decodeData method

@override Uint8List decodeData(String part)

Decodes base64 part data leniently.

RFC 2045 section 6.8 requires decoders to ignore any character outside of the base64 alphabet, e.g. line breaks or white space, and a missing padding is added, so that broken input does not throw.

Implementation

@override
Uint8List decodeData(final String part) {
  final buffer = StringBuffer();
  for (final code in part.codeUnits) {
    if (_isBase64Char(code)) {
      buffer.writeCharCode(code);
    } else if (code == AsciiRunes.runeEquals) {
      // the padding ends the data
      break;
    }
  }
  var cleaned = buffer.toString();
  final remainder = cleaned.length % 4;
  if (remainder == 1) {
    // a single trailing character cannot encode anything
    cleaned = cleaned.substring(0, cleaned.length - 1);
  } else if (remainder > 1) {
    cleaned = cleaned.padRight(cleaned.length + 4 - remainder, '=');
  }
  try {
    return base64.decode(cleaned);
  } on FormatException catch (e) {
    print('unable to decode base64 data: ${e.message}');

    return Uint8List(0);
  }
}