[db] add Base() method

Author: dustinxie

db/db_versioned.go

@@ -32,6 +32,9 @@ type (
 	VersionedDB interface {
 		lifecycle.StartStopper
 
+		// Base returns the underlying KVStore
+		Base() KVStore
+
 		// Put insert or update a record identified by (namespace, key)
 		Put(uint64, string, []byte, []byte) error
 
@@ -59,8 +62,8 @@ type (
 
 	// Namespace specifies the name and key length of the versioned namespace
 	Namespace struct {
-		ns     string
-		keyLen uint32
+		Ns     string
+		KeyLen uint32
 	}
 )
 
@@ -70,7 +73,7 @@ type BoltDBVersionedOption func(*BoltDBVersioned)
 func VnsOption(ns ...Namespace) BoltDBVersionedOption {
 	return func(k *BoltDBVersioned) {
 		for _, v := range ns {
-			k.vns[v.ns] = int(v.keyLen)
+			k.vns[v.Ns] = int(v.KeyLen)
 		}
 	}
 }
@@ -122,6 +125,10 @@ func (b *BoltDBVersioned) addVersionedNamespace() error {
 	return nil
 }
 
+func (b *BoltDBVersioned) Base() KVStore {
+	return b.db
+}
+
 // Put writes a <key, value> record
 func (b *BoltDBVersioned) Put(version uint64, ns string, key, value []byte) error {
 	if !b.db.IsReady() {

db/kvstore_versioned.go

@@ -13,6 +13,11 @@ import (
 	"github.com/iotexproject/iotex-core/v2/pkg/lifecycle"
 )
 
+const (
+	// MetadataNamespace is the default namespace to store metadata
+	MetadataNamespace = "metadata"
+)
+
 type (
 	// KvVersioned is a versioned key-value store, where each key has multiple
 	// versions of value (corresponding to different heights in a blockchain)
@@ -44,6 +49,9 @@ type (
 	KvVersioned interface {
 		lifecycle.StartStopper
 
+		// Base returns the underlying KVStore
+		Base() KVStore
+
 		// Version returns the key's most recent version
 		Version(string, []byte) (uint64, error)
 
@@ -94,6 +102,10 @@ func (b *KvWithVersion) Stop(ctx context.Context) error {
 	return b.db.Stop(ctx)
 }
 
+func (b *KvWithVersion) Base() KVStore {
+	return b.db.Base()
+}
+
 // Put writes a <key, value> record
 func (b *KvWithVersion) Put(ns string, key, value []byte) error {
 	return b.db.Put(b.version, ns, key, value)