Internet DRAFT - draft-ietf-extra-imap-uidonly
draft-ietf-extra-imap-uidonly
Network Working Group A. Melnikov
Internet-Draft Isode
Intended status: Experimental A. P. Achuthan
Expires: 7 June 2024 V. Nagulakonda
A. Singh
Yahoo!
L. Alves
5 December 2023
IMAP Extension for only using and returning UIDs
draft-ietf-extra-imap-uidonly-06
Abstract
The UIDONLY extension to the Internet Message Access Protocol (RFC
3501/RFC 9051) allows clients to enable a mode in which information
about mailbox changes is returned using only UIDs. Message numbers
are not returned in responses, and can't be used in requests once
this extension is enabled. This helps both clients and servers to
reduce resource usage required to maintain a map between message
numbers and UIDs.
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 7 June 2024.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 2
2. Document Conventions . . . . . . . . . . . . . . . . . . . . 3
3. The UIDONLY extension . . . . . . . . . . . . . . . . . . . . 3
3.1. Enabling UIDONLY extension . . . . . . . . . . . . . . . 4
3.2. Changes to FETCH/STORE/SEARCH/COPY/MOVE . . . . . . . . . 4
3.3. Changes to UID FETCH/UID STORE . . . . . . . . . . . . . 4
3.4. Changes to EXPUNGE/UID EXPUNGE . . . . . . . . . . . . . 5
3.5. Changes to UID SEARCH . . . . . . . . . . . . . . . . . . 5
3.6. Changes to how other mailbox changes are announced . . . 5
3.7. Interaction with CONDSTORE and QRESYNC extensions . . . . 6
3.8. Interaction with other extensions . . . . . . . . . . . . 6
4. Formal syntax . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. Changes/additions to the IMAP4 capabilities registry . . 7
7. Alternative solutions not taken . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 8
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction and Overview
This document defines an extension to the Internet Message Access
Protocol [RFC3501] for eliminating use of message numbers. This
extension is compatible with both IMAP4rev1 [RFC3501] and IMAP4rev2
[RFC9051].
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The UIDONLY extension of the Internet Message Access Protocol (RFC
3501/RFC 9051) allows clients to request that servers only use and
return UIDs. This helps both clients and servers to reduce resource
usage required for maintenance of message number to UID map.
2. Document Conventions
In protocol examples, this document uses a prefix of "C: " to denote
lines sent by the client to the server, and "S: " for lines sent by
the server to the client. Lines prefixed with "// " are comments
explaining the previous protocol line. These prefixes and comments
are not part of the protocol. Lines without any of these prefixes
are continuations of the previous line, and no line break is present
in the protocol unless specifically mentioned.
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.
Other capitalised words are names of IMAP commands or responses
[RFC3501][RFC9051] or keywords from this document.
3. The UIDONLY extension
An IMAP server advertises support for the UIDONLY extension by
including the "UIDONLY" capability in the CAPABILITY response/
response code.
Once the UIDONLY extension is enabled (see Section 3.1), the client
MUST NOT use message sequence numbers (including the special marker
"*") in any arguments to IMAP commands, and the server MUST return
tagged BAD response if the client uses message sequence numbers. The
server SHOULD include the UIDREQUIRED response code in such BAD
responses (see below). Additionally, once the UIDONLY extension is
enabled, the server MUST NOT return message sequence numbers in any
response.
The UIDREQUIRED response code is defined as follows:
UIDREQUIRED The server returns UIDREQUIRED response code when the client
issues a command that includes message numbers instead of UIDs
once UIDONLY extension is enabled.
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C: 07 FETCH 10000:14589 (UID FLAGS)
S: 07 OK [UIDREQUIRED] Message numbers are not allowed
once UIDONLY is enabled
The UIDONLY extension affects how information about new, expunged or
changed messages is returned in unsolicited responses. In
partucular, it affects responses to UID FETCH/UID STORE/EXPUNGE/UID
EXPUNGE, as well as how unsolicited mailbox changes are announced.
The following subsections describe changes introduced by this
extension in more details.
