of current implementations. However there are two backward compatible
improvements to the protocol introduced in this standard
that increase the future useability of the protocol: matching on the fully
qualified name of the XML fragment root, and the introduction of a standard
mechanism of removing stored data. Because the protocol defined herein is not identical to 'jabber:iq:private', a new namespace name is used: 'http://jabber.org/protocol/private-xml'.</p>
<p>This protocol is designed to provide a simple interface to XML data storage
on XMPP servers. The simple interface eases the implementation burden for the most
basic data storage use-cases (e.g. storing simple client preferences on the server).
More sophisticated XML data storage protocols should be built on top of, or compatible
with this standard.</p>
</section1>
<section1topic='private-xml Namespace'>
<section2topic='Description'>
<p>A Jabber client can store any arbitrary XML on the server side by sending an
&IQ; chunk of type "set" to the server with a &QUERY; child scoped by the
'http://jabber.org/protocol/private-xml' namespace. The &QUERY; element MUST contain a single, arbitrary
XML fragment. That fragment MUST be scoped by its
own namespace. Any existing data stored on the server with the same fully qualified
element name (tag name + namespace) is replaced by the new data.</p>
<p>The data can then be retrieved by sending an &IQ;
of type "get" with a &QUERY; child scoped by the 'http://jabber.org/protocol/private-xml' namespace,
which in turn MUST contain a single child element scoped by the namespace used
for storage of that fragment. The fully qualified element name is used to locate
matching XML data on the server. If no matching data is found, the server will
respond with the empty query child element and not an error.</p>
<p>Finally, existing data on the server can be removed by sending an &IQ;
of type "set" with a &QUERY; child scoped by the 'http://jabber.org/protocol/private-xml' namespace and
containing an 'action' attribute with value 'delete',
which in turn MUST contain a single child element scoped by the namespace used
for storage of that fragment. The fully qualified element name is used to locate
matching XML data on the server. The server responds with a successful result
whether a matching data fragment was found or not (it's successful because the
provided data no longer exits on the server). Deleting data using this method is
indistinguishable from setting an empty XML fragment as far as the behavior this
protoco is concerned. However, deleting data MUST remove the data from the server
which may be implemented differently than the case of setting the data to an empty
element. This may have significance in the context of future advanced XML storage protocols.
Using the basic private XML data storage protocol, Jabber entities can create, read, update, and delete
private data on the server. The data stored might be
anything, as long as it is valid XML. One typical usage for this namespace is the
server-side storage of client preferences.</p>
</section2>
<section2topic='Methods'>
<tablecaption='Description of Acceptable Methods'>
<tr><td>get</td><td>Sent with a blank query to retrieve the private data from the server.</td></tr>
<tr><td>set</td><td>Sent with the private XML data contained inside of a query.</td></tr>
<tr><td>set action='delete'</td><td>Sent with a blank query to delete private data from the server.</td></tr>
<tr><td>result</td><td>Returns the private data from the server.</td></tr>
<tr><td>error</td><td>There was an error processing the request. The exact error can be found in the child error element.</td></tr>
</table>
</section2>
<section2topic='Elements'>
<p>The root element of this namespace is query. A single child
element with a proper namespace must be included otherwise the server will
respond with error code 406. Only one element can be queried or set in a
single IQ request. However, multiple elements, each containing data,
can be stored independently on the server using separate set queries.</p>
<p>If a user attempts to get or set http://jabber.org/protocol/private-xml data that belongs to another user, the server must return an error to the sender. The error commonly used is 503 (Service Unavailable).</p>
<examplecaption='User Attempts to Get or Set Data for Another User'><![CDATA[
<p>Certain namespaces are reserved in Jabber (namespaces beginning with 'jabber:' or 'http://jabber.org/', as well as 'vcard-temp'). If a user attempts to get or set http://jabber.org/protocol/private-xml data in a reserved namespace, historically some server implementations have chosen to return an error (commonly 406 [Not Acceptable]) to the sender. Such behavior is not required in order to comply with this document, but may be encountered by clients when interacting with some current server implementations.</p>
