LEMONADE P. Resnick
Internet-Draft QUALCOMM Incorporated
Expires: June 11, 2005 December 11, 2004
Internet Message Access Protocol (IMAP) CATENATE Extension
draft-ietf-lemonade-catenate-03
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Copyright (C) The Internet Society (2004).
Abstract
The CATENATE extension to the Internet Message Access Protocol (IMAP)
allows clients to create messages on the IMAP server which may
contain a combination of new data along with parts of (or entire)
messages already on the server. Using this extension, the client can
catenate parts of an already existing message on to a new message
without having to first download the data and then upload it back to
the server.
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1. Introduction
The CATENATE extension to the Internet Message Access Protocol (IMAP)
[1] allows the client to create a message on the server which can
include the text of messages (or parts of messages) that already
exist on the server without having to FETCH them and APPEND them back
to the server. The CATENATE command works much like the APPEND
command except that, instead of a single message literal, the command
can take as arguments any combination of message literals (as
described in IMAP [1]) and message URLs (as described in the IMAP URL
Scheme [2] specification). The server takes all of the pieces and
catenates them into the output message.
There are some obvious uses for the CATENATE command. The motivating
use case for this command was to provide a way for a
resource-constrained client to compose a message for subsequent
submission which contains data that already exists in that client's
IMAP store. Because the client does not have to download and
re-upload potentially large message parts, bandwidth and processing
limitations do not have as much impact. In addition, since CATENATE
creates the message in the client's IMAP store, the command also
addresses the desire of the client to archive a copy of a sent
message without having to upload the message twice. (Mechanisms for
sending the message are outside of the scope of this document.)
CATENATE can also be used to copy parts of a message to another
mailbox for archival purposes while getting rid of undesired parts.
In environments where server storage is limited, a client could get
rid of large message parts by copying over only the necessary parts
and then deleting the original message. CATENATE could also be used
to add data to a message such as prepending message header fields or
including other data by making a copy of the original and catenating
the new data.
2. The CATENATE Capability
A server which supports this extension returns "CATENATE" as one of
the responses to the CAPABILITY command.
3. The CATENATE command
Arguments: mailbox name
message parameter list or NIL
one or more message parts to catenate, specified as:
message literal
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or
message (or message part) URL
Responses: no specific responses for this command
Result:
OK - catenate completed
NO - catenate error: can't append to that mailbox, error in flags
or date/time or message text, or can't fetch that data
BAD - command unknown or arguments invalid
The CATENATE command concatenates all of the message parts and
appends them as a new message to the end of the specified mailbox.
The message parameters defined in this document for the message
parameter list are a parenthesized flag list (indicated by "FLAGS")
and date/time string (indicated by "DATE") that are used just as they
are in the APPEND command, setting the flags and the internal date,
respectively. The subsequent command parameters specify the message
parts that are appended sequentially to the output message.
If a message literal is specified (indicated by the "TEXT"), the
octets following the count are appended just as they would be with
the APPEND command. If a message URL is specified (indicated by
"URL"), the octets of the body part pointed to by that URL are
appended, as if the literal returned in a FETCH BODY response were
put in place of the message part specifier. The CATENATE command
does not cause the \Seen flag to be set for any catenated body part.
Note: This document only describes the behavior of the CATENATE
command using a message URL (as defined by [2]) which refers to a
specific message or message part in the currently selected mailbox
on the current IMAP server. (Because of that, the CATENATE
command is valid in the selected state for purposes of this
specification.) Use of a URL that refers to anything other than a
message or message part from the currently selected mailbox on the
current IMAP server is outside of the scope of this document,
would require an extension to this specification, and a server
implementing only this specification would return NO to such a
request.
The client is responsible for making sure that the catenated message
is in the format of an RFC 2822 [3] message. This includes inserting
appropriate MIME [4] boundaries between body parts if necessary.
Responses behave just as the APPEND command. If the server
implements the IMAP UIDPLUS extension [5], it will also return an
APPENDUID response code in the tagged OK response. Two response
codes are provided in section 4 which can be used in the tagged NO
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response if the CATENATE command fails.
4. Response Codes
When a CATENATE command fails it may return a response code that
describes a reason for the failure.
