Delayed Messages

1. Delayed Messages

​ When a client publishes a message using the special topic prefix $delayed/{DelayInteval}, the delayed publishing feature is triggered, allowing messages to be published after a user-configured time interval.

The specific format of a delayed publishing topic is as follows:

  $delayed/{DelayInterval}/{TopicName}

• $delayed: Messages that use $delay as the topic prefix are all treated as messages that need to be published with a delay. The delay interval is determined by the content of the next topic level.
• {DelayInterval}: Specifies the time interval for delayed publishing of the MQTT message, in seconds. The maximum allowed interval is 4294967 seconds. If {DelayInterval} cannot be parsed as an integer, the message is discarded and the client receives no information.
• {TopicName}: The topic name of the MQTT message.

For example:

• $delayed/15/property/post: The MQTT message is published to the topic property/post after 15 seconds.
• $delayed/60/a/b: The MQTT message is published to a/b after 1 minute.
• $delayed/3600/$SYS/topic: The MQTT message is published to $SYS/topic after 1 hour.

Below Is the Delayed Message List

Message Id

Topic

QoS (Quality of Service)

Node

Client Id

Publish Time

Retained

Operation

Remaining Delay Time

Delay Time

Retained Message Details

Supports plainText, Json, and Hex parsing

Using MQTTX to Simulate Delayed Publishing

Start an MQTTX client

Edit a delayed message topic; here the delay is 15 seconds: $delayed/15/info/post

Send the delayed message. Note: you can create another client first and then send the delayed message

Create a new client and subscribe to the topic /info/post

From the demo above, we can get the result: the client on node A sends the topic $delayed/15/info/post, whose actual published topic is info/post, and the client on node B has subscribed

to the topic info/post. After waiting 15 seconds, the client on node B receives the message on the delayed topic.