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I-D ACTION:draft-dkarp-imap-comment-00.txt
A New Internet-Draft is available from the on-line Internet-Drafts
directories.
Title : The IMAP COMMENT Extension
Author(s) : D. Karp
Filename : draft-karp-imap-comment-00.txt
Pages : 0
Date : 2006-11-29
The COMMENT extension to the Internet Message Access Protocol [IMAP]
permits a client to attach free-form text comments to messages stored
in a mailbox on the server. These comments are persistent, public,
mutable, readable, and searchable.
A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-karp-imap-comment-00.txtNetwork Working Group D. Karp
Internet-Draft Zimbra
Expires: June 2, 2007 November 29, 2006
IMAP4 COMMENT Extension
draft-karp-imap-comment-00
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Copyright Notice
Copyright (C) The IETF Trust (2006).
Abstract
The COMMENT extension to the Internet Message Access Protocol [IMAP]
permits a client to attach free-form text comments to messages stored
in a mailbox on the server. These comments are persistent, public,
mutable, readable, and searchable.
1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. If a single "C:" or "S:" label applies to
multiple lines, then the line breaks between those lines are for
editorial clarity only and are not part of the actual protocol
exchange.
2. Introduction and Overview
At present, there is no way for a client to associate an arbitrary
mutable text comment with a message in an IMAP mailbox short of
altering the message's body. This document specifies an extension to
IMAP that permits clients to associate a single optional piece of
text metadata with a message. The value of such a comment is a
string of one or more octets comprising UTF-8 [UTF8] characters, or
NIL when a comment is not set.
The syntax for associating comments with messages and retrieving
message comments is designed to closely parallel the existing syntax
for setting and retrieving mutable message flags. In addition, the
same permissions are required for modifying and retrieving comments
as are required for setting and fetching keywords. Should the
mailbox also support the [CONDSTORE] extension, changes to message
comments qualify as mailbox changes and MUST increment the affected
message's MODSEQ attribute and the mailbox's HIGHESTMODSEQ attribute.
If a server supports comments, then it MUST store all comment data
persistently. The server MAY NOT support "session-only" comments
along the lines of "session" flags as defined in the IMAP base
specification.
Comments MUST be shared publicly with all users who have permission
to read and write them. In this respect, they behave as "shared
flags" as described in section 5.2 of [ACLPLUS]. The server MAY NOT
present a different view of message comments to different users with
read access on a mailbox.
An IMAP server that supports the COMMENT extension MUST return
"COMMENT" in its CAPABILITY response.
3. IMAP Protocol Changes
3.1. COMMENT Parameter to SELECT and EXAMINE
This document defines a single optional select parameter, "COMMENT",
which tells the server that it MUST return changes to message
comments in unsolicited FETCH responses (see section 3.2) for the
duration of the session. This is the only way to enable COMMENT data
in unsolicited FETCH responses; such responses are NOT implicitly
enabled by the use of any other command described in this document.
The enabling of COMMENT does not carry over from one SELECT/EXAMINE
to another within the same IMAP connection.
Example:
C: A001 SELECT INBOX (COMMENT)
S: * 236 EXISTS
S: * 0 RECENT
S: * OK [UNSEEN 228]
S: * OK [UIDVALIDITY 1]
S: * OK [UIDNEXT 713]
S: * FLAGS (\Answered \Deleted \Draft \Flagged \Seen)
S: * OK [PERMANENTFLAGS (\Answered \Deleted \Draft \Flagged
\Seen \*)]
S: * OK [COMMENT 8096]
S: A001 OK [READ-WRITE] SELECT completed, COMMENT enabled
This document also adds a new response code, COMMENT. In the course
of a successful SELECT or EXAMINE, any server that advertises the
COMMENT capability MUST return an untagged OK response containing the
COMMENT response code:
OK [COMMENT <max-comment-length>]
where <max-comment-length> is the maximum length (in octets) of a
comment in the mailbox. If the server cannot support comments for
the mailbox, <max-comment-length> MUST be 0.
3.2. COMMENT Message Data Item for the FETCH Command
This document adds a COMMENT message data item to the FETCH command.
This allows users to retrieve the comments associated with a range of
messages in the currently-selected mailbox:
Example:
C: A002 FETCH 1:2 (UID COMMENT)
S: * 1 FETCH (UID 288 COMMENT NIL)
S: * 2 FETCH (UID 289 COMMENT "This is the message's comment")
S: A002 OK FETCH completed
Unsolicited FETCH responses indicating changes in a message's comment
MUST include the full new value of the COMMENT message data item.
3.3. COMMENT Message Data Item for the STORE command
This document adds new message data items to the STORE command for
setting and removing comments on messages in the selected mailbox:
COMMENT <new-comment>
Replace the comment for the messsage with the argument. The
new value of the comment is returned as if a FETCH of the
COMMENT had been requested.
