Access child storage over RPC. (#2586)

* Access child storage over RPC.

* Address review grumbles.

* Test happy case in child_storage rpc.

* Remove stray printlns

* Fix line widths.

* Bump runtime again.

* Fix genesis storage root calculation for light clients.

* Don't pass values to full_storage_root child_delta.

substrate/core/state-machine/src/backend.rs

@@ -88,7 +88,22 @@ pub trait Backend<H: Hasher> {
 	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)>;
 
 	/// Get all keys with given prefix
-	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>>;
+	fn keys(&self, prefix: &[u8]) -> Vec<Vec<u8>> {
+		let mut all = Vec::new();
+		self.for_keys_with_prefix(prefix, |k| all.push(k.to_vec()));
+		all
+	}
+
+	/// Get all keys of child storage with given prefix
+	fn child_keys(&self, child_storage_key: &[u8], prefix: &[u8]) -> Vec<Vec<u8>> {
+		let mut all = Vec::new();
+		self.for_keys_in_child_storage(child_storage_key, |k| {
+			if k.starts_with(prefix) {
+				all.push(k.to_vec());
+			}
+		});
+		all
+	}
 
 	/// Try convert into trie backend.
 	fn try_into_trie_backend(self) -> Option<TrieBackend<Self::TrieBackendStorage, H>>;
@@ -286,7 +301,9 @@ impl<H: Hasher> Backend<H> for InMemory<H> {
 		I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
 		<H as Hasher>::Out: Ord,
 	{
-		let existing_pairs = self.inner.get(&None).into_iter().flat_map(|map| map.iter().map(|(k, v)| (k.clone(), Some(v.clone()))));
+		let existing_pairs = self.inner.get(&None)
+			.into_iter()
+			.flat_map(|map| map.iter().map(|(k, v)| (k.clone(), Some(v.clone()))));
 
 		let transaction: Vec<_> = delta.into_iter().collect();
 		let root = trie_root::<H, _, _, _>(existing_pairs.chain(transaction.iter().cloned())
@@ -307,7 +324,9 @@ impl<H: Hasher> Backend<H> for InMemory<H> {
 	{
 		let storage_key = storage_key.to_vec();
 
-		let existing_pairs = self.inner.get(&Some(storage_key.clone())).into_iter().flat_map(|map| map.iter().map(|(k, v)| (k.clone(), Some(v.clone()))));
+		let existing_pairs = self.inner.get(&Some(storage_key.clone()))
+			.into_iter()
+			.flat_map(|map| map.iter().map(|(k, v)| (k.clone(), Some(v.clone()))));
 
 		let transaction: Vec<_> = delta.into_iter().collect();
 		let root = child_trie_root::<H, _, _, _>(
@@ -326,11 +345,24 @@ impl<H: Hasher> Backend<H> for InMemory<H> {
 	}
 
 	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
-		self.inner.get(&None).into_iter().flat_map(|map| map.iter().map(|(k, v)| (k.clone(), v.clone()))).collect()
+		self.inner.get(&None)
+			.into_iter()
+			.flat_map(|map| map.iter().map(|(k, v)| (k.clone(), v.clone())))
+			.collect()
 	}
 
-	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>> {
-		self.inner.get(&None).into_iter().flat_map(|map| map.keys().filter(|k| k.starts_with(prefix)).cloned()).collect()
+	fn keys(&self, prefix: &[u8]) -> Vec<Vec<u8>> {
+		self.inner.get(&None)
+			.into_iter()
+			.flat_map(|map| map.keys().filter(|k| k.starts_with(prefix)).cloned())
+			.collect()
+	}
+
+	fn child_keys(&self, storage_key: &[u8], prefix: &[u8]) -> Vec<Vec<u8>> {
+		self.inner.get(&Some(storage_key.to_vec()))
+			.into_iter()
+			.flat_map(|map| map.keys().filter(|k| k.starts_with(prefix)).cloned())
+			.collect()
 	}
 
 	fn try_into_trie_backend(

substrate/core/state-machine/src/proving_backend.rs

@@ -162,10 +162,14 @@ impl<'a, S, H> Backend<H> for ProvingBackend<'a, S, H>
 		self.backend.pairs()
 	}
 
-	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>> {
+	fn keys(&self, prefix: &[u8]) -> Vec<Vec<u8>> {
 		self.backend.keys(prefix)
 	}
 
+	fn child_keys(&self, child_storage_key: &[u8], prefix: &[u8]) -> Vec<Vec<u8>> {
+		self.backend.child_keys(child_storage_key, prefix)
+	}
+
 	fn storage_root<I>(&self, delta: I) -> (H::Out, Self::Transaction)
 		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
 	{

substrate/core/state-machine/src/trie_backend.rs

@@ -105,7 +105,7 @@ impl<S: TrieBackendStorage<H>, H: Hasher> Backend<H> for TrieBackend<S, H> where
 		}
 	}
 
-	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>> {
+	fn keys(&self, prefix: &[u8]) -> Vec<Vec<u8>> {
 		let mut read_overlay = S::Overlay::default();
 		let eph = Ephemeral::new(self.essence.backend_storage(), &mut read_overlay);