<section2topic="MIX Channels in Roster"anchor="concepts-roster">
<p>
When a user joins a MIX channel, the channel is included in the user's roster. There are two reasons for this.
</p>
<ol>
<li>It enables a client to determine which channels the user has joined and so may expect messages and/or presence updates from (dependent on what the user has subscribed to).</li>
<li>
When the user has chosen to share presence with the channel, it enables this to happen using standard presence mechanisms. This avoids the need for MIX-specific mechanisms for clients to update presence on a channel. When a client comes online, presence information will be sent to each MIX channel that the user participates in. This will update other channel participants. It will also lead to a presence update for each MIX channel being sent to the client. So a user will receive channel presence information as the user comes online, in contrast to being subsequent to a MUC Join.
</li>
</ol>
</section2>
<section2topic="Behaviour of MIX Participant's Server"anchor="concepts-mix-participant-server">
<p>
A MIX channel does not send messages and presence directly to the MIX client of a channel participant, but addresses them to the participant using the participant's bare JID. The participant's server MUST then handle these messages and pass them on to zero, one or multiple clients. To enable MIX to work, this behaviour is necessary and so the server of every MIX client MUST follow the rules set out in this specification.
This approach enables flexible support of multiple clients for a MIX channel participant.
The MIX model is that a user will join a channel over an extended period, and that the user (not a specific client used by the user) joins the channel. The primary subscription is with the client's bare JID.
There are a number of MIX requirements on behaviour of the MIX Participant's server, which are summarized here:
</p>
<ol>
<li>Messages from a MIX client to a MIX channel will go direct to the MIX service. They are relayed, but not modified, by the participant's server.</li>
<li>Messages from a MIX channel to a MIX client are always sent to the MIX participant's server (addressed by bare JID) and MUST be handled by the MIX participant's server.</li>
<li>All MIX messages received by the MIX participant's server for a participant MUST be stored using MAM in the participant's archive.</li>
<li>The MIX participant's server will only forward messages to online clients and will not forward messages if no clients are online.
This means that a MIX client needs to resynchronize with all MIX channels when it comes online. This message synchronization will happen between the MIX client and the MAM archive held on the MIX participant's server.</li>
<li>The MIX client will generally send management and other messages directly to the MIX channel and this MUST be done except where specifically noted. </li>
<li>The user's roster contains each MIX channel to which the user is subscribed. To achieve this the user's server needs to manage the roster on behalf of the user. For this reason, MIX join and leave commands MUST be sent by a client to the user's server. This enables the user's server to correctly manage the roster on behalf of the user.</li>
</ol>
<p>
Messages from a MIX channel to a MIX participant (which will be of type=groupchat) and presence information are sent to the participant's server using the participant's bare JID. This means that the MIX participant's server MUST implement a modification of the standard &rfc6121; message processing rules.
</p>
<p>
The core MIX specification sets out how the MIX channel interacts directly with XMPP clients and with the MIX participant's server. Behaviour of the MIX participant's server is also specified in this MIX specification.
</p>
</section2>
<section2topic="User Presence in MIX"anchor="concepts-presence">
<p>
MIX channels store presence of each online client for a user that chooses to publish presence. Presence is stored in the presence node and is encoded using a full proxy JID. Where a user publishes presence for one or more clients, this information is available to all users subscribing to the channel presence.
</p>
<p>
Channel participants can send messages to clients publishing their presence by sending them to the full proxy JID published in the presence node. These stanzas MAY be routed to the client by the MIX channel. The choice to do this is dependent on MIX channel policy. For example, a disco request MAY be routed through the MIX channel to the client.
</p>
<p>
Presence updates are distributed by a channel to the bare JID of subscribers and then the subscriber's server will distribute to each of the subscriber's currently online clients.
Private messages MAY be sent to channel participants if allowed by channel policy. Private messages are
addressed to the user's bare proxy JID determined from the participants node, and routed by the MIX to the user's bare real JID, where standard distribution rules will apply.
</p>
</section2>
<section2topic="Proxy JIDs and JID Visibility"anchor="proxy-jid">
MIX channels have three modes controlling JID visibility:
</p>
<tablecaption="JID Visibility Modes">
<tr><th>Mode</th><th>Description</th></tr>
<tr><td>'JID Visible'</td><td>In these channels all participant JIDs are visible to all channel participants.</td></tr>
<tr><td>'JID Maybe Visible'</td><td>In these channels, participant JIDs are visible to all channel participants when participant preference allows.</td></tr>
<tr><td>'JID Hidden'</td><td>In these channels, no participant JIDs are visible to channel participants, but they are visible to channel administrators.</td></tr>
</table>
<p>
A channel participant MAY specify a preference for JID visibility for the channel, with one of the following values:
<tr><td>'Prefer Visible'</td><td>The users JID will be visible if the channel is JID Visible or JID Maybe Visible channels and hidden if the channel is JID Hidden. </td></tr>
<tr><td>'Prefer Hidden'</td><td>The user's JID will be hidden if the channel is JID Maybe Visible and shown if the channel is JID Visible .</td></tr>
<tr><td>'Enforce Hidden'</td><td>The user's JID will never be shown and the user will be removed from channel if channel mode is changed to JID Visible.</td></tr>
<tr><td>'Enforce Visible'</td><td>The users JID will always be shown and the user will be removed from channel if mode is changed to 'JID Hidden'.</td></tr>
In order to address requirement 7 (a mechanism of JID harvesting), the JID visibility modes of the previous section are defined. MUC achieves this by using Nicks to identify room occupants. This has problems with Nick changing and with multiple active clients for the same user. MIX identifies channel participants by a proxy JID, which is an anonymized stable JID format identifier for each participant. This mapping is used for all channels, as it means that all channels have the same logic and it is straightforward to switch between JID visible and JID hidden channels.
MIX also standardizes the mechanism for mapping between proxy JID and the participant's real JID, so that this can be used by a MIX client. Note that a MUC implementation will need a similar mapping mechanism, but this mechanism is not standardized. MIX maintains three mappings as PubSub nodes to support the necessary mappings:
</p>
<ol>
<li>Participants. This is a list of proxy JIDs of users who have joined the channel. This list is visible to all channel participants. It MAY contain a Nick for each participant. This enables a MIX client to provide a user friendly display of each participant.</li>
<li>JID Map. This contains a mapping of each participant’s real JID with the associated proxy JID. It is used by the MIX channel. For JID Visible channels, it is also accessible to all channel participants, who may use it to display the real JID of each participant.</li>
<li>JIMD Maybe Visible Map. This is used for JID Maybe Visible channels. It contains a mapping from the participant’s real JID with the associated proxy JID, for participants that have elected to share their JID. This enables channel participants to access those JIDs that are shared in a JID Maybe Visible channel. </li>
The primary representation of a participant in a MIX channel is a proxy JID, which is an anonymized JID using the same domain as the channel and with the name of the channel encoded, using the format "<generated identifier>#<channel>@<mix domain>". The generated identifier MUST NOT contain the '#', '/' or '@' characters. The Channel name MAY contain the '#' character. For example in the channel 'coven@mix.shakespeare.example', the user 'hag66@shakespeare.example' might have a proxy JID of '123456#coven@mix.shakespeare.example'. The reason for the proxy JID is to support JID Hidden channels. Proxy JIDs are also used in JID Visible channels, for consistency and to enable switching of JID visibility. The "urn:xmpp:mix:nodes:jidmap" node maps from proxy JID to real JID. Servers and clients MUST determine that a JID is a proxy JID from context and MUST NOT infer that a JID is a proxy JID because it contains the '#' character.
