Programming Jabber

Messaging

We’ve been using the term “message” in quite a general sense, to represent data passing from one Jabber entity to another. In fact, as we’ll see in Chapter 5, there are different sorts of messages—and each one has a certain role within the whole context of the Jabber protocol. They are sometimes referred to as elements, and there are three of them: <message/>, <iq/>, and <presence/>.

Note

Actually, there are four, but the fourth, <route/>, is only used in the server to route messages between the various components. More details on <route/> can be found in Section 4.1.2.3 in Chapter 4.

The <message/> element has five types—normal, chat, groupchat, headline, and error. The <iq/> and <presence/> elements also have types to distinguish and describe their usage and context. The <iq/> element has the types get, set, result, and error, while the <presence/> element has, among others, the types available and unavailable. Details can be seen in Table 2-1.

Furthermore, we already know that these elements can be extended using namespaces. Each element and type, and each of the pre-defined namespaces (those that begin jabber:) have been designed with specific scenarios in mind. An example of a headline <message/> element containing an extension qualified by a predefined namespace is shown in Example 2-3.

Table 2-1. Jabber elements and types

Element	Tag	Types
Message	<message>	normal, chat, groupchat, headline, error
IQ	<iq>	get, set, result, error
Presence