Network Working Group M. Douglass Internet-Draft Spherical Cow Group Updates: 5545 (if approved) May 5, 2018 Intended status: Standards Track Expires: November 6, 2018 Calendar subscription upgrades draft-douglass-subscription-upgrade-03 Abstract This specification introduces an approach to allow subscribers to calendar feeds to upgrade to a more performant protocol. This specification updates [RFC5545] to add the value DELETED to the STATUS property. 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 https://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 November 6, 2018. Copyright Notice Copyright (c) 2018 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 (https://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 Douglass Expires November 6, 2018 [Page 1] Internet-Draft Calendar subscription upgrades May 2018 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions Used in This Document . . . . . . . . . . . . 3 2. Enhanced GET . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Deletions . . . . . . . . . . . . . . . . . . . . . . . . 3 2.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Changes to the iCalendar specifications . . . . . . . . . . . 6 3.1. Redefined Status property . . . . . . . . . . . . . . . . 6 4. Discovering alternative access methods . . . . . . . . . . . 8 5. Link relation subscribe-caldav . . . . . . . . . . . . . . . 8 6. Link relation subscribe-caldav-auth . . . . . . . . . . . . . 8 7. Link relation subscribe-webdav-sync . . . . . . . . . . . . . 8 8. Link relation subscribe-enhanced-get . . . . . . . . . . . . 9 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 11.1. Link Relation Registrations . . . . . . . . . . . . . . 9 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 13. Normative References . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Open issues . . . . . . . . . . . . . . . . . . . . 11 Appendix B. Change log . . . . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction Currently clients subscribe to calendar feeds as an ics file which is often published as a resource accessible using the unofficial 'webcal' scheme. The only available option for updating that resource is the usual HTTP polling of cached resources using Etags. There is the usual tension between clients wishing to see a timely response to changes and servers not wishing to be overloaded by frequent requests for possibly large amounts of data. This specification introduces an approach whereby clients can discover a more performant access method. Given the location of the resource as an ics file, the client can perfom an OPTIONS request on the resource and inspect the returned headers which will offer a number of alternative access methods. Douglass Expires November 6, 2018 [Page 2] Internet-Draft Calendar subscription upgrades May 2018 Given that many clients already support CalDAV this provides an easy upgrade path for those clients. CalDAV and DAV subsets are specified here to allow lighter weight implementations. 1.1. 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]. 2. Enhanced GET 2.1. Introduction This is a lightweight protocol which allows simple clients to efficiently discover and download changes in the targeted resource. It has many similarities to WebDAV sync and for a server could be implemented as an extension of the specification. In this protocol the Etag is used as the sync change token. By adding the If-None-Match header field to the vary header field we can ensure intermediate caching proxies will be able to cache different versions of the data. The resource is treated as a set of individual events each of which may be updated or deleted separately. The client will first fetch the entire ics file. On subsequent requests it uses the Prefer header with a value of "return=minimal" to indicate that it wants a set of changes since the last fetch. 2.2. Deletions When an entity (VEVENT, VTODO or other valid top-level component) is deleted from the source data the server needs to be able to inform a client of the deletion. This specification introduces a new value for the STATUS property of DELETED. On the first conditional GET after the entity has been deleted a skeleton, but valid, entity will be returned with STATUS: DELETED. The receiving client is free to remove the entity or update it's STATUS property. On subsequent conditional fetches the entity will not be returned. Douglass Expires November 6, 2018 [Page 3] Internet-Draft Calendar subscription upgrades May 2018 2.3. Examples This is an example of the initial request and response from a server that supports the extended GET protocol. >> Request << GET /events.ics HTTP/1.1 Host: example.com Accept: text/calendar >> Response << HTTP/1.1 200 OK Content-Length: xxxx ETag: "1234" current ETag (for conditional GET) Vary: Prefer, If-None-Match so caching proxy can key off of client?s ETag (sync token) and preference BEGIN:VCALENDAR: ? /* full feed */ END:VCALENDAR This is an example of the subsequent request and response when no changes have occurred. The Accept header field indicates that a VPATCH