Programming Jabber

The newsagent script as a component

Until now, the examples we’ve used, such as cvsmsg, HostAlive, and keyassist (shown in Chapter 8), have all existed as Jabber clients. That is, they’ve performed a service while connected to the Jabber server via the JSM. There’s nothing wrong with this. Indeed, it’s more than just fine to build Jabber-based mechanisms using a Jabber client stub connection; that way, your script, through its identity—the user JID—can avail itself of all the IM-related functions that the JSM offers—presence, storage and forwarding of messages, and so on. Perhaps even more interesting is that the mechanism needs only an account, a username, and a password on a Jabber server to be part of the big connected picture.

However, we know from Chapter 4 that there are other entities that connect to Jabber to provide services. These entities are called components. You can look at components as philosophically less “transient” than their client-connected brethren and also closer to the Jabber server in terms of function and connection.

We know from Section 4.1.1 that there are various ways to connect a component: library load, STDIO, and TCP sockets. The first two dictate that the component will be located on the same host as the jabberd backbone to which it connects, although a Jabber server could consist of a collection of jabberds running on separate hosts. The TCP sockets connection type uses a socket connection between the component and the jabberd backbone, over ...