Network Working Group C. Daboo
Internet-Draft A. Stone
Expires: September 24, 2009 March 23, 2009
Sieve Email Filtering: Include Extension
draft-ietf-sieve-include-00
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Abstract
The Sieve Email Filtering "include" extension permits users to
include one Sieve script inside another. This can make managing
large scripts or multiple sets of scripts much easier, as well as
supporting common 'libraries' of scripts. Users are able to include
their own personal scripts or site-wide scripts provided by the local
Sieve implementation.
Change History (to be removed prior to publication as an RFC)
Changes from daboo-06 to ietf-00:
a. None
Changes from -05 to -06:
a. Aaron Stone joins as author.
b. Removed | characters from the script examples.
c. Updated draft references to published RFCs.
Changes from -04 to -05:
a. Fixed examples.
b. Relaxed requirement that imported/exported variables be set
before being used.
Changes from -03 to -04:
a. Fixed missing 2119 definitions.
b. Defined interaction with variables through use of import and
export commands.
Changes from -02 to -03:
a. Refreshing expired draft (updated for nits).
b. Syntax -> Usage.
c. Updated to 3028bis reference.
Changes from -01 to -02:
a. Minor formatting changes only - refreshing expired draft.
Changes from -00 to -01:
a. Added IPR boiler plate.
b. Re-ordered sections at start to conform to RFC style.
c. Moved recursion comment into General Considerations section.
d. Switched to using optional parameter to indicate personal vs
global.
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e. Explicitly state that an error occurs when a missing script is
included.
Open Issues (to be resolved prior to publication as an RFC)
a. Interaction with variables (scoping). Should variables be
carried over between scripts that are included? Or should
variables defined in an included script be local to that script
only?
Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Include Extension . . . . . . . . . . . . . . . . . . . . . . 4
3.1. General Considerations . . . . . . . . . . . . . . . . . . 4
3.2. Control Structure Include . . . . . . . . . . . . . . . . 5
3.3. Control Structure Return . . . . . . . . . . . . . . . . . 8
3.4. Interaction with Variables . . . . . . . . . . . . . . . . 8
3.4.1. Control Structure Import . . . . . . . . . . . . . . . 8
3.4.2. Control Structure Export . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5.1. "include" Extension Registration . . . . . . . . . . . . . 10
6. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction and Overview
Its convenient to be able to break SIEVE [RFC5228] scripts down into
smaller components which can be reused in a variety of different
circumstances. For example, users may want to have a default script
and a special 'vacation' script, the later being activated when the
user goes on vacation. In that case the default actions should
continue to be run, but a vacation command should be executed first.
One option is to edit the default script to add or remove the
vacation command as needed. Another is to have a vacation script
that simply has a vacation command and then includes the default
script.
2. Conventions Used in This Document
Conventions for notations are as in SIEVE [RFC5228] Section 1.1.
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 [RFC2119].
3. Include Extension
3.1. General Considerations
Sieve implementations that implement the "include", "return",
"export" and "import" commands described below have an identifier of
"include" for use with the capability mechanism. If any of the
"include", "return", "export" or "import" commands are used in a
script, the "include" capability MUST be listed in the "require"
statement in that script.
Sieve implementations must track the use of actions in included
scripts so that implicit "keep" behavior can be properly determined
based on whether any actions have executed in any script.
Sieve implementations are allowed to limit the total number of nested
included scripts, but MUST provide for a total of at least three
levels of nested scripts including the top-level script. An error
MUST be generated either when the script is uploaded to the Sieve
repository, or when the script is executed, if any nesting limit is
exceeded. If such an error is detected whilst processing a Sieve
script, an implicit "keep" action MUST be executed to prevent loss of
any messages.
Sieve implementations MUST ensure that recursive includes are not
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possible. i.e. if script "A" includes script "B", and script "B"
includes script "A" an error MUST be generated either when the script
is uploaded to the Sieve repository, or when the script is executed.
If such an error is detected whilst processing a Sieve script, an
implicit "keep" action MUST be executed to prevent loss of any
messages.
Sieve implementations MUST handle missing scripts being referenced
via an includes in an existing script. An error MUST be generated
when a missing included script is discovered during execution. If
such an error is detected an implicit "keep" action MUST be executed
to prevent loss of any messages.
If the Sieve "variables" extension [RFC5229] is present, an issue
arises with the "scope" of variables defined in scripts that may
include each other. For example, if a script defines the variable
"${status}" with one particular meaning or usage, and another defines
"${status}" with a different meaning, then if one script includes the
other there is an issue as to which "${status}" is being referenced.
To solve this problem, Sieve implementations MUST follow the scoping
rules defined in Section 3.4 and support the "import" and "export"
commands defined there.
3.2. Control Structure Include
Usage: include [<location: LOCATION>] <value: string>
LOCATION = ":personal" / ":global"
The "include" command includes an optional "location" parameter, and
a single string argument representing the name of the script to
include in the main script at that point.
The "location" parameter defaults to ":personal" if not specified.
The "location" has the following meanings:
:personal
Indicates that the named script is stored in the user's own
personal (private) Sieve repository.
:global
Indicates that the named script is stored in a site-wide Sieve
repository, accessible to all users of the Sieve system.
The included script MUST be a valid Sieve script, including having
necessary "require" statements for all optional capabilities used by
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the script. The scope of a "require" statement in an included script
is for that script only, not the including script. e.g. if script "A"
includes script "B", and script "B" uses the "fileinto" extension,
script "B" must have a "require" statement for "fileinto",
irrespective of whether script "A" has one. In addition, if script
"A" does not have a "require" statement for "fileinto", "fileinto"
cannot be used anywhere in script "A", even after inclusion of script
"B".
