Internet Engineering Task Force (IETF) C. Daboo

Internet Engineering Task Force (IETF) C. Daboo
Request for Comments: 8607 Apple
Category: Informational A. Quillaud
ISSN: 2070-1721 Oracle
K. Murchison, Ed.
FastMail
June 2019

Calendaring Extensions to WebDAV (CalDAV): Managed Attachments

Abstract

This specification adds an extension to the Calendaring Extensions to
WebDAV (CalDAV) to allow attachments associated with iCalendar data
to be stored and managed on the server.

This specification documents existing code deployed by multiple
vendors. It is published as an Informational specification rather
than Standards Track due to its noncompliance with multiple best
current practices of HTTP.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8607.

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Copyright Notice

Copyright (c) 2019 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Rationale for Informational Status . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Discovering Support for Managed Attachments . . . . . . . 5
3.3. POST Request for Managing Attachments . . . . . . . . . . 6
3.3.1. action Query Parameter . . . . . . . . . . . . . . . 6
3.3.2. rid Query Parameter . . . . . . . . . . . . . . . . . 6
3.3.3. managed-id Query Parameter . . . . . . . . . . . . . 7
3.4. Adding Attachments . . . . . . . . . . . . . . . . . . . 7
3.5. Updating Attachments . . . . . . . . . . . . . . . . . . 10
3.6. Removing Attachments via POST . . . . . . . . . . . . . . 13
3.7. Adding Existing Managed Attachments via PUT . . . . . . . 15
3.8. Updating Attachments via PUT . . . . . . . . . . . . . . 15
3.9. Removing Attachments via PUT . . . . . . . . . . . . . . 15
3.10. Retrieving Attachments . . . . . . . . . . . . . . . . . 15
3.11. Error Handling . . . . . . . . . . . . . . . . . . . . . 16
3.12. Additional Considerations . . . . . . . . . . . . . . . . 17
3.12.1. Quotas . . . . . . . . . . . . . . . . . . . . . . . 17
3.12.2. Access Control . . . . . . . . . . . . . . . . . . . 17
3.12.3. Redirects . . . . . . . . . . . . . . . . . . . . . 18
3.12.4. Processing Time . . . . . . . . . . . . . . . . . . 18
3.12.5. Automatic Cleanup by Servers . . . . . . . . . . . . 18
3.12.6. Sending Scheduling Messages with Attachments . . . . 18
3.12.7. Migrating Calendar Data . . . . . . . . . . . . . . 18
4. Modifications to iCalendar Syntax . . . . . . . . . . . . . . 19
4.1. SIZE Property Parameter . . . . . . . . . . . . . . . . . 19
4.2. FILENAME Property Parameter . . . . . . . . . . . . . . . 19
4.3. MANAGED-ID Property Parameter . . . . . . . . . . . . . . 20
5. Additional Message Header Fields . . . . . . . . . . . . . . 20

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5.1. Cal-Managed-ID Response Header Field . . . . . . . . . . 20
6. Additional WebDAV Properties . . . . . . . . . . . . . . . . 21
6.1. CALDAV:managed-attachments-server-URL Property . . . . . 21
6.2. CALDAV:max-attachment-size Property . . . . . . . . . . . 22
6.3. CALDAV:max-attachments-per-resource Property . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8.1. Parameter Registrations . . . . . . . . . . . . . . . . . 24
8.2. Message Header Field Registrations . . . . . . . . . . . 25
8.2.1. Cal-Managed-ID . . . . . . . . . . . . . . . . . . . 25
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Normative References . . . . . . . . . . . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . 27
Appendix A. Example Involving Recurring Events . . . . . . . . . 28
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34

1. Introduction

The iCalendar [RFC5545] data format is used to represent calendar
data and is used with iCalendar Transport-independent
Interoperability Protocol (iTIP) [RFC5546] to handle scheduling
operations between calendar users.

[RFC4791] defines the Calendaring Extensions to WebDAV (CalDAV),
based on HTTP [RFC7230], for accessing calendar data stored on a
server.

Calendar users often want to include attachments with their calendar
data events or tasks (for example, a copy of a presentation or the
meeting agenda). iCalendar provides an "ATTACH" property whose value
is either the inline Base64 encoded attachment data or a URL
specifying the location of the attachment data.

Use of inline attachment data is not ideal with CalDAV because the
data would need to be uploaded to the server each time a change to
the calendar data is made, even minor changes such as a change to the
summary. Whilst a client could choose to use a URL value instead,
the problem then becomes where and how the client discovers an
appropriate URL to use and how it ensures that only those attendees
listed in the event or task are able to access it.

This specification solves this problem by having the client send the
attachment to the server, separately from the iCalendar data, and
having the server add appropriate "ATTACH" properties in the
iCalendar data as well as manage access privileges. The server can
also provide additional information to the client about each
attachment in the iCalendar data, such as the size and an identifier.

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1.1. Rationale for Informational Status

Although this extension to CalDAV has wide deployment, its design
does not comply with some of the best current practices of HTTP,
namely:

o All operations on attachments are modeled as HTTP POST operations,
where the actual type of operation is specified using a query
parameter instead of using separate HTTP POST, PUT, and DELETE
methods where appropriate.

o Specific query strings are hardwired into the protocol in
violation of Section 2.4 of [RFC7320].

Additionally, this extension misuses the Content-Disposition header
field [RFC6266] as a request header field to convey a filename for an
attachment rather than using an existing request header field
suitable for that purpose, such as "Slug" (see Section 9.7 of
[RFC5023]).

Rather than creating interoperability problems with deployed code by
updating the design of this extension to be compliant with best
current practices and to allow this specification to be placed on the
Standards Track, it was decided to simply document how existing
implementations interoperate and to publish the document as
Informational.

