclude) => return Ok(()),
 			FromOverseer::Communication { msg } => match msg {
 				CandidateValidationMessage::ValidateFromChainState(

polkadot/node/core/chain-api/src/lib.rs

@@ -89,7 +89,7 @@ where
 		match ctx.recv().await? {
 			FromOverseer::Signal(OverseerSignal::Conclude) => return Ok(()),
 			FromOverseer::Signal(OverseerSignal::ActiveLeaves(_)) => {},
-			FromOverseer::Signal(OverseerSignal::BlockFinalized(_)) => {},
+			FromOverseer::Signal(OverseerSignal::BlockFinalized(..)) => {},
 			FromOverseer::Communication { msg } => match msg {
 				ChainApiMessage::BlockNumber(hash, response_channel) => {
 					let _timer = subsystem.metrics.time_block_number();

polkadot/node/core/runtime-api/src/lib.rs

@@ -152,7 +152,7 @@ async fn run<Client>(
 			req = ctx.recv().fuse() => match req? {
 				FromOverseer::Signal(OverseerSignal::Conclude) => return Ok(()),
 				FromOverseer::Signal(OverseerSignal::ActiveLeaves(_)) => {},
-				FromOverseer::Signal(OverseerSignal::BlockFinalized(_)) => {},
+				FromOverseer::Signal(OverseerSignal::BlockFinalized(..)) => {},
 				FromOverseer::Communication { msg } => match msg {
 					RuntimeApiMessage::Request(relay_parent, request) => {
 						subsystem.spawn_request(relay_parent, request);

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

@@ -416,7 +416,7 @@ where
 			.filter(|(_peer, view)| {
 				// collect all direct interests of a peer w/o ancestors
 				state
-					.cached_live_candidates_unioned(view.0.iter())
+					.cached_live_candidates_unioned(view.heads.iter())
 					.contains_key(&candidate_hash)
 			})
 			.map(|(peer, _view)| peer.clone())
@@ -619,7 +619,7 @@ where
 	let _timer = metrics.time_process_incoming_peer_message();
 
 	// obtain the set of candidates we are interested in based on our current view
-	let live_candidates = state.cached_live_candidates_unioned(state.view.0.iter());
+	let live_candidates = state.cached_live_candidates_unioned(state.view.heads.iter());
 
 	// check if the candidate is of interest
 	let live_candidate = if let Some(live_candidate) = live_candidates.get(&message.candidate_hash) {
@@ -707,7 +707,7 @@ where
 		.filter(|(_peer, view)| {
 			// peers view must contain the candidate hash too
 			state
-				.cached_live_candidates_unioned(view.0.iter())
+				.cached_live_candidates_unioned(view.heads.iter())
 				.contains_key(&message_id.0)
 		})
 		.map(|(peer, _)| -> PeerId { peer.clone() })
@@ -781,7 +781,7 @@ impl AvailabilityDistributionSubsystem {
 				})) => {
 					// handled at view change
 				}
-				FromOverseer::Signal(OverseerSignal::BlockFinalized(_)) => {}
+				FromOverseer::Signal(OverseerSignal::BlockFinalized(..)) => {}
 				FromOverseer::Signal(OverseerSignal::Conclude) => {
 					return Ok(());
 				}

polkadot/node/network/availability-distribution/src/tests.rs

@@ -17,7 +17,7 @@
 use super::*;
 use assert_matches::assert_matches;
 use polkadot_erasure_coding::{branches, obtain_chunks_v1 as obtain_chunks};
-use polkadot_node_network_protocol::ObservedRole;
+use polkadot_node_network_protocol::{view, ObservedRole};
 use polkadot_node_subsystem_util::TimeoutExt;
 use polkadot_primitives::v1::{
 	AvailableData, BlockData, CandidateCommitments, CandidateDescriptor, GroupIndex,
@@ -33,11 +33,6 @@ use sp_application_crypto::AppKey;
 use sp_keystore::{SyncCryptoStore, SyncCryptoStorePtr};
 use std::{sync::Arc, time::Duration};
 
-macro_rules! view {
-		( $( $hash:expr ),* $(,)? ) => [
-			View(vec![ $( $hash.clone() ),* ])
-		];
-	}
 
 macro_rules! delay {
 	($delay:expr) => {

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

@@ -212,8 +212,8 @@ impl BitfieldDistribution {
 						// defer the cleanup to the view change
 					}
 				}
-				FromOverseer::Signal(OverseerSignal::BlockFinalized(hash)) => {
-					tracing::trace!(target: LOG_TARGET, hash = %hash, "block finalized");
+				FromOverseer::Signal(OverseerSignal::BlockFinalized(hash, number)) => {
+					tracing::trace!(target: LOG_TARGET, hash = %hash, number = %number, "block finalized");
 				}
 				FromOverseer::Signal(OverseerSignal::Conclude) => {
 					tracing::trace!(target: LOG_TARGET, "Conclude");
@@ -770,13 +770,7 @@ mod test {
 	use std::sync::Arc;
 	use std::time::Duration;
 	use assert_matches::assert_matches;
-	use polkadot_node_network_protocol::ObservedRole;
-
-	macro_rules! view {
-		( $( $hash:expr ),* $(,)? ) => [
-			View(vec![ $( $hash.clone() ),* ])
-		];
-	}
+	use polkadot_node_network_protocol::{view, ObservedRole};
 
 	macro_rules! launch {
 		($fut:expr) => {
@@ -833,7 +827,7 @@ mod test {
 		let validator = SyncCryptoStore::sr25519_generate_new(&*keystore, ValidatorId::ID, None)
 			.expect("generating sr25519 key not to fail");
 
