Add config for client-side traffic stats rate-limit cache.

This is a no-op change since the config is not used yet, and
the feature flag will be gradually rolled out instead of enabled
by default.
However, this change is necessary for follow-up changes to enable
toggling the feature and configuring its behavior through device
configuration flags.

This change includes:

 1. Disable the service-side cache flag if the client-side flag
    is enabled.
 2. Since the apps don't have enough permission to check the
    feature flag from DeviceConfig. Provides a binder interface
    for returning per-UID config,
    which only returns cache enabled if the SDK level is V+
    or the app's target SDK is V+.

Test: atest FrameworksNetTests:android.net.connectivity.android.net.TrafficStatsTest \
      FrameworksNetTests:android.net.connectivity.com.android.server.net.NetworkStatsServiceTest \
      CtsNetTestCases:android.net.cts.NetworkStatsBinderTest \
      FrameworksNetIntegrationTests:com.android.server.net.integrationtests.NetworkStatsIntegrationTest
Bug: 343260158
Change-Id: Id9761e4aea65fabe6466c875b787e178317a1da2
diff --git a/framework-t/src/android/net/INetworkStatsService.aidl b/framework-t/src/android/net/INetworkStatsService.aidl
index ce57a4a..b459a13 100644
--- a/framework-t/src/android/net/INetworkStatsService.aidl
+++ b/framework-t/src/android/net/INetworkStatsService.aidl
@@ -25,6 +25,7 @@
 import android.net.UnderlyingNetworkInfo;
 import android.net.netstats.IUsageCallback;
 import android.net.netstats.StatsResult;
+import android.net.netstats.TrafficStatsRateLimitCacheConfig;
 import android.net.netstats.provider.INetworkStatsProvider;
 import android.net.netstats.provider.INetworkStatsProviderCallback;
 import android.os.IBinder;
@@ -104,4 +105,7 @@
 
      /** Clear TrafficStats rate-limit caches. */
      void clearTrafficStatsRateLimitCaches();
+
+     /** Get rate-limit cache config. */
+     TrafficStatsRateLimitCacheConfig getRateLimitCacheConfig();
 }
diff --git a/framework-t/src/android/net/netstats/TrafficStatsRateLimitCacheConfig.aidl b/framework-t/src/android/net/netstats/TrafficStatsRateLimitCacheConfig.aidl
new file mode 100644
index 0000000..cdf0b7c
--- /dev/null
+++ b/framework-t/src/android/net/netstats/TrafficStatsRateLimitCacheConfig.aidl
@@ -0,0 +1,42 @@
+/**
+ * Copyright (c) 2024, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netstats;
+
+/**
+ * Configuration for the TrafficStats rate limit cache.
+ *
+ * @hide
+ */
+@JavaDerive(equals=true, toString=true)
+@JavaOnlyImmutable
+parcelable TrafficStatsRateLimitCacheConfig {
+
+    /**
+     * Whether the cache is enabled for V+ device or target Sdk V+ apps.
+     */
+    boolean isCacheEnabled;
+
+    /**
+     * The duration for which cache entries are valid, in milliseconds.
+     */
+    int expiryDurationMs;
+
+    /**
+     * The maximum number of entries to store in the cache.
+     */
+    int maxEntries;
+}
diff --git a/service-t/src/com/android/server/net/NetworkStatsService.java b/service-t/src/com/android/server/net/NetworkStatsService.java
index ba706d9..fb712a1 100644
--- a/service-t/src/com/android/server/net/NetworkStatsService.java
+++ b/service-t/src/com/android/server/net/NetworkStatsService.java
@@ -127,6 +127,7 @@
 import android.net.netstats.IUsageCallback;
 import android.net.netstats.NetworkStatsDataMigrationUtils;
 import android.net.netstats.StatsResult;
+import android.net.netstats.TrafficStatsRateLimitCacheConfig;
 import android.net.netstats.provider.INetworkStatsProvider;
 import android.net.netstats.provider.INetworkStatsProviderCallback;
 import android.net.netstats.provider.NetworkStatsProvider;
@@ -491,6 +492,9 @@
     private final TrafficStatsRateLimitCache mTrafficStatsIfaceCache;
     @Nullable
     private final TrafficStatsRateLimitCache mTrafficStatsUidCache;
+    // A feature flag to control whether the client-side rate limit cache should be enabled.
+    static final String TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG =
+            "trafficstats_client_rate_limit_cache_enabled_flag";
     static final String TRAFFICSTATS_SERVICE_RATE_LIMIT_CACHE_ENABLED_FLAG =
             "trafficstats_rate_limit_cache_enabled_flag";
     static final String BROADCAST_NETWORK_STATS_UPDATED_RATE_LIMIT_ENABLED_FLAG =
@@ -498,6 +502,7 @@
     private final boolean mIsTrafficStatsServiceRateLimitCacheEnabled;
     private final int mTrafficStatsRateLimitCacheExpiryDuration;
     private final int mTrafficStatsServiceRateLimitCacheMaxEntries;
+    private final TrafficStatsRateLimitCacheConfig mTrafficStatsRateLimitCacheClientSideConfig;
     private final boolean mBroadcastNetworkStatsUpdatedRateLimitEnabled;
 
