[core] Refactored ACK window management to avoid false error reports

srtcore/core.cpp

@@ -1053,7 +1053,7 @@ void srt::CUDT::clearData()
     // XXX use some constant for this 16
     m_iDeliveryRate     = 16;
     m_iByteDeliveryRate = 16 * m_iMaxSRTPayloadSize;
-    m_iAckSeqNo         = 0;
+    m_iAckJournal       = 0;
     m_tsLastAckTime     = steady_clock::now();
 
     // trace information
@@ -8543,7 +8543,7 @@ int srt::CUDT::sendCtrlAck(CPacket& ctrlpkt, int size)
         // than sequence number (it's a "journal" for ACK request-response,
         // and starts from 0, unlike sequence, which starts from a random
         // number), but still the numbers are from exactly the same domain.
-        m_iAckSeqNo = CAckNo::incack(m_iAckSeqNo);
+        m_iAckJournal = CAckNo::incack(m_iAckJournal);
         data[ACKD_RCVLASTACK] = m_iRcvLastAck;
         data[ACKD_RTT] = m_iSRTT;
         data[ACKD_RTTVAR] = m_iRTTVar;
@@ -8572,12 +8572,12 @@ int srt::CUDT::sendCtrlAck(CPacket& ctrlpkt, int size)
             }
             // ELSE: leave the buffer with ...UDTBASE size.
 
-            ctrlpkt.pack(UMSG_ACK, &m_iAckSeqNo, data, ctrlsz);
+            ctrlpkt.pack(UMSG_ACK, &m_iAckJournal, data, ctrlsz);
             m_tsLastAckTime = steady_clock::now();
         }
         else
         {
-            ctrlpkt.pack(UMSG_ACK, &m_iAckSeqNo, data, ACKD_FIELD_SIZE * ACKD_TOTAL_SIZE_SMALL);
+            ctrlpkt.pack(UMSG_ACK, &m_iAckJournal, data, ACKD_FIELD_SIZE * ACKD_TOTAL_SIZE_SMALL);
         }
         bufflock.unlock();
 
@@ -8586,7 +8586,7 @@ int srt::CUDT::sendCtrlAck(CPacket& ctrlpkt, int size)
         nbsent = m_pSndQueue->sendto(m_PeerAddr, ctrlpkt, m_SourceAddr);
         DebugAck(CONID() + "sendCtrl(UMSG_ACK): ", local_prevack, ack);
 
-        m_ACKWindow.store(m_iAckSeqNo, m_iRcvLastAck);
+        m_ACKWindow.store(m_iAckJournal, m_iRcvLastAck);
 
         enterCS(m_StatsLock);
         m_stats.rcvr.sentAck.count(1);
@@ -8956,19 +8956,21 @@ void srt::CUDT::processCtrlAckAck(const CPacket& ctrlpkt, const time_point& tsAr
     int32_t ack = 0;
 
     // Calculate RTT estimate on the receiver side based on ACK/ACKACK pair.
-    const int rtt = m_ACKWindow.acknowledge(ctrlpkt.getAckSeqNo(), ack, tsArrival);
-
-    if (rtt == -1)
+    int rtt = 0;
+    const ACKWindow::Status astat = m_ACKWindow.acknowledge(ctrlpkt.getAckSeqNo(), tsArrival, (ack), (rtt));
+    if (astat != ACKWindow::OK)
     {
-        if (ctrlpkt.getAckSeqNo() > (m_iAckSeqNo - static_cast<int>(ACK_WND_SIZE)) && ctrlpkt.getAckSeqNo() <= m_iAckSeqNo)
+        if (astat != ACKWindow::OLD) // ignore old - can't measure, but that's not a problem
         {
             string why;
             if (frequentLogAllowed(FREQLOGFA_ACKACK_OUTOFORDER, tsArrival, (why)))
             {
-                LOGC(inlog.Note,
-                    log << CONID() << "ACKACK out of order, skipping RTT calculation "
-                    << "(ACK number: " << ctrlpkt.getAckSeqNo() << ", last ACK sent: " << m_iAckSeqNo
-                    << ", RTT (EWMA): " << m_iSRTT << ")." << why);
+                // For WIPED and ROGUE report this by an error log; this is an unwanted situation.
+                LOGC(inlog.Error,
+                        log << CONID() << "IPE/EPE: ACK node overwritten when acknowledging "
+                        << ctrlpkt.getAckSeqNo()
+                        << (astat == ACKWindow::WIPED ? ": No such node recorded when ACKing"
+                            : ": ROGUE journal value"));
             }
 #if SRT_ENABLE_FREQUENT_LOG_TRACE
             else
@@ -8977,13 +8979,8 @@ void srt::CUDT::processCtrlAckAck(const CPacket& ctrlpkt, const time_point& tsAr
             }
 #endif
 
-            return;
         }
 
-        LOGC(inlog.Error,
-             log << CONID() << "ACK record not found, can't estimate RTT "
-                 << "(ACK number: " << ctrlpkt.getAckSeqNo() << ", last ACK sent: " << m_iAckSeqNo
-                 << ", RTT (EWMA): " << m_iSRTT << ")");
         return;
     }
 

srtcore/core.h

@@ -1138,7 +1138,7 @@ class CUDT
     int32_t m_iDebugPrevLastAck;
 #endif
     int32_t m_iRcvLastAckAck;                    // (RCV) Latest packet seqno in a sent ACK acknowledged by ACKACK. RcvQTh (sendCtrlAck {r}, processCtrlAckAck {r}, processCtrlAck {r}, connection {w}).
-    int32_t m_iAckSeqNo;                         // Last ACK sequence number
+    int32_t m_iAckJournal;                       // Last ACK sequence number
     sync::atomic<int32_t> m_iRcvCurrSeqNo;       // (RCV) Largest received sequence number. RcvQTh, TSBPDTh.
     int32_t m_iRcvCurrPhySeqNo;                  // Same as m_iRcvCurrSeqNo, but physical only (disregarding a filter)
     bool m_bBufferWasFull;                        // Indicate that RX buffer was full last time a ack was sent