A "stop" command in an included script MUST stop all script
processing, including the processing of the scripts that include the
current one. The "return" command (described below) stops processing
of the current script only, and allows the scripts that include it to
continue.
Examples:
The user has four scripts stored in their personal repository:
"default"
This is the default active script that includes several others.
require ["include"];
include :personal "always_allow";
include :global "spam_tests";
include :personal "my_spam_tests";
include :personal "mailing_lists";
"always_allow"
This script special cases some correspondent email addresses and
makes sure any message containing those addresses are always kept.
if header :is "From" "boss@example.com"
{
keep;
}
elsif header :is "From" "ceo@example.com"
{
keep;
}
"my_spam_tests"
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This script does some user-specific spam tests to catch spam
messages not caught by the site-wide spam tests.
require ["reject"];
if header :contains "Subject" "XXXX"
{
reject;
}
elsif header :is "From" "money@example.com"
{
reject;
}
"mailing_lists"
This script looks for messages from different mailing lists and
files each into a mailbox specific to the mailing list.
require ["fileinto"];
if header :is "Sender" "owner-ietf-mta-filters@imc.org"
{
fileinto "lists.sieve";
}
elsif header :is "Sender" "owner-ietf-imapext@imc.org"
{
fileinto "lists.imapext";
}
There is one script stored in the global repository:
"spam_tests"
This script does some site-wide spam tests which any user at the
site can include in their own scripts at a suitable point. The
script content is kept up to date by the site administrator.
require ["reject"];
if anyof (header :contains "Subject" "$$",
header :contains "Subject" "Make money")
{
reject;
}
The "include" command may appear anywhere in the script where a
control structure is legal.
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Example:
require ["include"];
if anyof (header :contains "Subject" "$$",
header :contains "Subject" "Make money")
{
include "my_reject_script";
}
3.3. Control Structure Return
Usage: return
The "return" command stops processing of the currently included
script only and returns processing control to the script which
includes it. If used in the main script (i.e. not in an included
script), it has the same effect as the "stop" command, including the
appropriate "keep" action if no other actions have been executed up
to that point.
3.4. Interaction with Variables
In order to avoid problems of variables in an included script
"overwriting" those from the script that includes it, this
specification requires that all variables defined in a script MUST be
kept "private" to that script by default - i.e. they are not
"visible" to other scripts. This ensures that two script authors
cannot inadvertently cause problems by choosing the same name for a
variable.
However, sometimes there is a need to make a variable defined in one
script available to others. This specification defines the new
commands "export" and "import" to alter the default behavior of
variable scoping to allow variables to be "seen" by other scripts.
The "export" command takes a list of variable names defined in a
script and makes those available to any script that explicitly wants
to use them. The "import" command allows a script to gain access to
variables that have been explicitly made available by other scripts.
The explicit use of "export and "import", coupled with the default
behavior of variables only having local scope, ensures that multiple
scripts cannot inadvertently overwrite each others variables.
3.4.1. Control Structure Import
Usage: import <value: string-list>
The "import" command contains a string list argument that defines one
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or more names of variables exported by other scripts which should be
made available to the current script.
The "import" command, if present, MUST be used immediately after any
"require" commands (at least one of which will be present listing the
"include" extension). Multiple "import" commands are allowed. An
error occurs if an "import" command appears after a command other
than "require" or "import". Use of the "import" command makes the
listed variables immediately available for use in the body of the
script that uses it.
If an "import" command lists a variable that has not been exported by
any other script at that point during the Sieve execution process,
then an error MUST occur.
Example:
require ["variables", "fileinto", "include"];
import "test";
if header :contains "Subject" "${test}"
{
fileinto "INBOX.spam-${test};
}
3.4.2. Control Structure Export
Usage: export <value: string-list>
The "export" command contains a string list argument that defines one
or more names of variables defined in the current script which should
be made available to any scripts that run during the current Sieve
script execution process.
The "export" command, if present, MUST be used immediately after any
"require" or "import" commands. Multiple "export" commands are
allowed. An error occurs if an "export" command appears after a
command other than "require", "import" or "export".
An error occurs if an "export" command lists a variable that is
listed in an "import" command preceding it in the current script.
Example:
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require ["variables", "include"];
export "test";
set "test" "$$"
include "spam_filter_script";
set "test" "Make money"
include "spam_filter_script";
Example:
require ["variables", "include"];
import "test";
export "test-mailbox";
if header :contains "Subject" "${test}"
{
set "test-mailbox" "INBOX.spam-${test};
include "fileinto-script"
}
4. Security Considerations
Sieve implementations MUST ensure adequate security for the global
script repository to prevent unauthorized changes to global scripts.
Beyond that, the "include" extension does not raise any security
considerations that are not present in the base Sieve protocol, and
these issues are discussed in Sieve.
5. IANA Considerations
The following template specifies the IANA registration of the Sieve
extension specified in this document:
5.1. "include" Extension Registration
Capability name: include
Description: add the "include" command to execute other Sieve
scripts.
RFC number: this RFC
Contact address: the Sieve discussion list <ietf-mta-filters@imc.org>
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6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5228] Guenther, P. and T. Showalter, "Sieve: An Email Filtering
Language", RFC 5228, January 2008.
[RFC5229] Homme, K., "Sieve Email Filtering: Variables Extension",
RFC 5229, January 2008.
Appendix A. Acknowledgments
Thanks to Ken Murchison, Rob Siemborski, Alexey Melnikov, Marc Mutz
and Kjetil Torgrim Homme for comments and corrections.
Authors' Addresses
Cyrus Daboo
Email: cyrus@daboo.name
Aaron Stone
Email: aaron@serendipity.palo-alto.ca.us
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