</p>
<p>
The mapping of real bare JID to proxy JID is defined when a participant joins a channel. While a user is a participant in a Channel, the mapping between real JID and proxy JID MUST NOT be changed. This mapping must be maintained after the user leaves the channel. Proxy JID values MUST NOT be re-used. If a JID that left a channel joins the channel again the same proxy JID MAY be used again or a different new proxy JID MAY be assigned.
</p>
<p>
The example real full JIDs in this specification are aligned the anticipated new format that splits the resource into two parts. The first part is UUID that is a stable and fixed value for the client and is anticipated to be a fixed format which may well be UUID 4. The second part is server assigned and will vary with each session. A realistic JID with resource is: 'hag66@shakespeare.example/d104f6a7-97e9-477f-8947-e4a37691d7ee/7533375f2cd'. This specification uses examples of the style: 'hag66@shakespeare.example/UUID-a1j/7533' which are aligned to real resources, but more compact. CITATION TO BE ADDED. If the final specification differs from this, the examples will be updated.
</p>
<p>
The full JIDs held in the presence nodes are anonymized using a similar mechanism. First the bare JID is mapped to a bare proxy JID, using the mapping held in the "urn:xmpp:mix:nodes:jidmap" node for the bare JID. Then the resource is replaced with a generated value. For example, 'hag66@shakespeare.example/UUID-a1j/7533' in the channel coven might have a proxy JID of '123456#coven@mix.shakespeare.example/789'. There is no client visible mapping of proxy full JIDs maintained as this is not needed. The MIX channel will need to maintain a mapping, to support directly addressing clients, such as for client to client disco#info queries. While an full proxy JID is held in the presence node, the mapping to real JID MUST NOT be changed. When adding a client to the presence node, the server MAY add the same anonymized JID as used before by that client, or it MAY create a different anonymized JID.
<tr><td>Messages</td><td>'urn:xmpp:mix:nodes:messages'</td><td>For distributing messages to the channel. Each item of this node will contain a message sent to the channel.</td><td>Message</td><td>Message</td></tr>
<tr><td>Participants</td><td>'urn:xmpp:mix:nodes:participants'</td><td>For storing the list of participants and the associated nick. Channel participants are added when they join the channel and removed when they leave </td><td>Join/Leave/Set Nick</td><td>PubSub</td></tr>
<tr><td>JID Map</td><td>'urn:xmpp:mix:nodes:jidmap'</td><td>For storing a list of bare proxy JIDs from the participants node with a 1:1 mapping to the corresponding real JIDs.</td><td>Automatic</td><td>PubSub</td></tr>
<tr><td>JID Maybe Visible Map</td><td>'urn:xmpp:mix:nodes:jidmap-visible'</td><td>For storing a list of bare proxy JIDs from the participants node with a 1:1 mapping to the corresponding real JIDs for participants that choose to share real JIDs in a channel with JID Maybe Visible mode.</td><td>Automatic</td><td>PubSub</td></tr>
<tr><td>Presence</td><td>'urn:xmpp:mix:nodes:presence'</td><td>For storing information about the availability status of online participants, which MAY include multiple clients for a single participant.</td><td>Presence</td><td>Presence</td></tr>
<tr><td>Information</td><td>'urn:xmpp:mix:nodes:info'</td><td>For storing general channel information, such as description. </td><td>PubSub</td><td>PubSub</td></tr>
<tr><td>Allowed</td><td>'urn:xmpp:mix:nodes:allowed'</td><td>For storing JIDs that are allowed to be channel participants.</td><td>PubSub</td><td>PubSub</td></tr>
<tr><td>Banned</td><td>'urn:xmpp:mix:nodes:banned'</td><td>For storing JIDs that are not allowed to be channel participants. </td><td>PubSub</td><td>PubSub</td></tr>
All of the standard nodes are OPTIONAL. A channel providing a service similar to MUC will typically use all of the standard nodes, but other channels MAY use any combination of these nodes.
MIX provides mechanisms to allow users to conveniently subscribe to a chosen set of nodes and to unsubscribe to all nodes with a single operation. Some nodes are accessed and managed with PubSub, whereas other nodes define MIX specific mechanisms for their use, as shown in the last two columns of the table.
</p>
<p>
MIX also makes use of two nodes for support of Avatars. These nodes and their use is defined in &xep0084;. These nodes MAY be created as part of a MIX channel, where it is desired to publish an avatar associated with the channel.
The structure of each of the standard nodes defined by MIX is now considered in more detail in the rest of this section, after explaining roles.
</p>
<section3topic="Roles"anchor="roles">
<p>
There are a number of MIX roles for each channel, listed in the following table. Rights will be assigned to the various roles in the channel configuration node.
</p>
<tablecaption="Channel Roles">
<tr><th>Role</th><th>Membership and Rights</th></tr>
<tr><td>Owners</td><td>These are owners of the channel, as specified in the channel configuration node. Only owners are allowed to modify the channel configuration node.</td></tr>
<tr><td>Administrators</td><td>Administrators are defined in the channel configuration node. Administrators have update rights to the Allowed Node and Banned Node, so they can control which users are allowed to participate in a channel. </td></tr>
<tr><td>Participants</td><td>Participants are users listed by JID in the participants node.</td></tr>
<tr><td>Allowed</td><td>Allowed is the set of JIDs that are participants or are allowed to become participants. A JID is allowed if it does not match an entry in the banned node and either it matches an entry in the allowed node or the allowed node is not present. </td></tr>
<tr><td>Anyone</td><td>Any user, including users in the banned node.</td></tr>
</table>
<p>
There MUST always be at least one Owner set for a Channel. Administrators are optional and do not need to be set. Administrators and Owners MAY be participants but are not required to be. Owners and Administrators are configured in the information node. Participants and Allowed are specified in separate nodes.
Rights are defined in a strictly hierarchical manner following the order of this table, so that for example Owners will always have rights that Administrators have.
<p>The JID Map node is used to associate a proxy bare JID to its corresponding real bare JID. It is a PubSub node with the 'node' attribute set to 'urn:xmpp:mix:nodes:jidmap'. The JID Map node MUST have one entry for each entry in the Participants node. This value is added when a user joins the channel and is removed when the user leaves the channel.
Each item is identified by proxy bare JID, mapping to the real bare JID. This node is used to give administrator access to real JIDs and participant access to real JIDs in jid-visible channels. This node MUST NOT be modified directly using pubsub.
In JID Visible channels, all participants MAY subscribe to this node. In JID Hidden and JID Maybe Visible channels, only administrators can subscribe. The JID Map node is a permanent node with one item per participant. Information is stored in a <participant/> element qualified by the 'urn:xmpp:mix:1' namespace. The real JID is stored in a <jid/> child element of the <participant/> element. </p>
<p>The JID Maybe Visible Map node is a similar node to the JID Map node that is used in addition to the JID Map Node in JID Maybe Visible channels. It is a PubSub node with the 'node' attribute set to 'urn:xmpp:mix:nodes:jidmap-visible'. All participants may subscribe to and access this node. It uses the same encoding as JID Map node and all participant JIDs MUST be included. Where a participant's preference is to not share the JID, the encoded participant value is the proxy JID. This will enable a user looking up a JID to clearly determine that the user preference is to not share the JID and to clearly distinguish this case from an erroneous proxy JID.
The presence node contains the presence value for clients belonging to participants that choose to publish presence to the channel. A MIX channel MAY require that all participants publish presence, so that active channel participants are visible. It is not possible to enforce this in the server, so participants in a channel with this option MUST publish presence. Each item in the presence node is identified by the full proxy JID, and contains the current presence value for that JID. The presence is encoded in the same way as data that would be sent in a presence stanza using a <presence/> element qualified by the 'jabber:client' namespace. The full proxy JID is always used in this node. In MIX it is possible to have a 'presence-less channel' by not using this node. Access Control MAY be set to enforce that for each of the full JIDs in this list, the bare JID MUST be in the participants list.