3.1. Enabling UIDONLY extension
As the UIDONLY extension affects how information about new, expunged
or changed messages is returned in unsolicited responses, it has to
be enabled by the client first using the ENABLE command.
S: * OK [CAPABILITY IMAP4rev1 ENABLE CONDSTORE QRESYNC UIDONLY
AUTH=SCRAM-SHA-256]
C: 01 ENABLE UIDONLY
S: * ENABLED UIDONLY
S: 01 OK ENABLE completed
3.2. Changes to FETCH/STORE/SEARCH/COPY/MOVE
When UIDONLY is enabled, FETCH, STORE, SEARCH, COPY and MOVE commands
are prohibited and MUST result in a tagged BAD response. Clients
should instead use UID FETCH, UID STORE, UID SEARCH, UID COPY or UID
MOVE respectively.
3.3. Changes to UID FETCH/UID STORE
When UIDONLY is enabled, all FETCH responses that would be returned
by UID FETCH/UID STORE are replaced by UIDFETCH responses.
Note that UIDFETCH response contains the same response data items as
specified for the FETCH response. The UID is always returned at the
beginning of a UIDFETCH response, and it can also appear in UID
response data item, if requested by the client. While UID response
data item is redundant when requested, it can simplify updating of
existing (non UIDONLY) implementations to support UIDONLY.
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C: 10 UID FETCH 25900:26600 (FLAGS)
[...]
S: * 25996 UIDFETCH (FLAGS (\Seen))
S: * 25997 UIDFETCH (FLAGS (\Flagged \Answered))
S: * 26600 UIDFETCH (FLAGS ())
S: 10 OK FETCH completed
C: 11 UID FETCH 25900:26600 (UID FLAGS)
S: * 25900 UIDFETCH (FLAGS (\Seen) UID 25900)
S: * 25902 UIDFETCH (FLAGS (\Flagged) UID 25902)
S: * 26310 UIDFETCH (FLAGS (\Answered) UID 26310)
S: * 26311 UIDFETCH (FLAGS () UID 26311)
S: * 26498 UIDFETCH (FLAGS (\Answered) UID 26498)
[...]
S: 11 OK FETCH completed
3.4. Changes to EXPUNGE/UID EXPUNGE
When UIDONLY is enabled, all EXPUNGED responses that would be
returned by EXPUNGE/UID EXPUNGE are replaced by VANISHED responses,
as defined in [RFC7162]. Note that a server that implements UIDONLY
extension is not required (but allowed) to also implement CONDSTORE
and/or QRESYNC extensions.
C: 12 EXPUNGE
S: * VANISHED 405,407,410,425
S: 12 OK expunged
3.5. Changes to UID SEARCH
The "<sequence set>" UID SEARCH criterion is prohibited (and results
in tagged BAD response) once UIDONLY is enabled. Clients should use
ALL or "UID <sequence set>" UID SEARCH criterion instead.
3.6. Changes to how other mailbox changes are announced
When UIDONLY is enabled, all changes to flags (and other dynamic
message attributes) are returned using UIDFETCH responses, instead of
FETCH responses.
Similarly, all expunged messages are announced using VANISHED
responses instead of EXPUNGE responses.
This extension doesn't affect EXISTS or RECENT responses.
UID MOVE/UID COPY commands SHOULD return COPYUID response code, as
specified in [RFC4315].
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Use of UIDNOTSTICKY response code (see [RFC4315]) is not compatible
with the UIDONLY extension. I.e. a server that advertises UIDONLY
extension MUST NOT return UIDNOTSTICKY response code.
C: 15 UID move 597 "Archives/2023/2023-05"
S: * OK [COPYUID 1685977201 597 2] UID MOVE
S: * VANISHED 597
S: 15 OK UID MOVE Completed
3.7. Interaction with CONDSTORE and QRESYNC extensions
CONDSTORE extension is compatible with the UIDONLY extension. The
MODSEQ message data item is returned in UIDFETCH responses instead of
FETCH responses.
