From 08feb25f76d8f1c773e50a4e4ada6fb3ca742fa1 Mon Sep 17 00:00:00 2001
From: Oliver Schramm <oliver.schramm97@gmail.com>
Date: Sat, 9 Jan 2021 19:55:14 +0100
Subject: [PATCH] Don't ack unreceived packets

---
 Hazel.UnitTests/UdpReliabilityTests.cs | 30 ++++++++++++++++++++++++++
 Hazel/Udp/UdpConnection.Reliable.cs    | 12 ++++++-----
 2 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/Hazel.UnitTests/UdpReliabilityTests.cs b/Hazel.UnitTests/UdpReliabilityTests.cs
index d313cdf..ef36485 100644
--- a/Hazel.UnitTests/UdpReliabilityTests.cs
+++ b/Hazel.UnitTests/UdpReliabilityTests.cs
@@ -46,6 +46,36 @@ namespace Hazel.UnitTests
             }
         }
 
+        [TestMethod]
+        public void TestAcksForNotReceivedMessages()
+        {
+            List<MessageReader> messagesReceived = new List<MessageReader>();
+
+            UdpConnectionTestHarness dut = new UdpConnectionTestHarness();
+            dut.DataReceived += evt =>
+            {
+                messagesReceived.Add(evt.Message);
+            };
+
+            MessageWriter data = MessageWriter.Get(SendOption.Reliable);
+
+            SetReliableId(data, 1);
+            dut.Test_Receive(data);
+
+            SetReliableId(data, 3);
+            dut.Test_Receive(data);
+
+            MessageReader ackPacket = dut.BytesSent[1];
+            // Must be ack
+            Assert.AreEqual(4, ackPacket.Length);
+
+            byte recentPackets = ackPacket.Buffer[3];
+            // Last packet was not received
+            Assert.AreEqual(0, recentPackets & 1);
+            // The packet before that was.
+            Assert.AreEqual(1, (recentPackets >> 1) & 1);
+        }
+
         private static void SetReliableId(MessageWriter data, int i)
         {
             ushort id = (ushort)i;
diff --git a/Hazel/Udp/UdpConnection.Reliable.cs b/Hazel/Udp/UdpConnection.Reliable.cs
index 8fc3d7e..46ffc49 100644
--- a/Hazel/Udp/UdpConnection.Reliable.cs
+++ b/Hazel/Udp/UdpConnection.Reliable.cs
@@ -311,9 +311,6 @@ namespace Hazel.Udp
             //Get the ID form the packet
             id = (ushort)((b1 << 8) + b2);
 
-            //Send an acknowledgement
-            SendAck(id);
-
             /*
              * It gets a little complicated here (note the fact I'm actually using a multiline comment for once...)
              * 
@@ -338,6 +335,8 @@ namespace Hazel.Udp
              * 
              * So...
              */
+
+            bool result = true;
             
             lock (reliableDataPacketsMissing)
             {
@@ -381,12 +380,15 @@ namespace Hazel.Udp
                     //See if we're missing it, else this packet is a duplicate as so we return false
                     if (!reliableDataPacketsMissing.Remove(id))
                     {
-                        return false;
+                        result = false;
                     }
                 }
             }
 
-            return true;
+            // Send an acknowledgement
+            SendAck(id);
+
+            return result;
         }
 
         /// <summary>
-- 
2.39.5