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Calendar Server Extension C. Daboo
E. York
Apple Inc.
September 19, 2012
Shared and Published Calendars in CalDAV
Abstract
This specification defines an extension to CalDAV that enables the
sharing of calendars between users on a CalDAV server.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Notifications . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Additional Principal Properties . . . . . . . . . . . . . 5
4.1.1. CS:notification-URL Property . . . . . . . . . . . . . 6
4.2. Properties on Notification Resources . . . . . . . . . . . 6
4.2.1. CS:notificationtype Property . . . . . . . . . . . . . 6
5. Shared Calendaring . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Feature Discovery . . . . . . . . . . . . . . . . . . . . 7
5.2. Additional Properties for Calendars . . . . . . . . . . . 7
5.2.1. DAV:resourcetype Property . . . . . . . . . . . . . . 7
5.2.2. CS:invite Property . . . . . . . . . . . . . . . . . . 8
5.2.3. CS:allowed-sharing-modes Property . . . . . . . . . . 8
5.2.4. CS:shared-url Property . . . . . . . . . . . . . . . . 9
5.3. Sharer Actions on Shared Calendars . . . . . . . . . . . . 9
5.3.1. Sharing or Unsharing a Calendar . . . . . . . . . . . 9
5.3.2. Manipulating Sharees of a Shared Calendar . . . . . . 10
5.3.2.1. Example: Successful Sharee Add Request . . . . . . 11
5.3.2.2. Example: Successful Multiple Sharee Change
Request . . . . . . . . . . . . . . . . . . . . . 11
5.4. Sharee Actions on Shared Calendars . . . . . . . . . . . . 12
5.4.1. Replying to a Sharing Invite . . . . . . . . . . . . . 12
5.4.2. Removing a Shared Calendar . . . . . . . . . . . . . . 13
5.5. General Considerations . . . . . . . . . . . . . . . . . . 13
5.5.1. Access Levels . . . . . . . . . . . . . . . . . . . . 13
5.5.2. Allowing or Disallowing Sharing . . . . . . . . . . . 13
5.5.3. Per-user WebDAV Properties . . . . . . . . . . . . . . 14
5.5.4. Per-user Calendar Data . . . . . . . . . . . . . . . . 14
5.5.5. Scheduling . . . . . . . . . . . . . . . . . . . . . . 15
6. XML Element Definitions . . . . . . . . . . . . . . . . . . . 16
6.1. CS:shared-owner . . . . . . . . . . . . . . . . . . . . . 16
Daboo & York [Page 1]
CalDAV Sharing and Publishing September 2012
6.2. CS:shared . . . . . . . . . . . . . . . . . . . . . . . . 17
6.3. CS:can-be-shared . . . . . . . . . . . . . . . . . . . . . 17
6.4. CS:can-be-published . . . . . . . . . . . . . . . . . . . 18
6.5. CS:user . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.6. CS:invite-noresponse . . . . . . . . . . . . . . . . . . . 18
6.7. CS:invite-deleted . . . . . . . . . . . . . . . . . . . . 19
6.8. CS:invite-accepted . . . . . . . . . . . . . . . . . . . . 19
6.9. CS:invite-declined . . . . . . . . . . . . . . . . . . . . 19
6.10. CS:invite-invalid . . . . . . . . . . . . . . . . . . . . 20
6.11. CS:access . . . . . . . . . . . . . . . . . . . . . . . . 20
6.12. CS:read . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.13. CS:read-write . . . . . . . . . . . . . . . . . . . . . . 21
6.14. CS:summary . . . . . . . . . . . . . . . . . . . . . . . . 21
6.15. CS:invite-notification . . . . . . . . . . . . . . . . . . 22
6.16. CS:uid . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.17. CS:hosturl . . . . . . . . . . . . . . . . . . . . . . . . 23
6.18. CS:organizer . . . . . . . . . . . . . . . . . . . . . . . 23
6.19. CS:common-name . . . . . . . . . . . . . . . . . . . . . . 23
6.20. CS:first-name . . . . . . . . . . . . . . . . . . . . . . 24
6.21. CS:last-name . . . . . . . . . . . . . . . . . . . . . . . 24
6.22. CS:invite-reply . . . . . . . . . . . . . . . . . . . . . 24
6.23. CS:in-reply-to . . . . . . . . . . . . . . . . . . . . . . 25
6.24. CS:notification . . . . . . . . . . . . . . . . . . . . . 25
6.25. CS:dtstamp . . . . . . . . . . . . . . . . . . . . . . . . 26
6.26. CS:share . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.27. CS:set . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.28. CS:remove . . . . . . . . . . . . . . . . . . . . . . . . 27
6.29. CS:shared-as . . . . . . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
10. Normative References . . . . . . . . . . . . . . . . . . . . . 28
Appendix A. Change History . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Daboo & York [Page 2]
CalDAV Sharing and Publishing September 2012
1. Introduction
CalDAV [RFC4791] provides a way for calendar users to store calendar
data and exchange this data via scheduling operations. Based on the
WebDAV [RFC4918] protocol, it also includes the ability to manage
access to calendar data via the WebDAV ACL [RFC3744] extension.
