waved: add wallet.dbbackend for the lwwallet backend

Expose lwwallet's wallet database backend selection as a daemon config
option and CLI flag, so the network directory can be made to hold SQLite
databases only. The default is unchanged.

The value is rejected at config-validation time rather than passed
through blindly: an unknown backend would otherwise only surface when
the operator first tries to create or unlock the wallet, which for an
auto-unlocking daemon means a failed startup with the cause several
layers down.

The option is deliberately not settable per wallet lifetime: lwwallet
refuses to resolve a backend whose counterpart's database file is
already present, so a change on an initialized network directory fails
with the file it found rather than creating an empty second wallet.

Author: guggero

cmd/waved/main.go

@@ -338,6 +338,10 @@ func registerWalletFlags(f *pflag.FlagSet, cfg *waved.Config) {
 		"wallet.esploraurl", cfg.Wallet.EsploraURL,
 		"esplora REST API URL (required for lwwallet)",
 	)
+	f.String(
+		"wallet.dbbackend", cfg.Wallet.DBBackend,
+		"wallet database backend for lwwallet (bolt, sqlite)",
+	)
 	f.String(
 		"wallet.feeurl", cfg.Wallet.FeeURL,
 		"fee-estimate JSON endpoint URL (required for btcwallet)",

docs/daemon_cli_guide.md

@@ -130,6 +130,7 @@ waved \
 | `--wallet.btcwallet_filterheaderssource` | | Filter header import source for btcwallet fast sync |
 | `--wallet.pollinterval` | `30s` | Esplora poll interval (lwwallet only) |
 | `--wallet.recoverywindow` | `100` | Address look-ahead window (lwwallet only) |
+| `--wallet.dbbackend` | `bolt` | Wallet database backend (lwwallet only): `bolt` or `sqlite`; fixed once the wallet is created |
 | `--wallet.password_file` | | Auto-unlock password file path (lwwallet/btcwallet) |
 | `--lnd.host` | `localhost:10009` | lnd gRPC address |
 | `--lnd.tlspath` | | Path to lnd TLS certificate |

sample-waved.conf

@@ -192,6 +192,13 @@
 # Address recovery look-ahead window for lwwallet.
 # wallet.recoverywindow=100
 
+# Database backend for the lwwallet wallet database: bolt or sqlite. Both keep
+# the database in the network data directory. Pick sqlite to keep the directory
+# free of a BoltDB file, for instance so a backup can copy it with a single
+# storage engine's guarantees. The backend cannot be changed once the wallet
+# has been created.
+# wallet.dbbackend=bolt
+
 # Path to a file containing the wallet password for auto-unlock at startup.
 # wallet.password_file=
 

waved/config.go

@@ -1123,6 +1123,13 @@ type WalletConfig struct {
 	// automatically without requiring an UnlockWallet RPC call.
 	PasswordFile string `mapstructure:"password_file"`
 
+	// DBBackend selects the database engine the lwwallet backend
+	// keeps btcwallet's wallet database in: "bolt" (the default) uses
+	// the classic BoltDB file, "sqlite" uses a SQLite database so the
+	// network directory holds no BoltDB file at all. Both live in the
+	// network directory. Only used when Type is "lwwallet".
+	DBBackend string `mapstructure:"dbbackend"`
+
 	// BtcwalletPeers is a list of host:port addresses for neutrino
 	// to connect to exclusively (no DNS seeding). Only used when
 	// Type is "btcwallet".
@@ -1198,6 +1205,7 @@ func DefaultConfig() *Config {
 			Type:           DefaultWalletType,
 			PollInterval:   DefaultEsploraPollInterval,
 			RecoveryWindow: DefaultRecoveryWindow,
+			DBBackend:      lwwallet.DBBackendBolt,
 		},
 		Swap: &SwapConfig{
 			ServerTransport: RPCTransportGRPC,
@@ -1401,6 +1409,20 @@ func (c *Config) validateWalletConfig() error {
 			c.Wallet.EsploraURL = esploraURL
 		}
 
+		// Reject an unknown database backend here rather than at
+		// wallet-unlock time: a typo would otherwise only surface
+		// once the operator tries to use the wallet.
+		switch c.Wallet.DBBackend {
+		case "", lwwallet.DBBackendBolt, lwwallet.DBBackendSQLite:
+			// An empty value keeps the lwwallet default.
+
+		default:
+			return fmt.Errorf("unknown wallet.dbbackend %q, valid "+
+				"values: %s, %s", c.Wallet.DBBackend,
+				lwwallet.DBBackendBolt,
+				lwwallet.DBBackendSQLite)
+		}
+
 	case WalletTypeBtcwallet:
 		// Neutrino has no mempool visibility, so fee estimation
 		// always requires an external API. An empty value falls

waved/config_wallet_dbbackend_test.go

@@ -0,0 +1,59 @@
+package waved
+
+import (
+	"testing"
+
+	"github.com/lightninglabs/wavelength/lwwallet"
+	"github.com/stretchr/testify/require"
+)
+
+// TestConfigValidateWalletDBBackend checks that the lwwallet database
+// backend selector only accepts the backends lwwallet implements, so a
+// typo fails at startup instead of at wallet-unlock time.
+func TestConfigValidateWalletDBBackend(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		backend string
+		wantErr string
+	}{
+		{
+			name: "unset keeps the default",
+		},
+		{
+			name:    "bolt",
+			backend: lwwallet.DBBackendBolt,
+		},
+		{
+			name:    "sqlite",
+			backend: lwwallet.DBBackendSQLite,
+		},
+		{
+			name:    "unknown backend",
+			backend: "postgres",
+			wantErr: "unknown wallet.dbbackend",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			cfg := DefaultConfig()
+			cfg.Network = "regtest"
+			cfg.Wallet.Type = WalletTypeLwwallet
+			cfg.Wallet.EsploraURL = "http://127.0.0.1:3000"
+			cfg.Wallet.DBBackend = tc.backend
+
+			err := cfg.Validate()
+			if tc.wantErr != "" {
+				require.ErrorContains(t, err, tc.wantErr)
+
+				return
+			}
+
+			require.NoError(t, err)
+		})
+	}
+}

waved/rpc_wallet.go

@@ -696,14 +696,15 @@ func isWrongPassphraseErr(err error) bool {
 
 // selfManagedWalletExists probes whether a wallet database has been
 // created for the configured self-managed wallet backend. Only the
-// chain params and data directory are consulted; the probe does not
-// open the database on native builds.
+// chain params, data directory and database backend are consulted; the
+// probe does not open a database that does not exist yet.
 func (s *Server) selfManagedWalletExists() (bool, error) {
 	switch s.cfg.Wallet.Type {
 	case WalletTypeLwwallet:
 		return lwwallet.WalletExists(lwwallet.Config{
 			ChainParams: s.chainParams,
 			DBDir:       s.cfg.NetworkDir(),
+			DBBackend:   s.cfg.Wallet.DBBackend,
 		})
 
 	case WalletTypeBtcwallet:

waved/server.go

@@ -1993,6 +1993,7 @@ func (s *Server) startLwwallet(ctx context.Context, seed []byte,
 		PollInterval:   pollInterval,
 		RecoveryWindow: recoveryWindow,
 		DBDir:          networkDir,
+		DBBackend:      s.cfg.Wallet.DBBackend,
 		Log:            fn.Some(s.subLogger(lwwallet.Subsystem)),
 	})
 	if err != nil {