decodeStreamData function

Uint8List? decodeStreamData(PdfDocumentParser parser, PdfDictToken dict, Uint8List raw)

Applies the filters of dict over raw.

Handles /FlateDecode (with and without a zlib header) and /ASCIIHexDecode, including the /DecodeParms predictor that follows a Flate stream. Returns null when the filter is not supported — LZW, DCT, JPX and RunLength do not show up in content streams or in /ToUnicode in practice.

Implementation

Uint8List? decodeStreamData(
    PdfDocumentParser parser, PdfDictToken dict, Uint8List raw) {
  var data = raw;
  final predictor =
      PdfParserXref.readPredictorParams(parser.resolve(dict.values['/DecodeParms']));

  for (final filter in _filterNames(parser, dict.values['/Filter'])) {
    switch (filter) {
      case '/FlateDecode':
      case '/Fl':
        final inflated = _inflate(data);
        if (inflated == null) return null;
        // A predictor left in place would decode to garbage, silently.
        data = PdfParserPredictor.apply(inflated, predictor);
        break;
      case '/ASCIIHexDecode':
      case '/AHx':
        data = _asciiHexDecode(data);
        break;
      default:
        return null;
    }
  }
  return data;
}