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Re: MQTT

From: Christoph Krey via curl-library <curl-library_at_cool.haxx.se>
Date: Wed, 15 Apr 2020 20:01:47 +0200

Hello,

>
> I tried doing:
>
> ./curl 'mqtt://test.mosquitto.org/de.wsv/pegel/cm/ems/emshoern' --output -
>
> That topic currently has a retained message with content "582". The
> response I get from curl is:
>
> curl: (8) Weird server reply
> de.wsv/pegel/cm/ems/emshoern582

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.
>
>> ./curl mqtt://test.mosquitto.org/de.wsv/#
>> ./curl 'mqtt://test.mosquitto.org/de.wsv/#'
>>
>> Which I would expect would subscribe using the multilevel wildcard '#'. I
>> tried both forms to try and be sure that it wasn't the shell swallowing the
>> #.
>
> '#' is special in URLs, as it marks a fragment. You need to URL encoded such
> characters as %23.
>

Good to know!
>
> 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.

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

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Received on 2020-04-15