/** * 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); } /* Shutdown libxml */ xmlCleanupParser(); /* * this is to debug memory for regression tests */ xmlMemoryDump(); 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"); exit(1); } #endif