From b5d00ca5bc86bd9a95efdf0956e1e8374bf9f661 Mon Sep 17 00:00:00 2001
From: Vivek Jain <jain.vivek.anand@gmail.com>
Date: Mon, 23 Sep 2024 13:45:35 -0700
Subject: [PATCH] tcp: (fixes #1126) Fix bytesAcked calculation in ProcessAck

* Updated the `bytesAcked` assignment to use `currentDelivered` instead
of calculating it from `ackNumber` and `oldHeadSequence` for better
accuracy in acknowledgment handling.
* Added `currentDelivered` and `oldHeadSequence` to the NS_LOG_FUNCTION
call for improved logging and debugging.
---
 src/internet/model/tcp-socket-base.cc | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/internet/model/tcp-socket-base.cc b/src/internet/model/tcp-socket-base.cc
index fd3cff380..361dfb7f4 100644
--- a/src/internet/model/tcp-socket-base.cc
+++ b/src/internet/model/tcp-socket-base.cc
@@ -1964,7 +1964,7 @@ TcpSocketBase::ProcessAck(const SequenceNumber32& ackNumber,
                           uint32_t currentDelivered,
                           const SequenceNumber32& oldHeadSequence)
 {
-    NS_LOG_FUNCTION(this << ackNumber << scoreboardUpdated);
+    NS_LOG_FUNCTION(this << ackNumber << scoreboardUpdated << currentDelivered << oldHeadSequence);
     // RFC 6675, Section 5, 2nd paragraph:
     // If the incoming ACK is a cumulative acknowledgment, the TCP MUST
     // reset DupAcks to zero.
@@ -2030,7 +2030,7 @@ TcpSocketBase::ProcessAck(const SequenceNumber32& ackNumber,
     {
         // Please remember that, with SACK, we can enter here even if we
         // received a dupack.
-        bytesAcked = ackNumber - oldHeadSequence;
+        bytesAcked = currentDelivered;
         uint32_t segsAcked = bytesAcked / m_tcb->m_segmentSize;
         m_bytesAckedNotProcessed += bytesAcked % m_tcb->m_segmentSize;
         bytesAcked -= bytesAcked % m_tcb->m_segmentSize;
@@ -2041,6 +2041,8 @@ TcpSocketBase::ProcessAck(const SequenceNumber32& ackNumber,
             bytesAcked += m_tcb->m_segmentSize;
             m_bytesAckedNotProcessed -= m_tcb->m_segmentSize;
         }
+        NS_LOG_DEBUG("Set segsAcked: " << segsAcked
+                                       << " based on currentDelivered: " << currentDelivered);
 
         // Dupack count is reset to eventually fast-retransmit after 3 dupacks.
         // Any SACK-ed segment will be cleaned up by DiscardUpTo.