Subject: Re: [Simple] Does "Require: eventlist" indicate that the URI is a list?

From: Adam Roach <[email-masked]>
Date: Fri, 05 Dec 2008 16:38:35 -0600

On 11/27/08 4:16 AM, Avshalom Houri wrote:
>
> Since the evenlist package (RFC 4662) requires the inclusion of the 
> "Require:
> eventlist" header, does the server that gets a request with such a 
> header can
> assume that the subscribed to URI is a list and not a single presence?

No. Clients should not be including a "Require: eventlist" in a 
SUBSCRIBE; RFC 4662 addresses this point:

   Including "eventlist" in a "Require" header field in a SUBSCRIBE
   request serves no purpose except to break interoperability in certain
   cases, and is consequently NOT RECOMMENDED.

>
> I recall that in the past it was indicated that issue is a deployment 
> issue and
> there should be some internal indication in the URI itself if it is a 
> list or
> single subscription but in real life there may be deployments where 
> the PS/RLS
> does not control the component that can tell it if the URI is a list 
> or a single
> entity.

Even if it does not "control" that entity (however you define that word 
in this context), the RLS needs to be able to, at the very least, query 
that entity in order to retrieve the membership of the list. If that 
query successfully returns a list of resources, then the URI corresponds 
to a list. If that query does not successfully return a list of 
resources, then the URI does not correspond to a list.

/a
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---

From: Avshalom Houri <[email-masked]>
Date: Sat, 6 Dec 2008 18:29:49 +0200

[email-masked] wrote on 06/12/2008 00:38:35:

> Adam Roach <[email-masked]> 
> Sent by: [email-masked]
> 
> 06/12/2008 00:39
> 
> To
> 
> Avshalom Houri/Haifa/IBM@IBMIL
> 
> cc
> 
> [email-masked]
> 
> Subject
> 
> Re: [Simple] Does "Require: eventlist" indicate that the URI is a list?
> 

My mistake I meant the "Supported" header.

> resources, then the URI does not correspond to a list.

The issue here is that the fact that there is no indication that the URI
means a list causes a lot of issues in deployments:
- The list server may not be available for some time.
- This is really a URI for the list but the list was not created yet.

These type of issues add more complexity to any SIP deployment.

I think that there should be some way to indicate that the URI is a list 
or
a single subscription.

---

From: Adam Roach <[email-masked]>
Date: Sat, 06 Dec 2008 11:17:01 -0600

> My mistake I meant the "Supported" header.

Ah, that makes more sense. The answer is still "no." The client only 
knows whether it is willing to process a list for the resource -- it is 
the authoritative source regarding its own behavior, and nothing else. 
It is not the authority about what is and is not a list -- that 
responsibility clearly must reside in the network.

> I think that there should be some way to indicate that the URI is a 
> list or
> a single subscription.

That doesn't help. If the client gets it wrong (and if you've been to a 
SIPit, you are fully aware that some subset of clients will get it 
wrong), then the server needs to be able to detect this fact, and react 
accordingly. In order to do that, it must have access to the 
authoritative information regarding whether a specific URI is a list.

/a