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Versions: (draft-melnikov-imapext-multimailbox-search) 00 01 02 03 04 05 06 07 RFC 6237

Message ORGanization Working Group                              B. Leiba
Internet-Draft                                       Huawei Technologies
Updates: 4466 (if approved)                                  A. Melnikov
Intended status: Standards Track                           Isode Limited
Expires: December 20, 2010                                 June 18, 2010


                  IMAP4 Multimailbox SEARCH Extension
                 draft-ietf-morg-multimailbox-search-03

Abstract

   The IMAP4 specification allows the searching only of the selected
   mailbox.  A user often wants to search multiple mailboxes, and a
   client that wishes to support this must issue a series of SELECT and
   SEARCH commands, waiting for each to complete before moving on to the
   next.  This extension allows a client to search multiple mailboxes
   with one command, limiting the round-trips and waiting for various
   searches to complete, and not requiring disruption of the currently
   selected mailbox.  This also uses MAILBOX and TAG fields in ESEARCH
   responses, allowing a client to pipeline the searches if it chooses.

Note

   A revised version of this draft document will be submitted to the RFC
   editor as a Proposed Standard for the Internet Community.  Discussion
   and suggestions for improvement are requested, and should be sent to
   morg@ietf.org.

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 http://datatracker.ietf.org/drafts/current/.

   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 December 20, 2010.

Copyright Notice




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   Copyright (c) 2010 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
   (http://trustee.ietf.org/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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.    Introduction  . . . . . . . . . . . . . . . . . . . . . . . . 3
   1.1.  Conventions used in this document . . . . . . . . . . . . . . 3

   2.    Extensions to UID SEARCH command  . . . . . . . . . . . . . . 3
   2.1.  The ESEARCH response  . . . . . . . . . . . . . . . . . . . . 4
   2.2.  Source options -- specifying mailboxes to search  . . . . . . 5

   3.    Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 6

   4.    Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . 6

   5.    Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 7

   6.    Security Considerations . . . . . . . . . . . . . . . . . . . 8

   7.    IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8

   8.    Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 8

   9.    Normative References  . . . . . . . . . . . . . . . . . . . . 9

         Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . 9













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1.  Introduction

   The IMAP4 specification allows the searching only of the selected
   mailbox.  A user often wants to search multiple mailboxes, and a
   client that wishes to support this must issue a series of SELECT and
   SEARCH commands, waiting for each to complete before moving on to the
   next.  The commands can't be pipelined, because the server might run
   them in parallel, and the untagged SEARCH responses could not then be
   distinguished from each other.

   This extension allows a client to search multiple mailboxes with one
   command, and includes MAILBOX and TAG fields in the ESEARCH response,
   yielding the following advantages:

   o  A single command limits the number of round-trips needed to search
      a set of mailboxes.

   o  A single command eliminates the need to wait for one search to
      complete before starting the next.

   o  A single command allows the server to optimize the search, if it
      can.

   o  A command that is not dependent upon the selected mailbox
      eliminates the need to disrupt the selection state, or to open
      another IMAP connection.

   o  The MAILBOX and TAG fields in the responses allow a client to
      distinguish which responses go with which search (and which
      mailbox).  A client can safely pipeline these search commands
      without danger of confusion.

1.1.  Conventions used in this document

   In examples, "C:" indicates lines sent by a client that is connected
   to a server.  "S:" indicates lines sent by the server to the client.

   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 [RFC2119].


2.  Extensions to UID SEARCH command








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   Arguments:  OPTIONAL source options
               OPTIONAL result options
               OPTIONAL charset specification (see [RFC2978])
               searching criteria (one or more)

   Responses:  REQUIRED untagged response: ESEARCH

   Result:     OK - search completed
               NO - error: cannot search that charset or criteria
               BAD - command unknown or arguments invalid

   This section further updates definition of the UID SEARCH command
   described in section 2.6.1 of [RFC4466] (initially described in
   section 6.4.4 of [RFC3501] and extended by [RFC4731]).

   The UID SEARCH command is extended to allow for optional source and
   result options.  This document does not define any new result options
   (see Section 3.1 of [RFC4731]).  A server that supports this
   extension includes [[fix-for-pub-1: "X-DRAFT-I03-MMBX" (changes for
   publication)]] in its IMAP capability string.

2.1.  The ESEARCH response

   Unless specified otherwise by a description of a result option, in
   the presence of a search source option the server MUST return ESEARCH
   responses [RFC4731] instead of the corresponding SEARCH responses.
   Because message numbers are not useful for mailboxes that are not
   selected, the responses need information about UIDs, not message
   numbers.  Therefore, this extension only applies to UID SEARCH, and
   trying to specify source options on plain SEARCH results in a tagged
   BAD response.  This is true even if the source options specify that
   only the selected mailbox be searched.

