Subject: [imapext] IMAP REPLACE extension

From: Stu Brandt <[email-masked]>
Date: Wed, 29 Apr 2015 09:45:11 -0400

As promised, here's a draft of a REPLACE extension.

Since the most obvious question is going to be "Why REPLACE and not an 
option on APPEND?",  I'll answer it straight away...

First, APPEND is valid in the authenticated state. REPLACE requires the 
selected state. I chose not to generate a mixed state scenario for 
APPEND. Secondly, REPLACE is similar to MOVE in that it avoids a number 
of issues that come with a serialized non-atomic sequence attempting to 
perform a single operation. MOVE is not an option on COPY, so I chose to 
follow the same precedent.

Here's the writeup.

------------------------------------------------------------------------

Network Working Group                                          S. Brandt
Internet-Draft                                                       AOL
Intended status: Standards Track                          April 29, 2015
Expires: October 31, 2015

                          IMAP REPLACE Extension
                       draft-brandt-imap-replace-00

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
    replacment 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 http://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 October 31, 2015.

Copyright Notice

    Copyright (c) 2015 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
    (http://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.

Brandt                  Expires October 31, 2015                [Page 1]
Internet-Draft           IMAP REPLACE Extension               April 2015

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  . . . . . . . . . .   4
      3.5.  IMAP State Diagram Impacts  . . . . . . . . . . . . . . .   5
    4.  Interaction with other extensions . . . . . . . . . . . . . .   5
      4.1.  RFC 4314, ACL . . . . . . . . . . . . . . . . . . . . . .   6
      4.2.  RFC 4469, CATENATE  . . . . . . . . . . . . . . . . . . .   6
      4.3.  RFC 4315, UIDPLUS . . . . . . . . . . . . . . . . . . . .   6
      4.4.  RFC 6785, IMAP Events in Sieve  . . . . . . . . . . . . .   6
      4.5.  RFC 7162, CONDSTORE/QRESYNC . . . . . . . . . . . . . . .   6
    5.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   6
    6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
    7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
    8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
    9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
      9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
      9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
    Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

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 [RFC2119].

    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.

    Using commands from the base IMAP specification, replacement of a
    message involves 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

Brandt                  Expires October 31, 2015                [Page 2]
Internet-Draft           IMAP REPLACE Extension               April 2015

    version be lost.  The REPLACE command is intended to provide an
    atomic alternative to the existing non-atomic sequence.

    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 an atomic encapsulation
    of STORE + UID EXPUNGE + APPEND.  Servers that support the REPLACE
    command MUST guarantee atomicity; either the specified message is
    completely replaced by the supplied message, or the specified message
    is left unmodified and no part of the supplied message data is
    stored.  Servers supporting REPLACE also 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

    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

Brandt                  Expires October 31, 2015                [Page 3]
Internet-Draft           IMAP REPLACE Extension               April 2015

    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 <[email-masked]>
      C: Subject: happy new year !!
      C: To: [email-masked]
      C: Message-Id: <[email-masked]>
      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: * 4 EXPUNGE
      S: A003 OK [APPENDUID 1 2000] 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.

    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 <[email-masked]>
      C: Subject: happy new year !!
      C: To: [email-masked]
      C: Message-Id: <[email-masked]>
      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: * 4 EXPUNGE
      S: A004 OK [APPENDUID 1 2001] 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

Brandt                  Expires October 31, 2015                [Page 4]
Internet-Draft           IMAP REPLACE Extension               April 2015

    selected mailbox.  These operations will appear to the client as a
    single action.  This has the same effect as the following sequence:

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

    In the cited sequence, the original message is removed first to avoid
    possible quota implications of APPENDing new data first.
    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 produced do not occur, and the response codes are
    different.  In particular, the response codes for EXPUNGE and APPEND
    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 or
    modified state; any untagged EXPUNGE response MUST NOT be sent until
    all actions are successfully completed.  Additionally, the target
    mailbox MUST NOT be modified until all actions are successfully
    completed.

