Network Working Group K. T. Homme Document: draft-homme-sieve-variables-01.txt University of Oslo Expires October 17, 2003 17 Apr 2003 Sieve -- Variables Extension Status of this Memo This document is an Internet-Draft and is subject to 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 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference mate¡ rial 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 To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Distribution of this memo is unlimited. Abstract In advanced filtering rule sets, it is useful to keep state or con¡ figuration details across rules. This extension adds an action to store data in variables, an action to retrieve the current time, changes the interpolation of strings, and supplies a new test so that the value of a string can be examined. 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 Homme [Page 1]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 <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 informa¡ tion 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. Changes since -00 a) allow generic time zone names, without requiring implementations to support it. added a "${timezone}" variable so that the user can check if the implementation does support the time zone name he wants. the default time zone was changed to localtime again. b) allow back references from :matches as well as :regex. c) added a section on implementation limits. d) clarified global scope so that it spans include. e) clarified that this draft only affects scripts which require "vari¡ ables". f) changed modifiers into being tagged arguments for SET, added prece¡ dence table. g) added optional COMPARATOR to SET to solve the internationalisation problem with :lower etc. h) the name of the variable being SET is passed in a string to conform with overall Sieve grammar. this string is explicitly disallowed from containing variable references. 0.3. Open Issues a) should we include more predefined variables to access the time? (weekday, week number (US, EU and/or ISO?), name of month, name of weekday, ...) could use strftime(3c) as a list of what to offer, but the names should be in English. b) this extension is particularily useful if fileinto creates new folders on demand. [SIEVE] doesn't prohibit this, and currently some implementations will create new folders automatically, others won't. c) the NOTIFY draft has variables, too. it would be nice if the syn¡ tax for the two extensions agreed. a changed NOTIFY can be used on its own without the variables extension, the user simply won't be Homme [Page 2]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 able to configure the notification message to include different snippets from the message. 1. Introduction This is an extension to the Sieve language defined by [SIEVE]. It adds support for storing and referencing data in string variables. The mechanisms detailed in this document will only apply to Sieve scripts which include a require clause for the "variables" extension. The require clauses themselves are not affected by this extension. 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 "variables". 3. Interpretation of strings This extension changes the semantics of quoted-string, multi-line- literal and multi-line-dotstuff found in [SIEVE] to enable the inclu¡ sion of the value of variables. The syntax follows [ABNF]. variable-ref = "${" variable-name "}" variable-name = num-variable / identifier num-variable = 1*DIGIT When the string is evaluated, substrings matching variable-ref shall be replaced by the value of variable-name. Only one pass through the string shall be done. Variable names are case insensitive. Unknown variables are replaced by the empty string. As per the grammar, illegal variable names leaves the would-be variable-ref verbatim, since it doesn't match the variable-ref syntax. Examples: "&%${}!" => unchanged, as the empty string is an illegal identifier "${doh!}" => unchanged, as "!" is illegal in identifiers The variable company holds the value "ACME". No other variables are set. "${full}" => the empty string "${company}" => "ACME" "${President, ${Company} Inc.}" => "${President, ACME Inc.}" The expanded string MUST use the variable values which are current when control reaches the statement the string is part of. Homme [Page 3]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 3.1. Quoting The semantics of quoting using backslash are not changed: backslash quoting is resolved before doing variable substitution. Examples: "${fo\o}" => ${foo} => the expansion of variable foo. "${fo\\o}" => ${fo\o} => illegal identifier => left verbatim. "\${foo}" => ${foo} => the expansion of variable foo. "\\${foo}" => \${foo} => a backslash character followed by the expansion of variable foo. If it is required to include a character sequence such as "${beep}" verbatim in a text literal, the user can define a variable to circum¡ vent expansion to the empty string. Example: set dollar "$" set text "regarding ${dollar}{beep}" 3.2. Numeric variables The decimal value of the numeric variable name will index the list of matching strings from the most recently evaluated match of type ":matches" or ":regex". The list is empty if the match was unsuc¡ cessful. For ":matches", the list will contain one string for each wildcard in the match pattern. Each string holds what the corresponding wildcard expands to, possibly the empty string. The wildcards expand greed¡ ily. For ":regex", the list will contain the strings corresponding to the group operators. The groups are ordered by the position of the open¡ ing parenthesis, from left to right. The first string in the list has index 1. If the index is out of range, the empty string will be substituted. Index 0 returns the number of strings in the list. Example: require [ "fileinto", "regex", "variables" ]; if header :regex "List-ID" "<(.*)@" { fileinto "lists.${1}"; stop; } # this is equivalent to the above: if header :matches "List-ID" "<*@" { fileinto "lists.${1}"; stop; } if header :matches [ "To", "Cc" ] "coyote@**.com" { Homme [Page 4]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 # ${0} is always "2", and ${2} is always the empty string. fileinto "business.${1}"; stop; } else { # ${0} is always "0" stop; } 4. Action Commands This extension defines two actions, "set" and "setdate", both of which MUST be supported by an implementation of this extension. 