# MQTT (WIP) MQTT (Message Queuing Telemetry Transport) is a lightweight, publish-subscribe network protocol that transports messages between devices. Designed for constrained environments, it is ideal for machine-to-machine (M2M) or Internet of Things (IoT) scenarios. MQTT operates over TCP/IP and aims to be simple and efficient, ensuring high performance and reliability even on low-bandwidth networks. In MQTT, topics are used to filter and direct messages between clients. A topic is a string, typically representing a hierarchy, that defines the destination of the message. Topics are case-sensitive and use a forward slash (`/`) as a delimiter to create levels of hierarchy. For example, `home/kitchen/temperature` and `home/livingroom/humidity` are distinct topics. ## Creating an MQTT instance ### Creating an MQTT instance The `create` function creates an MQTT instance with which a client connection to an MQTT broker over an arbitrary transport method (TCP, TLS, WebSocket, ecc) can be [created](#connect). The MQTT client automatically handles the following: * Regular server pings * QoS flow * Automatic reconnections * Start publishing before being connected Simply drag the `create` function onto the board, name your instance and trigger.

### Deleting an MQTT instance Drag the `delete` function onto the board, insert the name of the instance to be deleted and trigger it.

## MQTT functions ### connect With the connect function, you can connect the MQTT instance to a broker. To create the connection, drag the connect function onto the board. Insert `url: {url}` into the url field, where you replace the curly brackets and their content with your URL. The following protocols are supported: `mqtt`, `mqtts`, `tcp`, `tls`, `ws`, `wss`, `wxs`, `alis`. Then, in the second input field, add `options: {}` as the main key and insert the following parameters in object format in the brackets as needed.

Parameter	Type	Default	Description
username	String		The username required by your broker, if any.
password	String		The password required by your broker, if any.
wsOptions	Object	`{}`	Specific options for WebSockets. Have a look at: https://github.com/websockets/ws/blob/master/doc/ws.md.
keepalive	Integer	`60`	Keep alive interval, set to 0 to disable.
reschedulePings	Boolean	`true`	Reschedule ping messages after sending packets.
protocolId	String	`MQTT`	Protocol ID
protocolVersion	Integer	`4`	Protocol Version
clean	Boolean	`true`	Set to false to receive QoS 1 and 2 messages while offline.
reconnectPeriod	Integer	`1000`	Interval between two reconnections in milliseconds. Disable auto reconnect by setting to 0.
connectTimeout	Integer	`30000`	Time to wait before a CONNACK is received in milliseconds.
queueQoSZero	Boolean	`true`	If connection is broken, queue outgoing QoS zero messages.
autoUseTopicAlias	Boolean	`false`	Enabling automatic Topic Alias assign functionality.
resubscribe	Boolean	`true`	If connection is broken and reconnects, subscribed topics are automatically subscribed again.

### publish With the publish function, you can send a message to a topic. Insert the topic in the first box, the message in the second one and lastly, decide on the options to publish with. The options need to be constructed as an object, with the highest key being `options` with the following three parameters nested inside, as needed:

Parameter	Type	Default	Description
qos	Integer	0	Quality of Service level
retain	Boolean	false	Whether to retain the message or not. For an explanation of retained messages, see here.
dup	Boolean	false	Marks the message as duplicate.

### publishJson The `publishJson` function works in the same way as the [publish](#publish) function, but delivers a JSON message instead. Therefore, in the second input field, you should insert a JSON object. ### subscribe With the `subscribe` function, you can subscribe to one or multiple topics. If you only want to subscribe to one topic or with a wildcard, insert the topic in the first input box and the qos setting in the second one. If you want to subscribe to multiple topics, ignore the options box and insert an object into the topic input box in the following scheme: ```javascript topic1: {qos: 0} topic2: {qos: 1} ``` {% hint style="info" %} #### Topic Wildcards MQTT supports two types of wildcards for subscribing to multiple topics: 1. **Single-level wildcard (`+`)**: Matches exactly one topic level. For instance, `home/+/temperature` matches `home/kitchen/temperature` and `home/livingroom/temperature`. 2. **Multi-level wildcard (`#`)**: Matches all subsequent levels. For example, `home/#` matches `home/kitchen/temperature`, `home/livingroom/humidity`, and any other topic starting with `home/`. Using these wildcards, you can flexibly subscribe to a range of topics. {% endhint %} ### onJsonMessage The `onJsonMessage` function needs to be triggered once after the app is started to start listening to events. It then converts the received events into JSON objects. ### onStringMessage The `onStringMessage` function needs to be triggered once after the app is started to start listening to events. It then converts the received events into strings. ### onBinaryMessage The `onBinaryMessage` function needs to be triggered once after the app is started to start listening to events. It leaves the received events in binary format. ### unsubscribe With the unsubscribe function, you can remove a subscription by inserting the topic name in the input field and triggering. ### end With `end`, you can disconnect from the MQTT broker. The disconnect may take a second, but can be forced to immediately happen, without waiting for the inflight messages to be handled, by inserting `forced: true` in the input field. ### isConnected `isConnected` simply returns `true` if a connection to an MQTT broker is open and `false` if not.

### isReconnecting With `isReconnecting` you can check if the client is currently trying to reconnect to the MQTT broker. A reconnection in progress is indicated by `true`.

Checking if MQTT connection is being reestablished

### getLastMessageId You can output the message ID of the last message sent by the client with `getLastMessageId`.