Re: [cf-dev] Do you use CoapClient API?

[Simon Bernard <contact@xxxxxxxxxxxxxxx>]

Le 28/04/2016 13:15, Kraus Achim (INST/ESY1) a écrit :
> Hi Simon,
> Hi Matthias,
>
> [MK] The result, that this is now possible …
>
> I would say, it "pretends" that is now possible :-).
>
> But though Simon already clarified, that this was not his intention, I'm not sure, if we should continue to discuss the "intention".
>
> Therefore I would like to point more to the details, what happens, if the CoAP client receives two notifies for the same blockwise
> resource. Without E-Tag option, I would assume, that the first (deprecated notify according the OBSERVE Option)
> would possible report a "invalid" content (mixedup versions of the resources). So I'm just afraid of invalid content.
I'm not sure but as we have 2 exchanges in memory and each one use a 
different token, I guess that the content should not be mixed.
https://tools.ietf.org/html/draft-ietf-core-block-18#section-3.4
> Mit freundlichen Grüßen / Best regards
>
> Achim Kraus
>
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> Von: cf-dev-bounces@xxxxxxxxxxx [mailto:cf-dev-bounces@xxxxxxxxxxx] Im Auftrag von Kovatsch Matthias
> Gesendet: Donnerstag, 28. April 2016 12:44
> An: Californium (Cf) developer discussions
> Betreff: Re: [cf-dev] Do you use CoapClient API?
>
> From: cf-dev-bounces@xxxxxxxxxxx [cf-dev-bounces@xxxxxxxxxxx] on behalf of Simon Bernard [contact@xxxxxxxxxxxxxxx
>
> Le 28/04/2016 09:10, Kraus Achim (INST/ESY1) a écrit :
>
> Hi Simon,
>   
> ➢  What do you mean by several notifications transfered?
>   
> > This is the case where notifications is sent using blockwised (block2). If you send notification faster then server are able to handle (using block2), you can have several notification handle at the same time. Before as we have only one exchange for all the notifications, we dropped the older notifications. Now we are able to handle several at the same time.
>   
> If a resource, which is transferred blockwise, changes more frequently than you can transfer it, there is no guarantee that you still can read the old one!
> Only the “memory monster approach of californium with its own in memory copy” will do that. For the most embedded devices I would guess, that they
> could only provided the last version. (The blockwise therefore mentions to use E-Tag option to ensure, that the blocks of the resource belongs to the same
> version of the resource).
> Just to be clear about this point. This new behavior is not a wish, this is just a consequence. I just try to be exhaustive about the behavior changes.
>
> [MK] The result, that this is now possible is an indicator that the concept behind Observe is now violated. The whole point of Observe is to make state synchronization scalable. Did you have a look at Carsten's mail that I forwarded (Re: Events, Subscriptions, Link Bindings, and RESThooks)?
>
> Best regards
> Matthias
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