Programming Jabber

Jabber’s Building Blocks

At this stage we’ve got a good impression of the structure of Jabber: what different elements make up a Jabber system, how entities in Jabber are addressed, and how communication between these entities is carried.

Now it’s time to look at what gets carried—the fragments that we touched upon in the previous section. These fragments are the heart and soul of Jabber—the lifeblood that courses through Jabber’s veins carrying information back and forth—these fragments in many ways define what Jabber is, what it stands for.

Surprisingly, when we look closely at these fragments, with Jabber’s capabilities as a messaging platform in mind, we see that there are only three basic elements involved—<message/>, <presence/>, and <iq/>. Three different types of XML fragments, each with a different purpose. But with these three fragment types—these elements—all that Jabber promises, and more, can be achieved.

Now let’s look at each of these Jabber elements in greater detail. But before we do, let’s dive into the XML stream and pull out a handful of XML fragments to get us in the mood. Example 5-3 shows a chunk of conversation between a Jabber client and a Jabber server, which occurred immediately after the connection and authentication stages.

Note

Although any conversation between two Jabber entities is contained within two XML documents exchanged in streams, the traditional way to represent both documents at the same time is to use prefixes to show whether a fragment ...