/**
* section: XPath
* synopsis: Load a document, locate subelements with XPath, modify
* said elements and save the resulting document.
* purpose: Shows how to make a full round-trip from a load/edit/save
* usage: xpath2 <xml-file> <xpath-expr> <new-value>
* test: xpath2 test3.xml '//discarded' discarded > xpath2.tmp ; diff xpath2.tmp
xpath2.res ; rm xpath2.tmp
* author: Aleksey Sanin and Daniel Veillard
* copy: see Copyright for the status of this software.
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <libxml/tree.h>
#include <libxml/parser.h>
#include <libxml/xpath.h>
#include <libxml/xpathInternals.h>
#if defined(LIBXML_XPATH_ENABLED) && defined(LIBXML_SAX1_ENABLED) && \
defined(LIBXML_OUTPUT_ENABLED)
static void usage(const char *name);
/* free the document */
xmlFreeDoc(doc);
return(0);
}
/**
* update_xpath_nodes:
* @nodes: the nodes set.
* @value: the new value for the node(s)
*
* Prints the @nodes content to @output.
*/
static void
update_xpath_nodes(xmlNodeSetPtr nodes, const xmlChar* value) {
int size;
int i;
assert(value);
size = (nodes) ? nodes->nodeNr : 0;
/*
* NOTE: the nodes are processed in reverse order, i.e. reverse document
* order because xmlNodeSetContent can actually free up descendant
* of the node and such nodes may have been selected too ! Handling
* in reverse order ensure that descendant are accessed first, before
* they get removed. Mixing XPath and modifications on a tree must be
* done carefully !
*/
for(i = size - 1; i >= 0; i--) {
assert(nodes->nodeTab[i]);
xmlNodeSetContent(nodes->nodeTab[i], value);
/*
* All the elements returned by an XPath query are pointers to
* elements from the tree *except* namespace nodes where the XPath
* semantic is different from the implementation in libxml2 tree.
* As a result when a returned node set is freed when
* xmlXPathFreeObject() is called, that routine must check the
* element type. But node from the returned set may have been removed
* by xmlNodeSetContent() resulting in access to freed data.
* This can be exercised by running
* valgrind xpath2 test3.xml '//discarded' discarded
* There is 2 ways around it:
* - make a copy of the pointers to the nodes from the result set
* then call xmlXPathFreeObject() and then modify the nodes
* or
* - remove the reference to the modified nodes from the node set
* as they are processed, if they are not namespace nodes.
*/
if (nodes->nodeTab[i]->type != XML_NAMESPACE_DECL)
nodes->nodeTab[i] = NULL;
}
}
#else
int main(void) {
fprintf(stderr, "XPath support not compiled in\n");
exit(1);
}
#endif
/* free the document */
xmlFreeDoc(doc);
return(0);
}
/**
* update_xpath_nodes:
* @nodes: the nodes set.
* @value: the new value for the node(s)
*
* Prints the @nodes content to @output.
*/
static void
update_xpath_nodes(xmlNodeSetPtr nodes, const xmlChar* value) {
int size;
int i;
assert(value);
size = (nodes) ? nodes->nodeNr : 0;
/*
* NOTE: the nodes are processed in reverse order, i.e. reverse document
* order because xmlNodeSetContent can actually free up descendant
* of the node and such nodes may have been selected too ! Handling
* in reverse order ensure that descendant are accessed first, before
* they get removed. Mixing XPath and modifications on a tree must be
* done carefully !
*/
for(i = size - 1; i >= 0; i--) {
assert(nodes->nodeTab[i]);
xmlNodeSetContent(nodes->nodeTab[i], value);
/*
* All the elements returned by an XPath query are pointers to
* elements from the tree *except* namespace nodes where the XPath
* semantic is different from the implementation in libxml2 tree.
* As a result when a returned node set is freed when
* xmlXPathFreeObject() is called, that routine must check the
* element type. But node from the returned set may have been removed
* by xmlNodeSetContent() resulting in access to freed data.
* This can be exercised by running
* valgrind xpath2 test3.xml '//discarded' discarded
* There is 2 ways around it:
* - make a copy of the pointers to the nodes from the result set
* then call xmlXPathFreeObject() and then modify the nodes
* or
* - remove the reference to the modified nodes from the node set
* as they are processed, if they are not namespace nodes.
*/
if (nodes->nodeTab[i]->type != XML_NAMESPACE_DECL)
nodes->nodeTab[i] = NULL;
}
}
#else
int main(void) {
fprintf(stderr, "XPath support not compiled in\n");
exit(1);
}
#endif
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