Internet DRAFT - draft-pot-webdav-resource-sharing
draft-pot-webdav-resource-sharing
Network Working Group E. Pot
Internet-Draft fruux GmbH
Expires: July 14, 2016 C. Daboo
E. York
Apple Inc.
January 11, 2016
WebDAV Resource Sharing
draft-pot-webdav-resource-sharing-03
Abstract
This specification defines an extension to WebDAV that enables the
sharing of resources between users on a WebDAV server.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 14, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. High-level overview . . . . . . . . . . . . . . . . . . . . . 4
4. Sharing a resource . . . . . . . . . . . . . . . . . . . . . 4
4.1. Advertising resource sharing support . . . . . . . . . . 5
4.2. Required privileges . . . . . . . . . . . . . . . . . . . 5
4.3. Sharing POST request . . . . . . . . . . . . . . . . . . 5
4.3.1. Example: Sharing a resource . . . . . . . . . . . . . 6
4.3.2. Example: Multiple sharee changes . . . . . . . . . . 7
4.4. New WebDAV properties on shared resources . . . . . . . . 8
4.4.1. DAV:share-access Property . . . . . . . . . . . . . . 8
4.4.2. DAV:invite Property . . . . . . . . . . . . . . . . . 9
4.4.3. DAV:sharer-resource-uri Property . . . . . . . . . . 10
4.5. Handling the share process . . . . . . . . . . . . . . . 10
4.5.1. The invitation process . . . . . . . . . . . . . . . 10
4.5.2. Instant sharing . . . . . . . . . . . . . . . . . . . 11
4.6. Notification Definitions . . . . . . . . . . . . . . . . 11
4.6.1. Invite Notification . . . . . . . . . . . . . . . . . 11
4.6.1.1. Example: An invite notification . . . . . . . . . 11
4.6.2. Invite Reply . . . . . . . . . . . . . . . . . . . . 13
4.6.2.1. Example: An invite reply . . . . . . . . . . . . 13
4.7. Sharee Actions on Shared Resources . . . . . . . . . . . 14
4.7.1. Replying to a Sharing Invite . . . . . . . . . . . . 14
4.7.1.1. Example: Accepting an invite . . . . . . . . . . 15
4.7.2. Ignoring an invitation . . . . . . . . . . . . . . . 15
4.7.3. Making modifications to a shared resource . . . . . . 15
4.7.4. Removing a shared resource . . . . . . . . . . . . . 16
4.8. General Considerations . . . . . . . . . . . . . . . . . 16
4.8.1. Per-instance WebDAV Properties . . . . . . . . . . . 16
4.8.2. Sharees and instances . . . . . . . . . . . . . . . . 16
4.8.3. Relationship between sharing access levels and WebDAV
ACL . . . . . . . . . . . . . . . . . . . . . . . . . 17
5. XML Element Definitions . . . . . . . . . . . . . . . . . . . 18
5.1. DAV:share-resource . . . . . . . . . . . . . . . . . . . 18
5.2. DAV:share . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3. DAV:share-invite-notification . . . . . . . . . . . . . . 19
5.4. DAV:share-reply-notification . . . . . . . . . . . . . . 20
5.5. DAV:invite . . . . . . . . . . . . . . . . . . . . . . . 21
5.6. DAV:share-access . . . . . . . . . . . . . . . . . . . . 22
5.7. DAV:invite-reply . . . . . . . . . . . . . . . . . . . . 23
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
6.1. Forced shares . . . . . . . . . . . . . . . . . . . . . . 23
6.2. Notification spamming . . . . . . . . . . . . . . . . . . 24
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
9. Normative References . . . . . . . . . . . . . . . . . . . . 25
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Appendix A. Backwards compatibility . . . . . . . . . . . . . . 26
Appendix B. Change History (to be removed prior to publication
as an RFC . . . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
Users of CalDAV [RFC4791] and CardDAV [RFC6352] often require a
mechanism to share a calendar or address book collection with other
users.
This specification introduces a mechanism that allows users of WebDAV
servers to invite another user to share a resource or WebDAV
collection. The invited user can either accept or reject the invite,
which is communicated back to the sharer. If the user chooses to
accept the invite, the shared resource will then appear in a location
on the server that's accessible by the invitee.
There are existing mechanism that address similar use-cases, such as
using WebDAV ACL [RFC3744] for fine-grained access control.
