QIODevice::read() always returns 0 for open random-access devices

/*!
    For open random-access devices, this function returns the size of the
    device. For open sequential devices, bytesAvailable() is returned.

    If the device is closed, the size returned will not reflect the actual
    size of the device.

    \sa isSequential(), pos()
*/
qint64 QIODevice::size() const
{
    return d_func()->isSequential() ? bytesAvailable() : qint64(0);
}