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IMAP4 Response Code for Command Progress Notifications.

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9585.
Author Marco Bettini
Last updated 2024-05-31 (Latest revision 2024-04-04)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Associated WG milestone
Dec 2023
Document shepherd Kenneth Murchison
Shepherd write-up Show Last changed 2023-11-29
IESG IESG state Became RFC 9585 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Murray Kucherawy
Send notices to,
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
IANA expert review state Expert Reviews OK
EXTRA                                                         M. Bettini
Internet-Draft                                           Open-Xchange Oy
Intended status: Standards Track                            4 April 2024
Expires: 6 October 2024

        IMAP4 Response Code for Command Progress Notifications.


   This document defines a new IMAP untagged response code,
   "INPROGRESS", that provides structured numeric progress status
   indication for long-running commands.

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

   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 6 October 2024.

Copyright Notice

   Copyright (c) 2024 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 (
   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  CAPABILITY Identification . . . . . . . . . . . . . . . . . .   3
   4.  The "INPROGRESS" Response Code  . . . . . . . . . . . . . . .   3
   5.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Internet Message Access Protocol (IMAP) [RFC9051] commands can
   require a considerable amount of time to be completed by the server.
   In these cases, the client has no information about the progress of
   the commands.  It is already possible to expose updates with a
   generic untagged response, like "* OK Still on it, 57% done";
   however, this does not provide a standard way to communicate with the
   client and allow it to inform the user of the progress of the long-
   running actions.

   This document extends the Internet Message Access Protocol (IMAP)
   [RFC9051] with:

   *  a new "INPROGRESS" response code [RFC5530].  The new response code
      provides consistent means for a client to receive a progress
      update notifications on command completion status.

   *  a new "INPROGRESS" capability [RFC9051].  The new capability
      informs the client that the server emits progress update
      notifications, via the "INPROGRESS" response code

2.  Conventions Used in This Document

   "Conventions" are basic principles or procedures.  Document
   conventions are noted in this section.

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

   The word "can" (not "may") is used to refer to a possible
   circumstance or situation, as opposed to an optional facility of the

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   Conventions for notations are as in [RFC9051] and [RFC5530].

   In examples, "C:" and "S:" indicate lines sent by the client and
   server, respectively.  Note that each line includes the terminating

3.  CAPABILITY Identification

   IMAP servers that support this extension MUST include "INPROGRESS" in
   the response list to the CAPABILITY command.

4.  The "INPROGRESS" Response Code

   The server MAY send the "INPROGRESS" Response Code to notify the
   client about the progress of the commands in execution, or simply to
   prevent the client from timing out and terminating the connection.
   The notifications MAY be sent for any IMAP command.  If the server
   elects to send notifications, it is RECOMMENDED that these are sent
   every 10-15 seconds.

   The response code is meant to appear embedded inside an untagged OK
   reply.  The response code MUST NOT appear in a tagged response (the
   command has completed and further progress notifications make no

   The response code MAY embed a list of details, composed in order of:

   1.  CMD-TAG: the cmd-tag [RFC9051] that originated the long-running
       command.  If the tag is not available, or if it contains the "]"
       character, it MUST be set to NIL.  This still produces a usable
       notification, unless multiple commands are in flight
       simultaneously.  A client can ensure reception of notifications
       with cmd-tag(s) by simply refraining from the use of character
       "]" in the originating command tags.

   2.  PROGRESS: a number indicating the number of items processed so
       far.  The number MUST be non-negative and SHOULD be monotonically
       increasing.  If the PROGRESS is not available, both PROGRESS and
       GOAL MUST be set to NIL.

   3.  GOAL: a number indicating the total number of items to be
       processed.  The number MUST be positive and it SHOULD NOT change
       between successive notifications for the same command (i.e. for
       the same cmd-tag).  This is the number that PROGRESS is expected
       to reach after the completion of the command and therefore it
       MUST be strictly greater than PROGRESS.  If the GOAL is not
       known, it MUST be set to NIL.

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   If the response code does not embed a list of details, all details
   are to be interpreted as NIL.

   The server can provide the progress notification details with
   different degrees of completeness:

   - bare keepalive
     * OK [INPROGRESS] Hang in there..
   - keepalive with an indication of the command tag
     * OK [INPROGRESS ("tag" NIL NIL)] Hang in there..
   - progress indication with unknown GOAL
     * OK [INPROGRESS ("tag" 175 NIL)] Processed 175 items so far
   - progress indication with the indication of the GOAL
     * OK [INPROGRESS ("tag" 175 1000)] Processed 17% of the items


     C: A001 search text "this will be slow"
       [13 seconds later]
     S: * OK [INPROGRESS ("A001" 454 1000)] Processed 45% of the items
       [14 seconds later]
     S: * OK [INPROGRESS ("A001" 999 1000)] Processed 99% of the items
       [5 seconds later]
     S: * SEARCH 447 735
     S: A001 OK Search completed (23.387 + 0.004 + 0.017 secs).

