






Network Working Group                                        K. Murchison
Document: draft-murchison-sieve-regex-06.txt           Oceana Matrix Ltd.
Expires January 5, 2003                                      30 June 2002


                    Sieve -- Regular Expression Extension


Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.  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
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    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
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    To view the list Internet-Draft Shadow Directories, see
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    Distribution of this memo is unlimited.

Copyright Notice

    Copyright (C) The Internet Society 2002. All Rights Reserved.


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.










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                           Table of Contents



Status of this Memo  . . . . . . . . . . . . . . . . . . . . . . . .   1

Copyright Notice . . . . . . . . . . . . . . . . . . . . . . . . . .   1

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1

0.     Meta-information on this draft  . . . . . . . . . . . . . . .   3

0.1.   Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   3

0.2.   Noted Changes . . . . . . . . . . . . . . . . . . . . . . . .   3

0.2.1  since -05 . . . . . . . . . . . . . . . . . . . . . . . . . .   3

0.2.2  since -04 . . . . . . . . . . . . . . . . . . . . . . . . . .   3

0.3.   Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .   3

1.     Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4

2.     Capability Identifier . . . . . . . . . . . . . . . . . . . .   4

3.     Regex Match Type  . . . . . . . . . . . . . . . . . . . . . .   4

4.     Security Considerations . . . . . . . . . . . . . . . . . . .   6

5.     Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6

6.     Author's Address  . . . . . . . . . . . . . . . . . . . . . .   7

Appendix A.  References  . . . . . . . . . . . . . . . . . . . . . .   7

Appendix B.  Full Copyright Statement  . . . . . . . . . . . . . . .   8














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0.     Meta-information on this draft

    This information is intended to facilitate discussion.  It will be
    removed when this document leaves the Internet-Draft stage.


0.1.   Discussion

    This draft is intended to be an extension to the Sieve mail filtering
    language, available from the RFC repository as
    <ftp://ftp.ietf.org/rfc/rfc3028.txt>.

    This draft and the Sieve language itself are being discussed on the
    MTA Filters mailing list at <ietf-mta-filters@imc.org>.  Subscription
    requests can be sent to <ietf-mta-filters-request@imc.org> (send an
    email message with the word "subscribe" in the body).  More
    information on the mailing list along with a WWW archive of back
    messages is available at <http://www.imc.org/ietf-mta-filters/>.


0.2.   Noted Changes


0.2.1  since -05

    Added open issue regarding localization/internationalization.

    Added that implementations SHOULD reject regexes not supported by
    this extension.

    Editorial changes.


0.2.2  since -04

    Editorial changes.


0.3.   Open Issues

    The major open issue with this draft is what to do, if anything,
    about localization/internationalization.  Are [POSIX.2] collating
    sequences and character equivalents sufficient?







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1.  Introduction

    This is an extension to the Sieve language defined by [SIEVE] for
    comparing strings to regular expressions.

    Conventions for notations are as in [SIEVE] section 1.1, including
    use of [KEYWORDS].


2.  Capability Identifier

    The capability string associated with the extension defined in this
    document is "regex".


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 [SIEVE].  For
    convenience, the "MATCH-TYPE" syntax element defined in [SIEVE] 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 [POSIX.2].  Any regular expression not defined by



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    [POSIX.2], as well as [POSIX.2] 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 table provides a brief summary of the regular
    expressions that MUST be supported.  This table is presented here
    only as a guideline.  [POSIX.2] should be used as the definitive
    reference.


    +------------+-----------------------------------------------------+
    | Expression |  Pattern                                            |
    +------------+-----------------------------------------------------+
    |                Items to match a single character                 |
    +------------+-----------------------------------------------------+
    |     .      |  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 [POSIX.2], a double-backslash is      |
    |            |  required as per section 2.4.2 of [SIEVE].          |
    +------------+-----------------------------------------------------+
    |   Items to be used within a bracket expression (localization)    |
    +------------+-----------------------------------------------------+
    |   [: :]    |  Character class (alnum, alpha, blank, cntrl,       |
    |            |  digit, graph, lower, print, punct, space,          |
    |            |  upper, xdigit).                                    |
    |   [= =]    |  Character equivalents.                             |
    |   [. .]    |  Collating sequence.                                |
    +------------+-----------------------------------------------------+
    |  Quantifiers - Items to count the preceding regular expression   |
    +------------+-----------------------------------------------------+
    |     ?      |  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.      |
    +------------+-----------------------------------------------------+





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    +------------+-----------------------------------------------------+
    | Expression |  Pattern                                            |
    +------------+-----------------------------------------------------+
    |              Anchoring - Items to match positions                |
    +------------+-----------------------------------------------------+
    |     ^      |  Match the beginning of the line or string.         |
    |     $      |  Match the end of the line or string.               |
    +------------+-----------------------------------------------------+
    |                        Other constructs                          |
    +------------+-----------------------------------------------------+
    |     |      |  Alternation.  Match either of the separated        |
    |            |  regular expressions.                               |
    |    ( )     |  Group the enclosed regular expression(s).          |
    +------------+-----------------------------------------------------+


4.  Security Considerations

    Security considerations are discussed in [SIEVE].  It is believed
    that this extension doesn't 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 "(.*)*".


5.  Acknowledgments

    Thanks to Tim Showalter, Alexey Melnikov, Tony Hansen, Phil Pennock
    and Jutta Degener for their help with this document.


















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6.  Author's Address

    Kenneth Murchison
    Oceana Matrix Ltd.
    21 Princeton Place
    Orchard Park, NY 14127

    Phone: (716) 662-8973
    EMail: ken@oceana.com


Appendix A.  References

     [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", Harvard University, RFC 2119, March, 1997.


     [SIEVE] Showalter, T., "Sieve: A Mail Filtering Language", Miraˇ
         point, Inc., RFC 3028, January 2001.


     [POSIX.2], "Portable Operating System Interface (POSIX). Part 2,
         Shell and utilities", National Institute of Standards and Techˇ
         nology (U.S.).



























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Appendix B.  Full Copyright Statement

    Copyright (C) The Internet Society 2002. All Rights Reserved.

    This document and translations of it may be copied and furnished to
    others, and derivative works that comment on or otherwise explain it
    or assist in its implementation may be prepared, copied, published
    and distributed, in whole or in part, without restriction of any
    kind, provided that the above copyright notice and this paragraph
    are included on all such copies and derivative works.  However, this
    document itself may not be modified in any way, such as by removing
    the copyright notice or references to the Internet Society or other
    Internet organizations, except as needed for the purpose of develop-
    ing Internet standards in which case the procedures for copyrights
    defined in the Internet Standards process must be followed, or as
    required to translate it into languages other than English.

    The limited permissions granted above are perpetual and will not be
    revoked by the Internet Society or its successors or assigns.

    This document and the information contained herein is provided on an
    "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
    TASK FORCE DISCLAIMS 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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