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  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Jingle File Transfer</title>
  <abstract>This specification defines a Jingle application type for transferring files between two entities. The protocol provides a modular framework that enables the exchange of information about the file to be transferred as well as the negotiation of parameters such as the transport to be used.</abstract>
  &LEGALNOTICE;
  <number>0234</number>
  <status>Deferred</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XEP-0047</spec>
    <spec>XEP-0065</spec>
    <spec>XEP-0096</spec>
    <spec>XEP-0166</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>NOT_YET_ASSIGNED</shortname>
  &stpeter;
  <revision>
    <version>0.15</version>
    <date>2012-02-08</date>
    <initials>psa</initials>
    <remark><p>Updated to track revisions to XEP-0300.</p></remark>
  </revision>
  <revision>
    <version>0.14</version>
    <date>2011-06-29</date>
    <initials>psa</initials>
    <remark>
      <ul>
        <li>Defined file description format separate from XEP-0096</li>
        <li>Modified the checksum format to reuse the &lt;hashes/&gt; element from XEP-0300</li>
        <li>Described the process of aborting a file transfer</li>
        <li>Clarified the order of events (Jingle, then transport) when the session is terminated</li>
        <li>Added section on determining spport, including service discovery feature for multi-file support</li>
        <li>Removed the 'urn:xmpp:jingle:apps:file-transfer:info:2' namespace by putting all elements into the 'urn:xmpp:jingle:apps:file-transfer:3' namespace</li>
        <li>Incremented namespace version from 2 to 3</li>
      </ul>
    </remark>
  </revision>
  <revision>
    <version>0.13</version>
    <date>2011-06-01</date>
    <initials>psa</initials>
    <remark><p>Added multi-file use case; updated spec to reflect XEP-0260 and XEP-0261; added algorithm attribute from XEP-0096; increased namespace versions from 1 to 2.</p></remark>
  </revision>
  <revision>
    <version>0.12</version>
    <date>2011-01-05</date>
    <initials>psa</initials>
    <remark><p>Clarified usage of Jingle actions as well as several ambiguous points in the text, including use of the range feature from XEP-0096.</p></remark>
  </revision>
  <revision>
    <version>0.11</version>
    <date>2010-02-19</date>
    <initials>psa</initials>
    <remark><p>Added session-info message and namespace for communicating the file hash.</p></remark>
  </revision>
  <revision>
    <version>0.10</version>
    <date>2010-02-11</date>
    <initials>psa</initials>
    <remark><p>Described the file retrieval case; updated referenced namespaces.</p></remark>
  </revision>
  <revision>
    <version>0.9</version>
    <date>2009-02-19</date>
    <initials>psa</initials>
    <remark>
      <ul>
        <li>Moved Jingle definitions of S5B and IBB transports to standalone documents.</li>
        <li>Because the jingle-s5b and jingle-ibb transport methods are backward-incompatible, incremented protocol version number from 0 to 1 and changed namespace from urn:xmpp:jingle:apps:file-transfer:0 to urn:xmpp:jingle:apps:file-transfer:2.</li>
        <li>Moved transport fallback scenario to XEP-0260.</li>
      </ul>
    </remark>
  </revision>
  <revision>
    <version>0.8</version>
    <date>2008-09-30</date>
    <initials>psa</initials>
    <remark><p>Corrected fallback scenario to use transport-replace and transport-accept.</p></remark>
  </revision>
  <revision>
    <version>0.7</version>
    <date>2008-09-25</date>
    <initials>psa</initials>
    <remark>
      <ul>
        <li>Deleted content-replace from session flows.</li>
        <li>Modified namespaces to incorporate namespace versioning.</li>
        <li>Cleaned up XML schemas.</li>
      </ul>
    </remark>
  </revision>
  <revision>
    <version>0.6</version>
    <date>2008-07-31</date>
    <initials>psa</initials>
    <remark><p>Harmonized with XEP-0166; modified fallback to use transport-replace and transport-accept.</p></remark>
  </revision>
  <revision>
    <version>0.5</version>
    <date>2008-06-05</date>
    <initials>psa</initials>
    <remark><p>Modified fallback scenario to use content-replace action during pending state.</p></remark>
  </revision>
  <revision>
    <version>0.4</version>
    <date>2008-06-04</date>
    <initials>psa</initials>
    <remark><p>Harmonized negotiation flows with other Jingle application types.</p></remark>
  </revision>
  <revision>
    <version>0.3</version>
    <date>2008-05-29</date>
    <initials>psa</initials>
    <remark><p>Corrected and more clearly explained negotiation flows for consistency with XEP-0166 and other Jingle specifications.</p></remark>
  </revision>
  <revision>
    <version>0.2</version>
    <date>2008-03-20</date>
    <initials>psa</initials>
    <remark><p>Added transport negotiation scenario.</p></remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2008-03-05</date>
    <initials>psa</initials>
    <remark><p>Initial published version.</p></remark>
  </revision>
  <revision>
    <version>0.0.3</version>
    <date>2008-02-29</date>
    <initials>psa</initials>
    <remark><p>Corrected use of content-replace action; specified that the In-Band Bytestreams transport method is mandatory-to-implement but must have the lowest preference order.</p></remark>
  </revision>
  <revision>
    <version>0.0.2</version>
    <date>2008-02-28</date>
    <initials>psa</initials>
    <remark>Modified negotiation flow to use new content-replace action.</remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2008-01-29</date>
    <initials>psa</initials>
    <remark>First draft.</remark>
  </revision>
</header>

