保持MQTT客户端连接始终处于活动状态

Question

I am using CloudMQTT as a MQTT broker in my Pub-Sub based application. I am using my publisher to publish data to the CloudMQTT server over a topic, and I plan to subscribe to the broker on my webpage to recieve the transmitted information.

I am using this procedure to create a Client(subscriber): https://www.cloudmqtt.com/docs-php.html

Code goes as follows:

// subscribe.php
require("phpMQTT.php");

$host = "hostname"; 
$port = port;
$username = "username"; 
$password = "password"; 

$mqtt = new phpMQTT($host, $port, "ClientID".rand()); 

if(!$mqtt->connect(true,NULL,$username,$password)){
  exit(1);
}

//currently subscribed topics
$topics['topic'] = array("qos"=>0, "function"=>"procmsg");
$mqtt->subscribe($topics,0);

while($mqtt->proc()){        
}

$mqtt->close();
function procmsg($topic,$msg){
  echo "Msg Recieved: $msg";
}

Here is the phpMQTT.php file: https://github.com/bluerhinos/phpMQTT/blob/master/phpMQTT.php

However, the issue in this case is that it recieves data only when the webpage is open.. I want to keep the connection alive even if the webpage is not open to always recieve published messages, how can I do it?

EDIT : I might be open to using some other technology on the server to handle this subscription process, if anyone can recommend some alternatives

Answer 1

PHP's typically mode of operation is to start a process, wait for an HTTP connection, handle the request and then start a new process. This doesn't fit well with the typical MQTT mode of having a long-running process; hence closing the MQTT connection when you close the web page.

It is possible to subscribe to a MQTT topic in a long-running CLI PHP script, but you will have to have some other mechanism to keep the process running. There are a lot of different ways of doing this, depending on your preferences and operating system:

• a script started using /etc/rc.local at system startup
• using a init.d script
• using a process manager, such as DJB's daemontools or runit
• If you are using Ubuntu, then upstart is a popular mechanism

Searching stackoverflow finds the following related question and several answers:

• Run php script as daemon process