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Versions: (draft-melnikov-sieve-convert) 00 01 02 03 04 05 06 RFC 6558

Sieve Working Group                                          A. Melnikov
Internet-Draft                                             Isode Limited
Intended status: Standards Track                                  Q. Sun
Expires: January 26, 2012                                       B. Leiba
                                                                   K. Li
                                                     Huawei Technologies
                                                           July 25, 2011


        Sieve Extension for  converting messages before delivery
                      draft-ietf-sieve-convert-02

Abstract

   This document describes how IMAP CONVERT can be used within Sieve to
   transform messages before final delivery.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 26, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.    Introduction  . . . . . . . . . . . . . . . . . . . . . . . . 3
   1.1.  Conventions Used in this Document . . . . . . . . . . . . . . 3

   2.    "convert" action  . . . . . . . . . . . . . . . . . . . . . . 3
   2.1.  Interaction with other actions  . . . . . . . . . . . . . . . 4

   3.    Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.1.  Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.2.  Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   3.3.  Example 3 . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   3.4.  Example 4 . . . . . . . . . . . . . . . . . . . . . . . . . . 6

   4.    Security Considerations . . . . . . . . . . . . . . . . . . . 7

   5.    IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7

   6.    Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 7

   7.    Normative References  . . . . . . . . . . . . . . . . . . . . 7

         Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . 8




























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1.  Introduction

   The IMAP CONVERT extension [RFC5259] adds an IMAP command for
   performing client-controlled conversions on whole messages or their
   body parts.  This document defines a similar extension to the Sieve
   mail filtering language [RFC5228], which reuses the conversion
   parameters and framework established by IMAP CONVERT.

1.1.  Conventions Used in this Document

   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 RFC 2119 [RFC2119].

   Conventions for notations are as in Sieve [RFC5228] section 1.1,
   including the use of ABNF [RFC5234].


2.  "convert" action

   Usage: convert  <quoted-from-mime-type: string>
           <quoted-to-mime-type: string>
           <transcoding-params: string-list>

   The "convert" action specifies that body parts with "quoted-from-
   mime-type" MIME type be converted to "quoted-to-mime-type" MIME type
   using conversion parameters specified in "transcoding-params".  Each
   conversion parameter value has the following syntax: "<transcoding-
   param>=<transcoding-param-value>", where <transcoding-param> and
   <transcoding-param-value> are defined in CONVERT [RFC5259].  Messages
   that don't have any body parts with the "quoted-from-mime-type" MIME
   type are not affected by the conversion.

   The "convert" action can be used with Sieve MIME Part Tests
   [RFC5703], in the case that some, but not all of the body parts need
   to be converted, or where different body parts might require
   different conversions.  When the "convert" action appears in a
   "foreverypart" loop, it applies only to the body part being
   processed, and not to any other body parts (see Section 3.2 for an
   example).

   When the "convert" action appears outside a "foreverypart" loop, the
   conversion applies equally to all body parts -- that is, all body
   parts that have the "quoted-from-mime-type" are converted, using the
   same transcoding parameters.

   Implementations ought to defer any actual conversion until the final
   resolution of other actions, to avoid doing conversions unnecessarily



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   in cases where the message is not retained (such as where the
   resolution is "discard").

2.1.  Interaction with other actions

   Whether the actual conversion has been done yet or not, a "convert"
   action effectively changes the message, and all subsequent actions,
   including any other "convert" actions, apply to the changed message.
   The "convert" action does not affect the applicability of other
   actions; any action that was applicable before the "convert" is
   equally applicable to the changed message afterward.

   When a disposition-type action, such as "fileinto" or "redirect", is
   encountered, the state of the message with respect to conversions is
   "locked in" for that disposition-type action.  Whether the
   implementation performs the action at that point or batches it for
   later, it MUST perform the action on the message as it stood at the
   time, and MUST NOT include subsequent conversions encountered later
   in the script processing.  Therefore, the sequence "convert,
   fileinto, convert, fileinto" will store two different versions of the
   message: the first "fileinto" uses only the first conversion, while
   the second uses both.  See Section 3.4 for an example of how this can
   be used.

   Convert actions are cumulative, and each conversion operates on the
   message as it stands after all prior conversions.  See the fourth
   block of Section 3.4 for an example of how this might be tricky.

   Because the implicit keep, if it is in effect, acts on the final
   state of the message, all conversions are performed before any
   implicit keep.


