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Versions: 00 01 02 03 04 05 06 07 RFC 5182

Document: draft-melnikov-imap-search-res-02.txt           A. Melnikov
Intended category: Standard Track                          Isode Ltd.
Expires: December 2005                                      June 2005

         IMAP extension for referencing the last SEARCH result

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2005).  All Rights Reserved.


   Many IMAP clients use the result of a SEARCH command as the input to
   perform another operation, for example fetching the found messages,
   deleting them or copying them to another mailbox.

   This can be achieved using standard IMAP operations described in RFC

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   2501, however this would be suboptimal: the server will send the list
   of found messages to the client, after that the client will have to
   parse the list, reformat it and send it back to the server.  The
   client can't pipeline the SEARCH command with the subsequent command.

   This document proposes an IMAP extension that allows a client to tell
   a server to use the result of the latest SEARCH (or UID SEARCH)
   command as an input to any subsequent command.

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 keywords "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in
   this document when typed in uppercase are to be interpreted as
   defined in "Key words for use in RFCs to Indicate Requirement Levels"

   <<Other editorial comments/questions are shown like this.>>

2.   New sequence element for referencing the result of the last SEARCH

   The SEARCH result reference extension described in this document is
   present in any IMAP4 implementation which returns "X-DRAFT-
   I02-SEARCHRES" as one of the supported capabilities in the CAPABILITY
   command response. <<Note to the RFC Editor: the capability name will
   change upon publication as an RFC>>.

   The SEARCH result reference extension defines a new SEARCH result
   option [IMAPABNF] "SAVE" that tells the server to remember the result
   of the SEARCH or UID SEARCH command (as well as any command based on
   SEARCH, e.g. SORT [SORT]) and store it in an internal variable that
   we will reference as the "search result variable". The client can use
   the "$" marker in message (or UID) sequence in order to indicate that
   the server should substitute it with the list of messages from the
   search result variable.  Thus the client can use the result of the
   latest remembered SEARCH command as a parameter to another command.
   The search result marker has several advantages:
    * it avoids wasted bandwidth and associated delay;
    * it allows the client to pipeline a SEARCH command with a
      subsequent FETCH/STORE/COPY/UID EXPUNGE [UIDPLUS] command;
    * the client doesn't need to spend time reformatting the
      result of a SEARCH command into a message set used in

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      the subsequent command;
    * it allows the server to perform optimizations.

   Upon successful completion of SELECT or EXAMINE command, the current
   search result variable is reset to the empty sequence.  <<Change this
   to "1:*" if this is more useful?>>

   A successful SEARCH command with the SAVE result option sets the
   value of the search result variable to the list of messages found in
   the SEARCH command. For example, if no messages were found, the
   search result variable will contain the empty list.  A failed SEARCH
   command (any SEARCH command that caused the server to return BAD or
   NO tagged response) or a successful SEARCH command with no SAVE
   result option doesn't change the search result variable.

   Note that the SAVE result option also instructs the server not to
   send any messages found by the SEARCH command. <<Is there a need in a
   separate option that doesn't suppress output?>>

   When a message listed in the search result variable is EXPUNGEd, it
   is automatically removed from the list.  Implementors are reminded
   that if the server stores the list as a list of message numbers, it
   MUST automatically adjust them when sending any untagged EXPUNGE

   If the server decides to send a new UIDVALIDITY value while mailbox
   is opened, this causes resetting the search variable to the empty

   <<Implementation consideration: SEARCH returned message numbers, the
   next command is an UID command (or vice versa)>>

   <<Open Issues:

   1). Does this has to be extended to apply to other commands, e.g.

 2.1.   Examples

   1) The following example demonstrates how the client can use the
      result of a SEARCH command to FETCH headers of interesting

   Example:    C: A282 SEARCH RETURN (SAVE) FLAGGED SINCE 1-Feb-1994
                  NOT FROM "Smith"
               S: A282 OK SEARCH completed, result saved
               S: * 2 FETCH (UID 14 ...

