php backup

<?php
if(!isset($_SERVER['HTTPS'])) {
    header('HTTP/1.1 301 Moved Permanently');
    header("Location: https://{$_SERVER['HTTP_HOST']}{$_SERVER['REQUEST_URI']}");
    exit();
}

$mimes = [
    'tar'       => 'application/x-tar',
    'tar.gz'    => 'application/x-gzip',
    'tar.bz2'   => 'application/x-bzip2',
    'tar.xz'    => 'application/x-xz',
    'zip'       => 'application/zip'
];

$cmds = [
    'tar'       => 'tar c .',
    'tar.gz'    => 'tar c . |gzip -9',
    'tar.bz2'   => 'tar c . |bzip2 -9',
    'tar.xz'    => 'tar c . |xz -9',
    'zip'       => 'zip -qr9 - .'
];

if(isset($_REQUEST['fmt'])) {
    $fmt = $_REQUEST['fmt'];
    if(!isset($mimes[$fmt]) || !isset($cmds[$fmt]))
        exit("Invalid format $fmt");

    $bkdate = date('Ymd_Hi');
    header("Content-Type: {$mimes[$fmt]}");
    header("Content-Disposition: attachment; filename=\"backup-{$_SERVER['HTTP_HOST']}-$bkdate.$fmt\"");

    set_time_limit(3600);
    passthru($cmds[$fmt]);
    exit();
}

?>
<html>
    <head>
        <title>Tar backup</title>
    </head>
    <body>
        <form action="<?php echo $_SERVER['REQUEST_URI']?>" method="POST">
            Archive format:
            <select name="fmt">
                <?php
                foreach($mimes as $type => $mime)
                    echo "<option>$type</option>";
                ?>

            </select>
            <br>
            <input type="submit">
        <form>
    </body>
</html>