Add FEC state validation in debug builds

src/RtpAudioQueue.c

@@ -35,6 +35,52 @@ void RtpaInitializeQueue(PRTP_AUDIO_QUEUE queue) {
     memcpy(queue->rs->parity, parity, sizeof(parity));
 }
 
+static void validateFecBlockState(PRTP_AUDIO_QUEUE queue) {
+#ifdef LC_DEBUG
+    PRTPA_FEC_BLOCK lastBlock = queue->blockHead;
+
+    // The next sequence number must not be less than the oldest BSN unless we're in the
+    // starting state (prior to us setting nextRtpSequenceNumber and oldestRtpBaseSequenceNumber).
+    LC_ASSERT(!isBefore16(queue->nextRtpSequenceNumber, queue->oldestRtpBaseSequenceNumber) ||
+              (queue->nextRtpSequenceNumber == UINT16_MAX && queue->oldestRtpBaseSequenceNumber == 0));
+
+    if (lastBlock == NULL) {
+        return;
+    }
+
+    uint16_t lastSeqNum = lastBlock->fecHeader.baseSequenceNumber;
+    uint32_t lastTs = lastBlock->fecHeader.baseTimestamp;
+
+    // The head should not have a previous entry
+    LC_ASSERT(lastBlock->prev == NULL);
+
+    // The next sequence number must not exceed the first FEC block (otherwise it should have been dequeued and freed)
+    LC_ASSERT(isBefore16(queue->nextRtpSequenceNumber, queue->blockHead->fecHeader.baseSequenceNumber + RTPA_DATA_SHARDS));
+
+    // The first FEC block should not be before the oldest BSN (or we will drop packets that belong in that FEC block).
+    LC_ASSERT(!isBefore16(queue->blockHead->fecHeader.baseSequenceNumber, queue->oldestRtpBaseSequenceNumber));
+
+    PRTPA_FEC_BLOCK block = lastBlock->next;
+    while (block != NULL) {
+        // Ensure the list is sorted correctly
+        LC_ASSERT(isBefore16(lastSeqNum, block->fecHeader.baseSequenceNumber));
+        LC_ASSERT(isBefore32(lastTs, block->fecHeader.baseTimestamp));
+
+        // Ensure entry invariants are satisfied
+        LC_ASSERT(block->blockSize == lastBlock->blockSize);
+        LC_ASSERT(block->fecHeader.payloadType == lastBlock->fecHeader.payloadType);
+        LC_ASSERT(block->fecHeader.ssrc == lastBlock->fecHeader.ssrc);
+
+        // Ensure the list itself is consistent
+        LC_ASSERT(block->prev == lastBlock);
+        LC_ASSERT(block->next != NULL || queue->blockTail == block);
+
+        lastBlock = block;
+        block = block->next;
+    }
+#endif
+}
+
 static void freeFecBlockHead(PRTP_AUDIO_QUEUE queue) {
     PRTPA_FEC_BLOCK blockHead = queue->blockHead;
 
@@ -49,6 +95,8 @@ static void freeFecBlockHead(PRTP_AUDIO_QUEUE queue) {
 
     queue->oldestRtpBaseSequenceNumber = blockHead->fecHeader.baseSequenceNumber + RTPA_DATA_SHARDS;
 
+    validateFecBlockState(queue);
+
     free(blockHead);
 }
 
@@ -70,6 +118,8 @@ static PRTPA_FEC_BLOCK getFecBlockForRtpPacket(PRTP_AUDIO_QUEUE queue, PRTP_PACK
     uint16_t blockSize;
     uint8_t fecBlockPayloadType;
 
+    validateFecBlockState(queue);
+
     if (packet->packetType == 97) {
         if (length < sizeof(RTP_PACKET)) {
             Limelog("RTP audio data packet too small: %u\n", length);
@@ -201,6 +251,8 @@ static PRTPA_FEC_BLOCK getFecBlockForRtpPacket(PRTP_AUDIO_QUEUE queue, PRTP_PACK
         }
     }
 
+    validateFecBlockState(queue);
+
     return block;
 }
 
@@ -295,6 +347,7 @@ static bool completeFecBlock(PRTP_AUDIO_QUEUE queue, PRTPA_FEC_BLOCK block) {
 
         LC_ASSERT(recoveryErrors == 0);
     }
+
     free(droppedRtpPacket);
 #endif
 
@@ -329,8 +382,6 @@ static bool enforceQueueConstraints(PRTP_AUDIO_QUEUE queue) {
 }
 
 int RtpaAddPacket(PRTP_AUDIO_QUEUE queue, PRTP_PACKET packet, uint16_t length) {
-    LC_ASSERT(!queue->blockHead || isBefore16(queue->nextRtpSequenceNumber, queue->blockHead->fecHeader.baseSequenceNumber + RTPA_DATA_SHARDS));
-
     PRTPA_FEC_BLOCK fecBlock = getFecBlockForRtpPacket(queue, packet, length);
     if (fecBlock == NULL) {
         // Reject the packet
@@ -397,6 +448,9 @@ int RtpaAddPacket(PRTP_AUDIO_QUEUE queue, PRTP_PACKET packet, uint16_t length) {
             LC_ASSERT(fecBlock->nextDataPacketIndex == RTPA_DATA_SHARDS);
             freeFecBlockHead(queue);
         }
+        else {
+            validateFecBlockState(queue);
+        }
 
         return RTPQ_RET_HANDLE_NOW;
     }
@@ -430,6 +484,8 @@ int RtpaAddPacket(PRTP_AUDIO_QUEUE queue, PRTP_PACKET packet, uint16_t length) {
             queue->nextRtpSequenceNumber = queue->blockHead->fecHeader.baseSequenceNumber;
         }
 
+        validateFecBlockState(queue);
+
         return RTPQ_RET_PACKET_READY;
     }
 
@@ -437,6 +493,8 @@ int RtpaAddPacket(PRTP_AUDIO_QUEUE queue, PRTP_PACKET packet, uint16_t length) {
 }
 
 PRTP_PACKET RtpaGetQueuedPacket(PRTP_AUDIO_QUEUE queue, uint16_t customHeaderLength, uint16_t* length) {
+    validateFecBlockState(queue);
+
     // If we're returning audio data even with discontinuities, find the next data packet
     if (queue->blockHead != NULL && queue->blockHead->allowDiscontinuity) {
         PRTPA_FEC_BLOCK nextBlock = queue->blockHead;
@@ -458,6 +516,9 @@ PRTP_PACKET RtpaGetQueuedPacket(PRTP_AUDIO_QUEUE queue, uint16_t customHeaderLen
         if (nextBlock->nextDataPacketIndex == RTPA_DATA_SHARDS) {
             freeFecBlockHead(queue);
         }
+        else {
+            validateFecBlockState(queue);
+        }
     }
 
     // Return the next RTP sequence number by indexing into the most recent FEC block
@@ -478,6 +539,9 @@ PRTP_PACKET RtpaGetQueuedPacket(PRTP_AUDIO_QUEUE queue, uint16_t customHeaderLen
         if (nextBlock->nextDataPacketIndex == RTPA_DATA_SHARDS) {
             freeFecBlockHead(queue);
         }
+        else {
+            validateFecBlockState(queue);
+        }
 
         return packet;
     }