2. 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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

The notation used in this memo is the ABNF notation of [RFC5234] as
used by iCalendar [RFC5545]. Any syntax elements shown below that
are not explicitly defined in this specification come from iCalendar
[RFC5545].

3. Overview

There are four main operations a client needs to perform with
attachments for calendar data: add, update, remove, and retrieve.
The first three operations are carried out by the client issuing an
HTTP POST request on the calendar object resource to which the
attachment is associated and specifying the appropriate "action"
query parameter (see Section 3.3). In the case of the remove

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operation, the client can alternatively directly update the calendar
object resource and remove the relevant "ATTACH" properties (see
Section 3.9). The retrieve operation is accomplished by simply
issuing an HTTP GET request targeting the attachment URI specified by
the calendar resource's "ATTACH" property (see Section 3.10).

iCalendar data stored in a CalDAV calendar object resource can
contain multiple components when recurrences are involved. In such a
situation, the client needs to be able to target a specific
recurrence instance or multiple instances when adding or deleting
attachments. As a result, the POST request needs to provide a way
for the client to specify which recurrence instances should be
targeted for the attachment operation. This is accomplished through
use of additional query parameters on the POST Request-URI.

3.1. Requirements

A server that supports the features described in this specification
is REQUIRED to support the CalDAV "calendar-access" [RFC4791]
features.

In addition, such a server SHOULD support the "return=representation"
Prefer header field [RFC7240] preference on successful HTTP PUT and
POST requests targeting existing calendar object resources by
returning the new representation of that calendar resource (including
its new ETag header field value) in the response.

3.2. Discovering Support for Managed Attachments

A server supporting the features described in this specification MUST
include "calendar-managed-attachments" as a token in the DAV response
header field (as defined in Section 10.1 of [RFC4918]) from an
OPTIONS request on a calendar home collection.

A server might choose not to support the storing of managed
attachments on a per-recurrence-instance basis (i.e., they can only
be added to all instances as a whole). If that is the case, the
server MUST also include "calendar-managed-attachments-no-recurrence"
as a token in the DAV response header field from an OPTIONS request
on a calendar home collection. When that field is present, clients
MUST NOT attempt any managed attachment operations that target
specific recurrence instances.

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3.3. POST Request for Managing Attachments

An HTTP POST request is used to add, update, or remove attachments.
These requests are subject to the preconditions listed in
Section 3.11. The Request-URI will contain various query parameters
to specify the behavior.

3.3.1. action Query Parameter

The "action" query parameter is used to identify which attachment
operation the client is requesting. This parameter MUST be present
once on each POST request used to manage attachments. One of these
three values MUST be used:

attachment-add: Indicates an operation that is adding an attachment
to a calendar object resource. See Section 3.4 for more details.

attachment-update: Indicates an operation that is updating an
existing attachment on a calendar object resource. See
Section 3.5 for more details.

attachment-remove: Indicates an operation that is removing an
attachment from a calendar object resource. See Section 3.6 for
more details.

Example:

https://calendar.example.com/events/1.ics?action=attachment-add

3.3.2. rid Query Parameter

The "rid" query parameter is used to identify which recurrence
instances are being targeted by the client for the attachment
operation. This query parameter MUST contain one or more items,
separated by commas (denoted in ASCII as "0x2C"). The item values
can be in one of two forms:

Master instance: The value "M" (case insensitive) refers to the
"master" recurrence instance, i.e., the component that does not
include a "RECURRENCE-ID" property. This item MUST be present
only once.

Specific instance: A specific iCalendar instance is targeted by
using its "RECURRENCE-ID" value as the item value. That value
MUST correspond to the "RECURRENCE-ID" value as stored in the
calendar object resource (i.e., without any conversion to UTC).
If multiple items of this form are used, they MUST be unique
values. For example, to target a recurrence defined by property

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RECURRENCE-ID;TZID=America/Montreal:20111022T160000, the query
parameter rid=20111022T160000 would be used.

If the "rid" query parameter is not present, all recurrence instances
in the calendar object resource are targeted.

The "rid" query parameter MUST NOT be present in the case of an
update operation, or if the server chooses not to support per-
recurrence instance managed attachments (see Section 3.2).

Example (targeting the master instance and a specific overridden
instance):

https://calendar.example.com/events/1.ics?
action=attachment-add&rid=M,20111022T160000

3.3.3. managed-id Query Parameter

The "managed-id" query parameter is used to identify which "ATTACH"
property is being updated or removed. The value of this query
parameter MUST match the "MANAGED-ID" (Section 4.3) property
parameter value on the "ATTACH" property in the calendar object
resource instance(s) targeted by the request.

The "managed-id" query parameter MUST NOT be present in the case of
an add operation.

Example:

https://calendar.example.com/events/1.ics?
action=attachment-update&managed-id=aUNhbGVuZGFy

3.4. Adding Attachments

To add an attachment to an existing calendar object resource, the
following needs to occur:

1. The client issues a POST request targeted at the calendar object
resource structured as follows:

A. The Request-URI will include an "action" query parameter with
the value "attachment-add" (see Section 3.3.1).

B. If all recurrence instances are having an attachment added,
the "rid" query parameter is not present in the Request-URI.
If one or more specific recurrence instances are targeted,
then the Request-URI will include a "rid" query parameter
containing the list of instances (see Section 3.3.2).

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C. The body of the request contains the data for the attachment.

D. The client MUST include a valid Content-Type header field
describing the media type of the attachment (as required by
HTTP).

E. The client SHOULD include a Content-Disposition header field
[RFC6266] with a "type" parameter set to "attachment", and a
"filename" parameter that indicates the name of the
attachment. Note that the use of Content-Disposition as a
request header field is nonstandard and specific to this
protocol.

