Fast sync child trie support. (#9239)

* state machine proofs.

* initial implementation

* Remove todo.

* Extend test and fix import.

* fix no proof, with proof ko.

* fix start at logic.

* Restore response size.

* Rework comments.

* Add explicit ref

* Use compact proof.

* ref change

* elaborato on empty change set condition.

* KeyValueState renaming.

* Do not add two time child trie with same root to sync reply.

* rust format

* Fix merge.

* fix warnings and fmt

* fmt

* update protocol id to V2

substrate/client/api/src/backend.rs

@@ -42,7 +42,7 @@ use std::{
 	sync::Arc,
 };
 
-pub use sp_state_machine::Backend as StateBackend;
+pub use sp_state_machine::{Backend as StateBackend, KeyValueStates};
 use std::marker::PhantomData;
 
 /// Extracts the state backend type for the given backend.

substrate/client/api/src/lib.rs

@@ -39,7 +39,7 @@ pub use proof_provider::*;
 pub use sp_blockchain as blockchain;
 pub use sp_blockchain::HeaderBackend;
 
-pub use sp_state_machine::{ExecutionStrategy, StorageProof};
+pub use sp_state_machine::{CompactProof, ExecutionStrategy, StorageProof};
 pub use sp_storage::{ChildInfo, PrefixedStorageKey, StorageData, StorageKey};
 
 /// Usage Information Provider interface

substrate/client/api/src/proof_provider.rs

@@ -17,8 +17,9 @@
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 //! Proof utilities
-use crate::{ChangesProof, StorageProof};
+use crate::{ChangesProof, CompactProof, StorageProof};
 use sp_runtime::{generic::BlockId, traits::Block as BlockT};
+use sp_state_machine::{KeyValueStates, KeyValueStorageLevel};
 use sp_storage::{ChildInfo, PrefixedStorageKey, StorageKey};
 
 /// Interface for providing block proving utilities.
@@ -71,31 +72,43 @@ pub trait ProofProvider<Block: BlockT> {
 		key: &StorageKey,
 	) -> sp_blockchain::Result<ChangesProof<Block::Header>>;
 
-	/// Given a `BlockId` iterate over all storage values starting at `start_key` exclusively,
-	/// building proofs until size limit is reached. Returns combined proof and the number of
-	/// collected keys.
+	/// Given a `BlockId` iterate over all storage values starting at `start_keys`.
+	/// Last `start_keys` element contains last accessed key value.
+	/// With multiple `start_keys`, first `start_keys` element is
+	/// the current storage key of of the last accessed child trie.
+	/// at last level the value to start at exclusively.
+	/// Proofs is build until size limit is reached and always include at
+	/// least one key following `start_keys`.
+	/// Returns combined proof and the numbers of collected keys.
 	fn read_proof_collection(
 		&self,
 		id: &BlockId<Block>,
-		start_key: &[u8],
+		start_keys: &[Vec<u8>],
 		size_limit: usize,
-	) -> sp_blockchain::Result<(StorageProof, u32)>;
+	) -> sp_blockchain::Result<(CompactProof, u32)>;
 
 	/// Given a `BlockId` iterate over all storage values starting at `start_key`.
 	/// Returns collected keys and values.
+	/// Returns the collected keys values content of the top trie followed by the
+	/// collected keys values of child tries.
+	/// Only child tries with their root part of the collected content or
+	/// related to `start_key` are attached.
+	/// For each collected state a boolean indicates if state reach
+	/// end.
 	fn storage_collection(
 		&self,
 		id: &BlockId<Block>,
-		start_key: &[u8],
+		start_key: &[Vec<u8>],
 		size_limit: usize,
-	) -> sp_blockchain::Result<Vec<(Vec<u8>, Vec<u8>)>>;
+	) -> sp_blockchain::Result<Vec<(KeyValueStorageLevel, bool)>>;
 
 	/// Verify read storage proof for a set of keys.
-	/// Returns collected key-value pairs and a flag indicating if iteration is complete.
+	/// Returns collected key-value pairs and a the nested state
+	/// depth of current iteration or 0 if completed.
 	fn verify_range_proof(
 		&self,
 		root: Block::Hash,
-		proof: StorageProof,
-		start_key: &[u8],
-	) -> sp_blockchain::Result<(Vec<(Vec<u8>, Vec<u8>)>, bool)>;
+		proof: CompactProof,
+		start_keys: &[Vec<u8>],
+	) -> sp_blockchain::Result<(KeyValueStates, usize)>;
 }