feat(store/v2): Fallback to SC on queries (#19090)

store/root/store.go

@@ -105,13 +105,13 @@ func (s *Store) StateLatest() (uint64, store.ReadOnlyRootStore, error) {
 }
 
 func (s *Store) StateAt(v uint64) (store.ReadOnlyRootStore, error) {
-	// TODO(bez): Ensure the version <v> exists. We can utilize the GetCommitInfo()
-	// SC method once available.
+	// TODO(bez): We may want to avoid relying on the SC metadata here. Instead,
+	// we should add a VersionExists() method to the VersionedDatabase interface.
 	//
-	// Ref: https://github.com/cosmos/cosmos-sdk/pull/18736
-	// if err := s.stateCommitment.GetCommitInfo(v); err != nil {
-	// 	return nil, fmt.Errorf("failed to get commit info for version %d: %w", v, err)
-	// }
+	// Ref: https://github.com/cosmos/cosmos-sdk/issues/19091
+	if cInfo, err := s.stateCommitment.GetCommitInfo(v); err != nil || cInfo == nil {
+		return nil, fmt.Errorf("failed to get commit info for version %d: %w", v, err)
+	}
 
 	return NewReadOnlyAdapter(v, s), nil
 }
@@ -174,8 +174,23 @@ func (s *Store) Query(storeKey string, version uint64, key []byte, prove bool) (
 	}
 
 	val, err := s.stateStore.Get(storeKey, version, key)
-	if err != nil {
-		return store.QueryResult{}, err
+	if err != nil || val == nil {
+		// fallback to querying SC backend if not found in SS backend
+		//
+		// Note, this should only used during migration, i.e. while SS and IAVL v2
+		// are being asynchronously synced.
+		if val == nil {
+			bz, scErr := s.stateCommitment.Get(storeKey, version, key)
+			if scErr != nil {
+				return store.QueryResult{}, fmt.Errorf("failed to query SC store: %w", scErr)
+			}
+
+			val = bz
+		}
+
+		if err != nil {
+			return store.QueryResult{}, fmt.Errorf("failed to query SS store: %w", err)
+		}
 	}
 
 	result := store.QueryResult{
@@ -187,7 +202,7 @@ func (s *Store) Query(storeKey string, version uint64, key []byte, prove bool) (
 	if prove {
 		result.ProofOps, err = s.stateCommitment.GetProof(storeKey, version, key)
 		if err != nil {
-			return store.QueryResult{}, err
+			return store.QueryResult{}, fmt.Errorf("failed to get SC store proof: %w", err)
 		}
 	}
 

store/root/store_test.go

@@ -104,6 +104,31 @@ func (s *RootStoreTestSuite) TestQuery() {
 	s.Require().Equal([]byte("foo"), result.ProofOps[0].Key)
 }
 
+func (s *RootStoreTestSuite) TestGetFallback() {
+	sc := s.rootStore.GetStateCommitment()
+
+	// create a changeset and commit it to SC ONLY
+	cs := store.NewChangeset()
+	cs.Add(testStoreKey, []byte("foo"), []byte("bar"))
+
+	err := sc.WriteBatch(cs)
+	s.Require().NoError(err)
+
+	ci := sc.WorkingCommitInfo(1)
+	_, err = sc.Commit(ci.Version)
+	s.Require().NoError(err)
+
+	// ensure we can query for the key, which should fallback to SC
+	qResult, err := s.rootStore.Query(testStoreKey, 1, []byte("foo"), false)
+	s.Require().NoError(err)
+	s.Require().Equal([]byte("bar"), qResult.Value)
+
+	// non-existent key
+	qResult, err = s.rootStore.Query(testStoreKey, 1, []byte("non_existent_key"), false)
+	s.Require().NoError(err)
+	s.Require().Nil(qResult.Value)
+}
+
 func (s *RootStoreTestSuite) TestQueryProof() {
 	cs := store.NewChangeset()
 	// testStoreKey