get_headers_string method

Implementation

String? get_headers_string(HttpRequest req) {
  var canon_headers = <String>[];
  for (final key in req.headers.keys) {
    if (key.toLowerCase().startsWith('x-oss-')) {
      canon_headers.add(key.toLowerCase());
    }
  }
  canon_headers.sort((s1, s2) {
    return s1.compareTo(s2);
  });
  if (canon_headers.isNotEmpty) {
    final header_strings = canon_headers.map((key) {
      final v = req.headers[key];
      return "${key}:${v}";
    }).join("\n");
    return "${header_strings}\n";
  } else {
    return null;
  }
}