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xeps/xep-0259.xml
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<?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>Message Mine-ing</title>
<abstract>In servers that deliver messages intended for the bare JID to
all resources, the resource that claims a conversation notifies all
of the other resources of that claim.</abstract>
&LEGALNOTICE;
<number>0259</number>
<status>Deferred</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
<dependencies>
<spec>XMPP Core</spec>
<spec>XEP-0030</spec>
<spec>XEP-0045</spec>
<spec>XEP-0115</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>mine</shortname>
&hildjj;
<revision>
<version>0.1</version>
<date>2009-01-21</date>
<initials>psa</initials>
<remark><p>Initial published version.</p></remark>
</revision>
<revision>
<version>0.0.1</version>
<date>2008-10-22</date>
<initials>jjh</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1 topic='Introduction' anchor='intro'>
<p>At the time of original writing of this XEP, many XMPP servers
handle message stanzas sent to a user@host (or "bare") JID with no
resource by delivering that message only to the resource with
the highest priority for the target user. Some server
implementations, however, have chosen to send these messages to all
of the online resources for the target user. If the target user is
online with multiple resources when the orginal message is sent, a
conversation ensues on one of the user's devices; if the user
subsequently switches devices, parts of the conversation may end up
on the alternate device, causing the user to be confused, misled,
or annoyed.</p>
<p>This XEP proposes an approach for cleaning up the leftover
conversation shards on alternate devices, paving the way for servers
to deliver messages to multiple devices. As the basic approach, the
receiving server asks all of the resources of a user "whose message
is this?". The first resource to say "mine!" wins.</p>
</section1>
<section1 topic='Requirements' anchor='reqs'>
<ul>
<li>Large changes SHOULD NOT be required to existing servers</li>
<li>Clients that do not implement the new protocol MUST be able
participate in conversations</li>
<li>All messages MUST NOT be delivered to all devices at all
times, due to scale concerns</li>
<li>Clients that do not own the message MUST be notified
when a different device claims ownership of the message</li>
<li>Multiple clients MUST be able to uambiguosly decide which of
them owns a given message.</li>
</ul>
</section1>
<section1 topic='Use Cases' anchor='usecases'>
<section2 topic='Determining Support: Servers' anchor='disco_server'>
<p>If a server implements the Mine capability, it MUST specify the
'urn:xmpp:tmp:mine:0' feature in its service discovery
information features as specified in &xep0115; or &xep0030;.
Clients MUST NOT send ownership changes if their server does
not support this feature.</p>
<example caption='Client requests information about its own server'><![CDATA[
<iq type='get'
from='romeo@montague.net/orchard'
id='info1'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>]]></example>
<example caption='Server responds with mine feature'><![CDATA[
<iq type='get'
to='romeo@montague.net/home'
from='montague.net'
id='info1'>
<query xmlns='http://jabber.org/protocol/disco#info'>
...
<feature var='urn:xmpp:tmp:mine:0'/>
...
</query>
</iq>]]></example>
</section2>
<section2 topic='Determining Support: Clients' anchor='disco_client'>
<p>Clients that support this protocol MUST support <cite>XEP-0115</cite>, and MUST add the
'urn:xmpp:tmp:mine:0' feature to their entity capabilities, in
order to allow for potential server optimizations.</p>
<example caption='Romeo publishes his capabilities'><![CDATA[
<presence from='romeo@example.net/home'>
<c xmlns='http://jabber.org/protocol/caps'
hash='sha-1'
node='http://example.com/clients/Mine'
ver='j+5eLRCz6NP6IEPob80JB6sWR3Y='/>
</presence>
]]></example>
<example caption='Romeo responds to capabilities inquiry from his server'><![CDATA[
<iq from='romeo@example.net/home'
id='disco1'
to='example.net'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'
node='http://example.com/clients/Mine#/WmLAKHhB87dOqn5NUgxrr5NbfE='>
<identity category='client' type='pc' name='Mine'/>
<feature var='urn:xmpp:tmp:mine:0'/>
</query>
</iq>]]></example>
</section2>
<section2 topic='Receving a message to the bare JID' anchor='receiving'>
<p>When a server that implements the Mine capability receives a
message addressed to a user's bare JID, it MUST:</p>
<ul>
<li>Ensure that no "whose" element is already on the message.
