Re: [Cbor] [Anima] GRASP packet header extensions (CBOR question)

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 23 August 2022 22:51 UTC

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Date: Wed, 24 Aug 2022 10:51:12 +1200
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To: Toerless Eckert <tte@cs.fau.de>, Carsten Bormann <cabo@tzi.org>
Cc: anima@ietf.org, cbor@ietf.org
References: <Yv+miC76QMc887cJ@faui48e.informatik.uni-erlangen.de> <A303E7B3-A83F-4B04-9C6F-5143E4A0B54D@tzi.org> <5fa4a9c7-bc0a-cba0-04fb-4cf5e7777c9e@gmail.com> <4E167B3F-9C68-4333-BB76-36119B8F39DF@tzi.org> <fa2a8d32-929d-46ec-97b3-b67ad33c23b7@gmail.com> <YwNHvF1wzS0yaZGe@faui48e.informatik.uni-erlangen.de> <899DC56C-C1B5-4DC2-99DA-694B3FEF7C56@tzi.org> <YwSthGEEUDGgqqqz@faui48e.informatik.uni-erlangen.de>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Subject: Re: [Cbor] [Anima] GRASP packet header extensions (CBOR question)
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On 23-Aug-22 22:35, Toerless Eckert wrote:
> On Mon, Aug 22, 2022 at 08:43:57PM +0200, Carsten Bormann wrote:
> [... snip...]
>>> 2) Still want to understand .within correctly i think it does not doe
>>> not work as you hope above.
>>>
>>> Carsten claimed offlist, that in your above syntax, grasp-option would
>>> match some option that is not yet defined, as long as it matches
>>> option-structure. From reading rfc8610, i think this is wrong, because
>>> numeric-option is an AND between option and option-structure, so only
>>> any currently defined options will be matched. No extensibility to
>>> include any future options, even if they match option-structure.
>>
>> I’m not sure I understand the context of this, but yes, .within is a .and.  So you have to have both message-structure accept the message and the message choice as well.
>>
>> Obviously, we need a second layer of extensibility beyond adding new messages: adding new options to a message.
> 
> I think we've got that covered in our understanding.

Except that for me this will be a rare event since it requires
updates to the core part of GRASP, and should be avoided
unless essential.

> 
>> So each message production should have a *grasp-really-option at the end, where that stands for an actual (registered) option.
> 
> But that would not suffice to receive and ignore an option that
> was not specified in the CDDL at the time of the implementation of the
> receiver.

No, because *in any case* that is done by the programmer who writes
the decoder. The programmer needs text instructions; the CDDL cannot
provide those instructions.

> 
>>> Of course, i can be wrong, but then rfc8610 text is really misleading.
>>>
>>> 3) Here is what i propose:
>>>
>>>
>>>     grasp-option = valid-option / objective / any
>>>     valid-option = option .within option-structure
>>
>> (Valid-option is your grasp-really-option.)
>>
>>>     option-structure = [*any]
>>
>> No, an option starts with an option-type, so this should be
>>
>>     option-structure = [option-type, *any]
> 
> Oops. typo. Thanks
> 
>>>     option-type = uint
>>
>> Yep.
>>
>>
>>>
>>>
>>>     flood-message = [M_FLOOD, session-id, initiator, ttl,
>>>                     +[objective, (locator-option / [])], *grasp-option]
>>
>> Yes.
>>
>>>     "All other"-message = [ ... existing definitions ..., *grasp-option]
>>
>> Yes, that would be the whole-sale introduction of the second layer.
>> (Grasp-really-option, actually.)
>>
>> The [~message, *grasp-really-option] approach might be able to do this with fewer changes.
> 
> Hah. "~" is the unravel i was asking for in my other mail. Can that be
> used to do inline moficiation:
> 
>      flood-message = [ ~flood-message, *grasp-option ]
> 
> Or does that have to be a new name on the left-hand side ?
> 
>>> […]
>>
>>> We may also want to carve out ranges to indicate that an option received
>>> with such a numbe,if not known to the receiver must not be ignored but
>>> needs to result in an error condition.
>>
>> (Negative numbers would lend themselves to this…)
> 
> Right...
> 
>>> 5) M_FLOOD
>>>
>>> M_FLOOD still has the added issue, that it can have multiple objectives,
>>> and we do not have a way to express per-objective options. Which bugs me.
>>
>> … a fourth layer of extensibility…
> 
> Yeah. Still trying to find the killer use-case of two objectives requring different
> options to make that point.

My opinion today is that it was a mistake to allow multiple objectives in one
flood message. We should have stuck to a KISS approach.

    Brian

> 
> Thanks
>      Toerless
> 
>>
>> Grüße, Carsten
>>
>>
>