Paho Lua - MQTT Client Library Encyclopedia
Paho Lua Client library implements client-side subset of the MQTT protocol specification 3.1. An advantage of using Lua is that only a text editor is required for rapid development of simple MQTT client applications on many platforms. Cross compilation issues are avoided.
Overview of Paho Lua MQTT Client Library
| Paho Lua | |
|---|---|
| Language | PHP |
| License | EPL |
| Website | https://www.eclipse.org/paho/ |
| API Style | Asynchronous |
Initially part of Aiko Platform, this library is now part of Eclipse Paho project.
Features Supported by Paho Lua MQTT Client Library
| Feature | |
|---|---|
| MQTT 3.1 | Yes |
| MQTT 3.1.1 | Yes |
| LWT | Yes |
| SSL/TLS | Yes |
| Automatic Reconnect | No |
Advance Features Supported by Paho Lua MQTT Client Library
| Feature | Yes |
|---|---|
| QoS 0 | Yes |
| QoS 1 | Yes |
| QoS 2 | Yes |
| Authentication | Yes |
| Throttling | No |
Installation of Paho Lua MQTT Client Library
As I am writing easiest way to install Paho Lua Client is from sources using LuaRocks.
$ git clone https://git.eclipse.org/r/paho/org.eclipse.paho.mqtt.lua
$ cd org.eclipse.paho.mqtt.lua/
$ luarocks make rocks/paho-mqtt-0.3.0-1.rockspecYou are all set.
Note: tested on Lua 5.1.
How to Connect Paho Lua MQTT Client to an MQTT Broker?
This section shows the API usage how to connect with the library to a MQTT broker.
local mqtt = require 'paho.mqtt'
local client = mqtt.client.create('broker.mqttdashboard.com')
client:connect('paho-lua-client-sample-identifier')First step is creating MQTT client, here test.mosquitto.org is used as broker host. As port is not specified, 1183 is used by default. Then you can simply call client:connect() with a client identifier of your choice.
Connect with Username/Password
Authentication is just one additional line.
local client = mqtt.client.create('broker.mqttdashboard.com')
client:auth('user', 'Pa$$w0rd')
client:connect('paho-lua-client-sample-identifier')Calling client:auth() before client:connect() enables to set username and password.
How to Publish an MQTT Message Using Paho Lua MQTT Client Library
Once you are connected it is as simple as:
client:publish('topic/sample', 'fancy message')It publishes a fancy message on topic/sample.
How to Subscribe to An MQTT Message Using Paho Lua MQTT Client Library
local callback = function(topic, payload)
print(string.format('Hey, %s just received: %s.', topic, payload))
end
-- Connect
local client = mqtt.client.create('broker.mqttdashboard.com', 1883, callback)
client:connect('paho-lua-client-sample-identifier')
client:subscribe({'topic/sample'})You can subscribe on several topics by providing them to client:subscribe() in a table. Once something arrives on topic, callback defined at connection is called.
How to Unsubscribe to An MQTT Message Using Paho Lua MQTT Client Library
You no longer want to get message from a topic? Put it in a table and give it to
client:unsubscribe({'topic/sample'})You no longer want to get message from a topic? Put it in a table and give it to client:unsubscribe().
How to Disconnect From an MQTT Broker While Using Paho Lua?
client:disconnect()Quite self-explanatory.
Full Example Application of Using Paho Lua MQTT Client Library
local mqtt = require 'paho.mqtt'
local socket = require 'socket'
local stop = false
local callback = function(topic, payload)
print(string.format('Hey, %s just received: %s.', topic, payload))
if payload == 'stop' then
stop = true
end
end
-- Connect
local client = mqtt.client.create('broker.mqttdashboard.com', 1883, callback)
client:connect('paho-lua-client-sample-identifier')
-- Subscribe to topic
local topic = 'topic/sample'
client:subscribe({topic})
-- Wait for publication
math.randomseed(os.time())
while not stop do
-- Publish something on topic
local message = math.random(0, 1) == 0 and 'Go on child' or 'stop'
client:publish(topic, message)
-- Wait gently
client:handler()
socket.sleep(1)
end
-- Cleaning up
client:unsubscribe({topic})
client:disconnect()
client:destroy()What we are doing here is publishing random strings on topic/sample forever until being told to “stop”.
First we connect to broker.mqttdashboard.com on default port 1883. At connection, we define a callback to handle received messages.
Then we subscribe to topic/sample topic.
Now we publish a string on topic we just subscribed to, client:handler() checks for received messages. When there is one, callback(topic, message) is called to deal with it. We repeat this relentlessly.
Once this message is string “stop”, we stop looping, unsubscribe from topic/sample.
To clean all this, we disconnect from server and destroy our client to free allocated memory.
You can also find this example code at https://github.com/KINFOO/
Kévin KIN-FOO
Kévin is doing fine things at Sierra Wireless. He said that he loves his software simple.