format is most desirable but simple text/calendar is acceptable. >> Request << GET /events.ics HTTP/1.1 Host: example.com Accept: text/calendar; q=0.5, component=VPATCH, text/calendar; If-None-Match: ?1234? conditional request Prefer: return=minimal >> Response << HTTP/1.1 304 Not Modified Content-Length: 0 ETag: ?1234? Vary: Prefer, If-None-Match This is an example of the subsequent request and response when no changes have occurred. The Accept header field indicates that a VPATCH format is most desirable but simple text/calendar is acceptable. Douglass Expires November 6, 2018 [Page 4] Internet-Draft Calendar subscription upgrades May 2018 >> Request << GET /events.ics HTTP/1.1 Host: example.com Accept: text/calendar; q=0.5, component=VPATCH, text/calendar; If-None-Match: "1234" conditional request Prefer: return=minimal >> Response << HTTP/1.1 304 Not Modified Content-Length: 0 ETag: "1234" Vary: Prefer, If-None-Match This is an example of the subsequent request and response when changes have occurred and the server can create the minimal format. >> Request << GET /events.ics HTTP/1.1 Host: example.com Accept: text/calendar; q=0.5, component=VPATCH, text/calendar; If-None-Match: "1234" conditional request Prefer: return=minimal >> Response << HTTP/1.1 200 OK Content-Type: text/calendar Content-Length: xxxx ETag: "5678" current ETag (for conditional GET) Preference-Applied: return=minimal signals to client that stream is changes only Vary: Prefer, If-None-Match so caching proxy can key off of client?s ETag (sync token) and preference BEGIN:VCALENDAR: ... only new/changed events ... when not returning VPATCH, deleted events have STATUS:DELETED END:VCALENDAR This is an example of the subsequent request and response when changes have occurred and the server cannot create the minimal format - perhaps because of an old or invalid token. Note there is no Preference-Applied header field. Douglass Expires November 6, 2018 [Page 5] Internet-Draft Calendar subscription upgrades May 2018 >> Request << GET /events.ics HTTP/1.1 Host: example.com Accept: text/calendar; q=0.5, component=VPATCH, text/calendar; If-None-Match: "1234" conditional request Prefer: return=minimal >> Response << HTTP/1.1 200 OK Content-Type: text/calendar Content-Length: xxxx ETag: "5678" current ETag (for conditional GET) Vary: Prefer, If-None-Match so caching proxy can key off of client?s ETag (sync token) and preference BEGIN:VCALENDAR: ... full set of data END:VCALENDAR 3. Changes to the iCalendar specifications This specification updates [RFC5545] to add the value DELETED to the STATUS property. It also introduces the use of some properties to provide more information about the resource, for example the time range it covers. 3.1. Redefined Status property Property name: STATUS Purpose: This property defines the overall status or confirmation for the calendar component. Value Type: TEXT Property Parameters: IANA and non-standard property parameters can be specified on this property. Conformance: This property can be specified once in "VEVENT", "VTODO", or "VJOURNAL" calendar components. Description: In a group-scheduled calendar component, the property is used by the "Organizer" to provide a confirmation of the event to the "Attendees". For example in a "VEVENT" calendar component, the "Organizer" can indicate that a meeting is tentative, confirmed, or cancelled. In a "VTODO" calendar component, the Douglass Expires November 6, 2018 [Page 6] Internet-Draft Calendar subscription upgrades May 2018 "Organizer" can indicate that an action item needs action, is completed, is in process or being worked on, or has been cancelled. In a "VJOURNAL" calendar component, the "Organizer" can indicate that a journal entry is draft, final, or has been cancelled or removed. Format Definition: This property is defined by the following notation: status = "STATUS" statparam ":" statvalue CRLF statparam = *(";" other-param) statvalue = (statvalue-event / statvalue-todo / statvalue-jour) statvalue-event = "TENTATIVE" ;Indicates event is tentative. / "CONFIRMED" ;Indicates event is definite. / "CANCELLED" ;Indicates event was cancelled. / "DELETED" ;Indicates event was deleted. ;Status values for a "VEVENT" statvalue-todo = "NEEDS-ACTION" ;Indicates to-do needs action. / "COMPLETED" ;Indicates to-do completed. / "IN-PROCESS" ;Indicates to-do in process of. / "CANCELLED" ;Indicates to-do was cancelled. / "DELETED" ;Indicates to-do was deleted. ;Status values for "VTODO". statvalue-jour = "DRAFT" ;Indicates journal is draft. / "FINAL" ;Indicates journal is final. / "CANCELLED" ;Indicates journal is removed. / "DELETED" ;Indicates journal was deleted. ;Status values for "VJOURNAL". Example: Example: The following is an example of this property for a "VEVENT" calendar component: STATUS:TENTATIVE The following is an example of this property for a "VTODO" calendar component: STATUS:NEEDS-ACTION Douglass Expires November 6, 2018 [Page 7] Internet-Draft Calendar subscription upgrades May 2018 The following is an example of this property for a "VJOURNAL" calendar component: STATUS:DRAFT 4. Discovering alternative access methods The advertising of other access points is achieved through the use of the LINK header as defined in [RFC5988]. New link relation types are defined in this specification - each being associated with a protocol or protocol subset. These LINK headers will be delivered when a client carries out an OPTIONS request targeting the URL of the resource. 