<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Jingle Content Thumbnails</title>
  <abstract>This specification defines a way for a client to supply a preview image for Jingle content.</abstract>
  &LEGALNOTICE;
  <number>0264</number>
  <status>Deferred</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XEP-0096</spec>
    <spec>XEP-0231</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>thumbs</shortname>
  <author>
    <firstname>Marcus</firstname>
    <surname>Lundblad</surname>
    <email>ml@update.uu.se</email>
    <jid>mlundblad@jabber.org</jid>
  </author>
  &lance;
  <revision>
    <version>0.4</version>
    <date>2015-08-26</date>
    <initials>ljts</initials>
    <remark>
      <p>Changed format to use generic 'uri' attribute to allow for 'https:' and 'http:' URIs in addition to BoB 'cid:' URIs.</p>
      <p>Indicated that multiple thumbnails may be present.</p>
      <p>Expanded scope of use cases to be Jingle content in general, not just file transfer.</p>
    </remark>
  </revision>
  <revision>
    <version>0.3</version>
    <date>2009-04-27</date>
    <initials>ml</initials>
    <remark><p>Fixed typo in author's name :).</p></remark>
  </revision>
  <revision>
    <version>0.2</version>
    <date>2009-04-06</date>
    <initials>ml</initials>
    <remark><p>Add paragraph in security section about protecting against malicious thumbnail dimensions in offer. Fixed a typo.</p></remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2009-04-02</date>
    <initials>psa</initials>
    <remark><p>Initial published version.</p></remark>
  </revision>
  <revision>
    <version>0.0.3</version>
    <date>2009-03-10</date>
    <initials>ml</initials>
    <remark><p>Split use-case section into "Introduction", "Requirements", and "Use case".</p>
    </remark>
  </revision>
  <revision>
    <version>0.0.2</version>
    <date>2009-02-25</date>
    <initials>ml</initials>
    <remark><p>Removed service disovery.
Added missing namespace on thumnail elements.</p>
    </remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2009-02-23</date>
    <initials>ml</initials>
    <remark><p>First draft.</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='introduction'>
  <p>When offering a Jingle session, it can be helpful to provide a small preview of the offered content to help the session responder decide whether to accept or reject the session.</p>
  <p>This is particularly useful for file transfer content (especially image files), but can also be used for things such as video (e.g. using a still frame from the stream as the preview thumbnail), and even audio by using a small image of album cover art.</p>
</section1>
<section1 topic='Requirements' anchor='requirements'>
  <p>This documents defines a way to include a thumbnail image as an additional metadata in a Jingle content description.</p>
</section1>
<section1 topic='Use Cases' anchor='usecase'>
  <p>When a client wishes to supply a thumbnail in a content offer, it can do so by including an extra &lt;thumbnail/&gt; element as shown in the following example:</p>
  <example caption='Inclusion of a thumbnail in a Jingle file transfer offer'><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='nzu25s8'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='851ba2'>
    <content creator='initiator' name='a-file-offer'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:4' senders='initiator'>
        <file>
          <media-type>image/jpeg</media>
          <name>image.jpg</name>
          <size>3032449</size>
          <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
          <desc>This is a test. If this were a real file...</desc>
          <thumbnail xmlns='urn:xmpp:thumbs:1'
                     uri='cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org'
                     media-type='image/png'
                     width='128'
                     height='96'/>
        </file>
      </description>
      <transport .../>
    </content>
  </jingle>
</iq>]]></example>

  <p>Thumbnails MAY be included for Jingle content other than file transfer. For example, with Jingle RTP video a thumbnail could be included to show who is calling (either by capturing a still frame from the input stream or by using an existing profile image):</p>
  <example caption='Inclusion of a thumbnail in a Jingle RTP video session'><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='ih28sx61'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='webcam'>
      <description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
        <payload-type id='98' name='theora' clockrate='90000'>
          <parameter name='height' value='600'/>
          <parameter name='width' value='800'/>
          <parameter name='delivery-method' value='inline'/>
          <parameter name='configuration' value='somebase16string'/>
          <parameter name='sampling' value='YCbCr-4:2:2'/>
        </payload-type>
        <payload-type id='28' name='nv' clockrate='90000'/>
        <payload-type id='25' name='CelB' clockrate='90000'/>
        <payload-type id='32' name='MPV' clockrate='90000'/>
        <bandwidth type='AS'>128</bandwidth>
        <thumbnail xmlns='urn:xmpp:thumbs:1'
                   uri='cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org'
                   media-type='image/png'
                   width='128'
                   height='96'/>
      </description>
      <transport .../>
    </content>
  </jingle>
</iq>]]></example>

