sub get_descriptor
{
    my $self = shift;
    my $type = shift;
    my $index = shift;
    $self->_assert_open();

    my $buf = "\0" x MAX_BUFFER_SIZE;

    my $retlen = Device::USB::libusb_get_descriptor(
        $self->{handle}, $type, $index, $buf, MAX_BUFFER_SIZE
    );

    return if $retlen < 0;

    return substr( $buf, 0, $retlen );
}