 
@@ -691,8 +696,13 @@
             mEventLogger = null;
         }
 
+        mTrafficStatsRateLimitCacheClientSideConfig =
+                mDeps.getTrafficStatsRateLimitCacheClientSideConfig(mContext);
+        // If the client side cache feature is enabled, disable the service side
+        // cache unconditionally.
         mIsTrafficStatsServiceRateLimitCacheEnabled =
-                mDeps.isTrafficStatsServiceRateLimitCacheEnabled(mContext);
+                mDeps.isTrafficStatsServiceRateLimitCacheEnabled(mContext,
+                        mTrafficStatsRateLimitCacheClientSideConfig.isCacheEnabled);
         mBroadcastNetworkStatsUpdatedRateLimitEnabled =
                 mDeps.enabledBroadcastNetworkStatsUpdatedRateLimiting(mContext);
         mTrafficStatsRateLimitCacheExpiryDuration =
@@ -973,13 +983,42 @@
         }
 
         /**
-         * Whether the service side cache is enabled for V+ device or target Sdk V+ apps.
+         * Get client side traffic stats rate-limit cache config.
          *
          * This method should only be called once in the constructor,
          * to ensure that the code does not need to deal with flag values changing at runtime.
          */
-        public boolean isTrafficStatsServiceRateLimitCacheEnabled(@NonNull Context ctx) {
-            return DeviceConfigUtils.isTetheringFeatureNotChickenedOut(
+        @NonNull
+        public TrafficStatsRateLimitCacheConfig getTrafficStatsRateLimitCacheClientSideConfig(
+                @NonNull Context ctx) {
+            final TrafficStatsRateLimitCacheConfig config =
+                    new TrafficStatsRateLimitCacheConfig.Builder()
+                            .setIsCacheEnabled(DeviceConfigUtils.isTetheringFeatureEnabled(
+                                    ctx, TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG))
+                            .setExpiryDurationMs(getDeviceConfigPropertyInt(
+                                    NAMESPACE_TETHERING, TRAFFIC_STATS_CACHE_EXPIRY_DURATION_NAME,
+                                    DEFAULT_TRAFFIC_STATS_CACHE_EXPIRY_DURATION_MS))
+                            .setMaxEntries(getDeviceConfigPropertyInt(
+                                    NAMESPACE_TETHERING,
+                                    TRAFFIC_STATS_SERVICE_CACHE_MAX_ENTRIES_NAME,
+                                    DEFAULT_TRAFFIC_STATS_SERVICE_CACHE_MAX_ENTRIES))
+                            .build();
+            return config;
+        }
+
+        /**
+         * Determines whether the service-side rate-limiting cache is enabled.
+         *
+         * The cache is enabled for devices running Android V+ or apps targeting SDK V+
+         * if the `TRAFFICSTATS_SERVICE_RATE_LIMIT_CACHE_ENABLED_FLAG` feature flag
+         * is enabled and client-side caching is disabled.
+         *
+         * This method should only be called once in the constructor,
+         * to ensure that the code does not need to deal with flag values changing at runtime.
+         */
+        public boolean isTrafficStatsServiceRateLimitCacheEnabled(@NonNull Context ctx,
+                boolean clientCacheEnabled) {
+            return !clientCacheEnabled && DeviceConfigUtils.isTetheringFeatureNotChickenedOut(
                     ctx, TRAFFICSTATS_SERVICE_RATE_LIMIT_CACHE_ENABLED_FLAG);
         }
 
