5Internet Engineering Task Force (IETF) M. Bettini
6Request for Comments: 9585 Open-Xchange Oy
7Category: Standards Track May 2024
11 IMAP Response Code for Command Progress Notifications
15 This document defines a new IMAP untagged response code,
16 "INPROGRESS", that provides progress notifications regarding the
17 status of long-running commands.
21 This is an Internet Standards Track document.
23 This document is a product of the Internet Engineering Task Force
24 (IETF). It represents the consensus of the IETF community. It has
25 received public review and has been approved for publication by the
26 Internet Engineering Steering Group (IESG). Further information on
27 Internet Standards is available in Section 2 of RFC 7841.
29 Information about the current status of this document, any errata,
30 and how to provide feedback on it may be obtained at
31 https://www.rfc-editor.org/info/rfc9585.
35 Copyright (c) 2024 IETF Trust and the persons identified as the
36 document authors. All rights reserved.
38 This document is subject to BCP 78 and the IETF Trust's Legal
39 Provisions Relating to IETF Documents
40 (https://trustee.ietf.org/license-info) in effect on the date of
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43 to this document. Code Components extracted from this document must
44 include Revised BSD License text as described in Section 4.e of the
45 Trust Legal Provisions and are provided without warranty as described
46 in the Revised BSD License.
51 2. Conventions Used in This Document
52 3. CAPABILITY Identification
53 4. The "INPROGRESS" Response Code
55 6. Security Considerations
56 7. IANA Considerations
57 8. Normative References
62 IMAP commands [RFC9051] can require a considerable amount of time to
63 be completed by the server. In these cases, the client has no
64 information about the progress of the commands. It is already
65 possible to expose updates with a generic untagged response, like "*
66 OK Still on it, 57% done"; however, this does not provide a standard
67 way to communicate with the client and does not allow the server to
68 inform the client of the progress of the long-running actions.
70 This document extends the Internet Message Access Protocol (IMAP)
73 * a new "INPROGRESS" response code [RFC5530]. The new response code
74 provides a consistent means for a client to receive progress
75 notifications on command completion status.
77 * a new "INPROGRESS" capability [RFC9051]. The new capability
78 informs the client that the server emits progress notifications
79 via the "INPROGRESS" response code.
812. Conventions Used in This Document
83 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
84 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
85 "OPTIONAL" in this document are to be interpreted as described in
86 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
87 capitals, as shown here.
89 The word "can" (not "may") is used to refer to a possible
90 circumstance or situation, as opposed to an optional facility of the
93 Conventions for notations are as in [RFC9051] and [RFC5530].
95 In examples, "C:" and "S:" indicate lines sent by the client and
96 server, respectively. Note that each line includes the terminating
993. CAPABILITY Identification
102 the response list to the CAPABILITY command.
1044. The "INPROGRESS" Response Code
106 The server MAY send the "INPROGRESS" response code to notify the
107 client about the progress of the commands in execution or simply to
108 prevent the client from timing out and terminating the connection.
110 elects to send notifications, it is RECOMMENDED that these are sent
113 The response code is meant to appear embedded inside an untagged OK
114 reply. The response code MUST NOT appear in a tagged response (the
115 command has completed and further progress notifications make no
118 The response code MAY embed a list of details, which appear in the
121 1. CMD-TAG: the tag [RFC9051] that originated the long-running
123 character, it MUST be set to NIL. This still produces a usable
124 notification, unless multiple commands are in flight
125 simultaneously. A client can ensure reception of notifications
126 with tags by simply refraining from the use of the character "]"
127 in the originating command tags.
129 2. PROGRESS: a number indicating the number of items processed so
130 far. The number MUST be non-negative and SHOULD be monotonically
131 increasing. If the PROGRESS is not available, both PROGRESS and
132 GOAL MUST be set to NIL.
134 3. GOAL: a number indicating the total number of items to be
135 processed. The number MUST be positive, and it SHOULD NOT change
136 between successive notifications for the same command tag. This
137 is the number that PROGRESS is expected to reach after the
138 completion of the command; therefore, it MUST be greater than
139 PROGRESS. If the GOAL is not known, it MUST be set to NIL.
141 If the response code does not embed a list of details, all details
142 are to be interpreted as NIL.
144 The server can provide the progress details with different degrees of
148 * OK [INPROGRESS] Hang in there...
149 - keepalive with an indication of the command tag
150 * OK [INPROGRESS ("tag" NIL NIL)] Hang in there...