  <p>Multiple &lt;thumbnail/&gt; elements MAY be included to provide thumbnails of different sizes, media types, or URIs.</p>

  <p>If the provided URI has the scheme 'cid', then the thumbnail data MAY be requested using &xep0231;.</p>
</section1>

<section1 topic='Definition of the thumbnail Element' anchor='thumbnail_element'>
  <p>The following attributes are defined for the &lt;thumbnail/&gt; element.</p>
  <table caption='Attributes of the thumbnail Element'>
    <tr>
      <th>Attribute</th>
      <th>Description</th>
      <th>Inclusion</th>
    </tr>
    <tr>
      <td>uri</td>
      <td>A URI where the thumbnail data can be accessed (typically by using a URI scheme of 'cid:', 'https:', or 'http:'). If the URI scheme is 'cid:' then the identifier MUST refer to a bit of binary data as described in &xep0231;</td>
      <td>REQUIRED</td>
    </tr>
    <tr>
      <td>media-type</td>
      <td>The value of the 'media-type' attribute MUST match the syntax specified in &rfc2045;. That is, the value MUST include a top-level media type, the "/" character, and a subtype; in addition, it MAY include one or more optional parameters. The "type/subtype" string SHOULD be registered in the &ianamedia;, but MAY be an unregistered or yet-to-be-registered value.</td>
      <td>RECOMMENDED</td>
    </tr>
    <tr>
      <td>width</td>
      <td>The intended display width of the thumbnail image. Used as a hint for the receiving client to prepare the appropriate UI, such as a dialog window.</td>
      <td>OPTIONAL</td>
    </tr>
    <tr>
      <td>height</td>
      <td>The intended display height of the thumbnail image. Used as a hint for the receiving client to prepare the appropriate UI, such as a dialog window.</td>
      <td>OPTIONAL</td>
    </tr>
  </table>
</section1>
<section1 topic='Security Considerations' anchor='security'>
  <p>The inclusion of an image thumbnail may leak information about a transfer
otherwise taking place on an e2e encrypted file transfer stream. A client MAY
wish to not include a thumbnail.</p>
  <p>A client MUST NOT rely on the values specified for the width and height of a thumbnail to allocate a bitmap data buffer for the thumbnail, to prevent possible DoS attacks. Also a client SHOULD apply implementation-specific limits on the thumbnails, if using these values to pepare a UI element for the thumbnail image, e.g. with dimensions of 128x128 pixels, values exceeding these would then be truncated and the thumbnail image scaled down when received.</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
  <p>This document requires no interaction with &IANA;.</p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
    <p>This specification defines the following XML namespace:</p>
    <ul>
      <li>urn:xmpp:thumbs:1</li>
    </ul>
    <p>The &REGISTRAR; includes this namespace in the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
  </section2>
  <section2 topic='Protocol Versioning' anchor='registrar-versioning'>
    &NSVER;
  </section2>
</section1>
<section1 topic='XML Schema' anchor='schema'>
  <code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:thumbs:0'
    xmlns='urn:xmpp:thumbs:0'
    elementFormDefault='qualified'>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      xxx
    </xs:documentation>
  </xs:annotation>

  <xs:element name='thumbnail'>
    <xs:complexType>
      <xs:attribute name='uri' type='xs:anyURI' use='required'/>
      <xs:attribute name='media-type' type='xs:string' use='optional'/>
      <xs:attribute name='width' type='xs:integer' use='optional'/>
      <xs:attribute name='height' type='xs:integer' use='optional'/>
    </xs:complexType>
  </xs:element>
</xs:schema>
]]></code>
</section1>
</xep>
