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.

walletunlocker/service.go

@@ -13,6 +13,7 @@ import (
 	"github.com/lightningnetwork/lnd/aezeed"
 	"github.com/lightningnetwork/lnd/chanbackup"
 	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/btcwallet"
@@ -124,30 +125,28 @@ type UnlockerService struct {
 	// the WalletUnlocker service.
 	MacResponseChan chan []byte
 
-	chainDir       string
-	noFreelistSync bool
-	netParams      *chaincfg.Params
+	netParams *chaincfg.Params
 
 	// macaroonFiles is the path to the three generated macaroons with
 	// different access permissions. These might not exist in a stateless
 	// initialization of lnd.
 	macaroonFiles []string
 
-	// dbTimeout specifies the timeout value to use when opening the wallet
-	// database.
-	dbTimeout time.Duration
-
 	// resetWalletTransactions indicates that the wallet state should be
 	// reset on unlock to force a full chain rescan.
 	resetWalletTransactions bool
 
 	// LoaderOpts holds the functional options for the wallet loader.
 	loaderOpts []btcwallet.LoaderOption
+
+	// macaroonDB is an instance of a database backend that stores all
+	// macaroon root keys. This will be nil on initialization and must be
+	// set using the SetMacaroonDB method as soon as it's available.
+	macaroonDB kvdb.Backend
 }
 
 // New creates and returns a new UnlockerService.
-func New(chainDir string, params *chaincfg.Params, noFreelistSync bool,
-	macaroonFiles []string, dbTimeout time.Duration,
+func New(params *chaincfg.Params, macaroonFiles []string,
 	resetWalletTransactions bool,
 	loaderOpts []btcwallet.LoaderOption) *UnlockerService {
 
@@ -158,11 +157,8 @@ func New(chainDir string, params *chaincfg.Params, noFreelistSync bool,
 		// Make sure we buffer the channel is buffered so the main lnd
 		// goroutine isn't blocking on writing to it.
 		MacResponseChan:         make(chan []byte, 1),
-		chainDir:                chainDir,
 		netParams:               params,
 		macaroonFiles:           macaroonFiles,
-		dbTimeout:               dbTimeout,
-		noFreelistSync:          noFreelistSync,
 		resetWalletTransactions: resetWalletTransactions,
 		loaderOpts:              loaderOpts,
 	}
@@ -174,6 +170,12 @@ func (u *UnlockerService) SetLoaderOpts(loaderOpts []btcwallet.LoaderOption) {
 	u.loaderOpts = loaderOpts
 }
 
+// SetMacaroonDB can be used to inject the macaroon database after the unlocker
+// service has been hooked to the main RPC server.
+func (u *UnlockerService) SetMacaroonDB(macaroonDB kvdb.Backend) {
+	u.macaroonDB = macaroonDB
+}
+
 func (u *UnlockerService) newLoader(recoveryWindow uint32) (*wallet.Loader,
 	error) {
 
@@ -607,9 +609,8 @@ func (u *UnlockerService) ChangePassword(ctx context.Context,
 	// then close it again.
 	// Attempt to open the macaroon DB, unlock it and then change
 	// the passphrase.
-	netDir := btcwallet.NetworkDir(u.chainDir, u.netParams)
 	macaroonService, err := macaroons.NewService(
-		netDir, "lnd", in.StatelessInit, u.dbTimeout,
+		u.macaroonDB, "lnd", in.StatelessInit,
 	)
 	if err != nil {
 		return nil, err