PHP7 issue : socket_sendto occurred "Unknown host" - php

Question

Q :
Please let i know why socket_sendto function occurred Unknown host error
env
centos 7.9
php-fpm 7.4 AND php-fpm 8.1
in docker container
/etc/hosts
<docker net ip> <docker container id>
127.0.0.1 nd.domain.com
execution
php -q SERVER.php
source
#!/usr/local/bin/php -q
<?php
// error_reporting(E_ALL);
// set_time_limit(0);
// ob_implicit_flush();
$address = '0.0.0.0';
$port = 80;
echo "server now start\r\n";
$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP) or dir("create failed this socket");
if (!socket_set_option($socket, SOL_SOCKET, SO_REUSEADDR, 1)) {
echo 'Unable to set option on socket: '. socket_strerror(socket_last_error()) . PHP_EOL;
}
socket_bind($socket, $address, $port) or dir("Failed to bind to (".$address.":".$port.")");
echo "server binded\r\n";
$messageBuffer = "";
$clients = [];
while (true){
if (#socket_recvfrom($socket, $messageBuffer, 2048, MSG_WAITALL, $ip, $port)) {
$address = "$ip:$port";
echo "Receive data : " . $messageBuffer . " FROM " . $address. "\r\n";
if (!isset($clients[$address]))
$clients[$address] = array();
$data = "hello-world";
$client_ip = gethostbyname($address);
echo "callback - send to " . $client_ip . "\r\n";
if (#socket_sendto($socket, $data, strlen($data), 0, $client_ip, $port)) {
echo "sendto ok";
} else {
echo socket_strerror(socket_last_error($socket))."\r\n";
};
} else {
echo socket_strerror(socket_last_error($socket))."\r\n";
};
// $clients[$address]->handlePacket($buffer);
}
socket_close($socket);
//socket_close
// namespace cgiServer;
// include_once './server_fn.php';
// include_once './socketManager.php';
// include_once './socketManagerSessionCtl.php';
// // 무한정 실행하기 위해 시간한계를 0으로 설정한다.
// set_time_limit(0);
// // 대기할 IP 주소와 포트번호를 설정한다
// $unit = new \cgiServer\server\manageUnit('192.168.35.29', 9000);
// //서버 실행
// $unit->serverOpen();
// exit;
?>
server log
with php-fpm 8.1 (display error on)
server now start
server binded
Receive data : hello world FROM 123.123.123.12:12345
callback - send to 123.123.123.12:12345
Warning: socket_sendto(): Host lookup failed [-10000]: Unknown error -10000 in [err-path] on line 47
Unknown error -10000
with php-fpm 7.4 (display error off)
Receive data : 0101010101! FROM 123.123.123.12:12345
callback - send to 123.123.123.12:12345
Unknown host

Answer 1

$client_ip and $address returns 123.123.123.123:12345
$ip returns 123.123.123.123
so i replace like that
#socket_sendto($socket, $data, strlen($data), 0, $client_ip, $port)
to
#socket_sendto($socket, $data, strlen($data), 0, $ip, $port)