-		state.per_relay_parent = view.0.iter().map(|relay_parent| {(
+		state.per_relay_parent = view.heads.iter().map(|relay_parent| {(
 				relay_parent.clone(),
 				PerRelayParentData {
 					signing_context: signing_context.clone(),

polkadot/node/network/bridge/src/lib.rs

@@ -37,7 +37,7 @@ use polkadot_subsystem::messages::{
 	BitfieldDistributionMessage, PoVDistributionMessage, StatementDistributionMessage,
 	CollatorProtocolMessage,
 };
-use polkadot_primitives::v1::{AuthorityDiscoveryId, Block, Hash};
+use polkadot_primitives::v1::{AuthorityDiscoveryId, Block, Hash, BlockNumber};
 use polkadot_node_network_protocol::{
 	ObservedRole, ReputationChange, PeerId, PeerSet, View, NetworkBridgeEvent, v1 as protocol_v1
 };
@@ -254,6 +254,7 @@ enum Action {
 	ReportPeer(PeerId, ReputationChange),
 
 	ActiveLeaves(ActiveLeavesUpdate),
+	BlockFinalized(BlockNumber),
 
 	PeerConnected(PeerSet, PeerId, ObservedRole),
 	PeerDisconnected(PeerSet, PeerId),
@@ -274,6 +275,8 @@ fn action_from_overseer_message(
 	match res {
 		Ok(FromOverseer::Signal(OverseerSignal::ActiveLeaves(active_leaves)))
 			=> Action::ActiveLeaves(active_leaves),
+		Ok(FromOverseer::Signal(OverseerSignal::BlockFinalized(_hash, number)))
+			=> Action::BlockFinalized(number),
 		Ok(FromOverseer::Signal(OverseerSignal::Conclude)) => Action::Abort,
 		Ok(FromOverseer::Communication { msg }) => match msg {
 			NetworkBridgeMessage::ReportPeer(peer, rep) => Action::ReportPeer(peer, rep),
@@ -284,8 +287,6 @@ fn action_from_overseer_message(
 			NetworkBridgeMessage::ConnectToValidators { validator_ids, connected }
 				=> Action::ConnectToValidators { validator_ids, connected },
 		},
-		Ok(FromOverseer::Signal(OverseerSignal::BlockFinalized(_)))
-			=> Action::Nop,
 		Err(e) => {
 			tracing::warn!(target: LOG_TARGET, err = ?e, "Shutting down Network Bridge due to error");
 			Action::Abort
@@ -348,21 +349,25 @@ fn action_from_network_message(event: Option<NetworkEvent>) -> Action {
 	}
 }
 
-fn construct_view(live_heads: &[Hash]) -> View {
-	View(live_heads.iter().rev().take(MAX_VIEW_HEADS).cloned().collect())
+fn construct_view(live_heads: &[Hash], finalized_number: BlockNumber) -> View {
+	View {
+		heads: live_heads.iter().rev().take(MAX_VIEW_HEADS).cloned().collect(),
+		finalized_number
+	}
 }
 
 #[tracing::instrument(level = "trace", skip(net, ctx, validation_peers, collation_peers), fields(subsystem = LOG_TARGET))]
-async fn update_view(
+async fn update_our_view(
 	net: &mut impl Network,
 	ctx: &mut impl SubsystemContext<Message = NetworkBridgeMessage>,
 	live_heads: &[Hash],
 	local_view: &mut View,
+	finalized_number: BlockNumber,
 	validation_peers: &HashMap<PeerId, PeerData>,
 	collation_peers: &HashMap<PeerId, PeerData>,
 ) -> SubsystemResult<()> {
-	let new_view = construct_view(live_heads);
-	if *local_view == new_view { return Ok(())  }
+	let new_view = construct_view(live_heads, finalized_number);
+	if *local_view == new_view { return Ok(()) }
 
 	*local_view = new_view.clone();
 
@@ -413,7 +418,7 @@ async fn handle_peer_messages<M>(
 	for message in messages {
 		outgoing_messages.push(match message {
 			WireMessage::ViewUpdate(new_view) => {
-				if new_view.0.len() > MAX_VIEW_HEADS {
+				if new_view.heads.len() > MAX_VIEW_HEADS {
 					net.report_peer(
 						peer.clone(),
 						MALFORMED_VIEW_COST,
@@ -580,7 +585,8 @@ where
 
 	// Most recent heads are at the back.
 	let mut live_heads: Vec<Hash> = Vec::with_capacity(MAX_VIEW_HEADS);
-	let mut local_view = View(Vec::new());
+	let mut local_view = View::default();
+	let mut finalized_number = 0;
 
 	let mut validation_peers: HashMap<PeerId, PeerData> = HashMap::new();
 	let mut collation_peers: HashMap<PeerId, PeerData> = HashMap::new();
@@ -638,16 +644,27 @@ where
 				live_heads.extend(activated);
 				live_heads.retain(|h| !deactivated.contains(h));
 
-				update_view(
+				update_our_view(
 					&mut network_service,
 					&mut ctx,
 					&live_heads,
 					&mut local_view,
+					finalized_number,
 					&validation_peers,
 					&collation_peers,
 				).await?;
 			}
 
