Programming Jabber

The Conversation as XML Documents

The conversation is two-way, duplexed across a socket connection. On one side, the client sends an XML document to the server. On the other side, the server responds by sending an XML document to the client. Figure 5-3 shows the pair of XML documents being streamed across the TCP socket connection between client and server, over time.

Figure 5-3. A conversation between client and server as a pair of streamed XML documents

But what do we mean when we say that the conversation is an XML document? To answer this, consider this simple XML document:

<?xml version="1.0"?>
<roottag>
  <fragment1/>
  <fragment2/>
  <fragment3/>
  ...
  <fragmentN/>
</roottag>

The document starts with an XML declaration:

<?xml version="1.0"?>

which is immediately followed by the opening root tag. This root tag is significant because there can be only one (and, of course, its corresponding closing tag) in the whole document. In effect, it wraps and contextualizes the content of the document:

<roottag>
  ...
</roottag>

The real content of the document is made up of the XML fragments that come after the opening root tag:

<fragment1/>
<fragment2/>
<fragment3/>
...
<fragmentN/>

So, taking a connection between a Jabber client and a Jabber server as an example, this is exactly what we have. The server is listening on port 5222 for incoming client-initiated connections. Once a client ...