Child trie api changes BREAKING (#4857)

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

substrate/client/api/src/backend.rs

@@ -26,7 +26,7 @@ use sp_state_machine::{
 	ChangesTrieState, ChangesTrieStorage as StateChangesTrieStorage, ChangesTrieTransaction,
 	StorageCollection, ChildStorageCollection,
 };
-use sp_storage::{StorageData, StorageKey, ChildInfo};
+use sp_storage::{StorageData, StorageKey, PrefixedStorageKey, ChildInfo};
 use crate::{
 	blockchain::{
 		Backend as BlockchainBackend, well_known_cache_keys
@@ -280,6 +280,7 @@ impl<'a, State, Block> Iterator for KeyIterator<'a, State, Block> where
 		Some(StorageKey(next_key))
 	}
 }
+
 /// Provides acess to storage primitives
 pub trait StorageProvider<Block: BlockT, B: Backend<Block>> {
 	/// Given a `BlockId` and a key, return the value under the key in that block.
@@ -310,8 +311,7 @@ pub trait StorageProvider<Block: BlockT, B: Backend<Block>> {
 	fn child_storage(
 		&self,
 		id: &BlockId<Block>,
-		storage_key: &StorageKey,
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &StorageKey
 	) -> sp_blockchain::Result<Option<StorageData>>;
 
@@ -319,8 +319,7 @@ pub trait StorageProvider<Block: BlockT, B: Backend<Block>> {
 	fn child_storage_keys(
 		&self,
 		id: &BlockId<Block>,
-		child_storage_key: &StorageKey,
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key_prefix: &StorageKey
 	) -> sp_blockchain::Result<Vec<StorageKey>>;
 
@@ -328,8 +327,7 @@ pub trait StorageProvider<Block: BlockT, B: Backend<Block>> {
 	fn child_storage_hash(
 		&self,
 		id: &BlockId<Block>,
-		storage_key: &StorageKey,
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &StorageKey
 	) -> sp_blockchain::Result<Option<Block::Hash>>;
 
@@ -351,7 +349,7 @@ pub trait StorageProvider<Block: BlockT, B: Backend<Block>> {
 		&self,
 		first: NumberFor<Block>,
 		last: BlockId<Block>,
-		storage_key: Option<&StorageKey>,
+		storage_key: Option<&PrefixedStorageKey>,
 		key: &StorageKey
 	) -> sp_blockchain::Result<Vec<(NumberFor<Block>, u32)>>;
 }

substrate/client/api/src/light.rs

@@ -26,7 +26,7 @@ use sp_runtime::{
 	},
 	generic::BlockId
 };
-use sp_core::ChangesTrieConfigurationRange;
+use sp_core::{ChangesTrieConfigurationRange, storage::PrefixedStorageKey};
 use sp_state_machine::StorageProof;
 use sp_blockchain::{
 	HeaderMetadata, well_known_cache_keys, HeaderBackend, Cache as BlockchainCache,
@@ -81,12 +81,7 @@ pub struct RemoteReadChildRequest<Header: HeaderT> {
 	/// Header of block at which read is performed.
 	pub header: Header,
 	/// Storage key for child.
-	pub storage_key: Vec<u8>,
-	/// Child trie source information.
-	pub child_info: Vec<u8>,
-	/// Child type, its required to resolve `child_info`
-	/// content and choose child implementation.
-	pub child_type: u32,
+	pub storage_key: PrefixedStorageKey,
 	/// Child storage key to read.
 	pub keys: Vec<Vec<u8>>,
 	/// Number of times to retry request. None means that default RETRY_COUNT is used.
@@ -110,7 +105,7 @@ pub struct RemoteChangesRequest<Header: HeaderT> {
 	/// Proofs for roots of ascendants of tries_roots.0 are provided by the remote node.
 	pub tries_roots: (Header::Number, Header::Hash, Vec<Header::Hash>),
 	/// Optional Child Storage key to read.
-	pub storage_key: Option<Vec<u8>>,
+	pub storage_key: Option<PrefixedStorageKey>,
 	/// Storage key to read.
 	pub key: Vec<u8>,
 	/// Number of times to retry request. None means that default RETRY_COUNT is used.

substrate/client/api/src/proof_provider.rs

@@ -19,7 +19,7 @@ use sp_runtime::{
 	traits::{Block as BlockT},
 };
 use crate::{StorageProof, ChangesProof};
-use sp_storage::{ChildInfo, StorageKey};
+use sp_storage::{ChildInfo, StorageKey, PrefixedStorageKey};
 
 /// Interface for providing block proving utilities.
 pub trait ProofProvider<Block: BlockT> {
@@ -35,8 +35,7 @@ pub trait ProofProvider<Block: BlockT> {
 	fn read_child_proof(
 		&self,
 		id: &BlockId<Block>,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		keys: &mut dyn Iterator<Item=&[u8]>,
 	) -> sp_blockchain::Result<StorageProof>;
 
@@ -65,7 +64,7 @@ pub trait ProofProvider<Block: BlockT> {
 		last: Block::Hash,
 		min: Block::Hash,
 		max: Block::Hash,
-		storage_key: Option<&StorageKey>,
+		storage_key: Option<&PrefixedStorageKey>,
 		key: &StorageKey,
 	) -> sp_blockchain::Result<ChangesProof<Block::Header>>;
 }

substrate/client/chain-spec/src/chain_spec.rs

@@ -74,17 +74,14 @@ impl<G: RuntimeGenesis, E> BuildStorage for ChainSpec<G, E> {
 	fn build_storage(&self) -> Result<Storage, String> {
 		match self.genesis.resolve()? {
 			Genesis::Runtime(gc) => gc.build_storage(),
-			Genesis::Raw(RawGenesis { top: map, children: children_map }) => Ok(Storage {
+			Genesis::Raw(RawGenesis { top: map, children_default: children_map }) => Ok(Storage {
 				top: map.into_iter().map(|(k, v)| (k.0, v.0)).collect(),
-				children: children_map.into_iter().map(|(sk, child_content)| {
-					let child_info = ChildInfo::resolve_child_info(
-						child_content.child_type,
-						child_content.child_info.as_slice(),
-					).expect("chain spec contains correct content").to_owned();
+				children_default: children_map.into_iter().map(|(storage_key, child_content)| {
+					let child_info = ChildInfo::new_default(storage_key.0.as_slice());
 					(
-						sk.0,
+						storage_key.0,
 						StorageChild {
-							data: child_content.data.into_iter().map(|(k, v)| (k.0, v.0)).collect(),
+							data: child_content.into_iter().map(|(k, v)| (k.0, v.0)).collect(),
 							child_info,
 						},
 					)
@@ -103,22 +100,13 @@ impl<G: RuntimeGenesis, E> BuildStorage for ChainSpec<G, E> {
 
 type GenesisStorage = HashMap<StorageKey, StorageData>;
 
-#[derive(Serialize, Deserialize)]
-#[serde(rename_all = "camelCase")]
-#[serde(deny_unknown_fields)]
-struct ChildRawStorage {
-	data: GenesisStorage,
-	child_info: Vec<u8>,
-	child_type: u32,
-}
-
 #[derive(Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 #[serde(deny_unknown_fields)]
 /// Storage content for genesis block.
 struct RawGenesis {
 	top: GenesisStorage,
-	children: HashMap<StorageKey, ChildRawStorage>,
+	children_default: HashMap<StorageKey, GenesisStorage>,
 }
 
 #[derive(Serialize, Deserialize)]
@@ -291,23 +279,16 @@ impl<G: RuntimeGenesis, E: serde::Serialize + Clone> ChainSpec<G, E> {
 				let top = storage.top.into_iter()
 					.map(|(k, v)| (StorageKey(k), StorageData(v)))
 					.collect();
-				let children = storage.children.into_iter()
-					.map(|(sk, child)| {
-						let info = child.child_info.as_ref();
-						let (info, ci_type) = info.info();
-						(
-							StorageKey(sk),
-							ChildRawStorage {
-								data: child.data.into_iter()
-									.map(|(k, v)| (StorageKey(k), StorageData(v)))
-									.collect(),
-								child_info: info.to_vec(),
-								child_type: ci_type,
-							},
-					)})
+				let children_default = storage.children_default.into_iter()
+					.map(|(sk, child)| (
+						StorageKey(sk),
+						child.data.into_iter()
+							.map(|(k, v)| (StorageKey(k), StorageData(v)))
+							.collect(),
+					))
 					.collect();
 
-				Genesis::Raw(RawGenesis { top, children })
+				Genesis::Raw(RawGenesis { top, children_default })
 			},
 			(_, genesis) => genesis,
 		};

substrate/client/db/src/bench.rs

@@ -77,10 +77,9 @@ impl<B: BlockT> BenchmarkingState<B> {
 		};
 
 		state.reopen()?;
-		let child_delta = genesis.children.into_iter().map(|(storage_key, child_content)| (
-			storage_key,
+		let child_delta = genesis.children_default.into_iter().map(|(_storage_key, child_content)| (
+			child_content.child_info,
 			child_content.data.into_iter().map(|(k, v)| (k, Some(v))),
-			child_content.child_info
 		));
 		let (root, transaction): (B::Hash, _) = state.state.borrow_mut().as_mut().unwrap().full_storage_root(
 			genesis.top.into_iter().map(|(k, v)| (k, Some(v))),
@@ -129,11 +128,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for BenchmarkingState<B> {
 
 	fn child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.state.borrow().as_ref().ok_or_else(state_err)?.child_storage(storage_key, child_info, key)
+		self.state.borrow().as_ref().ok_or_else(state_err)?.child_storage(child_info, key)
 	}
 
 	fn exists_storage(&self, key: &[u8]) -> Result<bool, Self::Error> {
@@ -142,11 +140,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for BenchmarkingState<B> {
 
 	fn exists_child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<bool, Self::Error> {
-		self.state.borrow().as_ref().ok_or_else(state_err)?.exists_child_storage(storage_key, child_info, key)
+		self.state.borrow().as_ref().ok_or_else(state_err)?.exists_child_storage(child_info, key)
 	}
 
 	fn next_storage_key(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
@@ -155,11 +152,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for BenchmarkingState<B> {
 
 	fn next_child_storage_key(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.state.borrow().as_ref().ok_or_else(state_err)?.next_child_storage_key(storage_key, child_info, key)
+		self.state.borrow().as_ref().ok_or_else(state_err)?.next_child_storage_key(child_info, key)
 	}
 
 	fn for_keys_with_prefix<F: FnMut(&[u8])>(&self, prefix: &[u8], f: F) {
@@ -176,24 +172,22 @@ impl<B: BlockT> StateBackend<HashFor<B>> for BenchmarkingState<B> {
 
