diff --git a/framework-t/src/android/net/NetworkStatsCollection.java b/framework-t/src/android/net/NetworkStatsCollection.java
index 20c5f30..b6f6dbb 100644
--- a/framework-t/src/android/net/NetworkStatsCollection.java
+++ b/framework-t/src/android/net/NetworkStatsCollection.java
@@ -26,6 +26,7 @@
 import static android.net.NetworkStats.ROAMING_YES;
 import static android.net.NetworkStats.SET_ALL;
 import static android.net.NetworkStats.SET_DEFAULT;
+import static android.net.NetworkStats.SET_FOREGROUND;
 import static android.net.NetworkStats.TAG_NONE;
 import static android.net.NetworkStats.UID_ALL;
 import static android.net.NetworkTemplate.MATCH_BLUETOOTH;
@@ -50,6 +51,7 @@
 import android.telephony.SubscriptionPlan;
 import android.text.format.DateUtils;
 import android.util.ArrayMap;
+import android.util.ArraySet;
 import android.util.AtomicFile;
 import android.util.IndentingPrintWriter;
 import android.util.Log;
@@ -924,6 +926,100 @@
         }
     }
 
+
+    private static String str(NetworkStatsCollection.Key key) {
+        StringBuilder sb = new StringBuilder()
+                .append(key.ident.toString())
+                .append(" uid=").append(key.uid);
+        if (key.set != SET_FOREGROUND) {
+            sb.append(" set=").append(key.set);
+        }
+        if (key.tag != 0) {
+            sb.append(" tag=").append(key.tag);
+        }
+        return sb.toString();
+    }
+
+    // The importer will modify some keys when importing them.
+    // In order to keep the comparison code simple, add such special cases here and simply
+    // ignore them. This should not impact fidelity much because the start/end checks and the total
+    // bytes check still need to pass.
+    private static boolean couldKeyChangeOnImport(NetworkStatsCollection.Key key) {
+        if (key.ident.isEmpty()) return false;
+        final NetworkIdentity firstIdent = key.ident.iterator().next();
+
+        // Non-mobile network with non-empty RAT type.
+        // This combination is invalid and the NetworkIdentity.Builder will throw if it is passed
+        // in, but it looks like it was previously possible to persist it to disk. The importer sets
+        // the RAT type to NETWORK_TYPE_ALL.
+        if (firstIdent.getType() != ConnectivityManager.TYPE_MOBILE
+                && firstIdent.getRatType() != NetworkTemplate.NETWORK_TYPE_ALL) {
+            return true;
+        }
+
+        return false;
+    }
+
+    /**
+     * Compare two {@link NetworkStatsCollection} instances and returning a human-readable
+     * string description of difference for debugging purpose.
+     *
+     * @hide
+     */
+    @Nullable
+    public static String compareStats(
+            NetworkStatsCollection migrated, NetworkStatsCollection legacy) {
+        final Map<NetworkStatsCollection.Key, NetworkStatsHistory> migEntries =
+                migrated.getEntries();
+        final Map<NetworkStatsCollection.Key, NetworkStatsHistory> legEntries = legacy.getEntries();
+
+        final ArraySet<NetworkStatsCollection.Key> unmatchedLegKeys =
+                new ArraySet<>(legEntries.keySet());
+
+        for (NetworkStatsCollection.Key legKey : legEntries.keySet()) {
+            final NetworkStatsHistory legHistory = legEntries.get(legKey);
+            final NetworkStatsHistory migHistory = migEntries.get(legKey);
+
+            if (migHistory == null && couldKeyChangeOnImport(legKey)) {
+                unmatchedLegKeys.remove(legKey);
+                continue;
+            }
+
+            if (migHistory == null) {
+                return "Missing migrated history for legacy key " + str(legKey)
+                        + ", legacy history was " + legHistory;
+            }
+            if (!migHistory.isSameAs(legHistory)) {
+                return "Difference in history for key " + legKey + "; legacy history " + legHistory
+                        + ", migrated history " + migHistory;
+            }
+            unmatchedLegKeys.remove(legKey);
+        }
+
+        if (!unmatchedLegKeys.isEmpty()) {
+            final NetworkStatsHistory first = legEntries.get(unmatchedLegKeys.valueAt(0));
+            return "Found unmatched legacy keys: count=" + unmatchedLegKeys.size()
+                    + ", first unmatched collection " + first;
+        }
+
+        if (migrated.getStartMillis() != legacy.getStartMillis()
+                || migrated.getEndMillis() != legacy.getEndMillis()) {
+            return "Start / end of the collections "
+                    + migrated.getStartMillis() + "/" + legacy.getStartMillis() + " and "
+                    + migrated.getEndMillis() + "/" + legacy.getEndMillis()
+                    + " don't match";
+        }
+
+        if (migrated.getTotalBytes() != legacy.getTotalBytes()) {
+            return "Total bytes " + migrated.getTotalBytes() + " and " + legacy.getTotalBytes()
+                    + " don't match for collections with start/end "
+                    + migrated.getStartMillis()
+                    + "/" + legacy.getStartMillis();
+        }
+
+        return null;
+    }
+
     /**
      * the identifier that associate with the {@link NetworkStatsHistory} object to identify
      * a certain record in the {@link NetworkStatsCollection} object.
