Hi Dale,
The ambiguity exists in the "contact" header.
Contact = ("Contact" / "m" ) HCOLON
( STAR / (contact-param *(COMMA contact-param)))
contact-param = (name-addr / addr-spec) *(SEMI contact-params)
Since the contact can have multiple contact-params separated by comma and
the grammar for
contact-param supports addr-spec which doesnt have the "< LANGLE" and
">RANGLE" demarcators.
Regds
Anil N
"Dale R. Worley"
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Subject
Re: [Sip-implementors] ABNF Syntax
01/05/2006 08:24 for userinfo in SIP-URI
PM
On Thu, 2006-01-05 at 11:14 +0530, Praveen wrote:
> As per Sec 25.1 of RFC 3261 a userinfo part of SIP URI can
> contain *","* as acceptable character. But the SIP URI's can appear in
> multiples separated by COMMA in headers like Record-Route/ Route/
> Contact etc.,. contradicting the said rule. How we distinguish whether
> it is a user part or another followed URI, since COMMA is only separator
>
> for the list.
>
> Excerpts of the rule from RFC is as below
>
> userinfo = ( user / telephone-subscriber ) [ ":" password ] "@"
>
> user = 1*( unreserved / escaped / user-unreserved )
>
> user-unreserved = "&" / "=" / "+" / "$" / *","* / ";" / "?" / "/"
>
> Record-Route = "Record-Route" HCOLON rec-route *(*COMMA* rec-route)
The way you distinguish is that the context forces one interpretation of
the comma or another. An example is:
Record-Route: <sip:aaa,[EMAIL PROTECTED]>, <sip:[EMAIL PROTECTED]>
(The <...> are necessary because rec-route expands to name-addr.)
According to the grammar, this header is not ambiguous; there is no way
to produce it where the first comma is generated by the Record-Route
production.
The "problem" is that you cannot parse Record-Route by first splitting
the value at the commas and then parsing each part as a name-addr, you
need to parse each name-addr in order and then find and consume the
comma that would follow it.
Dale
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