WebDAV ACL [RFC3744] provides a way to manage fine-grained access
controls on WebDAV resources. Whilst this could be used directly to
manage sharing of calendars, experience has shown that client
developers are averse to using it due to its complexity. Instead a
simpler process for sharing calendars is preferred.
This extension defines a way for individual calendar users to share
calendars with other users. This is done via an "opt-in" process in
which a sharing invite is sent from the sharer to a sharee, allowing
the sharee to accept or decline. If the sharee accepts the sharing
invite, the shared calendar is made available to them in their own
calendar home collection (i.e., alongside their own personal
calendars). HTTP POST operations are used to manage the sharing
invitations and replies, and WebDAV properties are used to expose the
state of shared calendars.
2. 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.
The namespace "http://calendarserver.org/ns/" is used for XML
elements defined in this specification. When XML element types in
that namespace are referenced in this document outside of the context
of an XML fragment, the string "CS:" will be prefixed to the element
type names.
Terms Used:
Sharer A calendar user who is sharing a calendar with other calendar
users.
Daboo & York [Page 3]
CalDAV Sharing and Publishing September 2012
Sharee A calendar user to whom a calendar has been shared.
Sharing Invite A message sent by a sharer to a sharee to indicate
the status of a shared calendar.
Sharing Reply A message sent by a sharee to a sharer to indicate the
status of a shared calendar.
3. Overview
This section provides a basic overview of this protocol by way of a
simple use case of a sharer sharing a calendar with a single sharee.
To share a calendar with another user, the sharer's client executes
an HTTP POST request against the calendar collection resource for the
calendar to be shared. The POST request body will contain details of
the calendar user to whom the calendar is to be shared as well as the
access right to be granted to them. If the request succeeds, a
notification is sent to the sharee with details of the calendar being
shared to them.
The sharer's client will show the notification to the sharee and
present them with the choice to accept or decline the invitation to
the shared calendar. If the sharee chooses to decline, then nothing
changes for that sharee. If the sharee chooses to accept, then the
server automatically creates a new calendar collection resource in
the sharee's calendar home collection, and ensures that calendar
provides a mapping to the actual shared calendar of the sharer. Thus
the shared calendar is available to the sharee as just another
calendar in their calendar home. The server enforces the appropriare
access privileges for the sharee.
At any time, the sharer can inspect properties on the calendar
collection being shared, and determine the accept/decline status of
each sharee. Additional sharees can be added and existing ones
removed. The access privileges for existing sharees can also be
changed.
Once a sharee has a shared calendar set to appear in their calendar
home collection, they can remove it and decline the sharing invite by
simply having their client issue an HTTP DELETE request on the shared
calendar collection. That does not delete any calendar data, but
rather simply removes the "link" to the sharer's calendar collection
and sets the sharee's inviate status to declined.
Daboo & York [Page 4]
CalDAV Sharing and Publishing September 2012
4. Notifications
In order to facilitate the process of sharing invitations, this
specification defines a new generic notification mechanism for CalDAV
servers. When this feature is available, a CS:notification-URL
(Section 4.1.1) property appears on principal resources for those
principals who are able to receive notifications. That property
specifies a single DAV:href element whose content refers to a WebDAV
collection resource. Notification "messages" are deposited into this
collection and can be retrieved by clients and acted on accordingly.
The notification collection referenced by the CS:notification-URL
(Section 4.1.1) property MUST have a DAV:resourcetype property with
DAV:collection and CS:notification (Section 6.24) child elements.
Notification "messages" are XML documents stored as resources in the
notification collection. Each XML document contains a CS:
notification (Section 6.24) element as its root. The root element
contains a CS:dtstamp (Section 6.25) element, and one additional
element which represents the type of notification being conveyed in
the message. That child element will typically contain additional
content that describes the notification.
Each notification resource has a CS:notificationtype (Section 4.2.1)
property which contains as its single child element an empty element
that matches the child element of the notification resource XML
document root. Any attributes on the child element in the XML
document are also present in the property child element.