COMMENT.SILENT <new-comment>
Equivalent to COMMENT, but without returning the new value. If
CONDSTORE is enabled for the session, an unsolicted response
containing the message's new MODSEQ may still be returned.
The new comment must be either NIL or a non-empty octet sequence
shorter than the maximum comment length as specified in the SELECT
response. If the octet sequence is not valid UTF-8, the server MUST
return a tagged NO response with a "[BADCOMMENT NOTUTF8]" response
code. If the octet sequence exceeds the maximum comment length
supported by the mailbox, the server MUST return a tagged NO response
with a "[BADCOMMENT TOOBIG]" response code.
Example:
C: A003 STORE 1 COMMENT "This message now has a comment!"
S: * 1 FETCH (COMMENT "This message now has a comment!")
S: A003 OK STORE completed
C: A004 STORE 2 COMMENT.SILENT NIL
S: A004 OK STORE completed
3.4. COMMENT Search Key for the SEARCH Command
This document adds a new search key to the SEARCH command for
searching within message COMMENTs:
COMMENT <string>
Messages that contain the specified string in the message's
COMMENT. If <string> is zero-length, matches all messages with
non-NIL COMMENTs.
Example:
C: A005 SEARCH COMMENT "comment"
S: * SEARCH 1 12 44 156
S: A005 OK SEARCH completed
3.5. COMMENT Extension for the APPEND Command
This document adds a new APPEND extension (as per [IMAPABNF]) to
allow specification of a comment on an APPENDed message:
COMMENT <append-comment>
Specifies a comment for the appended message.
If the specified comment is not valid UTF-8, the server MUST return a
tagged NO response with a "[BADCOMMENT NOTUTF8]" response code. If
the specified comment exceeds the maximum comment length supported by
the target mailbox of the APPEND, the server MUST return a tagged NO
response with a "[BADCOMMENT TOOBIG]" response code.
Example:
C: A006 APPEND Sent COMMENT "Attached to new message" {14432+}
C: ...
S: A006 OK APPEND completed
3.6. COMMENT Interaction with the COPY Command
When copying a message from one mailbox to another, the server SHOULD
attempt to copy the message's comment along with the copied message.
If the server is unable to associate the comment with the copied
message -- for instance, because it exceeds the maximum comment
length in the target mailbox -- it SHOULD create the copy with a NIL
comment.
3.7. COMMENT Interaction with the ACL Extension
In general, read and write access to comments is governed by the same
rules that control read and write access to message flags.
When the [ACL] or [ACLPLUS] extensions are not present, users have
read-only access to comments when the mailbox is selected READ-ONLY
and read-write access to comments when the mailbox is selected
READ-WRITE.
When the [ACL] or [ACLPLUS] extensions are present, users have read
access to comments when they have been granted the "r" right on the
mailbox and write access to comments when they have been granted the
"w" right on the mailbox.
4. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) [ABNF] notation. Elements not defined here can be found
in the formal syntax of the ABNF [ABNF], UTF-8 [UTF8], IMAP [IMAP4],
and IMAP ABNF extensions [IMAPABNF] specifications.
Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of upper or lower case characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion.
append-ext =/ "COMMENT" SP comment-value
capability =/ "COMMENT"
comment-value = "NIL" / comment-text
comment-text = utf8-quoted / utf8-literal
fetch-att =/ "COMMENT"
msg-att-dynamic =/ "COMMENT" SP comment-value
resp-text-code =/ "BADCOMMENT" SP ("NOTUTF8" / "TOOBIG") /
"COMMENT" SP number
search-key =/ "COMMENT" string
select-param =/ "COMMENT"
store-att-flags =/ "COMMENT" [".SILENT"] SP comment-value
utf8-quoted = DQUOTE 1*(QUOTED-CHAR) DQUOTE
utf8-literal = "{" nz-number ["+"] "}" CRLF 1*(UTF8-char)
; Number represents the octet count
5. References
5.1. Normative References
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[IMAPABNF] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
ABNF", RFC 4466, April 2006.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[UTF8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
5.2. Informative References
[ACL] Myers, J., "IMAP4 ACL extension", RFC 2086, January 1997.
[ACLPLUS] Melnikov, A., "IMAP4 Access Control List (ACL)
Extension", RFC 4314, December 2005.
[CONDSTORE] Melnikov, A. and S. Hole, "IMAP Extension for Conditional
STORE Operation or Quick Flag Changes Resynchronization",
RFC 4551, June 2006.
Appendix A. Acknowledgments
Many thanks to Cyrus Daboo and Randall Gellens for their extensive
work developing the ANNNOTATE draft, upon which this draft is based.
Author's Address
Dan Karp
Zimbra
1500 Fashion Island Blvd.
Suite 100
San Mateo, CA 94404
USA
Email: dkarp@xxxxxxxxxx
URI: http://www.zimbra.com/
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