Clarifications for When to Use the name-addr Production in SIP Messages
RFC 8217

Internet Engineering Task Force (IETF) R. Sparks
Request for Comments: 8217 Oracle
Updates: 3261, 3325, 3515, 3892, 4508, August 2017
 5002, 5318, 5360, 5502
Category: Standards Track
ISSN: 2070-1721
Clarifications for When to Use the name-addr Production in SIP Messages
Abstract
 RFC 3261 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 RFC 3261 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 the RFCs that define extension SIP header fields using
 the alternative to clarify that the constraint applies (RFCs 3325,
 3515, 3892, 4508, 5002, 5318, 5360, and 5502).
Status of This Memo
 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF). It represents the consensus of the IETF community. It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG). Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8217.
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RFC 8217 name-addr Clarifications August 2017
Copyright Notice
 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors. All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document. Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document. Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
 3. Updates to RFC 3261 . . . . . . . . . . . . . . . . . . . . . 4
 4. Updates to RFCs Defining SIP Extension Header Fields . . . . 4
 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
 7. Normative References . . . . . . . . . . . . . . . . . . . . 5
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 6
 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
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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RFC 8217 name-addr Clarifications August 2017
 Section 20.39 of [RFC3261], 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 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 >).
 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 has been
 included, the requirement to use the name-addr form has not been
 consistently stated.
 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 it would very
 likely be interpreted differently. The characters after the comma,
 question mark, or semicolon will, in most cases, be interpreted as
 header field parameters or additional header field values as
 discussed in Section 7.3.1 of [RFC3261]. (An exception is the
 degenerate case of a URL like sip:10.0.0.1,@10.0.0.0 where it is
 possible to parse the comma via the 'user' production).
2. Terminology
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.
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RFC 8217 name-addr Clarifications August 2017
3. Updates to RFC 3261
 This text from 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 >). Any URI parameters are
 contained within these brackets. If the URI is not enclosed in
 angle brackets, any semicolon-delimited parameters are
 header-parameters, not URI parameters.
 is replaced with:
 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.
 When a URI appears in such a header field, any URI parameters MUST
 be contained within angle brackets (< and >). If the URI is not
 enclosed in angle brackets, any semicolon-delimited parameters are
 header-parameters, not URI parameters.
 The header fields defined in this specification that allow this
 choice are "To", "From", "Contact", and "Reply-To".
4. Updates to RFCs Defining SIP Extension Header Fields
 The following Standards Track RFCs: [RFC3515], [RFC3892], [RFC4508],
 and [RFC5360]
 and the following Informational RFCs: [RFC3325], [RFC5002],
 [RFC5318], 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 RFC 8217,
 the "addr-spec" form MUST NOT be used if its value would contain
 a comma, semicolon, or question mark.
 The status of these RFCs remains unchanged. In particular the status
 of the Informational RFCs remains Informational.
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RFC 8217 name-addr Clarifications August 2017
5. IANA Considerations
 This document does not require any IANA actions.
6. 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 very likely be
 misinterpreted by the receiving element.
7. Normative References
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", BCP 14, RFC 2119,
 DOI 10.17487/RFC2119, March 1997,
 <http://www.rfc-editor.org/info/rfc2119>.
 [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>.
 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
 Extensions to the Session Initiation Protocol (SIP) for
 Asserted Identity within Trusted Networks", RFC 3325,
 DOI 10.17487/RFC3325, November 2002,
 <http://www.rfc-editor.org/info/rfc3325>.
 [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>.
 [RFC3892] Sparks, R., "The Session Initiation Protocol (SIP)
 Referred-By Mechanism", RFC 3892, DOI 10.17487/RFC3892,
 September 2004, <http://www.rfc-editor.org/info/rfc3892>.
 [RFC4508] Levin, O. and A. Johnston, "Conveying Feature Tags with
 the Session Initiation Protocol (SIP) REFER Method",
 RFC 4508, DOI 10.17487/RFC4508, May 2006,
 <http://www.rfc-editor.org/info/rfc4508>.
 [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>.
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RFC 8217 name-addr Clarifications August 2017
 [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>.
 [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>.
 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
 May 2017, <http://www.rfc-editor.org/info/rfc8174>.
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, Dale Worley, and
 Yehoshua Gev.
Author's Address
 Robert Sparks
 Oracle
 Email: rjsparks@nostrum.com
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