</p>
<p>
This node MAY be subscribed to by users and this subscription MUST use the user's bare JID. So presence of online clients is sent to the user's server for each user subscribed to this node. Presence is always sent using standard presence protocol and MUST NOT be sent using pubsub protocol. Clients MUST NOT directly access the presence node using pubsub. The Presence node is a permanent PubSub node.
</p>
<examplecaption="Value of Presence Node"><![CDATA[
This node represents a list of JIDs that are allowed to become participants. If the Allowed node is not present, all JIDs are allowed. This node is accessed and managed using standard pubsub. The Allowed list is always considered in conjunction with the banned list, stored in the banned node. Only Administrators and Owners have write permission to the Allowed node and are also the only roles that are allowed to subscribe to this node. The Allowed node is a permanent node. Each item contains a real bare JID. The following example shows how the Allowed list can specify single JIDs and domains.
</p>
<examplecaption="Allowed Node"><![CDATA[
<itemsnode='urn:xmpp:mix:nodes:allowed'>
<itemid='shakespeare.example'/>
<itemid='alice@wonderland.example'/>
</items>
]]></example>
</section3>
<section3topic="Banned"anchor="banned-node">
<p>
This node represents a list of JIDs that are explicitly not allowed to become participants. The values in this list take priority over values in the Allowed node. This node is accessed and managed using standard pubsub Only Administrators and Owners have write permission to the Banned node and are also the only roles that are allowed to subscribe to this node. Each item contains a real bare JID. The Banned node can contain bare JIDs and/or domains. The Banned node is a permanent node.
The Configuration node holds the configuration of the channel as a single item, named by the date-time of the last update to the configuration. The Configuration node is a permanent node with a maximum of one item. Previous configuration history MAY be accessed by MAM. Users with read access to the configuration node MAY subscribe to the configuration node to get notification of configuration change. This node is accessed and managed using standard pubsub. The configuration node is OPTIONAL for a MIX channel. For example, configuration choices could be fixed and not exposed. A subset of the defined configuration options MAY be used and additional non-standard configuration options MAY be added. JIDs in the configuration MUST be real bare JIDs and not proxy JIDs. If configuration options to control functionality of the nature described here are provided, the options defined in this standard MUST be used. The following configuration attributes are defined:
<tr><td>'Last Change Made By'</td><td>Bare JID of the user making the last change.</td><td>jid-single</td><td>-</td><td>-</td></tr>
<tr><td>'Owner'</td><td>Bare JIDs with Owner rights as defined in ACL node. When a channel is created, the JID creating the channel is configured as an owner, unless this attribute is explicitly configured to another value.</td><td>jid-multi</td><td>-</td><td>-</td></tr>
<tr><td>'Administrator'</td><td>Bare JIDs with Administrator rights.</td><td>jid-multi</td><td>-</td><td>-</td></tr>
<tr><td>'End of Life'</td><td>The date and time at which the channel will be automatically removed by the server. If this is not set, the channel is permanent.</td><td>text-single</td><td>-</td><td>-</td></tr>
<tr><td>'Nodes Present'</td><td>Specifies which nodes are present. Presence of config nodes is implicit. Jidmap node MUST be present if participants node is present. 'avatar' means that both Avatar Data and Avatar Metadata nodes are present.</td><td>list-multi</td><td>'participants'; 'presence'; 'information'; 'allowed'; 'banned'; 'jidmap-visible'; 'avatar'</td><td>'participants'; 'presence'; 'information'; 'allowed'; 'banned'; 'jidmap-visible'; 'avatar'</td></tr>
<tr><td>'Messages Node Subscription'</td><td>Controls who can subscribe to messages node.</td><td>list-single</td><td>'participants'; 'allowed'; 'anyone'</td><td>'participants'</td></tr>
<tr><td>'Presence Node Subscription'</td><td>Controls who can subscribe to presence node.</td><td>list-single</td><td>'participants'; 'allowed'; 'anyone'</td><td>'participants'</td></tr>
<tr><td>'Participants Node Subscription'</td><td>Controls who can subscribe to participants node.</td><td>list-single</td><td>'participants'; 'allowed'; 'anyone'; 'nobody'; 'admins'; 'owners'</td><td>'participants'</td></tr>
<tr><td>'Information Node Subscription'</td><td>Controls who can subscribe to the information node.</td><td>list-single</td><td>'participants'; 'allowed'; 'anyone'</td><td>'participants'</td></tr>
<tr><td>'Allowed Node Subscription'</td><td>Controls who can subscribe to allowed node.</td><td>list-single</td><td>'participants'; 'allowed'; 'nobody'; 'admins'; 'owners' </td><td>'admins'</td></tr>
<tr><td>'Banned Node Subscription'</td><td>Controls who can subscribe to banned node.</td><td>list-single</td><td>'participants'; 'allowed'; 'nobody'; 'admins'; 'owners' </td><td>'admins'</td></tr>
<tr><td>'Configuration Node Access'</td><td>Controls who can subscribe to configuration node and who has read access to it.</td><td>list-single</td><td>'participants'; 'allowed'; 'nobody'; 'admins'; 'owners' </td><td>'owners'</td></tr>
<tr><td>'Information Node Update Rights'</td><td>Controls who can make changes to the information node</td><td>list-single</td><td>'participants'; 'admins'; 'owners' </td><td>'admins'</td></tr>
<tr><td>'Avatar Nodes Update Rights'</td><td>Controls who can make changes to the avatar data and metadata nodes</td><td>list-single</td><td>'participants'; 'admins'; 'owners' </td><td>'admins'</td></tr>
<tr><td>'Open Presence'</td><td>If selected, any client MAY register presence. If not selected, only clients with bare JID in the participants list are allowed to register presence.</td><td>boolean</td><td>-</td><td>false</td></tr>
<tr><td>'Participants Must Provide Presence'</td><td>If selected, all channel participants are REQUIRED to share presence information with the channel.</td><td>boolean</td><td>-</td><td>false</td></tr>
<tr><td>'User Message Retraction'</td><td>If this option is selected users will be able to retract messages that they have sent to the MIX channel.</td><td>boolean</td><td>-</td><td>false</td></tr>
<tr><td>'Administrator Message Retraction Rights'</td><td>This controls which group is able to retract any message sent to the MIX channel.</td><td>list-single</td><td>'nobody'; 'admins'; 'owners'</td><td>'owners'</td></tr>
<tr><td>'Participation Addition by Invitation from Participant'</td><td>This option extends a channel so that a channel participant has rights to invite and enable other users as participants.</td><td>boolean</td><td>-</td><td>false</td></tr>
<tr><td>'Private Messages'</td><td>If this option is selected, private messages MAY be used with the channel.</td><td>boolean</td><td>-</td><td>true</td></tr>
</table>
<p>
The configuration node is in &xep0004; format and includes all of the options used by the channel, including values for options using default values. This means that the value in the form can be directly mapped with the form returned by configuration administration commands. Configuration nodes will typically have a large number of elements. The following short example is provided to illustrate the syntax of the configuration node.
As part of the channel joining process, the user's server MUST add the MIX channel to the user's roster. This is done to share the user's presence status with the channel and channel participants subscribing to presence, when the user wishes this presence to be shared. These roster entries also enables the user's client to quickly determine which channels the user has joined. The user's server will need to record those roster entries that are associated with MIX channels in order to correctly handle MIX processing.
This roster entry will lead to the user's server correctly sending user's presence from all the user's MIX clients to the MIX channel. Where the user wishes to share presence, the roster subscription is configured with one way presence, as presence is sent to the MIX channel but no presence information about the MIX channel is sent to the user.