+			Action::BlockFinalized(number) => {
+				debug_assert!(finalized_number < number);
+
+				// we don't send the view updates here, but delay them until the next `Action::ActiveLeaves`
+				// otherwise it might break assumptions of some of the subsystems
+				// that we never send the same `ActiveLeavesUpdate`
+				// this is fine, we will get `Action::ActiveLeaves` on block finalization anyway
+				finalized_number = number;
+			},
+
 			Action::PeerConnected(peer_set, peer, role) => {
 				let peer_map = match peer_set {
 					PeerSet::Validation => &mut validation_peers,
@@ -660,7 +677,7 @@ where
 					hash_map::Entry::Occupied(_) => continue,
 					hash_map::Entry::Vacant(vacant) => {
 						let _ = vacant.insert(PeerData {
-							view: View(Vec::new()),
+							view: View::default(),
 						});
 
 						match peer_set {
@@ -669,7 +686,7 @@ where
 									NetworkBridgeEvent::PeerConnected(peer.clone(), role),
 									NetworkBridgeEvent::PeerViewChange(
 										peer,
-										View(Default::default()),
+										View::default(),
 									),
 								],
 								&mut ctx,
@@ -679,7 +696,7 @@ where
 									NetworkBridgeEvent::PeerConnected(peer.clone(), role),
 									NetworkBridgeEvent::PeerViewChange(
 										peer,
-										View(Default::default()),
+										View::default(),
 									),
 								],
 								&mut ctx,
@@ -753,6 +770,7 @@ mod tests {
 	use polkadot_node_subsystem_test_helpers::{
 		SingleItemSink, SingleItemStream, TestSubsystemContextHandle,
 	};
+	use polkadot_node_network_protocol::view;
 	use sc_network::Multiaddr;
 	use sp_keyring::Sr25519Keyring;
 
@@ -978,7 +996,7 @@ mod tests {
 				ObservedRole::Full,
 			).await;
 
-			let hash_a = Hash::from([1; 32]);
+			let hash_a = Hash::repeat_byte(1);
 
 			virtual_overseer.send(
 				FromOverseer::Signal(OverseerSignal::ActiveLeaves(ActiveLeavesUpdate::start_work(hash_a)))
@@ -986,7 +1004,7 @@ mod tests {
 
 			let actions = network_handle.next_network_actions(2).await;
 			let wire_message = WireMessage::<protocol_v1::ValidationProtocol>::ViewUpdate(
-				View(vec![hash_a])
+				view![hash_a]
 			).encode();
 
 			assert!(network_actions_contains(
@@ -1021,7 +1039,7 @@ mod tests {
 
 			network_handle.connect_peer(peer.clone(), PeerSet::Validation, ObservedRole::Full).await;
 
-			let view = View(vec![Hash::from([1u8; 32])]);
+			let view = view![Hash::repeat_byte(1)];
 
 			// bridge will inform about all connected peers.
 			{
@@ -1031,7 +1049,7 @@ mod tests {
 				).await;
 
 				assert_sends_validation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1075,7 +1093,7 @@ mod tests {
 				).await;
 
 				assert_sends_validation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1140,7 +1158,7 @@ mod tests {
 				).await;
 
 				assert_sends_validation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1152,7 +1170,7 @@ mod tests {
 				).await;
 
 				assert_sends_collation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1166,7 +1184,7 @@ mod tests {
 
 			// to show that we're still connected on the collation protocol, send a view update.
 
-			let hash_a = Hash::from([1; 32]);
+			let hash_a = Hash::repeat_byte(1);
 
 			virtual_overseer.send(
 				FromOverseer::Signal(OverseerSignal::ActiveLeaves(ActiveLeavesUpdate::start_work(hash_a)))
@@ -1174,7 +1192,7 @@ mod tests {
 
 			let actions = network_handle.next_network_actions(1).await;
 			let wire_message = WireMessage::<protocol_v1::ValidationProtocol>::ViewUpdate(
-				View(vec![hash_a])
+				view![hash_a]
 			).encode();
 
 			assert!(network_actions_contains(
@@ -1210,7 +1228,7 @@ mod tests {
 				).await;
 
 				assert_sends_validation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer_a.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer_a.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1222,7 +1240,7 @@ mod tests {
 				).await;
 
 				assert_sends_collation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer_b.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer_b.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1295,7 +1313,7 @@ mod tests {
 				).await;
 
 				assert_sends_validation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1307,13 +1325,13 @@ mod tests {
 				).await;
 
 				assert_sends_collation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
 
-			let view_a = View(vec![[1; 32].into()]);
-			let view_b = View(vec![[2; 32].into()]);
+			let view_a = view![Hash::repeat_byte(1)];
+			let view_b = view![Hash::repeat_byte(2)];
 
 			network_handle.peer_message(
 				peer.clone(),
@@ -1339,6 +1357,74 @@ mod tests {
 		});
 	}
 