Experiences has shown that client developers are averse to using it
due its complexity. Many implementations have chosen to only use
WebDAV ACL for communicating access control information to clients,
but not for modification. WebDAV ACL alone also does not provide the
means for a user to invite another user.
In this specification, HTTP POST operations are used to manage the
sharing invitations and replies, and WebDAV properties are used to
expose the state of shared resources.
This specification uses WebDAV notifications to communicate to users
there are outstanding invitations, or responses to invitations.
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:" are referenced in
this document outside of the context of an XML fragment, the string
"DAV:" will be prefixed to the element type names.
Terms Used:
Sharer A user who is sharing a resource with other users.
Sharee A user to whom a resource has been shared.
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Sharing Invite A message sent by a sharer to a sharee to notify a
sharee of an invitation or update.
Sharing Reply A message sent by a sharee to a sharer to indicate the
answer to an invite.
The DTD samples used in this document are for illustrative purposes
only. The conventions and restrictions described in [RFC4918]
section 17.
3. High-level overview
This section provides a basic overview of this protocol by way of a
simple use case of a sharer sharing a collection with a single
sharee.
To share a resource with another user, the sharer's client executes
an HTTP POST request against the resource that's to be shared. The
POST request body will contain details of the user to whom the
resource 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 resource 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 collection. If the sharee chooses to decline, then
nothing changes for that sharee. If the sharee chooses to accept,
then a new resource is created at a location that's accessible to the
sharee. The server enforces the appropriate access privileges for
the sharee.
At any time, the sharer can inspect properties on the resource 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 access to the shared resource, they can remove it
and decline the sharing invite by simply having their client issue an
HTTP DELETE request on the shared collection. That does not delete
any data, but rather simply removes the "link" to the sharer's
resource and sets the sharee's invite status to declined.
4. Sharing a resource
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4.1. Advertising resource sharing support
A server that supports the features described in this document MUST
include "resource-sharing" as a field in the DAV response header from
an OPTIONS request on any resource that supports these features.
A response to this OPTIONS request might look as follows:
HTTP/1.1 200 OK
Dav: 1,3,extended-mkcol,resource-sharing
Allow: GET,HEAD,POST,OPTIONS,PROPFIND,PROPPATCH
4.2. Required privileges
A server that supports sharing on a specific resource, MUST enforce
this using the "DAV:share" privilege. Privileges are defined in
[RFC3744].
The privilege MUST be non-abstract and MAY be protected. This
privilege MUST appear in the DAV:supported-privilege-set property for
resources that may be shared. In addition, it MUST appear in the
DAV:current-user-privilege-set property, if the user is in fact
allowed to share the resource. This mechanism is also used by a
client to discover sharing capabilities on specific resources.
4.3. Sharing POST request
To share a resource or revoke access to a shared resource, the client
must issue a POST request to the resource that the user wants to
share. The POST request MUST contain an XML document as its body,
with the root element being DAV:share-resource (Section 5.1).
The POST request MUST contain a Content-Type HTTP header, which MUST
contain "application/davshare+xml" as its value. Servers SHOULD
reject the request if this is not the case.
The DAV:share-resource element can contain one or more DAV:sharee
elements. Each DAV:sharee element MUST at least have a DAV:href
element containing a URI identifying the sharee.
The URI in DAV:href may be a principal-URL referring to a sharee host
on the same server, an email address or any other URI identifying a
user. In the case of the latter two, the sharee might not be a user
on the same server - though in that case how invitations are sent or
access is enabled is out of scope for this specification.
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The DAV:prop element is optional, and can be used to provide more
information about the sharee. The server MAY use this information
and later return it when information is requested about the list of
sharees. Any valid WebDAV property might be provided here, but it's
up to the discretion of the server what to support. A client SHOULD
provide at least a DAV:displayname property as a human- readable
string identifying the user.
The DAV:share-access element is required. It MUST contain one of the
following elements:
DAV:read When present this indicates that sharees can read
information from the resource, but cannot change it. This applies
to the resource, but if the shared resource is a collection, it
also applies to the collection's children.
DAV:read-write When present this indicates that sharees can read and
write information from the resource.
DAV:no-access When present this indicates that access to the
resource is revoked for the sharee.
Lastly, you may add the optional DAV:comment element. This element
may contain some information about the intent of the share, for the
sharee, this allows the sharee to send a short message.
4.3.1. Example: Sharing a resource
The following example grants read-write access to a resource
identified by "/calendars/users/cyrus/shared" to a sharee with email
address "mailto:eric@example.com".
