php经过socket检测服务器端口是否开放

/**
 * 检测端口是否开放
 * @param $ip
 * @param $port
 * @return string
 */
public function checkPort($ip,$port) {
    $sock = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
    socket_set_nonblock($sock);
    socket_connect($sock,$ip, $port);
    socket_set_block($sock);
    $return = @socket_select($r = array($sock), $w = array($sock), $f = array($sock), 3);
    socket_close($sock);
    switch($return)
    {
        case 2:
            echo "$ip:$port 关闭\n";
            break;
        case 1:
            echo "$ip:$port 打开\n";
            break;
        case 0:
            echo "$ip:$port 超时\n";
            break;
    }

}