F. The client MAY include a Prefer header field [RFC7240] with
the "return=representation" preference to request that the
modified calendar object resource be returned as the body of
a successful response to the POST request.

2. When the server receives the POST request, it does the following:

A. Validates that any recurrence instances referred to via the
"rid" query parameter are valid for the calendar object
resource being targeted.

B. Stores the supplied attachment data into a resource and
generates an appropriate URI for clients to access the
resource.

C. For each affected recurrence instance in the calendar object
resource targeted by the request, adds an "ATTACH" property
whose value is the URI of the stored attachment. The
"ATTACH" property MUST contain a "MANAGED-ID" property
parameter whose value is a unique identifier (within the
context of the server as a whole). The "ATTACH" property
SHOULD contain an "FMTTYPE" property parameter whose value
matches the Content-Type header field value from the request.
The "ATTACH" property SHOULD contain a "FILENAME" property
parameter whose value matches the value of the Content-
Disposition header field "filename" parameter value from the
request, taking into account the restrictions expressed in
Section 4.2. The "ATTACH" property SHOULD include a "SIZE"
property parameter whose value represents the size in octets
of the attachment. If a specified recurrence instance does
not have a matching component in the calendar object
resource, then the server MUST modify the calendar object
resource to include an overridden component with the
appropriate "RECURRENCE-ID" property.

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D. Upon successful creation of the attachment resource, and
modification of the targeted calendar object resource, it
MUST return an appropriate HTTP success status response and
include a "Cal-Managed-ID" header field containing the
"MANAGED-ID" property parameter value of the newly created
"ATTACH" property. The client can use the "Cal-Managed-ID"
header field value to correlate the attachment with "ATTACH"
properties added to the calendar object resource. If the
client included a Prefer header field with the
"return=representation" preference in the request, the server
SHOULD return the modified calendar object resource as the
body of the response. Otherwise, the server can expect that
the client will reload the calendar object resource with a
subsequent GET request to refresh any local cache.

In the following example, the client adds a new attachment to a
nonrecurring event and asks the server (via the Prefer header field
[RFC7240]) to return the modified version of that event in the
response.

>> Request <<

POST /events/64.ics?action=attachment-add HTTP/1.1
Host: cal.example.com
Content-Type: text/html; charset="utf-8"
Content-Disposition:attachment;filename=agenda.html
Content-Length: 59
Prefer: return=representation

<html>
<body>
<h1>Agenda</h1>
</body>
</html>

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>> Response <<

HTTP/1.1 201 Created
Content-Type: text/calendar; charset="utf-8"
Content-Length: 371
Content-Location: https://cal.example.com/events/64.ics
ETag: "123456789-000-111"
Cal-Managed-ID: 97S

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Server//EN
BEGIN:VEVENT
UID:[email protected]
DTSTAMP:20120201T203412Z
DTSTART:20120714T170000Z
DTEND:20120715T040000Z
SUMMARY:One-off meeting
ATTACH;MANAGED-ID=97S;FMTTYPE=text/html;SIZE=59;
FILENAME=agenda.html:https://cal.example.com/attach/64/34X22R
END:VEVENT
END:VCALENDAR

3.5. Updating Attachments

When an attachment is updated, the server MUST change the associated
"MANAGED-ID" property parameter and MAY change the "ATTACH" property
value. With this approach, clients are able to determine when an
attachment has been updated by some other client by looking for a
change to either the "ATTACH" property value or the "MANAGED-ID"
property parameter value.

To change the data of an existing managed attachment in a calendar
object resource, the following needs to occur:

1. The client issues a POST request targeted at the calendar object
resource structured as follows:

A. The Request-URI will include an "action" query parameter with
the value "attachment-update" (see Section 3.3.1).

B. The Request-URI will include a "managed-id" query parameter
with the value matching that of the "MANAGED-ID" property
parameter for the "ATTACH" property being updated (see
Section 3.3.3).

C. The body of the request contains the updated data for the
attachment.

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D. The client MUST include a valid Content-Type header field
describing the media type of the attachment (as required by
HTTP).

E. The client SHOULD include a Content-Disposition header field
[RFC6266] with a "type" parameter set to "attachment", and a
"filename" parameter that indicates the name of the
attachment.

F. The client MAY include a Prefer header field [RFC7240] with
the "return=representation" preference to request that the
modified calendar object resource be returned as the body of
a successful response to the POST request.

2. When the server receives the POST request, it does the following:

A. Validates that the "managed-id" query parameter is valid for
the calendar object resource.

B. Updates the content of the attachment resource corresponding
to that "managed-id" value with the supplied attachment data.

C. For each affected recurrence instance in the calendar object
resource targeted by the request, updates the "ATTACH"
property whose "MANAGED-ID" property parameter value matches
the "managed-id" query parameter. The "MANAGED-ID" property
parameter value is changed to allow other clients to detect
the update, and the property value (attachment URI) might
also be changed. The "ATTACH" property SHOULD contain a
"FMTTYPE" property parameter whose value matches the Content-
Type header field value from the request; this could differ
from the original value if the media type of the updated
attachment is different. The "ATTACH" property SHOULD
contain a "FILENAME" property parameter whose value matches
the Content-Disposition header field "filename" parameter
value from the request, taking into account the restrictions
expressed in Section 4.2. The "ATTACH" property SHOULD
include a "SIZE" property parameter whose value represents
the size in octets of the updated attachment.

D. Upon successful update of the attachment resource, and
modification of the targeted calendar object resource, it
MUST return an appropriate HTTP success status response and
include a "Cal-Managed-ID" header field containing the new
value of the "MANAGED-ID" property parameter. The client can
use the "Cal-Managed-ID" header field value to correlate the
attachment with "ATTACH" properties added to the calendar

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object resource. If the client included a Prefer header
field with the "return=representation" preference in the
request, the server SHOULD return the modified calendar
object resource as the body of the response. Otherwise, the
server can expect that the client will reload the calendar
object resource with a subsequent GET request to refresh any
local cache.

