wdiff rfc4731.original rfc4731.txt

Internet Draft
Network Working Group A. Melnikov
Document: draft-melnikov-imap-search-ret-03
Request for Comments: 4731 Isode Ltd
Expires: December 2006
Category: Standards Track D. Cridland
Inventure Systems Ltd
June
November 2006

IMAP4 extension Extension to SEARCH command Command for controlling what kind Controlling
What Kind of
information is returned
draft-melnikov-imap-search-ret-03 Information Is Returned

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Abstract

This document extends IMAP (RFC 3501) SEARCH and UID SEARCH commands
with several result options, which can control what kind of
information is returned. The following result options are defined:
minimal value, maximal value, all found messages messages, and number of found
messages.

Table of Contents

1. Introduction ....................................................2
2. Conventions Used in this This Document 2
2. Introduction 3 ...............................2
3. IMAP Protocol Changes 3
3.1 ...........................................2
3.1. New SEARCH/UID SEARCH Commands 3 Result Options .......................2
3.2. Interaction with CONDSTORE extension .......................4
4. Formal Syntax 6 ...................................................5
5. Security Considerations 7 .........................................6
6. IANA Considerations 7 .............................................6
7. References 7
7.1 Normative References 7
7.2 Informative References 8 ............................................6
8. Acknowledgments 8
9. Author's Addresses 8
10. Full Copyright Statement 8
11. Intellectual Property 9
12. Appendix A. Editorial. 9
12.1 Change Log 9
12.2 Open Issues for Discussion 10 .................................................6

1. Conventions Used in this Document

In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.

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 RFC 2119 [KEYWORDS].

<<Editorial comments and questions are enclosed like this>>

2. Introduction

[IMAPABNF] extended SEARCH and UID SEARCH commands with result
specifiers (also known as result options), which can control what
kind of information is returned.

A server advertising the X-DRAFT-I02-ESEARCH <<fix before
publication>> ESEARCH capability supports the following
result options: minimal value, maximal value, all found messages messages,
and number of found messages. These result options allows allow clients to
get SEARCH results in more convenient forms, while also saving
bandwidth required to transport the results, for example example, by finding
the first unseen message or returning the number of unseen or deleted
messages. Also, when a single MIN or a single MAX result option is
specified, servers can optimize execution of SEARCHes.

2. Conventions Used in This Document

In examples, "C:" and "S:" indicate lines sent by the client and
server, respectively.

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 RFC 2119 [KEYWORDS].

3. IMAP Protocol Changes

3.1

3.1. New SEARCH/UID SEARCH result options Result Options

The SEARCH/UID SEARCH commands are extended to allow for the
following result options:

MIN
Return the lowest message number/UID that satisfies the SEARCH
criteria.

If the SEARCH results in no matches, the server MUST NOT
include the MIN result option in the ESEARCH response,
however response; however,
it still MUST send the ESEARCH response.

MAX
Return the highest message number/UID that satisfies the SEARCH
criteria.

If the SEARCH results in no matches, the server MUST NOT
include the MAX result option in the ESEARCH response,
however response; however,
it still MUST send the ESEARCH response.

ALL
Return all message numbers/UIDs that satisfy the SEARCH
criteria. Unlike regular (unextended) SEARCH, the messages are
always returned using the sequence-set syntax. A sequence-
set sequence-set
representation may be more compact and can be used as is in a
subsequent command that accepts sequence-set. Note, the client
MUST NOT assume that messages/UIDs will be listed in any
particular order.

If the SEARCH results in no matches, the server MUST NOT
include the ALL result option in the ESEARCH response,
however response; however,
it still MUST send the ESEARCH response.

COUNT
Return number of the messages that satisfy the SEARCH criteria.
This result option MUST always be included in the ESEARCH
response.

If one or more result option options described above is are specified, the
extended SEARCH command MUST return a single ESEARCH response
[IMAPABNF], instead of the SEARCH response.

An extended UID SEARCH command MUST cause a an ESEARCH response with
the UID indicator present.

