collator protocol changes for elastic scaling (validator side) (#3302)

Fixes #3128.

This introduces a new variant for the collation response from the
collator that includes the parent head data. For now, collators won't
send this new variant. We'll need to change the collator side of the
collator protocol to detect all the cores assigned to a para and send
the parent head data in the case when it's more than 1 core.

- [x] validate approach
- [x] check head data hash

Author: ordian

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

@@ -466,6 +466,7 @@ async fn construct_and_distribute_receipt(
 	} = collation;
 
 	let persisted_validation_data_hash = validation_data.hash();
+	let parent_head_data = validation_data.parent_head.clone();
 	let parent_head_data_hash = validation_data.parent_head.hash();
 
 	// Apply compression to the block data.
@@ -551,12 +552,13 @@ async fn construct_and_distribute_receipt(
 	metrics.on_collation_generated();
 
 	sender
-		.send_message(CollatorProtocolMessage::DistributeCollation(
-			ccr,
+		.send_message(CollatorProtocolMessage::DistributeCollation {
+			candidate_receipt: ccr,
 			parent_head_data_hash,
 			pov,
+			parent_head_data,
 			result_sender,
-		))
+		})
 		.await;
 }
 

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

@@ -390,11 +390,11 @@ fn sends_distribute_collation_message() {
 
 	assert_eq!(to_collator_protocol.len(), 1);
 	match AllMessages::from(to_collator_protocol.pop().unwrap()) {
-		AllMessages::CollatorProtocol(CollatorProtocolMessage::DistributeCollation(
-			CandidateReceipt { descriptor, .. },
-			_pov,
-			..,
-		)) => {
+		AllMessages::CollatorProtocol(CollatorProtocolMessage::DistributeCollation {
+			candidate_receipt,
+			..
+		}) => {
+			let CandidateReceipt { descriptor, .. } = candidate_receipt;
 			// signature generation is non-deterministic, so we can't just assert that the
 			// expected descriptor is correct. What we can do is validate that the produced
 			// descriptor has a valid signature, then just copy in the generated signature
@@ -529,11 +529,11 @@ fn fallback_when_no_validation_code_hash_api() {
 
 	assert_eq!(to_collator_protocol.len(), 1);
 	match &to_collator_protocol[0] {
-		AllMessages::CollatorProtocol(CollatorProtocolMessage::DistributeCollation(
-			CandidateReceipt { descriptor, .. },
-			_pov,
-			..,
-		)) => {
+		AllMessages::CollatorProtocol(CollatorProtocolMessage::DistributeCollation {
+			candidate_receipt,
+			..
+		}) => {
+			let CandidateReceipt { descriptor, .. } = candidate_receipt;
 			assert_eq!(expect_validation_code_hash, descriptor.validation_code_hash);
 		},
 		_ => panic!("received wrong message type"),
@@ -619,15 +619,16 @@ fn submit_collation_leads_to_distribution() {
 
 		assert_matches!(
 			overseer_recv(&mut virtual_overseer).await,
-			AllMessages::CollatorProtocol(CollatorProtocolMessage::DistributeCollation(
-				ccr,
+			AllMessages::CollatorProtocol(CollatorProtocolMessage::DistributeCollation {
+				candidate_receipt,
 				parent_head_data_hash,
 				..
-			)) => {
+			}) => {
+				let CandidateReceipt { descriptor, .. } = candidate_receipt;
 				assert_eq!(parent_head_data_hash, parent_head.hash());
-				assert_eq!(ccr.descriptor().persisted_validation_data_hash, expected_pvd.hash());
-				assert_eq!(ccr.descriptor().para_head, dummy_head_data().hash());
-				assert_eq!(ccr.descriptor().validation_code_hash, validation_code_hash);
+				assert_eq!(descriptor.persisted_validation_data_hash, expected_pvd.hash());
+				assert_eq!(descriptor.para_head, dummy_head_data().hash());
+				assert_eq!(descriptor.validation_code_hash, validation_code_hash);
 			}
 		);
 

polkadot/node/core/prospective-parachains/src/lib.rs

@@ -36,8 +36,9 @@ use futures::{channel::oneshot, prelude::*};
 use polkadot_node_subsystem::{
 	messages::{
 		Ancestors, ChainApiMessage, FragmentTreeMembership, HypotheticalCandidate,
-		HypotheticalFrontierRequest, IntroduceCandidateRequest, ProspectiveParachainsMessage,
-		ProspectiveValidationDataRequest, RuntimeApiMessage, RuntimeApiRequest,
+		HypotheticalFrontierRequest, IntroduceCandidateRequest, ParentHeadData,
+		ProspectiveParachainsMessage, ProspectiveValidationDataRequest, RuntimeApiMessage,
+		RuntimeApiRequest,
 	},
 	overseer, ActiveLeavesUpdate, FromOrchestra, OverseerSignal, SpawnedSubsystem, SubsystemError,
 };
@@ -764,8 +765,14 @@ fn answer_prospective_validation_data_request(
 		Some(s) => s,
 	};
 