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POST /calendars/users/cyrus/shared/ HTTP/1.1
Host: calendar.example.com
Content-Type: application/davsharing+xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:share-resource xmlns:D="DAV:">
<D:sharee>
<D:href>mailto:eric@example.com</D:href>
<D:prop>
<D:displayname>Eric York</D:displayname>
</D:prop>
<D:comment>Shared workspace</D:comment>
<D:share-access>
<D:read-write />
</D:share-access>
</D:sharee>
</D:share-resource>
If the operation was successful, the server MUST respond with a 204
No Content HTTP status.
HTTP/1.1 200 OK
Cache-Control: no-cache
Date: Sat, 11 Nov 2006 09:32:12 GMT
4.3.2. Example: Multiple sharee changes
This example shows how multiple sharee's can be manipulated in a
single request. The sharee with email address
"mailto:eric@example.com" has their access downgraded to CS:read,
whilst another sharee is removed from the access list entirely.
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POST /calendars/users/cyrus/shared/ HTTP/1.1
Host: calendar.example.com
Content-Type: application/davsharing+xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:share-resource xmlns:D="DAV:">
<D:sharee>
<D:href>mailto:eric@example.com</D:href>
<D:share-access>
<D:read />
</D:share-access>
</D:sharee>
<D:sharee>
<D:href>mailto:wilfredo@example.com</D:href>
<D:share-access>
<D:no-access />
</D:share-access>
</D:sharee>
</D:share-resource>
4.4. New WebDAV properties on shared resources
The following new or modified WebDAV properties are defined for
resources and used to view or manipulate shared resources features.
4.4.1. DAV:share-access Property
Name: share-access
Namespace: DAV:
Purpose: Allows a client to see if a resource is a shared resource
and the access level.
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 MOVE
operations, but MUST NOT be preserved in COPY operations.
Description: Resources that are shared must have a DAV:share-mode
property. It's value should be one of two elements:
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* DAV:not-shared: Used to indicate that the resource is not
shared. This is the default, which means that if the
DAV:share-access is omitted, this value is implied.
* DAV:shared-owner: used to indicate that the resource is owned
by the current user and is being shared by them.
* DAV:read-write>: used to indicate that the resource is shared,
and the current instance is the 'shared instance' which has
read-write access.
* DAV:read: used to indicate that the resource is shared, and the
current instance is the 'shared instance', and only read access
is provided.
Definition:
<!ELEMENT share-access (not-shared|shared-owner|read-write|read)>
4.4.2. DAV:invite Property
Name: invite
Namespace: DAV:
Purpose: Used to show to whom a resource 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 MOVE
operations, but MUST NOT be preserved in COPY operations.
Description: This WebDAV property is present on a resource that has
been shared by the owner, or on the resources for the sharees. It
provides a list of users to whom the resource has been shared,
along with the "status" of the sharing invites sent to each user.
In addition, servers SHOULD include a DAV:principal XML element on
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 DAV:sharee XML
elements for other sharees.
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4.4.3. DAV:sharer-resource-uri Property
Name: sharer-resource-uri
Namespace: DAV:
Purpose: A unique URI that identifies the shared 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]).
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
Description: This WebDAV property SHOULD be present on a shared
resource. Its content is a single DAV:href element whose value is
the URL of the sharer's resource being shared. The property MUST
contain a URI that uniquely identifies the original shared
resource. The URI MAY refer to a resource hosted on the same
server, but MAY also refer to a URN. A key requirement is that
this URI remains stable during the life-time of a share.
4.5. Handling the share process
This specification supports two major processes for sharing a
resource. The server can either immediately set up the newly shared
resource, or the server can provide an invitation process. The
former might be useful in small trusted team settings, whereas the
invitation process might be used in public servers, where it's
desirable for users to explicitly opt-in to getting access to newly
shared resources.
This specification provides a invitation and notification mechanism.
It might also be possible that servers provide their own out-of-band
mechanism for this, but this should not affect clients.
4.5.1. The invitation process
If the server opts to support the standard invitation process, the
server MUST support WebDAV notifications.
Sharees for a resource MUST appear up in the DAV:invite
(Section 4.4.2) property. Each sharee will have one of the following
elements:
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DAV:invite-noresponse The sharee was invited, but has not yet
responded to the invite.
DAV:invite-accepted The sharee has accepted the invite.
DAV:invite-declined The sharee has declined the invite.
DAV:invite-invalid The invitation was invalid or could not be
delivered.