 	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		f: F,
 	) {
 		if let Some(ref state) = *self.state.borrow() {
-			state.for_keys_in_child_storage(storage_key, child_info, f)
+			state.for_keys_in_child_storage(child_info, f)
 		}
 	}
 
 	fn for_child_keys_with_prefix<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 		f: F,
 	) {
 		if let Some(ref state) = *self.state.borrow() {
-			state.for_child_keys_with_prefix(storage_key, child_info, prefix, f)
+			state.for_child_keys_with_prefix(child_info, prefix, f)
 		}
 	}
 
@@ -205,13 +199,12 @@ impl<B: BlockT> StateBackend<HashFor<B>> for BenchmarkingState<B> {
 
 	fn child_storage_root<I>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		delta: I,
 	) -> (B::Hash, bool, Self::Transaction) where
 		I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
 	{
-		self.state.borrow().as_ref().map_or(Default::default(), |s| s.child_storage_root(storage_key, child_info, delta))
+		self.state.borrow().as_ref().map_or(Default::default(), |s| s.child_storage_root(child_info, delta))
 	}
 
 	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
@@ -224,11 +217,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for BenchmarkingState<B> {
 
 	fn child_keys(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 	) -> Vec<Vec<u8>> {
-		self.state.borrow().as_ref().map_or(Default::default(), |s| s.child_keys(storage_key, child_info, prefix))
+		self.state.borrow().as_ref().map_or(Default::default(), |s| s.child_keys(child_info, prefix))
 	}
 
 	fn as_trie_backend(&mut self)

substrate/client/db/src/changes_tries_storage.rs

@@ -26,6 +26,7 @@ use sp_trie::MemoryDB;
 use sc_client_api::backend::PrunableStateChangesTrieStorage;
 use sp_blockchain::{well_known_cache_keys, Cache as BlockchainCache};
 use sp_core::{ChangesTrieConfiguration, ChangesTrieConfigurationRange, convert_hash};
+use sp_core::storage::PrefixedStorageKey;
 use sp_database::Transaction;
 use sp_runtime::traits::{
 	Block as BlockT, Header as HeaderT, HashFor, NumberFor, One, Zero, CheckedSub,
@@ -482,7 +483,7 @@ where
 	fn with_cached_changed_keys(
 		&self,
 		root: &Block::Hash,
-		functor: &mut dyn FnMut(&HashMap<Option<Vec<u8>>, HashSet<Vec<u8>>>),
+		functor: &mut dyn FnMut(&HashMap<Option<PrefixedStorageKey>, HashSet<Vec<u8>>>),
 	) -> bool {
 		self.build_cache.read().with_changed_keys(root, functor)
 	}

substrate/client/db/src/lib.rs

@@ -159,11 +159,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for RefTrackingState<B> {
 
 	fn child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.state.child_storage(storage_key, child_info, key)
+		self.state.child_storage(child_info, key)
 	}
 
 	fn exists_storage(&self, key: &[u8]) -> Result<bool, Self::Error> {
@@ -172,11 +171,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for RefTrackingState<B> {
 
 	fn exists_child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<bool, Self::Error> {
-		self.state.exists_child_storage(storage_key, child_info, key)
+		self.state.exists_child_storage(child_info, key)
 	}
 
 	fn next_storage_key(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
@@ -185,11 +183,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for RefTrackingState<B> {
 
 	fn next_child_storage_key(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.state.next_child_storage_key(storage_key, child_info, key)
+		self.state.next_child_storage_key(child_info, key)
 	}
 
 	fn for_keys_with_prefix<F: FnMut(&[u8])>(&self, prefix: &[u8], f: F) {
@@ -202,21 +199,19 @@ impl<B: BlockT> StateBackend<HashFor<B>> for RefTrackingState<B> {
 
 	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		f: F,
 	) {
-		self.state.for_keys_in_child_storage(storage_key, child_info, f)
+		self.state.for_keys_in_child_storage(child_info, f)
 	}
 
 	fn for_child_keys_with_prefix<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 		f: F,
 	) {
-		self.state.for_child_keys_with_prefix(storage_key, child_info, prefix, f)
+		self.state.for_child_keys_with_prefix(child_info, prefix, f)
 	}
 
 	fn storage_root<I>(&self, delta: I) -> (B::Hash, Self::Transaction)
@@ -228,14 +223,13 @@ impl<B: BlockT> StateBackend<HashFor<B>> for RefTrackingState<B> {
 
 	fn child_storage_root<I>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		delta: I,
 	) -> (B::Hash, bool, Self::Transaction)
 		where
 			I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
 	{
-		self.state.child_storage_root(storage_key, child_info, delta)
+		self.state.child_storage_root(child_info, delta)
 	}
 
 	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
@@ -248,11 +242,10 @@ impl<B: BlockT> StateBackend<HashFor<B>> for RefTrackingState<B> {
 
 	fn child_keys(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 	) -> Vec<Vec<u8>> {
-		self.state.child_keys(storage_key, child_info, prefix)
+		self.state.child_keys(child_info, prefix)
 	}
 
 	fn as_trie_backend(&mut self)
@@ -631,16 +624,10 @@ impl<Block: BlockT> sc_client_api::backend::BlockImportOperation<Block> for Bloc
 			return Err(sp_blockchain::Error::GenesisInvalid.into());
 		}
 
-		for child_key in storage.children.keys() {
-			if !well_known_keys::is_child_storage_key(&child_key) {
-				return Err(sp_blockchain::Error::GenesisInvalid.into());
-			}
-		}
-
-		let child_delta = storage.children.into_iter().map(|(storage_key, child_content)|	(
-			storage_key,
-			child_content.data.into_iter().map(|(k, v)| (k, Some(v))), child_content.child_info),
-		);
+		let child_delta = storage.children_default.into_iter().map(|(_storage_key, child_content)|(
+			child_content.child_info,
+			child_content.data.into_iter().map(|(k, v)| (k, Some(v))),
+		));
 
 		let mut changes_trie_config: Option<ChangesTrieConfiguration> = None;
 		let (root, transaction) = self.old_state.full_storage_root(
@@ -1808,7 +1795,7 @@ pub(crate) mod tests {
 
 			op.reset_storage(Storage {
 				top: storage.iter().cloned().collect(),
-				children: Default::default(),
+				children_default: Default::default(),
 			}).unwrap();
 			op.set_block_data(
 				header.clone(),
@@ -1894,7 +1881,7 @@ pub(crate) mod tests {
 
 			op.reset_storage(Storage {
 				top: storage.iter().cloned().collect(),
-				children: Default::default(),
+				children_default: Default::default(),
 			}).unwrap();
 
 			key = op.db_updates.insert(EMPTY_PREFIX, b"hello");

substrate/client/db/src/storage_cache.rs

@@ -542,11 +542,10 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 
 	fn child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		let key = (storage_key.to_vec(), key.to_vec());
+		let key = (child_info.storage_key().to_vec(), key.to_vec());
 		let local_cache = self.cache.local_cache.upgradable_read();
 		if let Some(entry) = local_cache.child_storage.get(&key).cloned() {
 			trace!("Found in local cache: {:?}", key);
@@ -564,7 +563,7 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 			}
 		}
 		trace!("Cache miss: {:?}", key);
-		let value = self.state.child_storage(storage_key, child_info, &key.1[..])?;
+		let value = self.state.child_storage(child_info, &key.1[..])?;
 
 		// just pass it through the usage counter
 		let value =	self.usage.tally_child_key_read(&key, value, false);
@@ -579,20 +578,18 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 
 	fn exists_child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<bool, Self::Error> {
-		self.state.exists_child_storage(storage_key, child_info, key)
+		self.state.exists_child_storage(child_info, key)
 	}
 
 	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		f: F,
 	) {
-		self.state.for_keys_in_child_storage(storage_key, child_info, f)
+		self.state.for_keys_in_child_storage(child_info, f)
 	}
 
 	fn next_storage_key(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
@@ -601,11 +598,10 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 
 	fn next_child_storage_key(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.state.next_child_storage_key(storage_key, child_info, key)
+		self.state.next_child_storage_key(child_info, key)
 	}
 
 	fn for_keys_with_prefix<F: FnMut(&[u8])>(&self, prefix: &[u8], f: F) {
@@ -618,12 +614,11 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 
 	fn for_child_keys_with_prefix<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 		f: F,
 	) {
-		self.state.for_child_keys_with_prefix(storage_key, child_info, prefix, f)
+		self.state.for_child_keys_with_prefix(child_info, prefix, f)
 	}
 
 	fn storage_root<I>(&self, delta: I) -> (B::Hash, Self::Transaction)
@@ -635,14 +630,13 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 
 	fn child_storage_root<I>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		delta: I,
 	) -> (B::Hash, bool, Self::Transaction)
 		where
 			I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
 	{
-		self.state.child_storage_root(storage_key, child_info, delta)
+		self.state.child_storage_root(child_info, delta)
 	}
 
 	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
@@ -655,11 +649,10 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 
 	fn child_keys(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 	) -> Vec<Vec<u8>> {
-		self.state.child_keys(storage_key, child_info, prefix)
+		self.state.child_keys(child_info, prefix)
 	}
 
 	fn as_trie_backend(&mut self) -> Option<&TrieBackend<Self::TrieBackendStorage, HashFor<B>>> {
@@ -758,11 +751,10 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Syncin
 
 	fn child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.caching_state().child_storage(storage_key, child_info, key)
+		self.caching_state().child_storage(child_info, key)
 	}
 
 	fn exists_storage(&self, key: &[u8]) -> Result<bool, Self::Error> {
@@ -771,20 +763,18 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Syncin
 
 	fn exists_child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<bool, Self::Error> {
-		self.caching_state().exists_child_storage(storage_key, child_info, key)
+		self.caching_state().exists_child_storage(child_info, key)
 	}
 
 	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		f: F,
 	) {
-		self.caching_state().for_keys_in_child_storage(storage_key, child_info, f)
+		self.caching_state().for_keys_in_child_storage(child_info, f)
 	}
 
 	fn next_storage_key(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
@@ -793,11 +783,10 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Syncin
 
 	fn next_child_storage_key(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.caching_state().next_child_storage_key(storage_key, child_info, key)
+		self.caching_state().next_child_storage_key(child_info, key)
 	}
 
 	fn for_keys_with_prefix<F: FnMut(&[u8])>(&self, prefix: &[u8], f: F) {
@@ -810,12 +799,11 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Syncin
 
 	fn for_child_keys_with_prefix<F: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 		f: F,
 	) {
-		self.caching_state().for_child_keys_with_prefix(storage_key, child_info, prefix, f)
+		self.caching_state().for_child_keys_with_prefix(child_info, prefix, f)
 	}
 
 	fn storage_root<I>(&self, delta: I) -> (B::Hash, Self::Transaction)
@@ -827,14 +815,13 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Syncin
 
 	fn child_storage_root<I>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		delta: I,
 	) -> (B::Hash, bool, Self::Transaction)
 		where
 			I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
 	{
-		self.caching_state().child_storage_root(storage_key, child_info, delta)
+		self.caching_state().child_storage_root(child_info, delta)
 	}
 
