Internet DRAFT - draft-douglass-subscription-upgrade
draft-douglass-subscription-upgrade
Network Working Group M. Douglass
Internet-Draft Spherical Cow Group
Updates: 5545 (if approved) May 5, 2018
Intended status: Standards Track
Expires: November 6, 2018
Calendar subscription upgrades
draft-douglass-subscription-upgrade-03
Abstract
This specification introduces an approach to allow subscribers to
calendar feeds to upgrade to a more performant protocol.
This specification updates [RFC5545] to add the value DELETED to the
STATUS property.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 6, 2018.
Copyright Notice
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. Enhanced GET . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Deletions . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Changes to the iCalendar specifications . . . . . . . . . . . 6
3.1. Redefined Status property . . . . . . . . . . . . . . . . 6
4. Discovering alternative access methods . . . . . . . . . . . 8
5. Link relation subscribe-caldav . . . . . . . . . . . . . . . 8
6. Link relation subscribe-caldav-auth . . . . . . . . . . . . . 8
7. Link relation subscribe-webdav-sync . . . . . . . . . . . . . 8
8. Link relation subscribe-enhanced-get . . . . . . . . . . . . 9
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
11.1. Link Relation Registrations . . . . . . . . . . . . . . 9
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
13. Normative References . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Open issues . . . . . . . . . . . . . . . . . . . . 11
Appendix B. Change log . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
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.
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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
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
2. Enhanced GET
2.1. Introduction
This is a lightweight protocol which allows simple clients to
efficiently discover and download changes in the targeted resource.
It has many similarities to WebDAV sync and for a server could be
implemented as an extension of the specification.
In this protocol the Etag is used as the sync change token. By
adding the If-None-Match header field to the vary header field we can
ensure intermediate caching proxies will be able to cache different
versions of the data.
The resource is treated as a set of individual events each of which
may be updated or deleted separately. The client will first fetch
the entire ics file. On subsequent requests it uses the Prefer
header with a value of "return=minimal" to indicate that it wants a
set of changes since the last fetch.
2.2. Deletions
When an entity (VEVENT, VTODO or other valid top-level component) is
deleted from the source data the server needs to be able to inform a
client of the deletion. This specification introduces a new value
for the STATUS property of DELETED.
On the first conditional GET after the entity has been deleted a
skeleton, but valid, entity will be returned with STATUS: DELETED.
The receiving client is free to remove the entity or update it's
STATUS property.
On subsequent conditional fetches the entity will not be returned.
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2.3. Examples
This is an example of the initial request and response from a server
that supports the extended GET protocol.
>> Request <<
GET /events.ics HTTP/1.1
Host: example.com
Accept: text/calendar
>> Response <<
HTTP/1.1 200 OK
Content-Length: xxxx
ETag: "1234" current ETag (for conditional GET)
Vary: Prefer, If-None-Match so caching proxy can key off of client?s ETag (sync token) and preference
BEGIN:VCALENDAR:
? /* full feed */
END:VCALENDAR
This is an example of the subsequent request and response when no
changes have occurred. The Accept header field indicates that a
VPATCH format is most desirable but simple text/calendar is
acceptable.
>> Request <<
GET /events.ics HTTP/1.1
Host: example.com
Accept: text/calendar; q=0.5, component=VPATCH, text/calendar;
If-None-Match: ?1234? conditional request
Prefer: return=minimal
>> Response <<
HTTP/1.1 304 Not Modified
Content-Length: 0
ETag: ?1234?
Vary: Prefer, If-None-Match
This is an example of the subsequent request and response when no
changes have occurred. The Accept header field indicates that a
VPATCH format is most desirable but simple text/calendar is
acceptable.
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>> Request <<
GET /events.ics HTTP/1.1
Host: example.com
Accept: text/calendar; q=0.5, component=VPATCH, text/calendar;
If-None-Match: "1234" conditional request
Prefer: return=minimal
>> Response <<
HTTP/1.1 304 Not Modified
Content-Length: 0
ETag: "1234"
Vary: Prefer, If-None-Match
This is an example of the subsequent request and response when
changes have occurred and the server can create the minimal format.
