From 7903c7c17e01950f27e0c27e2df8db1364a16f28 Mon Sep 17 00:00:00 2001
From: TheLastRar <TheLastRar@users.noreply.github.com>
Date: Sat, 6 Apr 2024 20:36:37 +0100
Subject: [PATCH] DEV9: Improve tracking of acknowledged data

---
 .../DEV9/Sessions/TCP_Session/TCP_Session.cpp | 11 +++++++++++
 pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.h |  3 +++
 .../Sessions/TCP_Session/TCP_Session_In.cpp   | 19 ++++++++++++-------
 .../Sessions/TCP_Session/TCP_Session_Out.cpp  |  2 ++
 4 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.cpp b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.cpp
index 2185ab9a14..f86d2c3cd2 100644
--- a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.cpp
+++ b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.cpp
@@ -39,11 +39,22 @@ namespace Sessions
 
 		_MySequenceNumber += amount;
 	}
+	void TCP_Session::UpdateReceivedAckNumber(u32 ack)
+	{
+		std::lock_guard numberlock(myNumberSentry);
+		if (GetDelta(ack, _ReceivedAckNumber) > 0)
+			_ReceivedAckNumber = ack;
+	}
 	u32 TCP_Session::GetMyNumber()
 	{
 		std::lock_guard numberlock(myNumberSentry);
 		return _MySequenceNumber;
 	}
+	u32 TCP_Session::GetOutstandingSequenceLength()
+	{
+		std::lock_guard numberlock(myNumberSentry);
+		return GetDelta(_MySequenceNumber, _ReceivedAckNumber);
+	}
 	std::tuple<u32, std::vector<u32>> TCP_Session::GetAllMyNumbers()
 	{
 		std::lock_guard numberlock(myNumberSentry);
diff --git a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.h b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.h
index 765574fdca..800466d219 100644
--- a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.h
+++ b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session.h
@@ -71,6 +71,7 @@ namespace Sessions
 		const int oldMyNumCount = 64;
 		u32 _MySequenceNumber = 1;
 		std::vector<u32> _OldMyNumbers;
+		u32 _ReceivedAckNumber = 1;
 		std::atomic<bool> myNumberACKed{true};
 
 	public:
@@ -89,7 +90,9 @@ namespace Sessions
 		PacketReader::IP::TCP::TCP_Packet* PopRecvBuff();
 
 		void IncrementMyNumber(u32 amount);
+		void UpdateReceivedAckNumber(u32 ack);
 		u32 GetMyNumber();
+		u32 GetOutstandingSequenceLength();
 		std::tuple<u32, std::vector<u32>> GetAllMyNumbers();
 		void ResetMyNumbers();
 
diff --git a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_In.cpp b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_In.cpp
index 4fce5d68c2..fde4339d29 100644
--- a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_In.cpp
+++ b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_In.cpp
@@ -67,13 +67,18 @@ namespace Sessions
 				return nullptr;
 		}
 
-		uint maxSize = 0;
-		if (sendTimeStamps)
-			maxSize = std::min<uint>(maxSegmentSize - 12, windowSize.load());
-		else
-			maxSize = std::min<uint>(maxSegmentSize, windowSize.load());
 
-		if (maxSize != 0 &&
+		//Note, windowSize will be updated before _ReceivedAckNumber, potential race condition
+		//in practice, we just get a smaller or -ve maxSize
+		const u32 outstanding = GetOutstandingSequenceLength();
+
+		int maxSize = 0;
+		if (sendTimeStamps)
+			maxSize = std::min<int>(maxSegmentSize - 12, windowSize.load() - outstanding);
+		else
+			maxSize = std::min<int>(maxSegmentSize, windowSize.load() - outstanding);
+
+		if (maxSize > 0 &&
 			myNumberACKed.load())
 		{
 			std::unique_ptr<u8[]> buffer;
@@ -90,7 +95,7 @@ namespace Sessions
 #endif
 			if (err != SOCKET_ERROR)
 			{
-				if (available > maxSize)
+				if (available > static_cast<uint>(maxSize))
 					Console.WriteLn("DEV9: TCP: Got a lot of data: %lu Using: %d", available, maxSize);
 
 				buffer = std::make_unique<u8[]>(maxSize);
diff --git a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_Out.cpp b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_Out.cpp
index 9eed93ca27..e67b31b005 100644
--- a/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_Out.cpp
+++ b/pcsx2/DEV9/Sessions/TCP_Session/TCP_Session_Out.cpp
@@ -442,6 +442,8 @@ namespace Sessions
 			myNumberACKed.store(true);
 		}
 
+		UpdateReceivedAckNumber(tcp->acknowledgementNumber);
+
 		if (tcp->sequenceNumber != expectedSeqNumber)
 		{
 			if (tcp->GetPayload()->GetLength() == 0)