Sieve Working Group K. Murchison Internet-Draft Carnegie Mellon University Expires: August 26, 2006 February 22, 2006 Sieve Email Filtering -- Regular Expression Extension draft-ietf-sieve-regex-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 on August 26, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract In some cases, it is desirable to have a string matching mechanism which is more powerful than a simple exact match, a substring match or a glob-style wildcard match. The regular expression matching mechanism defined in this draft should allow users to isolate just about any string or address in a message header or envelope. Meta-information (to be removed prior to publication as an RFC) This information is intended to facilitate discussion. Murchison Expires August 26, 2006 [Page 1] Internet-Draft Sieve -- Regex Extension February 2006 This document is intended to be an extension to the Sieve mail filtering language, available from the RFC repository as . This document and the Sieve language itself are being discussed on the MTA Filters mailing list at . Subscription requests can be sent to (send an email message with the word "subscribe" in the body). More information on the mailing list along with an archive of back messages is available at . Change History (to be removed prior to publication as an RFC) Changes from draft-murchison-sieve-regex-08: o Updated to XML source. o Documented interaction with variables. Open Issues (to be removed prior to publication as an RFC) o The major open issue with this draft is what to do, if anything, about localization/internationalization. Are [IEEE.1003-2.1992] collating sequences and character equivalents sufficient? Should we reference the unicode technical specification? Should we punt and publish the document as experimental? o Should we allow shorthands such as \\b (word boundary) and \\w (word character)? o Should we allow backreferences (useful for matching double words, etc.)? Murchison Expires August 26, 2006 [Page 2] Internet-Draft Sieve -- Regex Extension February 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Capability Identifier . . . . . . . . . . . . . . . . . . . . 5 3. Regex Match Type . . . . . . . . . . . . . . . . . . . . . . . 6 4. Interaction with Sieve Variables . . . . . . . . . . . . . . . 9 4.1. Match variables . . . . . . . . . . . . . . . . . . . . . 9 4.2. Set modifier :quoteregex . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Normative References . . . . . . . . . . . . . . . . . . . . . 12 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15 Murchison Expires August 26, 2006 [Page 3] Internet-Draft Sieve -- Regex Extension February 2006 1. Introduction This document describes an extension to the Sieve language defined by [I-D.ietf-sieve-3028bis] for comparing strings to regular expressions. Conventions for notations are as in [I-D.ietf-sieve-3028bis] section 1.1, including use of [RFC2119]. Murchison Expires August 26, 2006 [Page 4] Internet-Draft Sieve -- Regex Extension February 2006 2. Capability Identifier The capability string associated with the extension defined in this document is "regex". Murchison Expires August 26, 2006 [Page 5] Internet-Draft Sieve -- Regex Extension February 2006 3. Regex Match Type Commands that support matching may take the optional tagged argument ":regex" to specify that a regular expression match should be performed. The ":regex" match type is subject to the same rules and restrictions as the standard match types defined in [I-D.ietf-sieve- 3028bis]. For convenience, the "MATCH-TYPE" syntax element defined in [I-D.ietf-sieve-3028bis] is augmented here as follows: MATCH-TYPE =/ ":regex" Example: require "regex"; # Try to catch unsolicited email. if anyof ( # if a message is not to me (with optional +detail), not address :regex ["to", "cc", "bcc"] "me(\\\\+.*)?@company\\\\.com", # or the subject is all uppercase (no lowercase) header :regex :comparator "i;octet" "subject" "^[^[:lower:]]+$" ) { discard; # junk it } The ":regex" match type is compatible with both the "i;octet" and "i;ascii-casemap" comparators and may be used with them. Implementations MUST support extended regular expressions (EREs) as defined by [IEEE.1003-2.1992]. Any regular expression not defined by [IEEE.1003-2.1992], as well as [IEEE.1003-2.1992] basic regular expressions, word boundaries and backreferences are not supported by this extension. Implementations SHOULD reject regular expressions that are unsupported by this specification as a syntax error. The following tables provide a brief summary of the regular expressions that MUST be supported. This table is presented here only as a guideline. [IEEE.1003-2.1992] should be used as the definitive reference. Murchison Expires August 26, 2006 [Page 6] Internet-Draft Sieve -- Regex Extension February 2006 +------------+------------------------------------------------------+ | Expression | Pattern | +------------+------------------------------------------------------+ | . | Match any single character except newline. | | | | | [ ] | Bracket expression. Match any one of the enclosed | | | characters. A hypen (-) indicates a range of | | | consecutive characters. | | | | | [^ ] | Negated bracket expression. Match any one character | | | NOT in the enclosed list. A hypen (-) indicates a | | | range of consecutive characters. | | | | | \\ | Escape the following special character (match the | | | literal character). Undefined for other characters. | | | NOTE: Unlike [IEEE.1003-2.1992], a double-backslash | | | is required as per section 2.4.2 of | | | [I-D.ietf-sieve-3028bis]. | +------------+------------------------------------------------------+ Table 1: Items to match a single character +------------+------------------------------------------------------+ | Expression | Pattern | +------------+------------------------------------------------------+ | [: :] | Character class (alnum, alpha, blank, cntrl, digit, | | | graph, lower, print, punct, space, upper, xdigit). | | | | | [= =] | Character equivalents. | | | | | [. .] | Collating sequence. | +------------+------------------------------------------------------+ Table 2: Items to be used within a bracket expression (localization) Murchison Expires August 26, 2006 [Page 7] Internet-Draft Sieve -- Regex Extension February 2006 +------------+------------------------------------------------------+ | Expression | Pattern | +------------+------------------------------------------------------+ | ? | Match zero or one instances. | | | | | * | Match zero or more instances. | | | | | + | Match one or more instances. | | | | | {n,m} | Match any number of instances between n and m | | | (inclusive). {n} matches exactly n instances. {n,} | | | matches n or more instances. | +------------+------------------------------------------------------+ Table 3: Quantifiers - Items to count the preceding regular expression +------------+--------------------------------------------+ | Expression | Pattern | +------------+--------------------------------------------+ | ^ | Match the beginning of the line or string. | | | | | $ | Match the end of the line or string. | +------------+--------------------------------------------+ Table 4: Anchoring - Items to match positions +------------+------------------------------------------------------+ | Expression | Pattern | +------------+------------------------------------------------------+ | | | Alternation. Match either of the separated regular | | | expressions. | | | | | ( ) | Group the enclosed regular expression(s). | +------------+------------------------------------------------------+ Table 5: Other constructs Murchison Expires August 26, 2006 [Page 8] Internet-Draft Sieve -- Regex Extension February 2006 4. Interaction with Sieve Variables This extension is compatible with, and may be used in conjunction with the Sieve Variables extension [I-D.ietf-sieve-variables]. 4.1. Match variables A sieve interpreter which supports both "regex" and "variables", MUST set "match variables" (as defined by [I-D.ietf-sieve-variables] section 3.2) whenever the ":regex" match type is used. The list of match variables will contain the strings corresponding to the group operators in the regular expression. The groups are ordered by the position of the opening parenthesis, from left to right. Note that in regular expressions, expansions match as much as possible (greedy matching). Example: require ["fileinto", "regex", "variables"]; if header :regex "List-ID" "<(.*)@" { fileinto "lists.${1}"; stop; } # Imagine the header # Subject: [acme-users] [fwd] version 1.0 is out if header :regex "Subject" "^[(.*)] (.*)$" { # ${1} will hold "acme-users] [fwd" stop; } 4.2. Set modifier :quoteregex A sieve interpreter which supports both "regex" and "variables", MUST support the optional tagged argument ":quoteregex" for use with the "set" action. The ":quoteregex" modifier is subject to the same rules and restrictions as the standard modifiers defined in [I-D.ietf-sieve-variables] section 4. For convenience, the "MODIFIER" syntax element defined in [I-D.ietf- sieve-variables] is augmented here as follows: MODIFIER =/ ":quoteregex" This modifier adds the necessary quoting to ensure that the expanded text will only match a literal occurrence if used as a parameter to :regex. Every character with special meaning (".", "*", "?", etc.) is prefixed with "\" in the expansion. This modifier has a Murchison Expires August 26, 2006 [Page 9] Internet-Draft Sieve -- Regex Extension February 2006 precedence value of 20 when used with other modifiers. Murchison Expires August 26, 2006 [Page 10] Internet-Draft Sieve -- Regex Extension February 2006 5. IANA Considerations The following template specifies the IANA registration of the "regex" Sieve extension specified in this document: To: iana@iana.org Subject: Registration of new Sieve extension Capability name: regex Capability keyword: regex Capability arguments: N/A Standards Track/IESG-approved experimental RFC number: this RFC Person and email address to contact for further information: Kenneth Murchison E-Mail: murch@andrew.cmu.edu This information should be added to the list of Sieve extensions given on http://www.iana.org/assignments/sieve-extensions. Murchison Expires August 26, 2006 [Page 11] Internet-Draft Sieve -- Regex Extension February 2006 6. Security Considerations Security considerations are discussed in [I-D.ietf-sieve-3028bis]. It is believed that this extension does not introduce any additional security concerns. However, a poor implementation COULD introduce security problems ranging from degradation of performance to denial of service. If an implementation uses a third-party regular expression library, that library should be checked for potentially problematic regular expressions, such as "(.*)*". 7. Normative References [I-D.ietf-sieve-3028bis] Showalter, T. and P. Guenther, "Sieve: An Email Filtering Language", draft-ietf-sieve-3028bis-05 (work in progress), November 2005. [I-D.ietf-sieve-variables] Homme, K., "Sieve Extension: Variables", draft-ietf-sieve-variables-08 (work in progress), December 2005. [IEEE.1003-2.1992] Institute of Electrical and Electronics Engineers, "Information Technology - Portable Operating System Interface (POSIX) - Part 2: Shell and Utilities (Vol. 1)", IEEE Standard 1003.2, 1992. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Murchison Expires August 26, 2006 [Page 12] Internet-Draft Sieve -- Regex Extension February 2006 Appendix A. Acknowledgments Most of the text documenting the interaction with Sieve variables was taken from an early draft of Kjetil Homme's Sieve variables specification. Thanks to Tim Showalter, Alexey Melnikov, Tony Hansen, Phil Pennock, Jutta Degener, and Ned Freed for their help with this document. Murchison Expires August 26, 2006 [Page 13] Internet-Draft Sieve -- Regex Extension February 2006 Author's Address Kenneth Murchison Carnegie Mellon University 5000 Forbes Avenue Cyert Hall 285 Pittsburgh, PA 15213 US Phone: +1 412 268 2638 Email: murch@andrew.cmu.edu Murchison Expires August 26, 2006 [Page 14] Internet-Draft Sieve -- Regex Extension February 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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