[jdev] Re: VTD-XML version 1.6

Fri May 19 01:31:16 CDT 2006

crackeur at comcast.net schrieb:
>  
> you confused me even more...
> I thought IM apps exchange xml messages (usually small),

let me explain XMPP with this small example of a session:

the client connects, open the socket and the XML Document
C->S: <?xml version="1.0"?>
C->S: <stream:stream xmlns:stream="http://etherx.jabber.org/streams" 
xmlns="jabber:client" to="jabber.org" >

server accepts the socket and opens the XML document
S->C: <stream:stream xmlns='jabber:client' 
xmlns:stream='http://etherx.jabber.org/streams' from='jabber.org' 
id='596931'>

the client starts to authenticate
C->S: <iq type="get" to="jabber.org" id="auth_1" >
	<query xmlns="jabber:iq:auth">
		<username>alex</username>
	</query>
</iq>

S->C: <iq type="result" id="auth_1" >
	<query xmlns="jabber:iq:auth">
		<username>gnauck</username>
		<password/>
		<digest/>
		<resource/>
	</query>
       </iq>

C->S: <iq type="set" to="jabber.org" id="auth_2" >
	<query xmlns="jabber:iq:auth">
	 <username>gnauck</username>
	 <password>secret</password>
	 <resource>Psi</resource>
	</query>
       </iq>

S->C: <iq type="result" id="auth_2" />

C->S: <message type="chat" to="romeo at jabber.org" >	
	<body>Test</body>
      </message>

Client closes the connection, which means it closes the XML Document
C->S: </stream:stream>

Server is closing the XML Doc too
S->C: </stream:stream>

you see we have 2 complete XML Documents. The client doc and the server 
doc. Our messages, also called stanzas are the 1st level child elements 
of the document. If you see the stanzas as a single xml doc and not in 
the context of the whole document you loose the namespace of the 
stanzas, and your software is not namespace correct. This is why parsing 
XMPP XML is a bit tricky and the most out of the box parsers don't work 
very well without modifying them. My exapmple shows the old jabber style 
authentication. It gets even more complicated when using SASL, START-TLS 
and other stuff which resets the stream and opens the document again.

 > why do they exchange huge XML docs? It sounds not just bad, but
 > unnecessary...

i don' think so. Because of this XMPP is a very clean and solid 
protocol. Clean, simple, powerful, extensible.....

Alex