-	let mut head_data =
-		storage.head_data_by_hash(&request.parent_head_data_hash).map(|x| x.clone());
+	let (mut head_data, parent_head_data_hash) = match request.parent_head_data {
+		ParentHeadData::OnlyHash(parent_head_data_hash) => (
+			storage.head_data_by_hash(&parent_head_data_hash).map(|x| x.clone()),
+			parent_head_data_hash,
+		),
+		ParentHeadData::WithData { head_data, hash } => (Some(head_data), hash),
+	};
+
 	let mut relay_parent_info = None;
 	let mut max_pov_size = None;
 
@@ -783,7 +790,7 @@ fn answer_prospective_validation_data_request(
 		}
 		if head_data.is_none() {
 			let required_parent = &fragment_tree.scope().base_constraints().required_parent;
-			if required_parent.hash() == request.parent_head_data_hash {
+			if required_parent.hash() == parent_head_data_hash {
 				head_data = Some(required_parent.clone());
 			}
 		}

polkadot/node/core/prospective-parachains/src/tests.rs

@@ -19,7 +19,7 @@ use assert_matches::assert_matches;
 use polkadot_node_subsystem::{
 	errors::RuntimeApiError,
 	messages::{
-		AllMessages, HypotheticalFrontierRequest, ProspectiveParachainsMessage,
+		AllMessages, HypotheticalFrontierRequest, ParentHeadData, ProspectiveParachainsMessage,
 		ProspectiveValidationDataRequest,
 	},
 };
@@ -468,7 +468,7 @@ async fn get_pvd(
 	let request = ProspectiveValidationDataRequest {
 		para_id,
 		candidate_relay_parent,
-		parent_head_data_hash: parent_head_data.hash(),
+		parent_head_data: ParentHeadData::OnlyHash(parent_head_data.hash()),
 	};
 	let (tx, rx) = oneshot::channel();
 	virtual_overseer

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

@@ -27,7 +27,7 @@ use polkadot_node_network_protocol::{
 	PeerId,
 };
 use polkadot_node_primitives::PoV;
-use polkadot_primitives::{CandidateHash, CandidateReceipt, Hash, Id as ParaId};
+use polkadot_primitives::{CandidateHash, CandidateReceipt, Hash, HeadData, Id as ParaId};
 
 /// The status of a collation as seen from the collator.
 pub enum CollationStatus {
@@ -63,6 +63,8 @@ pub struct Collation {
 	pub parent_head_data_hash: Hash,
 	/// Proof to verify the state transition of the parachain.
 	pub pov: PoV,
+	/// Parent head-data needed for elastic scaling.
+	pub parent_head_data: HeadData,
 	/// Collation status.
 	pub status: CollationStatus,
 }

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

@@ -55,7 +55,7 @@ use polkadot_node_subsystem_util::{
 };
 use polkadot_primitives::{
 	AuthorityDiscoveryId, CandidateHash, CandidateReceipt, CollatorPair, CoreIndex, CoreState,
-	GroupIndex, Hash, Id as ParaId, SessionIndex,
+	GroupIndex, Hash, HeadData, Id as ParaId, SessionIndex,
 };
 
 use super::LOG_TARGET;
@@ -347,6 +347,7 @@ async fn distribute_collation<Context>(
 	receipt: CandidateReceipt,
 	parent_head_data_hash: Hash,
 	pov: PoV,
+	parent_head_data: HeadData,
 	result_sender: Option<oneshot::Sender<CollationSecondedSignal>>,
 ) -> Result<()> {
 	let candidate_relay_parent = receipt.descriptor.relay_parent;
@@ -465,7 +466,13 @@ async fn distribute_collation<Context>(
 
 	per_relay_parent.collations.insert(
 		candidate_hash,
-		Collation { receipt, parent_head_data_hash, pov, status: CollationStatus::Created },
+		Collation {
+			receipt,
+			parent_head_data_hash,
+			pov,
+			parent_head_data,
+			status: CollationStatus::Created,
+		},
 	);
 
