Should check offsets got from protobuf Objects

    std::unique_ptr<proto::PostScript> postscript =
      std::unique_ptr<proto::PostScript>(new proto::PostScript());
    if (!postscript->ParseFromArray(ptr + readSize - 1 - postscriptSize,
                                   static_cast<int>(postscriptSize))) {
      throw ParseError("Failed to parse the postscript from " +
                       stream->getName());
    }