When sharees are initially invited, they will get the DAV:invite-
noresponse status. When a sharee's access has been changed, they
will retain their existing status. When a sharee's access has been
revoked, they will no longer appear in the DAV:invite property.
After any of these mutations, sharees receive an Section 4.6.1 in
their notification collection. After the sharee has accepted or
declined the invite, their status will reflect this response.
4.5.2. Instant sharing
Implementing the invitation process is optional. It's also possible
for servers to immediately apply changes. The effect is that no
notifications may be needed, and the server behaves as if sharees
immediately accept invitations. Sharees listed in DAV:invite might
immediately receive a DAV:invite-accepted status.
4.6. Notification Definitions
In order to facilitate the process of sharing invitations, this
specification uses WebDAV notifications, and defines several new
notification types.
4.6.1. Invite Notification
When a sharer adds a new sharee to a resource, or updates a sharee,
an invite notification is added to the sharee's notification
collection.
The notification contains information about the shared resource, the
owner and how to respond to the invitation.
4.6.1.1. Example: An invite notification
This is an example of a response to a GET request on a correct invite
notification. Note that several HTTP response headers have been
removed for brevity.
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HTTP/1.1 200 OK
Content-Type: application/davnotification+xml
Content-Length: xxxx
<D:notification xmlns:D="DAV:">
<D:dtstamp>2014-08-05T13:38:02Z</D:dtstamp>
<D:share-invite-notification>
<D:principal>
<D:href>/principals/users/evert/</D:href>
</D:principal>
<D:invite-accepted />
<D:sharer-resource-uri>
<D:href>/calendars/users/evert/offdays/</D:href>
</D:sharer-resource-uri>
<D:share-access><D:read-write /></D:share-access>
<D:prop>
<D:displayname>Vacation days!!</D:displayname>
<D:resourcetype><D:collection /></D:resourcetype>
</D:prop>
<D:reply-url>
<D:href>?invite-reply</D:href>
</D:reply-url>
</D:share-invite-notification>
</D:notification>
In this notification, DAV:principal indicates which principal is the
sharer for the resource.
The notification MUST contain DAV:invite-accepted or DAV:invite-
noresponse to indicate the current invitation status of the sharee in
the shared resource. New invites to shares would carry the
DAV:invite-noresponse status. In case the sharee had accepted an
earlier invite, but it's access was changed or revoked, the
invitation will have a DAV:invite-accepted status.
DAV:sharer-resource-uri refers to the DAV:sharer-resource-uri that
the shared resource will have, and can be used to identify which
invitation refers to which existing shared resource. The element MAY
refer to the URI of the original shared resource, but may also be a
urn, or any other unique URI.
DAV:share-access MUST be one of DAV:read-write, DAV:read or DAV:no-
access. This indicates that the invitee either has read-write
access, read-only access or no access at all respectively.
DAV:reply-url appears for invitations to new shared resources. The
url in this property can be used for a sharee to accept or decline
the invite. DAV:reply-url only appears for sharees with the
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DAV:invite-noresponse status, and does not appear when DAV:share-
access is DAV:no-access.
The DAV:prop element is optional, and may contain a list of WebDAV
properties associated with the shared resource. Servers SHOULD at
least set the DAV:resourcetype, if available. This will allow a
client to know what kind of resource is being shared. Some clients
may only support responding to invites of certain kinds of resources.
For example, a calendaring user agent may only support CalDAV
calendars.
The DAV:comment element is also optional, and may return a brief
message from the sharer to the sharee. The sharer is able to specify
this in the original DAV:share-resource POST request.
4.6.2. Invite Reply
After a sharee has accepted or declined an invitation, the sharer
receives a share-reply-notification in their notification collection.
This notification contains information about which collection this
relates to, and who responded to the invite.
4.6.2.1. Example: An invite reply
This is an example of a response to a GET request on a correct invite
notification. Note that several HTTP response headers have been
removed for brevity.
HTTP/1.1 200 OK
Content-Type: application/davnotification+xml
Content-Length: xxxx
<D:notification xmlns:D="DAV:">
<D:dtstamp>2014-09-03T02:30:00Z</D:dtstamp>
<D:share-reply-notification>
<D:sharee>
<D:href>mailto:john@example.org</D:href>
<D:invite-declined />
</D:sharee>
<D:href>/calendars/users/evert/offdays/</D:href>
<D:comment>Sorry, I'm not interested</D:comment>
</D:share-reply-notification>
</D:notification>
In this notification, the DAV:sharee element MUST appear and contains
information about the updated status of the sharee in the shared
resource.