QRESYNC extension is compatible with the UIDONLY extension, but once
UIDONLY is enabled, the fourth SELECT QRESYNC parameter ("Message
Sequence Match Data", see Section 3.2.5.2 of [RFC7162]) MUST NOT be
used. The server MUST return a tagged BAD response if such parameter
is observed once UIDONLY is enabled.
3.8. Interaction with other extensions
IMAP extensions might define other commands that accept message
sequence numbers ("sequence-set" ABNF non terminal) Once UIDONLY is
enabled, server MUST reject such commands with tagged BAD response.
For example, SORT and THREAD [RFC5256] commands are prohibited,
similarly to the SEARCH command. However UID SORT and UID THREAD can
be used instead.
4. Formal syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF].
Non-terminals referenced but not defined below are as defined by
IMAP4 [RFC3501].
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.
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SP = <Defined in RFC 5234>
capability =/ "UIDONLY"
;; <capability> from [RFC3501]
message-data =/ uidfetch-resp
uidfetch-resp = uniqueid SP "UIDFETCH" SP msg-att
;; The uniqueid is the UID of the corresponding
;; message
message-data =/ expunged-resp
expunged-resp = <defines VANISHED response, see RFC 7162>
resp-text-code =/ "UIDREQUIRED"
5. Security Considerations
This IMAP extension is not believed to add any additional Security
Considerations beyond the ones that are generally applicable to
IMAP4rev1 [RFC3501] and IMAP4rev2 [RFC9051].
6. IANA Considerations
6.1. Changes/additions to the IMAP4 capabilities registry
IMAP4 capabilities are registered by publishing a standards track or
IESG approved Informational or Experimental RFC. The registry is
currently located at:
https://www.iana.org/assignments/imap4-capabilities
IANA is requested to add definition of the UIDONLY extension to this
registry with [RFCXXXX] as the reference.
IANA is also requested to add definition of the UIDREQUIRED response
code to the "IMAP Response Codes" registry with [RFCXXXX] as the
reference. The registry is currently located at:
https://www.iana.org/assignments/imap-response-codes/imap-response-codes.xhtml
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7. Alternative solutions not taken
An earlier draft of this document proposed use of FETCH responses
with the message number parameter always be set to 0. This was
judged to be too risky, as this could have caused unexpected side
effects and cache corruptions in client code that was not properly
updated to handle lack of message numbers.
8. Acknowledgments
Editors of this document would like to thank the following people who
provided useful comments and/or participated in discussions that lead
to this document, in particular: Arnt Gulbrandsen, Ken Murchison and
Bron Gondwana. This document is similar to draft-gulbrandsen-imap-
uidonly-00.txt, but some different syntactic choices were made in the
end.
9. Normative References
[ABNF] Crocker, D., Ed. and P. Overell, Ed., "Augmented BNF for
Syntax Specifications: ABNF", RFC 5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[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>.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/info/rfc3501>.
[RFC4315] Crispin, M., "Internet Message Access Protocol (IMAP) -
UIDPLUS extension", RFC 4315, DOI 10.17487/RFC4315,
December 2005, <https://www.rfc-editor.org/info/rfc4315>.
[RFC5256] Crispin, M. and K. Murchison, "Internet Message Access
Protocol - SORT and THREAD Extensions", RFC 5256,
DOI 10.17487/RFC5256, June 2008,
<https://www.rfc-editor.org/info/rfc5256>.
[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,
<https://www.rfc-editor.org/info/rfc7162>.
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[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>.
Index
U
U
UIDREQUIRED (response code)
Section 3, Paragraph 4.2.1
Authors' Addresses
Alexey Melnikov
Isode Limited
Email: alexey.melnikov@isode.com
URI: https://www.isode.com
Arun Prakash Achuthan
Yahoo Inc.
Email: arunprakash@myyahoo.com
Vikram Nagulakonda
Yahoo Inc.
Email: nvikram_imap@yahoo.com
Ashutosh Singh
Yahoo Inc.
Email: ashutoshvsingh@yahoo.com
Luis Alves
Email: luis.alves@lafaspot.com
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