



Network Working Group                                          S. Brandt
Internet-Draft                                                   Verizon
Intended status: Standards Track                        October 25, 2018
Expires: April 28, 2019


                         IMAP REPLACE Extension
                    draft-ietf-extra-imap-replace-03

Abstract

   This document defines an IMAP extension which can be used to replace
   an existing message in a message store with a new message.  Message
   replacement is a common operation for clients that automatically save
   drafts or notes as a user composes them.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 28, 2019.

Copyright Notice

   Copyright (c) 2018 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
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   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.




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Table of Contents

   1.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  REPLACE and UID REPLACE . . . . . . . . . . . . . . . . . . .   3
     3.1.  Advertising Support for REPLACE . . . . . . . . . . . . .   3
     3.2.  REPLACE Command . . . . . . . . . . . . . . . . . . . . .   3
     3.3.  UID REPLACE Command . . . . . . . . . . . . . . . . . . .   4
     3.4.  Semantics of REPLACE and UID REPLACE  . . . . . . . . . .   5
     3.5.  IMAP State Diagram Impacts  . . . . . . . . . . . . . . .   6
   4.  Interaction with other extensions . . . . . . . . . . . . . .   6
     4.1.  RFC 4314, ACL . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  RFC 4469, CATENATE  . . . . . . . . . . . . . . . . . . .   6
     4.3.  RFC 4315, UIDPLUS . . . . . . . . . . . . . . . . . . . .   8
     4.4.  RFC 6785, IMAP Events in Sieve  . . . . . . . . . . . . .   8
     4.5.  RFC 7162, CONDSTORE/QRESYNC . . . . . . . . . . . . . . .   8
     4.6.  RFC 8474, OBJECTID  . . . . . . . . . . . . . . . . . . .   8
     4.7.  RFC 3502, MULTIAPPEND . . . . . . . . . . . . . . . . . .   8
   5.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
     9.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [1] [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Formal syntax is defined by [RFC5234].

   Example lines prefaced by "C:" are sent by the client and ones
   prefaced by "S:" by the server.

2.  Overview

   This document defines an IMAP [RFC3501] extension to facilitate
   replacing an existing message with a new one.  This is accomplished
   by defining a new REPLACE command and extending the UID command to
   allow UID REPLACE.




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   Since there is no replace function in the base IMAP specification,
   clients have instead had to use a combination of three separate
   commands issued in serial fashion; APPEND, STORE, EXPUNGE.
   Pipelining of these three commands is not recommended since failure
   of any individual command should prevent subsequent commands from
   being executed lest the original message version be lost.

   Because of the non-atomic nature of the existing sequence,
   interruptions can leave messages in intermediate states which can be
   seen and acted upon by other clients.  Such interruptions can also
   strand older revisions of messages, thereby forcing the user to
   manually clean up multiple revisions of the same message in order to
   avoid wasteful quota consumption.  Additionally, the existing
   sequence can fail on APPEND due to an over-quota condition even
   though the subsequent STORE/EXPUNGE would free up enough space for
   the newly revised message.  And finally, server efficiencies may be
   possible with a single logical message replacement operation as
   compared to the existing APPEND/STORE/EXPUNGE sequence.

   In its simplest form, the REPLACE command is a single-command
   encapsulation of APPEND, STORE +flags \DELETED and UID EXPUNGE for a
   message, except that it avoids any of the quota implications or
   intermediate states associated with the 3 command sequence.  Server
   developers are encouraged to implement REPLACE as an atomic operation
   to simplify error handling, minimize operational concerns, and reduce
   potential security problems.  For systems where this is not possible,
   communication with the requesting client must ensure no confusion of
   message store state.  A server MUST NOT generate a response code for
   the STORE +flags \DELETED portion of the sequence.  Additionally,
   servers supporting the REPLACE command MUST NOT infer any inheritance
   of content, flags, or annotations from the message being replaced.

3.  REPLACE and UID REPLACE

3.1.  Advertising Support for REPLACE

   Servers that implement the REPLACE extension will return "REPLACE" as
   one of the supported capabilities in the CAPABILITY command response.

