| Network Working Group | C. Daboo |
| Internet-Draft | Apple |
| Intended status: Standards Track | October 18, 2012 |
| Expires: April 19, 2013 |
VALARM Extensions for iCalendar
draft-daboo-valarm-extensions-04
This document defines a set of extensions to the iCalendar VALARM component to enhance use of alarms and improve interoperability between clients and servers.
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The iCalendar [RFC5545] specification defines a set of components used to describe calendar data. One of those is the "VALARM" component which appears as a sub-component of "VEVENT" and "VTODO" components. The "VALARM" component is used to specify a reminder for an event or to-do. Different alarm actions are possible, as are different ways to specify how the alarm is triggered.
As iCalendar has become more widely used and as client-server protocols such as CalDAV [RFC4791] have become more popular, several issues with "VALARM" components have arisen. Most of these relate to the need to extend the existing "VALARM" component with new properties and behaviors to allow clients and servers to accomplish specific tasks in an interoperable manner. For example, clients typically need a way to specify that an alarm has been dismissed by a calendar user, or has been "snoozed" by a set amount of time. To date, this has been done through the use of custom "X-" properties specific to each client implementation, leading to poor interoperability.
This specification defines a set of extensions to "VALARM" components to cover common requirements for alarms not currently addressed in iCalendar. Each extension is defined in a separate section below. For the most part, each extension can be supported independently of the others, though in some cases one extension will require another. In addition, this specification describes mechanisms by which clients can interoperably implement common features such as "snoozing".
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].
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.
Section 3.6.6 of [RFC5545]defines the syntax for "VALARM" components and properties within them. However, as written, it is hard to extend this by adding, e.g., a new property common to all types of alarm. Since many of the extensions defined in this document need to extend the base syntax, an alternative form for the base syntax is defined here, with the goal of simplifying specification of the extensions.
alarmcext = "BEGIN" ":" "VALARM" CRLF
alarmprop
"END" ":" "VALARM" CRLF
alarmprop = *(
; the following are REQUIRED,
; but MUST NOT occur more than once
action / trigger /
; one set of action properties MUST be
; present and MUST match the action specified
; in the ACTION property
actionprops /
; the following is OPTIONAL,
; and MAY occur more than once
x-prop / iana-prop
)
actionprops = audiopropext / disppropext / emailpropext
audiopropext = *(
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat /
; the following is OPTIONAL,
; but MUST NOT occur more than once
attach
)
disppropext = *(
; the following are REQUIRED,
; but MUST NOT occur more than once
description /
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat
)
emailpropext = *(
; the following are all REQUIRED,
; but MUST NOT occur more than once
description / summary /
; the following is REQUIRED,
; and MAY occur more than once
attendee /
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat
)
A "VALARM" calendar component is re-defined by the following notation:
Several of the other extensions in this specification require identifying a specific instance of a "VALARM" component in an iCalendar stream. To aid that, this extension adds a "UID" property to "VALARM" components to allow a unique identifier to specified. The value of this property can then be used to refer uniquely to the "VALARM" component.
The "UID" property defined here follows the definition in Section 3.8.4.7 of [RFC5545]. In particular it MUST be a globally unique identifier.
alarmprop /= *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
uid
)
The "VALARM" component defined in Section 3 is extended here as:
It is often convenient to relate one or more "VALARM" components to other "VALARM" components (e.g., see Section 9). This can be accomplished if the "VALARM" components each have their own "UID" property (as per Section 4).
This specification updates the usage of the "RELATED-TO" property defined in Section 3.8.4.5 of [RFC5545] to enable its use with "VALARM" components. Specific types of relationships between "VALARM" components can be identified by registering new values for the "RELTYPE" property parameter defined in Section 3.2.15 of [RFC5545].
alarmprop /= *(
; the following is OPTIONAL,
; but MAY occur more than once
related
)
The "VALARM" component defined in Section 3 is extended here as:
Currently "VALARM" components have actions for audio, display and email. New types of action are of interest, e.g., SMS, instant messaging, etc. Rather then specify separate actions for these, an alternative is to define a "URI" action that allows any URI scheme to be used as an action, where it makes sense. Thus URI schemes for IM [RFC3860], SIP [RFC3261], TEL [RFC3966]etc could be used.
actionvalue /= "URI"
; Adds a new action for a "VALARM"
actionprop /= uriprop
; Re-defines the "VALARM" component to include
; "uriprop" as a new set of action properties
uriprop = *(
; the following is REQUIRED,
; and MUST occur only once
uri /
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat
)
This extension defines a new "URI" property value for use with the "ACTION" property in "VALARM" components. A new set of action properties is defined for "VALARM" components based on this new action as defined by the syntax below.
