Allow Backend::for_keys_in_child_storage to be aborted by the closure

client/db/src/bench.rs

@@ -350,7 +350,7 @@ impl<B: BlockT> StateBackend<HashFor<B>> for BenchmarkingState<B> {
 		}
 	}
 
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,

client/db/src/lib.rs

@@ -195,7 +195,7 @@ impl<B: BlockT> StateBackend<HashFor<B>> for RefTrackingState<B> {
 		self.state.for_key_values_with_prefix(prefix, f)
 	}
 
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,

client/db/src/storage_cache.rs

@@ -584,7 +584,7 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Cachin
 		self.state.exists_child_storage(child_info, key)
 	}
 
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,
@@ -766,7 +766,7 @@ impl<S: StateBackend<HashFor<B>>, B: BlockT> StateBackend<HashFor<B>> for Syncin
 		self.caching_state().exists_child_storage(child_info, key)
 	}
 
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,

client/light/src/backend.rs

@@ -441,7 +441,7 @@ impl<H: Hasher> StateBackend<H> for GenesisOrUnavailableState<H>
 		}
 	}
 
-	fn for_keys_in_child_storage<A: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<A: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		action: A,

primitives/state-machine/src/backend.rs

@@ -94,7 +94,8 @@ pub trait Backend<H: Hasher>: sp_std::fmt::Debug {
 	) -> Result<Option<StorageKey>, Self::Error>;
 
 	/// Retrieve all entries keys of child storage and call `f` for each of those keys.
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	/// Aborts as soon as `f` returns false.
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,
@@ -263,7 +264,7 @@ impl<'a, T: Backend<H>, H: Hasher> Backend<H> for &'a T {
 		(*self).child_storage(child_info, key)
 	}
 
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,

primitives/state-machine/src/ext.rs

@@ -422,6 +422,7 @@ where
 		self.overlay.clear_child_storage(child_info);
 		self.backend.for_keys_in_child_storage(child_info, |key| {
 			self.overlay.set_child_storage(child_info, key.to_vec(), None);
+			true
 		});
 	}
 

primitives/state-machine/src/proving_backend.rs

@@ -204,7 +204,7 @@ impl<'a, S, H> Backend<H> for ProvingBackend<'a, S, H>
 		self.0.child_storage(child_info, key)
 	}
 
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,

primitives/state-machine/src/trie_backend.rs

@@ -113,7 +113,7 @@ impl<S: TrieBackendStorage<H>, H: Hasher> Backend<H> for TrieBackend<S, H> where
 		self.essence.for_key_values_with_prefix(prefix, f)
 	}
 
-	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,

primitives/state-machine/src/trie_backend_essence.rs

@@ -190,7 +190,8 @@ impl<S: TrieBackendStorage<H>, H: Hasher> TrieBackendEssence<S, H> where H::Out:
 	}
 
 	/// Retrieve all entries keys of child storage and call `f` for each of those keys.
-	pub fn for_keys_in_child_storage<F: FnMut(&[u8])>(
+	/// Aborts as soon as `f` returns false.
+	pub fn for_keys_in_child_storage<F: FnMut(&[u8]) -> bool>(
 		&self,
 		child_info: &ChildInfo,
 		f: F,

primitives/trie/src/lib.rs

@@ -271,7 +271,8 @@ pub fn child_delta_trie_root<L: TrieConfiguration, I, A, B, DB, RD, V>(
 }
 
 /// Call `f` for all keys in a child trie.
-pub fn for_keys_in_child_trie<L: TrieConfiguration, F: FnMut(&[u8]), DB>(
+/// Aborts as soon as `f` returns false.
+pub fn for_keys_in_child_trie<L: TrieConfiguration, F: FnMut(&[u8]) -> bool, DB>(
 	keyspace: &[u8],
 	db: &DB,
 	root_slice: &[u8],
@@ -290,7 +291,9 @@ pub fn for_keys_in_child_trie<L: TrieConfiguration, F: FnMut(&[u8]), DB>(
 
 	for x in iter {
 		let (key, _) = x?;
-		f(&key);
+		if !f(&key) {
+			break;
+		}
 	}
 
 	Ok(())