The update operation does not take a "rid" query parameter and does
not add, or remove, any "ATTACH" property in the targeted calendar
object resource. To link an existing attachment to a new instance,
the client simply does a PUT on the calendar object resource, adding
an "ATTACH" property that duplicates the existing one (see
Section 3.7).

In the following example, the client updates an existing attachment
and asks the server (via the Prefer header field [RFC7240]) to return
the updated version of that event in the response.

>> Request <<

POST /events/64.ics?action=attachment-update&managed-id=97S HTTP/1.1
Host: cal.example.com
Content-Type: text/html; charset="utf-8"
Content-Disposition:attachment;filename=agenda.html
Content-Length: 96
Prefer: return=representation

<html>
<body>
<h1>Agenda</h1>
<p>Discuss attachment draft</p>
</body>
</html>

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>> Response <<

HTTP/1.1 200 OK
Content-Type: text/calendar; charset="utf-8"
Content-Length: 371
Content-Location: https://cal.example.com/events/64.ics
Cal-Managed-ID: 98S
ETag: "123456789-000-222"

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Server//EN
BEGIN:VEVENT
UID:[email protected]
DTSTAMP:20120201T203412Z
DTSTART:20120714T170000Z
DTEND:20120715T040000Z
SUMMARY:One-off meeting
ATTACH;MANAGED-ID=98S;FMTTYPE=text/html;SIZE=96;
FILENAME=agenda.html:https://cal.example.com/attach/64/34X22R
END:VEVENT
END:VCALENDAR

3.6. Removing Attachments via POST

To remove an existing attachment from a calendar object, the
following needs to occur:

1. The client issues a POST request targeted at the calendar object
resource structured as follows:

A. The Request-URI will include an "action" query parameter with
the value "attachment-remove" (see Section 3.3.1).

B. If all recurrence instances are having an attachment removed,
the "rid" query parameter is not present in the Request-URI.
If one or more specific recurrence instances are targeted,
then the Request-URI will include a "rid" query parameter
containing the list of instances (see Section 3.3.2).

C. The Request-URI will include a "managed-id" query parameter
with the value matching that of the "MANAGED-ID" property
parameter for the "ATTACH" property being removed (see
Section 3.3.3).

D. The body of the request will be empty.

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E. The client MAY include a Prefer header field [RFC7240] with
the "return=representation" preference to request that the
modified calendar object resource be returned as the body of
a successful response to the POST request.

2. When the server receives the POST request, it does the following:

A. Validates that any recurrence instances referred to via the
"rid" query parameter are valid for the calendar object
resource being targeted.

B. Validates that the "managed-id" query parameter is valid for
the calendar object resource and specific instances being
targeted.

C. For each affected recurrence instance in the calendar object
resource targeted by the request, removes the matching
"ATTACH" property. Note that if a specified recurrence
instance does not have a matching component in the calendar
object resource, then the server MUST modify the calendar
object resource to include an overridden component with the
appropriate "RECURRENCE-ID" property and the matching
"ATTACH" property removed. This latter case is actually
valid only if the master component does include the
referenced "ATTACH" property.

D. If the attachment resource is no longer referenced by any
instance of the calendar object resource, it can delete the
attachment resource to free up storage space.

E. Upon successful removal of the attachment resource and
modification of the targeted calendar object resource, it
MUST return an appropriate HTTP success status response. If
the client included a Prefer header field with the
"return=representation" preference in the request, the server
SHOULD return the modified calendar object resource as the
body of the response. Otherwise, the server can expect that
the client will reload the calendar object resource with a
subsequent GET request to refresh any local cache.

In the following example, the client deletes an existing attachment
by passing its "managed-id" value in the request. The Prefer header
field [RFC7240] is not set in the request so the calendar object
resource data is not returned in the response.

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>> Request <<

POST /events/64.ics?action=attachment-remove&managed-id=98S HTTP/1.1
Host: cal.example.com
Content-Length: 0

>> Response <<

HTTP/1.1 204 No Content
Content-Length: 0

3.7. Adding Existing Managed Attachments via PUT

Clients can make use of existing managed attachments by adding the
corresponding "ATTACH" property to calendar object resources (subject
to the restrictions described in Section 3.12.2).

If a managed attachment is used in more than calendar resource,
servers SHOULD NOT change either the "MANAGED-ID" property parameter
value or the "ATTACH" property value for these attachments; this
ensures that clients do not have to download the attachment data
again if they already have it cached. Additionally, servers SHOULD
validate "SIZE" property parameter values and replace incorrect
values with the actual sizes of existing attachments.

These PUT requests are subject to the preconditions listed in
Section 3.11.

3.8. Updating Attachments via PUT

Servers MUST NOT allow clients to update attachment data directly via
a PUT on the attachment URI (or via any other HTTP method that
modifies content). Instead, attachments can only be updated via use
of POST requests on the calendar data.

3.9. Removing Attachments via PUT

Clients can remove attachments by simply rewriting the calendar
object resource data to remove the appropriate "ATTACH" properties.
Servers MUST NOT allow clients to delete attachments directly via a
DELETE request on the attachment URI.

3.10. Retrieving Attachments

Clients retrieve attachments by issuing an HTTP GET request using the
value of the corresponding "ATTACH" property as the Request-URI,
taking into account the substitution mechanism associated with the
"CALDAV:managed-attachments-server-URL" property (see Section 6.1).

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3.11. Error Handling

This specification creates additional preconditions for the POST
method.

The new preconditions are:

(CALDAV:max-attachment-size): The attachment submitted in the POST
request MUST have an octet size less than or equal to the value of
the "CALDAV:max-attachment-size" property value (Section 6.2) on
the calendar collection of the target calendar resource.