+	#[test]
+	fn sent_views_include_finalized_number_update() {
+		test_harness(|test_harness| async move {
+			let TestHarness { mut network_handle, mut virtual_overseer } = test_harness;
+
+			let peer_a = PeerId::random();
+
+			network_handle.connect_peer(
+				peer_a.clone(),
+				PeerSet::Validation,
+				ObservedRole::Full,
+			).await;
+
+			let hash_a = Hash::repeat_byte(1);
+			let hash_b = Hash::repeat_byte(2);
+			let hash_c = Hash::repeat_byte(3);
+
+			virtual_overseer.send(
+				FromOverseer::Signal(OverseerSignal::BlockFinalized(hash_a, 1))
+			).await;
+			virtual_overseer.send(
+				FromOverseer::Signal(OverseerSignal::ActiveLeaves(ActiveLeavesUpdate::start_work(hash_b)))
+			).await;
+
+			let actions = network_handle.next_network_actions(1).await;
+			let wire_message = WireMessage::<protocol_v1::ValidationProtocol>::ViewUpdate(
+				View {
+					heads: vec![hash_b],
+					finalized_number: 1,
+				}
+			).encode();
+
+			assert!(network_actions_contains(
+				&actions,
+				&NetworkAction::WriteNotification(
+					peer_a.clone(),
+					PeerSet::Validation,
+					wire_message.clone(),
+				),
+			));
+
+			// view updates are issued even when `ActiveLeavesUpdate` is empty
+			virtual_overseer.send(
+				FromOverseer::Signal(OverseerSignal::BlockFinalized(hash_c, 3))
+			).await;
+			virtual_overseer.send(
+				FromOverseer::Signal(OverseerSignal::ActiveLeaves(ActiveLeavesUpdate::default()))
+			).await;
+
+			let actions = network_handle.next_network_actions(1).await;
+			let wire_message = WireMessage::<protocol_v1::ValidationProtocol>::ViewUpdate(
+				View {
+					heads: vec![hash_b],
+					finalized_number: 3,
+				}
+			).encode();
+
+			assert!(network_actions_contains(
+				&actions,
+				&NetworkAction::WriteNotification(
+					peer_a,
+					PeerSet::Validation,
+					wire_message.clone(),
+				),
+			));
+		});
+	}
+
 	#[test]
 	fn send_messages_to_peers() {
 		test_harness(|test_harness| async move {
@@ -1360,7 +1446,7 @@ mod tests {
 				).await;
 
 				assert_sends_validation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}
@@ -1372,7 +1458,7 @@ mod tests {
 				).await;
 
 				assert_sends_collation_event_to_all(
-					NetworkBridgeEvent::PeerViewChange(peer.clone(), View(Default::default())),
+					NetworkBridgeEvent::PeerViewChange(peer.clone(), View::default()),
 					&mut virtual_overseer,
 				).await;
 			}

polkadot/node/network/collator-protocol/src/collator_side.rs

@@ -714,7 +714,7 @@ pub(crate) async fn run(
 					}
 				},
 				Signal(ActiveLeaves(_update)) => {}
-				Signal(BlockFinalized(_)) => {}
+				Signal(BlockFinalized(..)) => {}
 				Signal(Conclude) => return Ok(()),
 			}
 		}
@@ -742,6 +742,7 @@ mod tests {
 	use polkadot_subsystem::{ActiveLeavesUpdate, messages::{RuntimeApiMessage, RuntimeApiRequest}};
 	use polkadot_node_subsystem_util::TimeoutExt;
 	use polkadot_subsystem_testhelpers as test_helpers;
+	use polkadot_node_network_protocol::view;
 
 	#[derive(Default)]
 	struct TestCandidateBuilder {
@@ -896,7 +897,7 @@ mod tests {
 			overseer_send(
 				virtual_overseer,
 				CollatorProtocolMessage::NetworkBridgeUpdateV1(
-					NetworkBridgeEvent::OurViewChange(View(hashes)),
+					NetworkBridgeEvent::OurViewChange(View { heads: hashes, finalized_number: 0 }),
 				),
 			).await;
 		}
@@ -1004,7 +1005,7 @@ mod tests {
 		overseer_send(
 			virtual_overseer,
 			CollatorProtocolMessage::NetworkBridgeUpdateV1(
-				NetworkBridgeEvent::OurViewChange(View(vec![test_state.relay_parent])),
+				NetworkBridgeEvent::OurViewChange(view![test_state.relay_parent]),
 			),
 		).await;
 	}
@@ -1144,7 +1145,7 @@ mod tests {
 		overseer_send(
 			virtual_overseer,
 			CollatorProtocolMessage::NetworkBridgeUpdateV1(
-				NetworkBridgeEvent::PeerViewChange(peer, View(Default::default())),
+				NetworkBridgeEvent::PeerViewChange(peer, view![]),
 			),
 		).await;
 	}
@@ -1213,7 +1214,7 @@ mod tests {
 		overseer_send(
 			virtual_overseer,
 			CollatorProtocolMessage::NetworkBridgeUpdateV1(
-				NetworkBridgeEvent::PeerViewChange(peer.clone(), View(hashes)),
+				NetworkBridgeEvent::PeerViewChange(peer.clone(), View { heads: hashes, finalized_number: 0 }),
 			),
 		).await;
 	}
@@ -1323,7 +1324,7 @@ mod tests {
 				CollatorProtocolMessage::NetworkBridgeUpdateV1(
 					NetworkBridgeEvent::PeerViewChange(
 						peer.clone(),
-						View(vec![test_state.relay_parent]),
+						view![test_state.relay_parent],
 					)
 				)
 			).await;

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

@@ -714,7 +714,7 @@ where
 
 			match msg {
 				Communication { msg } => process_msg(&mut ctx, msg, &mut state).await,
-				Signal(BlockFinalized(_)) => {}
+				Signal(BlockFinalized(..)) => {}
 				Signal(ActiveLeaves(_)) => {}
 				Signal(Conclude) => { break }
 			}
@@ -760,6 +760,7 @@ mod tests {
 
 	use polkadot_primitives::v1::{BlockData, CollatorPair};
 	use polkadot_subsystem_testhelpers as test_helpers;
+	use polkadot_node_network_protocol::view;
 
