# MQTT Module
| Since  | Origin / Contributor  | Maintainer  | Source  |
| :----- | :-------------------- | :---------- | :------ |
| 2015-01-23 | [Stephen Robinson](https://github.com/esar/contiki-mqtt), [Tuan PM](https://github.com/tuanpmt/esp_mqtt) | [Vowstar](https://github.com/vowstar) | [mqtt.c](../../../app/modules/mqtt.c)|


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`. Default is 1 (`true`).

#### Returns
MQTT client

#### Example
```lua
-- init mqtt client without logins, keepalive timer 120s
m = mqtt.Client("clientid", 120)

-- init mqtt client with logins, 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", 1883, 0, function(client)
  print("connected")
  -- Calling subscribe/publish only makes sense once the connection
  -- was successfully established. You can do that either here in the
  -- 'connect' callback or you need to otherwise make sure the
  -- connection was established (e.g. tracking connection status or in
  -- m:on("connect", function)).

  -- subscribe topic with qos = 0
  client:subscribe("/topic", 0, function(client) print("subscribe success") end)
  -- publish a message with data = hello, QoS = 0, retain = 0
  client:publish("/topic", "hello", 0, 0, function(client) print("sent") end)
end,
function(client, reason)
  print("failed reason: " .. reason)
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
`true` on success, `false` otherwise

## mqtt.client:connect()

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

#### Syntax
`mqtt:connect(host[, port[, secure[, autoreconnect]]][, function(client)[, function(client, reason)]])`

#### Parameters
- `host` host, domain or IP (string)
- `port` broker port (number), default 1883
- `secure` 0/1 for `false`/`true`, default 0. Take note of constraints documented in the [net module](net.md).
- `autoreconnect` 0/1 for `false`/`true`, default 0. This option is *deprecated*.
- `function(client)` callback function for when the connection was established
- `function(client, reason)` callback function for when the connection could not be established. No further callbacks should be called.

#### Returns
`true` on success, `false` otherwise

#### Notes

Don't use `autoreconnect`. Let me repeat that, don't use `autoreconnect`. You should handle the errors explicitly and appropriately for
your application. In particular, the default for `cleansession` above is `true`, so all subscriptions are destroyed when the connection
is lost for any reason.

In order to acheive a consistent connection, handle errors in the error callback. For example:

```
function handle_mqtt_error(client, reason) 
  tmr.create():alarm(10 * 1000, tmr.ALARM_SINGLE, do_mqtt_connect)
end

function do_mqtt_connect()
  mqtt:connect("server", function(client) print("connected") end, handle_mqtt_error)
end
```

In reality, the connected function should do something useful!

This is the description of how the `autoreconnect` functionality may (or may not) work.

> When `autoreconnect` is set, then the connection will be re-established when it breaks. No error indication will be given (but all the
> subscriptions may be lost if `cleansession` is true). However, if the
> very first connection fails, then no reconnect attempt is made, and the error is signalled through the callback (if any). The first connection
> is considered a success if the client connects to a server and gets back a good response packet in response to its MQTT connection request.
> This implies (for example) that the username and password are correct.

#### Connection failure callback reason codes:

| Constant | Value | Description |
|----------|-------|-------------|
|`mqtt.CONN_FAIL_SERVER_NOT_FOUND`|-5|There is no broker listening at the specified IP Address and Port|
|`mqtt.CONN_FAIL_NOT_A_CONNACK_MSG`|-4|The response from the broker was not a CONNACK as required by the protocol|
|`mqtt.CONN_FAIL_DNS`|-3|DNS Lookup failed|
|`mqtt.CONN_FAIL_TIMEOUT_RECEIVING`|-2|Timeout waiting for a CONNACK from the broker|
|`mqtt.CONN_FAIL_TIMEOUT_SENDING`|-1|Timeout trying to send the Connect message|
|`mqtt.CONNACK_ACCEPTED`|0|No errors. _Note: This will not trigger a failure callback._|
|`mqtt.CONNACK_REFUSED_PROTOCOL_VER`|1|The broker is not a 3.1.1 MQTT broker.|
|`mqtt.CONNACK_REFUSED_ID_REJECTED`|2|The specified ClientID was rejected by the broker. (See `mqtt.Client()`)|
|`mqtt.CONNACK_REFUSED_SERVER_UNAVAILABLE`|3|The server is unavailable.|
|`mqtt.CONNACK_REFUSED_BAD_USER_OR_PASS`|4|The broker refused the specified username or password.|
|`mqtt.CONNACK_REFUSED_NOT_AUTHORIZED`|5|The username is not authorized.|

## 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
- `retain` retain flag
- `function(client)` optional callback fired when PUBACK received.  NOTE: When calling publish() more than once, the last callback function defined will be called for ALL publish commands.
  

#### Returns
`true` on success, `false` otherwise

## mqtt.client:subscribe()

Subscribes to one or several topics.

#### Syntax
`mqtt:subscribe(topic, qos[, function(client)])`
`mqtt:subscribe(table[, function(client)])`

#### Parameters
- `topic` a [topic string](http://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices)
- `qos` QoS subscription level, default 0
- `table` array of 'topic, qos' pairs to subscribe to
- `function(client)` optional callback fired when subscription(s) succeeded.  NOTE: When calling subscribe() more than once, the last callback function defined will be called for ALL subscribe commands.

#### Returns
`true` on success, `false` otherwise

#### Example
```lua
-- subscribe topic with qos = 0
m:subscribe("/topic",0, function(conn) print("subscribe success") end)

-- or subscribe multiple topic (topic/0, qos = 0; topic/1, qos = 1; topic2 , qos = 2)
m:subscribe({["topic/0"]=0,["topic/1"]=1,topic2=2}, function(conn) print("subscribe success") end)
```

!!! caution

    Rather than calling `subscribe` multiple times you should use the multiple topics syntax shown in the above example if you want to subscribe to more than one topic at once.

## mqtt.client:unsubscribe()

Unsubscribes from one or several topics.

#### Syntax
`mqtt:unsubscribe(topic[, function(client)])`
`mqtt:unsubscribe(table[, function(client)])`

#### Parameters
- `topic` a [topic string](http://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices)
- `table` array of 'topic, anything' pairs to unsubscribe from
- `function(client)` optional callback fired when unsubscription(s) succeeded.  NOTE: When calling unsubscribe() more than once, the last callback function defined will be called for ALL unsubscribe commands.

#### Returns
`true` on success, `false` otherwise

#### Example
```lua
-- unsubscribe topic
m:unsubscribe("/topic", function(conn) print("unsubscribe success") end)

-- or unsubscribe multiple topic (topic/0; topic/1; topic2)
m:unsubscribe({["topic/0"]=0,["topic/1"]=0,topic2="anything"}, function(conn) print("unsubscribe success") end)
```