Dart download fragmented file

gistfile1.txt

import 'package:http/http.dart';
  static Future downloadFragmentedFile(String url, File localFile) async {
    final request = Request('get', Uri.parse(url));
    request.headers.addAll({"range": "bytes=0-"});
    StreamedResponse rs = await Client().send(request);
    var fileStream = localFile.openWrite();
    await rs.stream.pipe(fileStream);
  }