<section1 topic='Introduction' anchor='intro'>
  <p>&xep0096; was the original XMPP protocol extension for file transfer negotiation. However, that protocol has several drawbacks, most related to the &xep0095; protocol on which it depends:</p>
  <ol>
    <li>It does not enable a true, bidirectional negotiation; instead, the initiator sets the terms for the file transfer and the responder either accepts the terms or cancels the negotiation.</li>
    <li>It is the only technology in the Jabber/XMPP protocol "stack" that uses <cite>XEP-095: Stream Initiation</cite>. More modern technologies such as voice and video session negotiation use &xep0166;, and it would be helpful if implementors could re-use the same code for all negotiation use cases.</li>
  </ol>
  <p>To overcome these drawbacks, this specification defines a file transfer negotiation method that meets the following requirements:</p>
  <ul>
    <li>Use the session negotiation semantics from <cite>XEP-0166</cite>.</li>
    <li>Use &xep0260; and &xep0261;.</li>
    <li>Define a file description format that, unlike <cite>XEP-0096</cite> enables hash agility (via &xep0300;).</li>
    <li>Define a clear upgrade path from SI File Transfer to Jingle File Transfer.</li>
  </ul>
  <p>Jingle file transfer is only as reliable as the transports on which it depends. In particular, SOCKS5 Bytestreams ("S5B") does not always result in NAT or firewall traversal. To work around that problem, this specification requires all implementations to support as a fallback mechanism In-Band Bytestreams ("IBB"), which usually results in a successful (if slow) file transfer.</p>
  <p>Note: It is likely that a future version of this specification will also recommend implementation of a Jingle transport method that emulates the IETF's ICE-TCP technology, which is currently a work in progress (see &ice-tcp;); however, a future Jingle ICE-TCP transport method is dependent on the outcome of IETF work in this area.</p>
</section1>

