[xml] Streaming XPath in libxml2

[Ravi Reddy <ravi gs-lab com>]

Hi,

My apologies if this mailing list is not the intended target.

The version of libxml2 and the OS on which it is deployed is displayed
below.

-----------------------------------------------------------------------
shell$ xml2-config --version
2.6.11

shell$ cat /proc/version
Linux version 2.6.9-1.667smp (bhcompile tweety build redhat com) (gcc
version 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)) #1 SMP Tue Nov 2 14:59:52
EST 2004
-----------------------------------------------------------------------

I would like to know how to use streaming XPath. Googling on libxml2
about this shows favorable search results.

The usage scenario follows:

-----------------------------------------------------------------------
//
//open an XML file for reading
FILE *xmlFile;

if ((xmlFile = fopen(argv[1] , "r")) == NULL)
{
   ...
}

//
// read a chunk/fragment of XML
// Evaluate an XPath on the chunk of XML
do
{
   char buffer[BUFFER_SIZE];

   int readlen = fread (buffer, 1, BUFFER_SIZE, xmlFile);

   //
   // Parse the XML fragment
   xmlDocPtr doc = xmlSAXParseMemory(sax, buffer, BUFFER_SIZE, 0);

   if (doc != NULL)
   {
      xmlXPathContextPtr xpathCtx = xmlXPathNewContext(doc);
      xmlXPathObjectPtr xpathObj = xmlXPathEvalExpression(
                                   xpathExpr, xpathCtx);

      //
      // Print the XPath results

      xmlXPathFreeObject(xpathObj);
      xmlXPathFreeContext(xpathCtx);
      xmlFreeDoc(doc);
   }
} while (not end of XML file);
-----------------------------------------------------------------------

I understand that xmlSAXParseMemory needs a well-formed XML in-memory
buffer and not just a chunk.

For example, consider the XML

-----------------------------------------------------------------------
<foo>
   <bar>This is a really long string: 123456789012345678901234567890
   </bar>
</foo>
-----------------------------------------------------------------------

The chunks could be

-----------------------------------------------------------------------
Chunk 1:
<foo>
   <bar>This is a really long string: 1234567890

Chunk 2:
12345678901234567890</bar>
</foo>
-----------------------------------------------------------------------

Could you please tell me if streaming XPath is supported? If so, could
you please provide me a code sample that would parse a XML chunk and
evaluate XPaths on it.

Thanks much for your help.

Regards,
Ravi.