Added client function to delete a recent block (#8533)

* Implemented recent block removal

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/db/src/lib.rs

@@ -623,6 +623,7 @@ impl<Block: BlockT> HeaderMetadata<Block> for BlockchainDb<Block> {
 	}
 
 	fn remove_header_metadata(&self, hash: Block::Hash) {
+		self.header_cache.lock().remove(&hash);
 		self.header_metadata_cache.remove_header_metadata(hash);
 	}
 }
@@ -1972,6 +1973,59 @@ impl<Block: BlockT> sc_client_api::backend::Backend<Block> for Backend<Block> {
 		Ok((reverted, reverted_finalized))
 	}
 
+	fn remove_leaf_block(
+		&self,
+		hash: &Block::Hash,
+	) -> ClientResult<()> {
+		let best_hash = self.blockchain.info().best_hash;
+
+		if best_hash == *hash {
+			return Err(
+				sp_blockchain::Error::Backend(
+					format!("Can't remove best block {:?}", hash)
+				)
+			)
+		}
+
+		let hdr = self.blockchain.header_metadata(hash.clone())?;
+		if !self.have_state_at(&hash, hdr.number) {
+			return Err(
+				sp_blockchain::Error::UnknownBlock(
+					format!("State already discarded for {:?}", hash)
+				)
+			)
+		}
+
+		let mut leaves = self.blockchain.leaves.write();
+		if !leaves.contains(hdr.number, *hash) {
+			return Err(
+				sp_blockchain::Error::Backend(
+					format!("Can't remove non-leaf block {:?}", hash)
+				)
+			)
+		}
+
+		let mut transaction = Transaction::new();
+		if let Some(commit) = self.storage.state_db.remove(hash) {
+			apply_state_commit(&mut transaction, commit);
+		}
+		transaction.remove(columns::KEY_LOOKUP, hash.as_ref());
+		let changes_trie_cache_ops = self.changes_tries_storage.revert(
+			&mut transaction,
+			&cache::ComplexBlockId::new(
+				*hash,
+				hdr.number,
+			),
+		)?;
+
+		self.changes_tries_storage.post_commit(Some(changes_trie_cache_ops));
+		leaves.revert(hash.clone(), hdr.number);
+		leaves.prepare_transaction(&mut transaction, columns::META, meta_keys::LEAF_PREFIX);
+		self.storage.db.commit(transaction)?;
+		self.blockchain().remove_header_metadata(*hash);
+		Ok(())
+	}
+
 	fn blockchain(&self) -> &BlockchainDb<Block> {
 		&self.blockchain
 	}
@@ -3008,4 +3062,36 @@ pub(crate) mod tests {
 			}
 		}
 	}
+
+	#[test]
+	fn remove_leaf_block_works() {
+		let backend = Backend::<Block>::new_test_with_tx_storage(
+			2,
+			10,
+			TransactionStorageMode::StorageChain
+		);
+		let mut blocks = Vec::new();
+		let mut prev_hash = Default::default();
+		for i in 0 .. 2 {
+			let hash = insert_block(&backend, i, prev_hash, None, Default::default(), vec![i.into()], None);
+			blocks.push(hash);
+			prev_hash = hash;
+		}
+
+		// insert a fork at block 2, which becomes best block
+		let best_hash = insert_block(
+			&backend,
+			1,
+			blocks[0],
+			None,
+			sp_core::H256::random(),
+			vec![42.into()],
+			None
+		);
+		assert!(backend.remove_leaf_block(&best_hash).is_err());
+		assert!(backend.have_state_at(&prev_hash, 1));
+		backend.remove_leaf_block(&prev_hash).unwrap();
+		assert_eq!(None, backend.blockchain().header(BlockId::hash(prev_hash.clone())).unwrap());
+		assert!(!backend.have_state_at(&prev_hash, 1));
+	}
 }