   Presence of a source option in absence of a result option implies the
   "ALL" result option (see Section 3.1 of [RFC4731]).  Note that this
   is not the same as the result from the SEARCH command described in
   the IMAP base protocol.

   Source options describe which mailboxes must be searched for
   messages.  A UID SEARCH command with source options does not affect
   which mailbox, if any, is currently selected, regardless of which
   mailboxes are searched.

   For each mailbox satisfying the source options, a single ESEARCH
   response MUST be returned if any messages in that mailbox match the
   search criteria.  An ESEARCH response MUST NOT be returned for
   mailboxes that contain no matching messages.  This is true even when
   result options such as MIN, MAX, and COUNT are specified (see section



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   3.1 of [RFC4731]), and the values returned (lowest UID matched,
   highest UID matched, and number of messages matched, respectively)
   apply to the mailbox reported in that ESEARCH response.

   Note that it is now possible for a UID SEARCH command to return *no*
   untagged responses (no SEARCH nor ESEARCH responses), in the case
   that there are no matches to the search in any of the mailboxes that
   satisfy the source options.  Clients can detect this situation by
   finding the tagged OK response without having received any matching
   untagged ESEARCH responses.

   Each ESEARCH response MUST contain the MAILBOX, TAG, and UIDVALIDITY
   correlators.  Correlators allow clients to issue several UID SEARCH
   commands at once (pipelined).  The server MAY perform pipelined
   searches in parallel; or it MAY instead serialize them.

2.2.  Source options -- specifying mailboxes to search

   The source options, if present, MUST contain a mailbox specifier as
   defined in the IMAP NOTIFY extension [RFC5465], section 6 (using the
   "filter-mailboxes" ABNF item), with the following changes:

   1.  The "selected-delayed" specifier is not valid here.

   2.  A "subtree-one" specifier is added.  The "subtree" specifier
       results in a search of the specified mailbox and all selectable
       mailboxes that are subordinate to it, through an indefinitely
       deep hierarchy.  The "subtree-one" specifier results in a search
       of the specified mailbox and all selectable child mailboxes, one
       hierarchy level down.

   If "subtree" is specified, the server MUST defend against loops in
   the hierarchy (for example, those caused by recursive file-system
   links within the message store).  The server SHOULD do this by
   keeping track of the mailboxes that have been searched, and
   terminating the hierarchy traversal when a repeat is found.  If it
   can not do that, it MAY do it by limiting the hierarchy depth.

   If the source options are not present, the value "selected" is
   assumed -- that is, only the currently selected mailbox is searched.

   The "personal" source option is a particularly convenient way to
   search all of the current user's mailboxes.  Note that there is no
   way to use wildcard characters to search all mailboxes; the
   "mailboxes" source option does not do wildcard expansion.

   If the source options include (or default to) "selected", the IMAP
   session MUST be in "selected" state.  If the source options specify



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   other mailboxes and NOT "selected", then the IMAP session MUST be in
   either "selected" or "authenticated" state.  If the session is not in
   a correct state, the UID SEARCH command returns a "BAD" result.

   If the server supports the ACL [RFC4314] extension, then the logged
   in user is required to have the 'r' right for each mailbox she wants
   to search.  In addition, any mailboxes that are not explicitly named
   (accessed through "personal" or "subtree", for example) are required
   to have the "l" right.  Mailboxes matching the source options for
   which the logged in user lacks sufficient rights MUST be ignored by a
   multimailbox search.  In particular, ESEARCH responses MUST NOT be
   returned for those mailboxes.


3.  Open Issues

   [[Issues: This is a section of To-Do items and considerations before
   this draft is done.  This section will be worked through, emptied,
   and removed before we send this on.]]

   Interaction with IMAP Contexts [RFC5267] needs to be defined.

   Suggestion: UPDATE option of IMAP Notify [RFC5465] might have to be
   prohibited when both Context and this extension are used.  [Barry:
   But why?  Isn't this then the equivalent of doing many SEARCH
   commands with the UPDATE option?]

   There's a suggestion to add an EXCLUDE clause (with a nested search
   criteria).  For example, one might want to search "personal" but
   exclude "mailboxes (Trash Spam)".

   Cyrus suggests you can use metadata to tag mailboxes that you do or
   don't want to search, and use search criteria to exclude them (good
   for mailboxes that you NEVER want searched (as Trash and Spam,
   above)).


