doc/examples/xpath1.c

/** 
 * section: 	XPath
 * synopsis: 	Evaluate XPath expression and prints result node set.
 * purpose: 	Shows how to evaluate XPath expression and register 
 *          	known namespaces in XPath context.
 * usage:	xpath1 <xml-file> <xpath-expr> [<known-ns-list>]
 * author: 	Aleksey Sanin
 * 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>

void usage(const char *name);
int  execute_xpath_expression(const char* filename, const xmlChar* xpathExpr, const xmlChar* nsList);
int  register_namespaces(xmlXPathContextPtr xpathCtx, const xmlChar* nsList);
void print_xpath_nodes(xmlNodeSetPtr nodes, FILE* output);

int 
main(int argc, char **argv) {
    /* Parse command line and process file */
    if((argc < 3) || (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(execute_xpath_expression(argv[1], BAD_CAST argv[2], (argc > 3) ? BAD_CAST argv[3] : NULL) < 0) {
	usage(argv[0]);
	return(-1);
    }

    /* Shutdown libxml */
    xmlCleanupParser();
    
    return 0;
}

/**
 * usage:
 * @name:		the program name.
 *
 * Prints usage information.
 */
void 
usage(const char *name) {
    assert(name);
    
    fprintf(stderr, "Usage: %s <xml-file> <xpath-expr> [<known-ns-list>]\n", name);
    fprintf(stderr, "where <known-ns-list> is a list of known namespaces\n");
    fprintf(stderr, "in \"<prefix1>=<href1> <prefix2>=href2> ...\" format\n");
}

/**
 * execute_xpath_expression:
 * @filename:		the input XML filename.
 * @xpathExpr:		the xpath expression for evaluation.
 * @nsList:		the optional list of known namespaces in 
 *			"<prefix1>=<href1> <prefix2>=href2> ..." format.
 *
 * Parses input XML file, evaluates XPath expression and prints results.
 *
 * Returns 0 on success and a negative value otherwise.
 */
int 
execute_xpath_expression(const char* filename, const xmlChar* xpathExpr, const xmlChar* nsList) {
    xmlDocPtr doc;
    xmlXPathContextPtr xpathCtx; 
    xmlXPathObjectPtr xpathObj; 
    
    assert(filename);
    assert(xpathExpr);

    /* 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);
    }
    
    /* Register namespaces from list (if any) */
    if((nsList != NULL) && (register_namespaces(xpathCtx, nsList) < 0)) {
        fprintf(stderr,"Error: failed to register namespaces list \"%s\"\n", nsList);
        xmlXPathFreeContext(xpathCtx); 
        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);
    }

    /* Print results */
    print_xpath_nodes(xpathObj->nodesetval, stdout);

    /* Cleanup */
    xmlXPathFreeObject(xpathObj);
    xmlXPathFreeContext(xpathCtx); 
    xmlFreeDoc(doc); 
    
    return(0);
}

/**
 * register_namespaces:
 * @xpathCtx:		the pointer to an XPath context.
 * @nsList:		the list of known namespaces in 
 *			"<prefix1>=<href1> <prefix2>=href2> ..." format.
 *
 * Registers namespaces from @nsList in @xpathCtx.
 *
 * Returns 0 on success and a negative value otherwise.
 */
int 
register_namespaces(xmlXPathContextPtr xpathCtx, const xmlChar* nsList) {
    xmlChar* nsListDup;
    xmlChar* prefix;
    xmlChar* href;
    xmlChar* next;
    
    assert(xpathCtx);
    assert(nsList);

    nsListDup = xmlStrdup(nsList);
    if(nsListDup == NULL) {
	fprintf(stderr, "Error: unable to strdup namespaces list\n");
	return(-1);	
    }
    
    next = nsListDup; 
    while(next != NULL) {
	/* skip spaces */
	while((*next) == ' ') next++;
	if((*next) == '\0') break;

	/* find prefix */
	prefix = next;
	next = (xmlChar*)xmlStrchr(next, '=');
	if(next == NULL) {
	    fprintf(stderr,"Error: invalid namespaces list format\n");
	    free(nsListDup);
	    return(-1);	
	}
	*(next++) = '\0';	
	
	/* find href */
	href = next;
	next = (xmlChar*)xmlStrchr(next, ' ');
	if(next != NULL) {
	    *(next++) = '\0';	
	}

	/* do register namespace */
	if(xmlXPathRegisterNs(xpathCtx, prefix, href) != 0) {
	    fprintf(stderr,"Error: unable to register NS with prefix=\"%s\" and href=\"%s\"\n", prefix, href);
	    free(nsListDup);
	    return(-1);	
	}
    }
    
    free(nsListDup);
    return(0);
}

/**
 * print_xpath_nodes:
 * @nodes:		the nodes set.
 * @output:		the output file handle.
 *
 * Prints the @nodes content to @output.
 */
void
print_xpath_nodes(xmlNodeSetPtr nodes, FILE* output) {
    xmlNodePtr cur;
    int size;
    int i;
    
    assert(output);
    size = (nodes) ? nodes->nodeNr : 0;
    
    fprintf(output, "Result (%d nodes):\n", size);
    for(i = 0; i < size; ++i) {
	assert(nodes->nodeTab[i]);
	
	if(nodes->nodeTab[i]->type == XML_NAMESPACE_DECL) {
	    xmlNsPtr ns;
	    
	    ns = (xmlNsPtr)nodes->nodeTab[i];
	    cur = (xmlNodePtr)ns->next;
	    if(cur->ns) { 
	        fprintf(output, "= namespace \"%s\"=\"%s\" for node %s:%s\n", 
		    ns->prefix, ns->href, cur->ns->href, cur->name);
	    } else {
	        fprintf(output, "= namespace \"%s\"=\"%s\" for node %s\n", 
		    ns->prefix, ns->href, cur->name);
	    }
	} else if(nodes->nodeTab[i]->type == XML_ELEMENT_NODE) {
	    cur = nodes->nodeTab[i];   	    
	    if(cur->ns) { 
    	        fprintf(output, "= element node \"%s:%s\"\n", 
		    cur->ns->href, cur->name);
	    } else {
    	        fprintf(output, "= element node \"%s\"\n", 
		    cur->name);
	    }
	} else {
	    cur = nodes->nodeTab[i];    
	    fprintf(output, "= node \"%s\": type %d\n", cur->name, cur->type);
	}
    }
}