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new version of the variables draft
I just submitted a new version of the draft to IETF. I include it
here for convenience.
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.
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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
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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@xxxxxxx>. Subscription
requests can be sent to <ietf-mta-filters-request@xxxxxxx> (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
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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.
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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" {
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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} ${last_name},
I'm out, please leave a message after the meep.
.
;
"set" does not affect the implicit keep.
4.1.1. Modifiers
Modifiers are applied on value before it is stored in the variable.
Modifier names are case insensitive. Unknown modifiers MUST yield a
syntax error. More than one modifier can be specified, in which case
they are applied according to this precedence list, highest value
first:
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Internet Draft Sieve -- Variables Extension 17 Apr 2003
Precedence Modifier
-----------------------------
1 :length
-----------------------------
2 :lowerfirst
:upperfirst
-----------------------------
3 :lower
:upper
If two or more modifiers of the same precedence are used, they can be
applied in any order.
Examples:
set "var" "juMBlEd lETteRS" => "juMBlEd lETteRS"
set :length "var" "${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.
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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>
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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@xxxxxxxxxx
Appendix A. References
[ABNF] D. Crocker, Ed., "Augmented BNF for Syntax Specifica
tions: ABNF", Internet Mail Consortium, RFC 2234, Novem
ber 1997
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[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]
--
Kjetil T.