3.2.  REPLACE Command











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   Arguments:  message sequence number
               mailbox name
               OPTIONAL flag parenthesized list
               OPTIONAL date/time string
               message literal

   Responses: no specific responses for this command

   Result:     OK - replace completed
               NO - replace error; can't remove specified message
                    or can't add new message content
               BAD - command unknown or arguments invalid

   Example:
     C: A003 REPLACE 4 Drafts (\Seen \Draft) {312}
     S: + Ready for literal data
     C: Date: Thu, 1 Jan 2015 00:05:00 -0500 (EST)
     C: From: Fritz Schmidt <fritz.ze@example.org>
     C: Subject: happy new year !!
     C: To: miss.mitzy@example.org
     C: Message-Id: <B238822388-0100000@example.org>
     C: MIME-Version: 1.0
     C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
     C:
     C: Just saw the best fireworks show. Wish you were here.
     C:
     S: * OK [APPENDUID 1 2000] Replacement Message ready
     S: * 5 EXISTS
     S: * 4 EXPUNGE
     S: A003 OK Replace completed

3.3.  UID REPLACE Command

   This extends the first form of the UID command (see [RFC3501]
   Section 6.4.8) to add the REPLACE command defined above as a valid
   argument.  This form of REPLACE uses a UID rather than sequence
   number as its first parameter.














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   Example:
     C: A004 UID REPLACE 2000 Drafts (\Seen \Draft) {350}
     S: + Ready for literal data
     C: Date: Thu, 1 Jan 2015 00:06:00 -0500 (EST)
     C: From: Fritz Schmidt <fritz.ze@example.org>
     C: Subject: happy new year !!
     C: To: miss.mitzy@example.org
     C: Message-Id: <B238822389-0100000@example.org>
     C: MIME-Version: 1.0
     C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
     C:
     C: Just saw the best fireworks show. Wish you were here.
     C: Hopefully next year you can join us.
     C:
     S: * OK [APPENDUID 1 2001] Replacement Message ready
     S: * 5 EXISTS
     S: * 4 EXPUNGE
     S: A004 OK Replace completed

3.4.  Semantics of REPLACE and UID REPLACE

   The REPLACE and UID REPLACE commands take five arguments: a message
   identifier, a named mailbox, an optional parenthesized flag list, an
   optional message date/time string, and a message literal.  The
   message literal will be appended to the named mailbox, and the
   message specified by the message identifier will be removed from the
   selected mailbox.  These operations will appear to the client as a
   single action.  This has the same effect as the following sequence:

      1. APPEND
      2. [UID] STORE +FLAGS.SILENT \DELETED
      3. UID EXPUNGE

   In the cited sequence, the quota implications of the APPEND are
   evaluated within the context of the pending EXPUNGE so that only the
   net quota consumption is considered.  Additionally, the EXPUNGE
   portion of the sequence only applies to the specified message, not
   all messages flagged as \Deleted.

   Although the effect of REPLACE is identical to the steps above, the
   semantics are not identical; similar to MOVE [RFC6851], the
   intermediate states do not occur, and the response codes are
   different.  In particular, the response codes for APPEND and EXPUNGE
   will be returned while those for the STORE operation MUST NOT be
   generated.

   When an error occurs while processing REPLACE or UID REPLACE, the
   server MUST NOT leave the selected mailbox in an inconsistent state;



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   any untagged EXPUNGE response MUST NOT be sent until all actions are
   successfully completed.

   While it may be common for the named mailbox argument to match the
   selected mailbox for the common use case of replacing a draft, the
   REPLACE extension intentionally does not require the two to be the
   same.  As an example, it's possible to use the REPLACE command to
   replace a message in the \Drafts special-use mailbox (see [RFC6154])
   with a message in the \Sent special-use mailbox following message
   submission.

   Because of the similarity of REPLACE to APPEND, extensions that
   affect APPEND affect REPLACE in the same way.  Response codes such as
   TRYCREATE (see [RFC3501] Section 6.3.11), along with those defined by
   extensions, are sent as appropriate.  See Section 4 for more
   information about how REPLACE interacts with other IMAP extensions.

3.5.  IMAP State Diagram Impacts

   Unlike the APPEND command, which is valid in the authenticated state,
   the REPLACE and UID REPLACE commands MUST only be valid in the
   selected state.  This difference from APPEND is necessary since
   REPLACE operates on message sequence numbers.  Additionally, the
   REPLACE extension intentionally follows the convention for UID
   commands found in [RFC3501] section 6.4.8 in that the UID variant of
   the command does not support use from the authenticated state.

