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Hi,
For QoS > 0, message will never "fail" to get published. Paho
library will ensure that those message get published and received
by the broker. QoS > 0 messages always get queue (in memory),
are only removed when publish is successful (when on_publish is
called) and are retried if not received (IIRC, after waiting the
keepalive duration).
So if you only care about not losing message while the client is
running, Paho library already does it.
If you need on disk persistent queue, then your usage of sqlite
seems good. You do not need a timer to re-publish message (the
in-memory queue of paho library will handle it), but only
re-publish all messages from sqlite when your client restart.
Regards,
Pierre Fersing
Le 28/04/2017 à 07:48, Amr Bekhit a
écrit :
Hello all,
I'm using the Paho Python MQTT client 1.2.0. As far as I
can tell, the library provides the following mechanism for
checking that a message has been transmitted successfully:
first, the .publish method can return a success or error code
to indicate whether or not the client is connected. After
that, once the message has been transmitted successfully (the
definition of success varying depending on the QoS), the
on_publish callback is called.
However, I couldn't find any sort of mechanism that would
allow me to detect if a message was successfully queued for
publishing failed to get published. Does one exist? If not,
any recommendations on how such a thing would be implemented?
At the moment, I've got a transmit queue stored in an sqlite
database. Once the message has been successfully passed to
publish, I update the entry with the mid value, indicating
that the message is currently queued for transmission. The
on_publish callback is then responsible for removing the
message from the database. I'm thinking that I would need to
implement some sort of timer that regularly checks the
database and resets any messages that have been passed to
publish, but not been removed after a certain period of time.
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