</p>
<p>
If the user does not wish to publish presence information to the channel, the user's server will add the roster entry with mode subscription=none. The roster entry will be present to record that the user has joined the channel, but it will not send presence information to the channel. The user's server MUST do this when the user has chosen Presence preference of 'not share' as described below. If the user changes the value of the preference, the server MUST modify subscription mode to reflect this.
</p>
<p>
The user's server MUST remove this roster entry when the user leaves the channel.
</p>
<p>
A channel MAY publish an Avatar following &xep0084;. A client MAY make use of this information to associate an Avatar with the roster entry for a channel.
</p>
</section3>
<section3topic="User Preferences and Additional Information"anchor="usecase-visibilty-pref">
<p>A channel MAY store user preferences and parameters with each user. A user JID visibility preference has the following values:
</p>
<ol>
<li>'default'. In this setting, the channel default value will be used. This value is used if another value is not explicitly set. This means JID is visible for a JID Visible channel and JID is hidden for JID Hidden and JID Maybe Visible channels.</li>
<li>'never'. If this is set, JID will never be shared and user will be removed from the channel if its mode changes to JID Visible.</li>
<li>'always'. If this is set, JID will always be shared and users will be removed from the channel if its mode changes to JID Hidden.</li>
<li>'prefer not'. If this is set, JID will only be shared if mode is JID Visible.</li>
</ol>
<p>
The user MAY specify that no Private Messages are to be sent from the channel, and allow vCard retrieval.
</p>
<p>
The user MAY specify that presence is not to be shared, which will prevent the MIX Channel from sending a presence probe for the user on channel start-up. The user will also choose to not include the MIX channel in the user's roster, so that presence will not be updated. Where the channel configuration sets 'Participants Must Provide Presence', this variable MUST be set to 'Share'.
</p>
<p>
The following table sets out the standardized user preference values. A MIX implementation MAY use other values.
<p>When joining a channel, the client MAY specify one or more preference options as a &xep0004; form. In the response, the server MUST specify all of the user preferences supported by the server, with default values if the user has not requested a different value. The following example shows joining a channel and setting a preference. The following example shows the message sent from the user's server to the MIX channel, which will have been preceded by a message from the user's client to the user's server.</p>
<examplecaption="User Joins a Channel and Specifies a preference"><![CDATA[
<iqtype='set'
from='hag66@shakespeare.example'
to='coven@mix.shakespeare.example'
id='E6E10350-76CF-40C6-B91B-1EA08C332FC7'>
<joinxmlns='urn:xmpp:mix:1'>
<subscribenode='urn:xmpp:mix:nodes:messages'/>
<subscribenode='urn:xmpp:mix:nodes:presence'/>
<xxmlns='jabber:x:data'type='submit'>
<fieldvar='FORM_TYPE'type='hidden'>
<value>urn:xmpp:mix:1</value>
</field>
<fieldvar='JID Visibility'>
<value>never</value>
</field>
</x>
</join>
</iq>
]]></example>
<p>The following example shows the result of a successful join, which also reports all the user preferences. This example shows the message coming from the MIX channel to the user's server, which will be sent on to the user.</p>
<examplecaption="Channel Successfully Processes Join and returns the preferences set"><![CDATA[
<p>The client MAY also query the channel in order to find out which user preferences are supported and the options available. This will allow users to set options not specified in the standard, by providing a form template in the result. The request is encoded as a <user-preference/> child element of <iq/>. <user-preference/> is qualified by the 'urn:xmpp:mix:1' namespace. The result is encoded as a form child element in the <user-preference/> element.</p>
<examplecaption="User Requests and Recieves Preferences Template Form"><![CDATA[
A user MAY modify preferences using the corresponding set operation. The set MAY specify values for some or all attributes. All attributes are returned in the result.
<section3topic='Registering a Nick'anchor='usecase-user-register'>
<p>A nick MAY be associated with the user's bare JID. A user can register a nick with the MIX service. Nick registration can be used ensure that a user is able to use the same nick in all channels in the service and to prevent other users from using a registered nick. This can help achieve a consistent experience across a set of channels and prevent user confusion. Support for nick registration by a MIX service is OPTIONAL. Where nick registration is supported, nick registration MAY be OPTIONAL or MANDATORY.
Where a user has registered a Nick with the MIX service, it MAY be used by each channel according to policy for the channel. A channel MAY enforce use of a registered nick. A channel MUST NOT use a registered nick for any other participant.
</p>
<p>
In order to determine if a Nick is allowed to be registered, the user MAY use disco to determine capabilities of the MIX service.
</p>
<examplecaption="User Determines features of the MIX service"><![CDATA[
The response will be a list of features of the MIX channel. If Nick Registration is supported, then the result set will include <feature var="urn:xmpp:mix:1#nick-register"/>.
</p>
<p>
To register a nick with the MIX service the user sends
a register command to the service. This is encoded as a <register/> child element of an <iq/> element. The <register/> element is qualified by the urn:xmpp:mix:1' namespace. The nick is encoded in a <nick/> child element of the <register/> element. </p>
<examplecaption="User Registers with Service"><![CDATA[
<iqtype='set'
from='hag66@shakespeare.example/UUID-a1j/7533'
to='mix.shakespeare.example'
id='7nve413p'>
<registerxmlns='urn:xmpp:mix:1'>
<nick>thirdwitch</nick>
</register>
</iq>
]]></example>
<p>On success, the service informs the user of its nick. MIX SHOULD apply the "nickname" profile of the PRECIS OpaqueString class, as defined in &rfc7700; to the requested nick. This means that nick that is issued might be different from the nick that was requested.</p>
<p>
When an Nick is assigned, the MIX server MUST update the Participants Node in the channel to reflect this change. Any users subscribed to this node will be notified of the change of Nick.
</p>
<p>The following example shows an example of reporting successful Nick assignment.</p>
<examplecaption="Service Returns User of Nick"><![CDATA[
<iqtype='result'
to='mix.shakespeare.example'
from='hag66@shakespeare.example/UUID-a1j/7533'
id='7nve413p'>
<registerxmlns='urn:xmpp:mix:1'>
<nick>thirdwitch</nick>
</register>
</iq>
]]></example>
<p>If the requested nick is already taken and the MIX service does not assign an alternate nick, the MIX service MUST return a <conflict/> error:</p>
<p>If the register request does not contain a <nick/> element, then the MIX service MUST assign one. It is RECOMMENDED that the assigned nick is a UUID following &rfc4122;.
</p>
</section3>
<section3topic='Setting User Presence'anchor='usecase-user-presence'>
<p>
A user joins a channel over an extended period, and participation in a channel does not generally change when user goes online or offline. The user's participation in a channel is reflected by the user's bare JID in the participant node. All messages to the channel are sent to this JID.
</p>
<p>
A user MAY share presence information with the channel, for one or more online clients. Where a user shares presence information with a channel, the channel is entered by the user's server into the user's roster when the user subscribes to the channel. When an XMPP client comes online or changes presence status, this will be communicated by the user to the user's server using broadcast presence. The user's XMPP server is then responsible to share this presence information to each entry in the roster and in particular to each MIX channel in the roster. The MIX channel will update the "urn:xmpp:mix:nodes:presence" node with any change of status and the updated presence information and then share this updated presence with users subscribed to this node, as described below. When the user sets an explicit status, this is used to modify the presence node in the channel. When a client being used by the user goes offline, the associated server will send presence status "unavailable" to the MIX channel, which will cause the full JID for that client to be removed from the presence node.
