Add location backed system clock

This provides a permissionless way to use the location (e.g. GNSS)
provided time data for more accurate time keeping.

Test: atest LocationManagerTest#testGnssProvidedClock
Bug: 123530510
Change-Id: Ifbc45997868040abbb3e1399a8649911afb0af05

1 files changed, 31 insertions, 0 deletions

diff --git a/core/java/android/os/SystemClock.java b/core/java/android/os/SystemClock.java
index b254166303bc..a1432e602d75 100644
--- a/core/java/android/os/SystemClock.java
+++ b/core/java/android/os/SystemClock.java
@@ -19,6 +19,8 @@ package android.os;
 import android.annotation.NonNull;
 import android.app.IAlarmManager;
 import android.content.Context;
+import android.location.ILocationManager;
+import android.location.LocationTime;
 import android.util.Slog;
 
 import dalvik.annotation.optimization.CriticalNative;
@@ -313,4 +315,33 @@ public final class SystemClock {
             }
         };
     }
+
+    /**
+     * Returns a {@link Clock} that starts at January 1, 1970 00:00:00.0 UTC,
+     * synchronized using the device's location provider.
+     *
+     * @throws DateTimeException when the location provider has not had a location fix since boot.
+     */
+    public static @NonNull Clock currentGnssTimeClock() {
+        return new SimpleClock(ZoneOffset.UTC) {
+            private final ILocationManager mMgr = ILocationManager.Stub
+                    .asInterface(ServiceManager.getService(Context.LOCATION_SERVICE));
+            @Override
+            public long millis() {
+                LocationTime time;
+                try {
+                    time = mMgr.getGnssTimeMillis();
+                } catch (RemoteException e) {
+                    e.rethrowFromSystemServer();
+                    return 0;
+                }
+                if (time == null) {
+                    throw new DateTimeException("Gnss based time is not available.");
+                }
+                long currentNanos = elapsedRealtimeNanos();
+                long deltaMs = (currentNanos - time.getElapsedRealtimeNanos()) / 1000000L;
+                return time.getTime() + deltaMs;
+            }
+        };
+    }
 }