     C: A003 COPY 2000:4000 Meeting-Minutes
       [12 seconds later]
     S: * OK [INPROGRESS ("A003" 175 2001)] Still working on this...
       [14 seconds later]
     S: * OK [INPROGRESS ("A003" 440 2001)] Still working on this...
       [13 seconds later]
     S: * OK [INPROGRESS ("A003" 987 2001)] Still working on this...
       [14 seconds later]
     S: * OK [INPROGRESS ("A003" 1388 2001)] Still working on this...
       [14 seconds later]
     S: * OK [INPROGRESS ("A003" 1876 2001)] Still working on this...
       [9 seconds later]
     S: A003 OK Copy completed

   PROGRESS and GOAL SHOULD be counts of the kind of item being
   processed - in most cases, messages counts.  If that is not possible,
   the counts SHOULD be percentages, with goal set to 100 and progress
   varying between 0 and 99.

   The server SHOULD NOT send a progress notification where PROGRESS
   equals GOAL, as that would mean the command is completed.  In that
   case, the proper tagged response should be emitted instead.

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   If the command completes before the first server notification
   deadline, there will be no notifications at all.  The client MUST
   assume PROGRESS to be 0 and GOAL to be unknown until the server
   issues a notification for the command.

   While the server SHOULD keep GOAL constant and PROGRESS monotonically
   increasing, there are circumstances where this might not be possible.
   The client MUST be prepared to handle cases where the server cannot
   keep GOAL constant and/or PROGRESS monotonically increasing.  When
   the GOAL changes or the PROGRESS goes backward, the RECOMMENDED
   interpretation is that the previous GOAL has been reached, but the
   server discovered that further (long-running) work is required
   (either with known or unknown new GOAL),

   The client MAY disregard progress notifications entirely or process
   them only in relation to specific commands.  If a User Interface is
   involved, it is the client's duty to decide which of these commands
   are blocking on the user experience, since this may differ based on
   implementation details.

   Also, the client MUST NOT consider the values to be authoritative for
   any other use than evaluating the progress of the commands.  E.g.:
   the client must not use the GOAL field in place of the proper output
   of a SEARCH command to know the number of messages in a folder.

5.  Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form (ABNF) [RFC5234] notation.  Elements not defined here can be
   found in the formal syntax of the ABNF [RFC5234] and IMAP [RFC9051]

   Except as noted otherwise, all alphabetic characters are case-
   insensitive.  The use of uppercase or lowercase characters to define
   token strings are for editorial clarity only.  Implementations MUST
   accept these strings in a case-insensitive fashion.

   inprogress-tag              = quoted / nil
   inprogress-state-unknown    = nil    SP nil
   inprogress-state-counting   = number SP nil
   inprogress-state-known-goal = number SP nz-number

   inprogress-state = inprogress-state-unknown
                    / inprogress-state-counting
                    / inprogress-state-known-goal

   resp-text-code =/ "INPROGRESS" [ SP "(" inprogress-tag SP
                                           inprogress-state ")" ]

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6.  Security Considerations

   The details of the response code are not expected to disclose any
   information that isn't currently available from the command output.
   The progress details could be obtained anyway by sending a series of
   commands with different workloads - either by constructing data sets
   or searching in the appropriate way.

   The client must protect itself against data sent by a malicious
   server.  Specifically, the client should guard against values that
   can cause arithmetic exceptions, like GOAL = 0, GOAL/VALUE < 0, GOAL/
   VALUE >= 2^32 (these are not possible within a correct implementation
   of the ABNF syntax above), and VALUE > GOAL.  In these cases, the
   notification MUST be disregarded.

7.  IANA Considerations

   IANA is requested to add "INPROGRESS" to the "IMAP Response Codes"
   registry located at <
   codes>, with a reference to this document.

   IANA is requested to add "INPROGRESS" to the "IMAP Capabilities"
   registry located at <
   capabilities>, with a reference to this document.

8.  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,

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,

   [RFC5530]  Gulbrandsen, A., "IMAP Response Codes", RFC 5530,
              DOI 10.17487/RFC5530, May 2009,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

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   [RFC9051]  Melnikov, A., Ed. and B. Leiba, Ed., "Internet Message
              Access Protocol (IMAP) - Version 4rev2", RFC 9051,
              DOI 10.17487/RFC9051, August 2021,

Author's Address

   Marco Bettini
   Open-Xchange Oy
   Lars Sonckin kaari 10
   FI-02600 Espoo

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