Layer 2 received packet handling

impl/src/layer2/layer2_rx.c

@@ -0,0 +1,66 @@
+#include <string.h>
+#include <assert.h>
+#include <unistd.h>
+
+#include <errno.h>
+
+#include "layer2_rx.h"
+
+#include "packet_structs.h"
+
+#include "config.h"
+
+result_t layer2_rx_init(layer2_rx_t *ctx, int tun_fd)
+{
+	ctx->last_acked_seq = 0;
+	ctx->tun_fd = tun_fd;
+	return OK;
+}
+
+
+void layer2_rx_destroy(layer2_rx_t *ctx)
+{
+	(void)ctx;
+	// nothing to do here so far
+}
+
+
+result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t buf_len)
+{
+	// check the CRC
+	size_t packet_size = buf_len - crc_sizeof_key(PAYLOAD_CRC_SCHEME);
+
+	if(!crc_check_key(PAYLOAD_CRC_SCHEME, (unsigned char*)buf, packet_size)) {
+		LOG(LVL_ERR, "payload CRC check failed!");
+		return ERR_INTEGRITY;
+	}
+
+	// decode the header
+	layer2_packet_header_t header;
+
+	if(!layer2_decode_packet_header(buf, buf_len, &header)) {
+		LOG(LVL_ERR, "Header could not be decoded!");
+		return ERR_INTEGRITY;
+	}
+
+	ctx->last_acked_seq = header.rx_seq_nr;
+
+	size_t header_size = layer2_get_encoded_header_size(&header);
+
+	// extract the payload and forward it to the tun device
+	const uint8_t *payload = buf + header_size;
+	size_t payload_len = packet_size - header_size;
+
+	int ret = write(ctx->tun_fd, payload, payload_len);
+	if(ret < 0) {
+		LOG(LVL_ERR, "write: %s", strerror(errno));
+	}
+
+	return OK;
+}
+
+
+uint8_t layer2_rx_get_last_acked_seq(const layer2_rx_t *ctx)
+{
+	return ctx->last_acked_seq;
+}

impl/src/layer2/layer2_rx.h

@@ -0,0 +1,38 @@
+#ifndef LAYER2_RX_H
+#define LAYER2_RX_H
+
+#include <results.h>
+
+typedef struct {
+	uint8_t last_acked_seq;
+
+	int tun_fd;
+} layer2_rx_t;
+
+
+/*!\brief Initialize the layer 2 receiver context.
+ *
+ * \param ctx       The receiver context to initialize.
+ * \param tun_fd    The TUN device to read packets from.
+ * \returns OK if everything worked or a fitting error code.
+ */
+result_t layer2_rx_init(layer2_rx_t *ctx, int tun_fd);
+
+/*!\brief Destroy the given layer 2 receiver context.
+ */
+void layer2_rx_destroy(layer2_rx_t *ctx);
+
+/*!\brief Handle a received packet.
+ *
+ * \param ctx         The receiver context.
+ * \param buf         Where to write the encoded packet data.
+ * \param buf_len     Space available in the buffer.
+ * \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);
+
+/*!\brief Return the sequence number expected next by the other side.
+ */
+uint8_t layer2_rx_get_last_acked_seq(const layer2_rx_t *ctx);
+
+#endif // LAYER2_RX_H

impl/src/layer2/layer2_tx.c

@@ -14,11 +14,12 @@
 
 #define SEQ_NR_MASK 0xF
 
-result_t layer2_tx_init(layer2_tx_t *ctx)
+result_t layer2_tx_init(layer2_tx_t *ctx, int tun_fd)
 {
 	packet_queue_init(&ctx->packet_queue);
 	ctx->next_packet_index = 0;
 	ctx->next_seq_nr = 0;
+	ctx->tun_fd = tun_fd;
 	return OK;
 }
 
@@ -29,11 +30,11 @@ void layer2_tx_destroy(layer2_tx_t *ctx)
 }
 
 
-result_t layer2_tx_fill_packet_queue(layer2_tx_t *ctx, int tun_fd)
+result_t layer2_tx_fill_packet_queue(layer2_tx_t *ctx)
 {
 	struct pollfd pfd = {0};
 
