add dns_message_renderreset()

lib/dns/include/dns/message.h

@@ -450,6 +450,20 @@ dns_message_renderend(dns_message_t *msg);
  *	DNS_R_SUCCESS		-- all is well.
  */
 		      
+void
+dns_message_renderreset(dns_message_t *msg);
+/*
+ * Reset the message so that it may be rendered again.
+ *
+ * Notes:
+ *
+ *	If dns_message_renderbegin() has been called, dns_message_renderend()
+ *	must be called before calling this function.
+ *
+ * Requires:
+ *
+ *	'msg' be a valid message with rendering intent.
+ */
 
 isc_result_t
 dns_message_firstname(dns_message_t *msg, dns_section_t section);

lib/dns/message.c

@@ -1684,6 +1684,35 @@ dns_message_renderend(dns_message_t *msg)
 	return (DNS_R_SUCCESS);
 }
 
+void
+dns_message_renderreset(dns_message_t *msg)
+{
+	unsigned int i;
+	dns_name_t *name;
+	dns_rdataset_t *rds;
+
+	/*
+	 * Reset the message so that it may be rendered again.
+	 */
+
+	REQUIRE(DNS_MESSAGE_VALID(msg));
+	REQUIRE(msg->from_to_wire == DNS_MESSAGE_INTENTRENDER);
+
+	for (i = 0; i < DNS_SECTION_MAX; i++) {
+		msg->cursors[i] = NULL;
+		msg->counts[i] = 0;
+		for (name = ISC_LIST_HEAD(msg->sections[i]);
+		     name != NULL;
+		     name = ISC_LIST_NEXT(name, link)) {
+			for (rds = ISC_LIST_HEAD(name->list);
+			     rds != NULL;
+			     rds = ISC_LIST_NEXT(rds, link)) {
+				rds->attributes &= ~DNS_RDATASETATTR_RENDERED;
+			}
+		}
+	}
+}
+
 isc_result_t
 dns_message_firstname(dns_message_t *msg, dns_section_t section)
 {