One document matched: draft-ietf-sieve-convert-04.xml

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<rfc
  docName="draft-ietf-sieve-convert-04"
  category="std"
  ipr="trust200902"
  xml:lang="en">

  <front>
    <title abbrev="Sieve CONVERT">Sieve Extension for 
    converting messages before delivery</title>

    <author initials='A.' surname="Melnikov" fullname='Alexey Melnikov'>
      <organization>Isode Limited</organization>
      <address>
        <postal>
          <street>5 Castle Business Village</street>
          <street>36 Station Road</street>
          <city>Hampton</city>
          <region>Middlesex</region>
          <code>TW12 2BX</code>
          <country>UK</country>
        </postal>
        <email>Alexey.Melnikov@isode.com</email>
        <uri>http://www.melnikov.ca/</uri>
      </address>
    </author>
    
    <author initials="Q." surname="Sun" fullname="Qian Sun">
      <organization>Huawei Technologies</organization>
      <address>
        <postal>
          <street>Bantian Longgang</street>
          <city>Shenzhen</city>
          <region>Guandong</region>
          <code>518129</code>
          <country>P.R China</country>
        </postal>
        <phone>+86 755 28780808</phone>
        <email>sunqian@huawei.com</email>
      </address>
    </author>
    
    <author initials='B.' surname="Leiba" fullname='Barry Leiba'>
      <organization>Huawei Technologies</organization>
      <address>
        <phone>+1 646 827 0648</phone>
        <email>barryleiba@computer.org</email>
        <uri>http://internetmessagingtechnology.org/</uri>
      </address>
    </author>
  
    <author initials="K." surname="Li" fullname="Kepeng Li">
      <organization abbrev="Huawei Technologies">Huawei Technologies</organization>
      <address>
        <postal>
          <street>Huawei Base, Bantian, Longgang District</street>
          <city>Shenzhen</city>
          <region>Guangdong</region>
          <code>518129</code>
          <country>P. R. China</country>
        </postal>
        <phone>+86-755-28974289</phone>
        <email>likepeng@huawei.com</email>
      </address>
    </author>

    <date year="2011"/>

    <area>Applications</area>
    <workgroup>Sieve Working Group</workgroup>

    <keyword>Sieve</keyword>
    <keyword>CONVERT</keyword>

    <abstract>
      <t>
        This document describes how IMAP CONVERT can be used within Sieve
        to transform messages before final delivery.
      </t>
    </abstract>
  </front>

  <middle>
    <section anchor="Intro" title="Introduction" toc="default"> 
      <t>
        The IMAP CONVERT extension <xref target="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
        <xref target="RFC5228"/>, which reuses the conversion parameters and framework 
        established by IMAP CONVERT.
      </t>
      
      <section title="Conventions Used in this Document">
        <t>
          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
          <xref target="RFC2119"/>.
        </t>        
        <t>
          Conventions for notations are as in Sieve <xref target="RFC5228"/> section 1.1,
          including the use of ABNF <xref target="RFC5234"/>.
        </t>
      </section>
    </section>