 	#[derive(Clone)]
 	struct TestState {
@@ -872,7 +873,7 @@ mod tests {
 			overseer_send(
 				&mut virtual_overseer,
 				CollatorProtocolMessage::NetworkBridgeUpdateV1(
-					NetworkBridgeEvent::OurViewChange(View(vec![test_state.relay_parent]))
+					NetworkBridgeEvent::OurViewChange(view![test_state.relay_parent])
 				)
 			).await;
 
@@ -930,7 +931,7 @@ mod tests {
 			overseer_send(
 				&mut virtual_overseer,
 				CollatorProtocolMessage::NetworkBridgeUpdateV1(
-					NetworkBridgeEvent::OurViewChange(View(vec![test_state.relay_parent]))
+					NetworkBridgeEvent::OurViewChange(view![test_state.relay_parent])
 				)
 			).await;
 
@@ -1021,7 +1022,7 @@ mod tests {
 			overseer_send(
 				&mut virtual_overseer,
 				CollatorProtocolMessage::NetworkBridgeUpdateV1(
-					NetworkBridgeEvent::OurViewChange(View(vec![Hash::repeat_byte(0x42)]))
+					NetworkBridgeEvent::OurViewChange(view![Hash::repeat_byte(0x42)])
 				)
 			).await;
 
@@ -1049,7 +1050,7 @@ mod tests {
 			overseer_send(
 				&mut virtual_overseer,
 				CollatorProtocolMessage::NetworkBridgeUpdateV1(
-					NetworkBridgeEvent::OurViewChange(View(vec![test_state.relay_parent]))
+					NetworkBridgeEvent::OurViewChange(view![test_state.relay_parent])
 				)
 			).await;
 
@@ -1133,7 +1134,7 @@ mod tests {
 			overseer_send(
 				&mut virtual_overseer,
 				CollatorProtocolMessage::NetworkBridgeUpdateV1(
-					NetworkBridgeEvent::OurViewChange(View(vec![test_state.relay_parent]))
+					NetworkBridgeEvent::OurViewChange(view![test_state.relay_parent])
 				)
 			).await;
 

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

@@ -197,7 +197,7 @@ async fn handle_signal(
 
 			Ok(false)
 		}
-		OverseerSignal::BlockFinalized(_) => Ok(false),
+		OverseerSignal::BlockFinalized(..) => Ok(false),
 	}
 }
 
@@ -499,7 +499,7 @@ async fn handle_awaiting(
 	relay_parent: Hash,
 	pov_hashes: Vec<Hash>,
 ) {
-	if !state.our_view.0.contains(&relay_parent) {
+	if !state.our_view.contains(&relay_parent) {
 		report_peer(ctx, peer, COST_AWAITED_NOT_IN_VIEW).await;
 		return;
 	}
@@ -635,10 +635,10 @@ async fn handle_network_update(
 		NetworkBridgeEvent::PeerViewChange(peer_id, view) => {
 			if let Some(peer_state) = state.peer_state.get_mut(&peer_id) {
 				// prune anything not in the new view.
-				peer_state.awaited.retain(|relay_parent, _| view.0.contains(&relay_parent));
+				peer_state.awaited.retain(|relay_parent, _| view.contains(&relay_parent));
 
 				// introduce things from the new view.
-				for relay_parent in view.0.iter() {
+				for relay_parent in view.heads.iter() {
 					if let Entry::Vacant(entry) = peer_state.awaited.entry(*relay_parent) {
 						entry.insert(HashSet::new());
 

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

@@ -16,6 +16,7 @@ use polkadot_primitives::v1::{
 use polkadot_subsystem::messages::{RuntimeApiMessage, RuntimeApiRequest};
 use polkadot_node_subsystem_test_helpers as test_helpers;
 use polkadot_node_subsystem_util::TimeoutExt;
+use polkadot_node_network_protocol::view;
 
 fn make_pov(data: Vec<u8>) -> PoV {
 	PoV { block_data: BlockData(data) }
@@ -358,7 +359,7 @@ fn ask_validators_for_povs() {
 				PoVDistributionMessage::NetworkBridgeUpdateV1(
 					NetworkBridgeEvent::PeerViewChange(
 						test_state.validator_peer_id[i].clone(),
-						View(vec![current]),
+						view![current],
 					)
 				)
 			).await;
@@ -405,7 +406,7 @@ fn ask_validators_for_povs() {
 			PoVDistributionMessage::NetworkBridgeUpdateV1(
 				NetworkBridgeEvent::PeerViewChange(
 					test_state.validator_peer_id[2].clone(),
-					View(vec![next_leaf]),
+					view![next_leaf],
 				)
 			)
 		).await;
@@ -582,7 +583,7 @@ fn distributes_to_those_awaiting_and_completes_local() {
 
 			s
 		},
-		our_view: View(vec![hash_a, hash_b]),
+		our_view: view![hash_a, hash_b],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -665,7 +666,7 @@ fn we_inform_peers_with_same_view_we_are_awaiting() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -839,7 +840,7 @@ fn peer_view_change_leads_to_us_informing() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -851,7 +852,7 @@ fn peer_view_change_leads_to_us_informing() {
 		handle_network_update(
 			&mut state,
 			&mut ctx,
-			NetworkBridgeEvent::PeerViewChange(peer_a.clone(), View(vec![hash_a, hash_b])),
+			NetworkBridgeEvent::PeerViewChange(peer_a.clone(), view![hash_a, hash_b]),
 		).await;
 
