1 /**
2 * section: XPath
3 * synopsis: Load a document, locate subelements with XPath, modify
4 * said elements and save the resulting document.
5 * purpose: Shows how to make a full round-trip from a load/edit/save
6 * usage: xpath2 <xml-file> <xpath-expr> <new-value>
7 * test: xpath2 test3.xml '//discarded' discarded > xpath2.tmp && diff xpath2.tmp $(srcdir)/xpath2.res
8 * author: Aleksey Sanin and Daniel Veillard
9 * copy: see Copyright for the status of this software.
10 */
11 #include <stdlib.h>
12 #include <stdio.h>
13 #include <string.h>
14 #include <assert.h>
15
16 #include <libxml/tree.h>
17 #include <libxml/parser.h>
18 #include <libxml/xpath.h>
19 #include <libxml/xpathInternals.h>
20
21 #if defined(LIBXML_XPATH_ENABLED) && defined(LIBXML_SAX1_ENABLED) && \
22 defined(LIBXML_OUTPUT_ENABLED)
23
24
25 static void usage(const char *name);
26 static int example4(const char *filename, const xmlChar * xpathExpr,
27 const xmlChar * value);
28 static void update_xpath_nodes(xmlNodeSetPtr nodes, const xmlChar * value);
29
30
31 int
main(int argc,char ** argv)32 main(int argc, char **argv) {
33 /* Parse command line and process file */
34 if (argc != 4) {
35 fprintf(stderr, "Error: wrong number of arguments.\n");
36 usage(argv[0]);
37 return(-1);
38 }
39
40 /* Init libxml */
41 xmlInitParser();
42 LIBXML_TEST_VERSION
43
44 /* Do the main job */
45 if (example4(argv[1], BAD_CAST argv[2], BAD_CAST argv[3])) {
46 usage(argv[0]);
47 return(-1);
48 }
49
50 /* Shutdown libxml */
51 xmlCleanupParser();
52
53 /*
54 * this is to debug memory for regression tests
55 */
56 xmlMemoryDump();
57 return 0;
58 }
59
60 /**
61 * usage:
62 * @name: the program name.
63 *
64 * Prints usage information.
65 */
66 static void
usage(const char * name)67 usage(const char *name) {
68 assert(name);
69
70 fprintf(stderr, "Usage: %s <xml-file> <xpath-expr> <value>\n", name);
71 }
72
73 /**
74 * example4:
75 * @filename: the input XML filename.
76 * @xpathExpr: the xpath expression for evaluation.
77 * @value: the new node content.
78 *
79 * Parses input XML file, evaluates XPath expression and update the nodes
80 * then print the result.
81 *
82 * Returns 0 on success and a negative value otherwise.
83 */
84 static int
example4(const char * filename,const xmlChar * xpathExpr,const xmlChar * value)85 example4(const char* filename, const xmlChar* xpathExpr, const xmlChar* value) {
86 xmlDocPtr doc;
87 xmlXPathContextPtr xpathCtx;
88 xmlXPathObjectPtr xpathObj;
89
90 assert(filename);
91 assert(xpathExpr);
92 assert(value);
93
94 /* Load XML document */
95 doc = xmlParseFile(filename);
96 if (doc == NULL) {
97 fprintf(stderr, "Error: unable to parse file \"%s\"\n", filename);
98 return(-1);
99 }
100
101 /* Create xpath evaluation context */
102 xpathCtx = xmlXPathNewContext(doc);
103 if(xpathCtx == NULL) {
104 fprintf(stderr,"Error: unable to create new XPath context\n");
105 xmlFreeDoc(doc);
106 return(-1);
107 }
108
109 /* Evaluate xpath expression */
110 xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);
111 if(xpathObj == NULL) {
112 fprintf(stderr,"Error: unable to evaluate xpath expression \"%s\"\n", xpathExpr);
113 xmlXPathFreeContext(xpathCtx);
114 xmlFreeDoc(doc);
115 return(-1);
116 }
117
118 /* update selected nodes */
119 update_xpath_nodes(xpathObj->nodesetval, value);
120
121
122 /* Cleanup of XPath data */
123 xmlXPathFreeObject(xpathObj);
124 xmlXPathFreeContext(xpathCtx);
125
126 /* dump the resulting document */
127 xmlDocDump(stdout, doc);
128
129
130 /* free the document */
131 xmlFreeDoc(doc);
132
133 return(0);
134 }
135
136 /**
137 * update_xpath_nodes:
138 * @nodes: the nodes set.
139 * @value: the new value for the node(s)
140 *
141 * Prints the @nodes content to @output.
142 */
143 static void
update_xpath_nodes(xmlNodeSetPtr nodes,const xmlChar * value)144 update_xpath_nodes(xmlNodeSetPtr nodes, const xmlChar* value) {
145 int size;
146 int i;
147
148 assert(value);
149 size = (nodes) ? nodes->nodeNr : 0;
150
151 /*
152 * NOTE: the nodes are processed in reverse order, i.e. reverse document
153 * order because xmlNodeSetContent can actually free up descendant
154 * of the node and such nodes may have been selected too ! Handling
155 * in reverse order ensure that descendant are accessed first, before
156 * they get removed. Mixing XPath and modifications on a tree must be
157 * done carefully !
158 */
159 for(i = size - 1; i >= 0; i--) {
160 assert(nodes->nodeTab[i]);
161
162 xmlNodeSetContent(nodes->nodeTab[i], value);
163 /*
164 * All the elements returned by an XPath query are pointers to
165 * elements from the tree *except* namespace nodes where the XPath
166 * semantic is different from the implementation in libxml2 tree.
167 * As a result when a returned node set is freed when
168 * xmlXPathFreeObject() is called, that routine must check the
169 * element type. But node from the returned set may have been removed
170 * by xmlNodeSetContent() resulting in access to freed data.
171 * This can be exercised by running
172 * valgrind xpath2 test3.xml '//discarded' discarded
173 * There is 2 ways around it:
174 * - make a copy of the pointers to the nodes from the result set
175 * then call xmlXPathFreeObject() and then modify the nodes
176 * or
177 * - remove the reference to the modified nodes from the node set
178 * as they are processed, if they are not namespace nodes.
179 */
180 if (nodes->nodeTab[i]->type != XML_NAMESPACE_DECL)
181 nodes->nodeTab[i] = NULL;
182 }
183 }
184
185 #else
main(void)186 int main(void) {
187 fprintf(stderr, "XPath support not compiled in\n");
188 exit(1);
189 }
190 #endif
191