send empty SDATA batch if no recommendation is available yet, but in order to avoid loops only if no empty CDATA batch was received

src/libcharon/plugins/tnccs_20/batch/pb_tnc_batch.c

@@ -272,6 +272,8 @@ static status_t process_batch_header(private_pb_tnc_batch_t *this,
 								  PB_ERROR_UNEXPECTED_BATCH_TYPE);
 		goto fatal;
 	}
+	DBG1(DBG_TNC, "processing PB-TNC %N batch", pb_tnc_batch_type_names,
+												this->type);
 
 	/* Batch Length */
 	if (this->encoding.len != batch_len)
@@ -284,6 +286,13 @@ static status_t process_batch_header(private_pb_tnc_batch_t *this,
 	}
 
 	this->offset = PB_TNC_BATCH_HEADER_SIZE;
+
+	/* Register an empty CDATA batch with the state machine */
+	if (this->type == PB_BATCH_CDATA)
+	{
+		state_machine->set_empty_cdata(state_machine,
+									   this->offset == this->encoding.len);
+	}
 	return SUCCESS;
 
 fatal:
@@ -459,8 +468,7 @@ METHOD(pb_tnc_batch_t, process, status_t,
 	{
 		return FAILED;
 	}
-	DBG1(DBG_TNC, "processing PB-TNC %N batch", pb_tnc_batch_type_names,
-												this->type);
+
 	while (this->offset < this->encoding.len)
 	{
 		switch (process_tnc_msg(this))

src/libcharon/plugins/tnccs_20/state_machine/pb_tnc_state_machine.c

@@ -70,6 +70,11 @@ struct private_pb_tnc_state_machine_t {
 	 */
 	bool is_server;
 
+	/**
+	 * Informs whether last received PB-TNC CDATA Batch was empty
+	 */
+	bool empty_cdata;
+
 	/**
 	 * Current PB-TNC state
 	 */
@@ -265,6 +270,22 @@ METHOD(pb_tnc_state_machine_t, send_batch, bool,
 	return TRUE;
 }
 
+METHOD(pb_tnc_state_machine_t, get_empty_cdata, bool,
+	private_pb_tnc_state_machine_t *this)
+{
+	return this->empty_cdata;
+}
+
+METHOD(pb_tnc_state_machine_t, set_empty_cdata, void,
+	private_pb_tnc_state_machine_t *this, bool empty)
+{
+	if (empty)
+	{
+		DBG2(DBG_TNC, "received empty PB-TNC CDATA batch");
+	}
+	this->empty_cdata = empty;
+}
+
 METHOD(pb_tnc_state_machine_t, destroy, void,
 	private_pb_tnc_state_machine_t *this)
 {
@@ -283,6 +304,8 @@ pb_tnc_state_machine_t* pb_tnc_state_machine_create(bool is_server)
 			.get_state = _get_state,
 			.receive_batch = _receive_batch,
 			.send_batch = _send_batch,
+			.get_empty_cdata = _get_empty_cdata,
+			.set_empty_cdata = _set_empty_cdata,
 			.destroy = _destroy,
 		},
 		.is_server = is_server,

src/libcharon/plugins/tnccs_20/state_machine/pb_tnc_state_machine.h

@@ -72,6 +72,20 @@ struct pb_tnc_state_machine_t {
 	 */
 	bool (*send_batch)(pb_tnc_state_machine_t *this, pb_tnc_batch_type_t type);
 
+	/**
+	 * Informs whether the last received PB-TNC CDATA Batch was empty
+	 *
+	 * @result				TRUE if last received PB-TNC CDATA Batch was empty
+	 */
+	bool (*get_empty_cdata)(pb_tnc_state_machine_t *this);
+
+	/**
+	 * Store information whether the received PB-TNC CDATA Batch was empty
+	 *
+	 * @bool empty			set to TRUE if received PB-TNC CDATA Batch was empty
+	 */
+	void (*set_empty_cdata)(pb_tnc_state_machine_t *this, bool empty);
+
 	/**
 	 * Destroys a pb_tnc_state_machine_t object.
 	 */

src/libcharon/plugins/tnccs_20/tnccs_20.c

@@ -632,7 +632,17 @@ METHOD(tls_t, build, status_t,
 	if (this->batch_type == PB_BATCH_NONE && this->is_server &&
 		state == PB_STATE_SERVER_WORKING)
 	{
-		check_and_build_recommendation(this);
+		if (this->state_machine->get_empty_cdata(this->state_machine) ||
+			this->recs->have_recommendation(this->recs, NULL, NULL))
+		{
+			check_and_build_recommendation(this);
+		}
+		else
+		{
+			DBG2(DBG_TNC, "no recommendation available yet, "
+						  "sending empty PB-TNC SDATA batch");
+			this->batch_type = PB_BATCH_SDATA;
+		}
 	}
 
 	if (this->batch_type != PB_BATCH_NONE)