RCV erase undecrypted packet instead of dropping.

srtcore/buffer_rcv.cpp

@@ -206,6 +206,47 @@ int CRcvBuffer::insert(CUnit* unit)
     return 0;
 }
 
+int CRcvBuffer::erase(int32_t seqno)
+{
+    const int end_pos = incPos(m_iStartPos, m_iMaxPosOff);
+    // Drop by packet seqno range.
+    const int offset = CSeqNo::seqoff(m_iStartSeqNo, seqno);
+    if (offset < 0)
+    {
+        LOGC(rbuflog.Debug, log << "CRcvBuffer.erase(): nothing to erase. Requested @" << seqno
+            << ". Buffer start " << m_iStartSeqNo << ".");
+        return 0;
+    }
+
+    const int pos = incPos(m_iStartPos, offset);
+    if (!m_entries[pos].pUnit)
+        return 0;
+
+    const bool bMsgOrderFlag = packetAt(pos).getMsgOrderFlag();
+    releaseUnitInPos(pos);
+
+    if (m_bMessageAPI && !bMsgOrderFlag && !m_tsbpd.isEnabled())
+    {
+        --m_numOutOfOrderPackets;
+        if (pos == m_iFirstReadableOutOfOrder) {
+            m_iFirstReadableOutOfOrder = -1;
+            updateFirstReadableOutOfOrder();
+        }
+    }
+
+    HLOGC(rbuflog.Debug, log << "CRcvBuffer.erase(): @" << seqno << ".");
+
+    // Check if a unit before m_iFirstNonreadPos was erased.
+    const bool needUpdateNonreadPos = offset <= getRcvDataSize();
+    if (needUpdateNonreadPos)
+    {
+        m_iFirstNonreadPos = m_iStartPos;
+        updateNonreadPos();
+    }
+
+    return 1;
+}
+
 int CRcvBuffer::dropUpTo(int32_t seqno)
 {
     IF_RCVBUF_DEBUG(ScopedLog scoped_log);

srtcore/buffer_rcv.h

@@ -64,6 +64,12 @@ class CRcvBuffer
     // TODO: Previously '-2' also meant 'already acknowledged'. Check usage of this value.
     int insert(CUnit* unit);
 
+    /// Erase a packet from the buffer based on the packet sequence number.
+    /// The entry is marked EntryState_Empty. The CUnit is marked free.
+    /// @param seqno packet sequence number.
+    /// @return the number of packets erased.
+    int erase(int32_t seqno);
+
     /// Drop packets in the receiver buffer from the current position up to the seqno (excluding seqno).
     /// @param [in] seqno drop units up to this sequence number
     /// @return  number of dropped packets.

srtcore/core.cpp

@@ -9850,7 +9850,7 @@ int srt::CUDT::handleSocketPacketReception(const vector<CUnit*>& incoming, bool&
             }
         }
 
-        int buffer_add_result = m_pRcvBuffer->insert(u);
+        const int buffer_add_result = m_pRcvBuffer->insert(u);
         if (buffer_add_result < 0)
         {
             // The insert() result is -1 if at the position evaluated from this packet's
@@ -9878,17 +9878,16 @@ int srt::CUDT::handleSocketPacketReception(const vector<CUnit*>& incoming, bool&
                     adding_successful = false;
                     IF_HEAVY_LOGGING(exc_type = "UNDECRYPTED");
 
-                    // Drop a packet from the receiver buffer.
-                    // Dropping depends on the configuration mode. If message mode is enabled, we have to drop the whole message.
-                    // Otherwise just drop the exact packet.
-                    const int iDropCnt = (m_config.bMessageAPI)
-                        ? m_pRcvBuffer->dropMessage(SRT_SEQNO_NONE, SRT_SEQNO_NONE, u->m_Packet.getMsgSeq(m_bPeerRexmitFlag))
-                        : m_pRcvBuffer->dropMessage(u->m_Packet.getSeqNo(), u->m_Packet.getSeqNo(), SRT_MSGNO_NONE);
+                    // Erase the packet from the receiver buffer.
+                    // In message mode the whole message could be dropped.
+                    // However, when decryption fails the message number in the packet cannot be trusted.
+                    // The packet was added to the buffer based on the sequence number, therefore sequence number should be used to erase it from the buffer.
+                    // TODO: Erasing the packet means it has to be added back to the loss list.
+                    const int iEraseCnt = m_pRcvBuffer->erase(u->m_Packet.getSeqNo());
 
                     LOGC(qrlog.Warn, log << CONID() << "Decryption failed. Seqno %" << u->m_Packet.getSeqNo()
-                        << ", msgno " << u->m_Packet.getMsgSeq(m_bPeerRexmitFlag) << ". Dropping " << iDropCnt << ".");
+                        << ", msgno " << u->m_Packet.getMsgSeq(m_bPeerRexmitFlag) << ".");
                     ScopedLock lg(m_StatsLock);
-                    m_stats.rcvr.dropped.count(stats::BytesPackets(iDropCnt * rpkt.getLength(), iDropCnt));
                     m_stats.rcvr.undecrypted.count(stats::BytesPackets(rpkt.getLength(), 1));
                 }
             }

srtcore/srt.h

@@ -646,7 +646,7 @@ enum SRT_KM_STATE
     SRT_KM_S_NOSECRET      = 3, // Stream encrypted and no secret to decrypt Keying Material
     SRT_KM_S_BADSECRET     = 4 // Stream encrypted and wrong secret is used, cannot decrypt Keying Material
 #ifdef ENABLE_AEAD_API_PREVIEW
-    ,SRT_KM_S_BADCRYPTOMODE = 5  // Stream encrypted but wrong ccryptographic mode is used, cannot decrypt. Since v1.6.0.
+    ,SRT_KM_S_BADCRYPTOMODE = 5  // Stream encrypted but wrong cryptographic mode is used, cannot decrypt. Since v1.6.0.
 #endif
 };