MQTT Module

Since Origin / Contributor Maintainer Source
2015-01-23 Stephen Robinson, Tuan PM Vowstar mqtt.c

The client adheres to version 3.1.1 of the 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

-- 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", 1883, 0, function(client) print("connected") end, 
                                     function(client, reason) print("failed reason: "..reason) 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

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.
  • autoreconnect 0/1 for false/true, default 0
  • function(client) callback function for when the connection was established
  • function(client, reason) callback function for when the connection could not be established

Returns

true on success, false otherwise

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.

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)]) mqtt:subscribe(table[, function(client)])

Parameters

  • topic a topic string
  • 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

-- 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)

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
  • 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

-- 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)