<section1 topic='How It Works' anchor='protocol'>
  <p>This section provides a friendly introduction to Jingle file transfer.</p>
  <p>First, the party that wishes to initiate the file transfer determines the responder's capabilities (via &xep0030; or &xep0115;). Here we assume that the responder supports the following service discovery features:</p>
  <ul>
    <li>urn:xmpp:jingle:1 as described in <cite>XEP-0166</cite></li>
    <li>urn:xmpp:jingle:apps:file-transfer:3 as defined in this document &NSVER;</li>
    <li>urn:xmpp:jingle:transports:s5b:1 as defined in <cite>XEP-0260</cite></li>
    <li>urn:xmpp:jingle:transports:ibb:1 as defined in <cite>XEP-0261</cite></li>
  </ul>
  <p>The initiator then sends a Jingle session-initiation request to a potential responder. The content-type of the request specifies two things:</p>
  <ol>
    <li>An application type of "urn:xmpp:jingle:apps:file-transfer:3". In particular, the &lt;description/&gt; element contains an &lt;offer/&gt; element or a &lt;request/&gt; element that in turn contains one or more &lt;file/&gt; elements defining a file to be sent.</li>
    <li>An appropriate transport method. So far the suggested methods are jingle-s5b (<cite>XEP-0260</cite>) and, as a fallback, jingle-ibb (<cite>XEP-0261</cite>).</li>
  </ol>
  <p>Note: All attributes of the &lt;file/&gt; element are defined in <cite>XEP-0096</cite>, not in this specification.</p>
  <p>In this example, the initiator is &lt;romeo@montague.lit&gt;, the responder is &lt;juliet@capulet.lit&gt;, the application type is a file offer, and the transport method is jingle-s5b.</p>
  <p>The flow is as follows.</p>
  <code><![CDATA[
Initiator                    Responder
   |                             |
   |   session-initiate          |
   |   (with <offer/> or         | 
   |   <request/> and S5B)       |
   |---------------------------->|
   |   ack                       |
   |<----------------------------|
   |   session-accept            |
   |<----------------------------|
   |   ack                       |
   |---------------------------->|
   |   [ file transfer ]         |
   |============================>|
   |   session-terminate         |
   |<----------------------------|
   |   ack                       |
   |---------------------------->|
   |                             |
  ]]></code>
  <p>First the initiator sends a Jingle session-initiate.</p>
  <example caption="Initiator sends session-initiate"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='nzu25s8'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          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:3'>
        <offer>
          <file>
            <date>1969-07-21T02:56:15Z</date>
            <desc>This is a test. If this were a real file...</desc>
            <name>test.txt</name>
            <range/>
            <size>1022</size>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
          </file>
        </offer>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='vj3hs98y'>
        <candidate cid='hft54dqy'
                   host='192.168.4.1'
                   jid='romeo@montague.lit/orchard'
                   port='5086'
                   priority='8257636'
                   type='direct'/>
        <candidate cid='hutr46fe'
                   host='24.24.24.1'
                   jid='romeo@montague.lit/orchard'
                   port='5087'
                   priority='8258636'
                   type='direct'/>
      </transport>
    </content>
  </jingle>
</iq>
  ]]></example>
  <p>Note: As in <cite>XEP-0096</cite>, inclusion of the &lt;range/&gt; child of the &lt;file/&gt; element indicates that the initiatior supports ranged transfers as described below under <link url='#range'>Ranged Transfers</link>.</p>
  <p>Note: Computing the hash of the file before sending it can slow down the process of file transfer, since the sending application needs to process the file twice. The sender might prefer to send the hash after the file transfer has begun, using a transport-info message as described under <link url='#hash'>Communicating the Hash</link>.</p>
  <p>The responder immediately acknowledges receipt of the Jingle session-initiate.</p>
  <example caption="Responder acknowledges session-initiate"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='nzu25s8'
    to='romeo@montague.lit/orchard'
    type='result'/>
  ]]></example>
