Re: [Ace] ace-coap-est-08: using /skg with Accept Option set to TBD287

[Esko Dijk <[e-mail]>]

> It seems a totally adhoc way that totally subverts the content-type system.
> It really seems like we need to take this to CORE.

Well it's the definition of the multipart-ct that causes the subversion of the content-type system! CoAP as a protocol doesn't know about multipart. If we would like to re-use the proper CoAP content-type system, it means each possible combination of multipart that is being used or returned should get its own unique Content-Format ID assigned. Like Panos indicated that could amount in our case to 4 content-formats for /skg.
The use of a generic "multipart" type (62) effectively renders the CoAP content-format system useless for use in sub-content-format selection.

If not using this content-format system - using a query parameter is a fully CoAP compliant next-best way to handle this situation while still using the generic multipart type 62. The basic CoAP rules are thus still fulfilled, i.e. the resource offers type 62 and it returns type 62 always, while the query parameter merely influences the processing of POST on this resource as is quite common in HTTP/CoAP operations. For example in HTTP I could POST some data to a resource that creates different HTML layouts that can be selected by a query parameter:
 POST /genReport?layout=nice1
 { data }

It still returns one and the same content type (HTML) although the contents may be totally different, depending on the 'layout' parameter. Same reasoning goes for our multipart content-format. In CoAP semantics, the inner types of the multipart are in no way bound to the requested Content-Format and may be arbitrarily changed depending on query parameters. 

But I agree this can be taken to CoRE in context of the draft-multipart-ct discussion; see what people think about this issue.

Esko


-----Original Message-----
From: Michael Richardson <[e-mail]> 
Sent: Thursday, February 14, 2019 15:38
To: Panos Kampanakis (pkampana) <[e-mail]>
Cc: Klaus Hartke <[e-mail]>; Esko Dijk <[e-mail]>; [e-mail]
Subject: Re: [Ace] ace-coap-est-08: using /skg with Accept Option set to TBD287

Panos Kampanakis (pkampana) <[e-mail]> wrote:
    > Hmm, that is a fair point. I don't think it is warranted to register
    > four more content formats for all possible format combinations in the
    > multipart response.

    > It looks to me that your proposal of using Uri-Query in the request in
    > order for the client to define the supported formats of the requested
    > resource/response is a good one.

It seems a totally adhoc way that totally subverts the content-type system.
It really seems like we need to take this to CORE.

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