Re: [Sip] Question regarding conflicting grammar for IPV6 SIP URI andRFC 3986

["Dale Worley" <dworley at nortel.com>]

On Thu, 2008-12-18 at 19:09 -0500, Hadriel Kaplan wrote:
> The SIP URI is not the only one with this problem - RFC 3860 (im-URI),
> RFC 3859 (pres-URI), RFC 3508 (h323-URI), and who knows what else
> violate that rule.
> 
> Seems to me any "fixing" should be done to RFC 3986, probably as an
> errata.

Let's get a grip on the origin of the problem.

The generic URI grammar was stimulated by HTTP URIs.  They assume that
*if* the URI contains the designation of a host, it will be flagged by
the initial "//" -- and the syntax allows "all the standard syntaxes for
hosts" in that location.  Now if SIP URIs we constructed on that format,
we'd have "sip://dworley at nortel.com".  But I don't expect that to change
any time soon.

So let's ask, why are SIP URIs written as they are?  Clearly, it's
because they're based on e-mail addresses, or rather, the "mailto:"; URI
scheme:  "mailto:dworley at nortel.com --> sip:dworley at nortel.com".  Hmmm,
doesn't that mean that mailto: URIs have the same problem?  And, as
Hadriel notes, *all* the URIs based on the mailto: URI?  What have the
"mailto" people done about this?

That doesn't take long to look up:  Page 2 of RFC 2368 says:

     mailtoURL  =  "mailto:"; [ to ] [ headers ]
     to         =  #mailbox
     headers    =  "?" header *( "&" header )
     header     =  hname "=" hvalue
     hname      =  *urlc
     hvalue     =  *urlc

   "#mailbox" is as specified in RFC 822 [RFC822]. This means that it
   consists of zero or more comma-separated mail addresses, possibly
   including "phrase" and "comment" components. Note that all URL
   reserved characters in "to" must be encoded: in particular,
   parentheses, commas, and the percent sign ("%"), which commonly occur
   in the "mailbox" syntax.

So if you want an IPv6 address in your mailto: URI, you're going to have
to write the [...] as %5b...%5d.

As far as I can tell, the only reason that this rule does not extend
(uniformly!) to SIP URIs is that RFC 3261 explicitly forbids it.
Perhaps we could allow %-escapes in host-parts as part of the IPv6
upgrades to our software...

Dale


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