Retained message on load session for client re-connection

[Paolo Patierno]

Hi all,

I have a doubt on the MQTT 3.1.1 spec ... or at least it's not clear to me.

It's clear that after a SUBSCRIBE message for a "topic", if there is a retained message for that "topic" it is sent to the client as last known message.

Now, imagine that a client connect with clean-session 0 and subscribes to some topics. It starts to send SUBSCRIBE messages so it receive retained messages if present.
The client disconnect.
The client reconnect with clean-session 0 and the previous session is loader by the broker. It means that the client is already subscribed to "topic" and it doesn't need to send SUBSCRIBE. In this scenario, does it receive the retained message for "topic" ?

I'm a bit in doubt because the re-subscription isn't executed with a "real" SUBSCRIBE message but just from a re-loading session by the broker.

Thanks,
Paolo.

[Roger Light]

Hi Paolo,

My reading is that retained messages get sent each time a client sends
a SUBSCRIBE message and only then. In your example if the client
doesn't send a SUBSCRIBE message when it reconnects, it won't receive
any retained messages.

Cheers,

Roger

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[Paolo Patierno]

Hi Roger,

it seems the same for me. I agree with you but the spec isn't so clear on that.

Thanks,
Paolo.

[Andy Stanford-Clark]

yes, that's how it's meant to be
Andy