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

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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.

Sparks                       Standards Track                    [Page 1]
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.

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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.

Sparks                       Standards Track                    [Page 2]
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