>> Request <<
GET /events.ics HTTP/1.1
Host: example.com
Accept: text/calendar; q=0.5, component=VPATCH, text/calendar;
If-None-Match: "1234" conditional request
Prefer: return=minimal
>> Response <<
HTTP/1.1 200 OK
Content-Type: text/calendar
Content-Length: xxxx
ETag: "5678" current ETag (for conditional GET)
Preference-Applied: return=minimal signals to client that stream is changes only
Vary: Prefer, If-None-Match so caching proxy can key off of client?s ETag (sync token) and preference
BEGIN:VCALENDAR:
... only new/changed events
... when not returning VPATCH, deleted events have STATUS:DELETED
END:VCALENDAR
This is an example of the subsequent request and response when
changes have occurred and the server cannot create the minimal format
- perhaps because of an old or invalid token. Note there is no
Preference-Applied header field.
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>> Request <<
GET /events.ics HTTP/1.1
Host: example.com
Accept: text/calendar; q=0.5, component=VPATCH, text/calendar;
If-None-Match: "1234" conditional request
Prefer: return=minimal
>> Response <<
HTTP/1.1 200 OK
Content-Type: text/calendar
Content-Length: xxxx
ETag: "5678" current ETag (for conditional GET)
Vary: Prefer, If-None-Match so caching proxy can key off of client?s ETag (sync token) and preference
BEGIN:VCALENDAR:
... full set of data
END:VCALENDAR
3. Changes to the iCalendar specifications
This specification updates [RFC5545] to add the value DELETED to the
STATUS property. It also introduces the use of some properties to
provide more information about the resource, for example the time
range it covers.
3.1. Redefined Status property
Property name: STATUS
Purpose: This property defines the overall status or confirmation
for the calendar component.
Value Type: TEXT
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified once in "VEVENT",
"VTODO", or "VJOURNAL" calendar components.
Description: In a group-scheduled calendar component, the property
is used by the "Organizer" to provide a confirmation of the event
to the "Attendees". For example in a "VEVENT" calendar component,
the "Organizer" can indicate that a meeting is tentative,
confirmed, or cancelled. In a "VTODO" calendar component, the
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"Organizer" can indicate that an action item needs action, is
completed, is in process or being worked on, or has been
cancelled. In a "VJOURNAL" calendar component, the "Organizer"
can indicate that a journal entry is draft, final, or has been
cancelled or removed.
Format Definition:
This property is defined by the following notation:
status = "STATUS" statparam ":" statvalue CRLF
statparam = *(";" other-param)
statvalue = (statvalue-event
/ statvalue-todo
/ statvalue-jour)
statvalue-event = "TENTATIVE" ;Indicates event is tentative.
/ "CONFIRMED" ;Indicates event is definite.
/ "CANCELLED" ;Indicates event was cancelled.
/ "DELETED" ;Indicates event was deleted.
;Status values for a "VEVENT"
statvalue-todo = "NEEDS-ACTION" ;Indicates to-do needs action.
/ "COMPLETED" ;Indicates to-do completed.
/ "IN-PROCESS" ;Indicates to-do in process of.
/ "CANCELLED" ;Indicates to-do was cancelled.
/ "DELETED" ;Indicates to-do was deleted.
;Status values for "VTODO".
statvalue-jour = "DRAFT" ;Indicates journal is draft.
/ "FINAL" ;Indicates journal is final.
/ "CANCELLED" ;Indicates journal is removed.
/ "DELETED" ;Indicates journal was deleted.
;Status values for "VJOURNAL".
Example:
Example: The following is an example of this property for a "VEVENT"
calendar component:
STATUS:TENTATIVE
The following is an example of this property for a "VTODO" calendar
component:
STATUS:NEEDS-ACTION
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The following is an example of this property for a "VJOURNAL"
calendar component:
STATUS:DRAFT
4. Discovering alternative access methods
The advertising of other access points is achieved through the use of
the LINK header as defined in [RFC5988]. New link relation types are
defined in this specification - each being associated with a protocol
or protocol subset.