 	// If prospective parachains are disabled, a leaf should be known to peer.
@@ -763,20 +770,26 @@ async fn process_msg<Context>(
 		CollateOn(id) => {
 			state.collating_on = Some(id);
 		},
-		DistributeCollation(receipt, parent_head_data_hash, pov, result_sender) => {
+		DistributeCollation {
+			candidate_receipt,
+			parent_head_data_hash,
+			pov,
+			parent_head_data,
+			result_sender,
+		} => {
 			let _span1 = state
 				.span_per_relay_parent
-				.get(&receipt.descriptor.relay_parent)
+				.get(&candidate_receipt.descriptor.relay_parent)
 				.map(|s| s.child("distributing-collation"));
 			let _span2 = jaeger::Span::new(&pov, "distributing-collation");
 
 			match state.collating_on {
-				Some(id) if receipt.descriptor.para_id != id => {
+				Some(id) if candidate_receipt.descriptor.para_id != id => {
 					// If the ParaId of a collation requested to be distributed does not match
 					// the one we expect, we ignore the message.
 					gum::warn!(
 						target: LOG_TARGET,
-						para_id = %receipt.descriptor.para_id,
+						para_id = %candidate_receipt.descriptor.para_id,
 						collating_on = %id,
 						"DistributeCollation for unexpected para_id",
 					);
@@ -788,17 +801,18 @@ async fn process_msg<Context>(
 						runtime,
 						state,
 						id,
-						receipt,
+						candidate_receipt,
 						parent_head_data_hash,
 						pov,
+						parent_head_data,
 						result_sender,
 					)
 					.await?;
 				},
 				None => {
 					gum::warn!(
 						target: LOG_TARGET,
-						para_id = %receipt.descriptor.para_id,
+						para_id = %candidate_receipt.descriptor.para_id,
 						"DistributeCollation message while not collating on any",
 					);
 				},
@@ -835,20 +849,30 @@ async fn send_collation(
 	request: VersionedCollationRequest,
 	receipt: CandidateReceipt,
 	pov: PoV,
+	_parent_head_data: HeadData,
 ) {
 	let (tx, rx) = oneshot::channel();
 
 	let relay_parent = request.relay_parent();
 	let peer_id = request.peer_id();
 	let candidate_hash = receipt.hash();
 
-	// The response payload is the same for both versions of protocol
+	// The response payload is the same for v1 and v2 versions of protocol
 	// and doesn't have v2 alias for simplicity.
-	let response = OutgoingResponse {
-		result: Ok(request_v1::CollationFetchingResponse::Collation(receipt, pov)),
-		reputation_changes: Vec::new(),
-		sent_feedback: Some(tx),
-	};
+	// For now, we don't send parent head data to the collation requester.
+	let result =
+	// 	if assigned_multiple_cores {
+	// 	Ok(request_v1::CollationFetchingResponse::CollationWithParentHeadData {
+	// 		receipt,
+	// 		pov,
+	// 		parent_head_data,
+	// 	})
+	// } else {
+		Ok(request_v1::CollationFetchingResponse::Collation(receipt, pov))
+	// }
+	;
+	let response =
+		OutgoingResponse { result, reputation_changes: Vec::new(), sent_feedback: Some(tx) };
 
 	if let Err(_) = request.send_outgoing_response(response) {
 		gum::warn!(target: LOG_TARGET, "Sending collation response failed");
@@ -1027,9 +1051,13 @@ async fn handle_incoming_request<Context>(
 					return Ok(())
 				},
 			};
-			let (receipt, pov) = if let Some(collation) = collation {
+			let (receipt, pov, parent_head_data) = if let Some(collation) = collation {
 				collation.status.advance_to_requested();
-				(collation.receipt.clone(), collation.pov.clone())
+				(
+					collation.receipt.clone(),
+					collation.pov.clone(),
+					collation.parent_head_data.clone(),
+				)
 			} else {
 				gum::warn!(
 					target: LOG_TARGET,
@@ -1068,7 +1096,7 @@ async fn handle_incoming_request<Context>(
 				waiting.collation_fetch_active = true;
 				// Obtain a timer for sending collation
 				let _ = state.metrics.time_collation_distribution("send");
-				send_collation(state, req, receipt, pov).await;
+				send_collation(state, req, receipt, pov, parent_head_data).await;
 			}
 		},
 		Some(our_para_id) => {
@@ -1453,8 +1481,9 @@ async fn run_inner<Context>(
 				if let Some(collation) = next_collation {
 					let receipt = collation.receipt.clone();
 					let pov = collation.pov.clone();
+					let parent_head_data = collation.parent_head_data.clone();
 
-					send_collation(&mut state, next, receipt, pov).await;
+					send_collation(&mut state, next, receipt, pov, parent_head_data).await;
 				}
 			},
 			(candidate_hash, peer_id) = state.advertisement_timeouts.select_next_some() => {