See the <link url="#errors">Errors</link> section for processing.</li>
<li>Add a whose element to the message, containing an id
attribute with a new value</li>
<li>Ensure that the the same value of the "id" attribute is
never sent to the same session </li>
</ul>
<p>Messages that have been processed to include a valid "whose"
element, are now also considered an "ownership request"</p>
<example caption='Juliet sends Romeo an undirected message'><![CDATA[
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'>
<body>Wherefore art thou, Romeo?</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
</message>
]]></example>
<example caption='The ownership request, before broadcasting'><![CDATA[
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'>
<body>Wherefore art thou, Romeo?</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<whose xmlns='urn:xmpp:tmp:mine:0' id='4'/>
</message>
]]></example>
</section2>
<section2 topic='Broadcasting ownership requests' anchor='broadcast'>
<p>The receiving server MUST send a copy of the ownership request
to each of that user's non-negative priority resources. Each copy
of the message MUST contain a whose element, each of which has the
same id attribute.</p>
<example caption='Romeo&apos;s server forwards copies of the
message to all of his resources'><![CDATA[
<message
from='juliet@example.com/balcony'
to='romeo@example.net/home'
type='chat'>
<body>Wherefore art thou, Romeo?</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<whose xmlns='urn:xmpp:tmp:mine:0' id='4'/>
</message>
<message
from='juliet@example.com/balcony'
to='romeo@example.net/work'
type='chat'>
<body>Wherefore art thou, Romeo?</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<whose xmlns='urn:xmpp:tmp:mine:0' id='4'/>
</message>
<message
from='juliet@example.com/balcony'
to='romeo@example.net/mobile'
type='chat'>
<body>Wherefore art thou, Romeo?</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<whose xmlns='urn:xmpp:tmp:mine:0' id='4'/>
</message>
]]></example>
</section2>
<section2 topic='Claiming ownership' anchor='claim'>
<p>When one client for a receiving user detects that the user's
attention has been directed to a given message, that client MUST
send an ownership claim (mine!) to the bare JID of the receiving
user. If there was a thread element in the original message, it
MUST be included in the acceptance notification. There MUST NOT
be a body element in the message, and the message SHOULD use the
same message type as the ownership request. The mine element MUST
include an id element for each of the messages that the client
wants to accept. The mine element MUST include at least one
id.</p>
<example caption='Romeo&apos;s &quot;work&quot; client claims ownership'><![CDATA[
<message
to='romeo@example.net'
from='romeo@example.net/work'
type='chat'>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<mine xmlns='urn:xmpp:tmp:mine:0'>
<id>4</id>
</mine>
</message>
]]></example>
</section2>
<section2 topic='Notification of ownership claim' anchor='notification'>
<p>As with all messages sent to a bare JID at a server
implementing the Mine feature, the acceptance message MUST be
forwarded to all of the non-negative priority resources.</p>
<example caption='Each of Romeo&apos;s clients receives the claim'><![CDATA[
<message
to='romeo@example.net/home'
from='romeo@example.net/work'
type='chat'>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<mine xmlns='urn:xmpp:tmp:mine:0'>
<id>4</id>
</mine>
</message>
<message
to='romeo@example.net/work'
from='romeo@example.net/work'
type='chat'>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<mine xmlns='urn:xmpp:tmp:mine:0'>
<id>4</id>
</mine>
</message>
<message
to='romeo@example.net/mobile'
from='romeo@example.net/work'
type='chat'>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<mine xmlns='urn:xmpp:tmp:mine:0'>
<id>4</id>
</mine>
</message>
]]></example>
</section2>
<section2 topic='Claim processing' anchor='processing'>
<p>When a client receives an ownership claim that was sent from
that client for an ID that has not been previously claimed,
the client MUST note that the message associated with the ID has
been confirmed, and ignore any further ownership claims for
that ID.</p>
<p>When a client receives an ownership claim that was sent from
a different client of the same user for a ID that has not
been previously received, the client MUST note that the message
associated with the ID has been retracted, and ignore any further
ownership claims for that ID. Retracted messages SHOULD
be removed from the client's user interface, or otherwise marked
in some way as retracted.</p>
<p>Clients MUST ignore ownership claims for IDs for which they
have no corresponding message.</p>
<p>Assuming that messages are delivered and processed in order,
these rules should ensure that exactly one client resource has a
confirmed copy of the message</p>
</section2>
<section2 topic='Claims for Multi-User Chat rooms' anchor='muc'>
<p>The same approach that has been described for one-to-one
messages above can also be used by &xep0045; (MUC) rooms.
