lnd+walletunlocker: implement ChangePassword RPC

lnd.go

@@ -879,16 +879,25 @@ func waitForWalletPassword(grpcEndpoints, restEndpoints []string,
 	serverOpts []grpc.ServerOption, proxyOpts []grpc.DialOption,
 	tlsConf *tls.Config) (*WalletUnlockParams, error) {
 
-	// Set up a new PasswordService, which will listen
-	// for passwords provided over RPC.
+	// Set up a new PasswordService, which will listen for passwords
+	// provided over RPC.
 	grpcServer := grpc.NewServer(serverOpts...)
 
 	chainConfig := cfg.Bitcoin
 	if registeredChains.PrimaryChain() == litecoinChain {
 		chainConfig = cfg.Litecoin
 	}
+
+	// The macaroon files are passed to the wallet unlocker since they are
+	// also encrypted with the wallet's password. These files will be
+	// deleted within it and recreated when successfully changing the
+	// wallet's password.
+	macaroonFiles := []string{
+		filepath.Join(macaroonDatabaseDir, macaroons.DBFilename),
+		cfg.AdminMacPath, cfg.ReadMacPath, cfg.InvoiceMacPath,
+	}
 	pwService := walletunlocker.New(
-		chainConfig.ChainDir, activeNetParams.Params,
+		chainConfig.ChainDir, activeNetParams.Params, macaroonFiles,
 	)
 	lnrpc.RegisterWalletUnlockerServer(grpcServer, pwService)
 
@@ -951,9 +960,10 @@ func waitForWalletPassword(grpcEndpoints, restEndpoints []string,
 	wg.Wait()
 
 	// Wait for user to provide the password.
-	ltndLog.Infof("Waiting for wallet encryption password. " +
-		"Use `lncli create` to create wallet, or " +
-		"`lncli unlock` to unlock already created wallet.")
+	ltndLog.Infof("Waiting for wallet encryption password. Use `lncli " +
+		"create` to create a wallet, `lncli unlock` to unlock an " +
+		"existing wallet, or `lncli changepassword` to change the " +
+		"password of an existing wallet and unlock it.")
 
 	// We currently don't distinguish between getting a password to be used
 	// for creation or unlocking, as a new wallet db will be created if