Do not transmit an empty packet if an empty packet was received

impl/src/layer2/layer2_rx.c

@@ -29,7 +29,7 @@ void layer2_rx_destroy(layer2_rx_t *ctx)
 }
 
 
-result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t buf_len)
+result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t buf_len, bool *shall_ack)
 {
 	// check the CRC
 	size_t packet_size = buf_len - crc_sizeof_key(PAYLOAD_CRC_SCHEME);
@@ -52,8 +52,11 @@ result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t bu
 
 	ctx->last_acked_seq = header.rx_seq_nr;
 
+	*shall_ack = true;
+
 	switch(header.msg_type) {
 		case L2_MSG_TYPE_EMPTY:
+			*shall_ack = false;
 			LOG(LVL_DEBUG, "Empty packet: accepted ACK for %u.", ctx->last_acked_seq);
 			return OK; // do not write anything to the TUN device
 

impl/src/layer2/layer2_rx.h

@@ -2,6 +2,7 @@
 #define LAYER2_RX_H
 
 #include <results.h>
+#include <stdbool.h>
 
 typedef struct {
 	uint8_t last_acked_seq;
@@ -28,9 +29,10 @@ void layer2_rx_destroy(layer2_rx_t *ctx);
  * \param ctx         The receiver context.
  * \param buf         Where to write the encoded packet data.
  * \param buf_len     Space available in the buffer.
+ * \param shall_ack   Pointer to a boolean that is set to indicate whether this packet should be ACKed or not.
  * \returns           A result code from the packet handling procedure.
  */
-result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t buf_len);
+result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t buf_len, bool *shall_ack);
 
 /*!\brief Return the sequence number expected next by our side.
  */

impl/src/layer2/layer2_tx.c

@@ -160,7 +160,7 @@ void layer2_tx_restart(layer2_tx_t *ctx)
 }
 
 
-void layer2_tx_handle_ack(layer2_tx_t *ctx, uint8_t acked_seq)
+void layer2_tx_handle_ack(layer2_tx_t *ctx, uint8_t acked_seq, bool do_ack)
 {
 	ctx->next_packet_index = 0;
 
@@ -183,7 +183,7 @@ void layer2_tx_handle_ack(layer2_tx_t *ctx, uint8_t acked_seq)
 
 	LOG(LVL_DEBUG, "handling ack for seq_nr %u, removing %zu packets, %zu packets remaining.", acked_seq, packets_to_remove, packets_available);
 
-	if(packets_available == 0) {
+	if(do_ack && packets_available == 0) {
 		// no packets left in queue, but an acknowledgement must be
 		// transmitted. Add an empty packet to do that.
 		result_t res = layer2_tx_add_empty_packet(ctx, false);

impl/src/layer2/layer2_tx.h

@@ -63,8 +63,9 @@ void layer2_tx_restart(layer2_tx_t *ctx);
  *
  * \param ctx       The transmitter context.
  * \param acked_seq The acknowledged (= next expected) sequence number.
+ * \param do_ack    Whether an empty packet shall be generated if the queue is empty.
  */
-void layer2_tx_handle_ack(layer2_tx_t *ctx, uint8_t acked_seq);
+void layer2_tx_handle_ack(layer2_tx_t *ctx, uint8_t acked_seq, bool do_ack);
 
 /*!\brief Check if there are packets queued for transmission.
  */

impl/src/main.c

@@ -101,10 +101,11 @@ void cb_rx(rx_evt_t evt, const struct layer1_rx_s *rx, uint8_t *packet_data, siz
 
 			block_tx_for(TX_SWITCH_BACKOFF_END_OF_PACKET_MS);
 
-			result_t result = layer2_rx_handle_packet(&l2rx, packet_data, packet_len);
+			bool shall_ack;
+			result_t result = layer2_rx_handle_packet(&l2rx, packet_data, packet_len, &shall_ack);
 			switch(result) {
 				case OK:
-					layer2_tx_handle_ack(&l2tx, layer2_rx_get_last_acked_seq(&l2rx));
+					layer2_tx_handle_ack(&l2tx, layer2_rx_get_last_acked_seq(&l2rx), shall_ack);
 					m_rx_stats.successful_decodes++;
 					break;