php使用cUrl获取网址重定向之后的链接

function get_redirect_url($url,$ua=0){
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
    $httpheader[] = "Accept:*/*";
    $httpheader[] = "Accept-Encoding:gzip,deflate,sdch";
    $httpheader[] = "Accept-Language:zh-CN,zh;q=0.8";
    $httpheader[] = "Connection:close";
    curl_setopt($ch, CURLOPT_HTTPHEADER, $httpheader);
    curl_setopt($ch, CURLOPT_HEADER, true);
    if ($ua) {
        curl_setopt($ch, CURLOPT_USERAGENT, $ua);
    } else {
        curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Linux; U; Android 4.0.4; es-mx; HTC_One_X Build/IMM76D) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0");
    }
    curl_setopt($ch, CURLOPT_NOBODY, 1);
    curl_setopt($ch, CURLOPT_ENCODING, "gzip");
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    $ret = curl_exec($ch);
    curl_close($ch);
    preg_match("/Location: (.*?)\r\n/iU",$ret,$location);
    return $location[1];
}

//使用默认ua
echo get_redirect_url('http://example.com');
//使用自定义ua
$ua = 'Mozilla/5.0 (iPhone; CPU iPhone OS 13_3 like Mac OS X) AppleWebKit/604.3.5 (KHTML, like Gecko) Version/13.0 MQQBrowser/9.0.0 Mobile/15B87 Safari/604.1 MttCustomUA/2 QBWebViewType/1 WKType/1';
echo get_redirect_url('http://example.com'，$ua);