Parameter Value Encoding in iCalendar and vCard
The information below is for an old version of the document.
This is an older version of an Internet-Draft that was ultimately published as RFC 6868.
|Last updated||2013-01-01 (Latest revision 2012-10-22)|
|RFC stream||Internet Engineering Task Force (IETF)|
|IESG||IESG state||Waiting for AD Go-Ahead::Revised I-D Needed|
Needs a YES. Needs 10 more YES or NO OBJECTION positions to pass.
|Responsible AD||Barry Leiba|
|Send notices email@example.com, firstname.lastname@example.org, email@example.com|
Network Working Group C. Daboo Internet-Draft Apple Updates: 5545,6350 (if approved) October 22, 2012 Intended status: Standards Track Expires: April 25, 2013 Parameter Value Encoding in iCalendar and vCard draft-daboo-ical-vcard-parameter-encoding-02 Abstract This specification updates the iCalendar and vCard data formats to allow parameter values to include certain characters forbidden by the existing specifications. 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 25, 2013. Copyright Notice Copyright (c) 2012 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. Daboo Expires April 25, 2013 [Page 1] Internet-Draft Parameter Encoding October 2012 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . . 3 3. Parameter Value Encoding Scheme . . . . . . . . . . . . . . . . 3 3.1. iCalendar Example . . . . . . . . . . . . . . . . . . . . . 4 3.2. vCard Examples . . . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Appendix A. Choice of Quoting Mechanism . . . . . . . . . . . . . 5 Appendix B. Change History (To be removed by RFC Editor before publication) . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Daboo Expires April 25, 2013 [Page 2] Internet-Draft Parameter Encoding October 2012 1. 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" which 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 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 minimise 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]. 3. 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] and Section 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 used, the combination of ^ plus one other character is interpreted as a single character as per the table below: Daboo Expires April 25, 2013 [Page 3] Internet-Draft Parameter Encoding October 2012 +---------------------+----------------------------+ | Escape Sequence | Character | +---------------------+----------------------------+ | ^' (U+005E, U+0027) | U+0022 (Quotation Mark) | | ^n (U+005E, U+006E) | U+000A (Line Feed) | | ^^ (U+005E, U+005E) | U+005E (Circumflex Accent) | +---------------------+----------------------------+ When generating iCalendar or vCard parameter values, the characters in the second column above MUST be escaped using the sequence from the first column. When parsing iCalendar or vCard parameter values, the two character sequence from the first column MUST be replaced by the single character from the second column. If a ^ (U+005E) character is followed by any other character than the ones above, parsers SHOULD leave the ^ character in place. In addition to the escaping procedure outlined above, text parameter values MUST also have line break character sequences canonicalized into a single line feed (U+000A) character when the parameter value is generated. Specifically, any single carriage return character (U+000D) or the two character combination of carriage return followed by line feed (U+000D, U+000A) MUST be mapped to ^n in the generated parameter value. When parsing a parameter value with ^n, clients can replace that with the appropriate line break character sequence for the system they are running on. 3.1. iCalendar Example 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:firstname.lastname@example.org The unescaped parameter value is George Herman "Babe" Ruth 3.2. vCard Examples A "GEO" property with a "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 Daboo Expires April 25, 2013 [Page 4] Internet-Draft Parameter Encoding October 2012 The unescaped parameter value is (where each line is terminated by a line break character sequence) Pittsburgh Pirates 115 Federal St Pittsburgh, PA 15212 4. Security Considerations There are no additional security issues beyond those of iCalendar [RFC5545] and vCard [RFC6350]. 5. IANA Considerations There are none. 6. Acknowledgments Thanks to Michael Angstadt, Mike Douglass, Barry Leiba, Simon Perreault for feedback on this specification. 7. 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. [RFC6350] Perreault, S., "vCard Format Specification", RFC 6350, August 2011. Appendix A. Choice of Quoting Mechanism Having recognized the need for escaping parameters 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 in Section 3.1 might look like using \-escaping: ATTENDEE;CN="George Herman \"Babe\" Ruth":mailto:email@example.com Daboo Expires April 25, 2013 [Page 5] Internet-Draft Parameter Encoding October 2012 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. 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 implementations 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. Appendix B. Change History (To be removed by RFC Editor before publication) Changes in -02: 1. Removed unnecessary HTAB escaping. 2. Added appendix to describe why ^ was chosen as the escape mechanism. Changes in -01: 1. Tweaked vCard example line-folding. Daboo Expires April 25, 2013 [Page 6] Internet-Draft Parameter Encoding October 2012 Author's Address Cyrus Daboo Apple Inc. 1 Infinite Loop Cupertino, CA 95014 USA Email: firstname.lastname@example.org URI: http://www.apple.com/ Daboo Expires April 25, 2013 [Page 7]