4.1 BADURL Response
The BADURL response code is returned if the CATENATE fails to process
one of the specified URLs. Possible reasons for this are bad url
syntax, unrecognized URL schema, invalid message UID, invalid body
part. The BADURL response code contains the first URL specified as a
parameter to the CATENATE command that has caused the operation to
fail.
4.2 TOOBIG Response
The TOOBIG response code is returned if the resulting message will
exceed the 4Gb IMAP message limit. This might happen, for example,
if the client specifies 3 URLs for 2Gb messages. Note, that even if
the server doesn't return TOOBIG, it still has to be defensive
against misbehaving or malicious clients that try to construct a
message over 4Gb limit. The server may also wish to return the
TOOBIG response code if the resulting message exceeds the server
specific message size limit.
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5. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) [6] notation. Elements not defined here can be found in
the formal syntax of the ABNF [6] and IMAP [1] specifications. Note
that resp-text-code is extended from original IMAP [1] specification.
catenate = "CATENATE" SP mailbox SP parameters
1*(SP (text-literal / url))
parameters = ("(" parameter *(SP parameter) ")") / "NIL"
parameter = ("FLAGS" SP flag-list) / ("DATE" SP date-time)
text-literal = "TEXT" SP literal
url = "URL" SP astring
badurl_response_code = "BADURL" SP url-text
url-resp-text= 1*(%x01-09 / %x0B-0C / %x0E-5B / %x5D-FE)
; Any TEXT-CHAR except "]"
toobig_response_code = "TOOBIG"
resp-text-code =/ badurl_response_code / toobig_response_code
The astring in the definition of url and the url-text in the
definition of badurl_response_code contain an imapurl as defined by
[2].
6. Acknowledgments
Thanks to Alexey Melnikov for the Examples. Thanks to all of the
LEMONADE working group for their input.
7. Security Considerations
The CATENATE extension does not raise any security considerations
that are not present for the base protocol or in the use of IMAP
URLs, and these issues are discussed in the IMAP [1] and IMAP URL [2]
documents.
8. IANA Considerations
IMAP4 capabilities are registered by publishing a standards track or
IESG approved experimental RFC. The registry is currently located at
<http://www.iana.org/assignments/imap4-capabilities>. This document
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defines the CATENATE IMAP capability. IANA is requested to add this
capability to the registry.
Appendix A. Examples
Lines not starting with "C: " or "S: " are continuations of the
previous lines.
The original message in examples 1 and 2 below (UID = 20) has the
following structure:
multipart/mixed MIME message with two body parts:
1. text/plain
2. application/x-zip-compressed
Example 1: The following example demonstrates how a CATENATE client
can replace an attachment in a draft message, without the need to
download it to the client and upload it back.
C: A003 CATENATE Drafts FLAGS (\Seen \Draft $MDNSent)
URL "imap://imap.example.org/Drafts;UIDVALIDITY=385759045/;
UID=20;section=HEADER" TEXT {40}
S: + Ready for literal data
C: --------------030308070208000400050907
C: URL "imap://imap.example.org/Drafts;UIDVALIDITY=385759045/;
UID=20;section=1.1" TEXT {40}
S: + Ready for literal data
C: --------------030308070208000400050907
C: URL "imap://imap.example.org/Drafts;UIDVALIDITY=385759045/;
UID=30" {44}
S: + Ready for literal data
C: --------------030308070208000400050907--
C:
S: A003 OK CATENATE Completed
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Example 2: The following example demonstrates how CATENATE can be
used to replace edited text in a draft message, as well as header
fields for the top level message part (e.g. Subject has changed).
The previous version of the draft is marked as \Deleted. Note, that
the server also supports the UIDPLUS extension, so the APPENDUID
response code is returned in the successful OK response to the
CATENATE command.