 	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
@@ -847,11 +834,10 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Syncin
 
 	fn child_keys(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 	) -> Vec<Vec<u8>> {
-		self.caching_state().child_keys(storage_key, child_info, prefix)
+		self.caching_state().child_keys(child_info, prefix)
 	}
 
 	fn as_trie_backend(&mut self) -> Option<&TrieBackend<Self::TrieBackendStorage, HashFor<B>>> {

substrate/client/executor/src/integration_tests/mod.rs

@@ -186,7 +186,7 @@ fn storage_should_work(wasm_method: WasmExecutionMethod) {
 			b"foo".to_vec() => b"bar".to_vec(),
 			b"baz".to_vec() => b"bar".to_vec()
 		],
-		children: map![],
+		children_default: map![],
 	});
 	assert_eq!(ext, expected);
 }
@@ -220,7 +220,7 @@ fn clear_prefix_should_work(wasm_method: WasmExecutionMethod) {
 			b"aab".to_vec() => b"2".to_vec(),
 			b"bbb".to_vec() => b"5".to_vec()
 		],
-		children: map![],
+		children_default: map![],
 	});
 	assert_eq!(expected, ext);
 }

substrate/client/network/src/protocol.rs

@@ -30,7 +30,7 @@ use libp2p::core::{ConnectedPoint, connection::{ConnectionId, ListenerId}};
 use libp2p::swarm::{ProtocolsHandler, IntoProtocolsHandler};
 use libp2p::swarm::{NetworkBehaviour, NetworkBehaviourAction, PollParameters};
 use sp_core::{
-	storage::{StorageKey, ChildInfo},
+	storage::{StorageKey, PrefixedStorageKey, ChildInfo, ChildType},
 	hexdisplay::HexDisplay
 };
 use sp_consensus::{
@@ -1522,37 +1522,28 @@ impl<B: BlockT, H: ExHashT> Protocol<B, H> {
 
 		trace!(target: "sync", "Remote read child request {} from {} ({} {} at {})",
 			request.id, who, HexDisplay::from(&request.storage_key), keys_str(), request.block);
-		let proof = if let Some(child_info) = ChildInfo::resolve_child_info(request.child_type, &request.child_info[..]) {
-			match self.context_data.chain.read_child_proof(
-				&BlockId::Hash(request.block),
-				&request.storage_key,
-				child_info,
-				&mut request.keys.iter().map(AsRef::as_ref),
-			) {
-				Ok(proof) => proof,
-				Err(error) => {
-					trace!(target: "sync", "Remote read child request {} from {} ({} {} at {}) failed with: {}",
-						request.id,
-						who,
-						HexDisplay::from(&request.storage_key),
-						keys_str(),
-						request.block,
-						error
-					);
-					StorageProof::empty()
-				}
+		let prefixed_key = PrefixedStorageKey::new_ref(&request.storage_key);
+		let child_info = match ChildType::from_prefixed_key(prefixed_key) {
+			Some((ChildType::ParentKeyId, storage_key)) => Ok(ChildInfo::new_default(storage_key)),
+			None => Err("Invalid child storage key".into()),
+		};
+		let proof = match child_info.and_then(|child_info| self.context_data.chain.read_child_proof(
+			&BlockId::Hash(request.block),
+			&child_info,
+			&mut request.keys.iter().map(AsRef::as_ref),
+		)) {
+			Ok(proof) => proof,
+			Err(error) => {
+				trace!(target: "sync", "Remote read child request {} from {} ({} {} at {}) failed with: {}",
+					request.id,
+					who,
+					HexDisplay::from(&request.storage_key),
+					keys_str(),
+					request.block,
+					error
+				);
+				StorageProof::empty()
 			}
-		} else {
-			trace!(target: "sync", "Remote read child request {} from {} ({} {} at {}) failed with: {}",
-				request.id,
-				who,
-				HexDisplay::from(&request.storage_key),
-				keys_str(),
-				request.block,
-				"invalid child info and type",
-			);
-
-			StorageProof::empty()
 		};
 		self.send_message(
 			&who,
@@ -1610,14 +1601,16 @@ impl<B: BlockT, H: ExHashT> Protocol<B, H> {
 			request.first,
 			request.last
 		);
-		let storage_key = request.storage_key.map(|sk| StorageKey(sk));
 		let key = StorageKey(request.key);
+		let prefixed_key =  request.storage_key.as_ref()
+			.map(|storage_key| PrefixedStorageKey::new_ref(storage_key));
+		let (first, last, min, max) = (request.first, request.last, request.min, request.max);
 		let proof = match self.context_data.chain.key_changes_proof(
-			request.first,
-			request.last,
-			request.min,
-			request.max,
-			storage_key.as_ref(),
+			first,
+			last,
+			min,
+			max,
+			prefixed_key,
 			&key,
 		) {
 			Ok(proof) => proof,
@@ -1625,8 +1618,8 @@ impl<B: BlockT, H: ExHashT> Protocol<B, H> {
 				trace!(target: "sync", "Remote changes proof request {} from {} for key {} ({}..{}) failed with: {}",
 					request.id,
 					who,
-					if let Some(sk) = storage_key {
-						format!("{} : {}", HexDisplay::from(&sk.0), HexDisplay::from(&key.0))
+					if let Some(sk) = request.storage_key.as_ref() {
+						format!("{} : {}", HexDisplay::from(sk), HexDisplay::from(&key.0))
 					} else {
 						HexDisplay::from(&key.0).to_string()
 					},

substrate/client/network/src/protocol/light_client_handler.rs

@@ -58,7 +58,7 @@ use sc_client::light::fetcher;
 use sc_client_api::StorageProof;
 use sc_peerset::ReputationChange;
 use sp_core::{
-	storage::{ChildInfo, StorageKey},
+	storage::{ChildInfo, ChildType,StorageKey, PrefixedStorageKey},
 	hexdisplay::HexDisplay,
 };
 use smallvec::SmallVec;
@@ -617,35 +617,27 @@ where
 
 		let block = Decode::decode(&mut request.block.as_ref())?;
 
-		let proof =
-			if let Some(info) = ChildInfo::resolve_child_info(request.child_type, &request.child_info[..]) {
-				match self.chain.read_child_proof(
-					&BlockId::Hash(block),
-					&request.storage_key,
-					info,
-					&mut request.keys.iter().map(AsRef::as_ref)
-				) {
-					Ok(proof) => proof,
-					Err(error) => {
-						log::trace!("remote read child request from {} ({} {} at {:?}) failed with: {}",
-							peer,
-							HexDisplay::from(&request.storage_key),
-							fmt_keys(request.keys.first(), request.keys.last()),
-							request.block,
-							error);
-						StorageProof::empty()
-					}
-				}
-			} else {
+		let prefixed_key = PrefixedStorageKey::new_ref(&request.storage_key);
+		let child_info = match ChildType::from_prefixed_key(prefixed_key) {
+			Some((ChildType::ParentKeyId, storage_key)) => Ok(ChildInfo::new_default(storage_key)),
+			None => Err("Invalid child storage key".into()),
+		};
+		let proof = match child_info.and_then(|child_info| self.chain.read_child_proof(
+			&BlockId::Hash(block),
+			&child_info,
+			&mut request.keys.iter().map(AsRef::as_ref)
+		)) {
+			Ok(proof) => proof,
+			Err(error) => {
 				log::trace!("remote read child request from {} ({} {} at {:?}) failed with: {}",
 					peer,
 					HexDisplay::from(&request.storage_key),
 					fmt_keys(request.keys.first(), request.keys.last()),
 					request.block,
-					"invalid child info and type"
-				);
+					error);
 				StorageProof::empty()
-			};
+			}
+		};
 
 		let response = {
 			let r = api::v1::light::RemoteReadResponse { proof: proof.encode() };
@@ -704,23 +696,18 @@ where
 		let min = Decode::decode(&mut request.min.as_ref())?;
 		let max = Decode::decode(&mut request.max.as_ref())?;
 		let key = StorageKey(request.key.clone());
-		let storage_key =
-			if request.storage_key.is_empty() {
-				None
-			} else {
-				Some(StorageKey(request.storage_key.clone()))
-			};
+		let storage_key = if request.storage_key.is_empty() {
+			None
+		} else {
+			Some(PrefixedStorageKey::new_ref(&request.storage_key))
+		};
 
-		let proof = match self.chain.key_changes_proof(first, last, min, max, storage_key.as_ref(), &key) {
+		let proof = match self.chain.key_changes_proof(first, last, min, max, storage_key, &key) {
 			Ok(proof) => proof,
 			Err(error) => {
 				log::trace!("remote changes proof request from {} for key {} ({:?}..{:?}) failed with: {}",
 					peer,
-					if let Some(sk) = storage_key {
-						format!("{} : {}", HexDisplay::from(&sk.0), HexDisplay::from(&key.0))
-					} else {
-						HexDisplay::from(&key.0).to_string()
-					},
+					format!("{} : {}", HexDisplay::from(&request.storage_key), HexDisplay::from(&key.0)),
 					request.first,
 					request.last,
 					error);
@@ -1092,9 +1079,7 @@ fn serialize_request<B: Block>(request: &Request<B>) -> Result<Vec<u8>, prost::E
 		Request::ReadChild { request, .. } => {
 			let r = api::v1::light::RemoteReadChildRequest {
 				block: request.block.encode(),
-				storage_key: request.storage_key.clone(),
-				child_type: request.child_type.clone(),
-				child_info: request.child_info.clone(),
+				storage_key: request.storage_key.clone().into_inner(),
 				keys: request.keys.clone(),
 			};
 			api::v1::light::request::Request::RemoteReadChildRequest(r)
@@ -1113,7 +1098,8 @@ fn serialize_request<B: Block>(request: &Request<B>) -> Result<Vec<u8>, prost::E
 				last: request.last_block.1.encode(),
 				min: request.tries_roots.1.encode(),
 				max: request.max_block.1.encode(),
-				storage_key: request.storage_key.clone().unwrap_or_default(),
+				storage_key: request.storage_key.clone().map(|s| s.into_inner())
+					.unwrap_or_default(),
 				key: request.key.clone(),
 			};
 			api::v1::light::request::Request::RemoteChangesRequest(r)
@@ -1343,8 +1329,6 @@ mod tests {
 	use super::{Event, LightClientHandler, Request, Response, OutboundProtocol, PeerStatus};
 	use void::Void;
 