Notifications are automatically generated by the server (perhaps in
response to a client action) with an appropriate resource stored in
the notifications collection of the user to whom the notification is
targeted. Clients SHOULD monitor the notification collection looking
for new notification resources. When doing so, clients SHOULD look
at the CS:notificationtype (Section 4.2.1) property to ensure that
the notification is of a type that the client can handle. Once a
client has handled the notification in whatever way is appropriate it
SHOULD delete the notification resource. Servers MAY delete
notification resources on their own if they determine that the
notifications are no longer relevant or valid. Servers MAY coalesce
notifications as appropriate.
4.1. Additional Principal Properties
This section defines new properties for WebDAV principal resources as
defined in RFC3744 [RFC3744]. These properties are likely to be
protected but the server MAY allow them to be written by appropriate
users.
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CalDAV Sharing and Publishing September 2012
4.1.1. CS:notification-URL Property
Name: notification-URL
Namespace: http://calendarserver.org/ns/
Purpose: Identify the URL of the notification collection owned by
the associated principal resource.
Protected: This property SHOULD be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: This property is needed for a client to determine where
the notification collection of the current user is located so that
processing of notification messages can occur. If not present,
then the associated calendar user is not enabled for notification
messages on the server.
Definition:
<!ELEMENT notification-URL (DAV:href)>
4.2. Properties on Notification Resources
The following new WebDAV properties are defined for notification
resources.
4.2.1. CS:notificationtype Property
Name: notificationtype
Namespace: http://calendarserver.org/ns/
Purpose: Identify the type of notification of the corresponding
resource.
Protected: This property MUST be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
Daboo & York [Page 6]
CalDAV Sharing and Publishing September 2012
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
Description: This property allows a client, via a PROPFIND Depth:1
request, to quickly find notification messages that the client can
handle in a notification collection. The single child element is
the notification resource root element's child defining the
notification itself. This element MUST be empty, though any
attributes on the element in the notification resource MUST be
present in the property element.
Definition:
<!ELEMENT notificationtype (invite-notification | invite-reply)>
<!-- Child elements are empty but will have appropriate attributes.
Any valid notification message child element can appear.-->
5. Shared Calendaring
5.1. Feature Discovery
A server that supports the features described in this document MUST
include "calendarserver-sharing" as a field in the DAV response
header from an OPTIONS request on any resource that supports these
features.
5.2. Additional Properties for Calendars
The following new or modified WebDAV properties are defined for
calendar collections and used to view or manipulate shared calendar
features.
5.2.1. DAV:resourcetype Property
Calendar collections that are shared have addition elements listed in
their DAV:resourcetype property in addition to DAV:collection and
CALDAV:calendar.
o CS:shared-owner (Section 6.1): used to indicate that the calendar
is owned by the current user and is being shared by them.
o CS:shared (Section 6.2): used to indicate that the calendar is
owned by another user and is being shared to the current user.
Daboo & York [Page 7]
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5.2.2. CS:invite Property
Name: invite
Namespace: http://calendarserver.org/ns/
Purpose: Used to show to whom a calendar has been shared.
Protected: This property MUST be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
Description: This WebDAV property is present on a calendar
collection resource that has been shared by the owner, or on the
calendar collection resources of the sharees of the calendar. It
provides a list of users to whom the calendar has been shared,
along with the "status" of the sharing invites sent to each user.
In addition, servers SHOULD include a CS:organizer XML element on
calendar collection resources of the sharees to provide clients
with a fast way to determine who the sharer is. A server's local
privacy policy may prevent sharees from knowing about other
sharees on a shared calendar. If that is so server will not
include CS:user XML elements for other sharees.
Definition:
<!ELEMENT invite (organizer?, user*)>
5.2.3. CS:allowed-sharing-modes Property
Name: allowed-sharing-modes
Namespace: http://calendarserver.org/ns/
Purpose: Used to show which modes of sharing are supported on a
calendar collection.
Protected: This property MUST be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
Daboo & York [Page 8]
CalDAV Sharing and Publishing September 2012
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
Description: This WebDAV property is present on a calendar
collection resource that can been shared or published. It
provides a list of options indicating what sharing modes are
allowed as per Section 5.5.2.
Definition:
<!ELEMENT allowed-sharing-modes
(can-be-shared?, can-be-published?)>
5.2.4. CS:shared-url Property
Name: shared-url
Namespace: http://calendarserver.org/ns/
Purpose: Indicates the URL of the owner's copy of a shared calendar.
Protected: This property MUST be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
Description: This WebDAV property is present on a shared calendar
collection resource that appears in a sharee's calendar home
collection. Its content is a single DAV:href element whose value
is the URL of the sharer's calendar being shared.
