Programming Jabber

Component Instance: dnsrv

The dnsrv component, described by the configuration XML shown in Example 4-16 and shown in diagram form in Figure 4-12, provides routing logic and name resolution for packets that are destined for a nonlocal component, in other words, for a component that is running on another Jabber server.^[7]

Figure 4-12. Diagram view of dnsrv component instance

Example 4-16. jabber.xml configuration for the dnsrv component instance

<service id="dnsrv">

  <host/>

  <load>
    <dnsrv>./dnsrv/dnsrv.so</dnsrv>
  </load>

  <dnsrv xmlns="jabber:config:dnsrv">
  	<resend service="_jabber._tcp">s2s</resend>
  	<resend>s2s</resend>
  </dnsrv>

</service>

Once started, the component forks to spawn a child process that services the actual name resolution requests and the route determination. The component and its child communicate with a simple XML stream within which hostnames are passed to the child process in a “query” tag:

<host>update.jabber.org</host>

and answers are passed back in the form of attribute additions to the original query tag:

<host ip='208.245.212.100' to='s2s'>update.jabber.org</host>

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^[7] Or, for example, on a server offering another IM service (this is planned for the future).