lncfg: add new GetBackends which returns active DB backends

In this commit, we modify the existing `GetBackend` method to now be
called `GetBackends`. This new method will populate a new `RemoteDB`
attribute based on if the replicated backend is active or not. As is,
the local backend is used everywhere. An upcoming commit will once again
re-enable the remote backend, in a hybrid manner.

lncfg/db.go

@@ -48,18 +48,50 @@ func (db *DB) Validate() error {
 	return nil
 }
 
-// GetBackend returns a kvdb.Backend as set in the DB config.
+// DatabaseBackends is a two-tuple that holds the set of active database
-func (db *DB) GetBackend(ctx context.Context, dbPath string,
+// backends for the daemon. The two backends we expose are the local database
-	networkName string) (kvdb.Backend, error) {
+// backend, and the remote backend. The LocalDB attribute will always be
+// populated. However, the remote DB will only be set if a replicated database
+// is active.
+type DatabaseBackends struct {
+	// LocalDB points to the local non-replicated backend.
+	LocalDB kvdb.Backend
+
+	// RemoteDB points to a possibly networked replicated backend. If no
+	// replicated backend is active, then this pointer will be nil.
+	RemoteDB kvdb.Backend
+}
+
+// GetBackends returns a set of kvdb.Backends as set in the DB config.  The
+// local database will ALWAYS be non-nil, while the remote database will only
+// be populated if etcd is specified.
+func (db *DB) GetBackends(ctx context.Context, dbPath string,
+	networkName string) (*DatabaseBackends, error) {
+
+	var (
+		localDB, remoteDB kvdb.Backend
+		err               error
+	)
 
 	if db.Backend == EtcdBackend {
 		// Prefix will separate key/values in the db.
-		return kvdb.GetEtcdBackend(ctx, networkName, db.Etcd)
+		remoteDB, err = kvdb.GetEtcdBackend(ctx, networkName, db.Etcd)
+		if err != nil {
+			return nil, err
+		}
 	}
 
-	// The implementation by walletdb accepts "noFreelistSync" as the
+	localDB, err = kvdb.GetBoltBackend(
-	// second parameter, so we negate here.
+		dbPath, dbName, !db.Bolt.SyncFreelist,
-	return kvdb.GetBoltBackend(dbPath, dbName, !db.Bolt.SyncFreelist)
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return &DatabaseBackends{
+		LocalDB:  localDB,
+		RemoteDB: remoteDB,
+	}, nil
 }
 
 // Compile-time constraint to ensure Workers implements the Validator interface.

lnd.go

@@ -251,6 +251,7 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 		"minutes...")
 
 	startOpenTime := time.Now()
+
 	ctx := context.Background()
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
@@ -260,8 +261,8 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 			cfg.DB.Bolt.SyncFreelist)
 	}
 
-	chanDbBackend, err := cfg.DB.GetBackend(ctx,
+	databaseBackends, err := cfg.DB.GetBackends(
-		cfg.localDatabaseDir(), cfg.networkName(),
+		ctx, cfg.localDatabaseDir(), cfg.networkName(),
 	)
 	if err != nil {
 		ltndLog.Error(err)
@@ -271,7 +272,7 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 	// Open the channeldb, which is dedicated to storing channel, and
 	// network related metadata.
 	chanDB, err := channeldb.CreateWithBackend(
-		chanDbBackend,
+		databaseBackends.LocalDB,
 		channeldb.OptionSetRejectCacheSize(cfg.Caches.RejectCacheSize),
 		channeldb.OptionSetChannelCacheSize(cfg.Caches.ChannelCacheSize),
 		channeldb.OptionDryRunMigration(cfg.DryRunMigration),