How to know how many retained messages are in a broker.

[pdufrene]

Hi,
I am using MqttClient class to connect to external Mqtt Broker.
On this Broker, are published several messages with retained flag inside root/topic1, root/topic2, root/topic3, ...
By default I don't know how many topics are under root.

I would like to retrieve all topics payload, so I subscribe to root/#, that's fine.
Is there a way to know/detect when I have received all payloads ?
Said differently, is there a way to know how many topics are below the topic root ?

[gfoidl]

In general a broker / server should publish SYS Topics -- see that list for the information you need.

external Mqtt Broker

It may depend on the concrete product you are connection too if the desired info as available or published.