</p>
<p>
A channel MAY require that all channel participants share presence information with the channel, which is represented in the "urn:xmpp:mix:nodes:presence" node. If sharing presences is needed by the channel, an XMPP client conforming to this specification MUST share presence with the channel by including the channel in the user's roster. Note that the MIX service cannot generally enforce this, but it can require and enforce that when a message is sent to the channel, that the sender of the message is in the presence list.
</p>
<p>
Presence status and availability is set in a MIX channel by standard presence stanzas sent to the MIX channel by the user's server. Users wishing to receive presence updates will subscribe to the MIX channel presence node. Presence updates are sent out to subscribing participants using standard presence stanzas.
</p>
<p>
A user setting status is now used as an example. Unlike in &xep0045; where coming online is a special action, coming online in MIX is implicit when presence status is set. Going offline is a achieved by setting presence status to unavailable, which removes the client full JID entry from the presence node. When a user sets a presence status, the user's server sends updated presence to the MIX channel, and the MIX service then publishes the user's availability to the "urn:xmpp:mix:nodes:presence" node. If there is not an item named by the full JID of the client with updated presence status, this item is created. The sequence is shown in the following examples, starting with a client setting presences status on the connected server.</p>
<examplecaption="Client Sets Presence Status on Server">
The server then sends the presence information to roster entries. The following example then shows the presence message from the client's server to the MIX channel.
</p>
<examplecaption="Server sends Presence Status to MIX Channel">
<p>The user's presence information is then published by the service to the "urn:xmpp:mix:nodes:presence" node, with the 'publisher' attribute set to the user's participant identifier (the proxy JID). The MIX channel then broadcasts the presence change to all users who are subscribed to the "urn:xmpp:mix:nodes:presence" node. The presence stanza is sent from the full proxy JID of the client updating status.
Note that presence is associated with a client and so will have a full JID. The following example shows a presence message as distributed by the server to a presences subscriber.</p>
The presence is distributed to those subscribing to the MIX channel presence node using a standard XMPP presence stanza. The presence change is recorded on the "urn:xmpp:mix:nodes:presence" node. The history of this node will be held as PubSub format in the MAM archive, so that presence history can be viewed.
</p>
</section3>
<section3topic="Client Coming Online and Obtaining Presence from the Local Server"anchor="usecase-obtaining-presence">
<p>
The presence information for a channel is stored in the urn:xmpp:mix:nodes:presence node and distributed using standard presence stanzas to the server of each user subscribing to this presence node. The user's local server will then pass this presence information on to all online clients. This ensures that an online client is kept updated with presence.
When a client goes offline, it will cease getting presence updates. Presence updates will continue to flow to the user's local server, and so the local server is able maintain up to date presence state for the channel. The user's server MAY cache this presence information to optimize performance or MAY discard it.
</p>
<p>
When the client comes online, it will activate use of the MIX. The user's server will then send full presence status to the client using standard presence messages. This will enable the client to update presence information for the channel. Note that this does not need any interaction with the channel.
</p>
</section3>
<section3topic="Updating Presence on User's Server"anchor="usecase-server-presence-update">
<p>
In normal operation a MIX participant's server will hold accurate presence status for the channel which it provides to clients when they are activated. Incoming presence updates are immediately sent to active MIX clients.
</p>
<p>
There are two situations where a MIX participant's server will need to get presence status from the channel. The first time is when a user joins the channel as a participant and subscribes to presence. Upon this subscription the MIX channel will send to the participant's server (using the user's bare JID) presence for all of the items in the presence node using standard presence stanzas. This will give the participant's full current presence for the channel.
</p>
<p>
The second scenario is when the MIX participant's server needs to load or refresh presence status for a channel. This will be needed when the participant's server is started. This MIX participant's server requests presence update by sending a directed presence stanza to the MIX channel from the user's bare JID. The MIX channel can distinguish this from a presence update, which will always be sent from the clients full JID. This special presence stanza will send to the participant's server (using the user's bare JID) presence for all of the items in the presence node using standard presence stanzas.
</p>
</section3>
<section3topic="Determining Real JIDs"anchor="usecase-real-jids">
<p>
Presence information will provide a MIX client with the nicks and proxy JIDs for participants in a channel. Messages sent to a channel and retrieved from MAM archives will show the proxy JID and nick of the sender. It is sometimes useful to determine the real JID associated with proxy JID. This can always be done for JID Visible channels and can sometimes be done for JID Maybe Visible channels.
</p>
<p>
For current users JID visible rooms, the real JID is found by a PubSub lookup on the JID Map node. This is shown in the following example:
</p>
<examplecaption='Client looks up Real JID from Proxy JID'><![CDATA[
<iqfrom='hag66@shakespeare.example/UUID-c8y/1573'
id='kl2fax27'
to='coven@mix.shakespeare.example'
type='get'>
<pubsubxlns='http://jabber.org/protocol/pubsub'>
<itemsnode='urn:xmpp:mix:nodes:jidmap'>
<itemid='123456#coven@mix.shakespeare.example'/>
</items>
</pubsub>
</iq>
<iqfrom='coven@mix.shakespeare.example'
id='kl2fax27'
to='hag66@shakespeare.example/UUID-c8y/1573'
type='result'>
<pubsubxlns='http://jabber.org/protocol/pubsub'>
<itemsnode='urn:xmpp:mix:nodes:jidmap'>
<itemid='123456#coven@mix.shakespeare.example'>
<participantxmlns='urn:xmpp:mix:1'>
<jid>hecate@mix.shakespeare.example</jid>
</participant>
</item>
</items>
</pubsub>
<items>
</iq>]]> </example>
<p>For JID Maybe Visible rooms the lookup is performed on the JID Maybe Visible Map node. Note that where a user prefers to not share real JID, the result of this lookup of proxy JID will be the (same) proxy JID. </p>
<p>
When an older message is considered, it is possible that the proxy JID of the sender is not current. Such a JID can be looked up in the MAM Archive of the JID Map Node. This is shown in the following example:
</p>
<examplecaption='Client looks up Real JID from Proxy JID in MAM Archive'><![CDATA[
<p>When a client goes offline, this presence update is sent by the client's server to the MIX channel. From the client perspective, this is the same as any other presence change. Handling by the MIX channel is slightly different.</p>
<examplecaption="Client Goes Offline in the Channel"><![CDATA[
<presencetype='unavailable'
from='hag66@shakespeare.example/UUID-a1j/7533'
to='coven@mix.shakespeare.example'/>
]]></example>
<p>The MIX channel will retract (remove) the item in the presence node of the MIX channel identified by the client's full JID. The MIX channel will notify subscribers to the presence node of the user going offline by sending a presence stanza to the full JID of each client. The presence stanza will reference the full proxy JID of the client that is going offline, as shown in the following example:</p>
<examplecaption="Channel Distributes Notification of Client going Offline">
There is the possibility that the message associated with the user going offline will be lost. If this happens, "ghost" entries will appear in the presence node. A MIX service MAY take steps to address this, for example by probing client with a disco for presence items that remain unchanged for a long period.
</p>
<p>
It is desirable to prevent clients from going offline briefly and then coming back online again, as this will lead to "flapping presence". The RECOMMENDED approach to achieve this is use of &xep0198; to maintain an XMPP client connection in the event of short term TCP failure.
<section3topic="Retracting a Message"anchor="usecase-retract">
<p>
A MIX channel MAY support message retraction, where the sender of a messages or an authorized administrator deletes a message. A MIX channel MAY limit the time frame in which a message is allowed to be retracted, for example to prevent retraction of very old messages. When a messages is retracted the original message MAY be replaced by a tombstone. Message retraction is done by sending a special message that identifies the original message. This mechanism allows the retraction to be distributed on the same path as the original message so that all participating servers and clients MAY honour the retraction. The protocol to request retraction does this by adding to a message a <retract> element qualified by the 'urn:xmpp:mix:1' namespace. A retract messages MUST NOT have a body. The <retract> element MUST include an 'id' attribute that holds the MAM-ID of the original message. The message sender will need to look up the MAM-ID. The MAM-ID is the convenient message identification for message recipients. A message and it's retraction shown in the following example.
