Programming Jabber

Specifying clients as query targets

Many of these namespaces qualify queries that make just as much sense sent to a Jabber client as sent to a Jabber server or service. However, if you don’t compose the recipient JID correctly, you could end up with an unexpected response.

Let’s say you want to query the local time on Piers’ client, which is connected to the Jabber server at jabber.org:

SEND: <iq type='get' id='time_21' to='[e-mail]'>
        <query xmlns='jabber:iq:time'/>
      </iq>

You could get a response similar to this:

RECV: <iq type='error' id='time_21' from='[e-mail]'
          to='[e-mail]/home'>
        <query xmlns='jabber:iq:time'/>
        <error code='503'>Service Unavailable</error>
     </iq>

Why? This query isn’t addressed to a particular client or session. While <message/> elements can be addressed to a user JID in the form username@hostname and will be sent to the “primary” session according to presence priority, the recipients of <iq/> elements must be specified exactly. As we want to find out the time at Piers’ client, which has the associated resource desktop, we must specify that resource in the JID:

SEND: <iq type='get' id='time_21' to='[e-mail]/desktop'>
        <query xmlns='jabber:iq:time'/>
      </iq>

This will give us the response we’re looking for:

RECV: <iq type='result' id='time_21' to='qmacro@jabber/home'
	from='[e-mail]/desktop'>
        <query xmlns='jabber:iq:time'/> <utc>20010520T11:25:58</utc> <tz>CET</tz> <display>Sun May 20 13:25:58 2001</display> </query> ...