/*
 * call-seq:
 *  initialize_native(xml_sax, filename)
 *
 * Initialize the push parser with +xml_sax+ using +filename+
 */
static VALUE initialize_native(VALUE self, VALUE _xml_sax, VALUE _filename)
{
  xmlSAXHandlerPtr sax;

  Data_Get_Struct(_xml_sax, xmlSAXHandler, sax);
  
  const char * filename = NULL;

  if(_filename != Qnil) filename = StringValuePtr(_filename);

  xmlParserCtxtPtr ctx = xmlCreatePushParserCtxt(
      sax,
      (void *)self,
      NULL,
      0,
      filename
  );
  if(ctx == NULL)
    rb_raise(rb_eRuntimeError, "Could not create a parser context");

  DATA_PTR(self) = ctx;
  return self;
}