introduce a method for fetching relay chain header to RelayChainInterface

client/consensus/common/src/tests.rs

@@ -19,7 +19,7 @@ use crate::*;
 use async_trait::async_trait;
 use codec::Encode;
 use cumulus_client_pov_recovery::RecoveryKind;
-use cumulus_primitives_core::{InboundDownwardMessage, InboundHrmpMessage};
+use cumulus_primitives_core::{relay_chain::BlockId, InboundDownwardMessage, InboundHrmpMessage};
 use cumulus_relay_chain_interface::{
 	CommittedCandidateReceipt, OccupiedCoreAssumption, OverseerHandle, PHeader, ParaId,
 	RelayChainInterface, RelayChainResult, SessionIndex, StorageValue, ValidatorId,
@@ -207,6 +207,10 @@ impl RelayChainInterface for Relaychain {
 			})
 			.boxed())
 	}
+
+	async fn header(&self, _block_id: BlockId) -> RelayChainResult<Option<PHeader>> {
+		unimplemented!("Not needed for test")
+	}
 }
 
 fn build_block<B: InitBlockBuilder>(

client/network/src/tests.rs

@@ -16,6 +16,7 @@
 
 use super::*;
 use async_trait::async_trait;
+use cumulus_primitives_core::relay_chain::BlockId;
 use cumulus_relay_chain_inprocess_interface::{check_block_in_chain, BlockCheckStatus};
 use cumulus_relay_chain_interface::{
 	OverseerHandle, PHeader, ParaId, RelayChainError, RelayChainResult,
@@ -237,6 +238,18 @@ impl RelayChainInterface for DummyRelayChainInterface {
 				});
 		Ok(Box::pin(notifications_stream))
 	}
+
+	async fn header(&self, block_id: BlockId) -> RelayChainResult<Option<PHeader>> {
+		let hash = match block_id {
+			BlockId::Hash(hash) => hash,
+			BlockId::Number(num) => self.relay_client.hash(num)?.ok_or_else(|| {
+				RelayChainError::GenericError(format!("block with number {num} not found"))
+			})?,
+		};
+		let header = self.relay_client.header(hash)?;
+
+		Ok(header)
+	}
 }
 
 fn make_validator_and_api(

client/relay-chain-inprocess-interface/src/lib.rs

@@ -19,8 +19,9 @@ use std::{pin::Pin, sync::Arc, time::Duration};
 use async_trait::async_trait;
 use cumulus_primitives_core::{
 	relay_chain::{
-		runtime_api::ParachainHost, Block as PBlock, CommittedCandidateReceipt, Hash as PHash,
-		Header as PHeader, InboundHrmpMessage, OccupiedCoreAssumption, SessionIndex, ValidatorId,
+		runtime_api::ParachainHost, Block as PBlock, BlockId, CommittedCandidateReceipt,
+		Hash as PHash, Header as PHeader, InboundHrmpMessage, OccupiedCoreAssumption, SessionIndex,
+		ValidatorId,
 	},
 	InboundDownwardMessage, ParaId, PersistedValidationData,
 };
@@ -79,6 +80,7 @@ impl<T> Clone for RelayChainInProcessInterface<T> {
 impl<Client> RelayChainInterface for RelayChainInProcessInterface<Client>
 where
 	Client: ProvideRuntimeApi<PBlock>
+		+ HeaderBackend<PBlock>
 		+ BlockchainEvents<PBlock>
 		+ AuxStore
 		+ UsageProvider<PBlock>
@@ -110,6 +112,18 @@ where
 		)?)
 	}
 
+	async fn header(&self, block_id: BlockId) -> RelayChainResult<Option<PHeader>> {
+		let hash = match block_id {
+			BlockId::Hash(hash) => hash,
+			BlockId::Number(num) => self.full_client.hash(num)?.ok_or_else(|| {
+				RelayChainError::GenericError(format!("block with number {num} not found"))
+			})?,
+		};
+		let header = self.full_client.header(hash)?;
+
+		Ok(header)
+	}
+
 	async fn persisted_validation_data(
 		&self,
 		hash: PHash,
@@ -299,6 +313,7 @@ impl ExecuteWithClient for RelayChainInProcessInterfaceBuilder {
 	fn execute_with_client<Client, Api, Backend>(self, client: Arc<Client>) -> Self::Output
 	where
 		Client: ProvideRuntimeApi<PBlock>
+			+ HeaderBackend<PBlock>
 			+ BlockchainEvents<PBlock>
 			+ AuxStore
 			+ UsageProvider<PBlock>

client/relay-chain-interface/src/lib.rs

@@ -26,6 +26,7 @@ use jsonrpsee_core::Error as JsonRpcError;
 use parity_scale_codec::Error as CodecError;
 use sp_api::ApiError;
 
+use cumulus_primitives_core::relay_chain::BlockId;
 pub use cumulus_primitives_core::{
 	relay_chain::{
 		CommittedCandidateReceipt, Hash as PHash, Header as PHeader, InboundHrmpMessage,
@@ -110,6 +111,9 @@ pub trait RelayChainInterface: Send + Sync {
 	/// Get the hash of the current best block.
 	async fn best_block_hash(&self) -> RelayChainResult<PHash>;
 
+	/// Fetch the block header of a given height
+	async fn header(&self, block_id: BlockId) -> RelayChainResult<Option<PHeader>>;
+
 	/// Get the hash of the finalized block.
 	async fn finalized_block_hash(&self) -> RelayChainResult<PHash>;
 
@@ -293,4 +297,8 @@ where
 	) -> RelayChainResult<Pin<Box<dyn Stream<Item = PHeader> + Send>>> {
 		(**self).new_best_notification_stream().await
 	}
+
+	async fn header(&self, block_id: BlockId) -> RelayChainResult<Option<PHeader>> {
+		(**self).header(block_id).await
+	}
 }

client/relay-chain-rpc-interface/src/lib.rs

@@ -23,7 +23,9 @@ use cumulus_primitives_core::{
 	},
 	InboundDownwardMessage, ParaId, PersistedValidationData,
 };
-use cumulus_relay_chain_interface::{RelayChainError, RelayChainInterface, RelayChainResult};
+use cumulus_relay_chain_interface::{
+	PHeader, RelayChainError, RelayChainInterface, RelayChainResult,
+};
 use futures::{FutureExt, Stream, StreamExt};
 use polkadot_overseer::Handle;
 
@@ -33,6 +35,7 @@ use sp_state_machine::StorageValue;
 use sp_storage::StorageKey;
 use std::pin::Pin;
 
+use cumulus_primitives_core::relay_chain::BlockId;
 pub use url::Url;
 
 mod reconnecting_ws_client;
@@ -75,6 +78,19 @@ impl RelayChainInterface for RelayChainRpcInterface {
 			.await
 	}
 
+	async fn header(&self, block_id: BlockId) -> RelayChainResult<Option<PHeader>> {
+		let hash = match block_id {
+			BlockId::Hash(hash) => hash,
+			BlockId::Number(num) =>
+				self.rpc_client.chain_get_block_hash(Some(num)).await?.ok_or_else(|| {
+					RelayChainError::GenericError(format!("block with number {num} not found"))
+				})?,
+		};
+		let header = self.rpc_client.chain_get_header(Some(hash)).await?;
+
+		Ok(header)
+	}
+
 	async fn persisted_validation_data(
 		&self,
 		hash: RelayHash,