mirror of
https://github.com/moparisthebest/xeps
synced 2024-11-27 11:42:17 -05:00
198 lines
9.5 KiB
XML
198 lines
9.5 KiB
XML
<?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>MUC Self-Ping (Schrödinger's Chat)</title>
|
||
<abstract>This protocol extension for XEP-0045 Multi User Chat allows clients to check whether they are still joined to a chatroom.</abstract>
|
||
&LEGALNOTICE;
|
||
<number>xxxx</number>
|
||
<status>ProtoXEP</status>
|
||
<type>Standards Track</type>
|
||
<sig>Standards</sig>
|
||
<approver>Council</approver>
|
||
<dependencies>
|
||
<spec>XMPP Core</spec>
|
||
<spec>XEP-0001</spec>
|
||
<spec>Etc.</spec>
|
||
</dependencies>
|
||
<supersedes/>
|
||
<supersededby/>
|
||
<shortname>muc-selfping</shortname>
|
||
<author>
|
||
<firstname>Georg</firstname>
|
||
<surname>Lukas</surname>
|
||
<email>georg@op-co.de</email>
|
||
<jid>georg@yax.im</jid>
|
||
</author>
|
||
<revision>
|
||
<version>0.0.2</version>
|
||
<date>2018-08-06</date>
|
||
<initials>gl</initials>
|
||
<remark><p>Add handling for another corner case, change title to Council’s liking</p></remark>
|
||
</revision>
|
||
<revision>
|
||
<version>0.0.1</version>
|
||
<date>2018-07-31</date>
|
||
<initials>gl</initials>
|
||
<remark><p>First draft.</p></remark>
|
||
</revision>
|
||
</header>
|
||
<section1 topic='Introduction' anchor='intro'>
|
||
<p>The &xep0045; protocol was
|
||
not designed to handle s2s interruptions or message loss well. Rather
|
||
often, the restart of a server or a component causes a client to believe
|
||
that it is still joined to a given chatroom, while the chatroom service
|
||
does not know of this participant.</p>
|
||
<p>Existing approaches for re-synchronization are either inefficient
|
||
(presence updates and "silent" messages are reflected to all participants,
|
||
totalling to O(N²) stanzas per time unit), or mask message /
|
||
presence losses (the implicit join performed via the deprecated GC1.0
|
||
protocol).</p>
|
||
<p>This specification aims to provide the most efficient, albeit not the
|
||
most elegant, way for clients to periodically check whether they are still
|
||
joined to a chatroom.</p>
|
||
</section1>
|
||
<section1 topic='Requirements' anchor='reqs'>
|
||
<p>This specification only makes sense in the context of &xep0045;
|
||
chatrooms. It makes use of &xep0199; to perform periodic self-pings.</p>
|
||
<p>Server support for this extension is optional, but will significantly
|
||
improve the reliability with Multi-Session Nicks and mobile clients.</p>
|
||
</section1>
|
||
<section1 topic='Client Self-Presence Check' anchor='selfpresencecheck'>
|
||
<p>A typical connection between a client and a Multi-User-Chatroom (MUC)
|
||
goes through the client-to-server link, possibly a server-to-server link
|
||
and a typically local server-to-component link. If one of the involved
|
||
servers or the MUC component is restarted, or one of the links is
|
||
disturbed for some time, this can lead to the removal of some or all
|
||
participants from the affected MUCs, without the clients being informed.</p>
|
||
<p>To a participant, this looks like the MUC is silent (there is no chat
|
||
activity and no presence changes), making it hard to realize that the
|
||
connection was interrupted.</p>
|
||
<p>To prevent the bad usability effect (message loss, lack of reaction from
|
||
people in a chatroom), a client needs to actively check whether it is
|
||
still joined to a MUC.</p>
|
||
<section2 topic='Possible Protocol Approaches' anchor='possibleprotocols'>
|
||
<p>There are multiple alternative approaches for a client to test whether
|
||
it is still joined to a MUC:</p>
|
||
<ol>
|
||
<li><strong>Silent message</strong> (e.g. &xep0085;): this message will be reflected to
|
||
all MUC participants, causing unwanted traffic and potentially waking
|
||
up mobile devices without reason. If implemented by all clients, this
|
||
will result in O(N²) messages to the MUC.</li>
|
||
<li><strong>Presence update</strong>: if the MUC service implements the legacy GC1.0 protocol,
|
||
this will be treated as a join attempt, and the MUC will return the
|
||
full list of participants and full room history. The user's client
|
||
will however miss partial history (other participants leaving,
|
||
potentially also messages), and this has the same drawbacks as the
|
||
first solution.</li>
|
||
<li><strong>Private message to self</strong>: the client can send a MUC
|
||
private message to itself. However, not all MUCs support / allow
|
||
private messages, and there is no way to differentiate that from the
|
||
error responses.</li>
|
||
<li><strong>Private IQ to self</strong>: the client can send an IQ to
|
||
its own participant JID. MUCs typically do not forbid those, and
|
||
reflect the IQ request to the client (or another client of the same
|
||
user). Once that client responds to the reflected IQ, the response is
|
||
delivered to the initiating client as a sign of still being joined.
