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Internet Engineering Task Force (IETF)                          C. DabooRequest for Comments: 6868                                         AppleUpdates:5545,6321,6350,6351                            February 2013Category: Standards TrackISSN: 2070-1721Parameter Value Encoding in iCalendar and vCardAbstract   This specification updates the data formats for iCalendar (RFC 5545)   and vCard (RFC 6350) to allow parameter values to include certain   characters forbidden by the existing specifications.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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6868.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Daboo                        Standards Track                    [Page 1]

RFC 6868                   Parameter Encoding              February 2013Table of Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................23. Parameter Value Encoding Scheme .................................33.1. iCalendar Example ..........................................43.2. vCard Example ..............................................44. Security Considerations .........................................45. Acknowledgments .................................................46. Normative References ............................................5Appendix A. Choice of Quoting Mechanism ............................61.  Introduction   The iCalendar [RFC5545] specification defines a standard way to   describe calendar data.  The vCard [RFC6350] specification defines a   standard way to describe contact data.  Both of these use a similar   text-based data format.  Each iCalendar and vCard data object can   include "properties" that have "parameters" and a "value".  The value   of a "parameter" is typically a token or URI value, but a "generic"   text value is also allowed.  However, the syntax rules for both   iCalendar and vCard prevent the use of a double-quote character or   control characters in such values, though double-quote characters and   some subset of control characters are allowed in the actual property   values.   As more and more extensions are being developed for these data   formats, there is a need to allow at least double-quotes and line   feeds to be included in parameter values.  The \-escaping mechanism   used for property text values is not defined for use with parameter   values and cannot be easily used in a backwards-compatible manner.   This specification defines a new character escaping mechanism,   compatible with existing parsers and chosen to minimize any impact on   existing data.2.  Conventions Used in This Document   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   [RFC2119].Daboo                        Standards Track                    [Page 2]

RFC 6868                   Parameter Encoding              February 20133.  Parameter Value Encoding Scheme   This specification defines the ^ character (U+005E -- Circumflex   Accent) as an escape character in parameter values whose value type   is defined using the "param-value" syntax element (Section 3.1 of   iCalendar [RFC5545] andSection 3.3 of vCard [RFC6350]).  The   ^-escaping mechanism can be used when the value is either unquoted or   quoted (i.e., whether or not the value is surrounded by double-   quotes).   When generating iCalendar or vCard parameter values, the following   apply:   o  formatted text line breaks are encoded into ^n (U+005E, U+006E)   o  the ^ character (U+005E) is encoded into ^^ (U+005E, U+005E)   o  the " character (U+0022) is encoded into ^' (U+005E, U+0027)   When parsing iCalendar or vCard parameter values, the following   apply:   o  the character sequence ^n (U+005E, U+006E) is decoded into an      appropriate formatted line break according to the type of system      being used   o  the character sequence ^^ (U+005E, U+005E) is decoded into the ^      character (U+005E)   o  the character sequence ^' (U+005E, U+0027) is decoded into the "      character (U+0022)   o  if a ^ (U+005E) character is followed by any character other than      the ones above, parsers MUST leave both the ^ and the following      character in place   When converting between iCalendar and vCard text-based data formats   and alternative data-format representations such as XML (as described   in [RFC6321] and [RFC6351], respectively), implementations MUST   ensure that parameter value escape sequences are generated correctly   in the text-based format and are decoded when the parameter values   appear in the alternate data formats.Daboo                        Standards Track                    [Page 3]

RFC 6868                   Parameter Encoding              February 20133.1.  iCalendar Example   The following example is an "ATTENDEE" property with a "CN" parameter   whose value includes two double-quote characters.  The parameter   value is not quoted, as there are no characters in the value that   would trigger quoting as required by iCalendar.   ATTENDEE;CN=George Herman ^'Babe^' Ruth:mailto:babe@example.com   The unescaped parameter value is   George Herman "Babe" Ruth3.2.  vCard Example   The following example is a "GEO" property with an "X-ADDRESS"   parameter whose value includes several line feed characters.  The   parameter value is also quoted, since it contains a comma, which   triggers quoting as required by vCard.   GEO;X-ADDRESS="Pittsburgh Pirates^n115 Federal St^nPitt    sburgh, PA 15212":geo:40.446816,-80.00566   The unescaped parameter value (where each line is terminated by a   line break character sequence) is   Pittsburgh Pirates   115 Federal St   Pittsburgh, PA 152124.  Security Considerations   There are no additional security issues beyond those of iCalendar   [RFC5545] and vCard [RFC6350].5.  Acknowledgments   Thanks to Michael Angstadt, Tim Bray, Mike Douglass, Barry Leiba,   Simon Perreault, and Pete Resnick for feedback on this specification.Daboo                        Standards Track                    [Page 4]

RFC 6868                   Parameter Encoding              February 20136.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5545]  Desruisseaux, B., "Internet Calendaring and Scheduling              Core Object Specification (iCalendar)",RFC 5545,              September 2009.   [RFC6321]  Daboo, C., Douglass, M., and S. Lees, "xCal: The XML              Format for iCalendar",RFC 6321, August 2011.   [RFC6350]  Perreault, S., "vCard Format Specification",RFC 6350,              August 2011.   [RFC6351]  Perreault, S., "xCard: vCard XML Representation",RFC 6351, August 2011.Daboo                        Standards Track                    [Page 5]

RFC 6868                   Parameter Encoding              February 2013Appendix A.  Choice of Quoting Mechanism   Having recognized the need for escaping parameter values, the   question is what mechanism to use?  One obvious choice would be to   adopt the \-escaping used for property values.  However, that could   not be used as-is, because it escapes a double-quote as the sequence   of \ followed by double-quote.  Consider what the example inSection 3.1 might look like using \-escaping:   ATTENDEE;CN="George Herman \"Babe\" Ruth":mailto:babe@example.com   Existing iCalendar/vCard parsers know nothing about escape sequences   in parameters.  So they would parse the parameter value as:   George Herman \   i.e., the text between the first and second occurrence of a double-   quote.  However, the text after the second double-quote ought to be   either a : or a ; (to delimit the parameter value from the following   parameter or property) but is not, so the parser could legitimately   throw an error at that point because the data is syntactically   invalid.  Thus, for backwards-compatibility reasons, a double-quote   cannot be escaped using a sequence that itself includes a double-   quote, and hence the choice of using a single-quote in this   specification.   Another option would be to use a form of \-escaping modified for use   in parameter values only.  However, some incorrect, non-interoperable   use of \ in parameter values has been observed, and thus it is best   to steer clear of that to achieve guaranteed, reliable   interoperability.  Also, given that double-quote gets changed to   single-quote in the escape sequence for a parameter, but not for a   value, it is better to not give the impression that the same escape   mechanism (and thus code) can be used for both (which could lead to   other issues, such as an implementation incorrectly escaping a ; as   \; as opposed to quoting the parameter value).   The choice of ^ as the escape character was made based on the   requirement that an ASCII symbol (non-alphanumeric character) be   used, and it ought to be one least likely to be found in existing   data.Daboo                        Standards Track                    [Page 6]

RFC 6868                   Parameter Encoding              February 2013Author's Address   Cyrus Daboo   Apple Inc.   1 Infinite Loop   Cupertino, CA  95014   USA   EMail: cyrus@daboo.name   URI:http://www.apple.com/Daboo                        Standards Track                    [Page 7]