151 - progress notification with unknown GOAL
152 * OK [INPROGRESS ("tag" 175 NIL)] Processed 175 items so far
153 - progress notification with an indication of the GOAL
154 * OK [INPROGRESS ("tag" 175 1000)] Processed 17% of the items
158 C: A001 search text "this will be slow"
160 S: * OK [INPROGRESS ("A001" 454 1000)] Processed 45% of the items
162 S: * OK [INPROGRESS ("A001" 999 1000)] Processed 99% of the items
165 S: A001 OK Search completed (23.387 + 0.004 + 0.017 secs).
167 C: A003 COPY 2000:4000 Meeting-Minutes
169 S: * OK [INPROGRESS ("A003" 175 2001)] Still working on this...
171 S: * OK [INPROGRESS ("A003" 440 2001)] Still working on this...
173 S: * OK [INPROGRESS ("A003" 987 2001)] Still working on this...
175 S: * OK [INPROGRESS ("A003" 1388 2001)] Still working on this...
177 S: * OK [INPROGRESS ("A003" 1876 2001)] Still working on this...
179 S: A003 OK Copy completed
181 PROGRESS and GOAL SHOULD be counts of the kind of item being
182 processed -- in most cases, messages counts. If that is not
183 possible, the counts SHOULD be percentages, with GOAL set to 100 and
184 PROGRESS varying between 0 and 99.
186 The server SHOULD NOT send a progress notification where PROGRESS
187 equals GOAL, as that would mean the command is completed. In that
188 case, the proper tagged response should be emitted instead.
190 If the command completes before the first server notification
191 deadline, there will be no notifications at all. The client MUST
192 assume PROGRESS to be 0 and GOAL to be unknown until the server
193 issues a notification for the command.
195 While the server SHOULD keep GOAL constant and PROGRESS monotonically
196 increasing, there are circumstances where this might not be possible.
197 The client MUST be prepared to handle cases where the server cannot
198 keep GOAL constant and/or PROGRESS monotonically increasing. When
199 the GOAL changes or the PROGRESS goes backward, the RECOMMENDED
200 interpretation is that the previous GOAL has been reached, but the
201 server discovered that further (long-running) work is required (with
202 a new known or unknown GOAL).
204 The client MAY disregard progress notifications entirely or process
205 them only in relation to specific commands. If a user interface is
206 involved, it is the client's duty to decide which of these
207 notifications should emerge to the user interface and/or modify the
208 user's ability to interact in their presence, since this may differ
209 based on implementation details.
211 Also, the client MUST NOT consider the values to be authoritative for
212 any other use than evaluating the progress of the commands. For
213 example, the client must not use the GOAL field in place of the
214 proper output of a SEARCH command to know the number of messages in a
219 The following syntax specification uses the Augmented Backus-Naur
220 Form (ABNF) [RFC5234] notation. Elements not defined here can be
221 found in the formal syntax of the ABNF [RFC5234] and IMAP [RFC9051]
224 Except as noted otherwise, all alphabetic characters are case-
225 insensitive. The use of uppercase or lowercase characters to define
226 token strings are for editorial clarity only. Implementations MUST
227 accept these strings in a case-insensitive fashion.
229 inprogress-tag = quoted / nil
230 inprogress-state-unknown = nil SP nil
231 inprogress-state-counting = number SP nil
234 inprogress-state = inprogress-state-unknown
235 / inprogress-state-counting
236 / inprogress-state-known-goal
239 inprogress-state ")" ]
2416. Security Considerations
243 The details of the response code are not expected to disclose any
244 information that isn't currently available from the command output.
245 The progress details could be obtained anyway by sending a series of
246 commands with different workloads -- by either constructing data sets
247 or searching in the appropriate way.
249 The client must protect itself against data sent by a malicious
250 server. Specifically, the client should guard against values that
251 can cause arithmetic exceptions, like GOAL = 0, GOAL/VALUE < 0, GOAL/
252 VALUE ≥ 2^32 (these are not possible within a correct implementation
253 of the ABNF syntax above), and VALUE > GOAL. In these cases, the
254 notification MUST be disregarded.
2567. IANA Considerations
258 IANA has added "INPROGRESS" to the "IMAP Response Codes" registry
259 located at <https://www.iana.org/assignments/imap-response-codes>,
260 with a reference to this document.
262 IANA had added "INPROGRESS" to the "IMAP Capabilities" registry
263 located at <https://www.iana.org/assignments/imap-capabilities>, with
264 a reference to this document.
2668. Normative References
268 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
269 Requirement Levels", BCP 14, RFC 2119,
270 DOI 10.17487/RFC2119, March 1997,
271 <https://www.rfc-editor.org/info/rfc2119>.
273 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
274 Specifications: ABNF", STD 68, RFC 5234,
275 DOI 10.17487/RFC5234, January 2008,
276 <https://www.rfc-editor.org/info/rfc5234>.
278 [RFC5530] Gulbrandsen, A., "IMAP Response Codes", RFC 5530,
279 DOI 10.17487/RFC5530, May 2009,
280 <https://www.rfc-editor.org/info/rfc5530>.
282 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
283 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
284 May 2017, <https://www.rfc-editor.org/info/rfc8174>.
286 [RFC9051] Melnikov, A., Ed. and B. Leiba, Ed., "Internet Message
287 Access Protocol (IMAP) - Version 4rev2", RFC 9051,
288 DOI 10.17487/RFC9051, August 2021,
289 <https://www.rfc-editor.org/info/rfc9051>.
295 Lars Sonckin kaari 10
298 Email: marco.bettini@open-xchange.com