In this article, we will develop a PHP client for subscribing and publishing messages for MQTT communication using Mosquitto-PHP library available here.

1. Installing pecl

$sudo apt-get install php-pear

2. Install PHP developer packages

$sudo apt-get install php5-dev

3. Install Mosquitto-PHP library

sudo pecl install Mosquitto-alpha

4. Add extension=mosquitto.so under Dynamic Extensions of the file /etc/php5/cli/php.ini

5. Creating an MQTT subscriber ( sub.php ) using Mosquitto-PHP library

<?php

$client = new Mosquitto\Client();
$client->onConnect('connect');
$client->onDisconnect('disconnect');
$client->onSubscribe('subscribe');
$client->onMessage('message');
$client->connect("localhost", 1883, 60);
$client->subscribe('/#', 1);


while (true) {
        $client->loop();
        sleep(2);
}

$client->disconnect();
unset($client);

function connect($r) {
        echo "I got code {$r}\n";
}

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

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

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

6. Run the subscriber using php command line tool

$php sub.php

On executing the above command, we will get an output as shown below :

I got code 0
Subscribed to a topic

7. Test the MQTT subscriber using mosquitto_pub command line tool

$mosquitto_pub -h localhost -t "/mqtt" -m "HelloWorld"

On executing the above command, we will get an output as shown below :

Got a message on topic /mqtt with payload:HelloWorld

8. Creating an MQTT publisher ( pub.php ) using Mosquitto-PHP library

<?php

$client = new Mosquitto\Client();
$client->onConnect('connect');
$client->onDisconnect('disconnect');
$client->onPublish('publish');
$client->connect("localhost", 1883, 5);

while (true) {
        try{
                $client->loop();
                $mid = $client->publish('/mqtt', "Hello from PHP");
                $client->loop();
        }catch(Mosquitto\Exception $e){
                return;
        }
        sleep(2);
}

$client->disconnect();
unset($client);

function connect($r) {
        echo "I got code {$r}\n";
}

function publish() {
        global $client;
        echo "Mesage published\n";
        $client->disconnect();
}

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

9. Run the publisher using php command line tool

$php pub.php

On executing the above command, we will get a message as shown below :

I got code 0
Mesage published
Disconnected cleanly

Also, we can see the published message as shown below at the terminal where the subscriber ( sub.php ) is running :

I got code 0
Subscribed to a topic

Got a message on topic /mqtt with payload:Hello from PHP