Re: [core] WG Last Call on draft-ietf-core-conditional-attributes

[Christian Amsüss <[e-mail]>]

Hello Klaus, hello conditional-attributes authors,

On Thu, Jan 12, 2023 at 05:48:23PM +0100, Klaus Hartke wrote:
> Rather than interfering with under what conditions and in what way the
> server generates notifications, the draft should define how the server
> updates resource state and how the client can influence this.

I agree with most of the points in this review -- and would have
expected that after the 2019 Montreal meeting, the "projection" model
was already agreed on.

> An exception is an attribute like pmax, which makes a server send
> notifications that it wouldn't have to send with RFC7641. Such a
> change in protocol cannot be achieved by changing the way resource
> states are updated. Instead, the draft should describe it for what it
> is: a protocol extension. And for protocol extensions, we use options
> in CoAP.

I disagree on this point: pmax *can* be modelled as a projection. The
projected resource just needs to have a shorter Max-Age, and a
well-behaved CoAP server that maintains an observation will make sure
that observing clients receive a fresh representation (even if it was
unmodified) before. While that behavior of the server is not mandated,
there is a "server MAY wish to prevent that by sending a new
notification with the unchanged representation" in 7641, which I'm
regarding as best practice, and conditional-attributes server just have
even more reason to adhere to.

Thanks for writing this review
Christian

-- 
There's always a bigger fish.
  -- Qui-Gon Jinn