sub __load_zip {
    my ($filename) = @_;

    my $zip = Archive::Zip->new();

    if (ref $filename) {
        $zip->readFromFileHandle($filename) == Archive::Zip::AZ_OK or die("Cannot open data as Zip archive");
    } else {
        $zip->read($filename) == Archive::Zip::AZ_OK or die("Cannot open $filename as Zip archive");
    }
    
    return $zip;
}