3.  Examples

3.1.  Example 1

   In the following example, all "image/tiff" body parts of the message
   are converted to "image/jpeg" with image resolution of 320x240
   pixels.  The converted message is then subject to the implicit keep.

       require ["convert"];
       convert "image/tiff" "image/jpeg" "pix-x" "320" "pix-y" "240";








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3.2.  Example 2

   In the following example, all "image/tiff" body parts of the message
   are converted to "image/jpeg", as in Example 1.  Those messages are
   then filed into a mailbox called "INBOX.pics".  Other messages (those
   with no image/tiff body parts) are subject to the implicit keep, and
   have not been converted.

       require ["mime", "fileinto", "convert"];
       if header :mime :anychild :contenttype
                 "Content-Type" "image/tiff"
       {
         convert "image/tiff" "image/jpeg" "pix-x" "320" "pix-y" "240";
         fileinto "INBOX.pics";
       }

3.3.  Example 3

   In the following example, only "image/tiff" body parts with a
   Content-Disposition of "inline" are converted.  Matching parts that
   are larger than 500 kilobytes are converted using an image resolution
   of 640x480 pixels, and those smaller are converted to 320x240 pixels.
   The message disposition is not changed, so the implicit keep will be
   in effect unless something else in the script changes that.

       require ["mime", "foreverypart", "fileinto", "convert"];
       foreverypart
       {
         if header :mime :param "filename" :contains
                   "Content-Disposition" "inline"
         {
           if size :over "500K"
           {
             convert "image/tiff" "image/jpeg"
                     "pix-x" "640" "pix-y" "480";
           } else {
             convert "image/tiff" "image/jpeg"
                     "pix-x" "320" "pix-y" "240";
           }
         }
       }

       [... script continues ...]








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3.4.  Example 4

   The following example shows some tricky interactions between multiple
   "convert" actions and other disposition-type actions.

       require ["mime", "foreverypart",
                "fileinto", "redirect" "convert"];

       # The first "if" block will convert all image/tiff body parts
       # to 640x480 jpegs, and will file the message
       # into the "INBOX.pics" mailbox as converted at this point.
       if header :mime :anychild :contenttype
                 "Content-Type" "image/tiff"
       {
         convert "image/tiff" "image/jpeg" "pix-x" "640" "pix-y" "480";
         fileinto "INBOX.pics";
       }

       # The second block, the "foreverypart" loop, will convert all
       # inline jpegs to 320x240 resolution... including any tiff body
       # parts that had been converted in the first block, above.
       # Therefore, any tiff that had been converted to a 640x480 jpeg
       # will be re-converted to a 320x240 jpeg here if its
       # Content-Disposition is specified as "inline".
       foreverypart
       {
         if header :mime :param "filename" :contains
                   "Content-Disposition" "inline"
         {
           convert "image/jpeg" "image/jpeg"
                   "pix-x" "320" "pix-y" "240";
         }
       }

       # The third block will take any message that contains a header
       # field called "Mobile-Link" and redirect it to the user's
       # mobile address.  The redirected message will include both
       # conversions above, from block one and block two.
       if exists "Mobile-Link"
       {
         redirect "joe@mobile.example.com";
       }

       # The fourth block will file the message into "Tiff" if it
       # contains any tiff body parts.  But because of the earlier
       # conversion (in the first block), there will never be any
       # tiff body parts, so this "fileinto" will never happen.
       if header :mime :anychild :contenttype



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                 "Content-Type" "image/tiff"
       {
         fileinto "Tiff";
       }

       # Now, at the end of the script processing, the Sieve
       # processor will perform an implicit keep if none of
       # the "fileinto" and "redirect" actions were taken.
       # The kept message will include any conversions that
       # were done (that is, any from the second block).


4.  Security Considerations

   Security considerations given in IMAP CONVERT [RFC5259] and Sieve
   [RFC5228] are relevant to this document.  There are no additional
   security considerations resulting from combining the two.


5.  IANA Considerations

   IANA is requested to add the following registration to the Sieve
   Extensions registry, as defined in RFC 5228:

   Capability name:  convert
   Description:  adds a new tag to the fileinto action that enables
      Sieve script to perform a conversion on the message being
      delivered.
   RFC number:  this RFC
   Contact address:  The Sieve discussion list <sieve@ietf.org>


6.  Acknowledgements

   The authors also want to thank all who have contributed key insight
   and extensively reviewed and discussed the concepts of CONVERT.


7.  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.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.



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   [RFC5259]  Melnikov, A. and P. Coates, "Internet Message Access
              Protocol - CONVERT Extension", RFC 5259, July 2008.

   [RFC5703]  Hansen, T. and C. Daboo, "Sieve Email Filtering: MIME Part
              Tests, Iteration, Extraction, Replacement, and Enclosure",
              RFC 5703, October 2009.


Authors' Addresses

   Alexey Melnikov
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   Email: Alexey.Melnikov@isode.com
   URI:   http://www.melnikov.ca/


   Qian Sun
   Huawei Technologies
   Bantian Longgang
   Shenzhen, Guandong  518129
   P.R China

   Phone: +86 755 28780808
   Email: sunqian@huawei.com


   Barry Leiba
   Huawei Technologies

   Phone: +1 646 827 0648
   Email: barryleiba@computer.org
   URI:   http://internetmessagingtechnology.org/


   Kepeng Li
   Huawei Technologies
   Huawei Base, Bantian, Longgang District
   Shenzhen, Guangdong  518129
   P. R. China

   Phone: +86-755-28974289
   Email: likepeng@huawei.com




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