-	pfd.fd = tun_fd;
+	pfd.fd = ctx->tun_fd;
 	pfd.events = POLLIN;
 
 	layer2_packet_header_t header;
@@ -59,7 +60,7 @@ result_t layer2_tx_fill_packet_queue(layer2_tx_t *ctx, int tun_fd)
 			header.tx_seq_nr = ctx->next_seq_nr;
 
 			uint8_t packetbuf[2048];
-			ret = read(tun_fd, packetbuf, sizeof(packetbuf));
+			ret = read(ctx->tun_fd, packetbuf, sizeof(packetbuf));
 			if(ret < 0) {
 				LOG(LVL_ERR, "read: %s", strerror(errno));
 				return ERR_SYSCALL;

impl/src/layer2/layer2_tx.h

@@ -7,14 +7,21 @@
 
 typedef struct {
 	packet_queue_t packet_queue;
+
 	size_t next_packet_index;
 	uint8_t next_seq_nr;
+
+	int tun_fd;
 } layer2_tx_t;
 
 
 /*!\brief Initialize the layer 2 transmitter context.
+ *
+ * \param ctx       The transmitter context to initialize.
+ * \param tun_fd    The TUN device to read packets from.
+ * \returns OK if everything worked or a fitting error code.
  */
-result_t layer2_tx_init(layer2_tx_t *ctx);
+result_t layer2_tx_init(layer2_tx_t *ctx, int tun_fd);
 
 /*!\brief Destroy the given layer 2 transmitter context.
  */
@@ -22,9 +29,8 @@ void layer2_tx_destroy(layer2_tx_t *ctx);
 
 /*!\brief Fill the packet queue from the given TUN device.
  * \param ctx       The transmitter context.
- * \param tun_fd    File descriptor of the TUN device to read packets from.
  */
-result_t layer2_tx_fill_packet_queue(layer2_tx_t *ctx, int tun_fd);
+result_t layer2_tx_fill_packet_queue(layer2_tx_t *ctx);
 
 /*!\brief Encode the next packet for transmission.
  *

impl/src/layer2/packet_structs.c

@@ -33,6 +33,15 @@ size_t layer2_encode_packet_header(const layer2_packet_header_t *header, uint8_t
 }
 
 
+size_t layer2_get_encoded_header_size(const layer2_packet_header_t *header)
+{
+	assert(header->src_addr.length <= 4 && header->src_addr.length != 0);
+	assert(header->dst_addr.length <= 4 && header->dst_addr.length != 0);
+
+	return 2 + 2 * header->src_addr.length + 2 * header->dst_addr.length;
+}
+
+
 bool layer2_decode_packet_header(const uint8_t *encoded, size_t encoded_len, layer2_packet_header_t *header)
 {
 	// check if there are enough bytes for the minimum header size:
@@ -42,11 +51,11 @@ bool layer2_decode_packet_header(const uint8_t *encoded, size_t encoded_len, lay
 
 	header->msg_type = (encoded[0] >> 5) & 0x7;
 	header->tx_request = (encoded[0] & 0x10) != 0;
-	header->src_addr.length = (encoded[0] >> 2) & 0x3 + 1;
-	header->dst_addr.length = (encoded[0] >> 0) & 0x3 + 1;
+	header->src_addr.length = ((encoded[0] >> 2) & 0x3) + 1;
+	header->dst_addr.length = ((encoded[0] >> 0) & 0x3) + 1;
 
 	// check for the actually needed size
-	if(encoded_len < (2 + 2*header->src_addr.length + 2*header->dst_addr.length)) {
+	if(encoded_len < (2U + 2*header->src_addr.length + 2*header->dst_addr.length)) {
 		return false;
 	}
 

impl/src/layer2/packet_structs.h

@@ -47,6 +47,12 @@ typedef struct layer2_packet_header_s {
  */
 size_t layer2_encode_packet_header(const layer2_packet_header_t *header, uint8_t *encoded);
 
+/*!\brief Get the size of a layer2 packet header in encoded form.
+ * \param header   The header structure.
+ * \returns        The number of encoded bytes.
+ */
+size_t layer2_get_encoded_header_size(const layer2_packet_header_t *header);
+
 /*!\brief Decode a layer2 packet header from the received form.
  * \param encoded      A byte array containing the received header.
  * \param encoded_len  Length (in bytes) of the given encoded data.