-	const CHILD_INFO: ChildInfo<'static> = ChildInfo::new_default(b"foobarbaz");
-
 	type Block = sp_runtime::generic::Block<Header<u64, BlakeTwo256>, substrate_test_runtime::Extrinsic>;
 	type Handler = LightClientHandler<Block>;
 	type Swarm = libp2p::swarm::Swarm<Handler>;
@@ -1894,15 +1878,13 @@ mod tests {
 
 	#[test]
 	fn receives_remote_read_child_response() {
-		let info = CHILD_INFO.info();
 		let mut chan = oneshot::channel();
+		let child_info = ChildInfo::new_default(&b":child_storage:default:sub"[..]);
 		let request = fetcher::RemoteReadChildRequest {
 			header: dummy_header(),
 			block: Default::default(),
-			storage_key: b":child_storage:sub".to_vec(),
+			storage_key: child_info.prefixed_storage_key(),
 			keys: vec![b":key".to_vec()],
-			child_info: info.0.to_vec(),
-			child_type: info.1,
 			retry_count: None,
 		};
 		issue_request(Request::ReadChild { request, sender: chan.0 });
@@ -1997,15 +1979,13 @@ mod tests {
 
 	#[test]
 	fn send_receive_read_child() {
-		let info = CHILD_INFO.info();
 		let chan = oneshot::channel();
+		let child_info = ChildInfo::new_default(&b":child_storage:default:sub"[..]);
 		let request = fetcher::RemoteReadChildRequest {
 			header: dummy_header(),
 			block: Default::default(),
-			storage_key: b":child_storage:sub".to_vec(),
+			storage_key: child_info.prefixed_storage_key(),
 			keys: vec![b":key".to_vec()],
-			child_info: info.0.to_vec(),
-			child_type: info.1,
 			retry_count: None,
 		};
 		send_receive(Request::ReadChild { request, sender: chan.0 });

substrate/client/network/src/protocol/message.rs

@@ -477,11 +477,6 @@ pub mod generic {
 		pub block: H,
 		/// Child Storage key.
 		pub storage_key: Vec<u8>,
-		/// Child trie source information.
-		pub child_info: Vec<u8>,
-		/// Child type, its required to resolve `child_info`
-		/// content and choose child implementation.
-		pub child_type: u32,
 		/// Storage key.
 		pub keys: Vec<Vec<u8>>,
 	}

substrate/client/network/src/protocol/schema/light.v1.proto

@@ -67,13 +67,9 @@ message RemoteReadResponse {
 message RemoteReadChildRequest {
 	// Block at which to perform call.
 	bytes block = 2;
-	// Child Storage key.
+	// Child Storage key, this is relative
+	// to the child type storage location.
 	bytes storage_key = 3;
-	// Child trie source information.
-	bytes child_info = 4;
-	/// Child type, its required to resolve `child_info`
-	/// content and choose child implementation.
-	uint32 child_type = 5;
 	// Storage keys.
 	repeated bytes keys = 6;
 }

substrate/client/rpc-api/src/child_state/mod.rs

@@ -0,0 +1,69 @@
+// Copyright 2017-2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Substrate state API.
+
+use jsonrpc_derive::rpc;
+use sp_core::storage::{StorageKey, PrefixedStorageKey, StorageData};
+use crate::state::error::FutureResult;
+
+pub use self::gen_client::Client as ChildStateClient;
+
+/// Substrate child state API
+///
+/// Note that all `PrefixedStorageKey` are desierialized
+/// from json and not guaranted valid.
+#[rpc]
+pub trait ChildStateApi<Hash> {
+	/// RPC Metadata
+	type Metadata;
+
+	/// Returns the keys with prefix from a child storage, leave empty to get all the keys
+	#[rpc(name = "childstate_getKeys")]
+	fn storage_keys(
+		&self,
+		child_storage_key: PrefixedStorageKey,
+		prefix: StorageKey,
+		hash: Option<Hash>
+	) -> FutureResult<Vec<StorageKey>>;
+
+	/// Returns a child storage entry at a specific block's state.
+	#[rpc(name = "childstate_getStorage")]
+	fn storage(
+		&self,
+		child_storage_key: PrefixedStorageKey,
+		key: StorageKey,
+		hash: Option<Hash>
+	) -> FutureResult<Option<StorageData>>;
+
+	/// Returns the hash of a child storage entry at a block's state.
+	#[rpc(name = "childstate_getStorageHash")]
+	fn storage_hash(
+		&self,
+		child_storage_key: PrefixedStorageKey,
+		key: StorageKey,
+		hash: Option<Hash>
+	) -> FutureResult<Option<Hash>>;
+
+	/// Returns the size of a child storage entry at a block's state.
+	#[rpc(name = "childstate_getStorageSize")]
+	fn storage_size(
+		&self,
+		child_storage_key: PrefixedStorageKey,
+		key: StorageKey,
+		hash: Option<Hash>
+	) -> FutureResult<Option<u64>>;
+}

substrate/client/rpc-api/src/lib.rs

@@ -34,4 +34,5 @@ pub mod author;
 pub mod chain;
 pub mod offchain;
 pub mod state;
+pub mod child_state;
 pub mod system;

substrate/client/rpc-api/src/state/mod.rs

@@ -72,50 +72,6 @@ pub trait StateApi<Hash> {
 	#[rpc(name = "state_getStorageSize", alias("state_getStorageSizeAt"))]
 	fn storage_size(&self, key: StorageKey, hash: Option<Hash>) -> FutureResult<Option<u64>>;
 
-	/// Returns the keys with prefix from a child storage, leave empty to get all the keys
-	#[rpc(name = "state_getChildKeys")]
-	fn child_storage_keys(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		prefix: StorageKey,
-		hash: Option<Hash>
-	) -> FutureResult<Vec<StorageKey>>;
-
-	/// Returns a child storage entry at a specific block's state.
-	#[rpc(name = "state_getChildStorage")]
-	fn child_storage(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-		hash: Option<Hash>
-	) -> FutureResult<Option<StorageData>>;
-
-	/// Returns the hash of a child storage entry at a block's state.
-	#[rpc(name = "state_getChildStorageHash")]
-	fn child_storage_hash(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-		hash: Option<Hash>
-	) -> FutureResult<Option<Hash>>;
-
-	/// Returns the size of a child storage entry at a block's state.
-	#[rpc(name = "state_getChildStorageSize")]
-	fn child_storage_size(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-		hash: Option<Hash>
-	) -> FutureResult<Option<u64>>;
-
 	/// Returns the runtime metadata as an opaque blob.
 	#[rpc(name = "state_getMetadata")]
 	fn metadata(&self, hash: Option<Hash>) -> FutureResult<Bytes>;

substrate/client/rpc/src/state/mod.rs

@@ -28,7 +28,7 @@ use rpc::{Result as RpcResult, futures::{Future, future::result}};
 
 use sc_rpc_api::Subscriptions;
 use sc_client::{light::{blockchain::RemoteBlockchain, fetcher::Fetcher}};
-use sp_core::{Bytes, storage::{StorageKey, StorageData, StorageChangeSet}};
+use sp_core::{Bytes, storage::{StorageKey, PrefixedStorageKey, StorageData, StorageChangeSet}};
 use sp_version::RuntimeVersion;
 use sp_runtime::traits::Block as BlockT;
 
@@ -37,6 +37,7 @@ use sp_api::{Metadata, ProvideRuntimeApi, CallApiAt};
 use self::error::{Error, FutureResult};
 
 pub use sc_rpc_api::state::*;
+pub use sc_rpc_api::child_state::*;
 use sc_client_api::{ExecutorProvider, StorageProvider, BlockchainEvents, Backend};
 use sp_blockchain::{HeaderMetadata, HeaderBackend};
 
@@ -103,49 +104,6 @@ pub trait StateBackend<Block: BlockT, Client>: Send + Sync + 'static
 			.map(|x| x.map(|x| x.0.len() as u64)))
 	}
 
-	/// Returns the keys with prefix from a child storage, leave empty to get all the keys
-	fn child_storage_keys(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		prefix: StorageKey,
-	) -> FutureResult<Vec<StorageKey>>;
-
-	/// Returns a child storage entry at a specific block's state.
-	fn child_storage(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-	) -> FutureResult<Option<StorageData>>;
-
-	/// Returns the hash of a child storage entry at a block's state.
-	fn child_storage_hash(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-	) -> FutureResult<Option<Block::Hash>>;
-
-	/// Returns the size of a child storage entry at a block's state.
-	fn child_storage_size(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-	) -> FutureResult<Option<u64>> {
-		Box::new(self.child_storage(block, child_storage_key, child_info, child_type, key)
-			.map(|x| x.map(|x| x.0.len() as u64)))
-	}
-
 	/// Returns the runtime metadata as an opaque blob.
 	fn metadata(&self, block: Option<Block::Hash>) -> FutureResult<Bytes>;
 
@@ -204,7 +162,7 @@ pub trait StateBackend<Block: BlockT, Client>: Send + Sync + 'static
 pub fn new_full<BE, Block: BlockT, Client>(
 	client: Arc<Client>,
 	subscriptions: Subscriptions,
-) -> State<Block, Client>
+) -> (State<Block, Client>, ChildState<Block, Client>)
 	where
 		Block: BlockT + 'static,
 		BE: Backend<Block> + 'static,
@@ -214,9 +172,11 @@ pub fn new_full<BE, Block: BlockT, Client>(
 			+ ProvideRuntimeApi<Block> + Send + Sync + 'static,
 		Client::Api: Metadata<Block, Error = sp_blockchain::Error>,
 {
-	State {
-		backend: Box::new(self::state_full::FullState::new(client, subscriptions)),
-	}
+	let child_backend = Box::new(
+		self::state_full::FullState::new(client.clone(), subscriptions.clone())
+	);
+	let backend = Box::new(self::state_full::FullState::new(client, subscriptions));
+	(State { backend }, ChildState { backend: child_backend })
 }
 
 /// Create new state API that works on light node.
@@ -225,7 +185,7 @@ pub fn new_light<BE, Block: BlockT, Client, F: Fetcher<Block>>(
 	subscriptions: Subscriptions,
 	remote_blockchain: Arc<dyn RemoteBlockchain<Block>>,
 	fetcher: Arc<F>,
-) -> State<Block, Client>
+) -> (State<Block, Client>, ChildState<Block, Client>)
 	where
 		Block: BlockT + 'static,
 		BE: Backend<Block> + 'static,
@@ -235,14 +195,20 @@ pub fn new_light<BE, Block: BlockT, Client, F: Fetcher<Block>>(
 			+ Send + Sync + 'static,
 		F: Send + Sync + 'static,
 {
-	State {
-		backend: Box::new(self::state_light::LightState::new(
+	let child_backend = Box::new(self::state_light::LightState::new(
+			client.clone(),
+			subscriptions.clone(),
+			remote_blockchain.clone(),
+			fetcher.clone(),
+	));
+
+	let backend = Box::new(self::state_light::LightState::new(
 			client,
 			subscriptions,
 			remote_blockchain,
 			fetcher,
-		)),
-	}
+	));
+	(State { backend }, ChildState { backend: child_backend })
 }
 
