VCN: Refactor getPacketLossRatePercentage to return an object

Refactor getPacketLossRatePercentage to return an object instead of
an integer. This is for extending the Packet Loss Detector's ability
to handle inbound sequence number leap

This patch does not include any behavior changes

Bug: 332598276
Test: atest FrameworksVcnTests && atest CtsVcnTestCases
Change-Id: Ied42e581fb331ab0603225865236779f50cc4881

2 files changed, 129 insertions, 19 deletions

diff --git a/services/core/java/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java b/services/core/java/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java
index ed9fa65dee15..c5d333317013 100644
--- a/services/core/java/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java
+++ b/services/core/java/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java
@@ -16,8 +16,10 @@
 
 package com.android.server.vcn.routeselection;
 
+import static com.android.internal.annotations.VisibleForTesting.Visibility;
 import static com.android.server.vcn.util.PersistableBundleUtils.PersistableBundleWrapper;
 
+import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.content.BroadcastReceiver;
@@ -38,6 +40,10 @@ import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.annotations.VisibleForTesting.Visibility;
 import com.android.server.vcn.VcnContext;
 
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
 import java.util.BitSet;
 import java.util.Objects;
 import java.util.concurrent.TimeUnit;
@@ -56,8 +62,32 @@ import java.util.concurrent.TimeUnit;
 public class IpSecPacketLossDetector extends NetworkMetricMonitor {
     private static final String TAG = IpSecPacketLossDetector.class.getSimpleName();
 
-    @VisibleForTesting(visibility = Visibility.PRIVATE)
-    static final int PACKET_LOSS_UNAVALAIBLE = -1;
+    private static final int PACKET_LOSS_PERCENT_UNAVAILABLE = -1;
+
+    @Retention(RetentionPolicy.SOURCE)
+    @IntDef(
+            prefix = {"PACKET_LOSS_"},
+            value = {
+                PACKET_LOSS_RATE_VALID,
+                PACKET_LOSS_RATE_INVALID,
+            })
+    @Target({ElementType.TYPE_USE})
+    private @interface PacketLossResultType {}
+
+    /** Indicates a valid packet loss rate is available */
+    private static final int PACKET_LOSS_RATE_VALID = 0;
+
+    /**
+     * Indicates that the detector cannot get a valid packet loss rate due to one of the following
+     * reasons:
+     *
+     * <ul>
+     *   <li>The replay window did not proceed and thus all packets might have been delivered out of
+     *       order
+     *   <li>There are unexpected errors
+     * </ul>
+     */
+    private static final int PACKET_LOSS_RATE_INVALID = 1;
 
     // For VoIP, losses between 5% and 10% of the total packet stream will affect the quality
     // significantly (as per "Computer Networking for LANS to WANS: Hardware, Software and
@@ -307,24 +337,24 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
             return;
         }
 
-        final int packetLossRate =
+        final PacketLossCalculationResult calculateResult =
                 mPacketLossCalculator.getPacketLossRatePercentage(
                         mLastIpSecTransformState, state, getLogPrefix());
 
-        if (packetLossRate == PACKET_LOSS_UNAVALAIBLE) {
+        if (calculateResult.getResultType() == PACKET_LOSS_RATE_INVALID) {
             return;
         }
 
         final String logMsg =
-                "packetLossRate: "
-                        + packetLossRate
+                "calculateResult: "
+                        + calculateResult
                         + "% in the past "
                         + (state.getTimestampMillis()
                                 - mLastIpSecTransformState.getTimestampMillis())
                         + "ms";
 
         mLastIpSecTransformState = state;
-        if (packetLossRate < mPacketLossRatePercentThreshold) {
+        if (calculateResult.getPacketLossRatePercent() < mPacketLossRatePercentThreshold) {
             logV(logMsg);
             onValidationResultReceivedInternal(false /* isFailed */);
         } else {
@@ -343,7 +373,7 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
     @VisibleForTesting(visibility = Visibility.PRIVATE)
     public static class PacketLossCalculator {
         /** Calculate the packet loss rate between two timestamps */
-        public int getPacketLossRatePercentage(
+        public PacketLossCalculationResult getPacketLossRatePercentage(
                 @NonNull IpSecTransformState oldState,
                 @NonNull IpSecTransformState newState,
                 String logPrefix) {
@@ -359,7 +389,7 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
             if (oldSeqHi == newSeqHi || newSeqHi < replayWindowSize) {
                 // The replay window did not proceed and all packets might have been delivered out
                 // of order
-                return PACKET_LOSS_UNAVALAIBLE;
+                return PacketLossCalculationResult.invalid();
             }
 