Definition:
<!ELEMENT shared-url (DAV:href)>
5.3. Sharer Actions on Shared Calendars
5.3.1. Sharing or Unsharing a Calendar
To update an existing calendar to be shared, the sharer simply adds
one or more sharees to the calendar collection as per Section 5.3.2.
The server MUST update the DAV:resourcetype property on the calendar
collection to ensure it contains a CS:shared-owner XML element to
indicate the calendar collection is now shared.
Daboo & York [Page 9]
CalDAV Sharing and Publishing September 2012
To unshare a calendar, the sharer simply removes all sharees to the
CS:invite property of the calendar collection as per Section 5.3.2.
The server MUST update the DAV:resourcetype property on the calendar
collection to ensure it does not contain a CS:shared-owner XML
element to indicate the calendar collection is not shared.
5.3.2. Manipulating Sharees of a Shared Calendar
The sharer of a shared calendar is able to manipulate the sharee list
by issuing a POST request targeted at the calendar collection
resource. The POST request MUST contain an XML document as its body
with the root element being CS:share (Section 6.26).
The CS:share (Section 6.26) element in the POST requests MUST contain
one or more CS:set (Section 6.27) or CS:remove (Section 6.28)
elements. For each CS:set (Section 6.27) element, the server MUST
add the specified sharee access to the calendar. For each CS:remove
(Section 6.28) element the server MUST remove the specified sharee
access from the shared calendar. In each case the server MUST send a
notification message to any sharees whose status is changed (added,
modified or removed), indicating to them a change in status for the
shared calendar. The server SHOULD NOT send notification messages to
sharees whose status is unchanged.
Sharee's are identified via a DAV:href element whose value is either
a principal-URL for a sharee hosted on the same server, a calendar
user address or email address. In the case of the later two, the
sharee might not be a user on the same server - though in that case
how invitations are sent or access enabled is out of scope for this
specification. A server MAY change the sharee's "address" to any
suitable alternative that it might prefer when returning the list of
sharees via the CS:invite property (Section 5.2.2).
The client MAY include a CS:common-name (Section 6.19) element in the
CS:set (Section 6.27) element. When provided, the value represents
the common name for the sharee, and is returned in the list of
sharees via the CS:invite property (Section 5.2.2). The server MAY
change this to a suitable alternative when it is able to match the
sharee to a known user. If absent from the client request, the
server SHOULD add a CS:common-name when it is able to match the
sharee with a known user, and a common name for that user can be
determined.
When the sharee list on a shared calendar is changed, the server MUST
send notifications to each sharee to update them on their current
sharing status. This is accomplished by sending a CS:invite-
notification (Section 6.15) notification to each sharee.
Daboo & York [Page 10]
CalDAV Sharing and Publishing September 2012
5.3.2.1. Example: Successful Sharee Add Request
This example shows how to add a single sharee (with calendar user
address "mailto:eric@example.com") to a shared calendar with CS:read-
write access.
>> Request <<
POST /calendars/users/cyrus/shared/ HTTP/1.1
Host: calendar.example.com
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<CS:share xmlns:D="DAV:"
xmlns:CS="http://calendarserver.org/ns/">
<CS:set>
<D:href>mailto:eric@example.com</D:href>
<CS:common-name>Eric York</CS:common-name>
<CS:summary>Shared workspace</CS:summary>
<CS:read-write />
</CS:set>
</CS:share>
>> Response <<
HTTP/1.1 200 OK
Cache-Control: no-cache
Date: Sat, 11 Nov 2006 09:32:12 GMT
5.3.2.2. Example: Successful Multiple Sharee Change Request
This example shows how multiple sharee's can be manipulated in a
single request. The sharee with calendar user address
"mailto:eric@example.com" has their access downgraded to CS:read,
whilst another sharee is removed from the access list entirely.
Daboo & York [Page 11]
CalDAV Sharing and Publishing September 2012
>> Request <<
POST /calendars/users/cyrus/shared/ HTTP/1.1
Host: calendar.example.com
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<CS:share xmlns:D="DAV:"
xmlns:CS="http://calendarserver.org/ns/">
<CS:set>
<D:href>mailto:eric@example.com</D:href>
<CS:summary>Shared workspace</CS:summary>
<CS:read-write />
</CS:set>
<CS:remove>
<D:href>mailto:wilfredo@example.com</D:href>
</CS:remove>
</CS:share>
>> Response <<
HTTP/1.1 200 OK
Cache-Control: no-cache
Date: Sat, 11 Nov 2006 09:32:12 GMT
5.4. Sharee Actions on Shared Calendars
5.4.1. Replying to a Sharing Invite
When a sharee is invited to a shared calendar they can accept or
decline the invite by issuing a POST request to the sharee's calendar
home collection resource. The POST request MUST contain an XML
document as its body with the root element being CS:invite-reply
(Section 6.22).