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The DAV:href element MUST appear and refers to the resource the
sharer originally shared.
The DAV:comment element is optional, and may contain a message that
the sharee specified when responding to the invite.
4.7. Sharee Actions on Shared Resources
4.7.1. Replying to a Sharing Invite
When a sharee is invited to a shared resource they can accept or
decline the invite by issuing a POST request to the url specified in
the DAV:reply-url element, in the invitation notification. The POST
request MUST contain an XML document as its body with the root
element being DAV:invite-reply (Section 5.7).
The POST request MUST contain a Content-Type HTTP header, which MUST
contain "application/davshare+xml" as its value. Servers SHOULD
reject the request if this is not the case.
The DAV:invite-reply (Section 5.7) element in the POST request
specifies the accept or decline action via the DAV:invite-accepted or
DAV:invite-declined elements, and an optional DAV:comment element.
IF the invite was accepted, the body MUST also contain a DAV:create-
in element. This element contains a single DAV:href element, which
content is a URI that will be used as the parent for the new shared
resource.
The client MAY also provide a DAV:slug property. The server MAY use
the contents of this property to determine the name of the new
resource.
All usual preconditions for creating a resource at the DAV:create-in
target collection need to be taken into consideration.
Note that some servers may restrict where certain types of resources
may be created. A CalDAV server for instance, may only allow
calendars to be created in collections identified by the
CALDAV:calendar-home-set WebDAV property.
The client MAY also provide a small comment in the DAV:comment
element. This comment will be sent back to the sharer. Support for
DAV:comment is optional.
A successful response to an accepted invitation, SHOULD have a HTTP
201 status code, and MUST have a HTTP Location header, containing the
full url to the newly created resource.
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A successful response to a declined invitation, SHOULD contain a 200
or 204 HTTP status code.
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 DAV:share-reply-
notification (Section 5.4) notification to the sharer.
After the sharee has issued a reply, the server SHOULD also remove
the notification that contained the initial invite.
4.7.1.1. Example: Accepting an invite
This is an example of a request that the sharee would send to accept
an invitation.
POST /principals/users/evert/notifications/1000455.xml HTTP/1.1
Host: calendar.example.com
Content-Type: application/davsharing+xml; charset="utf-8"
<?xml version="1.0" encoding="utf-8" ?>
<D:invite-reply xmlns:D="DAV:">
<D:invite-accepted />
<D:create-in>
<D:href>/calendars/users/evert/</D:href>
</D:create-in>
<D:slug>Tech meetups</D:slug>
<D:comment>Thanks for the share!</D:comment>
</D:invite-reply>
4.7.2. Ignoring an invitation
For privacy reasons, sharees need to be able to remove invitations
without notifiying the sharer.
When the sharee issues a DELETE on an share-invite-notification, the
server MUST remove the notification, and MUST NOT let the sharer know
about this.
As a result, from the sharers perspective, the invitation status for
that principal will always remain as DAV:invite-noreply.
4.7.3. Making modifications to a shared resource
Any changes that a sharee makes to a shared resource should also be
reflected in the sharers instance of the resource.
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If the shared resource is a collection, any resources in the
collection, or in the collection's child-collections MUST also appear
in the sharers instance.
4.7.4. Removing a shared resource
To remove a shared resource a DELETE request is targeted at the
shared resource URI. When such a request is received the server MUST
remove the shared collection and automatically update the sharee's
status in the sharer's DAV:invite (Section 4.4.2) property.
4.8. General Considerations
4.8.1. Per-instance WebDAV Properties
Servers MUST support "per-instance" WebDAV properties on shared
resource and MAY support them on resources within shared collections.
A "per-instance" WebDAV property is one whose value can be set and
retrieved on an instance of a resource, but is not automatically
propagated to other instances of the same shared resource. For
example, a sharee may change a property on their instance of a shared
resource, but the instance of the owner of the resource will not see
this updated value.
For shared resources, the server MUST allow all users to write "per-
instance" WebDAV properties on the shared resources and MAY allow
property writes on resources within the shared resources. This is
required even in the case where the sharee has been granted read
access only (i.e., the ability to change the resource is disallowed).
This requirement ensures that sharees can always change "personal"
properties such as display names.
Servers MAY treat any dead property as per-instance.
Servers MUST NOT treat live properties as per-instance.
4.8.2. Sharees and instances
A point that may not be immediately obvious, is that there is a
separation between sharees and shared instances.