</p>
<examplecaption="User Retracts a Message"><![CDATA[
The MIX channel will allow a user to retract a message sent by the user if the 'Allow User Message Retraction' option is configured. The MIX channel will allow an administrative user to retract any message if the user is in the group specified by the 'Administrator Message Retraction Rights' option.
</p>
<p>
If the retraction message is accepted, it MUST be distributed to channel participants. This will allow retraction to happen in the MAM archive of each channel participant and to reflect the retraction in client GUI. A client receiving a retraction message SHOULD ensure that the retracted message is no longer displayed to the end user.
</p>
<p>
Two approaches to message retraction can be used. In the first approach, the retracted message is simply removed. This is appropriate where retraction is provided as a user service and the user has rights to remove messages sent from the record.
</p>
<p>
The second approach is to leave a tombstone, which if taken MUST be done in the following manner. It is recommended to use a tombstone, as simply deleting the message may cause confusion with MAM queries. Use of a tombstone is appropriate where it is desired to leave a record of the message that was redacted.
With this approach, the original message <body> is removed and replaced with a tombstone using the <retracted> element qualified by the 'urn:xmpp:mix:1' namespace that shows the JID of user performing the retraction and the time of the retraction.
</p>
<examplecaption="Retracted message tombstone in a MAM result"><![CDATA[
<section3topic='Telling another User about a Channel'anchor='usecase-user-tell'>
<p>
A convenient way to reference another channel is to use &xep0372; which enables the JID of a channel to be shared. This might be used simply to inform the message recipient about the channel or as mechanism to invite the user to join the channel. This is useful as an invitation mechanism to a channel that any user can join or where the invitee knows that the user is allowed to join (e.g., because the channel is for all users in an organization).
</p>
</section3>
<section3topic='Inviting another User to join a Channel that the user does not have Permission to Join'anchor='usecase-user-invite'>
<p> Invitation by reference, as described in the previous section, is a convenient approach to invite a user to join a channel that the user has permission to join. This section describes the approach used when the inviter has permission to grant rights for the invitee to become a channel participant. This might be because the inviter is an administrator of the channel or the channel or if the inviter is a channel participant and the channel allows invitation by participants (this channel capability is controlled by the channel configuration variable 'Participation Addition by Invitation from Participant'). Invitation by reference is used to avoid cluttering the allowed node with JIDs of users who are invited to join, but do not accept the invitation.
When a channel participant(the inviter) invites another user (the invitee) to join a channel, the following sequence of steps is followed:
</p>
<ol>
<li>The inviter checks using capability discovery that the invitee supports MIX.</li>
<li>The channel inviter sends to the channel requesting an invite for the invitee.</li>
<li>The channel sends an invitation to the inviter.</li>
<li>The inviter sends the invitation to the invitee.</li>
<li>The invitee MAY use the invitation to join the channel.</li>
<li>The invitee MAY send a response to the inviter, indicating if the invitation was accepted or declined.</li>
</ol>
<p>
The first step is for the inviter to request an invitation from the channel. The invitation contains inviter, invitee and a token. The channel will evaluate if the inviter has rights to issue the invitation. This will be because the inviter is a channel administrator or if the inviter is a channel participant and the channel allows invitation by participants. If the inviter has rights to make the invitation, the channel will return a token. The token is a string that the channel can subsequently use to validate an invitation. The format of the token is not specified in this standard. The encoded token MAY reflect a validity time. The invitation request is encoded as an <invite/> child element of an <iq/> element. The <invite/> element is qualified by the 'urn:xmpp:mix:1' namespace. <invite/> contains an <invitation/> child element, which contain <inviter/>, <invitee/>, <channel/> and <token/> child elements.
</p>
<examplecaption='Inviter Requests and Receives Invitation'><![CDATA[
<iqfrom='hag66@shakespeare.example/UUID-h5z/0253'
id='kl2fax27'
to='coven@mix.shakespeare.example'
type='get'>
<invitexmlns='urn:xmpp:mix:1'>
<invitee>cat@shakespeare.example</invitee>
</invite>
</iq>
<iqfrom='coven@mix.shakespeare.example'
id='kl2fax27'
to='hag66@shakespeare.example/UUID-h5z/0253'
type='result'>
<invitexmlns='urn:xmpp:mix:1'>
<invitation>
<inviter>hag66@shakespeare.example</inviter>
<invitee>cat@shakespeare.example</invitee>
<channel>coven@mix.shakespeare.example</channel>
<token>ABCDEF</token>
</invitation>
<invite/>
</iq>
]]></example>
<p>
The inviter can now send the invitee a message containing the invitation within the <message/> element, as shown in the following example.
</p>
<examplecaption='Inviter sends Invitation to Invitee'><![CDATA[
<p>The invitation can now be used by the invitee to join a channel. The <invitation/> child element is simply added to the standard channel <join/> element, so that the channel can validate the invitation using the token. If the allowed node is present and the invitee is not matched against any item, the channel MUST add the invitee to the allowed node as part of the join.</p>
<examplecaption="User Joins a Channel with an Invitation"><![CDATA[
<iqtype='set'
from='cat@shakespeare.example'
to='coven@mix.shakespeare.example'
id='E6E10350-76CF-40C6-B91B-1EA08C332FC7'>
<joinxmlns='urn:xmpp:mix:1'>
<subscribenode='urn:xmpp:mix:nodes:messages'/>
<invitation>
<inviter>hag66@shakespeare.example</inviter>
<invitee>cat@shakespeare.example</invitee>
<channel>coven@mix.shakespeare.example</channel>
<token>ABCDEF</token>
</invitation>
</join>
</iq>
]]></example>
<p>The invitee MAY send an acknowledgement back to the inviter, noting the status of the invitation.
This is encoded as an <invitation-ack/> child element of <message/> element. The <invitation-ack/> element is qualified by the 'urn:xmpp:mix:1' namespace. The <invitation-ack/> has an <invitation/> child element that encodes the invitation being acknowledged and a <value/> child element to encode the acknowledgement value.
<value/> has the following values:</p>
<ul>
<li>'Joined': The invitee has joined the channel.</li>
<li>'Declined': The invitee is not taking up the invitation.</li>
<li>'Acknowledged': The invitation is acknowledged, without information on action taken or planned.</li>
</ul>
<examplecaption='Invitee sends Acknowledgement to Inviter'><![CDATA[
Private Messages are used to provide communication with another channel participant through the MIX channel, without the initiating user knowing the real JID of the channel participant. A channel MAY support use of Private Messages. Private messages are standard XMPP messages and MUST NOT be groupchat. A message goes through a number of stages with different addressing. This is set out in the following table.
