XEP-0497: Pubsub Extended Subscriptions

3.1 Subscription Type¶

The type of subscription is defined by the 'var' attribute with a value of "{urn:xmpp:pubsub-ext-sub:0}type". This option MUST have the type "list-multi", and it MUST default to only the "items" value. The possible values for this field are:

• items: subscribe to items notification, which is equivalent to a usual node subscription as defined at XEP-0060 §6.1 Subscribe to a Node.
• metadata: subscribe to metadata updates, as explained in Metadata Notification.
• linked items: subscribe to items with "link" relationship to this node, as explained in Linked Items Notification.

3.2 Subscription Depth¶

The subscription depth is used when a client wants to subscribe to a parent node and all its descendants (up to requested depth). The "parent" relationship is explained in XEP-XXXX Pubsub Node Relationships.

The 'var' attribute for the subscription depth field MUST be "{urn:xmpp:pubsub-ext-sub:0}depth", and it MUST have a type of "text-single".

The value MUST be castable to a signed integer, and it MUST default to "0". This value indicates how many levels of descendants this subscription must apply to:

• "0" for subscribing only to items on this node (the default);
• "1" for subscribing to its items and direct children's items;
• "2" for subscribing to items including up to two descendant levels, and so forth.
• A negative value means unlimited depth is requested (i.e., subscription to the whole arborescence).

However, an implementation MAY limit the maximum depth for performance reasons; in such cases, it MUST be advertised through disco as explained in Discovering Support. When the subscription depth has a value different from "0", subscriptions must dynamically adapt to nodes added or removed within the arborescence: if a node gains a new "parent" relationship to any subscribed node, it will automatically become part of the subscription; conversely, if such a relationship is modified or the node is deleted, it will no longer be included in the subscription.

4.1 Request¶

In this example, Romeo is subscribing to the 'some-node-name' node and requesting to receive notifications for items, metadata updates, and linked items within the entire node hierarchy (unlimited depth).

<iq type='set'
  from='romeo@example.org/orchard'
  to='pubsub.example.org'
  id='sub-1'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
  <subscribe jid='romeo@example.org'
    node='some-node-name'/>
  <options>
    <x xmlns='jabber:x:data' type='submit'>
      <field var='FORM_TYPE' type='hidden'>
        <value>http://jabber.org/protocol/pubsub#subscribe_options</value>
      </field>
      <field var='{urn:xmpp:pubsub-ext-sub:0}type'>
        <value>items</value>
        <value>metadata</value>
        <value>linked items</value>
      </field>
      <field var='{urn:xmpp:pubsub-ext-sub:0}depth'>
        <value>-1</value>
      </field>
    </x>
  </options>
</pubsub>
</iq>
    

<iq type='result'
    from='pubsub.example.org'
    to='romeo@example.org/orchard'
    id='sub-1'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <subscription node='some-node-name'
      jid='romeo@example.org'
      subscription='subscribed'/>
  </pubsub>
</iq>
    

4.2 Notification Types¶

This section describes the notifications that are sent for each subscription type: items, metadata, and linked items.

<message from='pubsub.example.org' to='juliet@example.org/balcony' id='items-1'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='some-node-name'>
      <item id='item1'>
          <!-- … -->
      </item>
    </items>
  </event>
</message>

      <message from='pubsub.example.org' to='juliet@example.org/balcony' id='config-1'>
        <event xmlns='http://jabber.org/protocol/pubsub#event'>
          <configuration node='some-node-name'>
            <x xmlns='jabber:x:data' type='result'>
              <field var='FORM_TYPE' type='hidden'>
                <value>http://jabber.org/protocol/pubsub#meta-data</value>
              </field>
              <field var='pubsub#title'>
                <value>New Title</value>
              </field>
              <field var='pubsub#description'>
                <value>New Description</value>
              </field>
              <field var='pubsub#access_model'>
                <value>open</value>
              </field>
            </x>
          </configuration>
        </event>
      </message>
        

      <message from='pubsub.example.org' to='juliet@example.org/balcony' id='config-2'>
        <event xmlns='http://jabber.org/protocol/pubsub#event'>
          <configuration node='removed-node-name'>
            <x xmlns='jabber:x:data' type='result'>
              <field var='FORM_TYPE' type='hidden'>
                <value>http://jabber.org/protocol/pubsub#meta-data</value>
              </field>
              <field var='{urn:xmpp:pubsub-relationships:0}parent' />
            </x>
          </configuration>
        </event>
      </message>
        

<message from='pubsub.example.org' to='juliet@example.org/balcony' id='linked-1'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='urn:xmpp:pubsub-attachments:1/xmpp:juliet@capulet.lit?;node=urn%3Axmpp%3Amicroblog%3A0;item=balcony-restoration-afd1'>
      <item id='romeo@montague.lit'>
          <!-- … -->
      </item>
    </items>
  </event>
</message>

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1. XEP-0060: Publish-Subscribe <https://xmpp.org/extensions/xep-0060.html>.

2. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.

3. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.