[Sip-implementors] Tel URI having escape sequence in it

Paul Kyzivat

2014-07-09 20:51:48 UTC

Post by Jatin Kohli
Hi All
What should be the behavior of a SIP parser while decoding a To header having tel URI with escape sequence in it ?
To: <tel:%2A21%2A2246533682%23;phone-context=xyz.com>;tag=6348SIPpTag012
Is the above tel URI valid (wrt both RFCs 2806 and RFC 3966)?

According to 3261 the tel URI must first match the syntax addr-spec. It
does, because it matches absoluteURI, containing an opaque-part, which
allows the escaping. So far so good.

The next question is whether the escaping is to be replaced, according
to the sip defined mapping, before being reparsed according to its own
scheme syntax, or if the intent is simply to leave the escaping still in
place and parse it according to its scheme.

AFAIK there is nothing that really says, one way or the other. But since
escaping is intended to work around cases where you need to include
characters that sip doesn't otherwise allow, and since the target scheme
syntaxes can't have anticipated that, I think it only makes sense that
the escaping *is* replaced before reparsing.

Assuming that, then the uri becomes:
<tel:*21*2246533682#;phone-context=xyz.com>. This is valid according to
3966. It is not valid according to 2806 because that rfc doesn't allow
an fqdn as a phone-context. (It doesn't allow ".", and not all of the
alphabet. I have no idea what it was trying to do.)

Post by Jatin Kohli
What should be the behavior of a SIP parser on receipt of such a message?

Depends on whether you are processing the tel uri according the 3966 or
2806.

If you use 2806 and consider this invalid, then you can do as you wish.
You could ignore the error, since it is just the To-URI and that doesn't
necessarily affect anything.

If you want to reject it, then 400 is probably the response that best
reflects the problem.

If you attempt to continue processing the request, then you may
encounter additional errors if you don't "understand" this number. You
might end up wanting to return 404 Not Found. But that would be more
likely if this were in the R-URI. You really shouldn't be trying to find
the To-URI.

Thanks,
Paul

Post by Jatin Kohli
Thanks and regards
Jatin Kohli
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