allow save methods to return a object

lib/src/kdbx_file.dart

@@ -18,7 +18,7 @@ import 'package:xml/xml.dart' as xml;
 
 final _logger = Logger('kdbx_file');
 
-typedef FileSaveCallback = Future<int> Function(Uint8List bytes);
+typedef FileSaveCallback<T> = Future<T> Function(Uint8List bytes);
 
 class KdbxFile {
   KdbxFile(
@@ -57,7 +57,15 @@ class KdbxFile {
   Stream<Set<KdbxObject>> get dirtyObjectsChanged =>
       _dirtyObjectsChanged.stream;
 
-  Future<Uint8List> save([FileSaveCallback? saveBytes]) async {
+  static final FileSaveCallback<Uint8List> _saveToBytes =
+      (bytes) async => bytes;
+
+  // @Deprecated('Use [saveTo] instead.')
+  Future<Uint8List> save() async {
+    return kdbxFormat.save(this, _saveToBytes);
+  }
+
+  Future<T> saveTo<T>(FileSaveCallback<T> saveBytes) {
     return kdbxFormat.save(this, saveBytes);
   }
 

lib/src/kdbx_format.dart

@@ -577,19 +577,19 @@ class KdbxFormat {
   }
 
   /// Saves the given file.
-  Future<Uint8List> save(KdbxFile file, FileSaveCallback? saveBytes) async {
+  Future<T> save<T>(KdbxFile file, FileSaveCallback<T> saveBytes) async {
     _logger.finer('Saving ${file.body.rootGroup.uuid} '
         '(locked: ${file.saveLock.locked})');
     return file.saveLock.synchronized(() async {
       final savedAt = TimeSequence.now();
       final bytes = await _saveSynchronized(file);
-      if (saveBytes != null) {
+
       _logger.fine('Saving bytes.');
-        final byteCount = await saveBytes(bytes);
-        _logger.fine('Saved bytes. $byteCount');
-      }
+      final ret = await saveBytes(bytes);
+      _logger.fine('Saved bytes.');
+
       file.onSaved(savedAt);
-      return bytes;
+      return ret;
     });
   }
 

test/kdbx_dirty_save_test.dart

@@ -14,12 +14,11 @@ void main() {
       await file.save();
 
       const value1 = 'new';
-      const value2 = 'new2';
       entry.setString(TestUtil.keyTitle, PlainValue(value1));
       entry2.setString(TestUtil.keyTitle, PlainValue(value1));
       expect(file.isDirty, isTrue);
 
-      await file.save((bytes) async {
+      await file.saveTo((bytes) async {
         // must still be dirty as long as we are not finished saving.
         expect(file.isDirty, isTrue);
         expect(entry.isDirty, isTrue);
@@ -42,7 +41,7 @@ void main() {
 
       entry.setString(TestUtil.keyTitle, PlainValue(value2));
       entry2.setString(TestUtil.keyTitle, PlainValue(value2));
-      await file.save((bytes) async {
+      await file.saveTo((bytes) async {
         // must still be dirty as long as we are not finished saving.
         expect(file.isDirty, isTrue);
         expect(entry.isDirty, isTrue);