(CALDAV:max-attachments-per-resource): The addition of the
attachment submitted in the POST request MUST result in the target
calendar resource having a number of managed attachments less than
or equal to the value of the "CALDAV:max-attachments-per-resource"
property value (Section 6.3) on the calendar collection of the
target calendar resource.

(CALDAV:valid-action): The "action" query parameter in the POST
request MUST contain only one of the following three values:
"attachment-add", "attachment-update", or "attachment-remove".

(CALDAV:valid-rid): The "rid" query parameter in the POST request
MUST NOT be present with an "action=attachment-update" query
parameter and MUST contain the value "M" and/or values
corresponding to "RECURRENCE-ID" property values in the iCalendar
data targeted by the request.

(CALDAV:valid-managed-id): The "managed-id" query parameter in the
POST request MUST NOT be present with an "action=attachment-add"
query parameter and MUST contain a value corresponding to a
"MANAGED-ID" property parameter value in the iCalendar data
targeted by the request.

A POST request to add, modify, or delete a managed attachment results
in an implicit modification of the targeted calendar resource
(equivalent of a PUT). As a consequence, clients should also be
prepared to handle preconditions associated with this implicit PUT.
This includes (but is not limited to):

(CALDAV:max-resource-size) (from Section 5.3.2.1 of [RFC4791])

(DAV:quota-not-exceeded) (from Section 6 of [RFC4331])

(DAV:sufficient-disk-space) (from Section 6 of [RFC4331])

Daboo, et al. Informational [Page 16]

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A PUT request to add or modify an existing calendar object resource
can make reference to an existing managed attachment. The following
new precondition is defined:

(CALDAV:valid-managed-id-parameter): a "MANAGED-ID" property
parameter value in the iCalendar data in the PUT request is not
valid (e.g., does not match any existing managed attachment).

If a precondition for a request is not satisfied:

1. The response status of the request MUST either be 403 (Forbidden)
if the request should not be repeated because it will always
fail, or 409 (Conflict) if it is expected that the user might be
able to resolve the conflict and resubmit the request.

2. The appropriate XML element MUST be returned as the child of a
top-level DAV:error element in the response body.

3.12. Additional Considerations

3.12.1. Quotas

The WebDAV Quotas specification [RFC4331] defines two live WebDAV
properties (DAV:quota-available-bytes and DAV:quota-used-bytes) to
communicate storage quota information to clients. Server
implementations MAY choose to include managed attachment sizes when
calculating the amount of storage used by a particular resource.

3.12.2. Access Control

Access to the managed attachments referenced in a calendar object
resource SHOULD be restricted to only those calendar users who have
access to that calendar object either directly or indirectly (via
being an attendee who would receive a scheduling message).

When accessing a managed attachment, clients SHOULD be prepared to
authenticate with the server storing the attachment resource. The
credentials required to access the managed attachment store could be
different from the ones used to access the CalDAV server.

This specification only allows organizers of scheduled events to add
managed attachments. Servers MUST prevent attendees of scheduled
events from adding, updating, or removing managed attachments. In
addition, the server MUST prevent a calendar user from reusing a
managed attachment (based on its "managed-id" value), unless that
user is the one who originally created the managed attachment.

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3.12.3. Redirects

For POST requests that add or update attachment data, the server MAY
issue a 307 (Temporary Redirect) [RFC7231] or 308 (Permanent
Redirect) [RFC7538] response to require the client to reissue the
POST request using a different Request-URI. As a result, clients
SHOULD use the "100-continue" expectation defined in Section 5.1.1 of
[RFC7231]. Using this mechanism ensures that, if a redirect does
occur, the client does not needlessly send the attachment data.

3.12.4. Processing Time

Clients can expect servers to take a while to respond to POST
requests that include large attachment bodies. Servers SHOULD use
the 102 (Processing) interim response defined in Section 10.1 of
[RFC2518] to keep the client connection alive if the POST request
will take significant time to complete.

3.12.5. Automatic Cleanup by Servers

Servers MAY automatically remove attachment data, for example, to
regain the storage taken by unused attachments or as the result of a
virus scanning. When doing so, they SHOULD NOT modify calendar data
referencing those attachments. Instead, they SHOULD respond with 410
(Gone) to any request on the removed attachment URI.

3.12.6. Sending Scheduling Messages with Attachments

When a managed attachment is added, updated, or removed from a
calendar object resource, the server MUST ensure that a scheduling
message is sent to update any attendees with the changes, as per
[RFC6638].

3.12.7. Migrating Calendar Data

When exporting calendar data from a CalDAV server supporting managed
attachments, clients SHOULD remove all "MANAGED-ID" property
parameters from "ATTACH" properties in the calendar data. Similarly,
when importing calendar data from another source, clients SHOULD
remove any "MANAGED-ID" property parameters on "ATTACH" properties
(failure to do so will likely result in the server removing those
properties automatically).

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4. Modifications to iCalendar Syntax

4.1. SIZE Property Parameter

Parameter Name: SIZE

Purpose: To specify the size of an attachment.

Format Definition: This property parameter is defined by the
following notation:

sizeparam = "SIZE" "=" paramtext
; positive integers

Description: This property parameter MAY be specified on "ATTACH"
properties. It indicates the size in octets of the corresponding
attachment data. Since iCalendar integer values are restricted to
a maximum value of 2147483647, the current property parameter is
defined as text to allow an extended range to be used.

Example:

ATTACH;SIZE=1234:https://attachments.example.com/abcd.txt

4.2. FILENAME Property Parameter

Parameter Name: FILENAME

Purpose: To specify the filename of a managed attachment.