 		assert_matches!(
@@ -912,7 +913,7 @@ fn peer_complete_fetch_and_is_rewarded() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1002,7 +1003,7 @@ fn peer_punished_for_sending_bad_pov() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1067,7 +1068,7 @@ fn peer_punished_for_sending_unexpected_pov() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1130,7 +1131,7 @@ fn peer_punished_for_sending_pov_out_of_our_view() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1190,7 +1191,7 @@ fn peer_reported_for_awaiting_too_much() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1277,7 +1278,7 @@ fn peer_reported_for_awaiting_outside_their_view() {
 
 			s
 		},
-		our_view: View(vec![hash_a, hash_b]),
+		our_view: view![hash_a, hash_b],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1341,7 +1342,7 @@ fn peer_reported_for_awaiting_outside_our_view() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1420,7 +1421,7 @@ fn peer_complete_fetch_leads_to_us_completing_others() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};
@@ -1504,7 +1505,7 @@ fn peer_completing_request_no_longer_awaiting() {
 
 			s
 		},
-		our_view: View(vec![hash_a]),
+		our_view: view![hash_a],
 		metrics: Default::default(),
 		connection_requests: Default::default(),
 	};

polkadot/node/network/protocol/src/lib.rs

@@ -19,7 +19,7 @@
 #![deny(unused_crate_dependencies, unused_results)]
 #![warn(missing_docs)]
 
-use polkadot_primitives::v1::Hash;
+use polkadot_primitives::v1::{Hash, BlockNumber};
 use parity_scale_codec::{Encode, Decode};
 use std::convert::TryFrom;
 use std::fmt;
@@ -159,11 +159,32 @@ impl<M> NetworkBridgeEvent<M> {
 	}
 }
 
-/// A succinct representation of a peer's view. This consists of a bounded amount of chain heads.
+/// A succinct representation of a peer's view. This consists of a bounded amount of chain heads
+/// and the highest known finalized block number.
 ///
 /// Up to `N` (5?) chain heads.
 #[derive(Default, Debug, Clone, PartialEq, Eq, Encode, Decode)]
-pub struct View(pub Vec<Hash>);
+pub struct View {
+	/// A bounded amount of chain heads.
+	pub heads: Vec<Hash>,
+	/// The highest known finalized block number.
+	pub finalized_number: BlockNumber,
+}
+
+
+/// Construct a new view with the given chain heads and finalized number 0.
+/// NOTE: Use for tests only.
+/// # Example
+///
+/// ```ignore
+/// view![Hash::repeat_byte(1), Hash::repeat_byte(2)]
+/// ```
+#[macro_export]
+macro_rules! view {
+	( $( $hash:expr ),* $(,)? ) => {
+		View { heads: vec![ $( $hash.clone() ),* ], finalized_number: 0 }
+	};
+}
 
 impl View {
 	/// Replace `self` with `new`.
@@ -172,22 +193,22 @@ impl View {
 	pub fn replace_difference(&mut self, new: View) -> impl Iterator<Item = &Hash> {
 		let old = std::mem::replace(self, new);
 
-		self.0.iter().filter(move |h| !old.contains(h))
+		self.heads.iter().filter(move |h| !old.contains(h))
 	}
 
 	/// Returns an iterator of the hashes present in `Self` but not in `other`.
 	pub fn difference<'a>(&'a self, other: &'a View) -> impl Iterator<Item = &'a Hash> + 'a {
-		self.0.iter().filter(move |h| !other.contains(h))
+		self.heads.iter().filter(move |h| !other.contains(h))
 	}
 
 	/// An iterator containing hashes present in both `Self` and in `other`.
 	pub fn intersection<'a>(&'a self, other: &'a View) -> impl Iterator<Item = &'a Hash> + 'a {
-		self.0.iter().filter(move |h| other.contains(h))
+		self.heads.iter().filter(move |h| other.contains(h))
 	}
 
 	/// Whether the view contains a given hash.
 	pub fn contains(&self, hash: &Hash) -> bool {
-		self.0.contains(hash)
+		self.heads.contains(hash)
 	}
 }
 

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

@@ -938,7 +938,7 @@ impl StatementDistribution {
 							.or_insert(ActiveHeadData::new(validators, session_index));
 					}
 				}
-				FromOverseer::Signal(OverseerSignal::BlockFinalized(_block_hash)) => {
+				FromOverseer::Signal(OverseerSignal::BlockFinalized(..)) => {
 					// do nothing
 				}
 				FromOverseer::Signal(OverseerSignal::Conclude) => break,
@@ -1072,6 +1072,7 @@ mod tests {
 	use futures::executor::{self, block_on};
 	use sp_keystore::{CryptoStore, SyncCryptoStorePtr, SyncCryptoStore};
 	use sc_keystore::LocalKeystore;
+	use polkadot_node_network_protocol::view;
 
 	#[test]
 	fn active_head_accepts_only_2_seconded_per_validator() {
@@ -1326,9 +1327,9 @@ mod tests {
 
