Revert "BlockId removal: refactor: HeaderBackend::header (#1977)"

This reverts commit b7dff85939.

client/collator/src/lib.rs

@@ -422,7 +422,7 @@ mod tests {
 		let para_id = ParaId::from(100);
 		let announce_block = |_, _| ();
 		let client = Arc::new(TestClientBuilder::new().build());
-		let header = client.header(client.chain_info().genesis_hash).unwrap().unwrap();
+		let header = client.header(&BlockId::Number(0)).unwrap().unwrap();
 
 		let (sub_tx, sub_rx) = mpsc::channel(64);
 

client/relay-chain-minimal-node/src/blockchain_rpc_client.rs

@@ -381,9 +381,20 @@ fn block_local<T>(fut: impl Future<Output = T>) -> T {
 impl HeaderBackend<Block> for BlockChainRpcClient {
 	fn header(
 		&self,
-		hash: <Block as polkadot_service::BlockT>::Hash,
+		id: BlockId,
 	) -> sp_blockchain::Result<Option<<Block as polkadot_service::BlockT>::Header>> {
-		Ok(block_local(self.rpc_client.chain_get_header(Some(hash)))?)
+		let fetch_header = |hash| block_local(self.rpc_client.chain_get_header(Some(hash)));
+
+		match id {
+			BlockId::Hash(hash) => Ok(fetch_header(hash)?),
+			BlockId::Number(number) => {
+				if let Some(hash) = HeaderBackend::<Block>::hash(self, number)? {
+					Ok(fetch_header(hash)?)
+				} else {
+					Ok(None)
+				}
+			},
+		}
 	}
 
 	fn info(&self) -> Info<Block> {
@@ -414,7 +425,7 @@ impl HeaderBackend<Block> for BlockChainRpcClient {
 		id: sp_api::BlockId<Block>,
 	) -> sp_blockchain::Result<sp_blockchain::BlockStatus> {
 		let exists = match id {
-			BlockId::Hash(hash) => self.header(hash)?.is_some(),
+			BlockId::Hash(_) => self.header(id)?.is_some(),
 			BlockId::Number(n) => {
 				let best_header = block_local(self.rpc_client.chain_get_header(None))?;
 				if let Some(best) = best_header {