Format Definition: This property parameter is defined by the
following notation:

filenameparam = "FILENAME" "=" paramtext

Description: This property parameter MAY be specified on "ATTACH"
properties corresponding to managed attachments. Its value
provides information on how to construct a filename for storing
the attachment data. This parameter is very similar in nature to
the Content-Disposition header field "filename" parameter and
exposes the same security risks. As a consequence, clients MUST
follow the guidelines expressed in Section 4.3 of [RFC6266] when
consuming this property parameter value. Similarly, servers MUST
follow those same guidelines before storing a value.

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Example:

ATTACH;FILENAME=agenda.html:
https://attachments.example.com/rt452S

4.3. MANAGED-ID Property Parameter

Parameter Name: MANAGED-ID

Purpose: To uniquely identify a managed attachment.

Format Definition: This property parameter is defined by the
following notation:

managedidparam = "MANAGED-ID" "=" paramtext

Description: This property parameter MUST be specified on "ATTACH"
properties corresponding to managed attachments. Its value is
generated by the server and uniquely identifies a managed
attachment within the scope of the CalDAV server. This property
parameter MUST NOT be present in the case of unmanaged
attachments.

Example:

ATTACH;MANAGED-ID=aUNhbGVuZGFy:
https://attachments.example.com/abcd.txt

5. Additional Message Header Fields

5.1. Cal-Managed-ID Response Header Field

The Cal-Managed-ID response header field provides the value of the
"MANAGED-ID" property parameter corresponding to a newly added
"ATTACH" property.

ABNF:

Cal-Managed-ID = "Cal-Managed-ID" ":" paramtext
; "paramtext" is defined in Section 3.1 of [RFC5545]

Example:

Cal-Managed-ID:aUNhbGVuZGFy

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The Cal-Managed-ID header field MUST only be sent by an origin server
in response to a successful POST request with an "action" query
parameter set to "attachment-add" or "attachment-update". It MUST
only appear once in a response and MUST NOT appear in trailers.

The Cal-Managed-ID header field is end to end and MUST be forwarded
by intermediaries. Intermediaries MUST NOT insert, delete, or modify
a Cal-Managed-ID header field.

6. Additional WebDAV Properties

6.1. CALDAV:managed-attachments-server-URL Property

Name: managed-attachments-server-URL

Namespace: urn:ietf:params:xml:ns:caldav

Purpose: This property specifies the server base URI to use when
retrieving managed attachments.

Protected: This property MUST be protected as only the server can
update the value.

COPY/MOVE behavior: This property is only defined on a calendar home
collection, which cannot be moved or copied.

allprop behavior: This property SHOULD NOT be returned by a PROPFIND
DAV:allprop request.

Description: This property MAY be defined on a calendar home
collection. If present, it contains either a single DAV:href XML
element or none at all.

When one DAV:href element is present, its value MUST be an
absolute HTTP URI containing only the scheme (i.e., "https") and
authority (i.e., host and port) parts. Whenever a managed
attachment is to be retrieved via an HTTP GET, the client MUST
construct the actual URL of the attachment by substituting the
scheme and authority parts of the attachment URI (as stored in the
iCalendar "ATTACH" property) with the present WebDAV property
value.

When no DAV:href element is present, the client MUST substitute
the scheme and authority parts of the attachment URI with the
scheme and authority part of the calendar home collection absolute
URI.

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In the absence of this property, the client can consider the
attachment URI as its actual URL.

Definition:

<!ELEMENT managed-attachments-server-URL (DAV:href?)>

Example:

<C:managed-attachments-server-URL xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:href>https://attachstore.example.com</D:href>
</C:managed-attachments-server-URL>

6.2. CALDAV:max-attachment-size Property

Name: max-attachment-size

Namespace: urn:ietf:params:xml:ns:caldav

Purpose: This property provides a numeric value indicating the
maximum attachment size, in octets, that the server is willing to
accept when a managed attachment is stored on the server.

Protected: This property MUST be protected as it indicates limits
provided by the server.

COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.

allprop behavior: This property SHOULD NOT be returned by a PROPFIND
DAV:allprop request.

Description: The "CALDAV:max-attachment-size" property is used to
specify a numeric value that represents the maximum attachment
size, in octets, that the server is willing to accept when a
managed attachment is stored on the server. The property is
defined on the parent collection of the calendar object resource
to which the attachment is associated. Any attempt to store a
managed attachment exceeding this size MUST result in an error,
with the CALDAV:max-attachment-size precondition (Section 3.11)
being violated. In the absence of this property, the client can
assume that the server will allow storing an attachment of any
reasonable size.

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Definition:

<!ELEMENT max-attachment-size (#PCDATA)>


Example:

<C:max-attachment-size xmlns:C="urn:ietf:params:xml:ns:caldav"
>102400000</C:max-attachment-size>

6.3. CALDAV:max-attachments-per-resource Property

Name: max-attachments-per-resource

Namespace: urn:ietf:params:xml:ns:caldav

Purpose: This property provides a numeric value indicating the
maximum number of managed attachments across all instances of a
calendar object resource stored in a calendar collection.

Protected: This property MUST be protected as it indicates limits
provided by the server.

COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.

allprop behavior: This property SHOULD NOT be returned by a PROPFIND
DAV:allprop request.

Description: The "CALDAV:max-attachments-per-resource" property is
used to specify a numeric value that represents the maximum number
of managed attachments across all instances of a calendar object
resource stored in a calendar collection. Unmanaged attachments
are not counted toward that limit. The property is defined on the
parent collection of the calendar object resource to which the
attachment is associated. Any attempt to add a managed attachment
that would cause the calendar resource to exceed this limit MUST
result in an error, with the CALDAV:max-attachments-per-resource
precondition (Section 3.11) being violated. In the absence of
this property, the client can assume that the server can handle
any number of managed attachments per calendar resource.

