qint64 FileSource size return header size data- size footer size qint6

qint64 FileSource::size ()
{ 
    return (header.size() + data->size() + footer.size());
}

qint64 FileSource::readData(char* to, qint64 max)
{
    QByteArray buf;

    while ((curPos < header.size()) && buf.size() < max)
    {
        buf.append(header.at(curPos));
        curPos++;
    }
    while ((curPos < (header.size()+data->size())) && buf.size() < max)
    {
        data->seek(curPos - header.size());
        int toread;
        toread = max - buf.size();
        if (toread>(data->size() - (curPos - header.size()))) toread = data->size() - (curPos - header.size());
        buf.append(data->read(toread));
        curPos += toread;
    }
    while ((curPos < size()) && buf.size() < max)
    {
        buf.append(footer.at(curPos));
        curPos++;
    }

    strcpy(to, buf.data());

    qDebug() << buf;
    return buf.size();
}

qint64 FileSource::writeData ( const char *, qint64)
{
    return -1;
}