Note that future extensions to this document can allow servers to
return multiple ESEARCH responses for a single extended SEARCH
command. These extensions will have to describe how results from
multiple ESEARCH responses are to be amalgamated.

If the list of result options is empty, that requests the server to
return an ESEARCH response instead of the SEARCH response. This is
equivalent to "(ALL)".

Example: C: A282 SEARCH RETURN (MIN COUNT) FLAGGED
SINCE 1-Feb-1994 NOT FROM "Smith"
S: * ESEARCH (TAG "A282") MIN 2 COUNT 3
S: A282 OK SEARCH completed

Example: C: A283 SEARCH RETURN () FLAGGED
SINCE 1-Feb-1994 NOT FROM "Smith"
S: * ESEARCH (TAG "A283") ALL 2,10:11
S: A283 OK SEARCH completed

The following example demonstrates finding the first unseen message
as returned in the UNSEEN response code on a successful SELECT
command:

Example: C: A284 SEARCH RETURN (MIN) UNSEEN
S: * ESEARCH (TAG "A284") MIN 4
S: A284 OK SEARCH completed

The following example demonstrates that if the ESEARCH UID indicator
is present, all data in the ESEARCH response is referring to UIDs, UIDs;
for example example, the MIN result specifier will be followed by
an a UID.

Example: C: A285 UID SEARCH RETURN (MIN MAX) 1:5000
S: * ESEARCH (TAG "A285") UID MIN 7 MAX 3800
S: A285 OK SEARCH completed

The following example demonstrates returning the number of deleted
messages:

Example: C: A286 SEARCH RETURN (COUNT) DELETED
S: * ESEARCH (TAG "A286") COUNT 15
S: A286 OK SEARCH completed

3.2

3.2. Interaction with CONDSTORE extension

When the server supports both the X-DRAFT-I02-ESEARCH <<fix before
publication>> ESEARCH and the CONDSTORE
[CONDSTORE] extension, and the client requests one or more result
option described in section 3.1 together with the MODSEQ search
criterion in the same SEARCH/UID SEARCH command, then the server MUST
return the ESEARCH response containing the MODSEQ result option
(described in the following paragraph) instead of the extended SEARCH
response described in section 3.5 of [CONDSTORE].

If the SEARCH/UID SEARCH command contained a single MIN or MAX result
option, the MODSEQ result option contains the mod-sequence for the
found message. If the SEARCH/UID SEARCH command contained both MIN
and MAX result options and no ALL/COUNT option, the MODSEQ result
option contains the highest mod-sequence for the two returned
messages. Otherwise the MODSEQ result option contains the highest
mod-sequence for all messages being returned.

Example: The following example demonstrates how Example 15 from
[CONDSTORE] would look in the presence of one or more result option:

C: a1 SEARCH RETURN (MIN) MODSEQ "/flags/\\draft"
all 620162338
S: * ESEARCH (TAG "a1") MIN 2 MODSEQ 917162488
S: a1 OK Search complete

C: a2 SEARCH RETURN (MAX) MODSEQ "/flags/\\draft"
all 620162338
S: * ESEARCH (TAG "a2") MAX 23 MODSEQ 907162321
S: a2 OK Search complete

C: a3 SEARCH RETURN (MIN MAX) MODSEQ "/flags/\\draft"
all 620162338
S: * ESEARCH (TAG "a3") MIN 2 MAX 23 MODSEQ 917162488
S: a3 OK Search complete

C: a4 SEARCH RETURN (MIN COUNT) MODSEQ "/flags/\\draft"
all 620162338
S: * ESEARCH (TAG "a4") MIN 2 COUNT 10 MODSEQ 917162500
S: a4 OK Search complete

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], [CONDSTORE] [CONDSTORE], or [IMAPABNF].

