Building Instant Messaging and Chat over WebSocket with XMPP - The Definitive Guide to HTML5 WebSocket - page 66

capable of defragmenting characters into stanzas by understanding streaming XML.
Figure 4-5 shows the stanza-to-message alignment as described in the XMPP over
WebSocket subprotocol draft proposal. See Chapter 2 and Chapter 3 for discussions about
registering WebSocket subprotocol drafts.
Figure 4-5. Stanza-to-message alignment (XMPP over WebSocket subprotocol draft proposal)
This figure shows how WebSocket messages are aligned to XMPP stanzas in the case
where an XMPP server can directly communicate over WebSocket to a client.
Figure 4-6 shows an example where the stanza is not aligned to the message. This
figure shows how WebSocket messages do not need to be aligned to stanzas where a
proxy server accepts WebSocket connections and connects to the back-end XMPP server
over TCP.
Figure 4-6. No stanza-to-message alignment (WebSocket to TCP proxy)
Federation
Many IM networks are walled gardens. Users with accounts on a particular network can
only chat among themselves. Conversely, Jabber ( http://www.jabber.org ) is federated,
which means users on independently operated servers can communicate if the servers
cooperate. The Jabber network comprises thousands of servers on different domains and
millions of users. Configuring a server for federation is beyond the scope of this topic.
Here, we focus on connecting clients to a single server. You can later connect your server
to the larger federated world.