With the advent of a standard client/server protocol for calendaring and scheduling data ([RFC4791]) there is a need to specify which client or server should handle the presentation of an alarm when it is triggered. For example, calendar users want to be able to receive alarms at all times, even when their desktop client might be unavailable. Since the server is "always on", a service running on the server could monitor alarm status and, when appropriate, trigger those alarms. In addition it may be important for only the server or the client to be set to handle an alarm - and in some cases only specific servers or clients.
alarmprop /= *(
; the following is OPTIONAL,
; and MAY occur more than once
alarm-agent
)
To address this need, this specification defines an "ALARM-AGENT" iCalendar property that can be added to any "VALARM" component. This property specifies whether a client or server or both should be responsible for processing the alarm when it triggers. In addition, an "AGENT-ID" property parameter can be added to uniquely identify the client or server that should process the alarm. This is defined by the syntax below.
alarm-agent = "ALARM-AGENT" alarmagentparam ":"
alarmagentvalue CRLF
alarmagentparam = *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
(";" agentidparam) /
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
alarmagentvalue = "SERVER" / "CLIENT" / "BOTH" / "NONE" /
iana-token / x-name
ALARM-AGENT:SERVER ALARM-AGENT;AGENT-ID="tag:example.com,2011:cyrus-desktop":CLIENT
agentidparam = "AGENT-ID" "=" DQUOTE uri DQUOTE
ALARM-AGENT;AGENT-ID="http://calendar.example.com":SERVER
There is currently no way for a "VALARM" component to indicate whether it has been triggered and acknowledged. With the advent of a standard client/server protocol for calendaring and scheduling data ([RFC4791]) it is quite possible for an event with an alarm to exist on multiple clients in addition to the server. If each of those is responsible for performing the action when an alarm triggers, then multiple "alerts" are generated by different devices. In such a situation, a calendar user would like to be able to "dismiss" the alarm on one device and have it automatically dismissed on the others too.
Also, with recurring events that have alarms, it is important to know when the last alarm in the recurring set was acknowledged, so that the client can determine whether past alarms have been missed.
alarmprop /= *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
acknowledged
)
To address these needs, this specification adds an "ACKNOWLEDGED" property to "VALARM" components to indicate when the alarm was last sent or acknowledged. This is defined by the syntax below.
acknowledged = "ACKNOWLEDGED" acknowledgedparam ":" datetime CRLF
acknowledgedparam = *(
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
ACKNOWLEDGED:20090604T084500Z
Users often want to "snooze" an alarm, and this specification defines a standard approach to accomplish that.
To "snooze" an alarm, clients create a new "VALARM" component within the parent component of the "VALARM" that was triggered and is being "snoozed" (i.e., as a "sibling" component of the "VALARM" being snoozed). The new "VALARM" MUST be set to trigger at the user's chosen "snooze" interval after the original alarm triggered. Clients SHOULD use an absolute "TRIGGER" property with a "DATE-TIME" value specified in UTC. Clients SHOULD add a "RELATED-TO" property to the new "VALARM" component with a value set to the "UID" property value of the "VALARM" component being snoozed. If the "VALARM" component being snoozed does not already have a "UID" property, the client SHOULD add one. The "RELATED-TO" property added to the new "VALARM" component SHOULD include a "RELTYPE" property parameter with a value set to "SNOOZE".