4.  Interaction with other extensions

   This section describes how REPLACE interacts with some other IMAP
   extensions.

4.1.  RFC 4314, ACL

   The ACL rights [RFC4314] required for UID REPLACE are the union of
   the ACL rights required for UID STORE and UID EXPUNGE in the current
   mailbox, and APPEND in the target mailbox.

4.2.  RFC 4469, CATENATE

   Servers supporting both REPLACE and CATENATE [RFC4469] MUST support
   the addtional append-data and resp-text-code elements defined the
   Formal Syntax section of RFC4469 in conjunction with the REPLACE
   command.  When combined with CATENATE, REPLACE can become a quite
   efficient way for message manipulation.






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   Example:

     User composes message and attaches photo
     ----------------------------------------
     C: A010 APPEND Drafts (\Seen \Draft) {1201534}
     S: + Ready for literal data
     C: Date: Thu, 1 Jan 2015 00:10:00 -0500 (EST)
     C: From: Fritz Schmidt <fritz.ze@example.org>
     C: Message-ID: <B238822388-0100003@example.org>
     C: MIME-Version: 1.0
     C: Content-Type: multipart/mixed;
     C:         boundary="------------030305060306060609050804"
     C:
     C: --------------030305060306060609050804
     C: Content-Type: text/plain; charset=utf-8; format=flowed
     C: Content-Transfer-Encoding: 7bit
     C:
     C: Here is picture from the fireworks
     C:
     C: Yours...
     C: Fritz
     C:
     C: --------------030305060306060609050804
     C: Content-Type: image/jpeg;
     C:         name="Fireworks.jpg"
     C: Content-Transfer-Encoding: base64
     C: Content-Disposition: attachment;
     C:         filename="Fireworks.jpg"
     C:
       <large base64 encoded part goes here>
     C:
     C: --------------030305060306060609050804--
     S: A010 OK [APPENDUID 1 3002] APPEND complete

     User completes message with To: and Subject: fields
     ---------------------------------------------------
     C: A011 UID REPLACE 3002 Drafts CATENATE (TEXT {71}
     S: + Ready for literal data
     C: To: Mitzy <miss.mitzy@example.org>
     C: Subject: My view of the fireworks
     C:  URL "/Drafts/;UID=3002")
     S: * OK [APPENDUID 1 3003] Replacement Message ready
     S: * 5 EXISTS
     S: * 4 EXPUNGE
     S: A011 OK REPLACE completed






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4.3.  RFC 4315, UIDPLUS

   Servers supporting both REPLACE and UIDPLUS [RFC4315] SHOULD send
   APPENDUID in response to a UID REPLACE command.  For additional
   information see section 3 of RFC4315.  Servers implementing REPLACE
   and UIDPLUS are also advised to send the APPENDUID response code in
   an untagged OK before sending the EXPUNGE or replaced responses.
   (Sending the APPENDUID in the tagged OK as described in the UIDPLUS
   specification means that the client first receives an EXPUNGE for a
   message and afterwards APPENDUID for the new message.  It can be
   unnecessarily difficult to process that sequence usefully.)

4.4.  RFC 6785, IMAP Events in Sieve

   REPLACE applies to IMAP events in Sieve [RFC6785] in the same way
   that APPEND does.  Therefore, REPLACE can cause a Sieve script to be
   invoked with the imap.cause set to "APPEND".  Because the
   intermediate state of STORE +FLAGS.SILENT \DELETED is not exposed by
   REPLACE, no action will be taken that results in a imap.cause of
   FLAG.

4.5.  RFC 7162, CONDSTORE/QRESYNC

   Servers implementing both REPLACE and CONDSTORE/QRESYNC [RFC7162]
   MUST treat the message being replaced as if it were being removed
   with a UID EXPUNGE command.  Sections 3.2.9 and 3.2.10 of RFC 7162
   are particularly relevant for this condition.

4.6.  RFC 8474, OBJECTID

   Servers implementing both REPLACE and OBJECTID [RFC8474] MUST return
   different EMAILIDs for both the replaced and replacing messages.  The
   only exception to this is the case outlined in OBJECTID section 5.1
   when the server detects that both messages' immutable content are
   identical.

