Subject: [imapext] IMAP Replace update

From: Stu Brandt <[email-masked]>
Date: Mon, 20 Jul 2015 12:57:17 +0200

Based on discussion at IETF93, draft-brandt-imap-replace-01 has been 
submitted. The primary changes are a relaxing of the atomicity 
requirement and more information on the combination of REPLACE with 
CATENATE.  Feedback is certainly welcomed.

Here it is:

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

Network Working Group                                          S. Brandt
Internet-Draft                                                       AOL
Intended status: Standards Track                           July 20, 2015
Expires: January 21, 2016

                          IMAP REPLACE Extension
                       draft-brandt-imap-replace-01

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
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    This Internet-Draft will expire on January 21, 2016.

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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  . . . . . . . . . .   4
      3.5.  IMAP State Diagram Impacts  . . . . . . . . . . . . . . .   5
    4.  Interaction with other extensions . . . . . . . . . . . . . .   5
      4.1.  RFC 4314, ACL . . . . . . . . . . . . . . . . . . . . . .   5
      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
    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
    Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

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.

    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

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    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.  In
    handling a REPLACE command, 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.  Finally, the replaced and replacing messages SHOULD
    NOT be present in the mailbox at the same time.

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

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    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

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    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 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 state;
    any untagged EXPUNGE response MUST NOT be sent 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 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.

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.

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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 <[email-masked]>
      C: Message-ID: <[email-masked]>
      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 <[email-masked]>
      C: Subject: My view of the fireworks
      C:  URL "/Drafts/;UID=3002")
      S: * 5 EXISTS
      S: * 4 EXPUNGE
      S: A011 OK [APPENDUID 1 3003] 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.

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.

    capability     =/ "REPLACE"

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

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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

    The author would like to thank the participants of IMAPEXT with
    particular thanks to Arnt Gulbrandsen, Alexey Melkinov, and Chris
    Newman 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,
               <http://www.rfc-editor.org/info/rfc2119>.

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

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

    [RFC4315]  Crispin, M., "Internet Message Access Protocol (IMAP) -
               UIDPLUS extension", RFC 4315, DOI 10.17487/RFC4315,
               December 2005, <http://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,
               <http://www.rfc-editor.org/info/rfc4466>.

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

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    [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
               Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
               RFC5234, January 2008,
               <http://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, <http://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,
               <http://www.rfc-editor.org/info/rfc7162>.

9.2.  Informative References

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

Author's Address

    Stuart Brandt
    AOL
    43623 Preddy Ct
    Ashburn, VA  20147
    USA

    Email: [email-masked]

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---

From: Pete Maclean <[email-masked]>
Date: Wed, 22 Jul 2015 15:12:21 -0400

Stu,

Earlier I expressed some concerns about the design of REPLACE which, 
I came to realize, stemmed from a misunderstanding on my part as to 
how the command is intended to work.  Thank you for your kind and 
clarifying responses to those.

Reading this fresh document I find just one thing to comment on, the 
statement:  "Finally, the replaced and replacing messages SHOULD NOT 
be present in the mailbox at the same time."   I think this could be 
confusing because two mailboxes can be involved, as in the case you 
suggested of a message in a drafts folder being replaced by one in a 
sent folder.  And surely the admonition should apply equally well in 
such a case.  So maybe it would be better to say something 
like:  "Finally, the replaced and replacing messages SHOULD NOT both 
be present in the mailbox or mailboxes at the same time."

Pete Maclean

---

From: Stu Brandt <[email-masked]>
Date: Wed, 22 Jul 2015 21:55:28 +0200

Pete -

Thanks for catching that. I agree and have marked the correction for the 
next revision.

Stuart

On 7/22/15 9:12 PM, Pete Maclean wrote:
> Stu,
>
> Earlier I expressed some concerns about the design of REPLACE which, I 
> came to realize, stemmed from a misunderstanding on my part as to how 
> the command is intended to work.  Thank you for your kind and 
> such a case.  So maybe it would be better to say something like:  
> "Finally, the replaced and replacing messages SHOULD NOT both be 
> present in the mailbox or mailboxes at the same time."
>
> Pete Maclean
>
> _______________________________________________
> imapext mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/imapext