 /// State API with subscriptions support.
@@ -307,50 +273,6 @@ impl<Block, Client> StateApi<Block::Hash> for State<Block, Client>
 		self.backend.storage_size(block, key)
 	}
 
-	fn child_storage(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-		block: Option<Block::Hash>
-	) -> FutureResult<Option<StorageData>> {
-		self.backend.child_storage(block, child_storage_key, child_info, child_type, key)
-	}
-
-	fn child_storage_keys(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key_prefix: StorageKey,
-		block: Option<Block::Hash>
-	) -> FutureResult<Vec<StorageKey>> {
-		self.backend.child_storage_keys(block, child_storage_key, child_info, child_type, key_prefix)
-	}
-
-	fn child_storage_hash(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-		block: Option<Block::Hash>
-	) -> FutureResult<Option<Block::Hash>> {
-		self.backend.child_storage_hash(block, child_storage_key, child_info, child_type, key)
-	}
-
-	fn child_storage_size(
-		&self,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-		block: Option<Block::Hash>
-	) -> FutureResult<Option<u64>> {
-		self.backend.child_storage_size(block, child_storage_key, child_info, child_type, key)
-	}
-
 	fn metadata(&self, block: Option<Block::Hash>) -> FutureResult<Bytes> {
 		self.backend.metadata(block)
 	}
@@ -402,12 +324,98 @@ impl<Block, Client> StateApi<Block::Hash> for State<Block, Client>
 	}
 }
 
+/// Child state backend API.
+pub trait ChildStateBackend<Block: BlockT, Client>: Send + Sync + 'static
+	where
+		Block: BlockT + 'static,
+		Client: Send + Sync + 'static,
+{
+	/// Returns the keys with prefix from a child storage,
+	/// leave prefix empty to get all the keys.
+	fn storage_keys(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		prefix: StorageKey,
+	) -> FutureResult<Vec<StorageKey>>;
+
+	/// Returns a child storage entry at a specific block's state.
+	fn storage(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+	) -> FutureResult<Option<StorageData>>;
+
+	/// Returns the hash of a child storage entry at a block's state.
+	fn storage_hash(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+	) -> FutureResult<Option<Block::Hash>>;
+
+	/// Returns the size of a child storage entry at a block's state.
+	fn storage_size(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+	) -> FutureResult<Option<u64>> {
+		Box::new(self.storage(block, storage_key, key)
+			.map(|x| x.map(|x| x.0.len() as u64)))
+	}
+}
+
+/// Child state API with subscriptions support.
+pub struct ChildState<Block, Client> {
+	backend: Box<dyn ChildStateBackend<Block, Client>>,
+}
+
+impl<Block, Client> ChildStateApi<Block::Hash> for ChildState<Block, Client>
+	where
+		Block: BlockT + 'static,
+		Client: Send + Sync + 'static,
+{
+	type Metadata = crate::metadata::Metadata;
+
+	fn storage(
+		&self,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+		block: Option<Block::Hash>
+	) -> FutureResult<Option<StorageData>> {
+		self.backend.storage(block, storage_key, key)
+	}
+
+	fn storage_keys(
+		&self,
+		storage_key: PrefixedStorageKey,
+		key_prefix: StorageKey,
+		block: Option<Block::Hash>
+	) -> FutureResult<Vec<StorageKey>> {
+		self.backend.storage_keys(block, storage_key, key_prefix)
+	}
+
+	fn storage_hash(
+		&self,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+		block: Option<Block::Hash>
+	) -> FutureResult<Option<Block::Hash>> {
+		self.backend.storage_hash(block, storage_key, key)
+	}
+
+	fn storage_size(
+		&self,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+		block: Option<Block::Hash>
+	) -> FutureResult<Option<u64>> {
+		self.backend.storage_size(block, storage_key, key)
+	}
+}
+
 fn client_err(err: sp_blockchain::Error) -> Error {
 	Error::Client(Box::new(err))
 }
-
-const CHILD_RESOLUTION_ERROR: &str = "Unexpected child info and type";
-
-fn child_resolution_error() -> sp_blockchain::Error {
-	sp_blockchain::Error::Msg(CHILD_RESOLUTION_ERROR.to_string())
-}

substrate/client/rpc/src/state/state_full.rs

@@ -29,7 +29,8 @@ use sc_client_api::backend::Backend;
 use sp_blockchain::{Result as ClientResult, Error as ClientError, HeaderMetadata, CachedHeaderMetadata, HeaderBackend};
 use sc_client::BlockchainEvents;
 use sp_core::{
-	Bytes, storage::{well_known_keys, StorageKey, StorageData, StorageChangeSet, ChildInfo},
+	Bytes, storage::{well_known_keys, StorageKey, StorageData, StorageChangeSet,
+	ChildInfo, ChildType, PrefixedStorageKey},
 };
 use sp_version::RuntimeVersion;
 use sp_runtime::{
@@ -38,7 +39,7 @@ use sp_runtime::{
 
 use sp_api::{Metadata, ProvideRuntimeApi, CallApiAt};
 
-use super::{StateBackend, error::{FutureResult, Error, Result}, client_err, child_resolution_error};
+use super::{StateBackend, ChildStateBackend, error::{FutureResult, Error, Result}, client_err};
 use std::marker::PhantomData;
 use sc_client_api::{CallExecutor, StorageProvider, ExecutorProvider};
 
@@ -308,66 +309,6 @@ impl<BE, Block, Client> StateBackend<Block, Client> for FullState<BE, Block, Cli
 				.map_err(client_err)))
 	}
 
-	fn child_storage_keys(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		prefix: StorageKey,
-	) -> FutureResult<Vec<StorageKey>> {
-		Box::new(result(
-			self.block_or_best(block)
-				.and_then(|block| self.client.child_storage_keys(
-					&BlockId::Hash(block),
-					&child_storage_key,
-					ChildInfo::resolve_child_info(child_type, &child_info.0[..])
-						.ok_or_else(child_resolution_error)?,
-					&prefix,
-				))
-				.map_err(client_err)))
-	}
-
-	fn child_storage(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-	) -> FutureResult<Option<StorageData>> {
-		Box::new(result(
-			self.block_or_best(block)
-				.and_then(|block| self.client.child_storage(
-					&BlockId::Hash(block),
-					&child_storage_key,
-					ChildInfo::resolve_child_info(child_type, &child_info.0[..])
-						.ok_or_else(child_resolution_error)?,
-					&key,
-				))
-				.map_err(client_err)))
-	}
-
-	fn child_storage_hash(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-	) -> FutureResult<Option<Block::Hash>> {
-		Box::new(result(
-			self.block_or_best(block)
-				.and_then(|block| self.client.child_storage_hash(
-					&BlockId::Hash(block),
-					&child_storage_key,
-					ChildInfo::resolve_child_info(child_type, &child_info.0[..])
-						.ok_or_else(child_resolution_error)?,
-					&key,
-				))
-				.map_err(client_err)))
-	}
-
 	fn metadata(&self, block: Option<Block::Hash>) -> FutureResult<Bytes> {
 		Box::new(result(
 			self.block_or_best(block)
@@ -493,7 +434,7 @@ impl<BE, Block, Client> StateBackend<Block, Client> for FullState<BE, Block, Cli
 				let block = self.client.info().best_hash;
 				let changes = keys
 					.into_iter()
-					.map(|key| self.storage(Some(block.clone()).into(), key.clone())
+					.map(|key| StateBackend::storage(self, Some(block.clone()).into(), key.clone())
 						.map(|val| (key.clone(), val))
 						.wait()
 						.unwrap_or_else(|_| (key, None))
@@ -530,6 +471,82 @@ impl<BE, Block, Client> StateBackend<Block, Client> for FullState<BE, Block, Cli
 	}
 }
 
+impl<BE, Block, Client> ChildStateBackend<Block, Client> for FullState<BE, Block, Client> where
+	Block: BlockT + 'static,
+	BE: Backend<Block> + 'static,
+	Client: ExecutorProvider<Block> + StorageProvider<Block, BE> + HeaderBackend<Block>
+		+ HeaderMetadata<Block, Error = sp_blockchain::Error> + BlockchainEvents<Block>
+		+ CallApiAt<Block, Error = sp_blockchain::Error> + ProvideRuntimeApi<Block>
+		+ Send + Sync + 'static,
+	Client::Api: Metadata<Block, Error = sp_blockchain::Error>,
+{
+	fn storage_keys(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		prefix: StorageKey,
+	) -> FutureResult<Vec<StorageKey>> {
+		Box::new(result(
+			self.block_or_best(block)
+				.and_then(|block| {
+					let child_info = match ChildType::from_prefixed_key(&storage_key) {
+						Some((ChildType::ParentKeyId, storage_key)) => ChildInfo::new_default(storage_key),
+						None => return Err("Invalid child storage key".into()),
+					};
+					self.client.child_storage_keys(
+						&BlockId::Hash(block),
+						&child_info,
+						&prefix,
+					)
+				})
+				.map_err(client_err)))
+	}
+
+	fn storage(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+	) -> FutureResult<Option<StorageData>> {
+		Box::new(result(
+			self.block_or_best(block)
+				.and_then(|block| {
+					let child_info = match ChildType::from_prefixed_key(&storage_key) {
+						Some((ChildType::ParentKeyId, storage_key)) => ChildInfo::new_default(storage_key),
+						None => return Err("Invalid child storage key".into()),
+					};
+					self.client.child_storage(
+						&BlockId::Hash(block),
+						&child_info,
+						&key,
+					)
+				})
+				.map_err(client_err)))
+	}
+
+	fn storage_hash(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+	) -> FutureResult<Option<Block::Hash>> {
+		Box::new(result(
+			self.block_or_best(block)
+				.and_then(|block| {
+					let child_info = match ChildType::from_prefixed_key(&storage_key) {
+						Some((ChildType::ParentKeyId, storage_key)) => ChildInfo::new_default(storage_key),
+						None => return Err("Invalid child storage key".into()),
+					};
+					self.client.child_storage_hash(
+						&BlockId::Hash(block),
+						&child_info,
+						&key,
+					)
+				})
+				.map_err(client_err)))
+	}
+}
+
 /// Splits passed range into two subranges where:
 /// - first range has at least one element in it;
 /// - second range (optionally) starts at given `middle` element.

