storage: KV field -> store field in watchableStore

We need to access the underlying store to use its RangeEvents function.
It is not good to use unnecessary type conversion.

The underlying store is also needed for further store upon
watchableStore.

storage/watchable_store.go

@@ -25,7 +25,7 @@ import (
 type watchableStore struct {
 	mu sync.Mutex
 
-	KV
+	*store
 
 	// contains all unsynced watchers that needs to sync events that have happened
 	// TODO: use map to reduce cancel cost
@@ -41,7 +41,7 @@ type watchableStore struct {
 
 func newWatchableStore(path string) *watchableStore {
 	s := &watchableStore{
-		KV:     newStore(path),
+		store:  newStore(path),
 		synced: make(map[string][]*watcher),
 		stopc:  make(chan struct{}),
 	}
@@ -54,9 +54,9 @@ func (s *watchableStore) Put(key, value []byte) (rev int64) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
-	rev = s.KV.Put(key, value)
+	rev = s.store.Put(key, value)
 	// TODO: avoid this range
-	kvs, _, err := s.KV.Range(key, nil, 0, rev)
+	kvs, _, err := s.store.Range(key, nil, 0, rev)
 	if err != nil {
 		log.Panicf("unexpected range error (%v)", err)
 	}
@@ -72,11 +72,11 @@ func (s *watchableStore) DeleteRange(key, end []byte) (n, rev int64) {
 	defer s.mu.Unlock()
 
 	// TODO: avoid this range
-	kvs, _, err := s.KV.Range(key, end, 0, 0)
+	kvs, _, err := s.store.Range(key, end, 0, 0)
 	if err != nil {
 		log.Panicf("unexpected range error (%v)", err)
 	}
-	n, rev = s.KV.DeleteRange(key, end)
+	n, rev = s.store.DeleteRange(key, end)
 	for _, kv := range kvs {
 		s.handle(rev, storagepb.Event{
 			Type: storagepb.DELETE,
@@ -91,11 +91,11 @@ func (s *watchableStore) DeleteRange(key, end []byte) (n, rev int64) {
 func (s *watchableStore) TxnBegin() int64 {
 	s.mu.Lock()
 	s.tx = newOngoingTx()
-	return s.KV.TxnBegin()
+	return s.store.TxnBegin()
 }
 
 func (s *watchableStore) TxnPut(txnID int64, key, value []byte) (rev int64, err error) {
-	rev, err = s.KV.TxnPut(txnID, key, value)
+	rev, err = s.store.TxnPut(txnID, key, value)
 	if err == nil {
 		s.tx.put(string(key))
 	}
@@ -103,11 +103,11 @@ func (s *watchableStore) TxnPut(txnID int64, key, value []byte) (rev int64, err
 }
 
 func (s *watchableStore) TxnDeleteRange(txnID int64, key, end []byte) (n, rev int64, err error) {
-	kvs, _, err := s.KV.TxnRange(txnID, key, end, 0, 0)
+	kvs, _, err := s.store.TxnRange(txnID, key, end, 0, 0)
 	if err != nil {
 		log.Panicf("unexpected range error (%v)", err)
 	}
-	n, rev, err = s.KV.TxnDeleteRange(txnID, key, end)
+	n, rev, err = s.store.TxnDeleteRange(txnID, key, end)
 	if err == nil {
 		for _, kv := range kvs {
 			s.tx.del(string(kv.Key))
@@ -117,14 +117,14 @@ func (s *watchableStore) TxnDeleteRange(txnID int64, key, end []byte) (n, rev in
 }
 
 func (s *watchableStore) TxnEnd(txnID int64) error {
-	err := s.KV.TxnEnd(txnID)
+	err := s.store.TxnEnd(txnID)
 	if err != nil {
 		return err
 	}
 
-	_, rev, _ := s.KV.Range(nil, nil, 0, 0)
+	_, rev, _ := s.store.Range(nil, nil, 0, 0)
 	for k := range s.tx.putm {
-		kvs, _, err := s.KV.Range([]byte(k), nil, 0, 0)
+		kvs, _, err := s.store.Range([]byte(k), nil, 0, 0)
 		if err != nil {
 			log.Panicf("unexpected range error (%v)", err)
 		}
@@ -148,7 +148,7 @@ func (s *watchableStore) TxnEnd(txnID int64) error {
 func (s *watchableStore) Close() error {
 	close(s.stopc)
 	s.wg.Wait()
-	return s.KV.Close()
+	return s.store.Close()
 }
 
 func (s *watchableStore) Watcher(key []byte, prefix bool, startRev int64) (Watcher, CancelFunc) {
@@ -211,7 +211,7 @@ func (s *watchableStore) syncWatchersLoop() {
 
 // syncWatchers syncs the watchers in the unsyncd map.
 func (s *watchableStore) syncWatchers() {
-	_, curRev, _ := s.KV.Range(nil, nil, 0, 0)
+	_, curRev, _ := s.store.Range(nil, nil, 0, 0)
 
 	// filtering without allocating
 	// https://github.com/golang/go/wiki/SliceTricks#filtering-without-allocating
@@ -229,7 +229,7 @@ func (s *watchableStore) syncWatchers() {
 			nws = append(nws, w)
 			continue
 		}
-		evs, nextRev, err := s.KV.(*store).RangeEvents(w.key, end, int64(limit), w.cur)
+		evs, nextRev, err := s.store.RangeEvents(w.key, end, int64(limit), w.cur)
 		if err != nil {
 			w.stopWithError(err)
 			continue