Make genesis state locally-available on light client (#1622)

* make genesis state available on light client

* RemoteOrLocalCallExecutor

* code_is_executed_locally_or_remotely

* OnDemandOrGenesisState tests

* some comments

core/client/src/backend.rs

@@ -177,4 +177,7 @@ pub trait RemoteBackend<Block, H>: Backend<Block, H>
 where
 	Block: BlockT,
 	H: Hasher<Out=Block::Hash>,
-{}
+{
+	/// Returns true if the state for given block is available locally.
+	fn is_local_state_available(&self, block: &BlockId<Block>) -> bool;
+}

core/client/src/call_executor.rs

@@ -154,7 +154,7 @@ impl<B, E> Clone for LocalCallExecutor<B, E> where E: Clone {
 
 impl<B, E, Block> CallExecutor<Block, Blake2Hasher> for LocalCallExecutor<B, E>
 where
-	B: backend::LocalBackend<Block, Blake2Hasher>,
+	B: backend::Backend<Block, Blake2Hasher>,
 	E: CodeExecutor<Blake2Hasher> + RuntimeInfo,
 	Block: BlockT<Hash=H256>,
 {

core/client/src/in_mem.rs

@@ -465,17 +465,11 @@ where
 	}
 
 	fn reset_storage(&mut self, mut top: StorageMap, children: ChildrenStorageMap) -> error::Result<H::Out> {
-		if top.iter().any(|(k, _)| well_known_keys::is_child_storage_key(k)) {
-			return Err(error::ErrorKind::GenesisInvalid.into());
-		}
+		check_genesis_storage(&top, &children)?;
 
 		let mut transaction: Vec<(Option<Vec<u8>>, Vec<u8>, Option<Vec<u8>>)> = Default::default();
 
 		for (child_key, child_map) in children {
-			if !well_known_keys::is_child_storage_key(&child_key) {
-				return Err(error::ErrorKind::GenesisInvalid.into());
-			}
-
 			let (root, is_default, update) = self.old_state.child_storage_root(&child_key, child_map.into_iter().map(|(k, v)| (k, Some(v))));
 			transaction.consolidate(update);
 
@@ -662,6 +656,19 @@ where
 	H::Out: HeapSizeOf + Ord,
 {}
 
+impl<Block, H> backend::RemoteBackend<Block, H> for Backend<Block, H>
+where
+	Block: BlockT,
+	H: Hasher<Out=Block::Hash>,
+	H::Out: HeapSizeOf + Ord,
+{
+	fn is_local_state_available(&self, block: &BlockId<Block>) -> bool {
+		self.blockchain.expect_block_number_from_id(block)
+			.map(|num| num.is_zero())
+			.unwrap_or(false)
+	}
+}
+
 impl<Block: BlockT> Cache<Block> {
 	fn insert(&self, at: Block::Hash, authorities: Option<Vec<AuthorityIdFor<Block>>>) {
 		self.authorities_at.write().insert(at, authorities);
@@ -708,6 +715,19 @@ pub fn cache_authorities_at<Block: BlockT>(
 	blockchain.cache.insert(at, authorities);
 }
 
+/// Check that genesis storage is valid.
+pub fn check_genesis_storage(top: &StorageMap, children: &ChildrenStorageMap) -> error::Result<()> {
+	if top.iter().any(|(k, _)| well_known_keys::is_child_storage_key(k)) {
+		return Err(error::ErrorKind::GenesisInvalid.into());
+	}
+
+	if children.keys().any(|child_key| !well_known_keys::is_child_storage_key(&child_key)) {
+		return Err(error::ErrorKind::GenesisInvalid.into());
+	}
+
+	Ok(())
+}
+
 #[cfg(test)]
 mod tests {
 	use std::sync::Arc;