When the "snooze" alarm is triggered and dismissed the client SHOULD remove the corresponding "VALARM" component, or set the "ACKNOWLEDGED" property (see Section 8.1). Alternatively, if the "snooze" alarm is itself "snoozed", the client SHOULD remove the original "snooze" alarm and create a new one, with the appropriate trigger time and relationship set.
This specification adds the "SNOOZE" relationship type for use with the "RELTYPE" property defined in Section 3.2.15 of [RFC5545]. This is used to relate a "snoozed" "VALARM" component to the original alarm that the "snooze" was generated for.
VALARMs are currently triggered when a specific date-time is reached. It is also desirable to be able to trigger alarms based on location, e.g. when arriving at or departing from a particular location.
alarmprop /= *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
proximity /
; the following is OPTIONAL,
; and MAY occur more than once, but only
; when a PROXIMITY property is also present
structured-location
)
This specification adds the following properties to "VALARM" components to indicate when an alarm can be triggered based on location.
Typically, when a "PROXIMITY" property is used there is no need to specify a time-based trigger using the "TRIGGER" property. However, since "TRIGGER" is defined as a required property for a "VALARM" component, for backwards compatibility it has to be present, but ignored. To indicate a "TRIGGER" that is to be ignored, clients SHOULD use a value a long time in the past. A value of "19760401T005545Z" has been commonly used for that.
proximity = "PROXIMITY" proximityparam ":" proximityvalue CRLF
proximityparam = *(
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
proximityvalue = "ARRIVE" / "DEPART" / iana-token / x-name
PROXIMITY:ARRIVE
BEGIN:VALARM UID:77D80D14-906B-4257-963F-85B1E734DBB6 TRIGGER;VALUE=DATE-TIME:19760401T005545Z ACTION:DISPLAY PROXIMITY:DEPART STRUCTURE-LOCATION;VALUE=URI:geo:40.443,-79.945;u=10 DESCRIPTION:Remember to buy milk END:VALARM
The following example shows a "VALARM" component with a proximity trigger set to trigger when the device running the calendar user agent leaves the vicinity defined by the structured location property. Note use of the "u=" parameter with the "geo" URI to define the precision of the location determination.
Users often want to have a default alarm applied to new events that they create or to new invitations that arrive on a CalDAV [RFC4791] server. Since this behavior is expected to occur no matter which client a user is using, or whether any client is even connected at the time, it is beneficial if the server itself is responsible for managing the creation of the default alarm.
This specification defines four new WebDAV properties that can be used to specify different sets of default alarms. Clients can store "VALARM" components in these properties to setup the defaults. When a new event or todo is created on the server, the server will automatically add the default, as appropriate. When a new event or todo invitation is delivered to the calendar user, the server will automatically add the default alarm, as appropriate.
A server supporting the features described in this document MUST include "calendar-default-alarms" as a field in the DAV response header from an OPTIONS request on a calendar home or calendar collection.
The four new WebDAV properties are:
The WebDAV properties are defined on a calendar user's "calendar home" collection, or on individual calendar collections. When events or tasks are created in a calendar, the server will first inspect the WebDAV properties on the calendar collection to see if the appropriate property is present. If it is, the server will use the value of that property to set the default in the new component. If the property is not present on the calendar collection, the server will determine whether the property is present on the calendar home collection that contains the calendar collection. If present on the calendar home, the property value there is used as the default.
The WebDAV property value MUST be one or more "VALARM" components or the empty string. If an empty string is used, no default alarms are applied. Note that these values contain just the "BEGIN:VALARM...END:VALARM" data (i.e., syntactically the "alarmcext" element as per Section 3).
When adding a default alarm to an event or task, the server MUST ensure that a "DEFAULT-ALARM" property with a value of "TRUE" is present in the "VALARM" component.
If a "DESCRIPTION" property is present in the "VALARM" component, but its value is empty, the server SHOULD insert the value from any "SUMMARY" property of the component in which the default "VALARM" is being added.
A default alarm MUST NOT be added to individual event or task components in a calendar object resource being created, if a "VALARM" component is already present in the component.