C: A003 CATENATE Drafts FLAGS (\Seen \Draft $MDNSent) TEXT {738}
S: + Ready for literal data
C: Return-Path: <bar@example.org>
C: Received: from [127.0.0.2]
C: by rufus.example.org via TCP (internal) with ESMTPA;
C: Thu, 11 Nov 2004 16:57:07 +0000
C: Message-ID: <419399E1.6000505@example.org>
C: Date: Thu, 12 Nov 2004 16:57:05 +0000
C: From: Bob Ar <bar@example.org>
C: X-Accept-Language: en-us, en
C: MIME-Version: 1.0
C: To: foo@example.net
C: Subject: About our holiday trip
C: Content-Type: multipart/mixed;
C: boundary="------------030308070208000400050907"
C:
C: --------------030308070208000400050907
C: Content-Type: text/plain; charset=us-ascii; format=flowed
C: Content-Transfer-Encoding: 7bit
C:
C: Our travel agent has sent the updated schedule.
C:
C: Cheers,
C: Bob
C: --------------030308070208000400050907
C: URL "imap://imap.example.org/Drafts;UIDVALIDITY=385759045/;
UID=20;Section=1.2" TEXT {44}
S: + Ready for literal data
C: --------------030308070208000400050907--
C:
S: A003 OK [APPENDUID 385759045 45] CATENATE Completed
C: A004 UID STORE 20 +FLAGS.SILENT (\Deleted)
S: A004 OK STORE completed
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Example 3: The following example demonstrates how CATENATE can be
used to strip attachments. Below a PowerPoint attachment was
replaced by a small text part explaining that the attachment was
stripped.
C: A003 CATENATE Drafts FLAGS (\Seen \Draft $MDNSent)
URL "imap://imap.example.org/Drafts;UIDVALIDITY=385759045/;
UID=21;section=HEADER" TEXT {40}
S: + Ready for literal data
C: --------------030308070208000400050903
C: URL "imap://imap.example.org/Drafts;UIDVALIDITY=385759045/;
UID=21;section=1.1" TEXT {255}
S: + Ready for literal data
C: --------------030308070208000400050903
C: Content-type: text/plain; charset="us-ascii"
C: Content-transfer-encoding: 7bit
C:
C: This bodypart contained a Power Point presentation, that was
C: deleted upon your request.
C: --------------030308070208000400050903--
C:
S: A003 OK CATENATE Completed
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Example 4: The following example demonstrates a failed CATENATE
command. The server returns the BADURL response code to indicate
that one of the provided URLs is invalid. This example also
demonstrates how CATENATE can be used to construct a digest of
several messages.
C: A003 CATENATE Sent FLAGS (\Seen $MDNSent) TEXT {541}
S: + Ready for literal data
C: Return-Path: <foo@example.org>
C: Received: from [127.0.0.2]
C: by rufus.example.org via TCP (internal) with ESMTPA;
C: Thu, 11 Nov 2004 16:57:07 +0000
C: Message-ID: <419399E1.6000505@example.org>
C: Date: Thu, 21 Nov 2004 16:57:05 +0000
C: From: Farren Oo <foo@example.org>
C: X-Accept-Language: en-us, en
C: MIME-Version: 1.0
C: To: bar@example.org
C: Subject: Digest of the mailing list for today
C: Content-Type: multipart/digest;
C: boundary="------------030308070208000400050904"
C:
C: --------------030308070208000400050904
C: URL "imap://imap.example.org/INBOX;UIDVALIDITY=785799047/;
UID=11467" TEXT {40}
S: + Ready for literal data
C: --------------030308070208000400050904
C: URL "imap://imap.example.org/INBOX;UIDVALIDITY=785799047/;
UID=113330;section=1.5.9" TEXT {40}
S: + Ready for literal data
C: --------------030308070208000400050904
C: URL "imap://imap.example.org/INBOX;UIDVALIDITY=785799047/;
UID=11916" TEXT {44}
S: + Ready for literal data
C: --------------030308070208000400050904--
C:
S: A003 NO [BADURL "imap://imap.example.org/INBOX;UIDVALIDITY=785799047/
;UID=113330;section=1.5.9"] CATENATE has failed, one message expunged
9 Normative References
[1] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1",
RFC 3501, March 2003.
[2] Newman, C., "IMAP URL Scheme", RFC 2192, September 1997.
[3] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
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[4] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[5] Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June 1998.
[6] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
Author's Address
Peter W. Resnick
QUALCOMM Incorporated
5775 Morehouse Drive
San Diego, CA 92121-1714
US
Phone: +1 858 651 4478
EMail: presnick@qualcomm.com
URI: http://www.qualcomm.com/~presnick/
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