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.
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.
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.
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].
Burger Standards Track [Page 1]
RFC 5032 Search Within September 2007
When describing the general syntax, we omit some definitions, as RFC 3501 [RFC3501] defines them.
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.
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.
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.
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