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

capability =/ "X-DRAFT-I02-ESEARCH" "ESEARCH"

search-return-data = "MIN" SP nz-number /
"MAX" SP nz-number /
"ALL" SP sequence-set /
"COUNT" SP number
;; conforms to the generic
;; search-return-data syntax defined
;; in [IMAPABNF]

search-return-opt = "MIN" / "MAX" / "ALL" / "COUNT"
;; conforms to generic search-return-opt
;; syntax defined in [IMAPABNF]

When the CONDSTORE [CONDSTORE] IMAP extension is also supported supported,
the ABNF is updated as follows:

search-return-data =/ "MODSEQ" SP mod-sequence-value
;; mod-sequence-value is defined
;; in [CONDSTORE]

5. Security Considerations

In the general case case, the IMAP SEARCH/UID SEARCH command commands can be CPU
and/or IO intensive, and are seen by some as a potential attack point
for denial of service attacks, so some sites/implementations even
disable it them entirely. This is quite unfortunate, as SEARCH command
is one of the best examples demonstrating IMAP advantage over POP3.

The ALL and COUNT return options don't change how SEARCH is working
internally,
internally; they only change how information about found messages is
returned. MIN and MAX SEARCH result options described in this
document can lighten the load on IMAP servers, which chose servers that choose to optimize
SEARCHes containing only one or both of them.

It is believed that this extension doesn't raise any additional
security concerns not already discussed in [IMAP4].

6. IANA Considerations

IMAP4 capabilities are registered by publishing a standards track RFC
or IESG approved an IESG-approved experimental RFC. The registry is currently
located at <http://www.iana.org/assignments/imap4-capabilities>.

This document defines the X-DRAFT-I02-ESEARCH <<fix before
publication>> ESEARCH IMAP capability. capability, which IANA is requested to add this
capability added
to the registry.

7. References

7.1 Normative References

[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[IMAP4] Crispin, M., "Internet Message Access Protocol "INTERNET MESSAGE ACCESS PROTOCOL - Version VERSION
4rev1", RFC 3501, University of Washington, March 2003.

[ABNF] Crocker, D. (Ed.) and P. Overell , "Augmented BNF for
Syntax Specifications: ABNF", RFC 4234, October 2005.

[IMAPABNF] Melnikov, A. and C. Daboo, "Collected extensions Extensions to IMAP4
ABNF", RFC 4466, April 2006..

[CONDSTORE] Melnikov, A. and S. Hole, "IMAP Extension for Conditional
STORE", RFC 4551, June 2006.

8. Acknowledgments

Thanks to Michael Wener, Arnt Gulbrandsen, Cyrus Daboo, Mark
Crispin Crispin,
and Pete Maclean for comments and corrections.

9. Author's

Authors' Addresses

Alexey Melnikov
Isode Limited
5 Castle Business Village
36 Station Road
Hampton, Middlesex, TW12 2BX
UK

Email:

EMail: Alexey.Melnikov@isode.com

Dave A. Cridland
Inventure Systems Limited

Email:

EMail: dave.cridland@inventuresystems.co.uk
URL: http://invsys.co.uk/dave/

10.

Full Copyright Statement

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY SOCIETY, THE IETF TRUST,
AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE.

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

11.

Intellectual Property

The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
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Copies of IPR disclosures made to the IETF Secretariat and any
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The IETF invites any interested party to bring to its attention any
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12. Appendix A. Editorial.

<<Note to RFC editor: please delete this section before
publication>>

12.1 Change Log

00 Initial Revision.
01 Added search correlator. Clarified what should be returned if an
extended SEARCH produces no matches. Filled in "IANA
considerations" section. Updated references: updated ABNF and
added [IMAPABNF]. Changed semantics of the empty list of result
options (now equivalent to "(ALL)".
02 Clarified that clients can expect a single ESEARCH result to any
extended SEARCH command (for result options described in this
document). Added more text on intended purpose of
ietf-ipr@ietf.org.

Acknowledgement

Funding for the extension.
Added more examples. Updated reference to RFC Editor function is currently provided by the ABNF document.
03 Clarified interaction with CONDSTORE. Multiple editorial changes
to align with [IMAPABNF].
Internet Society.