Re: [mosquitto-dev] MQTT QoS 2 protocol problem

[Jos Vos <jos@xxxxxx>]

On Wed, Sep 19, 2018 at 06:48:10PM +0200, Manuel Domínguez Dorado wrote:

> AFAIK, message IDs don't guarantee the processing order of messages. Only
> having
> 
> max_inflight_messages *1*
> 
> would mosquitto preserve the processing order. That's... if you send
> messages 1, 2 and 3 to Mosquitto, Mosquitto will deliver them in that
> order. Otherwise, it cannot be assured.

Then the default Mosquitto configuration would not work according to
the spec (MQTT v3.1.1, paragraph 4.6 message ordering), AFAICS.

> Anyway, in relation to your problem with your second message not being
> "completed", from you log it seems that is the client the one that is not
> sending the PUBREL. The broker is sending PUBREC as expected. Which MQTT
> client are you using? Is it stable? In the past I had some problems when
> trying to send QoS2 message too fast to the broker, using an old version of
> PAHO.

This is all about the Dart MQTT library "mqtt_client" (used on Android
with Flutter), which is said to be a port of the C# nMQTT implementation.
Until now, I only have used Paho MQTT for Python (and Paho MQTT for JS
for a while) and I already found strange things in that Dart library
that appeared to be related to the same strange things in nMQTT :-(.

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