Merge "LocationFudger: cache must fetch default when missing" into main

4 files changed, 104 insertions, 18 deletions

diff --git a/services/core/java/com/android/server/location/fudger/LocationFudger.java b/services/core/java/com/android/server/location/fudger/LocationFudger.java
index 881538237746..bbd8aa1aac44 100644
--- a/services/core/java/com/android/server/location/fudger/LocationFudger.java
+++ b/services/core/java/com/android/server/location/fudger/LocationFudger.java
@@ -16,6 +16,9 @@
 
 package com.android.server.location.fudger;
 
+import static com.android.internal.location.geometry.S2CellIdUtils.LAT_INDEX;
+import static com.android.internal.location.geometry.S2CellIdUtils.LNG_INDEX;
+
 import android.annotation.FlaggedApi;
 import android.annotation.Nullable;
 import android.location.Location;
@@ -184,31 +187,33 @@ public class LocationFudger {
         synchronized (this) {
             cacheCopy = mLocationFudgerCache;
         }
-
+        double[] coarsened = new double[] {0.0, 0.0};
         // TODO(b/381204398): To ensure a safe rollout, two algorithms co-exist. The first is the
         // new density-based algorithm, while the second is the traditional coarsening algorithm.
         // Once rollout is done, clean up the unused algorithm.
+        // The new algorithm is applied if and only if (1) the flag is on, (2) the cache has been
+        // set, and (3) the cache has successfully queried the provider for the default coarsening
+        // value.
         if (Flags.populationDensityProvider() && Flags.densityBasedCoarseLocations()
-                && cacheCopy != null && cacheCopy.hasDefaultValue()) {
-            int level = cacheCopy.getCoarseningLevel(latitude, longitude);
-            double[] center = snapToCenterOfS2Cell(latitude, longitude, level);
-            latitude = center[S2CellIdUtils.LAT_INDEX];
-            longitude = center[S2CellIdUtils.LNG_INDEX];
+                && cacheCopy != null) {
+            if (cacheCopy.hasDefaultValue()) {
+                // New algorithm that snaps to the center of a S2 cell.
+                int level = cacheCopy.getCoarseningLevel(latitude, longitude);
+                coarsened = snapToCenterOfS2Cell(latitude, longitude, level);
+            } else {
+                // Try to fetch the default value. The answer won't come in time, but will be used
+                // for the next location to coarsen.
+                cacheCopy.fetchDefaultCoarseningLevelIfNeeded();
+                // Previous algorithm that snaps to a grid of width mAccuracyM.
+                coarsened = snapToGrid(latitude, longitude);
+            }
         } else {
-            // quantize location by snapping to a grid. this is the primary means of obfuscation. it
-            // gives nice consistent results and is very effective at hiding the true location (as
-            // long as you are not sitting on a grid boundary, which the random offsets mitigate).
-            //
-            // note that we quantize the latitude first, since the longitude quantization depends on
-            // the latitude value and so leaks information about the latitude
-            double latGranularity = metersToDegreesLatitude(mAccuracyM);
-            latitude = wrapLatitude(Math.round(latitude / latGranularity) * latGranularity);
-            double lonGranularity = metersToDegreesLongitude(mAccuracyM, latitude);
-            longitude = wrapLongitude(Math.round(longitude / lonGranularity) * lonGranularity);
+            // Previous algorithm that snaps to a grid of width mAccuracyM.
+            coarsened = snapToGrid(latitude, longitude);
         }
 
-        coarse.setLatitude(latitude);
-        coarse.setLongitude(longitude);
+        coarse.setLatitude(coarsened[LAT_INDEX]);
+        coarse.setLongitude(coarsened[LNG_INDEX]);
         coarse.setAccuracy(Math.max(mAccuracyM, coarse.getAccuracy()));
 
         synchronized (this) {
@@ -219,6 +224,21 @@ public class LocationFudger {
         return coarse;
     }
 
+    // quantize location by snapping to a grid. this is the primary means of obfuscation. it
+    // gives nice consistent results and is very effective at hiding the true location (as
+    // long as you are not sitting on a grid boundary, which the random offsets mitigate).
+    //
+    // note that we quantize the latitude first, since the longitude quantization depends on
+    // the latitude value and so leaks information about the latitude
+    private double[] snapToGrid(double latitude, double longitude) {
+        double[] center = new double[] {0.0, 0.0};
+        double latGranularity = metersToDegreesLatitude(mAccuracyM);
+        center[LAT_INDEX] = wrapLatitude(Math.round(latitude / latGranularity) * latGranularity);
+        double lonGranularity = metersToDegreesLongitude(mAccuracyM, latitude);
+        center[LNG_INDEX] = wrapLongitude(Math.round(longitude / lonGranularity) * lonGranularity);
+        return center;
+    }
+
     @VisibleForTesting
     protected double[] snapToCenterOfS2Cell(double latDegrees, double lngDegrees, int level) {
         long leafCell = S2CellIdUtils.fromLatLngDegrees(latDegrees, lngDegrees);
diff --git a/services/core/java/com/android/server/location/fudger/LocationFudgerCache.java b/services/core/java/com/android/server/location/fudger/LocationFudgerCache.java
index ce8bec8f0147..19ec38ce8ccc 100644
--- a/services/core/java/com/android/server/location/fudger/LocationFudgerCache.java
+++ b/services/core/java/com/android/server/location/fudger/LocationFudgerCache.java
@@ -76,6 +76,13 @@ public class LocationFudgerCache {
         asyncFetchDefaultCoarseningLevel();
     }
 
