Re: [paho-dev] MQTT C++ Paho Client - Delivers QOS2 message before hand-

[Rajesh Jangam <rajesh@xxxxxxxxxxx>]

Thanks Nick for your quick response. Appreciate it!

Got it, that clarifies it (we're maintaining in flight message ids).

A follow up question though:

What would happen let's say when the client restarts (while it was in middle of the QOS2 flow) and it has does not start a clean session?

In my use case, we are planning to invoke commands (like Power OFF, Decrease pressure etc.) on a machine (say a turbine/compressor etc.) that would be delivered from a central server using QOS2.

Thanks,

Rajesh

On Wed, Mar 11, 2015 at 2:22 PM, Nicholas O'Leary <nick.oleary@xxxxxxxxx> wrote:

Hi Rajesh,

The state it stores through the qos2 flow will ensure it does not deliver a duplicate message until the flow completes.

When it delivers the message on receipt of the publish, it must still store the ID of that message until the PUBREL/PUBCOMP exchange completes. That allows it to detect duplicate PUBLISHES arriving with the same ID.

Nick

On 11 March 2015 at 07:49, Rajesh Jangam <rajesh@xxxxxxxxxxx> wrote:

Hello,

I have a small question regarding handling of QOS2 messages.

I noticed that in the C++ client, we seem to be delivering the QOS2 message immediately

after receiving the PUBLISH message from the broker.

We assume that the next sequence PUBREC/PUBREL/PUBCOMP is going to complete fine.

It may lead to re-deliveries by the broker (in case the next sequence does not finish up properly).

Please let me know your opinion.

Regards,

Rajesh

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