From 6ac11da6e4d9b3121ccf42a5b3d260c69c672d1c Mon Sep 17 00:00:00 2001
From: NepDisk <nepdisk@noreply.codeberg.org>
Date: Sat, 28 Jun 2025 22:53:20 -0400
Subject: [PATCH] Try to fix issues with clients locking up due to never
 receiving acks back in case of dropped packets

https://github.com/Indev450/SRB2Kart-Saturn/pull/151
---
 src/d_net.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/src/d_net.c b/src/d_net.c
index 703f10cde..9e8ab5c57 100644
--- a/src/d_net.c
+++ b/src/d_net.c
@@ -324,11 +324,18 @@ static void RemoveAck(INT32 i)
 		Net_CloseConnection(node);
 }
 
+typedef enum
+{
+	GPACK_OK = 0,
+	GPACK_DUPLICATE,
+	GPACK_OUTOFORDER,
+} goodpacket_e;
+
 // We have got a packet, proceed the ack request and ack return
-static boolean Processackpak(void)
+static int Processackpak(void)
 {
 	INT32 i;
-	boolean goodpacket = true;
+	int goodpacket = GPACK_OK;
 	netnode_t *node = &nodes[doomcom->remotenode];
 
 	// Received an ack return, so remove the ack in the list
@@ -353,7 +360,7 @@ static boolean Processackpak(void)
 		{
 			DEBFILE(va("Discard(1) ack %d (duplicated)\n", ack));
 			duppacket++;
-			goodpacket = false; // Discard packet (duplicate)
+			goodpacket = GPACK_DUPLICATE; // Discard packet (duplicate)
 		}
 		else
 		{
@@ -363,10 +370,10 @@ static boolean Processackpak(void)
 				{
 					DEBFILE(va("Discard(2) ack %d (duplicated)\n", ack));
 					duppacket++;
-					goodpacket = false; // Discard packet (duplicate)
+					goodpacket = GPACK_DUPLICATE; // Discard packet (duplicate)
 					break;
 				}
-			if (goodpacket)
+			if (goodpacket == GPACK_OK)
 			{
 				// Is a good packet so increment the acknowledge number,
 				// Then search for a "hole" in the queue
@@ -427,12 +434,13 @@ static boolean Processackpak(void)
 					else // Buffer full discard packet, sender will resend it
 					{ // We can admit the packet but we will not detect the duplication after :(
 						DEBFILE("no more freeackret\n");
-						goodpacket = false;
+						goodpacket = GPACK_OUTOFORDER;
 					}
 				}
 			}
 		}
 	}
+	// return values: 0 = ok, 1 = duplicate, 2 = out of order
 	return goodpacket;
 }
 
@@ -1125,6 +1133,7 @@ boolean HGetPacket(void)
 	while(true)
 	{
 		//nodejustjoined = I_NetGet();
+		int goodpacket;
 		I_NetGet();
 
 		if (doomcom->remotenode == -1) // No packet received
@@ -1170,8 +1179,15 @@ boolean HGetPacket(void)
 		}*/
 
 		// Proceed the ack and ackreturn field
-		if (!Processackpak())
+		goodpacket = Processackpak();
+		if (goodpacket != GPACK_OK)
+		{
+			// resend the ACK in case the previous ACK didn't reach the client.
+			// prevents the client's netbuffer from locking up.
+			if (goodpacket == GPACK_DUPLICATE)
+				Net_SendAcks(doomcom->remotenode);
 			continue; // discarded (duplicated)
+		}
 
 		// A packet with just ackreturn
 		if (netbuffer->packettype == PT_NOTHING)