The CS:invite-reply (Section 6.22) element in the POST request
specifies the sharee who is replying in the DAV:href element, the
accept or decline action via the CS:invite-accepted or CS:invite-
declined elements, the URL of the shared calendar in the CS:hosturl
element, the unique identifier of the invite to which it is a reply
in the CS:in-reply-to element, and an optional CS:summary element.
The response to a POST request that accepts a shared calendar invite
MUST be an XML document containing CS:shared-as (Section 6.29) as its
root element. That root element contains a single DAV:href element
whose content is the URI of the shared calendar in the sharee's
calendar home created by the invite acceptance.
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When the sharee replies to an invite, the server SHOULD send a
notification to the sharer to update them on the change in the sharee
state. This is accomplished by sending a CS:invite-reply
(Section 6.22) notification to the sharer.
5.4.2. Removing a Shared Calendar
To remove a shared calendar from a sharee's calendar home collection
a DELETE request is targeted at the shared calendar URI. When such a
request is received the server MUST remove the shared calendar from
the sharee's calendar home and automatically update the sharee's
status in the sharer's calendar's CS:invite property.
5.5. General Considerations
5.5.1. Access Levels
Two levels of access ca be granted by a sharer to any sharee. These
are governed by the CS:access element used in the CS:invite/CS:user
element that specifies a shared user invite. CS:access contains a
single empty element that defines the type of access granted:
CS:read When present this indicates that sharees can read calendar
data but cannot change it.
CS:read-write When present this indicates that sharees can read and
write calendar data.
5.5.2. Allowing or Disallowing Sharing
Servers MAY support calendar sharing on a per-calendar basis - e.g.,
they could treat some calendars as always private (cannot be shared)
or always public (always shared). As a result clients need a way to
determine which calendar could be shared so they can enable or
disable sharing options on a per-calendar basis.
This specification adds a CS:allowed-sharing-modes (Section 5.2.3)
WebDAV property which servers can return on calendar collection
resources. This property contains XML elements that describe which
sharing or publishing capabilities can be supported by the
corresponding calendar collection:
CS:can-be-shared (Section 6.3): when present indicates that the
calendar collection can be shared. When not present, the calendar
collection cannot be shared.
CS:can-be-published (Section 6.4): when present indicates that the
calendar collection can be published. When not present, the
Daboo & York [Page 13]
CalDAV Sharing and Publishing September 2012
calendar collection cannot be published.
When not present on a calendar collection, sharing or publishing of
that calendar is not allowed. Clients SHOULD NOT attempt to use
requests to enable sharing or publishing targeted at those calendar
collections.
5.5.3. Per-user WebDAV Properties
Servers MUST support "per-user" WebDAV properties on shared calendar
collections and MAY support them on calendar object resources within
shared calendar collections. A "per-user" WebDAV property is one
whose value can be set and retrieved independently by each user with
appropriate access rights. e.g., user "A" changes the DAV:displayname
property on a shared calendar in their calendar home to "My
calendar", and user "B" changes the same property to "Shared" on the
same shared calendar in their calendar home. When each user
retrieves the property value they will see their own last stored
value and not the value of the other user.
For shared calendars, the server MUST allow all users to write "per-
user" WebDAV properties on the shared calendar collection and MAY
allow property writes on calendar object resources within the shared
calendar collection. This is required even in the case where the
sharee has been granted read access only (i.e., the ability to change
calendar data is disallowed). This requirement ensures that sharees
can always change "personal" properties such as calendar colors and
display names.
Servers MUST treat the following properties as "per-user":
DAV:displayname
CALDAV:calendar-description
CALDAV:schedule-calendar-transp
ICAL:calendar-color
Servers MAY treat any dead property as per-user.
Servers MUST NOT treat live properties as per-user.
5.5.4. Per-user Calendar Data
Servers MUST support "per-user" 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
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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-user:
TRANSP property
VALARM component
Servers MAY treat any non-standard X- iCalendar properties as per-
user.
When handling per-user data in recurring components, servers SHOULD
eliminate overridden instances when returning iCalendar data to
clients in the case where there are no differences between the
overridden component and the instance that could be derived from the
"master" recurrence component. For example, consider a daily
recurring event, Monday through Friday, initially defined without any
overridden instances, that is in a shared calendar. If user "A"
overrides the Tuesday instance and adds their own "VALARM" component
only, then when user "A" later retrieves the data again they would
see that overridden instance, but when user "B" does so, they would
not. This ensures that each user sees the most "compact"
representation of the calendar data.
