nc-photos/app/lib/file_extension.dart

import 'dart:io';

import 'package:mime/mime.dart';
import 'package:path/path.dart' as path_lib;

extension FileExtension on File {
  Future<String?> readMime() async {
    final header = await openRead(0, defaultMagicNumbersMaxLength)
        .expand((element) => element)
        .toList();
    return lookupMimeType(path, headerBytes: header);
  }

  String get filename => path_lib.basename(path);
}