Network Working Group Arnt Gulbrandsen Request for Comments: DRAFT Oryx Mail Systems GmbH September 2006 The IMAP ENABLE Extension draft-gulbrandsen-imap-enable-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 in March, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The ENABLE extension allows an IMAP client to enable certain IMAP extensions explicitly. 1. Conventions Used in This Document The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD Gulbrandsen Expires March 2007 [Page 1] Internet-draft September 2006 NOT", and "MAY" in this document are to be interpreted as described in "Key words for use in RFCs to Indicate Requirement Levels" [KEYWORDS]. Formal syntax is defined by [ABNF] as modified by [IMAP] and [IMAPABNF]. Example lines prefaced by "C:" are sent by the client and ones prefaced by "S:" by the server. The five characters [...] means that something has been elided. 2. Overview [CONDSTORE], [ANNOTATE] and some extensions under consideration at the moment use various commands to enable server extensions. CONDSTORE, for example, uses a SELECT or FETCH parameter. However, SELECT starts a session and FETCH fetches messages. This extension adds a command, ENABLE, which enables such extensions without causing any other effect. An IMAP server which supports ENABLE advertises this by including the word ENABLE in its capability list. 3. The ENABLE Command Arguments: capability names Result: OK: Relevant capabilities enabled BAD: No arguments, or syntax error in an argument The ENABLE command takes a list of capability names, and requests the server to enable the named extensions. Once enabled using ENABLE, each extension remains active until the IMAP connection is closed. For each argument, the server does the following: - If the argument is not an extension known to the server, the server MUST ignore the argument. - If the argument is an extension known to the server, and it does not make sense to enable the extension in this way, the server MUST ignore the argument. (For example, ENABLE ID does nothing because [ID] does not need to be enabled in the server prior to being used.) - If the argument is an extension is supported by the server and which needs to be enabled, the server MUST enable the extension for the duration of the connection. At present this applies only to CONDSTORE. Gulbrandsen Expires March 2007 [Page 2] Internet-draft September 2006 In this example, the client enables CONDSTORE: C: a ENABLE CONDSTORE S: a OK Conditional Store enabled In the next example, the client asks about the server capabilities, the server tells the client only what's usable prior to login, the client enables CONDSTORE and X-GOOD-IDEA, then it logs in. C: a CAPABILITY S: * CAPABILITY IMAP4rev1 AUTH=CRAM-MD5 AUTH=DIGEST-MD5 ID LITERAL+ S: a OK foo C: b ENABLE CONDSTORE X-GOOD-IDEA S: b OK foo C: c LOGIN d e S: c OK foo C: d CAPABILITY S: * CAPABILITY IMAP4rev1 ID LITERAL+ CONDSTORE S: d OK foo After command b, the client does not know whether CONDSTORE and X- GOOD-IDEA are enabled. After command d, the client learns that the server supports CONDSTORE but not X-GOOD-IDEA, so it knows that CONDSTORE is enabled. 4. Formal Syntax The following syntax specification uses the Augmented Backus-Naur Form (ABNF) notation as specified in [ABNF]. [IMAP] defines the non- terminals "capability" and "command-any". 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 =/ "ENABLE" command-any =/ "ENABLE" 1*(SP capability) 5. Security considerations This document does not add any new security considerations to IMAP. Gulbrandsen Expires March 2007 [Page 3] Internet-draft September 2006 6. IANA considerations The IANA is requested to add ENABLE to the list of IMAP extensions. 7. Credits The idea for this draft came from Randy Gellens. Alexey Melnikov thought it was a good idea. The author of this document typed it down and added the open issues section. 8. Normative References [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, Brandenburg Internetworking, Demon Internet Ltd, October 2005. [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997. [IMAP] Crispin, "Internet Message Access Protocol - Version 4rev1", RFC 3501, University of Washington, June 2003. [IMAPABNF] Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF", RFC 4466, Isode Ltd., April 2006. 8. Informative References [CONDSTORE] Melnikov, Hole, "IMAP Extension for Conditional STORE Operation or Quick Flag Changes Resynchronization", RFC 4551, Isode Ltd., June 2006. [ID] Showalter, "IAMP4 ID extension", RFC 2971, Mirapoint Inc., October 2000. Gulbrandsen Expires March 2007 [Page 4] Internet-draft September 2006 10. Author's Address Arnt Gulbrandsen Oryx Mail Systems GmbH Schweppermannstr. 8 D-81671 Muenchen Germany Fax: +49 89 4502 9758 Email: arnt@oryx.com Open Issues [Note to RFC editor: Please delete before publishing.] Is a DISABLE command necessary? Is there any benefit to it? Is there any benefit to not having a DISABLE? Is there any benefit to restricting the capabilities that can be specified with ENABLE? Should ENABLE be a command-nonauth, so clients have to declare their desires right at the start? That might simplify some server implementations, particularly proxies. Servers would have to ignore any capability names they don't know. At the moment a client can "enable" any capability, even ones not advertised by the server. This allows a client to enable all it can support right at the start, even though the server won't advertise its capabilities until after LOGIN/STARTTLS. Gulbrandsen Expires March 2007 [Page 5] Internet-draft September 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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