Install and Config Mosquitto (MQTT broker server)

MQTT is a super lightweight IoT protocol on TCP/IP with …8 bits header. Send and receive messages with others in “topic” like as a chatroom.

Install Mosquitto (MQTT Broker Server)

Install MQTT broker on server

dnf -y install epel-release
dnf -y install mosquitto
systemctl enable mosquitto
systemctl start mosquitto

Create user and password (exp: admin):

mosquitto_passwd -c /etc/mosquitto/passwd admin

Sercurity config:

Open file /etc/mosquitto/mosquitto.conf to add this config to require password when connect:

allow_anonymous false
password_file /etc/mosquitto/passwd

Config listener port, encrypt, protocol:

Add this content to /etc/mosquitto/mosquitto.conf :

listener 1883 localhost# or listener 1883 if open 1883 to network
listener 8883
certfile /etc/letsencrypt/live/domain.com/cert.pem
cafile /etc/letsencrypt/live/domain.com/fullchain.pem
keyfile /etc/letsencrypt/live/domain.com/privkey.pem
listener 8083
protocol websockets
certfile /etc/letsencrypt/live/domain.com/cert.pem
cafile /etc/letsencrypt/live/domain.com/fullchain.pem
keyfile /etc/letsencrypt/live/domain.com/privkey.pem

Restart service

systemctl daemon-reload
systemctl restart mosquitto

Open firewall port

firewall-cmd --permanent --add-port=1883/tcpfirewall-cmd --permanent --add-port=8083/tcpfirewall-cmd --permanent --add-port=8883/tcp
firewall-cmd --reload

Practice MQTT: publish and subscribe

In example, the topic is “test”. So, it can be any thing you want (test/001, myroom/test/001,…).

From your server’s terminal:

A listener:

mosquitto_sub -h localhost -t test -u "admin" -P "Icg...." -p 1883

A publisher:

mosquitto_pub -h localhost -t test -m "hello world" -u "admin" -P "Icg...." -p 1883

From other computer:

From browsers, server url like as: wss://domain.com:8883 (SSL).

A listener:

mosquitto_sub -h domain.com -t test -u "admin" -P "Icg...." -p 8883 --cafile "C:\Program Files\Mosquitto\ca-bundle.crt" --insecure

A publisher:

mosquitto_pub -h domain.com -t test -m "hello world" -u "admin" -P "Icg...." -p 8883 --cafile "C:\Program Files\Mosquitto\ca-bundle.crt" --insecure

ca.crt is the CA certificate file. It’s the same SSL provider’s SSL CA certificate which broker used. Your path is in “” if has space character.

More parameters:

-r: mark as retain message (save this message to send to new subscribers). Just for “pub” command.

-q 0: (0 or 1 or 2) to mark quality:

0 send once, accept losing
1 send once or more
2 send exactly once

– d: write log for debug

– n: Send “null”, so “-m” is not accept

– A 192.0.0.1: Send to exactly IP client you want to send

-f something.txt: send file (string in the file)

-k 60: keep alive in this time (by seconds). After this time, broker and client will ping to check connect is alive or closed.

-I “sometext”: set ClientID prefix. Suffixe is created automaticly.

-i “sometext”: Set Client id exactly

-t: Set Topic name (/topic/ or mix topic):

/topic/+/t1/: Start with /topic/, many topic, end with /t1/
/topic/#: All topic start with /topic/

When you send a message to /topic/learning/english/2022/. So all subscribers listen on /topic/ or /learning/ or /english/ or /2022/, everyone received the message

–will-payload : mark as the message which broker help you to send to your topic when you go out (unsub, or timeout). If not set, the null will be sent.
–will-qos : Set QoS to testament message (the wills)
–will-retain : Save this wills to send to new subscribers.
–will-topic : Set topic you want to send the wills

Your backend app just is a Client!

Demo PHP client (backend)

Source: https://github.com/bluerhinos/phpMQTT

Install by Composer (just fo PHP backend):

composer require bluerhinos/phpmqtt=@dev

Examples folder: vendor/bluerhinos/phpmqtt/examples

Config your connection info.

In subscribe.php write your custom function to do something when receive a message on topic:

function procMsg($topic, $msg){
		echo 'Msg Recieved: ' . date('r') . "\n";
		echo "Topic: {$topic}\n\n";
		echo "\t$msg\n\n";
}

Your PHP file need to include this library:

require('../phpMQTT.php');

Example: 2 functions to reply message:

function procMsg($topic, $msg){
		echo 'Msg Recieved: ' . date('r') . "\n";
		echo "Topic: {$topic}\n\n";
		echo "\t$msg\n\n";
		if($msg == "hello world"){
			reply($topic, $msg);
			// require("publish.php");
		}
		
}
function reply($topic, $msg){
	$server = 'localhost';     // change if necessary
	$port = 1883;                     // change if necessary
	$username = 'admin';                   // set your username
	$password = 'Icg@...';                   // set your password
	$client_id = 'phpMQTT-publisher1'; // make sure this is unique for connecting to sever - you could use uniqid()
	
	$explode = explode("/", $topic);
	$from_client_id = $explode['2'];
	$explode['2'] = $client_id;
	$new_topic = implode("/",$explode);
			// echo $from_client_id;
			
	// $topic_mix = preg_replace($to_client_id, $client_id, $topic);
	$mqtt = new Bluerhinos\phpMQTT($server, $port, $client_id);
	if ($mqtt->connect(true, NULL, $username, $password)) {
		$mqtt->publish($new_topic, 'Yes, Hello '. $from_client_id .' on ' . $new_topic .' at ' . date('r'), 0, false);
		$mqtt->close();
	} else {
		echo "Time out!\n";
	}
}