Overview

The Publish and Receive MQTT Messages node allows for sending and receiving metadata from the pipeline to a MQTT topic at a periodic interval or based on a trigger. This integration is useful for applications requiring real-time data exchange and monitoring.

Inputs & Outputs

Input media: Raw Video.
Output media: Raw Video.
Output metadata: topics, -topic, --last_message, --messages, --topic_delta, any_topic_delta, all_topic_delta.

Properties

Property	Description	Type	Default	Required
`publish_topic`	MQTT topic to publish to. Use Jinja2 template syntax to customize the topic using metadata.	`string`	`null`	No
`publish_with_retain`	If true, marks all published messages to be retained by MQTT broker.	`bool`	`false`	No
`trigger_type`	When to collect metadata. Options: Custom Trigger (`custom_trigger`): Collect metadata when a custom trigger is fired; Auto Trigger (`auto_trigger`): Collect metadata when significant node properties change; Interval (`periodic`): Collect metadata periodically; Startup (`startup`): Collect metadata on the first frame of the source; Shutdown (`shutdown`): Collect metadata when the deployment shuts down.	`enum`	`auto_trigger`	Yes
`trigger`	Send a MQTT message when this condition evaluates to true. Conditional on `trigger_type` being `custom_trigger`.	trigger-condition	`null`	No
`interval`	How frequently to send message. Set to 0 to publish every time metadata is collected. Unit: seconds.	`number`	`0`	Yes
`format`	Message Format. Options: JSON (Dynamic keys) (`json`): Send metadata as JSON with dynamic keys. Use certain attributes, e.g. ROI names, as keys. Useful for JSON path operations; JSON (Static keys) (`json_static`): Send metadata as JSON with static keys. Convert all attributes to a named static key; Custom Body (`custom_body`): Send custom body.	`enum`	`json`	Yes
`custom_body_template`	Use Jinja2 template syntax to customize the body of the message. Conditional on `format` being `custom_body`.	`string`	`{}`	Yes
`subscribe_topic`	Comma separated list of MQTT topics to subscribe to. Use Jinja2 template syntax to customize the topic using metadata. Inserts metadata from topic into node metadata.	`string`	`null`	No
`sanitize_messages`	Replace invalid characters in topic name with underscores so you can use them in trigger conditions.	`bool`	`true`	No
`persist_last_message`	If true, retains latest message in node metadata for each topic.	`bool`	`true`	No
`mqtt_protocol`	MQTT Protocol. Options: MQTT (`mqtt`); MQTT with SSL (`mqtts`); MQTT over Websocket (`ws`); MQTT over Websocket with SSL (`wss`).	`enum`	`mqtt`	No
`mqtt_host`	MQTT Host	`string`	`null`	Yes
`mqtt_port`	Port number to connect to. Leave blank to use default port based on MQTT Protocol.	`string`	`null`	No
`credential_type`	Credential Type. Options: Username and Password (`username_password`); Certificate (`certificate`).	`enum`	`username_password`	No
`username`	Username. Conditional on `credential_type` being `username_password`.	`string`	`null`	No
`password`	Password. Conditional on `credential_type` being `username_password`.	`string`	`null`	No
`certificate`	Certificate. Conditional on `credential_type` being `certificate`.	`string`	`null`	Yes
`certificate_key`	Certificate Key. Conditional on `credential_type` being `certificate`.	`string`	`null`	Yes
`validate_cert`	Validate SSL Certificate?	`bool`	`false`	No
`lastwill_message`	Lastwill Message	`string`	`null`	No
`lastwill_topic`	Use Jinja2 template syntax to customize the topic using metadata.	`string`	`null`	No
`debug`	Log Debug Messages?	`bool`	`false`	No

Template Syntax

custom_body_template, lastwill_message, lastwill_topic, publish_topic, and subscribe_topic uses Jinja2 Template Syntax for customizing the body of the MQTT message.

Variables available to the template:

Variable	Description
`meta`	Frame metadata. Contains keys like `nodes`, `objects`, and other custom metadata inserted by Custom function node.
`application_id`	The application ID of the deployment that produced this metadata.
`application_name`	The application name of the deployment that produced this metadata.
`deployment_id`	The deployment ID of the deployment that produced this metadata.
`deployment_name`	The deployment name of the deployment that produced this metadata.
`gateway_id`	The gateway ID of the deployment that produced this metadata.
`gateway_name`	The gateway name of the deployment that produced this metadata.

Example templates

Static text content:

Text content

Reference specific metadata:

{{ deployment_id }}

Metadata reinserted as is:

{{ meta | tojson }}

Output Metadata

The fields below are declared by this node's metadata schema; the JSON values are representative examples.

Path	Type	Description
`nodes.<node_id>.topics.<topic>.topic_delta`	`boolean`	When this topic has one or more new messages
`nodes.<node_id>.topics.<topic>.last_message`	`string`	Last message received for this topic
`nodes.<node_id>.topics.<topic>.messages`	`array`	All messages received for a topic.
`nodes.<node_id>.any_topic_delta`	`boolean`	When any topic has one or more new messages
`nodes.<node_id>.all_topic_delta`	`boolean`	When all topics have one or more new messages
`nodes.<node_id>.type`	`string`	Identifies the node type that produced this metadata.

JSON example

{
  "nodes": {
    "mqtt1": {
      "type": "mqtt",
      "topics": {
        "topic1": {
          "last_message": "message",
          "messages": ["message"],
          "topic_delta": true
        }
      },
      "any_topic_delta": true,
      "all_topic_delta": true
    }
  },
}