Add MQTT source/destination

[harpesichord]

This needs some documentation to show what config options are needed, but it allows you to subscribe to an MQTT topic to receive messages or send messages to a topic.

[abraithwaite]

First off, this looks amazing! It's very insightful to see how you're using it and thinking about the code.

I realized a little late in the review that I hadn't been paying close enough attention to the generic implementation type being types.Event.

This is one particular area that I think is important to distinguish the framework from the daemon (and perhaps break apart the library from the daemon).

You see, I imagined the framework to provide primitives where things like MQTT, Kafka, Redis, etc, would implement kawa.Source[[]byte], and consumers of these low-level APIs would do the serialization as another layer on top. Kawa the daemon, for example, would be one of those consumers of kawa the library.

All that being said, I think this is useful and we should merge it. But it definitely led to me confusing myself about how you were using msg.Value and json.Marshaling the rawLog.

This is definitely something that should be in the docs. Would especially love to hear your thoughts on it too!

[ejcx]

Any reason we shouldn't merge this @harpesichord ?

[harpesichord]

I was going to consider Alan's points. I'll probably look at it again Sunday evening and then maybe we can merge Sunday night or Monday morning.

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On Fri, Aug 11, 2023, 7:03 PM Evan J Johnson ***@***.***> wrote: Any reason we shouldn't merge this @harpesichord <https://github.com/harpesichord> ? — Reply to this email directly, view it on GitHub <#22 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABDRAUI2JGHNNSZOGJDUD2LXU2237ANCNFSM6AAAAAA3GIMMLM> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[harpesichord]

@abraithwaite Can you check this again, make sure I followed your new pattern correctly.

[abraithwaite]

Awesome, thank you! This is precisely what I had in mind :-)

It still feels a bit awkward having the extra indirection wrapping the event type just for kawad, but I think it will make the sources and destinations in the library much more broadly useful.