Implement xccdf_session_result_reset function in XCCDF session API

This change adds a new public xccdf_session_result_reset function
to the XCCDF session API.

This function resets XCCDF session results, so xccdf_session_evaluate
could be called again from a clean state, without having to call
xccdf_session_free, which would imply to parse the XCCDF file again.

This function resets XCCDF policies, session rules, skipped rules,
OVAL system characteristics and OVAL results.

src/OVAL/oval_agent.c

@@ -255,6 +255,19 @@ int oval_agent_reset_session(oval_agent_session_t * ag_sess) {
 	return 0;
 }
 
+void oval_agent_reset_syschar(oval_agent_session_t * ag_sess) {
+	oval_syschar_model_reset(ag_sess->sys_model);
+}
+
+void oval_agent_reset_results(oval_agent_session_t * ag_sess) {
+#if defined(OVAL_PROBES_ENABLED)
+	oval_results_model_free(ag_sess->res_model);
+	ag_sess->res_model = oval_results_model_new_with_probe_session(
+			ag_sess->def_model, ag_sess->sys_models, ag_sess->psess);
+	oval_probe_session_reinit(ag_sess->psess, ag_sess->sys_model);
+#endif
+}
+
 int oval_agent_abort_session(oval_agent_session_t *ag_sess)
 {
 	if (ag_sess == NULL) {

src/OVAL/public/oval_agent_api.h

@@ -96,6 +96,16 @@ OSCAP_API struct oval_result_definition * oval_agent_get_result_definition(oval_
  */
 OSCAP_API int oval_agent_reset_session(oval_agent_session_t * ag_sess);
 
+/**
+ * Clean system characteristics that were generated in this agent session
+ */
+OSCAP_API void oval_agent_reset_syschar(oval_agent_session_t * ag_sess);
+
+/**
+ * Clean results that were generated in this agent session
+ */
+OSCAP_API void oval_agent_reset_results(oval_agent_session_t * ag_sess);
+
 /**
  * Abort a running probe session
  */

src/XCCDF/public/xccdf_session.h

@@ -81,6 +81,14 @@ OSCAP_API struct xccdf_session *xccdf_session_new_from_source(struct oscap_sourc
  */
 OSCAP_API void xccdf_session_free(struct xccdf_session *session);
 
+/**
+ * Reset xccdf_session results.
+ * This function resets XCCDF policies, session rules, skipped rules, OVAL system characteristics and OVAL results.
+ * @memberof xccdf_session
+ * @param session to reset results from.
+ */
+OSCAP_API void xccdf_session_result_reset(struct xccdf_session *session);
+
 /**
  * Retrieves the filename the session was created with
  * @memberof xccdf_session

src/XCCDF/xccdf_session.c

@@ -362,6 +362,40 @@ void xccdf_session_free(struct xccdf_session *session)
 	free(session);
 }
 
+static void _xccdf_session_reset_oval_agents_syschar(struct xccdf_session *session)
+{
+	if (session->oval.agents != NULL) {
+		for (int i=0; session->oval.agents[i]; i++) {
+			oval_agent_reset_syschar(session->oval.agents[i]);
+		}
+	}
+}
+
+static void _xccdf_session_reset_oval_agents_results(struct xccdf_session *session)
+{
+	if (session->oval.agents != NULL) {
+		for (int i=0; session->oval.agents[i]; i++) {
+			oval_agent_reset_results(session->oval.agents[i]);
+		}
+	}
+}
+
+void xccdf_session_result_reset(struct xccdf_session *session)
+{
+	if (session->xccdf.policy_model != NULL) {
+		oscap_list_free(session->xccdf.policy_model->policies, (oscap_destruct_func) xccdf_policy_free);
+		session->xccdf.policy_model->policies = oscap_list_new();
+	}
+
+	oscap_list_free(session->rules, (oscap_destruct_func) free);
+	session->rules = oscap_list_new();
+	oscap_list_free(session->skip_rules, (oscap_destruct_func) free);
+	session->skip_rules = oscap_list_new();
+
+	_xccdf_session_reset_oval_agents_syschar(session);
+	_xccdf_session_reset_oval_agents_results(session);
+}
+
 const char *xccdf_session_get_filename(const struct xccdf_session *session)
 {
 	return oscap_source_readable_origin(session->source);