回答

首先是服务端，一定要位于公网上，我们以udp为例，其实tcp也是一样的，代码如下：

<?php
 
$arr = [];
 
 
$server = new Swoole\Server('0.0.0.0', 9503, SWOOLE_PROCESS, SWOOLE_SOCK_UDP);
$server->set([
    "worker_num" => 1
]);
$server->on('packet', function ($server, $data, $clientInfo) use (&$arr){
    $list = explode("\n", $data);
    foreach ($list as $value) {
        $data = json_decode($value, 1);
        if ($data) {
            if ($data["do"] == "reg") {
                $arr[$data["user"]] = $clientInfo;
                var_dump($arr);
                $server->sendTo($clientInfo['address'], $clientInfo['port'], "Server：");
//                $server->send($fd, "ok\n");
            } else if ($data["do"] == "get") {
                $server->sendTo($clientInfo['address'], $clientInfo['port'],
                    json_encode($arr[$data["user"]]));
//                $server->send($fd, json_encode($arr[$data["user"]]));
                //
//                $server->send($arr[$data["user"]]["fd"], json_encode($arr[$data["user"]]));
            } else {
 
            }
        }
    }
//$server->sendTo($clientInfo['address'], $clientInfo['port'], "Server：{$data}");
});
 
$server->start();

其中一个client2位于局域网中，他发送消息给服务器后，其实已经将自己的路由器的对外ip与地址告知服务器了。

<?php
$client = new Swoole\Client(SWOOLE_SOCK_UDP, SWOOLE_SOCK_SYNC);
 
$r = $client->sendto('服务器ip', 9503, json_encode(["do"=>"reg", "user"=>"client2", "passwd" => "passwd"]) . "\n");
$ret = $client->recv();
while (1) {
    $ret = $client->recv();
    if ($ret) {
        var_dump($ret);
 
    }
    sleep(1);
}
$client->close();

这个时候我们在另外一个地方的client1想要直接发送消息给client2，先告知服务器他的对外ip与端口号，然后获取client1的对外ip与端口号，最后直接发送udp消息给client2的对外ip和端口，这个时候client2正好正在等待，于是就获取了client1直接发送的消息，完成的打洞，那么client2想直接发送信息给client1也要获取client1的对外ip与端口。

<?php
 
$client = new Swoole\Client(SWOOLE_SOCK_UDP, SWOOLE_SOCK_SYNC);
 
$r = $client->sendto('服务器ip', 9503, json_encode(["do"=>"reg", "user"=>"client1", "passwd" => "passwd"]) . "\n");
echo $client->recv();
$r = $client->sendto('服务器ip', 9503, json_encode(["do"=>"get", "user"=>"client2"]) . "\n");
$ret = $client->recv();
$data = json_decode($ret, 1);
while (1) {
    $r = $client->sendto($data["address"], $data["port"], "test" . "\n");
    var_dump($r);
    sleep(3);
}
 

tcp打洞也是一样。