 	#[test]
 	fn peer_view_update_sends_messages() {
-		let hash_a = [1; 32].into();
-		let hash_b = [2; 32].into();
-		let hash_c = [3; 32].into();
+		let hash_a = Hash::repeat_byte(1);
+		let hash_b = Hash::repeat_byte(2);
+		let hash_c = Hash::repeat_byte(3);
 
 		let candidate = {
 			let mut c = CommittedCandidateReceipt::default();
@@ -1338,8 +1339,8 @@ mod tests {
 		};
 		let candidate_hash = candidate.hash();
 
-		let old_view = View(vec![hash_a, hash_b]);
-		let new_view = View(vec![hash_b, hash_c]);
+		let old_view = view![hash_a, hash_b];
+		let new_view = view![hash_b, hash_c];
 
 		let mut active_heads = HashMap::new();
 		let validators = vec![
@@ -1474,9 +1475,9 @@ mod tests {
 
 	#[test]
 	fn circulated_statement_goes_to_all_peers_with_view() {
-		let hash_a = [1; 32].into();
-		let hash_b = [2; 32].into();
-		let hash_c = [3; 32].into();
+		let hash_a = Hash::repeat_byte(1);
+		let hash_b = Hash::repeat_byte(2);
+		let hash_c = Hash::repeat_byte(3);
 
 		let candidate = {
 			let mut c = CommittedCandidateReceipt::default();
@@ -1489,15 +1490,15 @@ mod tests {
 		let peer_b = PeerId::random();
 		let peer_c = PeerId::random();
 
-		let peer_a_view = View(vec![hash_a]);
-		let peer_b_view = View(vec![hash_a, hash_b]);
-		let peer_c_view = View(vec![hash_b, hash_c]);
+		let peer_a_view = view![hash_a];
+		let peer_b_view = view![hash_a, hash_b];
+		let peer_c_view = view![hash_b, hash_c];
 
 		let session_index = 1;
 
 		let peer_data_from_view = |view: View| PeerData {
 			view: view.clone(),
-			view_knowledge: view.0.iter().map(|v| (v.clone(), Default::default())).collect(),
+			view_knowledge: view.heads.iter().map(|v| (v.clone(), Default::default())).collect(),
 		};
 
 		let mut peer_data: HashMap<_, _> = vec![

polkadot/node/overseer/src/lib.rs

@@ -1415,13 +1415,10 @@ where
 			self.on_head_deactivated(deactivated)
 		}
 
-		// Most of the time we have a leave already closed when it is finalized, so we check here if there are actually
-		// any updates before sending it to the subsystems.
-		if !update.is_empty() {
-			self.broadcast_signal(OverseerSignal::ActiveLeaves(update)).await?;
-		}
 
-		self.broadcast_signal(OverseerSignal::BlockFinalized(block.hash)).await?;
+		self.broadcast_signal(OverseerSignal::BlockFinalized(block.hash, block.number)).await?;
+		// broadcast `ActiveLeavesUpdate` even if empty to issue view updates
+		self.broadcast_signal(OverseerSignal::ActiveLeaves(update)).await?;
 
 		Ok(())
 	}
@@ -2061,7 +2058,7 @@ mod tests {
 					deactivated: [first_block_hash, second_block_hash].as_ref().into(),
 					..Default::default()
 				}),
-				OverseerSignal::BlockFinalized(third_block_hash),
+				OverseerSignal::BlockFinalized(third_block_hash, 3),
 			];
 
 			loop {

polkadot/node/subsystem-util/src/lib.rs

@@ -808,7 +808,7 @@ where
 					jobs.send_msg(to_job.relay_parent(), to_job).await;
 				}
 			}
-			Ok(Signal(BlockFinalized(_))) => {}
+			Ok(Signal(BlockFinalized(..))) => {}
 			Err(err) => {
 				tracing::error!(
 					job = Job::NAME,

polkadot/node/subsystem/src/lib.rs

@@ -28,7 +28,7 @@ use futures::prelude::*;
 use futures::channel::{mpsc, oneshot};
 use futures::future::BoxFuture;
 
-use polkadot_primitives::v1::Hash;
+use polkadot_primitives::v1::{Hash, BlockNumber};
 use async_trait::async_trait;
 use smallvec::SmallVec;
 
@@ -89,8 +89,8 @@ impl PartialEq for ActiveLeavesUpdate {
 pub enum OverseerSignal {
 	/// Subsystems should adjust their jobs to start and stop work on appropriate block hashes.
 	ActiveLeaves(ActiveLeavesUpdate),
-	/// `Subsystem` is informed of a finalized block by its block hash.
-	BlockFinalized(Hash),
+	/// `Subsystem` is informed of a finalized block by its block hash and number.
+	BlockFinalized(Hash, BlockNumber),
 	/// Conclude the work of the `Overseer` and all `Subsystem`s.
 	Conclude,
 }

polkadot/primitives/src/v0.rs

@@ -991,9 +991,9 @@ mod tests {
 		assert_eq!(h.as_ref().len(), 32);
 
 		let _payload = collator_signature_payload(
-			&Hash::from([1; 32]),
+			&Hash::repeat_byte(1),
 			&5u32.into(),
-			&Hash::from([2; 32]),
+			&Hash::repeat_byte(2),
 		);
 	}
 }

polkadot/primitives/src/v1.rs

@@ -825,10 +825,10 @@ mod tests {
 		assert_eq!(h.as_ref().len(), 32);
 
 		let _payload = collator_signature_payload(
-			&Hash::from([1; 32]),
+			&Hash::repeat_byte(1),
 			&5u32.into(),
-			&Hash::from([2; 32]),
-			&Hash::from([3; 32]),
+			&Hash::repeat_byte(2),
+			&Hash::repeat_byte(3),
 		);
 	}
 }

polkadot/roadmap/implementers-guide/src/node/utility/network-bridge.md

@@ -63,9 +63,7 @@ If we are connected to the same peer on both peer-sets, we will send the peer tw
 
