> In GRASP (RFC8990] we define the GRASP message structure as follows:
>
> message-structure = [MESSAGE_TYPE, session-id, ?initiator, *grasp-option]
>
> MESSAGE_TYPE = 0..255
> session-id = 0..4294967295 ; up to 32 bits
> grasp-option = any
>
> Then we've defined a few MESSAGE_TYPEs of which the one we are primarily
> interested in now is:
>
> flood-message = [M_FLOOD, session-id, initiator, ttl,
> +[objective, (locator-option / [])]]
>
> (its also the most difficult one).
>
> objective = [ objective-name, objective-flags, loop-count, ?objective-value ]
> objective-name = text
> objective-value = any
> […]
> So now the question is how we want to generically as possible extend the
> header.
> Our specific first goal is a signature extension, but hopefully we don't
> need to discuss this here (in this thread), as its not a CBOR/CDDL encoding
> question.
>
> Brians suggestion, if i understand him right would be something like this:
>
> EXTENSION_TYPE = 0..255
There is no reason to limit this to 255.
➔ EXTENSION_TYPE = uint
(Do you plan to creat a registry for these?
> grasp-extension = [ EXTENSION_TYPE, *any ]
This is of course possible.
CBOR also has tags, which might be a more natural structure.
> grasp-option /= grasp-extension
This doesn’t make sense: grasp-option already is any, so adding alternatives is
not going to have any effect.
Why are you using grasp-option here in any case?
You should be using your grasp-extension right away.
>
> flood-message = [M_FLOOD, session-id, initiator, ttl,
> +[objective, (locator-option / [])], *grasp-option ]
➔ flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])], *grasp-extension ]
> […]
> Questions:
>
> - Is it ok. to expect the analysis to have to do two steps (e.g.: A1, A2 or
> B3, B4)
> to decide whats' next (i called that lookahead in another mail thread).
I don’t understand the question. To find the end of +[objective, …], you look
for the first element of the [M_FLOOD, …] array that doesn’t match the
structure [[text…]…] that each of +[objective…] resolves to.
> - does "grasp-option /= grasp-extension" work.
It sure “works”, but doesn’t do anything.
> I ask because previously grasp-option
> was "any", so logically i am not sure if CDDL expect to pick the alternative
> that
> is more specific,
No; choices are tried in sequence (“prioritized choice" [1]).
[1]: https://www.rfc-editor.org/rfc/rfc8610.html#appendix-A
There is no point in mixing grasp-extension up with the wild card grasp-option.
Grüße, Carsten
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