无法使用Mosquitto-PHP连接到Mosquitto服务器

Question

我在centos服务器上安装了mosquitto broker。为了沟通，我安装了Mosquitto-php库。发布者和订阅者在同一台服务器上正常工作，但当我尝试从这个centos服务器发布消息并从本地机器（ubuntu）运行订阅者脚本时，然后收到以下错误 -

PHP Fatal error: Uncaught MosquittoException: The client is not currently connected. in /home/sujit/Desktop/php_test.php:12
Stack trace:
#0 /home/sujit/Desktop/php_test.php(12): MosquittoClient->subscribe('#', 1)
#1 {main}
thrown in /home/sujit/Desktop/php_test.php on line 12

Mosquitto-PHP库已安装在本地计算机上。

下面是我正在运行的subscriber.php文件 -

<?php
define('BROKER', 'ip address of server');
define('PORT', 1883);
define('CLIENT_ID', "pubclient_" . getmypid());

$client = new MosquittoClient(CLIENT_ID);
$client->onConnect('connect');
$client->onDisconnect('disconnect');
$client->onSubscribe('subscribe');
$client->onMessage('message');
$client->connect(BROKER, PORT, 60);
$client->subscribe('#', 1); // Subscribe to all messages

$client->loopForever();

function connect($r) {
        echo "Received response code {$r}
";
}

function subscribe() {
        echo "Subscribed to a topic
";
}

function message($message) {
        printf("Got a message on topic %s with payload:
%s
", $message->topic, $message->payload);
}

function disconnect() {
        echo "Disconnected cleanly
";
}