 ### Overseer Signal: BlockFinalized
 
-We obtain the number of the block hash in the event by issuing a `ChainApiMessage::BlockNumber` request and then issue a `ProtocolMessage::ViewUpdate` to each connected peer on each peer-set. We also issue a `NetworkBridgeEvent::OurViewChange` to each  event handler for each protocol.
-
-If we are connected to the same peer on both peer-sets, we will send the peer two view updates as a result.
+We update our view's `finalized_number` to the provided one and delay `ProtocolMessage::ViewUpdate` and `NetworkBridgeEvent::OurViewChange` till the next `ActiveLeavesUpdate`.
 
 ### Network Event: Peer Connected
 
@@ -98,8 +96,6 @@ Map the message onto the corresponding [Event Handler](#event-handlers) based on
 
 ### ConnectToValidators
 
-> TODO: Currently, this request is limited to the validators in the current session.
-
 - Determine the DHT keys to use for each validator based on the relay-chain state and Runtime API.
 - Recover the Peer IDs of the validators from the DHT. There may be more than one peer ID per validator.
 - Send all `(ValidatorId, PeerId)` pairs on the response channel.

polkadot/runtime/parachains/src/inclusion.rs

@@ -1575,7 +1575,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1609,7 +1609,7 @@ mod tests {
 				let mut candidate_a = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1617,7 +1617,7 @@ mod tests {
 				let mut candidate_b = TestCandidateBuilder {
 					para_id: chain_b,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([2; 32]),
+					pov_hash: Hash::repeat_byte(2),
 					persisted_validation_data_hash: make_vdata_hash(chain_b).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1667,7 +1667,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1698,13 +1698,13 @@ mod tests {
 
 			// candidate not in parent context.
 			{
-				let wrong_parent_hash = Hash::from([222; 32]);
+				let wrong_parent_hash = Hash::repeat_byte(222);
 				assert!(System::parent_hash() != wrong_parent_hash);
 
 				let mut candidate = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: wrong_parent_hash,
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 					..Default::default()
 				}.build();
@@ -1737,7 +1737,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: thread_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(thread_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1777,7 +1777,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: thread_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(thread_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1790,7 +1790,7 @@ mod tests {
 				);
 
 				// change the candidate after signing.
-				candidate.descriptor.pov_hash = Hash::from([2; 32]);
+				candidate.descriptor.pov_hash = Hash::repeat_byte(2);
 
 				let backed = block_on(back_candidate(
 					candidate,
@@ -1816,7 +1816,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1865,7 +1865,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -1905,7 +1905,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					new_validation_code: Some(vec![5, 6, 7, 8].into()),
 					persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 					hrmp_watermark: RELAY_PARENT_NUM,
@@ -1949,7 +1949,7 @@ mod tests {
 				let mut candidate = TestCandidateBuilder {
 					para_id: chain_a,
 					relay_parent: System::parent_hash(),
-					pov_hash: Hash::from([1; 32]),
+					pov_hash: Hash::repeat_byte(1),
 					persisted_validation_data_hash: [42u8; 32].into(),
 					hrmp_watermark: RELAY_PARENT_NUM,
 					..Default::default()
@@ -2048,7 +2048,7 @@ mod tests {
 			let mut candidate_a = TestCandidateBuilder {
 				para_id: chain_a,
 				relay_parent: System::parent_hash(),
-				pov_hash: Hash::from([1; 32]),
+				pov_hash: Hash::repeat_byte(1),
 				persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 				hrmp_watermark: RELAY_PARENT_NUM,
 				..Default::default()
@@ -2061,7 +2061,7 @@ mod tests {
 			let mut candidate_b = TestCandidateBuilder {
 				para_id: chain_b,
 				relay_parent: System::parent_hash(),
-				pov_hash: Hash::from([2; 32]),
+				pov_hash: Hash::repeat_byte(2),
 				persisted_validation_data_hash: make_vdata_hash(chain_b).unwrap(),
 				hrmp_watermark: RELAY_PARENT_NUM,
 				..Default::default()
@@ -2074,7 +2074,7 @@ mod tests {
 			let mut candidate_c = TestCandidateBuilder {
 				para_id: thread_a,
 				relay_parent: System::parent_hash(),
-				pov_hash: Hash::from([3; 32]),
+				pov_hash: Hash::repeat_byte(3),
 				persisted_validation_data_hash: make_vdata_hash(thread_a).unwrap(),
 				hrmp_watermark: RELAY_PARENT_NUM,
 				..Default::default()
@@ -2220,7 +2220,7 @@ mod tests {
 			let mut candidate_a = TestCandidateBuilder {
 				para_id: chain_a,
 				relay_parent: System::parent_hash(),
-				pov_hash: Hash::from([1; 32]),
+				pov_hash: Hash::repeat_byte(1),
 				persisted_validation_data_hash: make_vdata_hash(chain_a).unwrap(),
 				new_validation_code: Some(vec![1, 2, 3].into()),
 				hrmp_watermark: RELAY_PARENT_NUM,