             // Get the expected packet count by assuming there is no packet loss. In this case, SA
@@ -386,10 +416,11 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
                     || actualPktCntDiff < 0
                     || actualPktCntDiff > expectedPktCntDiff) {
                 logWtf(TAG, "Impossible values for expectedPktCntDiff or" + " actualPktCntDiff");
-                return PACKET_LOSS_UNAVALAIBLE;
+                return PacketLossCalculationResult.invalid();
             }
 
-            return 100 - (int) (actualPktCntDiff * 100 / expectedPktCntDiff);
+            final int percent = 100 - (int) (actualPktCntDiff * 100 / expectedPktCntDiff);
+            return PacketLossCalculationResult.valid(percent);
         }
     }
 
@@ -409,4 +440,59 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
     private static long getPacketCntInReplayWindow(@NonNull IpSecTransformState state) {
         return BitSet.valueOf(state.getReplayBitmap()).cardinality();
     }
+
+    @VisibleForTesting(visibility = Visibility.PRIVATE)
+    public static class PacketLossCalculationResult {
+        @PacketLossResultType private final int mResultType;
+        private final int mPacketLossRatePercent;
+
+        private PacketLossCalculationResult(@PacketLossResultType int type, int percent) {
+            mResultType = type;
+            mPacketLossRatePercent = percent;
+        }
+
+        /** Construct an instance that contains a valid packet loss rate */
+        public static PacketLossCalculationResult valid(int percent) {
+            return new PacketLossCalculationResult(PACKET_LOSS_RATE_VALID, percent);
+        }
+
+        /** Construct an instance indicating the inability to get a valid packet loss rate */
+        public static PacketLossCalculationResult invalid() {
+            return new PacketLossCalculationResult(
+                    PACKET_LOSS_RATE_INVALID, PACKET_LOSS_PERCENT_UNAVAILABLE);
+        }
+
+        @PacketLossResultType
+        public int getResultType() {
+            return mResultType;
+        }
+
+        public int getPacketLossRatePercent() {
+            return mPacketLossRatePercent;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(mResultType, mPacketLossRatePercent);
+        }
+
+        @Override
+        public boolean equals(@Nullable Object other) {
+            if (!(other instanceof PacketLossCalculationResult)) {
+                return false;
+            }
+
+            final PacketLossCalculationResult rhs = (PacketLossCalculationResult) other;
+            return mResultType == rhs.mResultType
+                    && mPacketLossRatePercent == rhs.mPacketLossRatePercent;
+        }
+
+        @Override
+        public String toString() {
+            return "mResultType: "
+                    + mResultType
+                    + " | mPacketLossRatePercent: "
+                    + mPacketLossRatePercent;
+        }
+    }
 }
diff --git a/tests/vcn/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java b/tests/vcn/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java
index fdf8fb8d3c41..0a83a53a7b59 100644
--- a/tests/vcn/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java
+++ b/tests/vcn/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java
@@ -19,7 +19,6 @@ package com.android.server.vcn.routeselection;
 import static android.net.vcn.VcnManager.VCN_NETWORK_SELECTION_IPSEC_PACKET_LOSS_PERCENT_THRESHOLD_KEY;
 import static android.net.vcn.VcnManager.VCN_NETWORK_SELECTION_POLL_IPSEC_STATE_INTERVAL_SECONDS_KEY;
 
-import static com.android.server.vcn.routeselection.IpSecPacketLossDetector.PACKET_LOSS_UNAVALAIBLE;
 import static com.android.server.vcn.util.PersistableBundleUtils.PersistableBundleWrapper;
 
 import static org.junit.Assert.assertEquals;
@@ -44,6 +43,7 @@ import android.net.IpSecTransformState;
 import android.os.OutcomeReceiver;
 import android.os.PowerManager;
 