Rooms that want to participate MUST send the
'urn:xmpp:tmp:mine:0' feature in the room's disco info. The room
MUST then perform the role of the server in the above
descriptions, ensuring that unique ID's are assigned to all
outbound groupchat messages that were addressed to the bare JID of
the room. Ownership claims MUST be sent to the bare JID of the
<strong>room</strong>, not the receiving user.</p>
<p>This capability might be used to distribute questions to
multiple experts in a room, such that a single expert answers a
question.</p>
<example caption='Message is sent to the room'><![CDATA[
<message
from='hag66@shakespeare.lit/pda'
to='darkcave@chat.shakespeare.lit'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
</message>]]></example>
<example caption='Room forwards message to all participants as ownership request'><![CDATA[
<message
from='darkcave@chat.shakespeare.lit/thirdwitch'
to='crone1@shakespeare.lit/desktop'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
<whose xmlns='urn:xmpp:tmp:mine:0' id='5'/>
</message>
<message
from='darkcave@chat.shakespeare.lit/thirdwitch'
to='wiccarocks@shakespeare.lit/laptop'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
<whose xmlns='urn:xmpp:tmp:mine:0' id='5'/>
</message>
<message
from='darkcave@chat.shakespeare.lit/thirdwitch'
to='hag66@shakespeare.lit/pda'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
<whose xmlns='urn:xmpp:tmp:mine:0' id='5'/>
</message>
]]></example>
<example caption='A participant claims ownership'><![CDATA[
<message
to='darkcave@chat.shakespeare.lit'
from='crone1@shakespeare.lit/desktop'
type='groupchat'>
<mine xmlns='urn:xmpp:tmp:mine:0'>
<id>5</id>
</mine>
</message>
]]></example>
</section2>
</section1>
<section1 topic='Error Cases' anchor='errors'>
<section2 topic='Invalid "whose"' anchor='bad_whose'>
<p>A server receives a message addressed to the bare JID of a
user, from a different user than the one in the to address,
containing a "whose" or "mine" element, it MUST NOT forward the
message on to any clients. This case is always either an attack,
a misconfiguration, or the result of bad code. If the user in the
from address is already known to the user in the to address (for
example, to user in the to address has a presence subscription to
the user in the from address), the server MAY send back a helpful
"bad-request" error.</p>
<example caption='Romeo responds to a bad request from his friend Juliet'><![CDATA[
<message
to='juliet@example.com/balcony'
from='romeo@example.net'
type='error>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<body>My client runneth over</body>
<whose xmlns='urn:xmpp:tmp:mine:0' id='4'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<text>Yours</text>
</error>
</message>
]]></example>
<p>However, if the user in the from address is not known to the user
in the to address, or the server perfers not to send helpful
errors, the server MUST treat the message as if it was addressed
to an unknown user. Otherwise, sending a message with an invalid
"whose" or "mine" could allow an attacker to probe for valid users
at a site.</p>
</section2>
</section1>
<section1 topic='Business Rules' anchor='rules'>
<section2 topic='Generating IDs' anchor='generate'>
<p>The value of the id attribute sent by servers MUST be
valid output from the NODEPREP profile of stringprep.</p>
</section2>
<section2 topic="ID Semantics" anchor="semantics">
<p>The value of the id resource is completely opqaque;
receiving clients MUST NOT use any apparent order or semantic in
the value of the id to perform optimizations or business
logic.</p>
</section2>
<section2 topic='Comparing IDs' anchor='compare'>
<p>Clients MUST only compare the value of ID's for equality,
never for order. ID's MUST be compared for equality
octet-for-octet or codepoint-for-codepoint; a basic string
comparison with no extra canonicalization.</p>
</section2>
<section2 topic='Accepting Multiple IDs' anchor='multiple'>
<p>A client MAY send multiple id elements in an accceptance.
Clients that receive a notification with multiple IDs MUST process
each ID individually, as if multiple claims had been sent.</p>
</section2>
<section2 topic='When to send?' anchor='when'>
<p>To avoid race conditions and edge cases (including
invisibility), if both the client and server support the Mine
capability, the client SHOULD send ownership queries regardless
of whether or not the client sees other resources for the same
user online, or the capabilities of those other resources.</p>
</section2>
<section2 topic='Legacy Clients' anchor='unsupported_clients'>
<p>Clients that do not implement the Mine capability MAY be sent
notifications by the server. The server MAY be optimized to
avoid these notifications, however.</p>
</section2>
</section1>
<section1 topic='Implementation Notes' anchor='impl'>
<p>Some examples of events that might lead to a client sending an
ownsership claim:</p>
<ul>
<li>Clicking on a toast notification for the message</li>
<li>Bringing the client window to the front within a short time
after receiving the message, where the message is then displayed
to the user</li>
<li>Bringing the tab containing the message to the front</li>
<li>Beginning to type a response to the message</li>
<li>Closing the window containing the message at least several
seconds after the message was received</li>
<li>Clicking an accept button next to a message</li>
<li>Shutting down the screen saver while the message is in the
top-most window</li>
<li>A camera notices the user's eyes directed at the message</li>
</ul>
</section1>
<section1 topic='Accessibility Considerations' anchor='access'>
<p>Some care should be given to the events that can cause ownsership
claims, particularly in the MUC client implementations, such that
users with different abilities all have a chance to claim ownership.</p>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>Clients MUST ignore acceptance notifications received from other users.</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'>
<p>This XEP proposes the new namespace 'urn:xmpp:tmp:mine:0'.</p>
</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:tmp:mine:0'
xmlns='urn:xmpp:tmp:mine:0'
elementFormDefault='qualified'>
<xs:element name='whose'>
<xs:complexType>
<xs:attribute name='id' type='xs:string' use='required'/>
</xs:complexType>
</xs:element>
<xs:element name='mine'>
<xs:complexType>
<xs:sequence>
<xs:element ref='id' minOccurs='1' maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='id'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'/>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:schema>
]]></code>
</section1>
</xep>