substrate/client/rpc/src/state/state_light.rs

@@ -48,17 +48,19 @@ use sc_client::{
 	},
 };
 use sp_core::{
-	Bytes, OpaqueMetadata, storage::{StorageKey, StorageData, StorageChangeSet},
+	Bytes, OpaqueMetadata,
+	storage::{StorageKey, PrefixedStorageKey, StorageData, StorageChangeSet},
 };
 use sp_version::RuntimeVersion;
 use sp_runtime::{generic::BlockId, traits::{Block as BlockT, HashFor}};
 
-use super::{StateBackend, error::{FutureResult, Error}, client_err};
+use super::{StateBackend, ChildStateBackend, error::{FutureResult, Error}, client_err};
 
 /// Storage data map of storage keys => (optional) storage value.
 type StorageMap = HashMap<StorageKey, Option<StorageData>>;
 
 /// State API backend for light nodes.
+#[derive(Clone)]
 pub struct LightState<Block: BlockT, F: Fetcher<Block>, Client> {
 	client: Arc<Client>,
 	subscriptions: Subscriptions,
@@ -233,69 +235,7 @@ impl<Block, F, Client> StateBackend<Block, Client> for LightState<Block, F, Clie
 		block: Option<Block::Hash>,
 		key: StorageKey,
 	) -> FutureResult<Option<Block::Hash>> {
-		Box::new(self
-			.storage(block, key)
-			.and_then(|maybe_storage|
-				result(Ok(maybe_storage.map(|storage| HashFor::<Block>::hash(&storage.0))))
-			)
-		)
-	}
-
-	fn child_storage_keys(
-		&self,
-		_block: Option<Block::Hash>,
-		_child_storage_key: StorageKey,
-		_child_info: StorageKey,
-		_child_type: u32,
-		_prefix: StorageKey,
-	) -> FutureResult<Vec<StorageKey>> {
-		Box::new(result(Err(client_err(ClientError::NotAvailableOnLightClient))))
-	}
-
-	fn child_storage(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-	) -> FutureResult<Option<StorageData>> {
-		let block = self.block_or_best(block);
-		let fetcher = self.fetcher.clone();
-		let child_storage = resolve_header(&*self.remote_blockchain, &*self.fetcher, block)
-			.then(move |result| match result {
-				Ok(header) => Either::Left(fetcher.remote_read_child(RemoteReadChildRequest {
-					block,
-					header,
-					storage_key: child_storage_key.0,
-					child_info: child_info.0,
-					child_type,
-					keys: vec![key.0.clone()],
-					retry_count: Default::default(),
-				}).then(move |result| ready(result
-					.map(|mut data| data
-						.remove(&key.0)
-						.expect("successful result has entry for all keys; qed")
-						.map(StorageData)
-					)
-					.map_err(client_err)
-				))),
-				Err(error) => Either::Right(ready(Err(error))),
-			});
-
-		Box::new(child_storage.boxed().compat())
-	}
-
-	fn child_storage_hash(
-		&self,
-		block: Option<Block::Hash>,
-		child_storage_key: StorageKey,
-		child_info: StorageKey,
-		child_type: u32,
-		key: StorageKey,
-	) -> FutureResult<Option<Block::Hash>> {
-		Box::new(self
-			.child_storage(block, child_storage_key, child_info, child_type, key)
+		Box::new(StateBackend::storage(self, block, key)
 			.and_then(|maybe_storage|
 				result(Ok(maybe_storage.map(|storage| HashFor::<Block>::hash(&storage.0))))
 			)
@@ -518,6 +458,65 @@ impl<Block, F, Client> StateBackend<Block, Client> for LightState<Block, F, Clie
 	}
 }
 
+impl<Block, F, Client> ChildStateBackend<Block, Client> for LightState<Block, F, Client>
+	where
+		Block: BlockT,
+		Client: BlockchainEvents<Block> + HeaderBackend<Block> + Send + Sync + 'static,
+		F: Fetcher<Block> + 'static
+{
+	fn storage_keys(
+		&self,
+		_block: Option<Block::Hash>,
+		_storage_key: PrefixedStorageKey,
+		_prefix: StorageKey,
+	) -> FutureResult<Vec<StorageKey>> {
+		Box::new(result(Err(client_err(ClientError::NotAvailableOnLightClient))))
+	}
+
+	fn storage(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+	) -> FutureResult<Option<StorageData>> {
+		let block = self.block_or_best(block);
+		let fetcher = self.fetcher.clone();
+		let child_storage = resolve_header(&*self.remote_blockchain, &*self.fetcher, block)
+			.then(move |result| match result {
+				Ok(header) => Either::Left(fetcher.remote_read_child(RemoteReadChildRequest {
+					block,
+					header,
+					storage_key,
+					keys: vec![key.0.clone()],
+					retry_count: Default::default(),
+				}).then(move |result| ready(result
+					.map(|mut data| data
+						.remove(&key.0)
+						.expect("successful result has entry for all keys; qed")
+						.map(StorageData)
+					)
+					.map_err(client_err)
+				))),
+				Err(error) => Either::Right(ready(Err(error))),
+			});
+
+		Box::new(child_storage.boxed().compat())
+	}
+
+	fn storage_hash(
+		&self,
+		block: Option<Block::Hash>,
+		storage_key: PrefixedStorageKey,
+		key: StorageKey,
+	) -> FutureResult<Option<Block::Hash>> {
+		Box::new(ChildStateBackend::storage(self, block, storage_key, key)
+			.and_then(|maybe_storage|
+				result(Ok(maybe_storage.map(|storage| HashFor::<Block>::hash(&storage.0))))
+			)
+		)
+	}
+}
+
 /// Resolve header by hash.
 fn resolve_header<Block: BlockT, F: Fetcher<Block>>(
 	remote_blockchain: &dyn RemoteBlockchain<Block>,

substrate/client/rpc/src/state/tests.rs

@@ -21,7 +21,7 @@ use self::error::Error;
 use std::sync::Arc;
 use assert_matches::assert_matches;
 use futures01::stream::Stream;
-use sp_core::{storage::{well_known_keys, ChildInfo}, ChangesTrieConfiguration};
+use sp_core::{storage::ChildInfo, ChangesTrieConfiguration};
 use sp_core::hash::H256;
 use sc_block_builder::BlockBuilderProvider;
 use sp_io::hashing::blake2_256;
@@ -32,26 +32,28 @@ use substrate_test_runtime_client::{
 };
 use sp_runtime::generic::BlockId;
 
-const CHILD_INFO: ChildInfo<'static> = ChildInfo::new_default(b"unique_id");
+const STORAGE_KEY: &[u8] = b"child";
+
+fn prefixed_storage_key() -> PrefixedStorageKey {
+	let child_info = ChildInfo::new_default(&STORAGE_KEY[..]);
+	child_info.prefixed_storage_key()
+}
 
 #[test]
 fn should_return_storage() {
 	const KEY: &[u8] = b":mock";
 	const VALUE: &[u8] = b"hello world";
-	const STORAGE_KEY: &[u8] = b":child_storage:default:child";
 	const CHILD_VALUE: &[u8] = b"hello world !";
 
+	let child_info = ChildInfo::new_default(STORAGE_KEY);
 	let mut core = tokio::runtime::Runtime::new().unwrap();
 	let client = TestClientBuilder::new()
 		.add_extra_storage(KEY.to_vec(), VALUE.to_vec())
-		.add_extra_child_storage(STORAGE_KEY.to_vec(), CHILD_INFO, KEY.to_vec(), CHILD_VALUE.to_vec())
+		.add_extra_child_storage(&child_info, KEY.to_vec(), CHILD_VALUE.to_vec())
 		.build();
 	let genesis_hash = client.genesis_hash();
-	let client = new_full(Arc::new(client), Subscriptions::new(Arc::new(core.executor())));
+	let (client, child) = new_full(Arc::new(client), Subscriptions::new(Arc::new(core.executor())));
 	let key = StorageKey(KEY.to_vec());
-	let storage_key = StorageKey(STORAGE_KEY.to_vec());
-	let (child_info, child_type) = CHILD_INFO.info();
-	let child_info = StorageKey(child_info.to_vec());
 
 	assert_eq!(
 		client.storage(key.clone(), Some(genesis_hash).into()).wait()
@@ -69,7 +71,7 @@ fn should_return_storage() {
 	);
 	assert_eq!(
 		core.block_on(
-			client.child_storage(storage_key, child_info, child_type, key, Some(genesis_hash).into())
+			child.storage(prefixed_storage_key(), key, Some(genesis_hash).into())
 				.map(|x| x.map(|x| x.0.len()))
 		).unwrap().unwrap() as usize,
 		CHILD_VALUE.len(),
@@ -79,45 +81,36 @@ fn should_return_storage() {
 
 #[test]
 fn should_return_child_storage() {
-	let (child_info, child_type) = CHILD_INFO.info();
-	let child_info = StorageKey(child_info.to_vec());
+	let child_info = ChildInfo::new_default(STORAGE_KEY);
 	let core = tokio::runtime::Runtime::new().unwrap();
 	let client = Arc::new(substrate_test_runtime_client::TestClientBuilder::new()
-		.add_child_storage("test", "key", CHILD_INFO, vec![42_u8])
+		.add_child_storage(&child_info, "key", vec![42_u8])
 		.build());
 	let genesis_hash = client.genesis_hash();
-	let client = new_full(client, Subscriptions::new(Arc::new(core.executor())));
-	let child_key = StorageKey(
-		well_known_keys::CHILD_STORAGE_KEY_PREFIX.iter().chain(b"test").cloned().collect()
-	);
+	let (_client, child) = new_full(client, Subscriptions::new(Arc::new(core.executor())));
+	let child_key = prefixed_storage_key();
 	let key = StorageKey(b"key".to_vec());
 
 
 	assert_matches!(
-		client.child_storage(
+		child.storage(
 			child_key.clone(),
-			child_info.clone(),
-			child_type,
 			key.clone(),
 			Some(genesis_hash).into(),
 		).wait(),
 		Ok(Some(StorageData(ref d))) if d[0] == 42 && d.len() == 1
 	);
 	assert_matches!(
-		client.child_storage_hash(
+		child.storage_hash(
 			child_key.clone(),
-			child_info.clone(),
-			child_type,
 			key.clone(),
 			Some(genesis_hash).into(),
 		).wait().map(|x| x.is_some()),
 		Ok(true)
 	);
 	assert_matches!(
-		client.child_storage_size(
+		child.storage_size(
 			child_key.clone(),
-			child_info.clone(),
-			child_type,
 			key.clone(),
 			None,
 		).wait(),
@@ -130,7 +123,7 @@ fn should_call_contract() {
 	let core = tokio::runtime::Runtime::new().unwrap();
 	let client = Arc::new(substrate_test_runtime_client::new());
 	let genesis_hash = client.genesis_hash();
-	let client = new_full(client, Subscriptions::new(Arc::new(core.executor())));
+	let (client, _child) = new_full(client, Subscriptions::new(Arc::new(core.executor())));
 
 	assert_matches!(
 		client.call("balanceOf".into(), Bytes(vec![1,2,3]), Some(genesis_hash).into()).wait(),
@@ -146,7 +139,7 @@ fn should_notify_about_storage_changes() {
 
