Re: [mqtt] DUP bit on QoS=1 message can be used for QoS=2 delivery ?

[Nicholas O'Leary]

Hi,

Sorry I missed your question the first time around and it appears I've
replied to your repost rather than the original.

Cheers,
Nick


On 30 June 2012 04:51, cogitoergosum <nages...@gmail.com> wrote:
> May I please request you to consider the following flow ?
>
> 1. Client sends PUBLISH message on topic t0 with DUP=0, messageId=1 with
> QoS=1.
> 2. Broker logs the message.
> 3. Broker finds n subscribers interested in t0.
> 4. Broker starts delivering to all n subscribers. For every delivery, the
> broker maintains a delivery log to indicate a message has been sent to this
> client.
> 5. All deliveries made, broker sends a PUBACK to the publishing client.
>
> Suppose, by the time 4 is happening, the publishing client has decided that
> it was waited long enough for the PUBACK and resends a PUBLISH with DUP=1
> and messageId=1.
>
> 1. Broker notes the PUBLISH has DUP=1.
> 2. Broker looks up to see who have already received the message. (See 4
> above. Note that, it is possible that, by this time new subscribers would
> also have subscribed to this topic. This would make the list of interested
> subscribers > n. Similarly, the number of interested subscribers could also
> become < n.)
> 3. Broker delivers to all subscribers who haven't already received messages.
> 4. All deliveries made, broker sends a PUBACK to the publishing client.
>
> So, eventually all clients receive only one copy of message.
>
> What am I missing ?
>
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