Implementation method of combining Swoole with MQTT protocol

With the development of the Internet of Things, more and more applications require real-time data transmission and communication. Message Queuing Transport Protocol (MQTT) is a lightweight protocol suitable for small devices and low-bandwidth environments, and is often used for data transmission in IoT devices. As a high-performance, asynchronous, event-driven network communication framework, Swoole provides efficient implementation of the TCP/UDP/UnixSocket protocol and can be used in conjunction with the MQTT protocol to provide more efficient system communication.

This article will introduce how to use Swoole and MQTT protocols to communicate, and provide a feasible solution.

First, we need to understand the basic knowledge of the MQTT protocol. It is a protocol based on a publish/subscribe model that enables two-way communication between devices. There are two main roles in the MQTT protocol: publishers and subscribers. Publishers publish messages to topics, and subscribers can subscribe to topics of interest and receive messages published by publishers in real time. In the MQTT protocol, a topic is defined as a string as an identifier for publish/subscribe.

Next, we will implement the publish/subscribe model of the MQTT protocol in conjunction with the Swoole framework.

Before using Swoole to implement the MQTT protocol, we need to install the MQTT library. Swoole can use the php-mqtt library for MQTT communication, and we can use composer to install it:

composer require bluerhinos/phpmqtt dev-master

After successful installation, we can start using Swoole to communicate with the MQTT protocol.

First, we need to create a TCP server based on the Swoole framework. On this TCP server, we will use the MQTT protocol for data transmission. In the Swoole framework, we can create a TCP server through the following code:

$server = new SwooleServer('0.0.0.0', 9501, SWOOLE_PROCESS, SWOOLE_SOCK_TCP);

Next, we need to register the service hook when the server starts so that client requests can be processed. In this example, we will use onConnect, onReceive, and onClose methods:

$server->on('connect', function ($serv, $fd) {
    echo "Client: Connect.
";
});

$server->on('receive', function ($serv, $fd, $from_id, $data) {
    echo "Receive Data: $data
";

    // 处理MQTT消息
});

$server->on('close', function ($serv, $fd) {
    echo "Client: Close.
";
});

When receiving a client request, we will parse the MQTT message. Since the focus of this article is how to use Swoole to implement the MQTT protocol, we only focus on how to parse MQTT messages. MQTT messages can be easily parsed using the php-mqtt library. We can encapsulate it into a method:

function handleMqttMessage($client_id, $topic, $message)
{
    echo "Mqtt Message Received: 
";
    echo "Client ID: $client_id
";
    echo "Topic: $topic
";
    echo "Message: $message
";
}

The remaining work is to send the parsed data of the MQTT message to the client that wants to receive it. . In the MQTT protocol, we can communicate using the publish/subscribe mode to publish messages to specified topics. A client can subscribe to a topic of interest and then receive messages published on that topic. In the Swoole framework, we can use swoole_server->task() to send messages to specific clients.

The following code is to send the message to all clients subscribed to the corresponding topic after receiving the MQTT message:

$server->on('receive', function ($serv, $fd, $from_id, $data) {
    $mqtt = new BluerhinosphpMQTT('localhost', 1883, 'Swoole_Server');
    $mqtt->debug = false;
    if (!$mqtt->connect()) {
        exit(1);
    }
    $topics['topic_name'] = array('qos' => 0, 'function' => 'handleMqttMessage');
    $mqtt->subscribe($topics, 0);
    while ($mqtt->proc()) {
    };
    $mqtt->close();
    echo "Receive Data: $data
";

    $data = json_decode($data, true);
    $message = $data['message'];

    $client_ids = $serv->getClientList();
    foreach ($client_ids as $client_id) {
        $serv->task("$client_id:$message");
    }

});

Every time a client message is received, we will The subscribed topic calls the callback method handleMqttMessage() and then sends the message to the specified client.

Finally, we need to send the message to the client in the Task event:

$server->on('task', function ($serv, $task_id, $from_id, $data) {
    $client_id = strstr($data, ':', true);
    $message = substr(strstr($data, ':'), 1);
    $serv->send($client_id, $message);
});

The above code will send the message to the client and return a corresponding ACK message after successful transmission.

Summary
In this article, we learned how to use Swoole to implement the MQTT protocol. In this way, we can achieve efficient real-time communication and better handle client requests using an asynchronous, event-driven approach. The Swoole framework provides efficient TCP/UDP/UnixSocket protocol implementation, which has many advantages for both large enterprises and small projects. In the future, we can expect more applications to use Swoole and MQTT protocols for data transfer and communication.

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