When the client stores a new alarm in any of the WebDAV properties, servers MUST NOT change any existing calendar data within the calendar home or calendar where the WebDAV property is stored. This avoids the server having to rewrite potentially large amounts of calendar data to update the default alarm, and thus avoids the need for clients to re-download that data when they next synchronize with the server. The reasoning for this is described further in the next section.
Clients that support default alarms SHOULD allow users to set the four types of default provided by the WebDAV properties defined in Section 11.1. Clients SHOULD check for the presence of those properties and the calendar user's calendar home and individual calendars and use the values for defaults that they themselves apply.
Since existing calendar data with a default alarm is not changed when the default alarm property changes, clients SHOULD do the following:
The approach of not having the server rewrite existing calendar data when an alarm changes, and having the client "override" defaults in calendar data with the current default values is a compromise designed to provide some backwards compatibility with clients not supporting default alarm behavior.
When default alarms are being used it is necessary to know when a calendar user has set a default alarm that does nothing as opposed to specifying that no alarm be used. This is important because clients are expected to "override" any default alarm present in calendar data with the current value retrieved from the server. However, if the calendar user explicitly removed the default alarm, then the "override" does not happen.
actionvalue /= "NONE"
; Adds a new action for a "VALARM"
actionprop /= noneprop
; Re-defines the "VALARM" component to include
; "noneprop" as a new set of action properties
noneprop = (
; No properties used
)
This extension defines a new "NONE" property value for use with the "ACTION" property in "VALARM" components. A new set of action properties is defined for "VALARM" components based on this new action as defined by the syntax below. The "NONE" action is used solely to indicate a default alarm that does not alert the calendar user.
alarmprop /= *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
default-alarm
)
default-alarm = "DEFAULT-ALARM" defaultalarmparam ":"
boolean CRLF
defaultalarmparam = *(
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
TODO:talk about importance of stripping VALARMs from incoming iTIP. Talk about VALARMs being used to "spam" - particularly nasty if the server handles it.
This document defines the following new iCalendar properties to be added to the registry defined in Section 8.2.3 of [RFC5545]:
| Property | Status | Reference |
|---|---|---|
| ALARM-AGENT | Current | RFCXXXX, Section 7.1 |
| ACKNOWLEDGED | Current | RFCXXXX, Section 8.1 |
| PROXIMITY | Current | RFCXXXX, Section 10.1 |
| DEFAULT-ALARM | Current | RFCXXXX, Section 11.4 |
This document defines the following new iCalendar property parameters to be added to the registry defined in Section 8.2.4 of [RFC5545]:
| Property Parameter | Status | Reference |
|---|---|---|
| AGENT-ID | Current | RFCXXXX, Section 7.2 |
This document defines the following new iCalendar action to be added to the registry defined in Section 8.3.10 of [RFC5545]:
| Action | Status | Reference |
|---|---|---|
| URI | Current | RFCXXXX, Section 6 |
| NONE | Current | RFCXXXX, Section 11.3 |
This document defines the following new iCalendar relationship type to be added to the registry defined in Section 8.3.8 of [RFC5545]:
| Relationship Type | Status | Reference |
|---|---|---|
| SNOOZE | Current | RFCXXXX, Section 9.1 |
This document creates a new iCalendar registry for values of the "PROXIMITY" property:
| Value | Status | Reference |
|---|---|---|
| ARRIVE | Current | RFCXXXX, Section 10.1 |
| DEPART | Current | RFCXXXX, Section 10.1 |
This specification came about via discussions at the Calendaring and Scheduling Consortium. Also, thanks to the following for providing feedback: Bernard Desruisseaux, Mike Douglass, Jacob, Farkas, Jeffrey Harris, and Ciny Joy.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC4791] | Daboo, C., Desruisseaux, B. and L.M. Dusseault, "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791, March 2007. |
| [RFC5545] | Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, September 2009. |
| [RFC5870] | Mayrhofer, A. and C. Spanring, "A Uniform Resource Identifier for Geographic Locations ('geo' URI)", RFC 5870, June 2010. |
| [RFC3261] | Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. |
| [RFC3860] | Peterson, J., "Common Profile for Instant Messaging (CPIM)", RFC 3860, August 2004. |
| [RFC3966] | Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966, December 2004. |
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