Query available topics on broker

[Florian Pirchner]

Hi,

i am looking for a way to query all available topics on the broker. Every clients registers with a unique topic. If i would know all the topics available i could send messages to a single client using its unique topic.

So far i could not find a feature.

Thanks a lot,
Florian

[Carl Hörberg]

It's not a feature of the protocol, but maybe the server you use has such a (non-standard) feature.

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[Andy Piper]

Hi Florian, thanks for joining the group.

On Wednesday, 17 July 2013 12:05:54 UTC+1, Florian Pirchner wrote:

i am looking for a way to query all available topics on the broker. Every clients registers with a unique topic. If i would know all the topics available i could send messages to a single client using its unique topic.

So far i could not find a feature.

That feature is not part of the MQTT spec and would have to be something provided by a broker as some kind of extension. 

Nicholas Humfrey has a MQTT-HTTP bridge app (https://github.com/njh/mqtt-http-bridge) which does list out the topics which have *retained publications* on a broker (you can see an example at http://eclipse.mqttbridge.com for the m2m.eclipse.org mosquitto broker), but it does it by subscribing to the wildcard # topic and then keeping a record of everything returned, and it will not work with ephemeral topics / topics without retained publications on them. Note that there's an open issue https://github.com/njh/mqtt-http-bridge/issues/2 which talks about the fact that currently, not all MQTT brokers behave in the same manner - RabbitMQ, Apollo, moquette and others will not work with that bridge app and this method of querying topics.

Andy

[Florian Pirchner]

Hi Andy,

thanks a lot. I will checkout.

Best Florian