4.  Examples

   C: tag1 UID SEARCH IN ((mailboxes "folder1" subtree "folder2"))
   unseen
   C: tag2 UID SEARCH IN ((mailboxes "folder1" subtree-one "folder2"))
   subject "chad"
   S: * ESEARCH (TAG "tag1" MAILBOX "folder1" UIDVALIDITY 1) UID ALL
   4001,4003,4005,4007,4009
   S: * ESEARCH (TAG "tag2" MAILBOX "folder1" UIDVALIDITY 6789023554)
   UID ALL 195001:195004,169788
   S: * ESEARCH (TAG "tag1" MAILBOX "folder2/banana" UIDVALIDITY 503)



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   UID ALL 3002,4004
   S: * ESEARCH (TAG "tag1" MAILBOX "folder2/peach" UIDVALIDITY 3) UID
   ALL 921691
   S: tag1 OK done
   S: * ESEARCH (TAG "tag2" MAILBOX "folder2/salmon" UIDVALIDITY
   1111111) UID ALL 50003,50006,50009,50012
   S: tag2 OK done


5.  Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form (ABNF) as described in [RFC5234].  Terms not defined here are
   taken from [RFC3501], [RFC5465], or [RFC4466].

   filter-mailboxes-other =/  ("subtree-one" SP one-or-more-mailbox)
           ; Update definition from IMAP Notify [RFC5465]
           ; Add new "subtree-one" selector.

   filter-mailboxes-selected =  "selected"
           ; Update definition from IMAP Notify [RFC5465]
           ; We forbid the use of "selected-delayed".

   one-correlator =  ("TAG" SP tag-string) / ("MAILBOX" SP astring) /
           ("UIDVALIDITY" SP nz-number)
           ; Each correlator MUST appear exactly once

   scope-option =  scope-option-name [SP scope-option-value]
           ; No options defined here.  Syntax for future extensions.

   scope-option-name =  tagged-ext-label
           ; No options defined here.  Syntax for future extensions.

   scope-option-value =  tagged-ext-val
           ; No options defined here.  Syntax for future extensions.

   scope-options =  scope-option *(SP scope-option)
           ; A given option may only appear once
           ; No options defined here.  Syntax for future extensions.

   search =  "SEARCH" [SP search-source-opts] [SP search-return-opts]
           SP search-program
           ; Updates definition in IMAP4 ABNF [RFC4466]

   search-correlator =  SP "(" one-correlator *(SP one-correlator) ")"
           ; Updates definition in IMAP4 ABNF [RFC4466]





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   search-source-opts =  "IN" SP "(" source-mbox [SP
           "(" scope-options ")"] ")"

   source-mbox =  filter-mailboxes *(SP filter-mailboxes)
           ; filter-mailboxes is defined in IMAP Notify [RFC5465]
           ; See updated definition of filter-mailboxes-other, above.
           ; See updated definition of filter-mailboxes-selected, above.


6.  Security Considerations

   This extension to the IMAP UID SEARCH command allows a single command
   to search many mailboxes at once.  On the one hand, a client could do
   that by sending many IMAP SEARCH commands.  On the other hand, this
   makes it easier for a client to overwork a server, by sending a
   single command that results in an expensive search of tens of
   thousands of mailboxes.  Server implementations need to be aware of
   that, and provide mechanisms that prevent a client from adversely
   affecting other users.  Limitations on the number of mailboxes that
   may be searched in one command, and/or on the server resources that
   will be devoted to responding to a single client, are reasonable
   limitations for an implementation to impose.

   Implementations MUST, of course, apply access controls appropriately,
   limiting a user's access to UID SEARCH in the same way its access is
   limited for any other IMAP commands.  This extension has no data-
   access risks beyond what may be there in the unextended IMAP
   implementation.


7.  IANA Considerations

   IMAP4 capabilities are registered by publishing a standards track or
   IESG approved experimental RFC.  The registry is currently located
   here:


      http://www.iana.org/assignments/imap4-capabilities


   This document defines the IMAP capability [[fix-for-pub-2: X-DRAFT-
   I03-MMBX (changes for publication)]], and IANA is asked to add it to
   the registry.


8.  Acknowledgements

   The authors gratefully acknowledge feedback provided by Timo



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   Sirainen, Peter Coates and Arnt Gulbrandsen.


9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2978]  Freed, N. and J. Postel, "IANA Charset Registration
              Procedures", BCP 19, RFC 2978, October 2000.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

   [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
              RFC 4314, December 2005.

   [RFC4466]  Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
              ABNF", RFC 4466, April 2006.

   [RFC4731]  Melnikov, A. and D. Cridland, "IMAP4 Extension to SEARCH
              Command for Controlling What Kind of Information Is
              Returned", RFC 4731, November 2006.

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

   [RFC5267]  Cridland, D. and C. King, "Contexts for IMAP4", RFC 5267,
              July 2008.

   [RFC5465]  Gulbrandsen, A., King, C., and A. Melnikov, "The IMAP
              NOTIFY Extension", RFC 5465, February 2009.


Authors' Addresses

   Barry Leiba
   Huawei Technologies

   Phone: +1 646 827 0648
   Email: barryleiba@computer.org
   URI:   http://internetmessagingtechnology.org/









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

   Email: Alexey.Melnikov@isode.com
   URI:   http://www.melnikov.ca/










































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