IMAP4 Extension to SEARCH Command for Controlling What Kind of Information Is Returned
draft-melnikov-imap-search-ret-03

Internet Draft                                             A. Melnikov
Document: draft-melnikov-imap-search-ret-03                  Isode Ltd
Expires: December 2006                                     D. Cridland
                                                 Inventure Systems Ltd
                                                             June 2006

    IMAP4 extension to SEARCH command for controlling what kind of
                        information is returned
                   draft-melnikov-imap-search-ret-03
   
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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 and
   number of found messages.
   
   
Table of Contents

  1. Conventions Used in this Document                              2
  2. Introduction                                                   3
  3. IMAP Protocol Changes                                          3
     3.1 SEARCH/UID SEARCH Commands                                 3
  4. Formal Syntax                                                  6
  5. Security Considerations                                        7
  6. IANA Considerations                                            7
  7. References                                                     7
     7.1 Normative References                                       7
     7.2 Informative References                                     8
  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
     
   
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>> capability supports the following result options:
   minimal value, maximal value, all found messages and number of
   found messages. These result options allows clients to get SEARCH
   results in more convenient forms, while also saving bandwidth
   required to transport the results, for example 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.
   
   
   
3.   IMAP Protocol Changes

3.1  New SEARCH/UID SEARCH 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 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 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 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 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 described above is 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 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, for example the MIN result specifier will be followed by
   an 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  Interaction with CONDSTORE extension
   
   When the server supports both the X-DRAFT-I02-ESEARCH <<fix before
   publication>> 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] or [IMAPABNF].
   
   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.
   
     
     capability         =/ "X-DRAFT-I02-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
     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 general case IMAP SEARCH/UID SEARCH command can be CPU and/or IO
   intensive, so some sites/implementations even disable it 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, they only change how information about found messages
   is returned. MIN and MAX SEARCH result options described in this
   document can lighten load on IMAP servers, which chose 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
   or 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>> IMAP capability.  IANA is requested to add this
   capability to the registry.
   

7.   References

7.1  Normative References
   
   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", RFC 2119, March 1997.
   
   [IMAP4] Crispin, M., "Internet Message Access Protocol - 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 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 and Pete Maclean for comments and corrections.

9.   Author's Addresses
   
   Alexey Melnikov
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex, TW12 2BX
   UK
   
   Email: Alexey.Melnikov@isode.com
   
   
   Dave A. Cridland
   Inventure Systems Limited
   
   Email: dave.cridland@inventuresystems.co.uk
   URL: http://invsys.co.uk/dave/

10.  Full Copyright Statement
   
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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 the extension.
      Added more examples. Updated reference to the ABNF document.
   03   Clarified interaction with CONDSTORE. Multiple editorial changes
      to align with [IMAPABNF].