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Versions: 00 01 02 03

Network Working Group                                             E. Pot
Internet-Draft                                                fruux GmbH
Expires: December 29, 2016                                      C. Daboo
                                                              Apple Inc.
                                                           June 27, 2016


                       WebDAV: User Notifications
                   draft-pot-webdav-notifications-03

Abstract

   This specification defines an extension to WebDAV that allows the
   server to provide notifications to users.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 29, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  Requirements Overview . . . . . . . . . . . . . . . . . . . .   3
   4.  Notifications . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Mime type . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Additional Principal Properties . . . . . . . . . . . . .   4
       4.2.1.  DAV:notification-URL Property . . . . . . . . . . . .   4
     4.3.  Properties on Notification Resources  . . . . . . . . . .   5
       4.3.1.  DAV:notificationtype Property . . . . . . . . . . . .   5
     4.4.  XML Element Definitions . . . . . . . . . . . . . . . . .   6
       4.4.1.  DAV:notifications . . . . . . . . . . . . . . . . . .   6
       4.4.2.  DAV:notification  . . . . . . . . . . . . . . . . . .   6
       4.4.3.  DAV:dtstamp . . . . . . . . . . . . . . . . . . . . .   6
   5.  Notification Definitions  . . . . . . . . . . . . . . . . . .   7
     5.1.  System Status Notification  . . . . . . . . . . . . . . .   7
       5.1.1.  DAV:systemstatus Element Definition . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Backwards-compatibility with earlier drafts  . . . .  10
   Appendix B.  Change History (to be removed prior to publication
                as an RFC  . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   It is often useful for servers to communicate arbitrary information
   to the end-users of a WebDAV system, such as a system status, message
   of the day or to notify users of changes that were made to shared
   resources by other users.

   This specification defines a generic "notification" mechanism that
   allows a server to do that.  Whilst primarily aimed at CalDAV
   [RFC4791] and CardDAV [RFC6352] this mechanism has been designed to
   be adaptable to other applications of WebDAV [RFC4918].

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].





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   When XML element types in the namespace "DAV:" is referenced in this
   document outside of the context of an XML fragment, the string "DAV:"
   will be prefixed to the element type name.

   The DTD samples used in this document are for illustrative purposes
   only.  All XML documents in this document follow the conventions and
   restrictions described in [RFC4918] section 17.

3.  Requirements Overview

   To add support for WebDAV notifications, a server MUST at least have
   support for WebDAV Class 3 [RFC4918].

   WebDAV notifications also defines new properties on principal
   resources (RFC3744 [RFC3744]), which is defined in Section 4.2.1.

4.  Notifications

   When this feature is available, a DAV:notification-URL
   (Section 4.2.1) 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 DAV:notification-URL
   (Section 4.2.1) property MUST have a DAV:resourcetype property with
   DAV:collection and DAV:notifications (Section 4.4.1) child elements.

   Notification "messages" are XML documents stored as resources in the
   notification collection.  Each XML document contains a
   DAV:notification (Section 4.4.2) element as its root.  The root
   element contains a DAV:dtstamp 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 DAV:notificationtype (Section 4.3.1)
   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 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 DAV:notificationtype



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   (Section 4.3.1) 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.  Clients SHOULD remove notifications being
   displayed to a user when the notification resource is removed from
   the notification collection, to enable the user to dismiss a
   notification on one device and have it automatically removed from
   others.  Clients MUST ignore all notifications for types they do not
   recognize.  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.

   Servers MUST prevent clients from adding resources in the
   notification collection.

4.1.  Mime type

   The "application/davnotification+xml" MIME media type MUST be used
   for transfer of WebDAV notifications.

   This is an example of a Content-Type header:

   Content-Type: application/davnotification+xml

   HTTP GET requests that expect to receive a WebDAV notification
   resource, SHOULD include an "Accept" header that includes
   "application/davnotification+xml".

   Requests that do not include this header, SHOULD be rejected with a
   HTTP 406 status code.

4.2.  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.

4.2.1.  DAV:notification-URL Property

   Name:  notification-URL

   Namespace:  DAV:

   Purpose:  Identify the URL of the notification collection owned by
      the associated principal resource.

   Protected:  This property SHOULD be protected.



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   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 principal is not enabled for notification
      messages on the server.

   Definition:

   <!ELEMENT notification-URL (DAV:href)>

4.3.  Properties on Notification Resources

   The following new WebDAV properties are defined for notification
   resources.

4.3.1.  DAV:notificationtype Property

   Name:  notificationtype

   Namespace:  DAV:

   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]).

   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.




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   Definition:

   <!ELEMENT notificationtype ANY>
   <!-- Child elements are empty but will have appropriate attributes.
        Any valid notification message child element can appear.-->

4.4.  XML Element Definitions

4.4.1.  DAV:notifications

   Name:  notifications

   Namespace:  DAV:

   Purpose:  Indicates a notification collection.

