Calendar subscription upgrades
draft-douglass-subscription-upgrade-01

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Last updated 2017-02-16
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Network Working Group                                        M. Douglass
Internet-Draft                                       Spherical Cow Group
Updates: 5545,5546 (if approved)                       February 16, 2017
Intended status: Standards Track
Expires: August 20, 2017

                     Calendar subscription upgrades
                 draft-douglass-subscription-upgrade-01

Abstract

   This specification introduces an approach to allow subscribers to
   calendar feeds to upgrade to a more performant protocol.

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 August 20, 2017.

Copyright Notice

   Copyright (c) 2017 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   2
   2.  Changes to the iCalendar specifications . . . . . . . . . . .   3
   3.  Discovering alternative access methods  . . . . . . . . . . .   3
   4.  Link relation subscribe-caldav  . . . . . . . . . . . . . . .   3
   5.  Link relation subscribe-caldav-auth . . . . . . . . . . . . .   3
   6.  Link relation subscribe-webdav-sync . . . . . . . . . . . . .   4
   7.  Link relation subscribe-something-else  . . . . . . . . . . .   4
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   4
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     10.1.  Link Relation Registrations  . . . . . . . . . . . . . .   4
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   12. Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Open issues  . . . . . . . . . . . . . . . . . . . .   6
   Appendix B.  Change log . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Currently clients subscribe to calendar feeds as an ics file which is
   often published as a resource accessible using the unofficial
   'webcal' scheme.

   The only available option for updating that resource is the usual
   HTTP polling of cached resources using Etags.

   There is the usual tension between clients wishing to see a timely
   response to changes and servers not wishing to be overloaded by
   frequent requests for possibly large amounts of data.

   This specification introduces an approach whereby clients can
   discover a more performant access method.  Given the location of the
   resource as an ics file, the client can perfom an OPTIONS request on
   the resource and inspect the returned headers which will offer a
   number of alternative access methods.

   Given that many clients already support CalDAV this provides an easy
   upgrade path for those clients.  CalDAV and DAV subsets are specified
   here to allow lighter weight implementations.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and

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