Network Working Group E. Burger, Ed.
Request for Comments: 5032 BEA Systems, Inc.
Updates: 3501 September 2007
Category: Standards Track
WITHIN Search Extension to the IMAP Protocol
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document describes the WITHIN extension to IMAP SEARCH. IMAP
SEARCH returns messages whose internal date is within or outside a
specified interval. The mechanism described here, OLDER and YOUNGER,
differs from BEFORE and SINCE in that the client specifies an
interval, rather than a date. WITHIN is useful for persistent
searches where either the device does not have the capacity to
perform the search at regular intervals or the network is of limited
bandwidth and thus there is a desire to reduce network traffic from
sending repeated requests and redundant responses.
1. Introduction
This extension exposes two new search keys, OLDER and YOUNGER, each
of which takes a non-zero integer argument corresponding to a time
interval in seconds. The server calculates the time of interest by
subtracting the time interval the client presents from the current
date and time of the server. The server then either returns messages
older or younger than the resultant time and date, depending on the
search key used.
1.1. 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 [RFC2119].
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When describing the general syntax, we omit some definitions, as RFC
3501 [RFC3501] defines them.
2. Protocol Operation
An IMAP4 server that supports the capability described here MUST
return "WITHIN" as one of the server supported capabilities in the
CAPABILITY command.
For both the OLDER and YOUNGER search keys, the server calculates a
target date and time by subtracting the interval, specified in
seconds, from the current date and time of the server. The server
then compares the target time with the INTERNALDATE of the message,
as specified in IMAP [RFC3501]. For OLDER, messages match if the
INTERNALDATE is less recent than or equal to the target time. For
YOUNGER, messages match if the INTERNALDATE is more recent than or
equal to the target time.
Both OLDER and YOUNGER searches always result in exact matching, to
the resolution of a second. However, if one is doing a dynamic
evaluation, for example, in a context [CONTEXT], one needs to be
aware that the server might perform the evaluation periodically.
Thus, the server may delay the updates. Clients MUST be aware that
dynamic search results may not reflect the current state of the
mailbox. If the client needs a search result that reflects the
current state of the mailbox, we RECOMMEND that the client issue a
new search.
3. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation. Elements not defined here can be found in the
formal syntax of ABNF [RFC4234] and IMAP [RFC3501].
This document extends RFC 3501 [RFC3501] with two new search keys:
OLDER <interval> and YOUNGER <interval>.
search-key =/ ( "OLDER" / "YOUNGER" ) SP nz-number
; search-key defined in RFC 3501
4. Example
C: a1 SEARCH UNSEEN YOUNGER 259200
S: a1 * SEARCH 4 8 15 16 23 42
Search for all unseen messages within the past 3 days, or 259200
seconds, according to the server's current time.
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5. Security Considerations
The WITHIN extension does not raise any security considerations that
are not present in the base protocol. Considerations are the same as
for IMAP [RFC3501].
6. IANA Considerations
Per the IMAP RFC [RFC3501], registration of a new IMAP capability in
the IMAP Capability registry requires the publication of a standards-
track RFC or an IESG approved experimental RFC. The registry is
currently located at
<http://www.iana.org/assignments/imap4-capabilities>. This
standards-track document defines the WITHIN IMAP capability. IANA
has added this extension to the IANA IMAP Capability registry.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC3501] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 3501, March 2003.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
7.2. Informative References
[CONTEXT] Melnikov, D. and C. King, "Contexts for IMAP4", Work
in Progress, May 2006.
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Appendix A. Contributors
Stephane Maes and Ray Cromwell wrote the original version of this
document as part of P-IMAP, as well as the first versions for the
IETF. From an attribution perspective, they are clearly authors.
Appendix B. Acknowledgements
The authors want to thank all who have contributed key insight and
who have extensively reviewed and discussed the concepts of LPSEARCH.
They also thank the authors of its early introduction in P-IMAP.
We also want to give a special thanks to Arnt Gilbrandsen, Ken
Murchison, Zoltan Ordogh, and most especially Dave Cridland for their
review and suggestions. A special thank you goes to Alexey Melnikov
for his choice submission of text.
Author's Address
Eric W. Burger (editor)
BEA Systems, Inc.
USA
EMail: eric.burger@bea.com
URI: http://www.standardstrack.com
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