Swoole Coroutine System: dnsLookup

4.x is outdated, please check the latest version 22.x

Latest version: pecl install openswoole-22.1.2


<?php Swoole\Coroutine\System::dnsLookup(string $domain, float $timeout = 5): string|false



The hostname to lookup and query.


A float in seconds for how long before timing out the lookup. Because a float is used, 1.5 means 1.5 seconds. The lowest possible value is 0.001.


Returns a string of the IP address if successful and false when an error occurs, check swoole_last_error() for more details.


Get the IP address of a hostname.

This DNS lookup method is using the DNS set in /etc/resolve.conf.

Only IPv4 is supported and is based on UDP network communication instead of using libc which is used by gethostbyname functions.



Co::set(['dns_server' => '']);

    $ip = Swoole\Coroutine\System::dnsLookup("openswoole.com", 8);
    echo $ip;

Common errors and mistakes when using this function:

  • SWOOLE_ERROR_DNSLOOKUP_RESOLVE_FAILED: The domain name cannot be resolved, the query failed, check network connection
  • SWOOLE_ERROR_DNSLOOKUP_RESOLVE_TIMEOUT: The resolution timed out, the DNS server may be faulty, and the result cannot be returned within the specified time, increase the timeout parameter
Last updated on August 31, 2022