    Because of the similarity of REPLACE to APPEND, extensions that
    affect APPEND affect REPLACE in the same way.  Response codes such
    TRYCREATE (see [RFC3501] Section 6.3.11), as well as 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 command MUST only be valid in the selected state.  This
    difference from APPEND is necessary since REPLACE operates on message
    sequence numbers.

4.  Interaction with other extensions

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

Brandt                  Expires October 31, 2015                [Page 5]
Internet-Draft           IMAP REPLACE Extension               April 2015

4.1.  RFC 4314, ACL

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

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.

4.3.  RFC 4315, UIDPLUS

    Servers supporting both REPLACE and UIDPLUS [RFC4315] MUST send
    APPENDUID in response to a UID REPLACE command.  The only exceptions
    to this are the ones outlined for APPEND in RFC4315 section 3.

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.

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".

    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.

Brandt                  Expires October 31, 2015                [Page 6]
Internet-Draft           IMAP REPLACE Extension               April 2015

    capability     =/ "REPLACE"

    command-select =/ replace
    replace        = "REPLACE" SP seq-number SP mailbox append-message
    uid            = "UID" SP (copy / fetch/ search / store / move /
                               replace)

6.  Security Considerations

    This document is believed to add no security problems beyond those
    that may already exist with the base IMAP specificaiton.

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

9.  References

9.1.  Normative References

    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

    [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
               4rev1", RFC 3501, March 2003.

    [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
               RFC 4314, December 2005.

    [RFC4315]  Crispin, M., "Internet Message Access Protocol (IMAP) -
               UIDPLUS extension", RFC 4315, December 2005.

    [RFC4466]  Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
               ABNF", RFC 4466, April 2006.

    [RFC4469]  Resnick, P., "Internet Message Access Protocol (IMAP)
               CATENATE Extension", RFC 4469, April 2006.

    [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
               Specifications: ABNF", STD 68, RFC 5234, January 2008.

    [RFC6785]  Leiba, B., "Support for Internet Message Access Protocol
               (IMAP) Events in Sieve", RFC 6785, November 2012.

Brandt                  Expires October 31, 2015                [Page 7]
Internet-Draft           IMAP REPLACE Extension               April 2015

    [RFC7162]  Melnikov, A. and D. Cridland, "IMAP Extensions: Quick Flag
               Changes Resynchronization (CONDSTORE) and Quick Mailbox
               Resynchronization (QRESYNC)", RFC 7162, May 2014.

9.2.  Informative References

    [RFC6851]  Gulbrandsen, A. and N. Freed, "Internet Message Access
               Protocol (IMAP) - MOVE Extension", RFC 6851, January 2013.

Author's Address

    Stuart Brandt
    AOL
    43623 Preddy Ct
    Ashburn, VA  20147
    USA

    Email: [email-masked]

Brandt                  Expires October 31, 2015                [Page 8]

---

From: Alexey Melnikov <[email-masked]>
Date: Wed, 29 Apr 2015 17:09:10 +0100

Hi Stu,
This is a very good start, thank you for doing this!

On 29/04/2015 14:45, Stu Brandt wrote:
> First, APPEND is valid in the authenticated state. REPLACE requires 
> the selected state. I chose not to generate a mixed state scenario for 
> APPEND. Secondly, REPLACE is similar to MOVE in that it avoids a 
> number of issues that come with a serialized non-atomic sequence 
> attempting to perform a single operation. MOVE is not an option on 
> COPY, so I chose to follow the same precedent.
>
> Here's the writeup.
  [snip]
> 3.2. REPLACE Command
  [snip]
>      S: A003 OK [APPENDUID 1 2000] Replace completed
I think an untagged APPENDUID should be issued before expunge, so that 
the client can safely correlate the old and the new message, without
>      S: A004 OK [APPENDUID 1 2001] Replace completed
As above.

>    the ACL rights required for UID STORE, UID EXPUNGE,
Just to make this clearer, I would add "in the current mailbox"
> and APPEND.
"In the target mailbox".

Best Regards,
Alexey