Sharees (and sharers) are effectively only 'actors' in the sharing
process and allow shared instances to be created and modified. The
sharing "role" or access level that a user has when performing an
opteration on a shared resource, is dependent on which intance they
are accessing, not who the currently logged in principal is.
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To illustrate, take the DAV:share-access WebDAV property. This
property should always describe the access-level of the instance, not
the current user accessing the property.
An implication is that if an owner of a shared resource also has
direct access to a shared instance of a sharee (via normal WebDAV ACL
controls for example), requesting the share-access property on that
shared resource should always indicate DAV:read or DAV:read-write,
but never DAV:shared-owner.
Likewise, if a sharee also has direct access to the original shared
(owner) instance on the same server, the DAV:share-access property
should always return DAV:shared-owner.
This philosophy must be considered when designing the underlying
data-model of the server, and every feature in this specification.
That is: the sharing-role a user has when accessing a shared-
resource, is generally dependent on the resource being accessed, not
the current principal.
4.8.3. Relationship between sharing access levels and WebDAV ACL
This document describes a way for a user to grant access to other
resources, sidestepping WebDAV ACL [RFC3744].
WebDAV ACL is still relevant though. The DAV:share ACL privilege is
used to indicate that a user is allowed to share a resource.
This specification uses the DAV:read and DAV:read-write access levels
to indicate the access level of the shared resource.
These privileges don't directly correlate to ACL privileges. It's
left up to the implementor to decide which ACL privileges are the
most appropriate for both DAV:read and DAV:read-write.
The following is a suggestion: Sharees with a DAV:read share-access
level, may typically at least expect DAV:read, DAV:write-properties,
DAV:read-current-user-privilege set.
For DAV:read-write, this also includes DAV:write, DAV:write-content,
and if the shared resource is a collection, DAV:bind and DAV:unbind.
These privileges are typically applied to the shared resource and all
its child resources (if any).
There is no requirement for the shared instance to have a DAV:owner
element that refers to the original sharer. In fact, it SHOULD
probably be the sharee. Likewise, there is also no requirement for
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the original sharer to have any privileges to any of the sharee
instances.
5. XML Element Definitions
The following section contains a definition of all the XML elements
used in this document The definitions are written in the form of a
DTD. The DTD itself is strictly informational and is for reference
only.
It should be noted that several elements in the following sections
are repeated, sometimes with slightly different definitions. This is
because some of these elements have slightly different definitions
depending on the context in which they appear.
5.1. DAV:share-resource
The following section describes the DAV:share-resource element, which
is defined in Section 4.3
<!ELEMENT share-resource (sharee+)>
<!-- Each sharee represents a sharee -->
<!ELEMENT sharee (href, share-access, prop?, comment?)>
<!-- The sharee href, can be a mailto:, http: or any supported scheme -->
<!ELEMENT href (#PCDATA)>
<!-- Describes the access-level the user will get -->
<!ELEMENT share-access (read, read-write, no-access)>
<!-- Read-only access -->
<!ELEMENT read EMPTY>
<!-- Read-write access -->
<!ELEMENT read-write EMPTY>
<!-- Access is revoked -->
<!ELEMENT no-access EMPTY>
<!-- A list of properties describing the sharee, such as a displayname ->
<!ELEMENT prop ANY>
<!-- An optional message to the sharee by the sharer -->
<!ELEMENT comment (#PCDATA)>
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5.2. DAV:share
The share element is a WebDAV ACL [RFC3744] privilege that allows a
client to inspect whether a user may be allowed to share a resource.
The element is defined in Section 4.2.