 	{
 		let mut client = Arc::new(substrate_test_runtime_client::new());
-		let api = new_full(client.clone(), Subscriptions::new(Arc::new(remote)));
+		let (api, _child) = new_full(client.clone(), Subscriptions::new(Arc::new(remote)));
 
 		api.subscribe_storage(Default::default(), subscriber, None.into());
 
@@ -179,7 +172,7 @@ fn should_send_initial_storage_changes_and_notifications() {
 
 	{
 		let mut client = Arc::new(substrate_test_runtime_client::new());
-		let api = new_full(client.clone(), Subscriptions::new(Arc::new(remote)));
+		let (api, _child) = new_full(client.clone(), Subscriptions::new(Arc::new(remote)));
 
 		let alice_balance_key = blake2_256(&runtime::system::balance_of_key(AccountKeyring::Alice.into()));
 
@@ -215,7 +208,7 @@ fn should_send_initial_storage_changes_and_notifications() {
 fn should_query_storage() {
 	fn run_tests(mut client: Arc<TestClient>, has_changes_trie_config: bool) {
 		let core = tokio::runtime::Runtime::new().unwrap();
-		let api = new_full(client.clone(), Subscriptions::new(Arc::new(core.executor())));
+		let (api, _child) = new_full(client.clone(), Subscriptions::new(Arc::new(core.executor())));
 
 		let mut add_block = |nonce| {
 			let mut builder = client.new_block(Default::default()).unwrap();
@@ -434,7 +427,7 @@ fn should_return_runtime_version() {
 	let core = tokio::runtime::Runtime::new().unwrap();
 
 	let client = Arc::new(substrate_test_runtime_client::new());
-	let api = new_full(client.clone(), Subscriptions::new(Arc::new(core.executor())));
+	let (api, _child) = new_full(client.clone(), Subscriptions::new(Arc::new(core.executor())));
 
 	let result = "{\"specName\":\"test\",\"implName\":\"parity-test\",\"authoringVersion\":1,\
 		\"specVersion\":2,\"implVersion\":2,\"apis\":[[\"0xdf6acb689907609b\",3],\
@@ -458,7 +451,7 @@ fn should_notify_on_runtime_version_initially() {
 
 	{
 		let client = Arc::new(substrate_test_runtime_client::new());
-		let api = new_full(client.clone(), Subscriptions::new(Arc::new(core.executor())));
+		let (api, _child) = new_full(client.clone(), Subscriptions::new(Arc::new(core.executor())));
 
 		api.subscribe_runtime_version(Default::default(), subscriber);
 

substrate/client/service/src/builder.rs

@@ -1015,7 +1015,7 @@ ServiceBuilder<
 
 			let subscriptions = sc_rpc::Subscriptions::new(Arc::new(tasks_builder.spawn_handle()));
 
-			let (chain, state) = if let (Some(remote_backend), Some(on_demand)) =
+			let (chain, state, child_state) = if let (Some(remote_backend), Some(on_demand)) =
 				(remote_backend.as_ref(), on_demand.as_ref()) {
 				// Light clients
 				let chain = sc_rpc::chain::new_light(
@@ -1024,19 +1024,19 @@ ServiceBuilder<
 					remote_backend.clone(),
 					on_demand.clone()
 				);
-				let state = sc_rpc::state::new_light(
+				let (state, child_state) = sc_rpc::state::new_light(
 					client.clone(),
 					subscriptions.clone(),
 					remote_backend.clone(),
 					on_demand.clone()
 				);
-				(chain, state)
+				(chain, state, child_state)
 
 			} else {
 				// Full nodes
 				let chain = sc_rpc::chain::new_full(client.clone(), subscriptions.clone());
-				let state = sc_rpc::state::new_full(client.clone(), subscriptions.clone());
-				(chain, state)
+				let (state, child_state) = sc_rpc::state::new_full(client.clone(), subscriptions.clone());
+				(chain, state, child_state)
 			};
 
 			let author = sc_rpc::author::Author::new(
@@ -1059,6 +1059,7 @@ ServiceBuilder<
 
 			sc_rpc_server::rpc_handler((
 				state::StateApi::to_delegate(state),
+				state::ChildStateApi::to_delegate(child_state),
 				chain::ChainApi::to_delegate(chain),
 				maybe_offchain_rpc,
 				author::AuthorApi::to_delegate(author),

substrate/client/src/client.rs

@@ -25,8 +25,8 @@ use parking_lot::{Mutex, RwLock};
 use codec::{Encode, Decode};
 use hash_db::Prefix;
 use sp_core::{
-	ChangesTrieConfiguration, convert_hash, traits::CodeExecutor,
-	NativeOrEncoded, storage::{StorageKey, StorageData, well_known_keys, ChildInfo},
+	ChangesTrieConfiguration, convert_hash, traits::CodeExecutor, NativeOrEncoded,
+	storage::{StorageKey, PrefixedStorageKey, StorageData, well_known_keys, ChildInfo},
 };
 use sc_telemetry::{telemetry, SUBSTRATE_INFO};
 use sp_runtime::{
@@ -344,7 +344,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		last: Block::Hash,
 		min: Block::Hash,
 		max: Block::Hash,
-		storage_key: Option<&StorageKey>,
+		storage_key: Option<&PrefixedStorageKey>,
 		key: &StorageKey,
 		cht_size: NumberFor<Block>,
 	) -> sp_blockchain::Result<ChangesProof<Block::Header>> {
@@ -393,7 +393,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			fn with_cached_changed_keys(
 				&self,
 				root: &Block::Hash,
-				functor: &mut dyn FnMut(&HashMap<Option<Vec<u8>>, HashSet<Vec<u8>>>),
+				functor: &mut dyn FnMut(&HashMap<Option<PrefixedStorageKey>, HashSet<Vec<u8>>>),
 			) -> bool {
 				self.storage.with_cached_changed_keys(root, functor)
 			}
@@ -438,7 +438,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 					number: last_number,
 				},
 				max_number,
-				storage_key.as_ref().map(|x| &x.0[..]),
+				storage_key,
 				&key.0,
 			)
 			.map_err(|err| sp_blockchain::Error::ChangesTrieAccessFailed(err))?;
@@ -1109,12 +1109,11 @@ impl<B, E, Block, RA> ProofProvider<Block> for Client<B, E, Block, RA> where
 	fn read_child_proof(
 		&self,
 		id: &BlockId<Block>,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		keys: &mut dyn Iterator<Item=&[u8]>,
 	) -> sp_blockchain::Result<StorageProof> {
 		self.state_at(id)
-			.and_then(|state| prove_child_read(state, storage_key, child_info, keys)
+			.and_then(|state| prove_child_read(state, child_info, keys)
 				.map_err(Into::into))
 	}
 
@@ -1156,7 +1155,7 @@ impl<B, E, Block, RA> ProofProvider<Block> for Client<B, E, Block, RA> where
 		last: Block::Hash,
 		min: Block::Hash,
 		max: Block::Hash,
-		storage_key: Option<&StorageKey>,
+		storage_key: Option<&PrefixedStorageKey>,
 		key: &StorageKey,
 	) -> sp_blockchain::Result<ChangesProof<Block::Header>> {
 		self.key_changes_proof_with_cht_size(
@@ -1286,46 +1285,40 @@ impl<B, E, Block, RA> StorageProvider<Block, B> for Client<B, E, Block, RA> wher
 		)
 	}
 
-
 	fn child_storage_keys(
 		&self,
 		id: &BlockId<Block>,
-		child_storage_key: &StorageKey,
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key_prefix: &StorageKey
 	) -> sp_blockchain::Result<Vec<StorageKey>> {
 		let keys = self.state_at(id)?
-			.child_keys(&child_storage_key.0, child_info, &key_prefix.0)
+			.child_keys(child_info, &key_prefix.0)
 			.into_iter()
 			.map(StorageKey)
 			.collect();
 		Ok(keys)
 	}
 
-
 	fn child_storage(
 		&self,
 		id: &BlockId<Block>,
-		storage_key: &StorageKey,
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &StorageKey
 	) -> sp_blockchain::Result<Option<StorageData>> {
 		Ok(self.state_at(id)?
-			.child_storage(&storage_key.0, child_info, &key.0)
+			.child_storage(child_info, &key.0)
 			.map_err(|e| sp_blockchain::Error::from_state(Box::new(e)))?
 			.map(StorageData))
 	}
 
-
 	fn child_storage_hash(
 		&self,
 		id: &BlockId<Block>,
-		storage_key: &StorageKey,
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &StorageKey
 	) -> sp_blockchain::Result<Option<Block::Hash>> {
 		Ok(self.state_at(id)?
-			.child_storage_hash(&storage_key.0, child_info, &key.0)
+			.child_storage_hash(child_info, &key.0)
 			.map_err(|e| sp_blockchain::Error::from_state(Box::new(e)))?
 		)
 	}
@@ -1361,7 +1354,7 @@ impl<B, E, Block, RA> StorageProvider<Block, B> for Client<B, E, Block, RA> wher
 		&self,
 		first: NumberFor<Block>,
 		last: BlockId<Block>,
-		storage_key: Option<&StorageKey>,
+		storage_key: Option<&PrefixedStorageKey>,
 		key: &StorageKey
 	) -> sp_blockchain::Result<Vec<(NumberFor<Block>, u32)>> {
 		let last_number = self.backend.blockchain().expect_block_number_from_id(&last)?;
@@ -1392,7 +1385,7 @@ impl<B, E, Block, RA> StorageProvider<Block, B> for Client<B, E, Block, RA> wher
 				range_first,
 				&range_anchor,
 				best_number,
-				storage_key.as_ref().map(|x| &x.0[..]),
+				storage_key,
 				&key.0)
 				.and_then(|r| r.map(|r| r.map(|(block, tx)| (block, tx))).collect::<Result<_, _>>())
 				.map_err(|err| sp_blockchain::Error::ChangesTrieAccessFailed(err))?;

substrate/client/src/in_mem.rs

@@ -516,9 +516,9 @@ impl<Block: BlockT> backend::BlockImportOperation<Block> for BlockImportOperatio
 	fn reset_storage(&mut self, storage: Storage) -> sp_blockchain::Result<Block::Hash> {
 		check_genesis_storage(&storage)?;
 