impl/src/main.c

@@ -21,8 +21,10 @@
 #include "layer1/tx.h"
 #include "layer1/rx.h"
 
-#include "layer2/tundev.h"
 #include "layer2/layer2_tx.h"
+#include "layer2/layer2_rx.h"
+
+#include "layer2/tundev.h"
 
 #include "sdr/sdr.h"
 
@@ -43,6 +45,8 @@ static double next_tx_switch_time = 0.0;
 
 static rx_stats_t m_rx_stats;
 
+static layer2_rx_t l2rx;
+
 static void signal_handler(int signal, siginfo_t *info, void *ctx)
 {
 	(void)signal;
@@ -93,22 +97,24 @@ void cb_rx(rx_evt_t evt, const struct layer1_rx_s *rx, uint8_t *packet_data, siz
 			//hexdump(packet_data, packet_len < 64 ? packet_len : 64);
 			//LOG(LVL_INFO, "====================================");
 
-			m_rx_stats.successful_decodes++;
-
 			block_tx_for(TX_SWITCH_BACKOFF_END_OF_PACKET_MS);
 
-			unsigned int data_size = packet_len - crc_sizeof_key(PAYLOAD_CRC_SCHEME);
+			result_t result = layer2_rx_handle_packet(&l2rx, packet_data, packet_len);
+			switch(result) {
+				case OK:
+					m_rx_stats.successful_decodes++;
+					break;
 
-			// FIXME: move to layer 2
-			if(!crc_check_key(PAYLOAD_CRC_SCHEME, packet_data, data_size)) {
-				LOG(LVL_WARN, "payload CRC check failed!");
-				break;
+				case ERR_INTEGRITY:
+					LOG(LVL_ERR, "Packet could not be decoded by Layer 2.");
+					m_rx_stats.failed_decodes++;
+					break;
+
+				default: // all other errors
+					LOG(LVL_ERR, "layer2_rx_handle_packet() returned error code %u.", result);
+					break;
 			}
 
-			ret = write(m_tunfd, packet_data, data_size);
-			if(ret < 0) {
-				LOG(LVL_ERR, "write: %s", strerror(errno));
-			}
 			break;
 
 		case RX_EVT_PREAMBLE_FOUND:
@@ -179,7 +185,8 @@ int main(int argc, char **argv)
 	RESULT_CHECK(layer1_tx_init(&tx));
 	RESULT_CHECK(layer1_rx_init(&rx, cb_rx));
 
-	RESULT_CHECK(layer2_tx_init(&l2tx));
+	RESULT_CHECK(layer2_tx_init(&l2tx, m_tunfd));
+	RESULT_CHECK(layer2_rx_init(&l2rx, m_tunfd));
 
 	// ** Set up signal handling
 
@@ -217,7 +224,7 @@ int main(int argc, char **argv)
 		double now = get_hires_time();
 
 		// fill the TX queue from the TUN device
-		layer2_tx_fill_packet_queue(&l2tx, m_tunfd);
+		layer2_tx_fill_packet_queue(&l2tx);
 
 		if((now > next_tx_switch_time) && (on_air || !layer1_rx_is_busy(&rx))) {
 			if(layer2_tx_can_transmit(&l2tx)) {
@@ -355,6 +362,7 @@ int main(int argc, char **argv)
 	// ** Cleanup **
 
 	layer2_tx_destroy(&l2tx);
+	layer2_rx_destroy(&l2rx);
 
 	layer1_tx_shutdown(&tx);
 	layer1_rx_shutdown(&rx);

impl/src/results.h

@@ -13,6 +13,7 @@ typedef enum {
 	ERR_SYSCALL,        // a syscall failed. Use errno to determine the cause.
 	ERR_SOAPY,          // an error occurred in the SoapySDR library.
 	ERR_SDR,            // an error occurred in the SDR interface.
+	ERR_INTEGRITY,      // an integrity check failed (e.g. CRC of received packet is wrong)
 } result_t;
 
 #ifdef DEBUG_LIQUID