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Re: MQTT

From: Daniel Stenberg via curl-library <curl-library_at_cool.haxx.se>
Date: Wed, 15 Apr 2020 23:20:49 +0200 (CEST)

On Wed, 15 Apr 2020, Christoph Krey via curl-library wrote:

> in MQTT protocol, the server may start to send PUBLISH messages (especially
> if those are retained) before replying with SUBACK to a SUBSCRIBE.
>
> The current implementation in curl waits for a SUBACK or DISCONNECT after
> the SUBSCRIBE.
>
> The ‘failure’ return code in the SUBACK should be checked.

Ah, right. I clearly need more test cases to verify (and fix) exactly these
things. Thanks! I'll make this my next step in mqtt land.

>> We might need a way to tell curl to disconnect after a certain number of
>> responses or something…
>
> Other than the test broker in curl `mqttd` a real broker will not send
> DISCONNECT after sending a PUBLISH message.

I figured. That particular behavior was a shortcut I took knowingly until I
learn how things *should* be done.

Do brokers ever send DISCONNECT in normal circumstances?

> curl should either disconnect after a certain number of PUBLISH messages was
> received and after a timeout if no (new) message were received.

Good feedback indeed.

libcurl users can basically accomplish that using existing callbacks.

For command line tool users, I suspect we need to add options for this. 

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Received on 2020-04-15