</p>
<tablecaption="Setting From and To when sending Private Messages">
<tr><th>Message</th><th>From</th><th>To</th></tr>
<tr><td>First Message from Client to MIX Channel</td><td>Full JID of initiator's client</td><td>Proxy bare JID of responder</td></tr>
<tr><td>First Message from MIX Channel to responder's server</td><td>Proxy full JID of initiator's client</td><td>Bare JID of responder</td></tr>
<tr><td>First Message from responder's server to one or more of the responder's clients</td><td>Proxy full JID of initiator</td><td>Full JID of responder's client</td></tr>
<tr><td>Messages from responder's client to MIX Channel</td><td>Full JID of responder's client</td><td>Proxy full JID of initiator's client</td></tr>
<tr><td>Messages from MIX channel to initiator's client</td><td>Proxy full JID of responder's client</td><td>Full JID of initiator's client</td></tr>
<tr><td>Messages from initiator's client to MIX Channel</td><td>Full JID of initiator's client</td><td>Proxy full JID of responder's client</td></tr>
<tr><td>Message from MIX Channel to responder's client</td><td>Proxy full JID of initiator's client</td><td>Full JID of responder's client</td></tr>
</table>
<p>Private Messages MAY be archived using MAM by the XMPP servers associated with initiator and responder. Private Messages MUST NOT be archived by the MIX channel.</p>
<p>A client MAY request the vCard of a channel participant by sending a request through the channel. The MIX channel MAY pass this request on or MAY block it. vCard requests MAY use &xep0054; (vcard-temp) or &xep0292; (vCard4 over XMPP). The MIX channel does not process the vCard requests, but simply relays them on to real bare JID of the target. A MIX service MAY choose to relay one or both protocols. Where a MIX service relays one or both of these protocols, each protocol relayed MUST be advertised as a feature of the MIX service. In the following example, using vcard-temp, the requesting client sends a message to the bare proxy JID of the channel participant for which the vCard is desired.</p>
<examplecaption="Client directly requests vCard through channel"><![CDATA[
<iqfrom='hag66@shakespeare.example/UUID-c8y/1573'
id='lx09df27'
to='989898#coven@mix.shakespeare.example'
type='get'>
<vCardxmlns='vcard-temp'/>
</iq>
]]></example>
<p>The MIX channel MAY pass on the vCard request or MAY reject with an error, dependent on channel policy. The MIX service will then address the vCard request to the user's server (using bare JID) using a full proxy JID to hide the requester. </p>
<examplecaption="Channel passes on vCard request to the User's Server"><![CDATA[
For an active MIX Channel, the presence node is updated as channel participants change status and presence information is sent to the channel. When a MIX channel starts, typically when the associated MIX Service and Server start, there is a need to initialize the presence node. This is done by the XMPP server associated with the MIX channel sending out a presence probe for each channel participant, following the presence probe process specified in &rfc6121;. A presence probe MUST NOT be sent for users who have set presence preference to not sharing.
<section2topic='Administrative Use Cases'anchor='usecases-admin'>
<section3topic='Checking For Permission To Create a Channel'anchor='usecase-admin-check-create'>
<p>
MIX does not standardize an access control model for creating and deleting MIX channels. The choice is left to the MIX implementer, and could be a very simple or complex approach. A client can determine if it has permission to create a channel on a MIX service, which MAY be used to control options presented to the user. This is achieved by a disco command on the MIX service. If the 'urn:xmpp:mix:1#create-channel' feature is returned, the user is able to create a channel.
</p>
<examplecaption="Client determines Capability to Create a Channel"><![CDATA[
<section3topic="Converting a 1:1 Conversation to a Channel"anchor="usecase-admin-converting-chat">
<p>
A common use case for an ad hoc channel is where two users are engaged in a 1:1 chat and wish to broaden the discussion. Prior to bringing more users into a channel, using standard invitation process, there is a need to create and populate a channel. The first step is for one of the two users to create an ad hoc channel, as described in the previous section. The other user will then be invited, and can switch to the new channel.
</p>
<p>
It can also be useful to share some or all of the messages from the 1:1 discussion into the new channel. The mechanism to do this is to forward messages to be shared to the channel using &xep0297;. A body SHOULD NOT be used in the outer message.
Sharing history is optional. If history is shared, it MUST be done by the user creating the channel before the other user is invited. Any other use of forwarded messages MUST be treated as a channel participant forwarding a message to the channel and MUST NOT be treated as history sharing.
</p>
<examplecaption="Forwarding a message to create History"><![CDATA[
There are a number of security considerations with sharing 1:1 history in a channel. There may be sensitive information in the 1:1 history, and the user sharing this history should ensure that none of this is sensitive, prior to sharing in this way. The user creating the channel has potential to inject history messages which were not part of the history. It is recommended that the second user joining the channel to validate that the messages match the history and to take appropriate action if they do not.
<p>Authorized users, typically owners and sometimes administrators, MAY modify the channel information. The client MAY issue a pubsub get command to obtain a form that will facilitate update of the information node. The values in the form show current values, which be defaults or MAY have been explicitly set. In the following example, the channel name was previously set, but other values were not. </p>
<examplecaption="Getting Information Form"><![CDATA[
<iqfrom='hag66@shakespeare.example/UUID-a1j/7533'
id='lx09df27'
to='mix.shakespeare.example'
type='get'>
<pubsubxmlns='http://jabber.org/protocol/'>
<itemsnode='urn:xmpp:mix:nodes:info'/>
</pubsub>
</iq>
<iqfrom='mix.shakespeare.example'
id='lx09df27'
to='hag66@shakespeare.example/UUID-a1j/7533'
type='result'>
<pubsubxmlns='http://jabber.org/protocol/'>
<itemsnode='urn:xmpp:mix:nodes:info'>
<item>
<xxmlns='jabber:x:data'type='form'>
<fieldvar='FORM_TYPE'type='hidden'>
<value>urn:xmpp:mix:1</value>
</field>
<title>Information Node Modification</title>
<fieldtype='text-multi'
label='Channel Name'
var='Name'>
<value>Witches Coven</value>
</field>
<fieldtype='text-multi'
label='Channel Description'
var='Description'/>
<fieldtype='jid-single'
label='Channel Administrative Contact'
var='Contact'/>
</x>
</item>
</items>
</pubsub>
</iq>
]]></example>
<p> Updating the information node is done using a pubsub set command. The MIX channel MUST update the fields with values provided, leaving other fields unchanged. The result returns the id used in the information node item, which is the date/time of the modification. </p>
<p>Channel owners are allowed to modify the channel configuration. The client MAY issue a pubsub get command to obtain a form that will facilitate update of the configuration node. Other clients MAY be authorized to use this command to see the channel configuration, but only owners MAY update the configuration. The values in the form show current values, which MAY be defaults or MAY have been explicitly set. The following example shows a short form returned to illustrate the syntax. A typical configuration form will be much larger with many fields. Modifying channel configuration is done directly by a client. Note that an Owner MUST be specified. When the configuration node is modified, the server MUST set the 'Last Change Made By' attribute to the JID of the user making the change.
<p> Updating the information node is done using a pubsub set command. The MIX channel MUST update the fields with values provided, leaving other fields unchanged. The result returns the id used in the configuration node item, which is the date/time of the modification. </p>
Owners and Administrators are allowed to control which users can participate in a channel by use of Allowed and Banned lists using PubSub. These operations follow &xep0060; which sets out detailed protocol use and error handling.
Allowed and Banned lists MAY be read by PubSub get of the Banned and Allowed Nodes. This operation MAY be used by users as controlled by 'Allowed Node Subscription' and 'Banned Node Subscription' configuration node options (default Administrators).
When the MIX channel adds a JID to the banned node, other nodes in the MIX channel will be appropriately updated to reflect this change. In particular, the participants nodes and presence nodes will be updated to remove matching JIDs. This will have the effect of immediately removing the user from the channel. For this reason, there is no requirement to have the "kick" functionality of MUC, as this is achieved by banning the user.
</p>
</section3>
</section2>
</section1>
<section1topic="MIX Requirements on Participant's Server"anchor="mix-requirements-participant-server">
<p>
This section defines behaviour REQUIRED by MIX for servers supporting MIX participants. This provides the full MIX specification for clients and servers is set out in a single document. This functionality MUST be provided by servers used by clients that participate in MIX channels. In future, the specifications in this section MAY be moved to a separate XEP or it MAY be incorporated into
&xep0376; (PAM) which follows a similar model.
