Re: [xml] how do I...

Daniel Veillard <veillard redhat com> wrote:
On Tue, May 24, 2005 at 02:47:12PM -0600, Sebastian Kuzminsky wrote:
I've got a couple of processes that trade XML messages over the network.
The sender writes each XML message on a single newline-terminated line.
The receiver uses select and read, and reads until it gets a '\n',
then passes the line to xmlParseMemory and validates the resulting doc
with xmlValidateDtd.

This works well, but it's a little annoying to have to use '\n' as the
message separator.  What I'd really like is to let the sender spread
its message out over several lines if it wants, and have the receiver
detect the end-of-message without any gross hacks.

  By the definition of XML this is not possible. Packing multiple
XML document on a single stream without out of band markers is a frequent
but huge design flaws. The demonstration is obvious for anybody who
read the 2 first pages of the XML standard:

   First production of the XML specification:
   [1] document ::= prolog element Misc*

 Misc* means there is no potential limit to the number of Misc element at 
the end, and not finding one is a fatal error. 
 The direct result from this is that the parser must be told that the document
is finished. And libxml2 API being strictly conformant does not offer APIs
for what you want. 
 I strongly suggest you redesign your network format to include markers
or documents size in the pipe, the current state sounds broken.

Ok, thanks Daniel.

My network format already includes an end-of-document marker which never
appears inside the document ('\n'), so I guess I'm standards-compliant,
if only by dumb luck.  :)

Sebastian Kuzminsky
"Marie will know I'm headed south, so's to meet me by and by"
-Townes Van Zandt

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