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/**
* 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 $(srcdir)/xpath2.res
* 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);
static int example4(const char *filename, const xmlChar * xpathExpr,
const xmlChar * value);
static void update_xpath_nodes(xmlNodeSetPtr nodes, const xmlChar * value);
int
main(int argc, char **argv) {
/* Parse command line and process file */
if (argc != 4) {
fprintf(stderr, "Error: wrong number of arguments.\n");
usage(argv[0]);
return(-1);
}
/* Init libxml */
xmlInitParser();
LIBXML_TEST_VERSION
/* Do the main job */
if (example4(argv[1], BAD_CAST argv[2], BAD_CAST argv[3])) {
usage(argv[0]);
return(-1);
}
return 0;
}
/**
* usage:
* @name: the program name.
*
* Prints usage information.
*/
static void
usage(const char *name) {
assert(name);
fprintf(stderr, "Usage: %s <xml-file> <xpath-expr> <value>\n", name);
}
/**
* example4:
* @filename: the input XML filename.
* @xpathExpr: the xpath expression for evaluation.
* @value: the new node content.
*
* Parses input XML file, evaluates XPath expression and update the nodes
* then print the result.
*
* Returns 0 on success and a negative value otherwise.
*/
static int
example4(const char* filename, const xmlChar* xpathExpr, const xmlChar* value) {
xmlDocPtr doc;
xmlXPathContextPtr xpathCtx;
xmlXPathObjectPtr xpathObj;
assert(filename);
assert(xpathExpr);
assert(value);
/* Load XML document */
doc = xmlParseFile(filename);
if (doc == NULL) {
fprintf(stderr, "Error: unable to parse file \"%s\"\n", filename);
return(-1);
}
/* Create xpath evaluation context */
xpathCtx = xmlXPathNewContext(doc);
if(xpathCtx == NULL) {
fprintf(stderr,"Error: unable to create new XPath context\n");
xmlFreeDoc(doc);
return(-1);
}
/* Evaluate xpath expression */
xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);
if(xpathObj == NULL) {
fprintf(stderr,"Error: unable to evaluate xpath expression \"%s\"\n", xpathExpr);
xmlXPathFreeContext(xpathCtx);
xmlFreeDoc(doc);
return(-1);
}
/* update selected nodes */
update_xpath_nodes(xpathObj->nodesetval, value);
/* Cleanup of XPath data */
xmlXPathFreeObject(xpathObj);
xmlXPathFreeContext(xpathCtx);
/* dump the resulting document */
xmlDocDump(stdout, doc);
/* 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");
return 0;
}
#endif
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