Configure Non-Standard MQTT Options VerneMQ Supports.
Set the maximum size for client ids, MQTT v3.1 specifies a limit of 23 characters.
This option default to 23.
Usually, you'll configure permissions on your topic structures using ACLs. In addition to that, topic_max_depth sets a global maximum value for topic levels. This protects the broker from clients subscribing to arbitrary deep topic levels.
The default value for topic_max_depth is 10. As an example, this value will allow topics like a/b/c/d/e/f/g/h/i/k, that is 10 levels. A client running into the topic depth limit will be disconnected and an error will be logged.
This option allows persistent clients (those with clean_session set to false) to be removed if they do not reconnect within a certain time frame.
This is a non-standard option. As far as the MQTT specification is concerned, persistent clients are persisted forever.
The expiration period should be an integer followed by one of h, d, w, m, y for hour, day, week, month, and year; or never:
This option defaults to never.
Limit the maximum publish payload size in bytes that VerneMQ allows. Messages that exceed this size won't be accepted.
Defaults to 0, which means that all valid messages are accepted. MQTT specification imposes a maximum payload size of 268435455 bytes.