5.5.5. 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 calendar object resources are created, modified or deleted in
shared calendars by sharees, the following restrictions apply:
1. The "ORGANIZER" iCalendar property value in the iCalendar data
MUST match a calendar user address of the sharer (owner) of the
shared calendar. The DAV:owner WebDAV property MUST be present
on a shared calendar and MUST provide a reference to a principal-
URL of the sharer (owner) of the shared calendar. Clients can
use this value to determine what the allowed "ORGANIZER"
iCalendar property values are. The server MUST reject any
attempt by a sharee to create an iCalendar component with an
"ORGANIZER" property value other than the sharer (owner) of the
shared calendar.
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2. The server MUST reject any attempt by a sharee to MOVE a calendar
object resource in a shared calendar to some other collection.
3. When a sharee is listed as an Attendee in a calendar object
resource in a shared calendar, and 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.
4. The default calendar collection defined in Section 6.3 of
[RFC6638] MUST NOT be a calendar shared to the corresponding
calendar user.
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.
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.
6. XML Element Definitions
6.1. CS:shared-owner
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Name: shared-owner
Namespace: http://calendarserver.org/ns/
Purpose: Used to indicate that a calendar is being shared by the
owner.
Description: This property appears in the DAV:resourcetype property
on the calendar collection resource shared by a sharer. See
Section 5.2.
Definition:
<!ELEMENT shared-owner EMPTY>
6.2. CS:shared
Name: shared
Namespace: http://calendarserver.org/ns/
Purpose: Used to indicate that a calendar is being shared to a
sharee.
Description: This property appears in the DAV:resourcetype property
on a calendar collection resource that is shared to a sharee and
appears in the sharee's calendar home collection. See
Section 5.2.
Definition:
<!ELEMENT shared EMPTY>
6.3. CS:can-be-shared
Name: can-be-shared
Namespace: http://calendarserver.org/ns/
Purpose: Used to indicate that a calendar can be shared.
Description: This element indicates that a calendar can be shared
with other users. See Section 5.2.3
Definition:
<!ELEMENT can-be-shared EMPTY>
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6.4. CS:can-be-published
Name: can-be-published
Namespace: http://calendarserver.org/ns/
Purpose: Used to indicate that a calendar can be published.
Description: This element indicates that a calendar can be published
to anyone. See Section 5.2.3
Definition:
<!ELEMENT can-be-published EMPTY>
6.5. CS:user
Name: user
Namespace: http://calendarserver.org/ns/
Purpose: Used to show status of sharing invites sent to sharees.
Description: This element provides the "status" of a sharing invite
sent to a particular user. See Section 5.2.2.
Definition:
<!ELEMENT user (DAV:href, common-name?, (invite-noresponse |
invite-accepted | invite-declined | invite-invalid),
access, summary?)>
6.6. CS:invite-noresponse
Name: invite-noresponse
Namespace: http://calendarserver.org/ns/
Purpose: Sharing invite status.
Description: When used in a CS:user (Section 6.5) element, this
element is used to indicate that the sharee has never replied to
the corresponding sharing invite. When used in a CS:invite-
notification (Section 6.15) element, this element is used to
indicate to the sharee that a sharing reply is needed.
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Definition:
<!ELEMENT invite-noresponse EMPTY>
6.7. CS:invite-deleted
Name: invite-deleted
Namespace: http://calendarserver.org/ns/
Purpose: Sharing invite status.
Description: When used in a CS:invite-notification (Section 6.15)
element, this element is used to indicate to the sharee that a
shared calendar has been unshared by the sharer.
Definition:
<!ELEMENT invite-deleted EMPTY>
6.8. CS:invite-accepted
Name: invite-accepted
Namespace: http://calendarserver.org/ns/
Purpose: Sharing invite status.
Description: When used in a CS:user (Section 6.5) element, this
element is used to indicate that the sharee has accepted the
corresponding sharing invite. When used in a CS:invite-
notification (Section 6.15) element, this element is used to
indicate to the sharee that the sharing invite is an update for
one they previously accepted.
Definition:
<!ELEMENT invite-accepted EMPTY>
6.9. CS:invite-declined
Name: invite-declined
Namespace: http://calendarserver.org/ns/
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Purpose: Sharing invite status.
