XEP33: Tell limits in disco#info response using XEP128

Some time ago I explained why The limit of addresses in XEP33 must be fixed. Of the proposed solutions, I prefer #3: 'Configurable limit, and method to inform'.

A method to inform is using XEP-0128: Service Discovery Extensions, as proposed by Ralphm in a comment.

How does this work? Currently, when an entity wants to send a XEP33 stanza, it first checks if there is a XEP33-enabled service available. To check that, it queries disco#info to the service, and looks for in the response.

If we also use XEP128, the disco#info response will not only announce XEP33 support, but also announce which are the exact limits in effect in the service.

Let's see an example. The Jabber server capulet.com wants to send a stanza with XEP33 addresses to the Jabber server shakespeare.lit. The response announces XEP33 support, and also provides information of several limits:

<iq type='get'
 from='capulet.com'
 to='shakespeare.lit'
 id='disco1'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

<iq type='result'
 from='shakespeare.lit'
 to='capulet.com'
 id='disco1'>
<query xmlns='http://jabber.org/protocol/disco#info'>
 <identity
     category='server'
     type='im'
     name='shakespeare.lit jabber server'/>
 ...
 <feature var='http://jabber.org/protocol/address'/>
 <x xmlns='jabber:x:data' type='result'>
   <field var='FORM_TYPE' type='hidden'>
     <value>http://jabber.org/protocol/address</value>
   </field>
   <field var='limit-remote-user'>
     <value>20</value>
   </field>
   <field var='limit-remote-service'>
     <value>100</value>
   </field>
   <field var='limit-local-user'>
     <value>300</value>
   </field>
 </x>
 ...
</query>
</iq>