Re: [sipcore] draft-barnes-sipcore-rfc4244bis

"Francois Audet" <audet@nortel.com> Thu, 09 July 2009 23:39 UTC

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Date: Thu, 9 Jul 2009 18:39:18 -0500
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From: "Francois Audet" <audet@nortel.com>
To: "Paul Kyzivat" <pkyzivat@cisco.com>
Cc: SIPCORE <sipcore@ietf.org>, Dale Worley <dworley@nortel.com>
Subject: Re: [sipcore] draft-barnes-sipcore-rfc4244bis
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Ok, cool: we have agreement.

I'll put a note to help the reader. 

> -----Original Message-----
> From: Paul Kyzivat [mailto:pkyzivat@cisco.com] 
> Sent: Thursday, July 09, 2009 15:31
> To: Audet, Francois (SC100:3055)
> Cc: Worley, Dale (BL60:9D30); SIPCORE; Barnes, Mary (RICH2:AR00)
> Subject: Re: [sipcore] draft-barnes-sipcore-rfc4244bis
> 
> 
> 
> Francois Audet wrote:
> > Dale, Paul,
> > 
> > Good catch.
> > 
> > The intent was not to impose an ordering requirement: the 
> intent was 
> > to impose that the hi-index parameter be present.
> > 
> > Paul: in RFC4244 there was NO ordering requirement.
> 
> Yeah. Dale pointed that out. I just assumed it had been carried over.
> 
> > What we are trying to achieve with the ABNF is:
> > 
> > - No ordering requirement
> > - There MUST be exactly ONE hi-index
> > - There MUST be 0 or 1 hi-target parameter
> > - There MUST be 0 or 1 hi-aor parameter
> > - There MAY be any number of hi-extension
> 
> Its already a restriction that parameters (in general) may 
> appear only once. It gets asked about from time to time. I 
> forget where it says that.
> 
> So you might not even need to say it. Certainly most of the 
> other header parameter syntaxes don't say it but clearly intend it.
> 
> But it probably would be helpful to put it in the text.
> 
> > I now see the current ABNF fails miserably to do this...
> > But I don't think it's trivial to express in ABNF.
> 
> As I started to show, it is technically possible. But as Dale 
> responded, and I generally agree, it does make the abnf 
> complex. Also, once you introduce generic-param all bets are 
> off, since syntactically you can match one occurrence against 
> the explicit name and another occurrence against generic-param.
> 
> > So I think then that Dale's semantic is better, and we just need to 
> > clearly state that index must be present, and that there 
> can be only 0 
> > or 1 of each of hi-target and hi-aor.
> 
> I agree.
> 
> 	Paul
> 
> >> -----Original Message-----
> >> From: sipcore-bounces@ietf.org
> >> [mailto:sipcore-bounces@ietf.org] On Behalf Of Paul Kyzivat
> >> Sent: Thursday, July 02, 2009 11:40
> >> To: Worley, Dale (BL60:9D30)
> >> Cc: SIPCORE
> >> Subject: Re: [sipcore] draft-barnes-sipcore-rfc4244bis
> >>
> >> Dale,
> >>
> >> I agree with your concern about the BNF. A requirement about the 
> >> ordering of the params is problematic.
> >>
> >> OTOH, this is a revision to an existing RFC which had that 
> ordering 
> >> requirement. Its possible that relaxing it might lead to interop 
> >> problems.
> >>
> >> Perhaps the best one can do is put in a recommendation to make the 
> >> index first.
> >>
> >> Regarding indicating that the index is required: it can be done in 
> >> text, but it can also be done in the BNF, as follows:
> >>
> >>     History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)
> >>
> >>     hi-entry = hi-targeted-to-uri hi-param-list
> >>
> >>     hi-targeted-to-uri = name-addr
> >>
> >>     hi-param-list = *(SEMI hi-option) SEMI hi-index *(hi-option)
> >>
> >>     hi-option = hi-target / hi-aor / hi-extension
> >>
> >>     hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)
> >>
> >>     hi-target = "rc" / "cc" / "mp" / "rt"
> >>
> >>     hi-aor = "aor"
> >>
> >>     hi-extension = generic-param
> >>
> >>
> >> 	Thanks,
> >> 	Paul
> >>
> >>
> >> Dale Worley wrote:
> >>> Regarding the BNF for the History-Info header (section 4.1 in the 
> >>> draft version of -02):
> >>>
> >>> The current BNF requires that the "index" parameter appear
> >> immediately
> >>> after the URI, whereas other parameters appear after it:
> >>>
> >>>    History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)
> >>>
> >>>    hi-entry = hi-targeted-to-uri SEMI hi-index *(SEMI hi-param)
> >>>
> >>>    hi-targeted-to-uri = name-addr
> >>>
> >>>    hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)
> >>>
> >>>    hi-param = hi-target/hi-aor/hi-extension
> >>>
> >>>    hi-target = "rc" / "cc" / "mp" / "rt"
> >>>
> >>>    hi-aor = "aor"
> >>>
> >>>    hi-extension = generic-param
> >>>
> >>> IMHO, this is not a good way to organize the grammar, as it
> >> makes it
> >>> difficult to generate hi-entry's with generic code (there
> >> needs to be
> >>> some way to constrain the "index" parameter to be first),
> >> and violates
> >>> the general rule that the order of parameters is not significant.
> >>>
> >>> I propose to adjust the BNF to:
> >>>
> >>>    History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)
> >>>
> >>>    hi-entry = hi-targeted-to-uri *(SEMI hi-param)
> >>>
> >>>    hi-targeted-to-uri = name-addr
> >>>
> >>>    hi-param = hi-index / hi-target / hi-aor / hi-extension
> >>>
> >>>    hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)
> >>>
> >>>    hi-target = "rc" / "cc" / "mp" / "rt"
> >>>
> >>>    hi-aor = "aor"
> >>>
> >>>    hi-extension = generic-param
> >>>
> >>> Of course, the "index" parameter is still mandatory per the
> >> semantic
> >>> constraints listed earlier in section 4.1.
> >>>
> >>> I've also inserted into the hi-index BNF some spaces around the 
> >>> instances of "/" for better readability.
> >>>
> >>> Dale
> >>>
> >>>
> >>> _______________________________________________
> >>> sipcore mailing list
> >>> sipcore@ietf.org
> >>> https://www.ietf.org/mailman/listinfo/sipcore
> >>>
> >> _______________________________________________
> >> sipcore mailing list
> >> sipcore@ietf.org
> >> https://www.ietf.org/mailman/listinfo/sipcore
> >>
> > 
>