IMAPEXT A. Melnikov Internet-Draft Isode Limited Intended status: Standards Track T. Sirainen Expires: November 13, 2009 May 12, 2009 IMAP4 Extension for returning STATUS information in extended LIST draft-ietf-morg-status-in-list-01 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 13, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract Many IMAP clients display information about total number of messages/ total number of unseen messages in IMAP mailboxes. In order to do that they are forced to issue a LIST or LSUB command, to list all Melnikov & Sirainen Expires November 13, 2009 [Page 1]
Internet-Draft STATUS in IMAP LIST May 2009 available mailboxes, followed by a STATUS command for each mailbox found. This document provides an extension to LIST command that allows the client to request STATUS information for mailboxes together with other information typically returned by the LIST command. Note A revised version of this draft document will be submitted to the RFC editor as a Proposed Standard for the Internet Community. Discussion and suggestions for improvement are requested, and should be sent to morg@ietf.org. Table of Contents 1. Conventions used in this document . . . . . . . . . . . . . . . 3 2. STATUS return option to LIST command . . . . . . . . . . . . . 3 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6 Melnikov & Sirainen Expires November 13, 2009 [Page 2]
Internet-Draft STATUS in IMAP LIST May 2009 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 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 [Kwds]. 2. STATUS return option to LIST command [RFC3501] explicitly disallows mailbox patterns in the STATUS command. The main reason was to discourage frequent use of the STATUS command by clients, as it might be quite expensive for an IMAP server to perform. However this prohibition had resulted in an opposite effect: a new generation of IMAP clients appeared, that issues STATUS command for each mailbox returned by the LIST command. This behaviour is suboptimal to say at least: it wastes extra bandwidth and, in the case of a client that doesn't support IMAP pipelining, also degrades performance by using too many round trips. This document tries to remedy the situation by specifying a single command that can be used by the client to request all the necessary information. In order to achieve this goal this document is extending the LIST command command with a new return option: STATUS. This option takes STATUS data items as parameters. For each selectable mailbox matching the list pattern and selection options, the server MUST return an untagged LIST response followed by an untagged STATUS response containing the information requested in the STATUS return option. If an attempted STATUS for a listed mailbox fails because the mailbox can't be selected (e.g. if the "l" ACL right [ACL] is granted to the mailbox and the "r" right is not granted, or due to a race condition between LIST and STATUS changing the mailbox to \NoSelect), the STATUS response MUST NOT be returned and the LIST response MUST include the \NoSelect attribute. This means the server may have to buffer the LIST reply until it has successfully looked up the necessary STATUS information. If the server runs into unexpected problems while trying to look up the STATUS information, it MAY drop the corresponding STATUS reply. In such situation the LIST command would still return a tagged OK reply. Melnikov & Sirainen Expires November 13, 2009 [Page 3]
Internet-Draft STATUS in IMAP LIST May 2009 3. Examples C: A01 LIST "" % RETURN (STATUS (MESSAGES UNSEEN)) S: * LIST () "." "INBOX" S: * STATUS "INBOX" (MESSAGES 17 UNSEEN 16) S: * LIST () "." "foo" S: * STATUS "foo" (MESSAGES 30 UNSEEN 29) S: * LIST (\NoSelect) "." "bar" S: A01 OK List completed. "bar" mailbox isn't selectable, so it has no STATUS reply. C: A02 LIST (SUBSCRIBED RECURSIVEMATCH)"" % RETURN (STATUS (MESSAGES)) S: * LIST (\Subscribed) "." "INBOX" S: * STATUS "INBOX" (MESSAGES 17) S: * LIST () "." "foo" (CHILDINFO ("SUBSCRIBED")) S: A02 OK List completed. LIST reply for "foo" is returned because it has matching children, but no STATUS reply is returned because "foo" itself doesn't match the selection criteria. 4. Formal Syntax The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in [ABNF]. Terms not defined here are taken from [RFC3501], [LISTEXT]. return-option =/ status-option status-option = "STATUS" SP "(" status-att *(SP status-att) ")" ;; This ABNF production complies with ;; <option-extension> syntax. 5. Security Considerations This extension makes it a bit easier for clients to overload the server by requesting STATUS information for a large number of mailboxes. However as already noted in the introduction existing clients already try to do that by generating a large number of STATUS commands for each mailbox they are interested in. While performing STATUS information retrieval for big lists of mailboxes a server implementation needs to make sure that it can still serve other IMAP connections and yield execution to other connections, when necessary. Melnikov & Sirainen Expires November 13, 2009 [Page 4]
Internet-Draft STATUS in IMAP LIST May 2009 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-I00-LIST-STATUS [[anchor4: Note to RFC Editor: fix before publication]] IMAP capability. IANA is requested to add it to the registry. IANA is also requested to add the following new LIST-EXTENDED option to the IANA registry established by [LISTEXT]: To: iana@iana.org Subject: Registration of LIST-EXTENDED option STATUS LIST-EXTENDED option name: STATUS LIST-EXTENDED option type: RETURN LIST-EXTENDED option description: Causes the LIST command to return STATUS responses in addition to LIST responses. Published specification : XXXX. Security considerations: XXXX. Intended usage: COMMON Person and email address to contact for further information: Alexey Melnikov <Alexey.Melnikov@isode.com> Owner/Change controller: iesg@ietf.org 7. Acknowledgements Thanks to Philip Van Hoof who pointed out that STATUS and LIST commands should be combined in order to optimize traffic and number of round trips. Melnikov & Sirainen Expires November 13, 2009 [Page 5]
Internet-Draft STATUS in IMAP LIST May 2009 8. Normative References [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 5234, January 2008. [ACL] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", RFC 4314. [Kwds] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [LISTEXT] Leiba, B. and A. Melnikov, "IMAP4 LIST Command Extensions", RFC 5258, 2008. [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. Authors' Addresses Alexey Melnikov Isode Limited 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX UK Email: Alexey.Melnikov@isode.com URI: http://www.melnikov.ca/ Timo Sirainen Email: tss@iki.fi Melnikov & Sirainen Expires November 13, 2009 [Page 6]