|
||
</li>
|
||
<li><strong>Dedicated MUC IQ</strong>: a new type of IQ can be deployed
|
||
to let the client explicitly check whether it is still joined to a
|
||
MUC. However, this needs to be supported by the server, and the client
|
||
needs to implement a fallback solution.</li>
|
||
</ol>
|
||
<p>The private IQ is the most robust and traffic-efficient solution, and
|
||
it does not rely on server support. The &xep0199; protocol is
|
||
appropriate to use for this use case.</p>
|
||
</section2>
|
||
<section2 topic='Performing a Self-Ping' anchor='performingselfping'>
|
||
<p>After an adequate amount of silence from a given MUC (e.g. 15 minutes),
|
||
or from all MUCs from a given service domain, a client should initiate a
|
||
self-ping. If Juliet is joined as JuliC in the
|
||
characters@chat.shakespeare.lit MUC, her client will send the following
|
||
ping IQ:</p>
|
||
<example caption="Self-Ping by Juliet's Client"><![CDATA[
|
||
<iq from='juliet@capulet.lit/client' id='s2c1' type='get'
|
||
to='characters@chat.shakespeare.lit/JuliC'>
|
||
<ping xmlns='urn:xmpp:ping'/>
|
||
</iq>
|
||
]]></example>
|
||
<p>If Juliet's client is not joined, the MUC service will respond with a
|
||
<not-acceptable> error. Thus, her client can automatically attempt
|
||
a rejoin.</p>
|
||
<example caption="Server Response to a Non-Participant"><![CDATA[
|
||
<iq from='characters@chat.shakespeare.lit/JuliC' id='s2c1' type='error'
|
||
to='juliet@capulet.lit/client' >
|
||
<error type="cancel">
|
||
<not-acceptable xmlns="urn:ietf:params:xml:ns:xmpp-stanzas" />
|
||
</error>
|
||
</iq>
|
||
]]></example>
|
||
<p>If her client is joined, the IQ request will be forwarded to any one of
|
||
Juliet's joined clients.</p>
|
||
<example caption="Server Reflection of Ping"><![CDATA[
|
||
<iq from='characters@chat.shakespeare.lit/JuliC' id='c0ffee-s2c1' type='get'
|
||
to='juliet@capulet.lit/somerandomclient' >
|
||
<ping xmlns='urn:xmpp:ping'/>
|
||
</iq>
|
||
]]></example>
|
||
<p>Depending on the other client implementation and its connection status,
|
||
the IQ will be responded to eventually, in one of these ways, as
|
||
delivered to the "<tt>client</tt>" resource:</p>
|
||
<ul>
|
||
<li><strong>Successful IQ response</strong>: the client is still joined.</li>
|
||
<li><strong>Error (<service-unavailable> or
|
||
<feature-not-implemented>)</strong>: the client is joined, but
|
||
the pinged client does not implement &xep0199;.</li>
|
||
<li><strong>Error (<item-not-found>)</strong>: the client is
|
||
joined, but the participant just changed their name (e.g. initiated by
|
||
a different client).</li>
|
||
<li><strong>Any other error</strong>: the client is probably not
|
||
joined.</li>
|
||
<li><strong>Timeout (no response)</strong>: the MUC service (or another
|
||
client) is unreachable. The client may indicate the status to the user
|
||
and re-attempt the self-ping after some timeout, until it receives
|
||
either an error or a success response.</li>
|
||
</ul>
|
||
</section2>
|
||
<section2 topic='Server Optimization' anchor='serveroptimization'>
|
||
<p>The normal routing rules of the self-ping impose two round-trips: first
|
||
the initial ping from the client to the MUC, then the reflection of the
|
||
ping and its response (possibly to another client), and finally the
|
||
response to the initial IQ. If the other client is experiencing network
|
||
connectivity issues, which is often the case with mobile devices, the
|
||
ping request might never be responded to.</p>
|
||
<p>Therefore, a MUC service supporting this protocol may directly respond
|
||
to a participant's Ping request to the participant's own nickname, as
|
||
opposed to routing it to any of the participant's clients.</p>
|
||
</section2>
|
||
</section1>
|
||
<section1 topic='Implementation Notes' anchor='impl'>
|
||
<p>In Multi-Session-Nick scenarios, where multiple clients of the same user
|
||
are joined as the same participant, it is possible that another client
|
||
initiates a nickname change while a ping request is pending. In that case,
|
||
the ping might be responded to with <item-not-found>.</p>
|
||
<p>A client should not perform a self-ping after initiating a nickname
|
||
change, and before receiving the response to the nickname change from the
|
||
service, as it is not yet clear whether the new nickname will be accepted.
|
||
</p>
|
||
</section1>
|
||
<section1 topic='Security Considerations' anchor='security'>
|
||
<p>A MUC service implementation should not allow a non-participant to obtain
|
||
information about participants. This is however true irregardless of
|
||
implementing this specification.</p>
|
||
</section1>
|
||
<section1 topic='IANA Considerations' anchor='iana'>
|
||
<p>REQUIRED.</p>
|
||
</section1>
|
||
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
|
||
<p>REQUIRED.</p>
|
||
</section1>
|
||
<section1 topic='XML Schema' anchor='schema'>
|
||
<p>REQUIRED for protocol specifications.</p>
|
||
</section1>
|
||
</xep>
|