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               S: * 84 FETCH (UID 100 ...
               S: * 882 FETCH (UID 1115 ...
               S: A283 OK completed

   The client can also pipeline the two commands:

   Example:    C: A282 SEARCH RETURN (SAVE) FLAGGED SINCE 1-Feb-1994
                  NOT FROM "Smith"
               S: A282 OK SEARCH completed
               S: * 2 FETCH (UID 14 ...
               S: * 84 FETCH (UID 100 ...
               S: * 882 FETCH (UID 1115 ...
               S: A283 OK completed

   2) The following example demonstrates that the result of one SEARCH
      command can be used to subset the result of another SEARCH

   Example:    C: A300 SEARCH RETURN (SAVE) SINCE 1-Jan-2004 NOT FROM "Smith"
               S: A300 OK SEARCH completed
               C: A301 UID SEARCH UID $ SMALLER 4096
               S: * SEARCH 17 900 901
               S: A301 OK completed

   3) The following example demonstrates that a failed SEARCH doesn't
      invalidate the search result variable. It also shows that the "$"
      marker can be combined with other message numbers using the OR
      SEARCH criterion.
   Example:    C: B282 SEARCH RETURN (SAVE) SINCE 1-Feb-1994 NOT FROM "Smith"
               S: B282 OK SEARCH completed
               C: B283 SEARCH CHARSET KOI8-R (OR $ 1,3000:3021) TEXT {4}
               C: XXXX
               S: B283 NO [BADCHARSET UTF-8] KOI8-R is not supported
               C: B284 SEARCH CHARSET UTF-8 (OR $ 1,3000:3021) TEXT {8}
               C: YYYYYYYY
               S: * SEARCH 882 1102 3003 3005 3006
               S: B284 OK completed

        Note: Since this document is restricted to 7-bit ASCII text, it
        is not possible to show actual KOI8-R or UTF-8 data.  The "XXXX"
        and ""YYYYYYYY" are placeholders for what would be 4 and 8
        octets of 8-bit data in an actual transaction.

   3.   Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur

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   Form (ABNF) notation as specified in [ABNF]. Non-terminals referenced
   but not defined below are as defined in [IMAP4] 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-SEARCHRES"
                         ;;capability is defined in [IMAP4]

   <<fix capability name before publication>>

   sequence-set       =/ seq-last-command
                         ; Extend sequence-set to allow for "result of the
                         ; last command" indicator.

   seq-last-command   = "$"

   search-return-opt  = "SAVE"

   <<Do we need a non-silent option as well?>>

4.   Security Considerations

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

   <<However, this extension might require the server to keep additional
   state, that may be used to simplify Deny of Service attacks.>>

5.   Acknowledgments

   The author would like to thank Mark Crispin for reminding that this
   document has to be written, as well as for comments and corrections

   The author would also like to thank Dave Cridland for comments and
   corrections received.

6.   References

6.1. Normative references

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

   [ABNF] Crocker, D., and Overell, P. "Augmented BNF for Syntax
   Specifications: ABNF", RFC 2234, November 1997.  <<Updated>>

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

   [IMAPABNF] Melnikov, A., and C. Daboo, "Collected extensions to IMAP4
   ABNF", work in progress, draft-melnikov-imap-ext-abnf-XX.txt.

6.2. Informative references

   [UIDPLUS] Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June 1998.
   Updated by: Crispin, M., "Internet Message Access Protocol (IMAP) -
   UIDPLUS extension", work in progress, draft-crispin-imap-rfc2359bis-

   [SORT] Crispin, M. and  K. Murchison, "INTERNET MESSAGE ACCESS
   PROTOCOL - SORT AND THREAD EXTENSIONS", work in progress, draft-ietf-

7.   Author's Addresses

   Alexey Melnikov
   Isode Ltd.
   5 Castle Business Village,
   36 Station Road,
   Hampton, Middlesex,
   TW12 2BX, United Kingdom

   Email: Alexey.Melnikov@isode.com

8.   Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   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

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

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