  <p>The initiator then attempts to initiate a SOCKS5 Bytestream with the responder as described in <cite>XEP-0260</cite> and <cite>XEP-0065</cite>. In the meantime, the responder returns a Jingle session-accept. In the session-accept message, the &lt;file/&gt; element MAY contain a &lt;range/&gt; element to indicate that the receiver also supports ranged transfers as described below under <link url='#range'>Ranged Transfers</link>.</p>
  <example caption="Responder sends session-accept"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='jn2vs71g'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-accept'
          initiator='romeo@montague.lit/orchard'
          sid='851ba2'>
    <content creator='initiator' name='a-file-offer'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:3'>
        <offer>
          <file>
            <date>1969-07-21T02:56:15Z</date>
            <desc>This is a test. If this were a real file...</desc>
            <name>test.txt</name>
            <range/>
            <size>1022</size>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
          </file>
        </offer>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='vj3hs98y'>
        <candidate cid='ht567dq'
                   host='192.169.1.10'
                   jid='juliet@capulet.lit/balcony'
                   port='6539'
                   priority='8257636'
                   type='direct'/>
        <candidate cid='hr65dqyd'
                   host='134.102.201.180'
                   jid='juliet@capulet.lit/balcony'
                   port='16453'
                   priority='7929856'
                   type='assisted'/>
        <candidate cid='grt654q2'
                   host='2001:638:708:30c9:219:d1ff:fea4:a17d'
                   jid='juliet@capulet.lit/balcony'
                   port='6539'
                   priority='8257606'
                   type='direct'/>
      </transport>
    </content>
  </jingle>
</iq>
  ]]></example>
  <p>The initiator acknowledges the Jingle session-accept.</p>
  <example caption="Initiator acknowledges session-accept"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='jn2vs71g'
    to='juliet@capulet.lit/balcony'
    type='result'/>
  ]]></example>
  <p>Once one client has successfully created a connection, it sends a &lt;candidate-used/&gt; element to the peer inside a Jingle transport-info message. If a client receives a candidate-used notification it SHOULD continue trying to connect to candidates sent by its peer if it has not tried all candidates with a higher priority than the one successfully used by the peer.</p>
  <example caption="Initiator sends candidate-used in Jingle transport-info"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='hjdi8'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='transport-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='ex'>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
                 sid='vj3hs98y'>
        <candidate-used cid='hr65dqyd'/>
      </transport>
    </content>
  </jingle>
</iq>
  ]]></example>
  <p>The peer immediately acknowledges receipt.</p>
  <example caption="Responder acknowledges candidate-used message"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='hjdi8'
    to='romeo@montague.lit/orchard'
    type='result'/>
  ]]></example>
  <p>(See <cite>XEP-0260</cite> for further details.)</p>
  <p>Now the parties exchange the file using the negotiated transport (here, SOCKS5 Bytestreams).</p>
  <p>Once the transfer is completed, either party can acknowledge completion (see <link url='#multi'>Sending Multiple Files</link>) or terminate the Jingle session; preferably this is done by the entity that receives the file to ensure that the complete file (up to the advertised size) has been received.</p>
  <example caption="Receiver sends session-terminate"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='og61bvs98'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-terminate'
          sid='a73sjjvkla37jfea'>
    <reason>
      <success/>
    </reason>
  </jingle>
</iq>
  ]]></example>
  <p>After terminating the session, the parties would close the data transport as described in the relevant specification (e.g., <cite>XEP-0260</cite> or <cite>XEP-0261</cite>).</p>
  <p>For a description of the transport fallback scenario (from SOCKS5 Bytestreams to In-Band Bytestreams), refer to <cite>XEP-0260</cite>.</p>
</section1>