@@ -2143,6 +2182,20 @@
     }
 
     /**
+     * Determines whether to use the client-side cache for traffic stats rate limiting.
+     *
+     * This is based on the cache enabled feature flag. If enabled, the client-side cache
+     * is used for V+ devices or callers with V+ target sdk.
+     *
+     * @param callingUid The UID of the app making the request.
+     * @return True if the client-side cache should be used, false otherwise.
+     */
+    private boolean useClientSideCache(int callingUid) {
+        return mTrafficStatsRateLimitCacheClientSideConfig.isCacheEnabled && (SdkLevel.isAtLeastV()
+                || mDeps.isChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, callingUid));
+    }
+
+    /**
      * Determines whether to use the service-side cache for traffic stats rate limiting.
      *
      * This is based on the cache enabled feature flag. If enabled, the service-side cache
@@ -2238,6 +2291,19 @@
         }
     }
 
+    @Override
+    public TrafficStatsRateLimitCacheConfig getRateLimitCacheConfig() {
+        // Build a per uid config for the client based on the checking result.
+        final TrafficStatsRateLimitCacheConfig config =
+                new TrafficStatsRateLimitCacheConfig.Builder()
+                        .setIsCacheEnabled(useClientSideCache(Binder.getCallingUid()))
+                        .setExpiryDurationMs(
+                                mTrafficStatsRateLimitCacheClientSideConfig.expiryDurationMs)
+                        .setMaxEntries(mTrafficStatsRateLimitCacheClientSideConfig.maxEntries)
+                        .build();
+        return config;
+    }
+
     private NetworkStats.Entry getProviderIfaceStats(@Nullable String iface) {
         final NetworkStats providerSnapshot = getNetworkStatsFromProviders(STATS_PER_IFACE);
         final HashSet<String> limitIfaces;
@@ -3014,6 +3080,9 @@
             pw.print(TRAFFIC_STATS_SERVICE_CACHE_MAX_ENTRIES_NAME,
                     mTrafficStatsServiceRateLimitCacheMaxEntries);
             pw.println();
+            pw.print("trafficstats.client.cache.config",
+                    mTrafficStatsRateLimitCacheClientSideConfig);
+            pw.println();
 
             pw.decreaseIndent();
 
diff --git a/staticlibs/testutils/devicetests/com/android/testutils/SetFeatureFlagsRule.kt b/staticlibs/testutils/devicetests/com/android/testutils/SetFeatureFlagsRule.kt
index d5e91c2..7b970d3 100644
--- a/staticlibs/testutils/devicetests/com/android/testutils/SetFeatureFlagsRule.kt
+++ b/staticlibs/testutils/devicetests/com/android/testutils/SetFeatureFlagsRule.kt
@@ -57,6 +57,7 @@
      * @param enabled The desired state (true for enabled, false for disabled) of the feature flag.
      */
     @Target(AnnotationTarget.FUNCTION)
+    @Repeatable
     @Retention(AnnotationRetention.RUNTIME)
     annotation class FeatureFlag(val name: String, val enabled: Boolean = true)
 
diff --git a/tests/unit/java/com/android/server/net/NetworkStatsServiceTest.java b/tests/unit/java/com/android/server/net/NetworkStatsServiceTest.java
index 3a52927..b528480 100644
--- a/tests/unit/java/com/android/server/net/NetworkStatsServiceTest.java
+++ b/tests/unit/java/com/android/server/net/NetworkStatsServiceTest.java
@@ -78,6 +78,7 @@
 import static com.android.server.net.NetworkStatsService.NETSTATS_IMPORT_ATTEMPTS_COUNTER_NAME;
 import static com.android.server.net.NetworkStatsService.NETSTATS_IMPORT_FALLBACKS_COUNTER_NAME;
 import static com.android.server.net.NetworkStatsService.NETSTATS_IMPORT_SUCCESSES_COUNTER_NAME;
+import static com.android.server.net.NetworkStatsService.TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG;
 import static com.android.server.net.NetworkStatsService.TRAFFICSTATS_SERVICE_RATE_LIMIT_CACHE_ENABLED_FLAG;
 import static com.android.testutils.DevSdkIgnoreRuleKt.SC_V2;
 