Definition:

<!ELEMENT max-attachments-per-resource (#PCDATA)>


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Example:

<C:max-attachments-per-resource
xmlns:C="urn:ietf:params:xml:ns:caldav"
>12</C:max-attachments-per-resource>

7. Security Considerations

The security considerations in [RFC4791] and [RFC4918] apply to this
extension. Additionally, servers need to be aware that a client
could attack underlying storage by POSTing extremely large
attachments and could attack processing time by uploading a recurring
event with a large number of overrides and then repeatedly adding,
updating, and deleting attachments.

Malicious content could be introduced into the calendar server by way
of a managed attachment, and propagated to many end users via
scheduling. Servers SHOULD check managed attachments for malicious
or inappropriate content. Upon detecting such content, servers
SHOULD remove the attachment following the rules described in
Section 3.12.5.

8. IANA Considerations

8.1. Parameter Registrations

This specification defines the following new iCalendar property
parameters to be added to the "Parameters" registry defined in
Section 8.2.4 of [RFC5545]:

+------------+---------+-----------------------+
| Parameter | Status | Reference |
+------------+---------+-----------------------+
| SIZE | Current | RFC 8607, Section 4.1 |
| FILENAME | Current | RFC 8607, Section 4.2 |
| MANAGED-ID | Current | RFC 8607, Section 4.3 |
+------------+---------+-----------------------+

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8.2. Message Header Field Registrations

The message header fields below should be added to the "Permanent
Message Header Field Names" registry (see [RFC3864]).

8.2.1. Cal-Managed-ID

Header field name: Cal-Managed-ID

Protocol: http

Status: standard

Author/Change controller: IETF

Reference: this specification (Section 5.1)

Related information: none

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,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, DOI 10.17487/RFC2518, February 1999,
<https://www.rfc-editor.org/info/rfc2518>.

[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004,
<https://www.rfc-editor.org/info/rfc3864>.

[RFC4331] Korver, B. and L. Dusseault, "Quota and Size Properties
for Distributed Authoring and Versioning (DAV)
Collections", RFC 4331, DOI 10.17487/RFC4331, February
2006, <https://www.rfc-editor.org/info/rfc4331>.

[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
DOI 10.17487/RFC4791, March 2007,
<https://www.rfc-editor.org/info/rfc4791>.

Daboo, et al. Informational [Page 25]

RFC 8607 CalDAV-Managed Attachments June 2019

[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918,
DOI 10.17487/RFC4918, June 2007,
<https://www.rfc-editor.org/info/rfc4918>.

[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.

[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>.

[RFC6266] Reschke, J., "Use of the Content-Disposition Header Field
in the Hypertext Transfer Protocol (HTTP)", RFC 6266,
DOI 10.17487/RFC6266, June 2011,
<https://www.rfc-editor.org/info/rfc6266>.

[RFC6638] Daboo, C. and B. Desruisseaux, "Scheduling Extensions to
CalDAV", RFC 6638, DOI 10.17487/RFC6638, June 2012,
<https://www.rfc-editor.org/info/rfc6638>.

[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.

[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.

[RFC7240] Snell, J., "Prefer Header for HTTP", RFC 7240,
DOI 10.17487/RFC7240, June 2014,
<https://www.rfc-editor.org/info/rfc7240>.

[RFC7538] Reschke, J., "The Hypertext Transfer Protocol Status Code
308 (Permanent Redirect)", RFC 7538, DOI 10.17487/RFC7538,
April 2015, <https://www.rfc-editor.org/info/rfc7538>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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9.2. Informative References

[RFC5023] Gregorio, J., Ed. and B. de hOra, Ed., "The Atom
Publishing Protocol", RFC 5023, DOI 10.17487/RFC5023,
October 2007, <https://www.rfc-editor.org/info/rfc5023>.

[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>.

[RFC7320] Nottingham, M., "URI Design and Ownership", BCP 190,
RFC 7320, DOI 10.17487/RFC7320, July 2014,
<https://www.rfc-editor.org/info/rfc7320>.

[RFC8144] Murchison, K., "Use of the Prefer Header Field in Web
Distributed Authoring and Versioning (WebDAV)", RFC 8144,
DOI 10.17487/RFC8144, April 2017,
<https://www.rfc-editor.org/info/rfc8144>.

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RFC 8607 CalDAV-Managed Attachments June 2019

Appendix A. Example Involving Recurring Events

In the following example, the organizer of a recurring meeting makes
an unsuccessful attempt to add an agenda (HTML attachment) to the
corresponding calendar resource with a conditional request. Note
that the client includes both the Expect and Prefer header fields in
the request, thereby preventing itself from needlessly sending the
attachment data and requesting that the current resource be returned
in the failure response (see Section 3.2 of [RFC8144]).

>> Request <<

POST /events/65.ics?action=attachment-add HTTP/1.1
Host: cal.example.com
Content-Type: text/html; charset="utf-8"
Content-Disposition: attachment;filename=agenda.html
Content-Length: 80
If-Match: "abcdefg-000"
Expect: 100-continue
Prefer: return=representation

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>> Final Response <<

HTTP/1.1 412 Precondition Failed
Content-Type: text/calendar; charset="utf-8"
Content-Length: 929
Content-Location: https://cal.example.com/events/65.ics
ETag: "123456789-000-000"

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Server//EN
BEGIN:VTIMEZONE
LAST-MODIFIED:20040110T032845Z
TZID:America/Montreal
BEGIN:DAYLIGHT
DTSTART:20000404T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
TZNAME:EDT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:20001026T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:EST
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:[email protected]
DTSTAMP:20120201T203412Z
DTSTART;TZID=America/Montreal:20120206T100000
DURATION:PT1H
RRULE:FREQ=WEEKLY
SUMMARY:Planning Meeting
ORGANIZER:mailto:[email protected]
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:cyrus@exampl
e.com
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:arnaudq@exam
ple.com
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION:mailto:mike@exa
mple.com
END:VEVENT
END:VCALENDAR

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The organizer of a recurring meeting successfully adds an agenda
(HTML attachment) to the corresponding calendar resource. Attendees
of the meeting are granted read access to the newly created
attachment resource. Their own copy of the meeting is updated to
include the new "ATTACH" property pointing to the attachment
resource, and they are notified of the change via their scheduling
inbox.

