From 41ff743383d954f2347fb54a6794059b6aa49ec4 Mon Sep 17 00:00:00 2001
From: Xiuchao Wu <xiuchao@amazon.com>
Date: Thu, 13 Aug 2020 15:12:00 +0100
Subject: [PATCH] tcp: (merges !368) Fix assert in tx-buffer when loss rate
 high and w/o SACK

---
 src/internet/model/tcp-socket-base.cc |  1 +
 src/internet/model/tcp-tx-buffer.cc   | 22 +++++++++++++++++++++-
 src/internet/model/tcp-tx-buffer.h    | 13 +++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/internet/model/tcp-socket-base.cc b/src/internet/model/tcp-socket-base.cc
index ceae971e2..be2fdda72 100644
--- a/src/internet/model/tcp-socket-base.cc
+++ b/src/internet/model/tcp-socket-base.cc
@@ -1315,6 +1315,7 @@ TcpSocketBase::DoForwardUp (Ptr<Packet> packet, const Address &fromAddress,
       else
         {
           m_sackEnabled = false;
+          m_txBuffer->SetSackEnabled (false);
         }
 
       // When receiving a <SYN> or <SYN-ACK> we should adapt TS to the other end
diff --git a/src/internet/model/tcp-tx-buffer.cc b/src/internet/model/tcp-tx-buffer.cc
index 7e897b656..8d0f9925f 100644
--- a/src/internet/model/tcp-tx-buffer.cc
+++ b/src/internet/model/tcp-tx-buffer.cc
@@ -112,6 +112,18 @@ TcpTxBuffer::SetMaxBufferSize (uint32_t n)
   m_maxBuffer = n;
 }
 
+bool
+TcpTxBuffer::IsSackEnabled (void) const
+{
+  return m_sackEnabled;
+}
+
+void
+TcpTxBuffer::SetSackEnabled (bool enabled)
+{
+  m_sackEnabled = enabled;
+}
+
 uint32_t
 TcpTxBuffer::Available (void) const
 {
@@ -1379,7 +1391,15 @@ void
 TcpTxBuffer::AddRenoSack (void)
 {
   NS_LOG_FUNCTION (this);
-  NS_ASSERT (m_sentList.size () > 1);
+
+  if (m_sackEnabled)
+    {
+      NS_ASSERT (m_sentList.size () > 1);
+    }
+  else
+    {
+      NS_ASSERT (m_sentList.size () > 0);
+    }
 
   m_renoSack = true;
 
diff --git a/src/internet/model/tcp-tx-buffer.h b/src/internet/model/tcp-tx-buffer.h
index e92c272e6..e4e6144d8 100644
--- a/src/internet/model/tcp-tx-buffer.h
+++ b/src/internet/model/tcp-tx-buffer.h
@@ -166,6 +166,18 @@ public:
    */
   void SetMaxBufferSize (uint32_t n);
 
+  /**
+   * \brief check whether SACK is used on the corresponding TCP socket
+   */
+  bool IsSackEnabled (void) const;
+
+  /**
+   * \brief tell tx-buffer whether SACK is used on this TCP socket
+   *
+   * \param enabled whether sack is used
+   */
+  void SetSackEnabled (bool enabled);
+
   /**
    * \brief Returns the available capacity of this buffer
    * \returns available capacity in this Tx window
@@ -606,6 +618,7 @@ private:
   uint32_t m_dupAckThresh {0}; //!< Duplicate Ack threshold from TcpSocketBase
   uint32_t m_segmentSize {0}; //!< Segment size from TcpSocketBase
   bool     m_renoSack {false}; //!< Indicates if AddRenoSack was called
+  bool     m_sackEnabled {true}; //!< Indicates if SACK is enabled on this connection
 
   static Callback<void, TcpTxItem *> m_nullCb; //!< Null callback for an item
 };