Re: [lwip-users] MQTT Default Keepalive is 0, Mosquitto 2.0.12 requires a non-zero keep alive.

[Luciano Moretti]

Glad it helped.

The standard seems vague on what is to happen if there is no keepalive set. 

I agree that it's probably not something LwIP should change but something users need to be made aware of.

So far there's an issue filed 6 days ago with Mosquitto but no response from Mosquitto developers.

https://github.com/eclipse/mosquitto/issues/2309

On Thu, Sep 16, 2021, 12:06 AM Amr Elsayed <eng.amralsayed@gmail.com> wrote:

I read your message, before I was debugging the MQTT client and found I spent a good time debugging a connection refused from Mosquitto, after remembering your message and adding the keep-alive value, the problem got solved.

Thanks, yes it might need reconsideration but I think as in LWIP things need to be lightweight so only the minimum requirement of the standard should be the default as also Mosquitto does not represent the standard as far as I know.

Best Regards,

Amr.

On Wed, 15 Sept 2021 at 23:48, Luciano Moretti <luciano.moretti@gmail.com> wrote:

Found this issue today when we couldn't get our device to talk to a newly installed MQTT server: 

By default the LwIP MQTT Client sends a keepalive of 0 unless you set it yourself. Documentation in the header file says "0 to disable keep alive functionality"

Mosquitto 2.0.12 now requires a non-zero keep alive value.

Reading the MQTT specification it's not clear what should happen with a Keep Alive set to 0, stating "A Keep Alive value of zero (0) has the effect of turning off the keep alive mechanism. This means that, in this case, the Server is not required to disconnect the Client on the grounds of inactivity."  It's not required to disconnect, but it doesn't say that it can't immediately disconnect either.

Thought this might save some others some time.

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