Internet DRAFT - draft-bettini-imap-inprogress
draft-bettini-imap-inprogress
Network Working Group M. Bettini
Internet-Draft Open-Xchange Oy
Intended status: Standards Track 28 April 2023
Expires: 30 October 2023
IMAP4 Response Code for Command Progress Notifications.
draft-bettini-imap-inprogress-01
Abstract
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.
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This Internet-Draft will expire on 30 October 2023.
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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 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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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
protocol.
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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
CRLF.
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 (as
that implies the command has completed and that no further progress
notifications are needed).
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 "]"
characters, it MUST be replaced by NIL
2. PROGRESS: a number indicating the number of items processed so
far. If the PROGRESS is not available, both PROGRESS and GOAL
MUST be replaced by NIL.
3. GOAL: a number indicating the total number of items to be
processed. This is the number that PROGRESS is expected to reach
at the completion of the command. If the GOAL is not known, it
MUST be replaced by NIL.
The server can provide the progress notifications details with
different degrees of completeness:
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- bare keepalive
* OK [INPROGRESS] Hang in there..
- keepalive with 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
Example:
C: 001 search text very-long-to-complete
... time passes ...
S: * OK [INPROGRESS ("001" 454 1000)] Processed 45% of the items
... time passes ...
S: * OK [INPROGRESS ("001" 999 1000)] Processed 99% of the items
... time passes, but less than the threshold ...
S: [...] actual results for the command
S: 001 OK done
If all the details are NIL, the whole details section MAY be omitted,
i.e.:
* OK [INPROGRESS (NIL NIL NIL)] Working on it
can be replaced by:
* OK [INPROGRESS] Working on it
The cmd-tag detail MUST NOT contain "]". If that is the case, the
server MUST replace the cmd-tag with NIL. This still produces a
usable notification, unless multiple commands are in flight
simultaneously. A client can ensure to receive notifications with
cmd-tag(s) by simply refraining to embed the character "]" in the
originating command tags.
The PROGRESS number MUST be non-negative and SHOULD be monotonically
increasing.
The GOAL number MUST be positive when provided, and it SHOULD NOT
change between successive notifications for the same command (i.e.
for the same cmd-tag).
PROGRESS and GOAL SHOULD be counts of the kind of item being
processed - in most cases, message counts. If that is not possible,
the counts SHOULD be percentages (progress varies from 0 to 99 and
goal stays fixed at 100). In this case, the numbers are suffixed by
"%" and the goal MUST be 100%.
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The command is completed when PROGRESS equals GOAL. In this case the
server SHOULD NOT send a progress notification but just the proper
command completion. If the command isn't completed yet, PROGRESS
MUST be strictly less than GOAL.
If the command completes before the first server interval, there will
be no notifications. The client MUST assume PROGRESS=0 and GOAL
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 with specific commands. If a UI 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 authoritative for any
other use than evaluating commands progress. 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], IMAP [RFC9051] and
IMAP ABNF extension [RFC4466] specifications.
Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of uppercase or lowercase characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion.
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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-percentage = number "%" SP "100" "%"
inprogress-state = inprogress-state-unknown
/ inprogress-state-counting
/ inprogress-state-known-goal
/ inprogress-state-percentage
resp-text-code =/ "INPROGRESS" [ SP "(" inprogress-tag SP
inprogress-state ")" ]
6. Security Considerations
The details of the response code are not expected to disclose any
information that isn't currently available from commands output. The
progress details could be obtained anyway by a series of sending
commands with different workloads - either by constructing data sets
or searching in the appropriate way into them.
7. IANA Considerations
IANA is requested to add "INPROGRESS" to the "IMAP Response Codes"
registry located at <https://www.iana.org/assignments/imap-response-
codes>, with a reference to this document.
IANA is requested to add "INPROGRESS" to the "IMAP Capabilities"
registry located at <https://www.iana.org/assignments/imap-
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,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
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[RFC5530] Gulbrandsen, A., "IMAP Response Codes", RFC 5530,
DOI 10.17487/RFC5530, May 2009,
<https://www.rfc-editor.org/info/rfc5530>.
[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>.
[RFC9051] Melnikov, A., Ed. and B. Leiba, Ed., "Internet Message
Access Protocol (IMAP) - Version 4rev2", RFC 9051,
DOI 10.17487/RFC9051, August 2021,
<https://www.rfc-editor.org/info/rfc9051>.
Author's Address
Marco Bettini
Open-Xchange Oy
Lars Sonckin kaari 10
FI-02600 Espoo
Finland
Email: marco.bettini@open-xchange.com
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