4.1. Action set Syntax: set [MODIFIER] [COMPARATOR] <name: string> <value: string> The "set" action stores the specified value in the variable called name. name MUST be a constant string without variable references. The contents of name MUST conform to the syntax of identifier. An illegal name MUST cause a syntax error. The default comparator is "i;ascii-casemap". All variables have global scope: they are visible until processing stops. Variable names are case insensitive. Example: set "honorific" "Mr"; set "first_name" "Wile"; set "last_name" "Coyote"; set "vacation" text: Dear ${HONORIFIC} ${last_name}, I'm out, please leave a message after the meep. . ; "set" does not affect the implicit keep. 4.1.1. Modifiers Modifiers are applied on value before it is stored in the variable. Modifier names are case insensitive. Unknown modifiers MUST yield a syntax error. More than one modifier can be specified, in which case they are applied according to this precedence list, highest value first: Homme [Page 5]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 Precedence Modifier ----------------------------- 1 :length ----------------------------- 2 :lowerfirst :upperfirst ----------------------------- 3 :lower :upper If two or more modifiers of the same precedence are used, they can be applied in any order. Examples: set "var" "juMBlEd lETteRS" => "juMBlEd lETteRS" set :length "var" "${var}" => "15" set :lower "var" "${var}" => "jumbled letters" set :upperfirst "var" "${var}" => "JuMBlEd lETteRS" set :upperfirst :lower "var" "{$var}" => "Jumbled letters" 4.1.1.1. Modifier ":length" The value is the decimal number of letters in the expansion, con¡ verted to a string. 4.1.1.2. Case modifiers These modifiers change the letters of the text from upper to lower case or vice versa. The implementation MUST support US-ASCII, but is not required to handle the entire Unicode repertoire. The comparator specified SHOULD be consulted to establish which locale to use. 4.1.1.2.1. Modifier ":upper" All lower case letters are converted to their upper case counterpart. 4.1.1.2.2. Modifier ":lower" All upper case letters are converted to their lower case counterpart. 4.1.1.2.3. Modifier ":upperfirst" The first character of the string is converted to upper case if it is a letter and set in lower case. The rest of the string is left unchanged. Homme [Page 6]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 4.1.1.2.4. Modifier ":lowerfirst" The first character of the string is converted to lower case if it is a letter and set in upper case. The rest of the string is left unchanged. 4.2. Action setdate Syntax: setdate [ <time-zone: string> ] The value of time-zone SHOULD be a well-known name, or an offset rel¡ ative to UTC. All implementations MUST support the time-offset syn¡ tax time-offset = ( "+" / "-" ) 4DIGIT time-offset should be interpreted the same way as "zone" in [IMAIL]. Note: There is currently no registry for time zones. If IETF establishes one, its names SHOULD be used. In the absence of such a registry, [TZ] is the most widespread collection of time zone definitions and its use as a reference is RECOM¡ MENDED. If the time-zone is left out or not recognised, the local time zone SHOULD be used. The action setdate initialises a few variables: ${year} => the current year, "0000" .. "9999" ${month} => the current month, "01" .. "12" ${day} => the current day, "01" .. "31" ${hour} => the current hour, "00" .. "23" ${minute} => the current hour, "00" .. "59" ${second} => the current second, "00" .. "59" ${timezone} => the time zone in use. If the user specified a time zone which was recognised, ${timezone} will contain the name given. Otherwise, the value MUST be the server's default time zone in offset format. These variables SHOULD reference the time when execution of the Sieve script reaches the statement. All calls to setdate MUST refer to the same point in time. "setdate" does not affect the implicit keep. 5. Test string Syntax: string [MATCH-TYPE] [COMPARATOR] <source: string-list> <key-list: string-list> Homme [Page 7]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 The "string" test evaluates to true if any of the strings matches any key. The type of match defaults to ":is". 6. Implementation Limits An implementation of this draft MUST support at least 128 distinct variables. The supported length of variable names MUST be at least 32 characters. Each variable MUST be able to hold at least 4000 characters. Attempts to set the variable to a value larger than what the implementation supports MUST be treated as an error. Numeric variables ${1} through ${9} MUST be supported. Referencing higher indices than is supported is a syntax error which MUST be dis¡ covered at compile-time. If the string matching a wildcard or a regex group operator exceeds the maximum variable size, the implemen¡ tation SHOULD truncate it and MUST NOT treat it as an error. 7. Security Considerations When combined with the regex extension, strings can contain arbitrary values controlled by the sender of the e-mail if the author of the script isn't careful. The introduction of variables makes advanced decision making easier to write, but since no looping construct is provided, all Sieve scripts will terminate orderly. 8. Acknowledgments Thanks to Jutta Degener, Ned Freed, Lawrence Greenfield, Peder Stray and Nigel Swinson for valuable feedback. 9. Author's Address Kjetil T. Homme Frydens g 5B 0564 Oslo, Norway Phone: +47 9366 0091 E-mail: kjetilho@ifi.uio.no Appendix A. References [ABNF] D. Crocker, Ed., "Augmented BNF for Syntax Specifica¡ tions: ABNF", Internet Mail Consortium, RFC 2234, Novem¡ ber 1997 Homme [Page 8]
Internet Draft Sieve -- Variables Extension 17 Apr 2003 [IMAIL] P. Resnick, Ed., "Internet Message Format", QUALCOMM Incorporated, April 2001. [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", Mira¡ point, RFC 3028, January 2001. [TZ] Olson, A.D., et al, Time zone code and data, ftp://elsie.nci.nih.gov/pub/, updated periodically. Appendix B. Full Copyright Statement Copyright (C) The Internet Society 2003. 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 doc¡ ument 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 MER¡ CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Homme [Page 9]