+import com.android.server.vcn.routeselection.IpSecPacketLossDetector.PacketLossCalculationResult;
 import com.android.server.vcn.routeselection.IpSecPacketLossDetector.PacketLossCalculator;
 import com.android.server.vcn.routeselection.NetworkMetricMonitor.IpSecTransformWrapper;
 import com.android.server.vcn.routeselection.NetworkMetricMonitor.NetworkMetricMonitorCallback;
@@ -293,7 +293,9 @@ public class IpSecPacketLossDetectorTest extends NetworkEvaluationTestBase {
     }
 
     private void checkHandleLossRate(
-            int mockPacketLossRate, boolean isLastStateExpectedToUpdate, boolean isCallbackExpected)
+            PacketLossCalculationResult mockPacketLossRate,
+            boolean isLastStateExpectedToUpdate,
+            boolean isCallbackExpected)
             throws Exception {
         final OutcomeReceiver<IpSecTransformState, RuntimeException> xfrmStateReceiver =
                 startMonitorAndCaptureStateReceiver();
@@ -327,26 +329,32 @@ public class IpSecPacketLossDetectorTest extends NetworkEvaluationTestBase {
     @Test
     public void testHandleLossRate_validationPass() throws Exception {
         checkHandleLossRate(
-                2, true /* isLastStateExpectedToUpdate */, true /* isCallbackExpected */);
+                PacketLossCalculationResult.valid(2),
+                true /* isLastStateExpectedToUpdate */,
+                true /* isCallbackExpected */);
     }
 
     @Test
     public void testHandleLossRate_validationFail() throws Exception {
         checkHandleLossRate(
-                22, true /* isLastStateExpectedToUpdate */, true /* isCallbackExpected */);
+                PacketLossCalculationResult.valid(22),
+                true /* isLastStateExpectedToUpdate */,
+                true /* isCallbackExpected */);
         verify(mConnectivityManager).reportNetworkConnectivity(mNetwork, false);
     }
 
     @Test
     public void testHandleLossRate_resultUnavalaible() throws Exception {
         checkHandleLossRate(
-                PACKET_LOSS_UNAVALAIBLE,
+                PacketLossCalculationResult.invalid(),
                 false /* isLastStateExpectedToUpdate */,
                 false /* isCallbackExpected */);
     }
 
     private void checkGetPacketLossRate(
-            IpSecTransformState oldState, IpSecTransformState newState, int expectedLossRate)
+            IpSecTransformState oldState,
+            IpSecTransformState newState,
+            PacketLossCalculationResult expectedLossRate)
             throws Exception {
         assertEquals(
                 expectedLossRate,
@@ -362,14 +370,30 @@ public class IpSecPacketLossDetectorTest extends NetworkEvaluationTestBase {
             throws Exception {
         final IpSecTransformState newState =
                 newTransformState(rxSeqNo, packetCount, newReplayBitmap(packetInWin));
+        checkGetPacketLossRate(
+                oldState, newState, PacketLossCalculationResult.valid(expectedDataLossRate));
+    }
+
+    private void checkGetPacketLossRate(
+            IpSecTransformState oldState,
+            int rxSeqNo,
+            int packetCount,
+            int packetInWin,
+            PacketLossCalculationResult expectedDataLossRate)
+            throws Exception {
+        final IpSecTransformState newState =
+                newTransformState(rxSeqNo, packetCount, newReplayBitmap(packetInWin));
         checkGetPacketLossRate(oldState, newState, expectedDataLossRate);
     }
 
     @Test
     public void testGetPacketLossRate_replayWindowUnchanged() throws Exception {
         checkGetPacketLossRate(
-                mTransformStateInitial, mTransformStateInitial, PACKET_LOSS_UNAVALAIBLE);
-        checkGetPacketLossRate(mTransformStateInitial, 3000, 2000, 2000, PACKET_LOSS_UNAVALAIBLE);
+                mTransformStateInitial,
+                mTransformStateInitial,
+                PacketLossCalculationResult.invalid());
+        checkGetPacketLossRate(
+                mTransformStateInitial, 3000, 2000, 2000, PacketLossCalculationResult.invalid());
     }
 
     @Test