channeldb: preserve db version during init

Keep the top-level bucket creation introduced by PR #9653, since initialized
DBs can still be missing newer buckets such as the historical channel bucket.

Do not let the metadata bucket created during init make a fresh DB look
initialized. Use strict metadata reads so a missing metadata/dbp key is distinct
from a present DB version, then write metadata/dbp for genuinely fresh DBs.

Existing DBs with a metadata bucket but missing metadata/dbp are left for the
migration recovery path instead of being treated as latest.

channeldb/db.go

@@ -502,21 +502,36 @@ func initChannelDB(db kvdb.Backend) error {
 			return err
 		}
 
+		meta := &Meta{}
+		metaErr := FetchMeta(meta, tx)
+
 		for _, tlb := range dbTopLevelBuckets {
 			if _, err := tx.CreateTopLevelBucket(tlb); err != nil {
 				return err
 			}
 		}
 
-		meta := &Meta{}
-		// Check if DB is already initialized.
-		err := FetchMeta(meta, tx)
-		if err == nil {
+		switch {
+		// Metadata with a DB version already exists. Required
+		// top-level buckets were created above, so init is complete.
+		case metaErr == nil:
+			return nil
+
+		// There is no metadata bucket at all, so this is a fresh DB.
+		// Initialize the DB version after creating the required
+		// top-level buckets.
+		case errors.Is(metaErr, ErrMetaNotFound):
+			meta.DbVersionNumber = getLatestDBVersion(dbVersions)
+			return putMeta(meta, tx)
+
+		// The DB already has a metadata bucket but no version key.
+		// Leave recovery to the migration path, which can infer a
+		// safe starting version before writing the version key.
+		case errors.Is(metaErr, ErrDBVersionNotFound):
 			return nil
 		}
 
-		meta.DbVersionNumber = getLatestDBVersion(dbVersions)
-		return putMeta(meta, tx)
+		return metaErr
 	}, func() {})
 	if err != nil {
 		return fmt.Errorf("unable to create new channeldb: %w", err)

channeldb/error.go

@@ -42,6 +42,10 @@ var (
 	// created.
 	ErrMetaNotFound = fmt.Errorf("unable to locate meta information")
 
+	// ErrDBVersionNotFound is returned when the meta bucket exists, but
+	// the DB version key hasn't been written.
+	ErrDBVersionNotFound = fmt.Errorf("unable to locate db version")
+
 	// ErrNoClosedChannels is returned when a node is queries for all the
 	// channels it has closed, but it hasn't yet closed any channels.
 	ErrNoClosedChannels = fmt.Errorf("no channel have been closed yet")

channeldb/meta.go

@@ -46,7 +46,7 @@ type Meta struct {
 
 // FetchMeta fetches the metadata from boltdb and returns filled meta structure.
 func (d *DB) FetchMeta() (*Meta, error) {
-	var meta *Meta
+	meta := &Meta{}
 
 	err := kvdb.View(d, func(tx kvdb.RTx) error {
 		return FetchMeta(meta, tx)
@@ -70,11 +70,11 @@ func FetchMeta(meta *Meta, tx kvdb.RTx) error {
 
 	data := metaBucket.Get(dbVersionKey)
 	if data == nil {
-		meta.DbVersionNumber = getLatestDBVersion(dbVersions)
-	} else {
-		meta.DbVersionNumber = byteOrder.Uint32(data)
+		return ErrDBVersionNotFound
 	}
 
+	meta.DbVersionNumber = byteOrder.Uint32(data)
+
 	return nil
 }
 

channeldb/meta_test.go

@@ -603,6 +603,88 @@ func TestFetchMeta(t *testing.T) {
 	require.NoError(t, err)
 
 	require.Equal(t, LatestDBVersion(), meta.DbVersionNumber)
+
+	err = db.View(func(tx walletdb.ReadTx) error {
+		metaBucket := tx.ReadBucket(metaBucket)
+		require.NotNil(t, metaBucket)
+
+		versionBytes := metaBucket.Get(dbVersionKey)
+		require.Len(t, versionBytes, 4)
+		require.Equal(
+			t, LatestDBVersion(), byteOrder.Uint32(versionBytes),
+		)
+
+		return nil
+	}, func() {})
+	require.NoError(t, err)
+}
+
+// TestFetchMetaMissingDBVersion asserts that metadata with no DB version key is
+// reported as incomplete metadata.
+func TestFetchMetaMissingDBVersion(t *testing.T) {
+	t.Parallel()
+
+	backend, cleanup, err := kvdb.GetTestBackend(t.TempDir(), "cdb")
+	require.NoError(t, err)
+	t.Cleanup(cleanup)
+
+	err = kvdb.Update(backend, func(tx kvdb.RwTx) error {
+		_, err := tx.CreateTopLevelBucket(metaBucket)
+
+		return err
+	}, func() {})
+	require.NoError(t, err)
+
+	db := &DB{
+		Backend: backend,
+	}
+
+	_, err = db.FetchMeta()
+	require.ErrorIs(t, err, ErrDBVersionNotFound)
+
+	err = kvdb.View(backend, func(tx kvdb.RTx) error {
+		meta := &Meta{}
+		err := FetchMeta(meta, tx)
+		require.ErrorIs(t, err, ErrDBVersionNotFound)
+
+		return nil
+	}, func() {})
+	require.NoError(t, err)
+}
+
+// TestInitChannelDBCreatesMissingTopLevelBuckets asserts that initialized DBs
+// with missing top-level buckets are repaired during initialization.
+func TestInitChannelDBCreatesMissingTopLevelBuckets(t *testing.T) {
+	t.Parallel()
+
+	backend, cleanup, err := kvdb.GetTestBackend(t.TempDir(), "cdb")
+	require.NoError(t, err)
+	t.Cleanup(cleanup)
+
+	err = kvdb.Update(backend, func(tx kvdb.RwTx) error {
+		meta := &Meta{
+			DbVersionNumber: LatestDBVersion(),
+		}
+
+		return putMeta(meta, tx)
+	}, func() {})
+	require.NoError(t, err)
+
+	err = kvdb.View(backend, func(tx kvdb.RTx) error {
+		require.Nil(t, tx.ReadBucket(historicalChannelBucket))
+
+		return nil
+	}, func() {})
+	require.NoError(t, err)
+
+	require.NoError(t, initChannelDB(backend))
+
+	err = kvdb.View(backend, func(tx kvdb.RTx) error {
+		require.NotNil(t, tx.ReadBucket(historicalChannelBucket))
+
+		return nil
+	}, func() {})
+	require.NoError(t, err)
 }
 
 // TestMarkerAndTombstone tests that markers like a tombstone can be added to a