<section1 topic='Communicating the Hash' anchor='hash'>
  <p>At any time during the lifetime of the file transfer session, the hosting entity (i.e., the entity where the file resides) can communicate the checksum of the file to the receiving entity. This is done by sending a session-info message containing a &lt;checksum/&gt; element qualified by the 'urn:xmpp:jingle:apps:file-transfer:3' namespace, which in turn contains a &lt;file/&gt; element that MUST at least contain a child element of &lt;hash/&gt; qualified by the 'urn:xmpp:hashes:1' namespace and MAY contain other elements qualified by the 'urn:xmpp:jingle:apps:file-transfer:3' namespace (e.g. &lt;name/&gt; and &lt;date/&gt;). Each &lt;hash/&gt; element contains a checksum of the file contents produced in accordance with the hashing function specified by the 'algo' attribute, which MUST be one of the functions listed in the &ianahashes;.</p>
  <example caption="Hosting entity sends hash in session-info"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='kqh401b5'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <checksum xmlns='urn:xmpp:jingle:apps:file-transfer:3'>
      <file>
        <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
      </file>
    </checksum>
  </jingle>
</iq>
  ]]></example>
</section1>

<section1 topic='Aborting a Transfer' anchor='abort'>
  <p>If either party wishes to abort the transfer of a file but not the entire session (e.g., when the parties are exchanging multiple files), it SHOULD send a Jingle session-info message containing an &lt;abort/&gt; child element qualified by the 'urn:xmpp:jingle:apps:file-transfer:3' namespace.</p>
  <example caption="Initiator aborts transfer of file"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='hv9sx61j'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <abort xmlns='urn:xmpp:jingle:apps:file-transfer:3'>
      <file>
        <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
      </file>
    </abort>
  </jingle>
</iq>
  ]]></example>
  <p>If either party wishes to end the entire file transfer session instead of aborting transfer of a particular file, it MUST instead send a session-terminate message containing a reason of &lt;cancel/&gt; as described in <cite>XEP-0166</cite>.</p>
  <example caption="Receiver sends session-terminate"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='og61bvs98'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-terminate'
          sid='a73sjjvkla37jfea'>
    <reason>
      <cancel/>
    </reason>
  </jingle>
</iq>
  ]]></example>
  <p>After terminating the session, the parties would close the data transport as described in the relevant specification (e.g., <cite>XEP-0260</cite> or <cite>XEP-0261</cite>).</p>
</section1>

<section1 topic='Requesting a File' anchor='request'>
  <p>If the entity that hosts a file has advertised its existence (or if a previous file transfer attempt has failed and the receiver would like to initiate another attempt), the entity that wishes to receive the file can "pull" the file from the hosting entity. This is done by sending a Jingle session-initiate to the hosting entity, including a &DESCRIPTION; element qualified by the 'urn:xmpp:jingle:apps:file-transfer:3' namespace and containing a &lt;request/&gt; element that defines the requested file.</p>
  <example caption="Receiver requests hosted file"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='wsn361c3'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='uj3b2'>
    <content creator='initiator' name='a-file-request'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:3'>
        <request>
          <file>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
          </file>
        </request>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='xig361fj'>
        <candidate cid='ht567dq'
                   host='192.169.1.10'
                   jid='juliet@capulet.lit/balcony'
                   port='6539'
                   priority='8257636'
                   type='direct'/>
        <candidate cid='hr65dqyd'
                   host='134.102.201.180'
                   jid='juliet@capulet.lit/balcony'
                   port='16453'
                   priority='7929856'
                   type='assisted'/>
        <candidate cid='grt654q2'
                   host='2001:638:708:30c9:219:d1ff:fea4:a17d'
                   jid='juliet@capulet.lit/balcony'
                   port='6539'
                   priority='8257606'
                   type='direct'/>
      </transport>
    </content>
  </jingle>
</iq>
  ]]></example>
  <p>The parties would then complete a session negotiation flow similar to that outlined above for offering a file.</p>
  <p>Note: If the requesting entity knows the hash of the file, it can include only that metadata in its request. If not, the requesting entity needs to include enough metadata to uniquely identify the file, such as the date, name, and size. For similar considerations, see &rfc5547;.</p>
</section1>

<section1 topic='Ranged Transfers' anchor='range'>
  <p>As in <cite>XEP-0096</cite>, a transfer can include only part of a file (e.g., to restart delivery of a truncated transfer session at a point other than the start of the file). This is done using the &lt;range/&gt; element from <cite>XEP-0096</cite>. The usage is illustrated in the following examples.</p>
  <p>Let us imagine that the parties negotiate a file transfer session using, say, In-Band Bytestreams. During the transfer, the recipient goes offline unexpectedly and IBB stanzas from the sender to the recipient begin to bounce. When the recipient comes back online, the recipient could initiate a new Jingle session (to retrieve the file) and specify that it wants to receive all chunks after byte 270336 (which might be the 66th chunk of size 4096).</p>
  <example caption="Receiver requests hosted file, with range"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='wsn361c3'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='uj3b2'>
    <content creator='initiator' name='a-file-request'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:3'>
        <request>
          <file>
            <range offset='270336'/>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
          </file>
        </request>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='xig361fj'>
        <candidate cid='ht567dq'
                   host='192.169.1.10'
                   jid='juliet@capulet.lit/balcony'
                   port='6539'
                   priority='8257636'
                   type='direct'/>
        <candidate cid='hr65dqyd'
                   host='134.102.201.180'
                   jid='juliet@capulet.lit/balcony'
                   port='16453'
                   priority='7929856'
                   type='assisted'/>
        <candidate cid='grt654q2'
                   host='2001:638:708:30c9:219:d1ff:fea4:a17d'
                   jid='juliet@capulet.lit/balcony'
                   port='6539'
                   priority='8257606'
                   type='direct'/>
      </transport>
    </content>
  </jingle>
</iq>
  ]]></example>
  <p>Alternatively, the sender could initiate a new file transfer, indicating that it supports ranged transfers, and in the Jingle session-accept message the receiver could indicate that it wants the transfer to begin at the specified offset.</p>
</section1>

