Republish Action

The republish action is used to resend a new MQTT message. The Topic, QoS, Retain, and Payload of the new message can be specified by parameters.

Note that the message republish action does not terminate the delivery of the original messages. For example, if a message "t/1" is received by the republish action, and a new "t/2" message is republished, the delivery of "t/1" will not be terminated. Clients subscribed to the "t/1" topic will still receive the original message.

Create Rule and Action

1. Click on the Rule Engine -> Rules in the left navigation menu of the Dashboard.
2. Click the + Create button on the page and enter the following SQL example in the SQL text box:

SELECT

  *

FROM

  "t/1"

3. In the Action area, click + Add action and choose Data Forward -> Republish from the Action Type dropdown. Configure the following parameters:

   • Target Topic: The topic name to which the message is forwarded, with a default value of repub/to/${clientid}. The parameter type is String. You can use placeholder variables like ${repub/to/${clientid}}, which, when used in conjunction with rule SQL, represents using the publisher's clientid as a suffix. If you choose a custom business rule SQL, you can use other variables to replace it.

   • Target QoS: The QoS level of forwarded messages, with a default value of 0. The parameter type is an Integer or placeholder variable. You can use 0, 1, or 2, or placeholder variables like ${qos}, which, when used in conjunction with rule SQL, represents the original message's QoS level. If you choose a custom business rule SQL, you can use other Integer type variables to replace it.

   • Target Retain: The retain flag of the forwarded message. The parameter type is Boolean or placeholder variable. The optional values are false, true, or ${flags.retain}, with a default value of false. When used in conjunction with rule SQL, ${flags.retain} represents using the original message's Retain flag. For custom business rule SQL, you can use other Boolean-type variables as substitutes.

     Note

     When QoS and Retain are set using placeholder variables, if the parameters obtained from the message information are invalid (i.e., QoS is not 0, 1, or 2, and Retain is not true or false), the message will be discarded, and this action will be marked as failed.

   • Payload Template: The content of the forwarded message with the type as String. You can use placeholder variables like ${payload} to represent the original message's payload when used in conjunction with rule SQL. If you choose a custom business rule SQL, you can use other variables to replace it.

   • MQTT Properties: You can add predefined key-value pairs to configure the MQTT properties of the forwarded message. Optional keys include Payload-Format-Indicator, Message-Expiry-Interval, Content-Type, Response-Topic, Correlation-Data, Subscription-Identifier, Topic-Alias, and others, used to represent Payload format, message expiry time, content MIME type, request-response topic, message correlation, and more. For definitions, refer to the MQTT 5.0 specification.

   • User Properties: You can add custom key-value pairs to configure the user properties of the forwarded message, which represent custom message metadata.

     TIP

     MQTT properties and user properties provide richer message descriptions than topics and payloads, enabling the extension of MQTT's application scenarios with more semantic information.

   Once the configuration is complete, click the Confirm button. You will see that the action has been added.

4. Return to the Create Rule page and click the Create button at the bottom of the page.

   

Test Rule and Action

1. Use the desktop MQTT client MQTTX. Set the clientid to 123456, connect to the device, and subscribe to repub/to/#.

2. Post a message and you can see that the client received a message with the topic repub/to/123456.