[Twisted-Python] xmlstream problem

Gabriel Rossetti mailing_lists at evotex.ch
Wed May 21 10:06:01 EDT 2008

Ralph Meijer wrote:
> On Tue, 2008-05-20 at 17:50 +0200, Gabriel Rossetti wrote:
>> Hello,
>> I am using xmlstream.XmlStream to process...XML streams :-)
>> I'm having a bit of a problem, I have a client and a server, both 
>> protocols inherit from xmlstream.XmlStream. When the client sends 4 
>> messages, one after another, I get a parse error. I debugged my program, 
>> and the buffer the expat parser is given contains in effect, 4 messages 
>> consecutively like so :
>> str: 
>> <message>...</message><message>...</message><message>...</message><message>...</message>
>> (I replaced the child elements with "..." for your reading enjoyment)
>> and I get this Exception when debugging (otherwise it stays hidden) :
>> ExpatError: junk after document element: line 1, column 196
>> now column 196 is the end of the 1st msg's root element, I think it 
>> doesn't like the next message being right after the first.
> That's right. Streaming XML, as implemented by twisted.words.xish, works
> by exchanging two complete (virtual) XML documents, one in each
> direction. So, you need to have a root element around your messages,
> such as 'stream'. The unit of communication is first-level elements of
> that root element. So, you start out with sending the start tag of the
> root element, and then sending the messages.
> You would set up an observer for your messages like so:
>   def onMessage(message):
>       print "Got message!"
>   factory = XmlStreamFactory()
>   factory.addBootstrap("/message", onMessage)
>> I did 
>> override xmlstream.XmlStream.onDocumentEnd()
>> because I didn't want it to close the connection in between messages, 
>> but in my method I told it to initialize the stream using :
>> self._initializeStream()
>> I did this since I noticed that closing the connection forces a new 
>> parser to be created when the previous statement is called. The reason I 
>> don't want the connection to be closed is that I'd like a persistent 
>> connection to be held.
> There is no need to do this, what I showed above should meet your
> requirements. Also, this method is semi-private (leading _) for a
> reason.

Thank you, I understand better now, so I could send a "session" opening 
tag (e.g. <session_start>) from each side (one from the client when it 
connects and one from the server when the client connects), then 
exchange as manny messages as I want in between the two and then when I 
am done I send the closing tag (e.g. </session_start>)? Is that correct?


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