<!ELEMENT share EMPTY>
5.3. DAV:share-invite-notification
DAV:share-invite-notification is used within a WebDAV notification to
communicate to a sharee that a sharer is sharing a resource, or
changing the access level to a resource. DAV-share-invite-
notification is defined in Section 4.6.1
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<!-- Every notification has a DAV:notification root element -->
<!ELEMENT notification (dtstamp, share-invite-notification)>
<!-- This element has all the information about the notification -->
<!ELEMENT share-invite-notification ((invite-accepted|invite-noresponse),
sharer-resource-uri, principal, share-access, prop?, reply-url?, comment?)>;
<!-- Indicates that this was a new invitation -->
<!ELEMENT invite-noresponse EMPTY>
<!-- Indicates that this was an update to an existing invitation -->
<!ELEMENT invite-accepted EMPTY>
<!-- A uri that indentifies the original shared resource. -->
<!ELEMENT sharer-resource-uri (href)>
<!-- Information about the sharer -->
<!ELEMENT principal (href, prop?)>
<!-- Describes the access-level the user will get -->
<!ELEMENT share-access (read, read-write, no-access)>
<!-- Read-only access -->
<!ELEMENT read EMPTY>
<!-- Read-write access -->
<!ELEMENT read-write EMPTY>
<!-- Access is revoked -->
<!ELEMENT no-access EMPTY>
<!-- If it was a new share, where to respond to the invitation -->
<!ELEMENT reply-url (href)>
<!-- An optional comment from the sharer to the sharee -->
<!ELEMENT comment (#PCDATA)>
<!-- Common elements -->
<!ELEMENT href (#PCDATA)>
<!ELEMENT prop ANY>
5.4. DAV:share-reply-notification
DAV:share-reply-notification is a notification that appears in a
sharers notification collection when a sharee responded to an
invitation. It is defined in Section 4.6.2
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<!-- Every notification has a DAV:notification root element -->
<!ELEMENT notification (dtstamp, share-invite-notification)>
<!-- This element has all the information about the notification -->
<!ELEMENT share-reply-notification (sharee, href, comment?)
<!ELEMENT sharee (href, (invite-accepted|invite-declined), comment?)>
<!-- A reference to the owner's shared resource -->
<!ELEMENT href (#PCDATA)>
<!-- Indicates that the sharee accepted the invitation -->
<!ELEMENT invite-accepted EMPTY>
<!-- Indicates that the sharee declined the invitation -->
<!ELEMENT invite-declined EMPTY>
<!-- An optional comment from the sharer to the sharee -->
<!ELEMENT comment (#PCDATA)>
5.5. DAV:invite
DAV:invite is a live WebDAV property, defined in Section 4.4.2. This
property allows a sharer or sharee to inspect who has access to a
particular resource, their invitation status and access level.
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<!-- The invite WebDAV property -->
<!ELEMENT invite (sharee*)>
<!-- A person with access to the shared resource -->
<!ELEMENT sharee (href,
(invite-accepted|invite-declined|invite-invalid|invite-noresponse),
share-access, prop
)>
<!-- A reference to the user who access access to the share -->
<!ELEMENT href (#PCDATA)>
<!-- Indicates that the sharee accepted the invitation -->
<!ELEMENT invite-accepted EMPTY>
<!-- Indicates that the sharee declined the invitation -->
<!ELEMENT invite-declined EMPTY>
<!-- Indicates that the sharee has not responsed yet -->
<!ELEMENT invite-noresponse EMPTY>
<!-- Indicates that the server could not deliver the invitation -->
<!ELEMENT invite-invalid EMPTY>
<!-- The level of access the user has -->
<!ELEMENT share-access (read|read-write|shared-owner)>
<!-- The user has read access -->
<!ELEMENT read EMPTY>
<!-- The user has read-write access -->
<!ELEMENT read-write EMPTY>
<!-- The user is actually the owner of the share -->
<!ELEMENT shared-owner EMPTY>
<!-- A list of WebDAV properties describing the user. -->
<!ELEMENT prop ANY>
5.6. DAV:share-access
DAV:invite is a live WebDAV property, defined in Section 4.4.1. This
property allows sharer or sharee to inspect the sharing status of the
resource.
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<!-- The share-access WebDAV property -->
<!ELEMENT share-access (read|read-write|shared-owner|not-shared)>
<!-- The current instance is a read-only instance of the share -->
<!ELEMENT read EMPTY>
<!-- The current instance if a read-write instance of the share -->
<!ELEMENT read-write EMPTY>
<!-- The current instance if the original instance, owned by the sharee -->
<!ELEMENT shared-owner EMPTY>
<!-- The current instance is not shared at all -->
<!ELEMENT not-shared EMPTY>
5.7. DAV:invite-reply
DAV:invite-reply is the root element of a POST request that a sharee
would issue to respond to an invitation. It is defined in
Section 4.7.1.
<!ELEMENT invite-reply ((invite-accepted|invite-declined),
create-in?, slug?, comment?)>
<!-- The user is accepting the invite -->
<!ELEMENT invite-accepted EMPTY>
<!-- The user is declining the invite -->
<!ELEMENT invite-declined EMPTY>
<!-- When accepting the invite, the collection in which to create the new
instance in -->
<!ELEMENT create-in (href)>
<!ELEMENT href (#PCDATA)>
<!-- A hint for the server for a new resource name. -->
<!ELEMENT slug (#PCDATA)>
<!-- A comment by the sharee to the sharer -->
<!ELEMENT comment (#PCDATA)>
6. Security Considerations
6.1. Forced shares
When this specification is implemented without the use of the
notification flow, as described in Section 4.5.2, it may be possible
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that a malicious user can create unwanted resources for a target
user.
