/** 
 * verify_file:
 * @mngr:		the pointer to keys manager.
 * @xml_file:		the signed XML file name.
 *
 * Verifies XML signature in #xml_file.
 *
 * Returns 0 on success or a negative value if an error occurs.
 */
int 
verify_file(xmlSecKeysMngrPtr mngr, const char* xml_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr node = NULL;
    xmlSecDSigCtxPtr dsigCtx = NULL;
    int res = -1;
    
    assert(mngr);
    assert(xml_file);
    /* load file */
    doc = xmlParseFile(xml_file);
    if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
	fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
	goto done;	
    }
    
    /* find start node */
    node = xmlSecFindNode(xmlDocGetRootElement(doc), xmlSecNodeSignature, xmlSecDSigNs);
    if(node == NULL) {
	fprintf(stderr, "Error: start node not found in \"%s\"\n", xml_file);
	goto done;	
    }
    /* create signature context */
    dsigCtx = xmlSecDSigCtxCreate(mngr);
    if(dsigCtx == NULL) {
        fprintf(stderr,"Error: failed to create signature context\n");
	goto done;
    }
    /* limit the Reference URI attributes to empty or NULL */
    dsigCtx->enabledReferenceUris = xmlSecTransformUriTypeEmpty;
    
    /* limit allowed transforms for signature and reference processing */
    if((xmlSecDSigCtxEnableSignatureTransform(dsigCtx, xmlSecTransformInclC14NId) < 0) ||
       (xmlSecDSigCtxEnableSignatureTransform(dsigCtx, xmlSecTransformExclC14NId) < 0) ||
       (xmlSecDSigCtxEnableSignatureTransform(dsigCtx, xmlSecTransformSha1Id) < 0) ||
       (xmlSecDSigCtxEnableSignatureTransform(dsigCtx, xmlSecTransformRsaSha1Id) < 0)) {
        fprintf(stderr,"Error: failed to limit allowed signature transforms\n");
	goto done;
    }
    if((xmlSecDSigCtxEnableReferenceTransform(dsigCtx, xmlSecTransformInclC14NId) < 0) ||
       (xmlSecDSigCtxEnableReferenceTransform(dsigCtx, xmlSecTransformExclC14NId) < 0) ||
       (xmlSecDSigCtxEnableReferenceTransform(dsigCtx, xmlSecTransformSha1Id) < 0) ||
       (xmlSecDSigCtxEnableReferenceTransform(dsigCtx, xmlSecTransformEnvelopedId) < 0)) {
        fprintf(stderr,"Error: failed to limit allowed reference transforms\n");
	goto done;
    }
    /* in addition, limit possible key data to valid X509 certificates only */
    if(xmlSecPtrListAdd(&(dsigCtx->keyInfoReadCtx.enabledKeyData), BAD_CAST xmlSecKeyDataX509Id) < 0) {
        fprintf(stderr,"Error: failed to limit allowed key data\n");
	goto done;
    }
    
    /* Verify signature */
    if(xmlSecDSigCtxVerify(dsigCtx, node) < 0) {
        fprintf(stderr,"Error: signature verify\n");
	goto done;
    }
    /* check that we have only one Reference */
    if((dsigCtx->status == xmlSecDSigStatusSucceeded) && 
        (xmlSecPtrListGetSize(&(dsigCtx->signedInfoReferences)) != 1)) {
	
        fprintf(stderr,"Error: only one reference is allowed\n");
	goto done;
    }
        
    /* print verification result to stdout */
    if(dsigCtx->status == xmlSecDSigStatusSucceeded) {
	fprintf(stdout, "Signature is OK\n");
    } else {
	fprintf(stdout, "Signature is INVALID\n");
    }    
    /* success */
    res = 0;
done:    
    /* cleanup */
    if(dsigCtx != NULL) {
	xmlSecDSigCtxDestroy(dsigCtx);
    }
    
    if(doc != NULL) {
	xmlFreeDoc(doc); 
    }
    return(res);
}