Network Working Group N. Freed Internet-Draft Sun Microsystems Expires: September 20, 2007 March 19, 2007 Sieve Email Filtering: Ihave Extension draft-freed-sieve-ihave-00 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 on September 20, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document describes the "ihave" extension to the Sieve email filtering language. The "ihave" extension provides a means to write scripts that can take advantage of optional Sieve features but can still run when those optional features are not available. Change History (to be removed prior to publication as an RFC Changed the comparator used in the ihave test from "i;ascii-casemap" to "i;octet". Freed Expires September 20, 2007 [Page 1] Internet-Draft Sieve Ihave Extension March 2007 Updated the IANA registration template Simplified the semantics of ihave to be independent of block structure. Moved the environment extension to a separate document so the standards status of the two extensions can be different. 1. Introduction Sieve [I-D.ietf-sieve-3028bis] is a language for filtering email messages at or around the time of final delivery. It is designed to be implementable on either a mail client or mail server. It is suitable for running on a mail server where users may not be allowed to execute arbitrary programs, such as on black box Internet Message Access Protocol [RFC3501] servers, as it has no user-controlled loops or the ability to run external programs. A large number of sieve extensions have already been defined and more are sure to be created over time. Sieve's require clause is used to specify the extensions a particular sieve needs; an error results if the script's require clause calls for an extension that isn't available. This mechanism is sufficient in most situations. However, there can be cases where a script may be able to take advantage of an extension if it is available but can still function if it is not, possibly with some degradation of capabilities. The "ihave" extension provides a means to write scripts that make use of other extensions only when they are actually available. Ihave defines a new ihave test that takes a list of capability names as an argument and succeeds if all of the those capabilities are present. Additionally, specification of the "ihave" extension in the require clause disables parse-time checking of extension use in scripts; run- time checking must be used instead. 2. Conventions used in this document 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]. The terms used to describe the various components of the Sieve language are taken from [I-D.ietf-sieve-3028bis] section 1.1. Freed Expires September 20, 2007 [Page 2] Internet-Draft Sieve Ihave Extension March 2007 3. Capability Identifiers The capability string associated with the extension defined in this document is "ihave". 4. Ihave Test Usage: ihave The ihave test provides a means for Sieve scripts to test for the existence of a given extension prior to actually using it. The capabilities argument to ihave is the same as the similarly-named argument to the require control statement: It specifies the names of one or more Sieve extensions or comparators. Unlike most Sieve tests, ihave accepts no match or comparator arguments. The type of match for ihave is always ":is" and the comparator is always "i;octet". The strings in the capabilities list are constant strings in context of Sieve variables [I-D.ietf-sieve-variables]. It is an error to pass a non-constant string as an argument to ihave. The Sieve base specification demands that that all Sieve extensions used in a given script be specified in the initial require control statement. It is an error for a script to call for extensions the interpreter doesn't support or to attempt to use extensions that have not been listed in the script's require clause. Use of ihave changes Sieve interpreter behavior and the underlying requirements in the following ways: 1. Use of a given extension is allowed subsequent to the successful evaluation of an ihave test on that extension. The extension then operates just as if it had been specified in the script's require clause. The extension cannot be used prior to the evaluation of such a test and a runtime error MUST be generated if such usage is attempted. 2. Sieve interpreters normally have the option of checking extension use at either parse time or execution time. The specification of "ihave" in a script's require clause changes this behavior: Scripts MUST either defer extension checking to run time or else take the presence of ihave tests into account at parse time. Note that since ihave can be used inside of anyof, allof, and not tests full parse time checking of ihave may be very difficult to implement. Freed Expires September 20, 2007 [Page 3] Internet-Draft Sieve Ihave Extension March 2007 3. Although it makes little sense to do so, an extension can be specified in both the require control statement and in an ihave test. If this is done and the extension has been implemetned the extension can be used anywhere in the script and ihave test of that extension will always return true. 4. Using ihave to set a variable to a particular value and then testing that variable in another block is not permitted as it unduly complicates parse time analysis of scripts. Ihave is designed to be used with extensions that add tests, actions, or comparators. It MUST NOT be used with extensions that change how the content of Sieve scripts are interpreted such as the variables extension [I-D.ietf-sieve-variables] 5. Security Considerations The ihave extension is essentially a more flexible variant of Sieve's existing require mechanism. As such, it has no real effect on the security considerations associated with the use of Sieve. Of course all of the security considerations given in the base Sieve specification are still relevant. 6. IANA Considerations The following template specifies the IANA registration of the Sieve extension specified in this document: To: iana@iana.org Subject: Registration of new Sieve extension Capability name: ihave Description: The "ihave" extension provides a means to write scripts that make use of other extensions only when they are actually available. RFC number: RFC XXXX Contact address: Ned Freed This information should be added to the list of sieve extensions given on http://www.iana.org/assignments/sieve-extensions. 7. References Freed Expires September 20, 2007 [Page 4] Internet-Draft Sieve Ihave Extension March 2007 7.1. Normative references [I-D.ietf-sieve-3028bis] Guenther, P. and T. Showalter, "Sieve: An Email Filtering Language", draft-ietf-sieve-3028bis-12 (work in progress), February 2007, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative references [I-D.ietf-sieve-variables] Homme, K., "Sieve Mail Filtering Language: Variables Extension", draft-ietf-sieve-variables-08 (work in progress), December 2005, . [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. Author's Address Ned Freed Sun Microsystems 3401 Centrelake Drive, Suite 410 Ontario, CA 92761-1205 USA Phone: +1 909 457 4293 Email: ned.freed@mrochek.com Freed Expires September 20, 2007 [Page 5] Internet-Draft Sieve Ihave Extension March 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Freed Expires September 20, 2007 [Page 6]