XEP-xxxx: Pubsub Extended Discovery

3.1 Discovering Linked Nodes and Descendants¶

An entity can request to discover linked nodes and descendants by including a data form in the disco#items request. The form uses the namespace "urn:xmpp:pubsub-ext-disco:0" and MAY include the following fields:

• type: A "list-multi" field that indicates what kind of items should be returned. The values for this field MUST be either "items" or "nodes", and it defaults both "items" and "nodes". If "items" is selected, pubusb node items are returned; if "nodes" is selected, pubsub nodes are returned. Pubsub items MUST NOT be returned if "items" is not selected, and pubsub nodes MUST NOT be returned if "nodes" is not selected.
• linked_nodes: A boolean field that, when set to "true", indicates that linked nodes and/or their items should be included in the discovery results. The default value of this field MUST be "false".
• full_metadata: A boolean field that, when set to 'true', indicates that the full node metadata form (as specified in XEP-0060 §5.4 Discover Node Metadata) MUST be included with each discovered node. If this field is set to 'false', the Pubsub/PEP service MUST return only the necessary relationship fields ('{urn:xmpp:pubsub-relationships:0}parent' and/or '{urn:xmpp:pubsub-relationships:0}link'). The default value of this field MUST be 'false'.
• depth: A "text-single" field that specifies the number of layers of descendants to include. The value must be castable to an integer and defaults to 0. If the "linked_nodes" field is set to "false", descendant linked nodes (i.e., descendant nodes with a set "{urn:xmpp:pubsub-relationships:0}link" field) MUST NOT be included.

If the "urn:xmpp:pubsub-ext-disco:0" data form is present in the disco#items request, the rules differ from those specified in Publish-Subscribe (XEP-0060) [1]: contrary to what is outlined in §5.5 Discover Items for a Node, the "node" attribute MUST be specified for all items as it is necessary to know to which pubsub node a pubsub item is attached.

If a disco item is actually a pubsub node, a metadata form (as specified in XEP-0060 §5.4 Discover Node Metadata) MUST be included as a child of the disco <item> element.

If the 'full_metadata' field in the request's data form is set to "true", the full node metadata form MUST be included with each discovered node. If this field is set to "false", only the necessary relationship fields ("{urn:xmpp:pubsub-relationships:0}parent" and/or "{urn:xmpp:pubsub-relationships:0}link") MUST be returned.

If the item is a child node, its "{urn:xmpp:pubsub-relationships:0}parent" field MUST be present, and if it is a linked node, its "{urn:xmpp:pubsub-relationships:0}link" field MUST be present. This data form is necessary to identify the item as a pubsub node and to see its relationships, allowing the requestor to build the hierarchy.

<iq type='get'
  from='romeo@example.net/orchard'
  to='juliet@example.org'
  id='disco1'>
<query xmlns='http://jabber.org/protocol/disco#items' node='urn:xmpp:microblog:0'>
  <x xmlns='jabber:x:data' type='submit'>
    <field var='FORM_TYPE' type='hidden'>
      <value>urn:xmpp:pubsub-ext-disco:0</value>
    </field>
    <field var='type'>
      <value>nodes</value>
    </field>
    <field var='linked_nodes'>
      <value>true</value>
    </field>
    <field var='depth'>
      <value>1</value>
    </field>
  </x>
</query>
</iq>
    

<iq type='result'
  from='juliet@example.org'
  to='romeo@example.net/orchard'
  id='disco1'>
<query xmlns='http://jabber.org/protocol/disco#items' node='urn:xmpp:microblog:0'>
  <item jid='juliet@example.org' node='urn:xmpp:microblog:0:comments/balcony-restoration-afd1'>
    <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'>
        <value>urn:xmpp:microblog:0</value>
      </field>
    </x>
  </item>
  <item jid='juliet@example.org' node='urn:xmpp:pubsub-attachments:1/xmpp:juliet@capulet.lit?;node=urn%3Axmpp%3Amicroblog%3A0;item=balcony-restoration-afd1'>
    <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}link'>
        <value>urn:xmpp:microblog:0</value>
      </field>
    </x>
  </item>
</query>
</iq>
  

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

2. XEP-0059: Result Set Management <https://xmpp.org/extensions/xep-0059.html>.

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

4. 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/>.