-		let child_delta = storage.children.into_iter()
-			.map(|(storage_key, child_content)|
-				(storage_key, child_content.data.into_iter().map(|(k, v)| (k, Some(v))), child_content.child_info));
+		let child_delta = storage.children_default.into_iter()
+			.map(|(_storage_key, child_content)|
+				(child_content.child_info, child_content.data.into_iter().map(|(k, v)| (k, Some(v)))));
 
 		let (root, transaction) = self.old_state.full_storage_root(
 			storage.top.into_iter().map(|(k, v)| (k, Some(v))),
@@ -725,8 +725,9 @@ pub fn check_genesis_storage(storage: &Storage) -> sp_blockchain::Result<()> {
 		return Err(sp_blockchain::Error::GenesisInvalid.into());
 	}
 
-	if storage.children.keys().any(|child_key| !well_known_keys::is_child_storage_key(&child_key)) {
-		return Err(sp_blockchain::Error::GenesisInvalid.into());
+	if storage.children_default.keys()
+		.any(|child_key| !well_known_keys::is_child_storage_key(&child_key)) {
+			return Err(sp_blockchain::Error::GenesisInvalid.into());
 	}
 
 	Ok(())

substrate/client/src/light/backend.rs

@@ -24,7 +24,7 @@ use parking_lot::RwLock;
 use codec::{Decode, Encode};
 
 use sp_core::ChangesTrieConfiguration;
-use sp_core::storage::{well_known_keys, ChildInfo, OwnedChildInfo};
+use sp_core::storage::{well_known_keys, ChildInfo};
 use sp_core::offchain::storage::InMemOffchainStorage;
 use sp_state_machine::{
 	Backend as StateBackend, TrieBackend, InMemoryBackend, ChangesTrieTransaction,
@@ -312,17 +312,17 @@ impl<S, Block> BlockImportOperation<Block> for ImportOperation<Block, S>
 		self.changes_trie_config_update = Some(changes_trie_config);
 
 		// this is only called when genesis block is imported => shouldn't be performance bottleneck
-		let mut storage: HashMap<Option<(Vec<u8>, OwnedChildInfo)>, _> = HashMap::new();
+		let mut storage: HashMap<Option<ChildInfo>, _> = HashMap::new();
 		storage.insert(None, input.top);
 
 		// create a list of children keys to re-compute roots for
-		let child_delta = input.children.iter()
-			.map(|(storage_key, storage_child)| (storage_key.clone(), None, storage_child.child_info.clone()))
+		let child_delta = input.children_default.iter()
+			.map(|(_storage_key, storage_child)| (storage_child.child_info.clone(), None))
 			.collect::<Vec<_>>();
 
 		// make sure to persist the child storage
-		for (child_key, storage_child) in input.children {
-			storage.insert(Some((child_key, storage_child.child_info)), storage_child.data);
+		for (_child_key, storage_child) in input.children_default {
+			storage.insert(Some(storage_child.child_info), storage_child.data);
 		}
 
 		let storage_update = InMemoryBackend::from(storage);
@@ -386,13 +386,12 @@ impl<H: Hasher> StateBackend<H> for GenesisOrUnavailableState<H>
 
 	fn child_storage(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> ClientResult<Option<Vec<u8>>> {
 		match *self {
 			GenesisOrUnavailableState::Genesis(ref state) =>
-				Ok(state.child_storage(storage_key, child_info, key).expect(IN_MEMORY_EXPECT_PROOF)),
+				Ok(state.child_storage(child_info, key).expect(IN_MEMORY_EXPECT_PROOF)),
 			GenesisOrUnavailableState::Unavailable => Err(ClientError::NotAvailableOnLightClient),
 		}
 	}
@@ -407,13 +406,12 @@ impl<H: Hasher> StateBackend<H> for GenesisOrUnavailableState<H>
 
 	fn next_child_storage_key(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		key: &[u8],
 	) -> Result<Option<Vec<u8>>, Self::Error> {
 		match *self {
 			GenesisOrUnavailableState::Genesis(ref state) => Ok(
-				state.next_child_storage_key(storage_key, child_info, key)
+				state.next_child_storage_key(child_info, key)
 					.expect(IN_MEMORY_EXPECT_PROOF)
 			),
 			GenesisOrUnavailableState::Unavailable => Err(ClientError::NotAvailableOnLightClient),
@@ -436,27 +434,25 @@ impl<H: Hasher> StateBackend<H> for GenesisOrUnavailableState<H>
 
 	fn for_keys_in_child_storage<A: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		action: A,
 	) {
 		match *self {
 			GenesisOrUnavailableState::Genesis(ref state) =>
-				state.for_keys_in_child_storage(storage_key, child_info, action),
+				state.for_keys_in_child_storage(child_info, action),
 			GenesisOrUnavailableState::Unavailable => (),
 		}
 	}
 
 	fn for_child_keys_with_prefix<A: FnMut(&[u8])>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		prefix: &[u8],
 		action: A,
 	) {
 		match *self {
 			GenesisOrUnavailableState::Genesis(ref state) =>
-				state.for_child_keys_with_prefix(storage_key, child_info, prefix, action),
+				state.for_child_keys_with_prefix(child_info, prefix, action),
 			GenesisOrUnavailableState::Unavailable => (),
 		}
 	}
@@ -474,8 +470,7 @@ impl<H: Hasher> StateBackend<H> for GenesisOrUnavailableState<H>
 
 	fn child_storage_root<I>(
 		&self,
-		storage_key: &[u8],
-		child_info: ChildInfo,
+		child_info: &ChildInfo,
 		delta: I,
 	) -> (H::Out, bool, Self::Transaction)
 	where
@@ -483,7 +478,7 @@ impl<H: Hasher> StateBackend<H> for GenesisOrUnavailableState<H>
 	{
 		match *self {
 			GenesisOrUnavailableState::Genesis(ref state) => {
-				let (root, is_equal, _) = state.child_storage_root(storage_key, child_info, delta);
+				let (root, is_equal, _) = state.child_storage_root(child_info, delta);
 				(root, is_equal, Default::default())
 			},
 			GenesisOrUnavailableState::Unavailable =>

substrate/client/src/light/fetcher.rs

@@ -23,6 +23,7 @@ use std::marker::PhantomData;
 use hash_db::{HashDB, Hasher, EMPTY_PREFIX};
 use codec::{Decode, Encode};
 use sp_core::{convert_hash, traits::CodeExecutor};
+use sp_core::storage::{ChildInfo, ChildType};
 use sp_runtime::traits::{
 	Block as BlockT, Header as HeaderT, Hash, HashFor, NumberFor,
 	AtLeast32Bit, CheckedConversion,
@@ -135,7 +136,7 @@ impl<E, H, B: BlockT, S: BlockchainStorage<B>> LightDataChecker<E, H, B, S> {
 					number: request.last_block.0,
 				},
 				remote_max_block,
-				request.storage_key.as_ref().map(Vec::as_slice),
+				request.storage_key.as_ref(),
 				&request.key)
 			.map_err(|err| ClientError::ChangesTrieAccessFailed(err))?;
 			result.extend(result_range);
@@ -242,10 +243,14 @@ impl<E, Block, H, S> FetchChecker<Block> for LightDataChecker<E, H, Block, S>
 		request: &RemoteReadChildRequest<Block::Header>,
 		remote_proof: StorageProof,
 	) -> ClientResult<HashMap<Vec<u8>, Option<Vec<u8>>>> {
+		let child_info = match ChildType::from_prefixed_key(&request.storage_key) {
+			Some((ChildType::ParentKeyId, storage_key)) => ChildInfo::new_default(storage_key),
+			None => return Err("Invalid child type".into()),
+		};
 		read_child_proof_check::<H, _>(
 			convert_hash(request.header.state_root()),
 			remote_proof,
-			&request.storage_key,
+			&child_info,
 			request.keys.iter(),
 		).map_err(Into::into)
 	}
@@ -360,8 +365,6 @@ pub mod tests {
 	use sc_client_api::{StorageProvider, ProofProvider};
 	use sc_block_builder::BlockBuilderProvider;
 
-	const CHILD_INFO_1: ChildInfo<'static> = ChildInfo::new_default(b"unique_id_1");
-
 	type TestChecker = LightDataChecker<
 		NativeExecutor<substrate_test_runtime_client::LocalExecutor>,
 		BlakeTwo256,
@@ -411,11 +414,12 @@ pub mod tests {
 	fn prepare_for_read_child_proof_check() -> (TestChecker, Header, StorageProof, Vec<u8>) {
 		use substrate_test_runtime_client::DefaultTestClientBuilderExt;
 		use substrate_test_runtime_client::TestClientBuilderExt;
+		let child_info = ChildInfo::new_default(b"child1");
+		let child_info = &child_info;
 		// prepare remote client
 		let remote_client = substrate_test_runtime_client::TestClientBuilder::new()
 			.add_extra_child_storage(
-				b":child_storage:default:child1".to_vec(),
-				CHILD_INFO_1,
+				child_info,
 				b"key1".to_vec(),
 				b"value1".to_vec(),
 			).build();
@@ -428,15 +432,13 @@ pub mod tests {
 		// 'fetch' child read proof from remote node
 		let child_value = remote_client.child_storage(
 			&remote_block_id,
-			&StorageKey(b":child_storage:default:child1".to_vec()),
-			CHILD_INFO_1,
+			child_info,
 			&StorageKey(b"key1".to_vec()),
 		).unwrap().unwrap().0;
 		assert_eq!(b"value1"[..], child_value[..]);
 		let remote_read_proof = remote_client.read_child_proof(
 			&remote_block_id,
-			b":child_storage:default:child1",
-			CHILD_INFO_1,
+			child_info,
 			&mut std::iter::once("key1".as_bytes()),
 		).unwrap();
 
@@ -510,20 +512,18 @@ pub mod tests {
 
 	#[test]
 	fn storage_child_read_proof_is_generated_and_checked() {
+		let child_info = ChildInfo::new_default(&b"child1"[..]);
 		let (
 			local_checker,
 			remote_block_header,
 			remote_read_proof,
 			result,
 		) = prepare_for_read_child_proof_check();
-		let child_infos = CHILD_INFO_1.info();
 		assert_eq!((&local_checker as &dyn FetchChecker<Block>).check_read_child_proof(
 			&RemoteReadChildRequest::<Header> {
 				block: remote_block_header.hash(),
 				header: remote_block_header,
-				storage_key: b":child_storage:default:child1".to_vec(),
-				child_info: child_infos.0.to_vec(),
-				child_type: child_infos.1,
+				storage_key: child_info.prefixed_storage_key(),
 				keys: vec![b"key1".to_vec()],
 				retry_count: None,
 			},