Document: draft-melnikov-imap-search-res-00.txt A. Melnikov
Intended category: Standard Track Isode Ltd.
Expires: April 2005 October 2004
IMAP extension for referencing the last SEARCH result
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
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"
[KEYWORDS].
<<Other editorial comments/questions are shown like this.>>
2. New sequence element for referencing the result of the last SEARCH
command.
The SEARCH result reference extension described in this document is
present in any IMAP4 implementation which returns "X-DRAFT-
I00-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 REQUIREs that a compliant
server remembers the result of the latest SEARCH (also UID SEARCH,
SORT, UID SORT) command and stores 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. This way the client can use the result
of the latest SEARCH command as a parameter to another command.
<<Describe advantages of the extension: no need for the client to
send the result of the latest SEARCH as a message set (saving
bandwidth and even CPU); can pipeline SEARCH with subsequent
FETCH/STORE/COPY/UID EXPUNGE.>>
Upon successful completion of SELECT or EXAMINE command, the current
search result variable is reset to the empty sequence. <<Change this
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to "1:*" if this is more useful?>>
A successful SEARCH command 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) doesn't
change the search result variable.
When a message listed in the search result variable is EXPUNGEd, it
is automatically removed from the list. (Implementation note: if the
server stores the list as a list of message numbers, it MUST
automatically adjust them when sending any untagged EXPUNGE response)
If the server decides to send a new UIDVALIDITY value while mailbox
is opened, this causes resetting the search variable to the empty
list.
<<Implementation consideration: SEARCH returned message numbers, the
next command is an UID command (or vice versa)>>
When the mailbox is closed (explicitly or implicitly) the server MUST
forget the value of the search result variable. <<Is this redundant
because of the third paragraph?>>
<<Open Issues:
1). Does this has to be extended to apply to other commands?
2). Add a SEARCH command parameter that suppresses sending untagged
SEARCH result? >>
2.1. Examples
1) The following example demonstrates how the client can use the
result of a SEARCH command to FETCH headers of interesting
messages:
Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
S: * SEARCH 2 84 882
S: A282 OK SEARCH completed
C: A283 FETCH << (UID INTERNALDATE FLAGS RFC822.HEADER)
S: * 2 FETCH (UID 14 ...
S: * 84 FETCH (UID 100 ...
S: * 882 FETCH (UID 1115 ...
S: A283 OK completed
The client can also pipeline the two commands:
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Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
C: A283 FETCH << (UID INTERNALDATE FLAGS RFC822.HEADER)
S: * SEARCH 2 84 882
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
command:
Example: C: A300 SEARCH SINCE 1-Jan-2004 NOT FROM "Smith"
S: * SEARCH 3 16 18 21 501 502 503 504 508 611
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:
Example: C: B282 SEARCH SINCE 1-Feb-1994 NOT FROM "Smith"
S: * SEARCH 2 84 882 1102 2056
S: B282 OK SEARCH completed
C: B283 SEARCH CHARSET KOI8-R 1,<<,3000-3021 TEXT {4}
C: XXXX
S: B283 NO [BADCHARSET UTF-8] KOI8-R is not supported
C: B284 SEARCH CHARSET UTF-8 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 Form (ABNF) notation as specified in [ABNF]. Non-terminals
referenced but not defined below are as defined by [IMAP4].
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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.
seq-range =/ seq-last-command
; Extend seq-range to allow for "result of the
; last command" indicator.
seq-last-command= "<<"
4. Security Considerations
<<>> It is believed that this extension doesn't raise any
additional security concerns not already discussed in [IMAP4].
5. Acknowledgments
The author would like to thank Mark Crispin for reminding that
this document has to be written.
6. Normative references
[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.
[IMAP4] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 3501, University of Washington, March 2003.
<<SORT>>
<<UIDPLUS?>>
7. Author's Addresses
Alexey Melnikov
Isode Ltd.
5 Castle Business Village,
36 Station Road,
Hampton, Middlesex,
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TW12 2BX, United Kingdom
Email: Alexey.Melnikov@isode.com
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