<section1 topic='Sending Multiple Files' anchor='multi'>
  <p>The initiator can send multiple files by including multiple &lt;file/&gt; elements in its session-initiate message.</p>
  <example caption="Initiator sends session-initiate with multiple files"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='bv2gs986'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='h2va419i'>
    <content creator='initiator' name='a-file-offer'>
      <description xmlns='urn:xmpp:jingle:apps:file-transfer:3'>
        <offer>
          <file>
            <date>2011-06-01T15:58:15Z</date>
            <name>somefile.txt</name>
            <size>1234</size>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>a749930852c69ae5d2141d3766b1552d</hash>
          </file>
          <file>
            <date>2011-06-01T15:58:15Z</date>
            <name>anotherfile.txt</name>
            <size>2345</size>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>930852c69ae5d2141d3766b1552da749</hash>
          </file>
          <file>
            <date>2011-06-01T15:58:15Z</date>
            <name>yetanotherfile.txt</name>
            <size>3456</size>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>52c69ae5d2141d3766b1552da7499308</hash>
          </file>
        </offer>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='vj3hs98y'>
        <candidate cid='hft54dqy'
                   host='192.168.4.1'
                   jid='romeo@montague.lit/orchard'
                   port='5086'
                   priority='8257636'
                   type='direct'/>
        <candidate cid='hutr46fe'
                   host='24.24.24.1'
                   jid='romeo@montague.lit/orchard'
                   port='5087'
                   priority='8258636'
                   type='direct'/>
      </transport>
    </content>
  </jingle>
</iq>
  ]]></example>
  <p>The parties would negotiate the file transfer session as previously described.</p>
  <p>After exchange of the first file, the recipient SHOULD send a Jingle session-info message indicating receipt of the complete file.</p>
  <example caption="Receiver sends ack in session-info"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='jp2ba614'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <received xmlns='urn:xmpp:jingle:apps:file-transfer:3'>
      <file>
        <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>a749930852c69ae5d2141d3766b1552d</hash>
      </file>
    </received>
  </jingle>
</iq>
  ]]></example>
  <p>The hosting entity SHOULD NOT wait for arrival of the &lt;received/&gt; acknowledgement before starting to send the next file in its list.</p>
  <p>After the recipient has received all of the files, it SHOULD send a final acknowledgement and then terminate the session.</p>
  <p>After terminating the session, the parties would close the data transport as described in the relevant specification (e.g., <cite>XEP-0260</cite> or <cite>XEP-0261</cite>).</p>
  <p class='box'>OPEN ISSUE: Provide a way for the hosting entity to add more files to the original "manifest"?</p>
  <p>Support for transferring multiple files is OPTIONAL. If an application supports multi-file exchange, it MUST advertise a service discovery feature of "urn:xmpp:jingle:apps:file-transfer:multi".</p>
</section1>

