Network Working Group                                          R. Sparks
Internet-Draft                                                    Oracle
Updates: 3261, 3515, 5002, 5318, 5360,                     June 07, 2016
         5502 (if approved)
Intended status: Standards Track
Expires: December 9, 2016


Clarifications for when to use the name-addr production in SIP messages
               draft-sparks-sipcore-name-addr-guidance-00

Abstract

   RFC3261 constrained several SIP header fields whose grammar contains
   the "name-addr / addr-spec" alternative to use name-addr when certain
   characters appear.  Unfortunately it expressed the constraints with
   prose copied into each header field definition, and at least one
   header field was missed.  Further, the constraint has not been copied
   into documents defining extension headers whose grammar contains the
   alternative.

   This document updates RFC3261 to state the constraint generically,
   and clarifies that the constraint applies to all SIP header fields
   where there is a choice between using name-addr or addr-spec.  It
   also updates those extension SIP header fields that use the
   alternative to clarify that the constraint applies (RFCs 3261, 3515,
   5002, 5318, 5360, and 5502).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 9, 2016.







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Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Updates to RFC3261  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Updates to RFCs defining SIP Extension header fields  . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Instructions to the RFC Editor  . . . . . . . . . . . . . . .   4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   [RFC3261] defines several header fields that contain URIs to allow
   both a form that contains the bare URI (addr-spec) and one that
   provides a name and the URI (name-addr).  This subset, taken from the
   ABNF [RFC5234] specified in [RFC3261] shows the relevant part of the
   definition of the syntax of the "From" header field:

     From        =  ( "From" / "f" ) HCOLON from-spec
     from-spec   =  ( name-addr / addr-spec )
                    *( SEMI from-param )
     name-addr      =  [ display-name ] LAQUOT addr-spec RAQUOT
     addr-spec      =  SIP-URI / SIPS-URI / absoluteURI

   The prose in section 20.20 of [RFC3261], which discusses the "From"
   header field, constrains how the production may be used by saying:

      Even if the "display-name" is empty, the "name-addr" form
      MUST be used if the "addr-spec" contains a comma, question
      mark, or semicolon.




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   Section 20.39, which discusses the "To" header field contains no such
   constraining text.

   This constraint is specified slightly differently, but with the same
   intent, in the introduction to section 20:

     The Contact, From, and To header fields contain a URI.  If the URI
     contains a comma, question mark or semicolon, the URI MUST be
     enclosed in angle brackets (< and >).

   Unfortunately, this can be read to only apply to the Contact, From,
   and To header fields, making it necessary to provide the constraint
   explicitly in the prose discussing any other header field using the
   name-addr or addr-spec alternative.

   As extension header fields were standardized, the specifications
   sometimes failed to include the constraint.  Many errata have been
   entered to correct this omission.  When the constraint was called
   out, the form has not been consistent.

   This memo updates the specifications of SIP and its extensions to
   clarify that the constraint to use the name-addr form applies
   anywhere there is a choice between the name-addr and addr-spec
   production rules in the grammar for SIP header fields.

   It is important to note that a message formed without honoring the
   constraint will still be syntactically valid, but would be
   interpreted differently.  The characters after the comma, question
   mark, or semicolon would be interpreted as header field parameters or
   additional header field values as discussed in section 7.3.1 of
   [RFC3261].

2.  Updates to RFC3261

   This text from the introduction to section 20 of [RFC3261]:

     The Contact, From, and To header fields contain a URI.  If the URI
     contains a comma, question mark or semicolon, the URI MUST be
     enclosed in angle brackets (< and >).

   is replaced with:










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     When constructing the value of any SIP header field whose grammar
     allows choosing between name-addr and addr-spec, such as those
     that use the form '(name-addr / addr-spec)', the "addr-spec" form
     MUST NOT be used if its value would contain a comma, semicolon,
     or question mark.

     The header fields defined in this specification that allow this
     choice are "To", "From", "Contact",  and "Reply-To".

3.  Updates to RFCs defining SIP Extension header fields

   [RFC3515], [RFC5002], [RFC5318], [RFC5360], and [RFC5502] are updated
   to include:

     This RFC contains the definition of one or more SIP header fields
     that allow choosing between addr-spec and name-addr when
     constructing header field values. As specified in RFCxxxx,
     the "addr-spec" form MUST NOT be used if its value would contain
     a comma, semicolon, or question mark.

4.  IANA Considerations

   This memo has no considerations for IANA.

5.  Security Considerations

   The updates specified in this memo clarify a constraint on the
   grammar for producing SIP messages.  It introduces no new security
   considerations.  One pre-existing consideration is worth reiterating:
   messages produced without honoring the constraint will be mis-
   interpreted by the receiving element.

6.  Acknowledgments

   Brett Tate identified this issue in several extension documents,
   submitted several corresponding errata, and drove the discussion that
   led to this memo.  Substantive comments leading to this text were
   provided by Paul Kyzivat, Gonzalo Camarillo, and Dale Worley.

7.  Instructions to the RFC Editor

   Please remove this section in its entirety before publication as an
   RFC.

   Please replace any instances of RFCxxxx with the RFC number assigned
   to this memo.





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   This memo, if it is approved, obviates Errata 3744, 3894, and
   4648-4652 inclusive.

8.  Normative References

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [RFC3515]  Sparks, R., "The Session Initiation Protocol (SIP) Refer
              Method", RFC 3515, DOI 10.17487/RFC3515, April 2003,
              <http://www.rfc-editor.org/info/rfc3515>.

   [RFC5002]  Camarillo, G. and G. Blanco, "The Session Initiation
              Protocol (SIP) P-Profile-Key Private Header (P-Header)",
              RFC 5002, DOI 10.17487/RFC5002, August 2007,
              <http://www.rfc-editor.org/info/rfc5002>.

   [RFC5318]  Hautakorpi, J. and G. Camarillo, "The Session Initiation
              Protocol (SIP) P-Refused-URI-List Private-Header
              (P-Header)", RFC 5318, DOI 10.17487/RFC5318, December
              2008, <http://www.rfc-editor.org/info/rfc5318>.

   [RFC5360]  Rosenberg, J., Camarillo, G., Ed., and D. Willis, "A
              Framework for Consent-Based Communications in the Session
              Initiation Protocol (SIP)", RFC 5360,
              DOI 10.17487/RFC5360, October 2008,
              <http://www.rfc-editor.org/info/rfc5360>.

   [RFC5502]  van Elburg, J., "The SIP P-Served-User Private-Header
              (P-Header) for the 3GPP IP Multimedia (IM) Core Network
              (CN) Subsystem", RFC 5502, DOI 10.17487/RFC5502, April
              2009, <http://www.rfc-editor.org/info/rfc5502>.

Author's Address

   Robert Sparks
   Oracle

   Email: rjsparks@nostrum.com




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