4.7.  RFC 3502, MULTIAPPEND

   The REPLACE extension has no interaction with MULTIAPPEND [RFC3502].
   This document explicitly does not outline a method for replacing
   multiple messsages concurrently.

5.  Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form (ABNF) notation as specified in [RFC5234].  [RFC3501] defines
   the non-terminals "capability","command-select", "mailbox", and "seq-
   number".  [RFC4466] defines the non-terminal "append-message".



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   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.

   capability     =/ "REPLACE"

   command-select =/ replace
   replace        = "REPLACE" SP seq-number SP mailbox append-message
   uid            =/ replace


6.  Security Considerations

   This document is believed to add no security problems beyond those
   that may already exist with the base IMAP specification.  The REPLACE
   command may actually prevent some potential security problems because
   it avoids intermediate message states that could possibly be
   exploited by an attacker.

7.  IANA Considerations

   The IANA is requested to add REPLACE to the "IMAP 4 Capabilities"
   registry, http://www.iana.org/assignments/imap4-capabilities.

8.  Acknowledgements

   The author would like to thank the participants of IMAPEXT with
   particular thanks to Arnt Gulbrandsen, Alexey Melkinov, Chris Newman,
   and Bron Gondwana for their specific contributions.

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>.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
              <https://www.rfc-editor.org/info/rfc3501>.

   [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
              RFC 4314, DOI 10.17487/RFC4314, December 2005,
              <https://www.rfc-editor.org/info/rfc4314>.




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   [RFC4315]  Crispin, M., "Internet Message Access Protocol (IMAP) -
              UIDPLUS extension", RFC 4315, DOI 10.17487/RFC4315,
              December 2005, <https://www.rfc-editor.org/info/rfc4315>.

   [RFC4466]  Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
              ABNF", RFC 4466, DOI 10.17487/RFC4466, April 2006,
              <https://www.rfc-editor.org/info/rfc4466>.

   [RFC4469]  Resnick, P., "Internet Message Access Protocol (IMAP)
              CATENATE Extension", RFC 4469, DOI 10.17487/RFC4469, April
              2006, <https://www.rfc-editor.org/info/rfc4469>.

   [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>.

   [RFC6785]  Leiba, B., "Support for Internet Message Access Protocol
              (IMAP) Events in Sieve", RFC 6785, DOI 10.17487/RFC6785,
              November 2012, <https://www.rfc-editor.org/info/rfc6785>.

   [RFC7162]  Melnikov, A. and D. Cridland, "IMAP Extensions: Quick Flag
              Changes Resynchronization (CONDSTORE) and Quick Mailbox
              Resynchronization (QRESYNC)", RFC 7162,
              DOI 10.17487/RFC7162, May 2014,
              <https://www.rfc-editor.org/info/rfc7162>.

   [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>.

   [RFC8474]  Gondwana, B., Ed., "IMAP Extension for Object
              Identifiers", RFC 8474, DOI 10.17487/RFC8474, September
              2018, <https://www.rfc-editor.org/info/rfc8474>.

9.2.  Informative References

   [RFC3502]  Crispin, M., "Internet Message Access Protocol (IMAP) -
              MULTIAPPEND Extension", RFC 3502, DOI 10.17487/RFC3502,
              March 2003, <https://www.rfc-editor.org/info/rfc3502>.

   [RFC6154]  Leiba, B. and J. Nicolson, "IMAP LIST Extension for
              Special-Use Mailboxes", RFC 6154, DOI 10.17487/RFC6154,
              March 2011, <https://www.rfc-editor.org/info/rfc6154>.







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   [RFC6851]  Gulbrandsen, A. and N. Freed, Ed., "Internet Message
              Access Protocol (IMAP) - MOVE Extension", RFC 6851,
              DOI 10.17487/RFC6851, January 2013,
              <https://www.rfc-editor.org/info/rfc6851>.

9.3.  URIs

   [1] https://tools.ietf.org/html/bcp14

Author's Address

   Stuart Brandt
   Verizon
   22001 Loudoun County Parkway
   Ashburn, VA  20147
   USA

   Email: stujenerin@aol.com

































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