<section1 topic='Use of Jingle Actions' anchor='jingle'>
  <p>Jingle file transfer uses only a few of the actions defined in <cite>XEP-0166</cite>. Jingle usage is summarized in the following table.</p>
  <table caption='Jingle Actions Used in File Transfer'>
    <tr>
      <th>Action</th>
      <th>Use</th>
    </tr>
    <tr>
      <td>content-accept</td> 
      <td>Unused</td>
    </tr>
    <tr>
      <td>content-add</td> 
      <td>Unused</td>
    </tr>
    <tr>
      <td>content-modify</td> 
      <td>Unused</td>
    </tr>
    <tr>
      <td>content-reject</td> 
      <td>Unused</td>
    </tr>
    <tr>
      <td>content-remove</td> 
      <td>Unused</td>
    </tr>
    <tr>
      <td>description-info</td> 
      <td>Unused</td>
    </tr>
    <tr>
      <td>security-info</td> 
      <td>Unused</td>
    </tr>
    <tr>
      <td>session-accept</td> 
      <td>Accepting a file offer or request</td>
    </tr>
    <tr>
      <td>session-info</td> 
      <td>Communicating the file hash</td>
    </tr>
    <tr>
      <td>session-initiate</td> 
      <td>Initiating a file offer or request</td>
    </tr>
    <tr>
      <td>session-terminate</td> 
      <td>Ending a file transfer session</td>
    </tr>
    <tr>
      <td>transport-accept</td> 
      <td>Accepting fallback from S5B to IBB</td>
    </tr>
    <tr>
      <td>transport-info</td> 
      <td>Used in SOCKS5 Bytestreams</td>
    </tr>
    <tr>
      <td>transport-reject</td> 
      <td>Rejecting fallback from S5B to IBB</td>
    </tr>
    <tr>
      <td>transport-replace</td> 
      <td>Fallback from S5B to IBB</td>
    </tr>
  </table>
</section1>

<section1 topic='Implementation Notes' anchor='impl'>
  <section2 topic='Mandatory to Implement Technologies' anchor='impl-mti'>
    <p>All implementations MUST support the Jingle In-Band Bytestreams Transport Method (<cite>XEP-0261</cite>) as a reliable method of last resort. An implementation SHOULD support other transport methods as well, especially the Jingle SOCKS5 Bytestreams Transport Method (<cite>XEP-0260</cite>).</p>
  </section2>
  <section2 topic='Preference Order of Transport Methods' anchor='impl-pref'>
    <p>An application MAY present transport methods in any order, except that the Jingle In-Band Bytestreams Transport Method MUST be the lowest preference.</p>
  </section2>
  <section2 topic='Migration from XEP-0096' anchor='impl-migration'>
    <p>Support for Jingle file transfer can be determined through discovery of the 'urn:xmpp:jingle:apps:file-transfer:3' namespace &VNOTE;, via either service discovery (<cite>XEP-0030</cite>) or entity capabilities (<cite>XEP-0115</cite>). If the initiator knows that the responder supports Jingle file transfer, it SHOULD first attempt negotiation using Jingle rather than Stream Initiation.</p>
  </section2>
</section1>

<section1 topic='Determining Support' anchor='support'>
  <p>To advertise its support for the Jingle File Transfer, when replying to service discovery information ("disco#info") requests an entity MUST return URNs for any version of this protocol that the entity supports -- e.g., "urn:xmpp:jingle:apps:file-transfer:3" for this version &VNOTE;.</p>
  <example caption="Service discovery information request"><![CDATA[
<iq from='romeo@montague.lit/orchard'
    id='uw72g176'
    to='juliet@capulet.lit/balcony'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  ]]></example>
  <example caption="Service discovery information response"><![CDATA[
<iq from='juliet@capulet.lit/balcony'
    id='uw72g176'
    to='romeo@montague.lit/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='urn:xmpp:jingle:1'/>
    <feature var='urn:xmpp:jingle:apps:file-transfer:3'/>
    <feature var='urn:xmpp:jingle:transports:s5b:1'/>
    <feature var='urn:xmpp:jingle:transports:ibb:1'/>
  </query>
</iq>
  ]]></example>
  <p>As noted, if an application supports exchange of multiple files, it MUST advertise a service discovery feature of "urn:xmpp:jingle:apps:file-transfer:multi".</p>
  <p>In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.</p>
</section1>