   Description:  This XML element is used in a DAV:resourcetype element
      to indicate that the corresponding resource is a notification
      collection.

   Definition:

   <!ELEMENT notifications EMPTY>

4.4.2.  DAV:notification

   Name:  notification

   Namespace:  DAV:

   Purpose:  Notification message root element.

   Description:  The root element used in notification resources.

   Definition:

   <!ELEMENT notification (dtstamp, XXX) >
   <!-- Any notification type element can appear after
        DAV:dtstamp -->

4.4.3.  DAV:dtstamp

   Name:  dtstamp

   Namespace:  DAV:

   Purpose:  Date-time stamp.




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   Description:  DAV:dtstamp is an element whose content MUST conform to
      the "date-time" production in [RFC3339].  In addition, an
      uppercase "T" character MUST be used to separate date and time,
      and an uppercase "Z" character MUST be present.

   Definition:

   <!ELEMENT dtstamp (#PCDATA)>
   <!-- Value is a date-time in UTZ as per [RFC3339] -->

5.  Notification Definitions

   This section defines a set of common notification types.

5.1.  System Status Notification

   The system status notification is used to convey an URI and/or
   textual description to the user.  The assumption is that the URI
   points to a webpage where the current system status is described in
   detail, with the provided description being a summary of that.  A
   "type" attribute on the element is used to indicate the importance of
   the current status notification, and has the values "low", "medium"
   and "high", representing the increasing level of importance of the
   message respectively.

   Servers might have knowledge of an agent's language preferences, in
   which case it MAY localise the DAV:description value as appropriate
   based on the calendar user accessing the notification, but if it
   does, it SHOULD include an xml:lang attribute on the DAV:description
   element to indicate what language is being used.

5.1.1.  DAV:systemstatus Element Definition

   Name:  systemstatus

   Namespace:  DAV:

   Purpose:  Indicates a system status notification.

   Description:  This XML element is used in a DAV:notification element
      to describe a system status notification.

   Definition:

   <!ELEMENT systemstatus (DAV:href?, DAV:description?)>
   <!ATTLIST systemstatus type (low | medium | high) "low">
   <!-- One of DAV:href or DAV:description MUST be present -->




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   Example:  This is an example of the body of a notification resource
      for an emergency system outage:

   <?xml version="1.0" encoding="UTF-8"?>
   <D:notification xmlns:D="DAV:">
     <D:dtstamp>2011-12-09T06:12:53Z</D:dtstamp>
     <D:systemstatus type="high">
       <D:href>http://example.com/emergency_shutdown.html</D:href>
       <D:description xml:lang='en_US'>
           Emergency shutdown now
       </D:description>
     </D:systemstatus>
   </D:notification>

   Example:  This is an example of the WebDAV property on the example
      notification resource above:

   <?xml version="1.0" encoding="UTF-8"?>
   <D:notificationtype xmlns:D="DAV:">
     <D:systemstatus type="high" />
   </D:notificationtype>

6.  Security Considerations

   TBD: More?

7.  IANA Considerations

   This document defines a MIME media type for use of WebDAV
   notifications in an XML format.  This media type SHOULD be used for
   the transfer of WebDAV notifications.

   Type name:  application

   Subtype name:  davnotification+xml

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:  Identical to those of "application/xml" as
      described in RFC7303 [RFC7303].

   Security considerations:  See Section 6.

   Interoperability considerations:  There are no known interoperability
      issues.




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   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

   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.  References

9.1.  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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   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <http://www.rfc-editor.org/info/rfc3339>.

   [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>.

   [RFC7303]  Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
              DOI 10.17487/RFC7303, July 2014,
              <http://www.rfc-editor.org/info/rfc7303>.

9.2.  Informative References

   [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>.

   [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>.

Appendix A.  Backwards-compatibility with earlier drafts

   An earlier draft of this specification is already widely deployed
   among both servers and clients.

   That draft, informally known as 'caldav-notifications' largely uses
   the same structure as this specification, but where the "DAV:" xml
   namespace is used in this specification, the earlier draft uses
   "http://calendarserver.org/ns/".

   It is possible to conform to both that draft and this specification
   by either creating two different collections, as identified by
   "notification-URL" in each respective namespace.  Alternatively it's
   possible to use the same resource for both, but use content-
   negotation using the Accept header to ask the server for a specific
   representation of a notification.





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Appendix B.  Change History (to be removed prior to publication as an
             RFC

   Changes in -03:

   1.  Fixed a number of spelling / language issues..

   Changes in -02:

   1.  No significant changes.

   Changes in -01:

   1.  Added a paragraph about xml/dtd handling with a reference to
       RFC4917

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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