If this is a concern, taking advantage of the notification process is
highly recommended.
Malicious user may also be detected by monitoring malicious behavior,
or allowing users to block sharees using out-of-bound method.
6.2. Notification spamming
If a server does deploy the entire notification process, a user with
malicious intent may still generate a large amount of notifications
targetting other users.
Servers SHOULD at the very ensure that multiple share invitations for
the same resource are coalesced into a single invitation.
7. IANA Considerations
This document defines a MIME media type for XML documents used in for
sharing. This media type SHOULD be used for all POST requests in
this specification.
Type name: application
Subtype name: davsharing+xml
Required parameters: none
Optional parameters: none
Encoding considerations: Identical to those of "application/xml" as
described in RFC7303 [RFC7303].
Security considerations: N/A.
Interoperability considerations: There are no known interoperability
issues.
Published specification: This specification.
Applications that use this media type: No known applications
currently use this media type.
Fragment identifier considerations: N/A.
Additional information
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Deprecated alias names for this type N/A.
Magic number(s) N/A.
File extension(s) xml
Macintosh file type code(s) TEXT
Person & email address to contact for further information:
me@evertpot.com
Intended usage COMMON
Restrictions on usage There are no restrictions on where this media
Author See the "Authors' Addresses" section of this document.
Change Controller IETF
8. Acknowledgments
The authors would like to thank the members of the Calendaring and
Scheduling Consortium's SharingTechnical Committee. In particular,
the following individuals have made important contributions to this
work: Richard Brigham, John Chaffee, Michael Douglass and Ken
Murchison and Dave Thewlis.
This specification originated from work at the Calendaring and
Scheduling Consortium, which has supported the development and
testing of implementations of the specification.
9. 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>.
[RFC3744] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
Distributed Authoring and Versioning (WebDAV) Access
Control Protocol", RFC 3744, DOI 10.17487/RFC3744, May
2004, <http://www.rfc-editor.org/info/rfc3744>.
[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>.
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[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>.
[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. Backwards compatibility
This specification is based on an earlier effort, often referred to
as 'caldav-sharing'. It is possible to remain compatibile with this
specification, but it's important to be aware of a number of changes.
The earlier draft uses the http://calendarserver.org/ns/ namespace
for all its xml elements. This means that any WebDAV property
introduced in this specification, may need to have a similar property
in the old namespace.
XML documents as sent by POST requests and responses, and resources
returned from notifications can be distinguished by the use of the
Content-Type and Accept HTTP headers. The earlier draft does not
define new mime-types for these, but this specification does.
Appendix B. Change History (to be removed prior to publication as an
RFC
Changes in -03:
1. A major rewrite, making many xml elements self-consistent and
with other WebDAV specifications.
2. While all of the same data is still there, many xml elements
have changed.
3. Added 'Instant sharing' concept, making notifications
integration optional.
4. Removed DAV:share-mode
5. Added DAV:share-access
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6. Added a DAV:sharee element with a consistent set of information
about sharees.
7. Clarified the nature of DAV:invite-accepted element in
DAV:invite-notifaction documents.
8. Introduced the DAV:reply-url element.
9. DAV:sharer-instance-url is now DAV:sharer-instance-uri and may
contain other uris.
10. Added security concerns.
11. Complete rewrite of the XML Elements section, using DTDs.
12. DAV:invite-notification is now DAV:share-invite-notification.
13. DAV:reply-notification is now DAV:share-reply-notification.
14. Added design philosophy section.
15. Added information about relationship with WebDAV ACL.
Changes in -02:
1. Renamed DAV:shared-url to DAV:sharer-instance-url.
2. Introduced DAV:share-mode WebDAV property.
3. Removed additions to DAV:resource-type to indicate that a
resource is shared.
Changes in -01:
1. Fixed some issues in the DTD declatations of set-invitee and
remove-invitee.
2. Removed an unused normative reference.
3. Removed 'open issues' section.
4. Added a paragraph about xml/dtd handling with a reference to
RFC4917
5. Renamed DAV:share to DAV:share-resource for the POST request
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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/
Eric York
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
URI: http://www.apple.com/
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