nodemcu-firmware/docs/en/modules/mqtt.md

# MQTT Module

The client adheres to version 3.1.1 of the [MQTT](https://en.wikipedia.org/wiki/MQTT) protocol. Make sure that your broker supports and is correctly configured for version 3.1.1. The client is backwards incompatible with brokers running MQTT 3.1.

## mqtt.Client()

Creates a MQTT client.

#### Syntax
`mqtt.Client(clientid, keepalive, username, password[, cleansession])`

#### Parameters
- `clientid` client ID
- `keepalive` keepalive seconds
- `username` user name
- `password` user password
- `cleansession` 0/1 for `false`/`true`

#### Returns
MQTT client

#### Example
```lua
-- init mqtt client with keepalive timer 120sec
m = mqtt.Client("clientid", 120, "user", "password")

-- setup Last Will and Testament (optional)
-- Broker will publish a message with qos = 0, retain = 0, data = "offline" 
-- to topic "/lwt" if client don't send keepalive packet
m:lwt("/lwt", "offline", 0, 0)

m:on("connect", function(client) print ("connected") end)
m:on("offline", function(client) print ("offline") end)

-- on publish message receive event
m:on("message", function(client, topic, data) 
  print(topic .. ":" ) 
  if data ~= nil then
    print(data)
  end
end)

-- for TLS: m:connect("192.168.11.118", secure-port, 1)
m:connect("192.168.11.118", 1880, 0, function(client) print("connected") end)

-- Calling subscribe/publish only makes sense once the connection
-- was successfully established. In a real-world application you want
-- move those into the 'connect' callback or make otherwise sure the 
-- connection was established.

-- subscribe topic with qos = 0
m:subscribe("/topic",0, function(client) print("subscribe success") end)
-- publish a message with data = hello, QoS = 0, retain = 0
m:publish("/topic","hello",0,0, function(client) print("sent") end)

m:close();
-- you can call m:connect again
```

# MQTT Client


## mqtt.client:close()

Closes connection to the broker.

#### Syntax
`mqtt:close()`

#### Parameters
none

#### Returns
`nil`

## mqtt.client:connect()

Connects to the broker specified by the given host, port, and secure options.

#### Syntax
`mqtt:connect(host, port, secure, function(client))`

#### Parameters
- `host` host, domain or IP (string)
- `port` broker port (number)
- `secure` 0/1 for `false`/`true`, default 0. [As per #539](https://github.com/nodemcu/nodemcu-firmware/issues/539#issuecomment-170298120) secure connections use TLS 1.2.
- `function(client)` call back function for when the connection was established

#### Returns
`nil`

## mqtt.client:lwt()

Setup [Last Will and Testament](http://www.hivemq.com/blog/mqtt-essentials-part-9-last-will-and-testament) (optional). A broker will publish a message with qos = 0, retain = 0, data = "offline" to topic "/lwt" if client does not send keepalive packet.

#### Syntax
`mqtt:lwt(topic, message, qos, retain)`

#### Parameters
- `topic` the topic to publish to (string)
- `message` the message to publish, (buffer or string)
- `qos` QoS level, default 0
- `retain` retain flag, default 0

#### Returns
`nil`

## mqtt.client:on()

Registers a callback function for an event.

#### Syntax
`mqtt:on(event, function(client[, topic[, message]]))`

#### Parameters
- `event` can be "connect", "message" or "offline"
- `function(client[, topic[, message]])` callback function. The first parameter is the client. If event is "message", the 2nd and 3rd param are received topic and message (strings).

#### Returns
`nil`

## mqtt.client:publish()

Publishes a message.

#### Syntax
`mqtt:publish(topic, payload, qos, retain, function(client))`

#### Parameters
- `topic` the topic to publish to ([topic string](http://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices))
- `message` the message to publish, (buffer or string)
- `qos` QoS level, default 0
- `retain` retain flag, default 0
- `function(client)` callback fired when PUBACK received

#### Returns
`nil`

## mqtt.client:subscribe()

Subscribes to one or several topics.

#### Syntax
`mqtt:subscribe(topic, qos, function(client, topic, message))`

#### Parameters
- `topic` a [topic string](http://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices)
- `qos` QoS subscription level, default 0
- `function(client, topic, message)` callback fired when message received

#### Returns
`nil`