multi: make macaroon DB remote compatible

The macaroon root keys should also be stored to the remote database if a
replicated backend such as etcd is used.
This commit refactors the macaroons service and wallet unlocker to
accept a kvdb backend directly instead of creating the bolt instance
automatically.

lncfg/db.go

@@ -10,7 +10,8 @@ import (
 )
 
 const (
-	dbName = "channel.db"
+	channelDBName  = "channel.db"
+	macaroonDBName = "macaroons.db"
 
 	BoltBackend                = "bolt"
 	EtcdBackend                = "etcd"
@@ -19,6 +20,9 @@ const (
 	// NSChannelDB is the namespace name that we use for the combined graph
 	// and channel state DB.
 	NSChannelDB = "channeldb"
+
+	// NSMacaroonDB is the namespace name that we use for the macaroon DB.
+	NSMacaroonDB = "macaroondb"
 )
 
 // DB holds database configuration for LND.
@@ -100,6 +104,10 @@ type DatabaseBackends struct {
 	// contains the chain height hint related data.
 	HeightHintDB kvdb.Backend
 
+	// MacaroonDB points to a database backend that stores the macaroon root
+	// keys.
+	MacaroonDB kvdb.Backend
+
 	// Remote indicates whether the database backends are remote, possibly
 	// replicated instances or local bbolt backed databases.
 	Remote bool
@@ -110,14 +118,27 @@ type DatabaseBackends struct {
 }
 
 // GetBackends returns a set of kvdb.Backends as set in the DB config.
-func (db *DB) GetBackends(ctx context.Context, dbPath string) (
-	*DatabaseBackends, error) {
+func (db *DB) GetBackends(ctx context.Context, chanDBPath,
+	walletDBPath string) (*DatabaseBackends, error) {
 
 	// We keep track of all the kvdb backends we actually open and return a
 	// reference to their close function so they can be cleaned up properly
 	// on error or shutdown.
 	closeFuncs := make(map[string]func() error)
 
+	// If we need to return early because of an error, we invoke any close
+	// function that has been initialized so far.
+	returnEarly := true
+	defer func() {
+		if !returnEarly {
+			return
+		}
+
+		for _, closeFunc := range closeFuncs {
+			_ = closeFunc()
+		}
+	}()
+
 	if db.Backend == EtcdBackend {
 		etcdBackend, err := kvdb.Open(
 			kvdb.EtcdBackendName, ctx, db.Etcd,
@@ -127,10 +148,12 @@ func (db *DB) GetBackends(ctx context.Context, dbPath string) (
 		}
 		closeFuncs[NSChannelDB] = etcdBackend.Close
 
+		returnEarly = false
 		return &DatabaseBackends{
 			GraphDB:      etcdBackend,
 			ChanStateDB:  etcdBackend,
 			HeightHintDB: etcdBackend,
+			MacaroonDB:   etcdBackend,
 			Remote:       true,
 			CloseFuncs:   closeFuncs,
 		}, nil
@@ -138,8 +161,8 @@ func (db *DB) GetBackends(ctx context.Context, dbPath string) (
 
 	// We're using all bbolt based databases by default.
 	boltBackend, err := kvdb.GetBoltBackend(&kvdb.BoltBackendConfig{
-		DBPath:            dbPath,
-		DBFileName:        dbName,
+		DBPath:            chanDBPath,
+		DBFileName:        channelDBName,
 		DBTimeout:         db.Bolt.DBTimeout,
 		NoFreelistSync:    !db.Bolt.SyncFreelist,
 		AutoCompact:       db.Bolt.AutoCompact,
@@ -150,10 +173,25 @@ func (db *DB) GetBackends(ctx context.Context, dbPath string) (
 	}
 	closeFuncs[NSChannelDB] = boltBackend.Close
 
+	macaroonBackend, err := kvdb.GetBoltBackend(&kvdb.BoltBackendConfig{
+		DBPath:            walletDBPath,
+		DBFileName:        macaroonDBName,
+		DBTimeout:         db.Bolt.DBTimeout,
+		NoFreelistSync:    !db.Bolt.SyncFreelist,
+		AutoCompact:       db.Bolt.AutoCompact,
+		AutoCompactMinAge: db.Bolt.AutoCompactMinAge,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("error opening macaroon DB: %v", err)
+	}
+	closeFuncs[NSMacaroonDB] = macaroonBackend.Close
+
+	returnEarly = false
 	return &DatabaseBackends{
 		GraphDB:      boltBackend,
 		ChanStateDB:  boltBackend,
 		HeightHintDB: boltBackend,
+		MacaroonDB:   macaroonBackend,
 		CloseFuncs:   closeFuncs,
 	}, nil
 }