getSnapshotMetadata method

Implementation

@override
Future<SessionSnapshot?> getSnapshotMetadata(
  String snapshotId, {
  Map<String, dynamic>? context,
}) async {
  normalizeGetSnapshotOptions(snapshotId: snapshotId);
  final file = await _fileFor(snapshotId, context);
  if (!file.existsSync()) return null;
  // Let a corrupt / unreadable file throw, exactly as the full read
  // (`_snapshotById`) does, so a caller can tell corruption apart from "not
  // found" (a truncated file must not read as a missing snapshot).
  final json = jsonDecode(await file.readAsString()) as Map<String, dynamic>;
  // Promote the resolved sessionId before dropping `state` so identity (and
  // the pointer fast path in `getLatestSnapshotMetadata`) survives a row that
  // carried it only under `state`; then drop `state` so the (possibly large)
  // payload is never materialized into a SessionState.
  final sessionId =
      (json['sessionId'] as String?) ??
      (json['state'] as Map<String, dynamic>?)?['sessionId'] as String?;
  json.remove('state');
  if (sessionId != null) json['sessionId'] = sessionId;
  return SessionSnapshot.fromJson(json);
}