Re: [Lwip] [core] Proxies and observations: "All options MUST be identical"

[Klaus Hartke <[e-mail]>]

Christian Amsüss wrote:
> This is something that servers, especially proxies, should not try to
> enforce, because every case of a request with differing options (or
> FETCH payload) could just as well be a new observation from the client
> on the token whose observation cancellation got lost, or the client
> simply rebooted.

If it's a new observation, then the client should not use a token that
is still in use. RFC 7252 Section 5.3.1:

   The client SHOULD generate tokens in such a way that tokens currently
   in use for a given source/destination endpoint pair are unique.

This requirement is slightly relaxed when a client wants to
re-register its interest in a resource, but only under narrow
circumstances: namely that the request is (almost) identical.

This is a requirement for clients, however.

In case a server (or proxy in the role of a server) receives an
observation request with a token that is still in use, it must kill
the existing observation. RFC 7641 Section 4.1:

   The entry in the list of observers is keyed by the client endpoint
   and the token specified by the client in the request.  If an entry
   with a matching endpoint/token pair is already present in the list
   (which, for example, happens when the client wishes to reinforce its
   interest in a resource), the server MUST NOT add a new entry but MUST
   replace or update the existing one.

So the server already doesn't enforce the client requirement.

Klaus