    <section title='"convert" action'>
      <t>
        <list style="hanging" hangIndent="8">
          <t hangText="Usage: convert">
            <quoted-from-mime-type: string><vspace/>
            <quoted-to-mime-type: string><vspace/>
            <transcoding-params: string-list>
          </t>
        </list>
      </t>
      <t>
        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-name>=<transcoding-param-value>",
        where <transcoding-param-name> and <transcoding-param-value>
        are defined in CONVERT <xref target="RFC5259"/>.
        Messages that don't have any body parts with the "quoted-from-mime-type" MIME type
        are not affected by the conversion.
      </t>
      <t>
        The "convert" action can be used with Sieve MIME Part Tests <xref target="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 <xref target="Example2"/> for an example).
      </t>     
      <t>
        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.
      </t>     
      <t>
        If a "convert" action cannot be completed -- perhaps because the conversion failed,
        or because the requested conversion is not available -- the message MUST remain
        unchanged, and the script processing continues.
        In particular, no error condition is raised, and no partial conversions are allowed.
      </t>     
      <t>
        Implementations might defer any actual conversion until the the results of the
        conversion are needed for script processing, to avoid doing conversions unnecessarily.
        Consider the case wherein a "convert" action is processed, but a "discard" action
        results without the need to actually perform the conversion.
      </t>
      <section title='Interaction with other tests and actions'>
        <t>
          Whether the actual conversion has been done yet or not, a successful "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.
        </t>
        <t>
          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 <xref target="Example4"/> for an example of how this can be used.
        </t>
        <t>
          In addition, any tests done on the message and its parts will test the message
          after prior conversions have been done.  
          The fourth block of <xref target="Example4"/> shows an example of this situation.
        </t>
        <t>
          Convert actions are cumulative, and each conversion operates on the message as it
          stands after all prior conversions.
          See the fourth block of <xref target="Example4"/> for an example of how this
          might be tricky.
        </t>
        <t>
          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.
        </t>
      </section>
      <section title='"convert" as a test'>
        <t>
          To simplify testing for supported and successful conversions, the "convert" action
          can also be used as a test.  As such, it will attempt to perform the requested
          conversion(s), and will evaluate to "false" if and only if at least one conversion
          failed.  The failure can be because a conversion was unsupported, or because the
          data could not be converted (perhaps it had been corrupted in transit, or mislabelled
          at its origin).
        </t>
        <t>
          This creates a new type of Sieve action, a "testable action".
          The usage as a test is exactly the same as for an action, and it doubles as an action
          and a test of the action's result at the same time.
          See <xref target="Example2"/> for an example of how this test can be used.
        </t>
        <t>
          Note that defining this new testable action does not change the definitions of
          any other actions -- it does not imply that other actions can be used as tests.
          Future extensions might define other testable actions, but those specifications
          would be responsible for clearly specifying that.
        </t>
      </section>
    </section>
      
    <section title="Examples">
      <section anchor="Example1" title="Example 1">
        <t>
          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.
        </t>

        <figure>
<artwork><![CDATA[
    require ["convert"];
    convert "image/tiff" "image/jpeg" ["pix-x=320","pix-y=240"];
]]></artwork>
        </figure>
      </section>

      <section anchor="Example2" title="Example 2">
        <t>
          In the following example, all "image/tiff" body parts of the message
          are converted to "image/jpeg", as in Example 1.
          If the conversions were successful,
          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.
        </t>

        <figure>
<artwork><![CDATA[
    require ["mime", "fileinto", "convert"];
    if header :mime :anychild :contenttype
              "Content-Type" "image/tiff"
    {
     if (convert "image/tiff" "image/jpeg" ["pix-x=320","pix-y=240"])
     {
      fileinto "INBOX.pics";
     }
    }    
]]></artwork>
        </figure>
      </section>

      <section anchor="Example3" title="Example 3">
        <t>
          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.
        </t> 
        <figure>
<artwork><![CDATA[
    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 ...]
]]></artwork>
        </figure>
      </section>

      <section anchor="Example4" title="Example 4">
        <t>
          The following example shows some tricky interactions between multiple
          "convert" actions and other disposition-type actions.
        </t> 
        <figure>
<artwork><![CDATA[
    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
              "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).
]]></artwork>
        </figure>
      </section>
     
    </section>

    <section anchor="security" title="Security Considerations" toc="default">
      <t>
        Security considerations given in IMAP CONVERT <xref target="RFC5259"/>
        and Sieve <xref target="RFC5228"/> are relevant to this document.
        There are no additional security considerations resulting from combining the two.
      </t>
    </section>
        
    <section title="IANA Considerations">
      <t>
        IANA is requested to add the following registration to the
        Sieve Extensions registry, as defined in RFC 5228:
      </t>
            
      <t>
        <list style="hanging">
          <t hangText="Capability name:">convert</t>
          <t hangText="Description:">adds a new tag to the fileinto action
            that enables Sieve script to perform a conversion on the message
            being delivered.
          </t>
          <t hangText="RFC number:">this RFC</t>
          <t hangText="Contact address:">
            The Sieve discussion list <sieve@ietf.org>
          </t>
        </list>
      </t>
    </section>        
    
    <section title="Acknowledgements">
      <t>
        The authors also want to thank all who have contributed key insight
        and extensively reviewed and discussed the concepts of CONVERT.
      </t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      &RFC2119;  <!-- Keywords -->
      &RFC5228;  <!-- Sieve -->
      &RFC5234;  <!-- ABNF -->
      &RFC5259;  <!-- CONVERT -->
      &RFC5703;  <!-- MIME loops -->
    </references>
  </back>
</rfc>