>> Request <<

POST /events/65.ics?action=attachment-add HTTP/1.1
Host: cal.example.com
Content-Type: text/html; charset="utf-8"
Content-Disposition: attachment;filename=agenda.html
Content-Length: 80
If-Match: "123456789-000-000"
Expect: 100-continue
Prefer: return=representation

>> Interim Response <<

HTTP/1.1 100 Continue

>> Request Body <<

<html>
<body>
<h1>Agenda</h1>
<p>As usual</p>
</body>
</html>

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RFC 8607 CalDAV-Managed Attachments June 2019

>> Final Response <<

HTTP/1.1 201 Created
Content-Type: text/calendar; charset="utf-8"
Content-Length: 1043
Content-Location: https://cal.example.com/events/65.ics
ETag: "123456789-000-111"
Cal-Managed-ID: 97S

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Server//EN
BEGIN:VTIMEZONE
LAST-MODIFIED:20040110T032845Z
TZID:America/Montreal
BEGIN:DAYLIGHT
DTSTART:20000404T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
TZNAME:EDT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:20001026T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:EST
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:[email protected]
DTSTAMP:20120201T203412Z
DTSTART;TZID=America/Montreal:20120206T100000
DURATION:PT1H
RRULE:FREQ=WEEKLY
SUMMARY:Planning Meeting
ORGANIZER:mailto:[email protected]
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:cyrus@exampl
e.com
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:arnaudq@exam
ple.com
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION:mailto:mike@exa
mple.com
ATTACH;MANAGED-ID=97S;FMTTYPE=text/html;SIZE=80;
FILENAME=agenda.html:https://cal.example.com/attach/65/34X22R
END:VEVENT
END:VCALENDAR

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The organizer has a more specific agenda for the 20th of February
meeting. It is added to that particular instance of the meeting by
specifying the "rid" query parameter. Note that an overridden
instance is created with the "RECURRENCE-ID" property value matching
the value of the "rid" query parameter in the request. Also, note
that the server takes significant time to complete the request and
notifies the client accordingly.

>> Request <<

POST /events/65.ics?action=attachment-add&rid=20120220T100000 HTTP/1.1
Host: cal.example.com
Content-Type: text/html; charset="utf-8"
Content-Disposition: attachment;filename=agenda0220.html
Content-Length: 105
If-Match: "123456789-000-111"
Expect: 100-continue
Prefer: return=representation

>> Interim Response <<

HTTP/1.1 100 Continue

>> Request Body <<

<html>
<body>
<h1>Agenda</h1>
<p>Something different, for a change</p>
</body>
</html>

>> Interim Response <<

HTTP/1.1 102 Processing

>> Final Response <<

HTTP/1.1 201 Created
Content-Type: text/calendar; charset="utf-8"
Content-Length: 1661
Content-Location: https://cal.example.com/events/65.ics
ETag: "123456789-000-222"
Cal-Managed-ID: 33225

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RFC 8607 CalDAV-Managed Attachments June 2019

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Server//EN
BEGIN:VTIMEZONE
LAST-MODIFIED:20040110T032845Z
TZID:America/Montreal
BEGIN:DAYLIGHT
DTSTART:20000404T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
TZNAME:EDT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:20001026T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:EST
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:[email protected]
DTSTAMP:20120201T203412Z
DTSTART;TZID=America/Montreal:20120206T100000
DURATION:PT1H
RRULE:FREQ=WEEKLY
SUMMARY:Planning Meeting
ORGANIZER:mailto:[email protected]
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:cyrus@exampl
e.com
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:arnaudq@exam
ple.com
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION:mailto:mike@exa
mple.com
ATTACH;MANAGED-ID=97S;FMTTYPE=text/html;SIZE=80;
FILENAME=agenda.html:https://cal.example.com/attach/65/34X22R
END:VEVENT
BEGIN:VEVENT
UID:[email protected]
RECURRENCE-ID;TZID=America/Montreal:20120220T100000
DTSTAMP:20120201T203412Z
DTSTART;TZID=America/Montreal:20120220T100000
DURATION:PT1H
SUMMARY:Planning Meeting
ORGANIZER:mailto:[email protected]
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:cyrus@example.
com

Daboo, et al. Informational [Page 33]

RFC 8607 CalDAV-Managed Attachments June 2019

ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:mailto:arnaudq@exampl
e.com
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION:mailto:mike@examp
le.com
ATTACH;MANAGED-ID=33225;FMTTYPE=text/html;SIZE=105;
FILENAME=agenda0220.html:https://cal.example.com/attach/65/FGZ225
END:VEVENT
END:VCALENDAR

Acknowledgments

This specification came about via discussions at the Calendaring and
Scheduling Consortium. Thanks in particular to Mike Douglass and
Eric York.

Authors' Addresses

Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
United States of America

Email: [email protected]
URI: http://www.apple.com/

Arnaud Quillaud
Oracle Corporation
180, Avenue de l'Europe
Saint Ismier cedex 38334
France

Email: [email protected]
URI: http://www.oracle.com/

Kenneth Murchison (editor)
FastMail US LLC
1429 Walnut St, Suite 1201
Philadephia, PA 19102
United States of America

Email: [email protected]
URI: http://www.fastmail.com/

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