</p>
<section2topic="Server Identification of MIX Capabable Clients"anchor="server-identification-mix-clients">
<p>
A MIX User's server MUST determine which online clients support MIX. This will enable the server to send MIX traffic to all MIX capable clients. A MIX capable client MAY choose to come online and not advertise MIX capability. The mechanism for a server to discover client capability is described in <linkurl="#mix-client-discovery">Discovering Client MIX Capability</link>.
</p>
</section2>
<section2topic="Messages From MIX Channels"anchor="mix-from">
<p>
Messages from a MIX channel will usually go to the participant's server. The only exception to this is where the MIX channel is responding directly to messages from the client. Messages and presence distributed but a MIX channel will always be sent to the participant's server and addressed to the user's bare JID. The participant's server will simply send on the messages from the channel to each of the user's online clients which advertise MIX capability. If there are no such clients activated, the message is dropped.
</p>
<p>
Messages sent to the participant's sever will always be addressed to the user's bare JID. The participant’s server will modify the recipient to the full JID of each client to which the message is forwarded. The following example, repeated from earlier, shows a message distributed by a MIX channel and directed to the participant’s server with the participant's bare JID.
</p>
<examplecaption="Channel Reflects Message to Participants"><![CDATA[
<messagefrom='coven@mix.shakespeare.example'
to='hecate@shakespeare.example'
id='77E07BB0-55CF-4BD4-890E-3F7C0E686BBD'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
<mixxmlns='urn:xmpp:mix:1'>
<nick>thirdwitch</nick>
<jid>123456#coven@mix.shakespeare.example</jid>
</mix>
</message>
]]></example>
<p>
The server receiving the message will then deliver the messages to all online clients. Messages are delivered to all available online resources irrespective of
status and resource priority.
The following example shows how the participant's server modifies the inbound message to replace the bare JID in the 'to' with a full JID for each of two active MIX clients.
</p>
<examplecaption="Participant's Server Sends Modified Message to two Clients"><![CDATA[
<messagefrom='coven@mix.shakespeare.example'
to='hecate@shakespeare.example/UUID-x4r/2491'
id='77E07BB0-55CF-4BD4-890E-3F7C0E686BBD'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
<mixxmlns='urn:xmpp:mix:1'>
<nick>thirdwitch</nick>
<jid>123456#coven@mix.shakespeare.example</jid>
</mix>
</message>
<messagefrom='coven@mix.shakespeare.example'
to='hecate@shakespeare.example/UUID-b5b/0114'
id='77E07BB0-55CF-4BD4-890E-3F7C0E686BBD'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
<mixxmlns='urn:xmpp:mix:1'>
<nick>thirdwitch</nick>
<jid>123456#coven@mix.shakespeare.example</jid>
</mix>
</message>
]]></example>
</section2>
<section2topic="Messages To MIX Channels"anchor="user-server-to">
<p>
Messages sent by a MIX channel participant to the MIX channel are always sent from a MIX client directly to the channel. The participant's server relays the message but does not modify the messages.
</p>
</section2>
<section2topic="Client Determines MIX Capability of Local Server"anchor="user-server-client-capability">
<p>
Servers supporting the capabilities necessary to enable MIX clients MUST advertise this. A client wishing to use MIX MUST check for this capability in the server before using MIX. The capability is represented by the 'urn:xmpp:mix:account:0' feature.
</p>
<examplecaption="Client Determines MIX Capability of Local Server"><![CDATA[
<section2topic="MIX Management and Discovery"anchor="user-server-disco">
<p>
Most interaction between a MIX client and a MIX channel is directly between the client and the channel. The participant's server relays the message but does not modify the messages. In particular configuration management and discovery is direct. Interaction will be direct, unless explicitly stated otherwise.
</p>
</section2>
<section2topic="IQ Support on Local Server"anchor="mix-diso">
<p>
Channel Join and Leave functions operate indirectly through the participant's server. The reason for this is that where a channel shares user presence, the channel is included in the user's roster which is managed in the local server. The Join and Leave functions lead to roster changes and so they MUST go through the participant's server. This is included in each of the operations that work in this manner. The general mechanism to achieve this is illustrated by example in this section.
The client addresses indirect messages to the user's own bare JID, indicating the channel with the channel attribute. This is illustrated below.
</p>
<examplecaption="Client sends request to local server to Join a MIX Channel"><![CDATA[
<p>This is then modified by the local server and sent to the MIX channel. This is shown in the following example, repeated from the earlier specification of channel behaviour. </p>
<examplecaption="Participant's Server sends Join to MIX Channel"><![CDATA[
The MIX service will send the IQ response to indirect messages to the user's server using the user's bare JID. The user's server will then route the response back to the user's client.
The participant's server is responsible for ensuring that MIX channels are correctly entered into the user's roster when user's join MIX channels and for removing them when they leave.
</p>
<p>
The participant's server MUST ensure that only presence information from clients that advertise MIX capability is sent to the MIX channel. So, if a user has two online clients, but only one is MIX capable, then the channel will only receive presence information relating to the MIX client.
<p>It is useful for a MIX client to know which roster members are MIX channels, as this will facilitate convenient presentation of subscribed MIX channels to the user. A MIX client MAY request that the server return this additional information that annotates roster elements with MIX capability. The server MUST return the additional information. The request is made by extending the standard roster get request by adding a child element <annotate/> to the <query/> element. The <annotate/> element is qualified by the ‘urn:xmpp:mix:roster:0' namespace.</p>
<examplecaption="Roster Get Requesting MIX Information"><![CDATA[
<iqfrom='juliet@example.com/balcony'
id='bv1bs71f'
type='get'>
<queryxmlns='jabber:iq:roster'>
<annotatexmlns='urn:xmpp:mix:roster:0'/>
<query/>
</iq>
]]></example>
<p>A standard roster item is encoded as follows.</p>
MIX channels in the roster information returned in response to a request for this additional MIX information MUST have an element <channel/> qualified by the ‘urn:xmpp:mix:roster:0' namespace included in the roster item, as shown inf the following example.
</p>
<examplecaption="Roster Item Encoding of a MIX Channel"><![CDATA[
<itemjid='balcony@example.net'>
<channelxmlns='urn:xmpp:mix:roster:0'/>
</item>
]]></example>
<p>
Once a client has made an IQ request to return additional MIX information, the server MUST return this information on all subsequent roster updates that are sent by the server to the client. The server MUST NOT send additional MIX information when this has not been explicitly requested. It is anticipated that a client will fetch the roster after connection has been established and will set it's preference for this MIX capability information at that time.
Archive of MIX channel messages is done by the participant's server. Where a message is sent to the participant's server and discarded because there are no active clients, it will still be archived. This means that the messages will be available in the local archive and can be picked up by clients when they come online.
</p>
</section2>
</section1>
<section1topic="Supporting MIX and MUC together"anchor="mix-and-muc-together">
<p>
MIX is specified as a service that can be used independent of MUC and a MIX service MAY be implemented without MUC. If both MIX and MUC are implemented, three approaches are noted.
</p>
<ol>
<li>Entirely separate MIX and MUC implementation, with MIX and MUC using separate domains and MIX channels being completely separate from MUC rooms.</li>
<li>Fully integrated MIX and MUC implementation, with MIX and MUC sharing a single domain and rooms/channels equivalent.</li>
<li>Partially integrated MIX and MUC implementation, with MIX and MUC using separate domains, but rooms/channel are common. This means that each MIX channel will have MUC room of the same name and same participants.</li>
</ol>
<p>The fully integrated approach would be transparent to clients. The following example shows how a MIX service that also supported MUC would respond:</p>
<examplecaption="Service responds with Disco Info result showing MIX and MUC support"><