mqtt

MQTT publish/subscribe client for broker-based telemetry and control.

Available on: Flexs Q5C Flexs Q5 Pro Flexs Q5M

The mqtt object connects to an MQTT broker, publishes topics and subscribes with a callback. Requires firmware V91 or greater.

A robust pattern is to call mqtt.connect() at the top of every loop iteration: if the client is already connected it simply returns code 207 (Already Connected), and if the connection ever drops it will reconnect.

Functions

mqtt.connect() — Connects to an MQTT broker and registers topic subscriptions with a callback.
mqtt.publish() — Publishes a message to an MQTT topic.
mqtt.disconnect() — Disconnects from the MQTT broker; call before the script exits.

mqtt.connect()

mqtt.connect(options) → number

Connects to an MQTT broker and registers topic subscriptions with a callback.

Options object fields:

Field	Type	Meaning
`url`	string	Broker address, e.g. `"mqtt://172.16.220.22:1883"`.
`client`	string	MQTT client ID.
`subscribe`	array	Topic filters to subscribe, wildcards allowed, e.g. `["power_system/relays/+"]`.
`callback`	function	Called for each received message with an event object `{ retain, qos, message, topic }`.

The callback's event.message can be a JSON string (parse with JSON.parse) or binary data (convert with the bin functions).

Returns 0 on success, 207 if already connected; any other value is an error code.

Arguments

Name	Type	Required	Default	Description
options	object	yes	—	{ url, client, subscribe: [...], callback } — see table.

Returns

number 0 = connected, 207 = already connected, anything else = error code.

Example

function mqttSubscriberCallback(event){
  print("MQTT EVENT: ", string(event));
  // {"retain":false,"qos":0,"message":"Hello World","topic":"power_system/relays/1"}
}

let ret = mqtt.connect({
  url: "mqtt://172.16.220.22:1883",
  client: "Nikiah Repeater",
  subscribe: ["power_system/relays/+"],
  callback: mqttSubscriberCallback
});
print("connect:", ret); // 0 ok, 207 already connected

mqtt.publish()

mqtt.publish(topic, message) → number

Publishes a message to an MQTT topic.

Publishes message to topic. Message data can be text or binary: convert objects with string(obj) first, and pack numeric arrays to binary with bin.fromArray().

Arguments

Name	Type	Required	Default	Description
topic	string	yes	—	Topic to publish to, e.g. `"power_system/battery_voltage"`.
message	string \| binary	yes	—	Payload. Objects: `string(obj)`. Numeric arrays: `bin.fromArray()`.

Returns

number 0 on success, otherwise an error code.

Example

let ret = mqtt.publish("power_system/battery_voltage", string(14.34));
print("publish:", ret);

mqtt.disconnect()

mqtt.disconnect()

Disconnects from the MQTT broker; call before the script exits.

Make sure the client is disconnected before the script exits.

Example

mqtt.disconnect();