MQTT API Connector
Parameters
| Name | Values | Description |
|---|---|---|
| Type | MQTT | The connector type identifier. |
| Address | IP address or hostname | The MQTT broker's address. |
| Port | integer | The broker's MQTT port. |
| ClientId | string | The MQTT client identifier to connect with. |
| Username / Password | string | Broker credentials, if required. |
| Version | MQTT protocol version | The MQTT protocol version to connect with (e.g. v3.1.1 or v5.0.0). |
| QOS | 0, 1, or 2 | The default Quality of Service level for publishes (AtMostOnce/AtLeastOnce/ExactlyOnce). Defaults to AtLeastOnce. |
| Retain | true/false | Whether published messages are retained by the broker. Defaults to true unless explicitly set to false. |
| Persistent | true/false | Whether to request a persistent (non-clean) session from the broker. |
Overview
The MQTT connector provides tag-based subscription and on-demand publish access to a general-purpose MQTT broker, using MQTTnet. Unlike the device-level connectors, it has no polling loop of its own - all of its periodic work (connection monitoring, reconnection, and the heartbeat) runs inside a single dedicated background loop.
Incoming messages on a subscribed topic are written directly to whichever tag's Address matches that topic. Publishing (SENDDATA/PUBLISHDATA) is available on demand via connector methods.
The connector detects when the broker connection is lost and reconnects automatically without blocking - reconnection runs on its own dedicated background thread, and an explicit disconnect is issued before every reconnect attempt to avoid MQTTnet's own "not allowed to connect while connect/disconnect is pending" race.
Supported Tag Types:
Every MQTT payload is plain text, so there's no DataType disambiguation needed - the raw payload string is passed straight to each tag's own SetValue, and the tag type itself (BoolTag/IntTag/DecimalTag/StringTag/etc.) handles its own coercion.
| Tag Type | Address | Behaviour |
|---|---|---|
| Any standard tag | An MQTT topic, matched case-insensitively | Subscribed on connect; updated whenever a message arrives on that topic. |
Connector Methods
| Name | Arguments | Description |
|---|---|---|
| SendData | Topic | Builds a payload from a configured schema (populated via DATA|<field> args) and publishes it to the given topic. |
| PublishData | Topic, Data | Publishes an arbitrary payload to the given topic. |
| ResetTag | Name, Value | Sets a tag's value directly, without going through MQTT. |
Addressing
The Address field of a tag is the literal MQTT topic to subscribe to. Publishing is only available via RunMethod("SENDDATA"/"PUBLISHDATA") - there's no tag-driven "write triggers a publish" mechanism.