Network Working Group E. Pot
Internet-Draft fruux GmbH
Expires: July 14, 2016 C. Daboo
E. York
Apple Inc.
January 11, 2016
CalDAV Calendar Sharing
draft-pot-caldav-sharing-00
Abstract
This specification defines sharing calendars between users on a
CalDAV server.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Conventions Used in This Document . . . . . . . . . . . . . . 2
4. Calendar sharing . . . . . . . . . . . . . . . . . . . . . . 3
5. Per-instance calendar data . . . . . . . . . . . . . . . . . 3
6. Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . 3
7. Normative References . . . . . . . . . . . . . . . . . . . . 4
Appendix A. Change History . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Users of CalDAV [RFC4791] often require a mechanism to share a
calendar with other users.
In the past this use-case has been fulfilled by non-standard means.
This specification aims to describe a standard way for clients and
servers to share calendars.
Sharing calendars is for the most part completely implemented using
draft-pot-webdav-resource-sharing, but there are a few considerations
specific to CalDAV to ensure that mechanisms such as scheduling still
behaves as expected.
2. Open Issues
1. DAV:owner requirement for scheduling. I think this is
problematic...
2. I don't think we should allow sharees that have access to an
invite for which they are the attendee for, via the organizers
shared calendar, to allow them to make attendee-related changes.
The entire collection should operate as if the operation is on
behalf of the organizer.
3. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
When XML element types in the namespaces "DAV:" and
"urn:ietf:params:xml:ns:caldav" are referenced in this document
outside of the context of an XML fragment, the string "DAV:" and
"CALDAV:" will be prefixed to the element type names respectively.
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4. Calendar sharing
While the draft-pot-webdav-resource-sharing specification allows
sharing of potentially any resource on a server, this specification
only concerns itself with sharing calendar collections, as defined in
CalDAV [RFC4791].
Sharing of resources other than calendar collections is not addressed
in this specification.
5. Per-instance calendar data
Servers that support calendar sharing MUST support "per-instance"
calendar data in calendar object resources stored in shared
calendars. This allows each sharee and the sharer to store their own
alarms and free busy transparency status without "interfering" with
other users who also have access to the same calendar object
resources.
For calendaring object resources in shared calendar collections, the
server MUST treat the following iCalendar data objects as per-
instance:
TRANSP property
VALARM component
6. Scheduling
CalDAV Scheduling [RFC6638] defines how a CalDAV server carries out
scheduling operations when calendar object resources are created,
modified or deleted and include "ORGANIZER" and "ATTENDEE" iCalendar
properties.
When a user interacts with a shared instance of a calendar, the agent
and server must operate as if the operation is done on behalf of the
sharee.
That means that if a new scheduling resource is created, the server
MUST operate as if the calendar is a normal non-shared calendar owned
by the sharee. This means that when doing scheduling operations on a
shared calendar, the agents don't act on behalf of the original
instance.
If a user is creating a new scheduling resource on a shared calendar,
and an ATTENDEE listed on the scheduling resource also owns an
instance of the shared calendar, the server MAY not create a new
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resource for the ATTENDEE. This is to avoid events appearing
multiple times in a user's calendars.
A shared calendar MAY be specified in a user's CALDAV:schedule-
default-calendar-url.
A user that appears as an ATTENDEE in a calendar object resource in a
shared calendar, and DAV:read-write access is granted, the sharee is
allowed to change not only iCalendar data related to the Organizer,
but also data related to the Attendee. i.e., a sharee can change
their own participation status on the "ATTENDEE" iCalendar property
referring to them. Additionally, if the sharee is not listed as an
Attendee, and write access is granted, the sharee can add themselves
as an Attendee.
Following are additional considerations for scheduling with shared
calendars:
1. A scheduled iCalendar component could appear in more than one
calendar collection within a sharee's calendar home if the sharee
is an Attendee and the Organizer or other Attendees have shared a
calendar with the sharee that includes their copies of the
iCalendar component. It is important to note that the scheduled
component in the shared calendar could have different access
rights than the one in the sharee's owned calendar.
2. A scheduled iCalendar component appearing in a sharee's shared
calendar could include the sharee as an Attendee. For recurring
events, it is possible for the sharee to only be listed as an
Attendee in some instances, as opposed to all. Clients will need
to be aware of this when allowing sharee's to set their own
participation status.
3. In addition, when a shared calendar is first accepted by a
sharee, the server SHOULD set the CALDAV:schedule-calendar-transp
property to the value CALDAV:transparent to ensure newly accepted
shared calendars do not contribute to the sharee's freebusy time
until the sharee explicitly requests it.
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>.
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[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
DOI 10.17487/RFC4791, March 2007,
<http://www.rfc-editor.org/info/rfc4791>.
[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918,
DOI 10.17487/RFC4918, June 2007,
<http://www.rfc-editor.org/info/rfc4918>.
[RFC6352] Daboo, C., "CardDAV: vCard Extensions to Web Distributed
Authoring and Versioning (WebDAV)", RFC 6352,
DOI 10.17487/RFC6352, August 2011,
<http://www.rfc-editor.org/info/rfc6352>.
[RFC6638] Daboo, C. and B. Desruisseaux, "Scheduling Extensions to
CalDAV", RFC 6638, DOI 10.17487/RFC6638, June 2012,
<http://www.rfc-editor.org/info/rfc6638>.
[RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
DOI 10.17487/RFC7303, July 2014,
<http://www.rfc-editor.org/info/rfc7303>.
Appendix A. Change History
Authors' Addresses
Evert Pot
fruux GmbH
Koenigsstrasse 32
Muenster, NRW 48143
Germany
Email: me@evertpot.com
URI: https://fruux.com/
Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
Email: cyrus@daboo.name
URI: http://www.apple.com/
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Eric York
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
URI: http://www.apple.com/
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