lib/db: Refactor: use a Lowlevel type underneath Instance (ref #5198) (#5212)

This adds a thin type that holds the state associated with the
leveldb.DB, leaving the huge Instance type more or less stateless. Also
moves some keying stuff into the DB package so that other packages need
not know the keying specifics.

(This does not, yet, fix the cmd/stindex program, in order to keep the
diff size down. Hence the keying constants are still exported.)

lib/db/set.go

@@ -21,12 +21,13 @@ import (
 	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sync"
+	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
 type FileSet struct {
 	folder   string
 	fs       fs.Filesystem
-	db       *Instance
+	db       *instance
 	blockmap *BlockMap
 	meta     *metadataTracker
 
@@ -66,12 +67,14 @@ func init() {
 	}
 }
 
-func NewFileSet(folder string, fs fs.Filesystem, db *Instance) *FileSet {
+func NewFileSet(folder string, fs fs.Filesystem, ll *Lowlevel) *FileSet {
+	db := newInstance(ll)
+
 	var s = FileSet{
 		folder:      folder,
 		fs:          fs,
 		db:          db,
-		blockmap:    NewBlockMap(db, db.folderIdx.ID([]byte(folder))),
+		blockmap:    NewBlockMap(ll, folder),
 		meta:        newMetadataTracker(),
 		updateMutex: sync.NewMutex(),
 	}
@@ -310,7 +313,7 @@ func (s *FileSet) SetIndexID(device protocol.DeviceID, id protocol.IndexID) {
 
 func (s *FileSet) MtimeFS() *fs.MtimeFS {
 	prefix := s.db.keyer.GenerateMtimesKey(nil, []byte(s.folder))
-	kv := NewNamespacedKV(s.db, string(prefix))
+	kv := NewNamespacedKV(s.db.Lowlevel, string(prefix))
 	return fs.NewMtimeFS(s.fs, kv)
 }
 
@@ -320,15 +323,26 @@ func (s *FileSet) ListDevices() []protocol.DeviceID {
 
 // DropFolder clears out all information related to the given folder from the
 // database.
-func DropFolder(db *Instance, folder string) {
+func DropFolder(ll *Lowlevel, folder string) {
+	db := newInstance(ll)
 	db.dropFolder([]byte(folder))
 	db.dropMtimes([]byte(folder))
 	db.dropFolderMeta([]byte(folder))
-	bm := &BlockMap{
-		db:     db,
-		folder: db.folderIdx.ID([]byte(folder)),
-	}
+	bm := NewBlockMap(ll, folder)
 	bm.Drop()
+
+	// Also clean out the folder ID mapping.
+	db.folderIdx.Delete([]byte(folder))
+}
+
+// DropDeltaIndexIDs removes all delta index IDs from the database.
+// This will cause a full index transmission on the next connection.
+func DropDeltaIndexIDs(db *Lowlevel) {
+	dbi := db.NewIterator(util.BytesPrefix([]byte{KeyTypeIndexID}), nil)
+	defer dbi.Release()
+	for dbi.Next() {
+		db.Delete(dbi.Key(), nil)
+	}
 }
 
 func normalizeFilenames(fs []protocol.FileInfo) {