Re: [core] Sketch of "Keep it simple" / "Never reified union types"

[Christian Amsüss <[e-mail]>]

Hello Michael and CoRE,

On Mon, Mar 11, 2019 at 08:23:23AM -0700, Michael Koster wrote:
> In the spirit of handling "empty topic" case in the application layer,
> as we discussed, I propose to have the publisher be responsible to
> publish "nothing-here-to-see" as a topic's initial value if it has no
> initial value in the more meaningful content format. 
> 
> (Keeping in mind that, as defined, CoAP pub/sub only handles
> representations, and is not strictly a proxy for resource state,
> therefore should not be responsible for generating default
> representations in any particular content format, except the required
> link-format in the case of create-on-publish).
> 
> The pub-sub behavior would be to reply to READ/SUBSCRIBE only when
> something has been published. The topic creator is thus responsible to
> "promptly" publish nothing-here-to-see upon topic creation. Otherwise
> the broker simply acks any READ/SUBSCRIBE request and waits to send a
> response until something is published. 

That would mean that any faulty (or malicious) topic creator could force
the broker into (costly-to-maintain in terms of memory) long-poll
situations, I'd prefer not to do that. (An alternative would be that the
broker answers 5.03 "I'm not in a state to process this request, retry
later please" with some Max-Age).


My gut feeling is that the broker can be argued to be the authority on
the topic (at least formally it is) and would thus be justified to say
that "empty" is its current representation, but I'll need to read the
latest version of pubsub to argue that well (or be taught better).

> This way, the Accept-Any option and the nothing-here-to-see content
> formats may be defined in separate independent drafts, and the
> multipart format may be used with its potential accept-subformat
> options.

I agree that Accept-Any can (and probably should) be separate.

Kind regards
Christian

-- 
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  -- Bene Gesserit axiom