multi: Add a channel.db migration.

The new migration removes the sweeper-last-tx top level bucket
from the channel.db database.

channeldb/migration31/log.go

@@ -0,0 +1,14 @@
+package migration31
+
+import (
+	"github.com/btcsuite/btclog"
+)
+
+// log is a logger that is initialized as disabled.  This means the package will
+// not perform any logging by default until a logger is set.
+var log = btclog.Disabled
+
+// UseLogger uses a specified Logger to output package logging info.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}

channeldb/migration31/migration.go

@@ -0,0 +1,23 @@
+package migration31
+
+import (
+	"errors"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	"github.com/lightningnetwork/lnd/kvdb"
+)
+
+// DeleteLastPublishedTxTLB deletes the top level bucket with the key
+// "sweeper-last-tx".
+func DeleteLastPublishedTxTLB(tx kvdb.RwTx) error {
+	log.Infof("Deleting top-level bucket: %x ...", lastTxBucketKey)
+
+	err := tx.DeleteTopLevelBucket(lastTxBucketKey)
+	if err != nil && !errors.Is(err, walletdb.ErrBucketNotFound) {
+		return err
+	}
+
+	log.Infof("Deleted top-level bucket: %x", lastTxBucketKey)
+
+	return nil
+}

channeldb/migration31/migration_test.go

@@ -0,0 +1,48 @@
+package migration31
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/channeldb/migtest"
+	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	hexStr = migtest.Hex
+
+	// lastTxBefore is the "sweeper-last-tx" bucket before the migration.
+	// We fill the last-tx value with a dummy hex string because the actual
+	// value is not important when deleting the bucket.
+	lastTxBefore = map[string]interface{}{
+		"sweeper-last-tx": hexStr("0000"),
+	}
+)
+
+// TestDeleteLastPublishTxTLP asserts that the sweeper-last-tx bucket is
+// properly deleted.
+func TestDeleteLastPublishTxTLP(t *testing.T) {
+	t.Parallel()
+
+	// Prime the database with the populated sweeper-last-tx bucket.
+	before := func(tx kvdb.RwTx) error {
+		return migtest.RestoreDB(tx, lastTxBucketKey, lastTxBefore)
+	}
+
+	// After the migration, ensure that the sweeper-last-tx bucket was
+	// properly deleted.
+	after := func(tx kvdb.RwTx) error {
+		err := migtest.VerifyDB(tx, lastTxBucketKey, nil)
+		require.ErrorContains(
+			t, err,
+			fmt.Sprintf("bucket %s not found", lastTxBucketKey),
+		)
+
+		return nil
+	}
+
+	migtest.ApplyMigration(
+		t, before, after, DeleteLastPublishedTxTLB, false,
+	)
+}

channeldb/migration31/store.go

@@ -0,0 +1,9 @@
+package migration31
+
+var (
+	// lastTxBucketKey is the key that points to a bucket containing a
+	// single item storing the last published sweep tx.
+	//
+	// maps: lastTxKey -> serialized_tx
+	lastTxBucketKey = []byte("sweeper-last-tx")
+)