Description: When used in a CS:user (Section 6.5) element, this
element is used to indicate that the sharee has declined the
corresponding sharing invite. When used in a CS:invite-
notification (Section 6.15) element, this element is used to
indicate to the sharee that the sharing invite is an update for
one they previously declined.
Definition:
<!ELEMENT invite-declined EMPTY>
6.10. CS:invite-invalid
Name: invite-invalid
Namespace: http://calendarserver.org/ns/
Purpose: Sharing invite status.
Description: When used in a CS:user (Section 6.5) element, this
element is used to indicate that the corresponding sharee is not a
valid calendar user known to the server.
Definition:
<!ELEMENT invite-invalid EMPTY>
6.11. CS:access
Name: access
Namespace: http://calendarserver.org/ns/
Purpose: Shared calendar access level.
Description: When used in a CS:user (Section 6.5) element, this
element is used to indicate the sharing access level granted to
the corresponding sharee.
Definition:
<!ELEMENT access (read | read-write)>
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6.12. CS:read
Name: read
Namespace: http://calendarserver.org/ns/
Purpose: Shared calendar access level privilege.
Description: Indicates that the access level granted only allows
sharees to read data in the shared calendar (though they can write
per-user data (Section 5.5.4)).
Definition:
<!ELEMENT read EMPTY>
6.13. CS:read-write
Name: read-write
Namespace: http://calendarserver.org/ns/
Purpose: Shared calendar access level privilege.
Description: Indicates that the access level granted allows sharees
to read and write all data in the shared calendar, with the
exception of components that would trigger scheduling.
Definition:
<!ELEMENT read-write EMPTY>
6.14. CS:summary
Name: summary
Namespace: http://calendarserver.org/ns/
Purpose: Summary or title of shared calendar.
Description: A brief description of a shared calendar. This can be
used by sharers to communicate the nature of a shared calendar to
sharees, as well as used by sharees to indicate back to the sharer
how each sharee is refering to the shared calendar.
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Definition:
<!ELEMENT summary (#PCDATA)>
6.15. CS:invite-notification
Name: invite-notification
Namespace: http://calendarserver.org/ns/
Purpose: A notification used as a shared calendar invite.
Description: Defines a notification message sent automatically by
the server when a sharer adds, changes or removes a sharee from a
shared calendar. The DAV:href element specifies the calendar user
address of the sharee to whom the message was sent. The CALDAV:
supported-calendar-component-set is a copy of the matching WebDAV
property on the sharers calendar collection, to allow clients to
know what restrictions might apply to the shared calendar before
accepting it.
Definition:
<!ELEMENT invite-notification (
uid, DAV:href,
(invite-noresponse | invite-deleted |
invite-accepted | invite-declined),
access, hosturl, organizer,
summary?,
CALDAV:supported-calendar-component-set?>
6.16. CS:uid
Name: uid
Namespace: http://calendarserver.org/ns/
Purpose: Unique identifier.
Description: A unique identifier for an invitation to a shared
calendar.
Definition:
<!ELEMENT uid (#PCDATA)>
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6.17. CS:hosturl
Name: hosturl
Namespace: http://calendarserver.org/ns/
Purpose: Identifies the source URL of a shared calendar.
Description: Contains a single DAV:href element that refers to the
source of a shared calendar - i.e., the URL of the calendar shared
by the sharer.
Definition:
<!ELEMENT hosturl (DAV:href)>
6.18. CS:organizer
Name: organizer
Namespace: http://calendarserver.org/ns/
Purpose: Identifies the sharer of a shared calendar.
Description: Contains a single DAV:href element that identifies the
calendar user address of the sharer of a shared calendar, and an
optional CS:common-name element that matches that user, and an
option CS:first-name, CS:last-name pair of elements that match
that user. In some cases servers might have directory information
that includes only the common name, or only the first or last
name, and it is better to expose those directly to the client
as-is rather than to try and split or combine the attributes to
synthesize one set or the other.
Definition:
<!ELEMENT organizer (DAV:href,
CS:common-name?,
(CS:first-name, CS:last-name)?)>
6.19. CS:common-name
Name: common-name
Namespace: http://calendarserver.org/ns/
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Purpose: The common name of a sharer or sharee.
Description: The common name is optionally provided by a client when
adding a sharee and optionally included (or modified) by the
server when returning results for sharers or sharees and in
notifications.
Definition:
<!ELEMENT common-name (#PCDATA)>
6.20. CS:first-name
Name: first-name
Namespace: http://calendarserver.org/ns/
Purpose: The first name of a sharer or sharee.
Description: The first name is optionally included by the server
when returning results for sharers or sharees and in
notifications.
