MQTT Module

Since Origin / Contributor Maintainer Source
2019-01-28 Javier Peletier mqtt.c
2018-10-08 Tuan PM, Espressif mqtt.c

The client supports version 3.1 and 3.1.1 of the MQTT protocol. Make sure that the correct version is set with make menuconfig -> "Component config" -> "ESP-MQTT Configurations" -> "Enable MQTT protocol 3.1.1".

Unsupported transport modes

Even though the MQTT configuration offers the transport modes Websocket and Websocket Secure, they are currently not supported by the mqtt module.

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

-- 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 either an interger with 0/1 for false/true (default 0), or a table with optional entries
    • ca_cert CA certificate data in PEM format for server verify with SSL
    • client_cert client certificate data in PEM format for SSL mutual authentication
    • client_key client private key data in PEM format for SSL mutual authentication Note that both client_cert and client_key have to be provided for mutual authentication.
  • 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 (optional). A broker will publish a message with qos = 0, retain = 0, data = "offline" to topic "/lwt" if client does not send keepalive packet.

As the last will is sent to the broker when connecting, lwt() must be called BEFORE calling connect().  

The broker will publish a client's last will message once he NOTICES that the connection to the client is broken. The broker will notice this when:  - The client fails to send a keepalive packet for as long as specified in mqtt.Client()  - The tcp-connection is properly closed (without closing the mqtt-connection before) - The broker tries to send data to the client and fails to do so, because the tcp-connection is not longer open.

This means if you specified 120 as keepalive timer, just turn off the client device and the broker does not send any data to the client, the last will message will be published 120s after turning off the device.

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)
  • 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)])

Parameters

  • topic a topic string
  • qos QoS subscription level, default 0
  • 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

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

Caution

Rather than calling subscribe multiple times in a row, you should call the next subscribe from within the callback of the previous. A generic example is provided in mqtt_helpers.lua.

mqtt.client:unsubscribe()

Unsubscribes from one or several topics.

Syntax

mqtt:unsubscribe(topic[, function(client)])

Parameters

  • topic a topic string
  • 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.

Caution

Rather than calling unsubscribe multiple times in a row, you should call the next unsubscribe from within the callback of the previous. A generic example is provided in mqtt_helpers.lua.

Returns

true on success, false otherwise

Example

-- unsubscribe topic
m:unsubscribe("/topic", function(conn) print("unsubscribe success") end)