5. Link relation subscribe-caldav This specifies an access point which is a full implementation of caldav but requires no authentication. The end point allows the full range of reports as defined by the CalDAV specification. The client MUST follow the specification to determine exactly what operations are allowed on the access point - for example to determine if sync-report is supported. The URL MAY include some form of token to allow write access to the targeted collection. The client must check it's permissions to determine whether or not it has been granted write access. 6. Link relation subscribe-caldav-auth This specifies an access point which is a full implementation of caldav and requires authentication. This may allow read-write access to the resource. The client MUST follow the specification to determine exactly what operations are allowed on the access point - for example to determine if sync-report is supported. 7. Link relation subscribe-webdav-sync This specifies an access point which supports only webdav sync. This allows the client to issue a sync-report on the resource to obtain updates. NOTE: say something about initial startup - use ics to populate? Initial token? Douglass Expires November 6, 2018 [Page 8] Internet-Draft Calendar subscription upgrades May 2018 The client MUST follow that specification. 8. Link relation subscribe-enhanced-get This specifies an access point which supports something new. The client MUST follow that specification. 9. Security Considerations Applications using these properties need to be aware of the risks entailed in using the URIs provided as values. See [RFC3986] for a discussion of the security considerations relating to URIs. 10. Privacy Considerations Properties with a "URI" value type can expose their users to privacy leaks as any network access of the URI data can be tracked. Clients SHOULD NOT automatically download data referenced by the URI without explicit instruction from users. This specification does not introduce any additional privacy concerns beyond those described in [RFC5545]. 11. IANA Considerations 11.1. Link Relation Registrations This document defines the following new iCalendar properties to be added to the registry defined in Section 8.2.3 of [RFC5545]: +------------------------+-------------+--------------------+ | Relation Name | Description | Reference | +------------------------+-------------+--------------------+ | subscribe-caldav | Current | RFCXXXX, Section 5 | | subscribe-caldav_auth | Current | RFCXXXX, Section 6 | | subscribe-webdav-sync | Current | RFCXXXX, Section 7 | | subscribe-enhanced_get | Current | RFCXXXX, Section 8 | +------------------------+-------------+--------------------+ 12. Acknowledgements The author would also like to thank the members of the CalConnect Calendar Sharing technical committee and the following individuals for contributing their ideas and support: Marten Gajda, Ken Murchison Douglass Expires November 6, 2018 [Page 9] Internet-Draft Calendar subscription upgrades May 2018 The authors would also like to thank CalConnect the Calendaring and Scheduling Consortium for advice with this specification. 13. Normative References [I-D.ietf-calext-extensions] Daboo, C., "New Properties for iCalendar", draft-ietf- calext-extensions-05 (work in progress), August 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, DOI 10.17487/RFC2434, October 1998, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . [RFC4589] Schulzrinne, H. and H. Tschofenig, "Location Types Registry", RFC 4589, DOI 10.17487/RFC4589, July 2006, . [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, DOI 10.17487/RFC5545, September 2009, . [RFC5546] Daboo, C., Ed., "iCalendar Transport-Independent Interoperability Protocol (iTIP)", RFC 5546, DOI 10.17487/RFC5546, December 2009, . [RFC5988] Nottingham, M., "Web Linking", RFC 5988, DOI 10.17487/RFC5988, October 2010, . Douglass Expires November 6, 2018 [Page 10] Internet-Draft Calendar subscription upgrades May 2018 [W3C.REC-xml-20060816] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth Edition)", World Wide Web Consortium Recommendation REC- xml-20060816, August 2006, . Appendix A. Open issues restype values: Need to determine what if any registry of resource types already exists and use that. Appendix B. Change log v01 2017-07-28 MD o Examples o More text for extended get. Talk about deletions. v01 2017-02-17 MD o Add text about OPTIONS o Add text abut read/write CalDAV v00 2017-02-15 MD o First pass Author's Address Michael Douglass Spherical Cow Group 226 3rd Street Troy, NY 12180 USA Email: mdouglass@sphericalcowgroup.com URI: http://sphericalcowgroup.com Douglass Expires November 6, 2018 [Page 11]