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Managed client clean session support
Hi, I just would like to understand the rational behind the fact that the Managed client does not support Clean Session. Even if I implement my own managed client, because I need to recover the session I wonder if I'm missing something there. Regards.
Hi, the problem is that it requires some more complex subscription handling.
Lets say you just pass true via connecting. Then the managed client will still subscribe to all topics automatically (like at the moment). But then he will get all retained messages for that topic. If the session exists the subscriptions also exist at the server. So there is no need from the client to do this. But if the client ignores this fact he subscribes and then receives all retained messages.
This is not a problem in general but some users may don't want this. Other may accept it. So it should be configurable in my opinion or supported out of the box. So this means the subscriptions must be handled including a flag saying "this subscription is approved by the server". It has to be set only after a successful SubAck. Then after a reconnect the client must inspect the ConnectAck if the session is really existing. If the session is still new all subscriptions must be invalidated and subscribed again.
But if this flow works well it can happen that a client ID is used twice (by accident). If the second client creates a new session with other subscriptions the original client may find another session after taking over the connection and thinks that the session exists (and thus is his one). So the client will keep a broken set of subscriptions.
I hope this gives you a quick overview about the reasons which causes the not supported existing sesions (yet).
Best regards Christian
At the moment this is on low priority. I am mostly busy with MQTT v5 support. After this is done I will prepare some other tasks. But it is still possible to use the core Client and build a managed client with the exact required features.
Hi, this is exactly what I need. Nevertheless, for me it's ok to just set cleansession to false, I don't use retain messages on the same topic. So subscribing again will not result in unwanted behaviour I think. I'll try that.
I downloaded the managed client and modified a little bit to support clean session false, and it have been working perfectly in a small prod server. It would be great if the feature could be included in the nugget package but in the mean time if you need a workaround that's what you can do.
I also have this topic on my list but had no time to start it. So please be patient and wait some more time :smile:
@chkr1011
I'd like to use ManagedMqttClient with persisted sessions. I see that this PR has been merged already. Unfortunately 3.0.9-rc1 does not have it.
Would it be possible to publish an rc2 package?
