On 1/30/19 10:23 PM, Dale R. Worley wrote:
It's a fascinating problem. In a way, inserting a unregistered
attribute is forbidden, but any recipient is forbidden from objecting to
it.
OTOH, if the attribute is unregistered, you can't really say that the
endpoint using it in its answer is *wrong*, since there's no fixed
definition of the semantics of the attribute. Perhaps the endpoint
simply means "I received CustomAttribute:GID in the offer."
I think the actual answer is to be clever, and to define CustomAttribute
in such a way that simply copying it into the answer unchanged can be
detected and ignored.
The device that copies unknown attributes from the offer to the answer
is even more broken than those that use unregistered attributes. It can
break valid usage. So I would really lean on it to clean up its act.
Many attributes are defined so that mirroring the attribute in the
answer explicitly indicates support for it. So defining one so that
usage is ignored seems futile.
Presumably the offerer including the attribute is hoping for an answerer
that has the same understanding of it. But the two devices could have
independently chosen to appropriate the same name for two different
purposes. I guess they hope that if the name is sufficiently unique
then the probability of this happening is small enough to ignore.
Thanks,
Paul
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