fix: Packet loss now returns the value of the current frame instead of connection lifetime (#2004)

Author: JS Fauteux

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -34,6 +34,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Fixed `NetworkAnimator` issue where it was not taking the animation speed or state speed multiplier into consideration. (#1946)
 - Fixed `NetworkAnimator` issue where it was not properly synchronizing late joining clients if they joined while `Animator` was transitioning between states. (#1946)
 - Fixed `NetworkAnimator` issue where the server was not relaying changes to non-owner clients when a client was the owner. (#1946)
+- Fixed issue where the `PacketLoss` metric for tools would return the packet loss over a connection lifetime instead of a single frame. (#2004)
 
 ## [1.0.0-pre.9] - 2022-05-10
 

com.unity.netcode.gameobjects/Runtime/Transports/UTP/UnityTransport.cs

@@ -243,6 +243,15 @@ public struct SimulatorParameters
             PacketDropRate = 0
         };
 
+        private struct PacketLossCache
+        {
+            public int PacketsReceived;
+            public int PacketsDropped;
+            public float PacketLoss;
+        };
+
+        private PacketLossCache m_PacketLossCache = new PacketLossCache();
+
         private State m_State = State.Disconnected;
         private NetworkDriver m_Driver;
         private NetworkSettings m_NetworkSettings;
@@ -839,11 +848,22 @@ private float ExtractPacketLoss(NetworkConnection networkConnection)
             {
                 var sharedContext = (ReliableUtility.SharedContext*)sharedBuffer.GetUnsafePtr();
 
-                var packetReceived = (float)sharedContext->stats.PacketsReceived;
-                var packetDropped = (float)sharedContext->stats.PacketsDropped;
-                var packetLoss = packetReceived > 0 ? packetDropped / packetReceived : 0;
+                var packetReceivedDelta = (float)(sharedContext->stats.PacketsReceived - m_PacketLossCache.PacketsReceived);
+                var packetDroppedDelta = (float)(sharedContext->stats.PacketsDropped - m_PacketLossCache.PacketsDropped);
+
+                // There can be multiple update happening in a single frame where no packets have transitioned
+                // In those situation we want to return the last packet loss value instead of 0 to avoid invalid swings
+                if (packetDroppedDelta == 0 && packetReceivedDelta == 0)
+                {
+                    return m_PacketLossCache.PacketLoss;
+                }
+
+                m_PacketLossCache.PacketsReceived = sharedContext->stats.PacketsReceived;
+                m_PacketLossCache.PacketsDropped = sharedContext->stats.PacketsDropped;
+
+                m_PacketLossCache.PacketLoss = packetReceivedDelta > 0 ? packetDroppedDelta / packetReceivedDelta : 0;
 
-                return packetLoss;
+                return m_PacketLossCache.PacketLoss;
             }
         }
 

com.unity.netcode.gameobjects/Tests/Runtime/Metrics/PacketLossMetricsTests.cs

@@ -18,7 +18,7 @@ public class PacketLossMetricsTests : NetcodeIntegrationTest
     {
         protected override int NumberOfClients => 1;
         private readonly int m_PacketLossRate = 25;
-        private int m_DropInterval = 5;
+        private readonly int m_PacketLossRangeDelta = 5;
 
         public PacketLossMetricsTests()
             : base(HostOrServer.Server)
@@ -57,11 +57,12 @@ public IEnumerator TrackPacketLossAsServer()
         [UnityTest]
         public IEnumerator TrackPacketLossAsClient()
         {
-            double packetLossRate = m_PacketLossRate/100d;
+            double packetLossRateMinRange = (m_PacketLossRate-m_PacketLossRangeDelta) / 100d;
+            double packetLossRateMaxrange = (m_PacketLossRate + m_PacketLossRangeDelta) / 100d;
             var clientNetworkManager = m_ClientNetworkManagers[0];
             var waitForPacketLossMetric = new WaitForGaugeMetricValues((clientNetworkManager.NetworkMetrics as NetworkMetrics).Dispatcher,
                 NetworkMetricTypes.PacketLoss,
-                metric => Math.Abs(metric - packetLossRate) < Double.Epsilon);
+                metric => packetLossRateMinRange <= metric && metric <= packetLossRateMaxrange);
 
             for (int i = 0; i < 1000; ++i)
             {
@@ -75,7 +76,7 @@ public IEnumerator TrackPacketLossAsClient()
             yield return waitForPacketLossMetric.WaitForMetricsReceived();
 
             var packetLossValue = waitForPacketLossMetric.AssertMetricValueHaveBeenFound();
-            Assert.AreEqual(packetLossRate, packetLossValue);
+            Assert.That(packetLossValue, Is.InRange(packetLossRateMinRange, packetLossRateMaxrange));
         }
     }
 }