Programming Jabber

IM System Features

This book assumes you have a basic knowledge of features commonly found in IM systems. In case you don’t, here’s a brief rundown of features relevant to what we’ll be covering:

Presence

In many cases, there’s not much point in sending a quick message to someone if they’re not there. Presence is a term used in IM to describe the technique of exchanging information, in a controlled manner, about availability (or unavailability).

The idea is that when you connect to your IM server, your client sends an “I’m here” message that is relayed to your correspondents. It does the opposite when you disconnect. During the time you’re connected, you can vary the information about your availability to reflect your immediate situation (“just popped out for coffee,” “working on my resumé—don’t disturb me!”).

Buddy List™/roster

Both terms (the former comes from the original IM systems, the latter from Jabber) refer to a list of correspondents with whom you regularly communicate and from whom you receive presence information. Depending on the IM system, the list may be stored on the client or on the server. Storing the list on the client has the (tenuous) advantage of being accessible when you’re not connected to the server. Storing the list on the server means that you have a consistent roster content regardless of the client or workstation you happen to use—the list travels with you.

Jabber stores the roster on the server.

Push and pull

When you connect to an IM system, ...