@@ -129,6 +130,7 @@
 import android.net.TetheringManager;
 import android.net.UnderlyingNetworkInfo;
 import android.net.netstats.StatsResult;
+import android.net.netstats.TrafficStatsRateLimitCacheConfig;
 import android.net.netstats.provider.INetworkStatsProviderCallback;
 import android.net.wifi.WifiInfo;
 import android.os.Build;
@@ -622,8 +624,9 @@
         }
 
         @Override
-        public boolean isTrafficStatsServiceRateLimitCacheEnabled(Context ctx) {
-            return mFeatureFlags.getOrDefault(
+        public boolean isTrafficStatsServiceRateLimitCacheEnabled(Context ctx,
+                boolean isClientCacheEnabled) {
+            return !isClientCacheEnabled && mFeatureFlags.getOrDefault(
                     TRAFFICSTATS_SERVICE_RATE_LIMIT_CACHE_ENABLED_FLAG, false);
         }
 
@@ -644,6 +647,19 @@
         }
 
         @Override
+        public TrafficStatsRateLimitCacheConfig getTrafficStatsRateLimitCacheClientSideConfig(
+                @NonNull Context ctx) {
+            final TrafficStatsRateLimitCacheConfig config =
+                    new TrafficStatsRateLimitCacheConfig.Builder()
+                            .setIsCacheEnabled(mFeatureFlags.getOrDefault(
+                                    TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG, false))
+                            .setExpiryDurationMs(DEFAULT_TRAFFIC_STATS_CACHE_EXPIRY_DURATION_MS)
+                            .setMaxEntries(DEFAULT_TRAFFIC_STATS_SERVICE_CACHE_MAX_ENTRIES)
+                            .build();
+            return config;
+        }
+
+        @Override
         public boolean isChangeEnabled(long changeId, int uid) {
             return mCompatChanges.getOrDefault(changeId, true);
         }
@@ -2454,6 +2470,44 @@
         assertUidTotal(sTemplateWifi, UID_GREEN, 64L, 3L, 1024L, 8L, 0);
     }
 
+    @FeatureFlag(name = TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG, enabled = false)
+    @Test
+    public void testGetRateLimitCacheConfig_featureDisabled() {
+        mDeps.setChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, false);
+        assertFalse(mService.getRateLimitCacheConfig().isCacheEnabled);
+        mDeps.setChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, true);
+        assertFalse(mService.getRateLimitCacheConfig().isCacheEnabled);
+    }
+
+    @FeatureFlag(name = TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG)
+    @DevSdkIgnoreRule.IgnoreUpTo(Build.VERSION_CODES.UPSIDE_DOWN_CAKE)
+    @Test
+    public void testGetRateLimitCacheConfig_vOrAbove() {
+        mDeps.setChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, false);
+        assertTrue(mService.getRateLimitCacheConfig().isCacheEnabled);
+        mDeps.setChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, true);
+        assertTrue(mService.getRateLimitCacheConfig().isCacheEnabled);
+    }
+
+    @FeatureFlag(name = TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG)
+    @DevSdkIgnoreRule.IgnoreAfter(Build.VERSION_CODES.UPSIDE_DOWN_CAKE)
+    @Test
+    public void testGetRateLimitCacheConfig_belowV() {
+        mDeps.setChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, false);
+        assertFalse(mService.getRateLimitCacheConfig().isCacheEnabled);
+        mDeps.setChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, true);
+        assertTrue(mService.getRateLimitCacheConfig().isCacheEnabled);
+    }
+
+    @FeatureFlag(name = TRAFFICSTATS_CLIENT_RATE_LIMIT_CACHE_ENABLED_FLAG)
+    @FeatureFlag(name = TRAFFICSTATS_SERVICE_RATE_LIMIT_CACHE_ENABLED_FLAG)
+    @Test
+    public void testTrafficStatsRateLimitCache_clientCacheEnabledDisableServiceCache()
+            throws Exception {
+        mDeps.setChangeEnabled(ENABLE_TRAFFICSTATS_RATE_LIMIT_CACHE, true);
+        doTestTrafficStatsRateLimitCache(false /* expectCached */);
+    }
+
     @FeatureFlag(name = TRAFFICSTATS_SERVICE_RATE_LIMIT_CACHE_ENABLED_FLAG, enabled = false)
     @Test
     public void testTrafficStatsRateLimitCache_disabledWithCompatChangeEnabled() throws Exception {