Dynamic Topic Bridging

[david-katz]

Problem:
mosquitto is being used as a bridge for multiple local clients that are subscribing to topics on a remote MQTT broker.

There is a large number (1000s) of topics under the same root (a/1, a/2, a/2/x etc.) The local clients are only interested in a small subset (ca. 5) of all a/# topics, but will decide at runtime which of these topics are relevant to them.

The communications link between the bridge and the remote broker is expensive, so that messages on non-relevant topics must not be transmitted.

In order to solve this problem, I would like to discuss the possibility of introducing the following functionality to the mosquitto bridge:

• allow the bridge to be configured to bridge certain topic ranges (for instance a/#) without causing a subscription to happen on this range at bridge startup time.
• only if a subscription request is submitted by one of the bridge's local clients will a subscription be sent to the remote broker.
• when the local client unsubscribes, the subscription on the remote broker is also unsubscribed.

[ralight]

Sorry for the delay in responding, I'm completely swamped at work at the moment and that has an impact on the free time I have for mosquitto.

I think this sounds like an interesting idea and initially positive about it - but haven't had chance to think about the implications yet.

[aeri]

• only if a subscription request is submitted by one of the bridge's local clients will a subscription be sent to the remote broker.
• when the local client unsubscribes, the subscription on the remote broker is also unsubscribed.

I find these points really interesting, since the Issue is several years old, is it possible to do this with the latest versions of Mosquitto or is something similar planned?