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MQTT module
This module contains functions for send and receive information through [MQTT] (http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html).
Lua RTOS support for MQTT is build over [Eclipse Paho MQTT] (https://github.com/eclipse/paho.mqtt.c).
For use MQTT you need an internet connection, and credentials to connect to a MQTT broker. You can configure an internet connection in Lua RTOS through [Net module] (https://github.com/whitecatboard/Lua-RTOS-ESP32/wiki/Net-module).
MQTT (Message Queue Telemetry Transport) is an ISO standard (ISO/IEC PRF 20922) publish-subscribe-based "lightweight" messaging protocol for use on top of the TCP/IP protocol. It is designed for connections with remote locations where a "small code footprint" is required or the network bandwidth is limited.
The publish-subscribe messaging pattern requires a message broker. The broker is responsible for distributing messages to interested clients based on the topic of a message.
Creates a new mqtt client instance.
Arguments:
- clientid: client identifier
- host: broker domain name or ip
- port: broker port (tipically 1883)
- secure: true for secure communicacition (not tested), false for non-secure comunication
Returns: a client instance, or an exception. You must store this instance into a variable for further operations with it.
-- Creates an mqtt instance. Broker domain is xxxx.xx, at port 1883
client = mqtt.client("100", "xxxx.xx", 1883, false)
Connects the client instance to the broker.
Arguments:
- username: user name
- password: password
- Returns: nothing
Returns: nothing, or an exception.
-- Creates an mqtt instance. Broker domain is xxxx.xx, at port 1883
client = mqtt.client("100", "xxxx.xx", 1883, false)
-- Connect
client:connect("","")
Disconnects the client instance from the broker.
Arguments: nothing Returns: nothing, or an exception.
-- Creates an mqtt instance. Broker domain is xxxx.xx, at port 1883
client = mqtt.client("100", "xxxx.xx", 1883, false)
-- Connect
client:connect("","")
...
...
-- Disconnect
client:disconnect()
Publish a message to a topic.
Arguments:
- topic: topic name.
- payload: payload, a string with the information to publish packed on it.
- qos: quality of service, according to MQTT specs, can be either mqtt.QOS0, mqtt.QOS1, or mqtt.QOS2
Returns: nothing or an exception
-- Creates an mqtt instance. Broker domain is xxxx.xx, at port 1883
client = mqtt.client("100", "xxxx.xx", 1883, false)
-- Connect
client:connect("","")
-- Publish to topic
client:publish("/100", "hello", mqtt.QOS0)
Subscribe to a topic.
Arguments:
- topic: topic name.
- qos: quality of service, according to MQTT specs, can be either mqtt.QOS0, mqtt.QOS1, or mqtt.QOS2
- function: callback function that will be executed when a message is received on topic. This function takes 2 arguments: the message length, and the message.
Returns: nothing or an exception
-- Creates an mqtt instance. Broker domain is xxxx.xx, at port 1883
client = mqtt.client("100", "xxxx.xx", 1883, false)
-- Connect
client:connect("","")
-- Subscribe to topic
client:subscribe("/100", mqtt.QOS0, function(len, message)
print("new message received")
print("message length: "..len)
print("message: "..message)
end)