These LINK headers will be delivered when a client carries out an
OPTIONS request targeting the URL of the resource.
5. Link relation subscribe-caldav
This specifies an access point which is a full implementation of
caldav but requires no authentication. The end point allows the full
range of reports as defined by the CalDAV specification.
The client MUST follow the specification to determine exactly what
operations are allowed on the access point - for example to determine
if sync-report is supported.
The URL MAY include some form of token to allow write access to the
targeted collection. The client must check it's permissions to
determine whether or not it has been granted write access.
6. Link relation subscribe-caldav-auth
This specifies an access point which is a full implementation of
caldav and requires authentication. This may allow read-write access
to the resource.
The client MUST follow the specification to determine exactly what
operations are allowed on the access point - for example to determine
if sync-report is supported.
7. Link relation subscribe-webdav-sync
This specifies an access point which supports only webdav sync.
This allows the client to issue a sync-report on the resource to
obtain updates.
NOTE: say something about initial startup - use ics to populate?
Initial token?
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The client MUST follow that specification.
8. Link relation subscribe-enhanced-get
This specifies an access point which supports something new.
The client MUST follow that specification.
9. Security Considerations
Applications using these properties need to be aware of the risks
entailed in using the URIs provided as values. See [RFC3986] for a
discussion of the security considerations relating to URIs.
10. Privacy Considerations
Properties with a "URI" value type can expose their users to privacy
leaks as any network access of the URI data can be tracked. Clients
SHOULD NOT automatically download data referenced by the URI without
explicit instruction from users. This specification does not
introduce any additional privacy concerns beyond those described in
[RFC5545].
11. IANA Considerations
11.1. Link Relation Registrations
This document defines the following new iCalendar properties to be
added to the registry defined in Section 8.2.3 of [RFC5545]:
+------------------------+-------------+--------------------+
| Relation Name | Description | Reference |
+------------------------+-------------+--------------------+
| subscribe-caldav | Current | RFCXXXX, Section 5 |
| subscribe-caldav_auth | Current | RFCXXXX, Section 6 |
| subscribe-webdav-sync | Current | RFCXXXX, Section 7 |
| subscribe-enhanced_get | Current | RFCXXXX, Section 8 |
+------------------------+-------------+--------------------+
12. Acknowledgements
The author would also like to thank the members of the CalConnect
Calendar Sharing technical committee and the following individuals
for contributing their ideas and support:
Marten Gajda, Ken Murchison
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The authors would also like to thank CalConnect the Calendaring and
Scheduling Consortium for advice with this specification.
13. Normative References
[I-D.ietf-calext-extensions]
Daboo, C., "New Properties for iCalendar", draft-ietf-
calext-extensions-05 (work in progress), August 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 2434,
DOI 10.17487/RFC2434, October 1998,
<https://www.rfc-editor.org/info/rfc2434>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4589] Schulzrinne, H. and H. Tschofenig, "Location Types
Registry", RFC 4589, DOI 10.17487/RFC4589, July 2006,
<https://www.rfc-editor.org/info/rfc4589>.
[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)",
RFC 5545, DOI 10.17487/RFC5545, September 2009,
<https://www.rfc-editor.org/info/rfc5545>.
[RFC5546] Daboo, C., Ed., "iCalendar Transport-Independent
Interoperability Protocol (iTIP)", RFC 5546,
DOI 10.17487/RFC5546, December 2009,
<https://www.rfc-editor.org/info/rfc5546>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010,
<https://www.rfc-editor.org/info/rfc5988>.
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[W3C.REC-xml-20060816]
Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
Appendix A. Open issues
restype values: Need to determine what if any registry of resource
types already exists and use that.
Appendix B. Change log
v01 2017-07-28 MD
o Examples
o More text for extended get. Talk about deletions.
v01 2017-02-17 MD
o Add text about OPTIONS
o Add text abut read/write CalDAV
v00 2017-02-15 MD
o First pass
Author's Address
Michael Douglass
Spherical Cow Group
226 3rd Street
Troy, NY 12180
USA
Email: mdouglass@sphericalcowgroup.com
URI: http://sphericalcowgroup.com
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