Definition:
<!ELEMENT first-name (#PCDATA)>
6.21. CS:last-name
Name: last-name
Namespace: http://calendarserver.org/ns/
Purpose: The last name of a sharer or sharee.
Description: The last name is optionally included by the server when
returning results for sharers or sharees and in notifications.
Definition:
<!ELEMENT last-name (#PCDATA)>
6.22. CS:invite-reply
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Name: invite-reply
Namespace: http://calendarserver.org/ns/
Purpose: A notification used as a reply to a shared calendar invite.
Description: Defines a notification message sent automatically by
the server when a sharee replies to a shared calendar invite. The
DAV:href element specifies the calendar user address of the sharee
to whom the original invite message was sent.
Definition:
<!ELEMENT invite-reply (DAV:href,
(invite-accepted | invite-declined),
hosturl, in-reply-to, summary?>
6.23. CS:in-reply-to
Name: in-reply-to
Namespace: http://calendarserver.org/ns/
Purpose: Unique identifier.
Description: Specifies the unique identifier of the inviate message
that this notification message is a reply to.
Definition:
<!ELEMENT in-reply-to (#PCDATA)>
6.24. CS:notification
Name: notification
Namespace: http://calendarserver.org/ns/
Purpose: Notification message root element.
Description: The root element used in notification resources.
Definition:
<!ELEMENT notification (CS:dtstamp,
(invite-notification | invite-reply)>
<!-- Any notification type element can appear after CS:dtstamp,
this specification defines only the two listed above -->
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6.25. CS:dtstamp
Name: dtstamp
Namespace: http://calendarserver.org/ns/
Purpose: Date-time stamp.
Description: Contains the date-time stamp corresponding to the
creation of a notification message.
Definition:
<!ELEMENT dtstamp (#PCDATA)>
6.26. CS:share
Name: share
Namespace: http://calendarserver.org/ns/
Purpose: Describes changes to sharees.
Description: The root element used in POST requests on calendars by
sharers to manipulate the sharee list of a shared calendar.
Definition:
<!ELEMENT share (set | remove)*>
6.27. CS:set
Name: set
Namespace: http://calendarserver.org/ns/
Purpose: Sets access for a sharee.
Description: Used to add or modify sharee access to a shared
calendar. The specified access to the shared calendar is given to
the sharee.
Definition:
<!ELEMENT set (DAV:href, common-name?, summary?,
(read | read-write)>
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6.28. CS:remove
Name: remove
Namespace: http://calendarserver.org/ns/
Purpose: Removes access for a sharee.
Description: Used to remove sharee access to a shared calendar. All
access to the shared calendar is removed for the sharee.
Definition:
<!ELEMENT remove (DAV:href)>
6.29. CS:shared-as
Name: shared-as
Namespace: http://calendarserver.org/ns/
Purpose: Identifies a shared calendar.
Description: Returned by the server for a POST request by a sharee
accepting a shared calendar invite. The DAV:href element
specifies the URI of the calendar created by the acceptance.
Definition:
<!ELEMENT shared-as (DAV:href)>
7. Security Considerations
Per-user WebDAV properties and iCalendar data MUST only be accessible
by the user that created them.
Alarms set by the sharer SHOULD NOT be propagated to sharees by
default. Clients SHOULD NOT automatically enable triggering of
alarms on shared calendars that have just been accepted without
confirmation by the user.
TBD
8. IANA Considerations
This document does not require any actions on the part of IANA.
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9. Acknowledgments
This specification is the result of discussions between the Apple
calendar server and client teams.
10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3744] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
Distributed Authoring and Versioning (WebDAV)
Access Control Protocol", RFC 3744, May 2004.
[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
March 2007.
[RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918, June 2007.
[RFC6638] Daboo, C. and B. Desruisseaux, "Scheduling Extensions to
CalDAV", RFC 6638, June 2012.
Appendix A. Change History
Changes in -03:
1. Fixed access element DTD.
2. Remove MKxxx and PROPPATCH mechanism for upgrading/downgrading
shared state on a calendar collection. Instead the server
implicitly sets the state based on whether there are any sharees
or not..
3. Added CS:first-name and CS:last-name optional element to CS:
organizer.
4. Added CALDAV:supported-calendar-component-set optional element to
CS:invite-notification.
Changes in -02:
1. Removed read-write-shared access mode - now a server that does
not support shared scheduling should advertise that via a DAV
header
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Changes in -01:
1. Added CS:shared-url property
2. Clarified that notifications are only required to be sent when
sharee status is changed
Authors' Addresses
Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
Email: cyrus@daboo.name
URI: http://www.apple.com/
Eric York
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
Email:
URI: http://www.apple.com/
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