<section1 topic='Security Considerations' anchor='security'>
  <p>For historical reasons and for backward-compatibility with <cite>XEP-0096</cite>, the hashing algorithm used in computing the file checksum defaults to MD5. It is RECOMMENDED for implementations to use stronger hashing algorithms.</p>
  <p>In order to secure the data stream, implementations SHOULD use encryption methods appropriate to the transport method being used. For example, end-to-end encryption can be negotiated over either SOCKS5 Bytestreams or In-Band Bytestreams as described in <cite>XEP-0260</cite> and <cite>XEP-0261</cite>.</p>
  <p>Refer to <cite>XEP-0047</cite>, <cite>XEP-0065</cite>, <cite>XEP-0096</cite>, <cite>XEP-0260</cite>, and <cite>XEP-0261</cite> for related security considerations.</p>
</section1>

<section1 topic='IANA Considerations' anchor='iana'>
  <p>No interaction with &IANA; is required as a result of this document.</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:jingle:apps:file-transfer:3</li>
    </ul>
    <p>Upon advancement of this specification from a status of Experimental to a status of Draft, the &REGISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
  </section2>
  <section2 topic='Namespace Versioning' anchor='registrar-versioning'>
    &NSVER;
  </section2>
  <section2 topic='Service Discovery Features' anchor='registrar-features'>
    <p>The service discovery feature for advertising support for exchange of multiple files is "urn:xmpp:jingle:apps:file-transfer:multi".</p>
    <p>The registry submission is as follows.</p>
    <code caption='Registry Submission'><![CDATA[
<var>
  <name>urn:xmpp:jingle:apps:file-transfer:multi</name>
  <desc>Signals support for exchange of multiple files.</desc>
  <doc>XEP-0234</doc>
</var>
    ]]></code>
  </section2>
  <section2 topic='Jingle Application Formats' anchor='registrar-content'>
    <p>The XMPP Registrar shall include "file-transfer" in its registry of Jingle application formats. The registry submission is as follows:</p>
    <code><![CDATA[
<application>
  <name>file-transfer</name>
  <desc>Jingle sessions for the transfer of a file</desc>
  <transport>streaming</transport>
  <doc>XEP-0234</doc>
</application>
    ]]></code>
  </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:jingle:apps:file-transfer:3'
    xmlns='urn:xmpp:jingle:apps:file-transfer:3'
    elementFormDefault='qualified'>

  <xs:import namespace='urn:xmpp:hashes:1'/>

  <xs:element name='description'>
    <xs:complexType>
      <xs:choice>
        <xs:element name='offer' type='fileTransferElementType'/>
        <xs:element name='request' type='fileTransferElementType'/>
      </xs:choice>
    </xs:complexType>
  </xs:element>

  <xs:element name='abort' type='fileTransferElementType'/>

  <xs:element name='received' type='fileTransferElementType'/>

  <xs:element name='checksum' type='fileTransferElementType'/>

  <xs:complexType name='fileTransferElementType'>
    <xs:sequence>
      <xs:element name='file'/>
    </xs:sequence>
  </xs:complexType>

  <xs:element name='file'>
    <xs:complexType>
      <xs:sequence xmlns:h='urn:xmpp:hashes:1'>
        <xs:element name='date' type='xs:date'/>
        <xs:element name='name' type='xs:string'/>
        <xs:element name='size' type='xs:positiveInteger'/>
        <xs:element ref='h:hash' minOccurs='0' maxOccurs='unbounded'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

</xs:schema>
  ]]></code>
</section1>

<section1 topic='Acknowledgements' anchor='ack'>
  <p>Thanks to Diana Cionoiu, Olivier Crête, Viktor Fast, Waqas Hussain, Justin Karneges, Steffen Larsen, Yann Leboulanger, Marcus Lundblad, Robert McQueen, Joe Maissel, Glenn Maynard, Ali Sabil, Sjoerd Simons, Will Thompson, Matthew Wild, and Jiří Zárevúcky for their feedback.</p>
</section1>

</xep>