+    /** If the cache's default coarsening value hasn't been set, asynchronously fetches it. */
+    public void fetchDefaultCoarseningLevelIfNeeded() {
+        if (!hasDefaultValue()) {
+            asyncFetchDefaultCoarseningLevel();
+        }
+    }
+
     /** Returns true if the cache has successfully received a default value from the provider. */
     public boolean hasDefaultValue() {
         synchronized (mLock) {
diff --git a/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerCacheTest.java b/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerCacheTest.java
index 6b7eda26b945..c89048a06ce2 100644
--- a/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerCacheTest.java
+++ b/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerCacheTest.java
@@ -280,6 +280,51 @@ public class LocationFudgerCacheTest {
                 eq(POINT_IN_TIMES_SQUARE[1]), eq(numAdditionalCells), any());
     }
 
+    @Test
+    public void fetchDefaultCoarseningLevelIfNeeded_withDefaultValue_doesNotQueryProvider()
+            throws RemoteException {
+        // Arrange.
+        ProxyPopulationDensityProvider provider = mock(ProxyPopulationDensityProvider.class);
+        LocationFudgerCache cache = new LocationFudgerCache(provider);
+
+        ArgumentCaptor<IS2LevelCallback> argumentCaptor = ArgumentCaptor.forClass(
+                IS2LevelCallback.class);
+        verify(provider, times(1)).getDefaultCoarseningLevel(argumentCaptor.capture());
+
+        IS2LevelCallback cb = argumentCaptor.getValue();
+        cb.onResult(10);
+
+        assertThat(cache.hasDefaultValue()).isTrue();
+
+        // Act.
+        cache.fetchDefaultCoarseningLevelIfNeeded();
+
+        // Assert. The method is not called again.
+        verify(provider, times(1)).getDefaultCoarseningLevel(any());
+    }
+
+    @Test
+    public void fetchDefaultCoarseningLevelIfNeeded_withoutDefaultValue_doesQueryProvider()
+            throws RemoteException {
+        // Arrange.
+        ProxyPopulationDensityProvider provider = mock(ProxyPopulationDensityProvider.class);
+        LocationFudgerCache cache = new LocationFudgerCache(provider);
+
+        ArgumentCaptor<IS2LevelCallback> argumentCaptor = ArgumentCaptor.forClass(
+                IS2LevelCallback.class);
+        verify(provider, times(1)).getDefaultCoarseningLevel(argumentCaptor.capture());
+
+        IS2LevelCallback cb = argumentCaptor.getValue();
+        cb.onError();
+
+        assertThat(cache.hasDefaultValue()).isFalse();
+
+        // Act.
+        cache.fetchDefaultCoarseningLevelIfNeeded();
+
+        // Assert. The method is called again.
+        verify(provider, times(2)).getDefaultCoarseningLevel(any());
+    }
 
     @Test
     public void locationFudgerCache_canContainUpToMaxSizeItems() {
diff --git a/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerTest.java b/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerTest.java
index 49ff041e10b7..2e4652e6f48b 100644
--- a/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerTest.java
+++ b/services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerTest.java
@@ -222,6 +222,20 @@ public class LocationFudgerTest {
     }
 
     @Test
+    public void testDensityBasedCoarsening_ifFeatureIsEnabledButNoDefaultValue_defaultIsFetched() {
+        mSetFlagsRule.enableFlags(Flags.FLAG_DENSITY_BASED_COARSE_LOCATIONS);
+        mSetFlagsRule.enableFlags(Flags.FLAG_POPULATION_DENSITY_PROVIDER);
+        LocationFudgerCache cache = mock(LocationFudgerCache.class);
+        doReturn(false).when(cache).hasDefaultValue();
+
+        mFudger.setLocationFudgerCache(cache);
+
+        mFudger.createCoarse(createLocation("test", mRandom));
+
+        verify(cache).fetchDefaultCoarseningLevelIfNeeded();
+    }
+
+    @Test
     public void testDensityBasedCoarsening_ifFeatureIsEnabledAndDefaultIsSet_cacheIsUsed() {
         mSetFlagsRule.enableFlags(Flags.FLAG_DENSITY_BASED_COARSE_LOCATIONS);
         mSetFlagsRule.enableFlags(Flags.FLAG_POPULATION_DENSITY_PROVIDER);