diff --git a/service-t/src/com/android/server/net/NetworkStatsService.java b/service-t/src/com/android/server/net/NetworkStatsService.java
index 804e709..2c9f30c 100644
--- a/service-t/src/com/android/server/net/NetworkStatsService.java
+++ b/service-t/src/com/android/server/net/NetworkStatsService.java
@@ -44,6 +44,7 @@
 import static android.net.NetworkStats.TAG_ALL;
 import static android.net.NetworkStats.TAG_NONE;
 import static android.net.NetworkStats.UID_ALL;
+import static android.net.NetworkStatsCollection.compareStats;
 import static android.net.NetworkStatsHistory.FIELD_ALL;
 import static android.net.NetworkTemplate.MATCH_MOBILE;
 import static android.net.NetworkTemplate.MATCH_TEST;
@@ -95,7 +96,6 @@
 import android.content.pm.PackageManager;
 import android.content.res.Resources;
 import android.database.ContentObserver;
-import android.net.ConnectivityManager;
 import android.net.DataUsageRequest;
 import android.net.INetd;
 import android.net.INetworkStatsService;
@@ -1272,93 +1272,6 @@
         return true;
     }
 
-    private static String str(NetworkStatsCollection.Key key) {
-        StringBuilder sb = new StringBuilder()
-                .append(key.ident.toString())
-                .append(" uid=").append(key.uid);
-        if (key.set != SET_FOREGROUND) {
-            sb.append(" set=").append(key.set);
-        }
-        if (key.tag != 0) {
-            sb.append(" tag=").append(key.tag);
-        }
-        return sb.toString();
-    }
-
-    // The importer will modify some keys when importing them.
-    // In order to keep the comparison code simple, add such special cases here and simply
-    // ignore them. This should not impact fidelity much because the start/end checks and the total
-    // bytes check still need to pass.
-    private static boolean couldKeyChangeOnImport(NetworkStatsCollection.Key key) {
-        if (key.ident.isEmpty()) return false;
-        final NetworkIdentity firstIdent = key.ident.iterator().next();
-
-        // Non-mobile network with non-empty RAT type.
-        // This combination is invalid and the NetworkIdentity.Builder will throw if it is passed
-        // in, but it looks like it was previously possible to persist it to disk. The importer sets
-        // the RAT type to NETWORK_TYPE_ALL.
-        if (firstIdent.getType() != ConnectivityManager.TYPE_MOBILE
-                && firstIdent.getRatType() != NetworkTemplate.NETWORK_TYPE_ALL) {
-            return true;
-        }
-
-        return false;
-    }
-
-    @Nullable
-    private static String compareStats(
-            NetworkStatsCollection migrated, NetworkStatsCollection legacy) {
-        final Map<NetworkStatsCollection.Key, NetworkStatsHistory> migEntries =
-                migrated.getEntries();
-        final Map<NetworkStatsCollection.Key, NetworkStatsHistory> legEntries = legacy.getEntries();
-
-        final ArraySet<NetworkStatsCollection.Key> unmatchedLegKeys =
-                new ArraySet<>(legEntries.keySet());
-
-        for (NetworkStatsCollection.Key legKey : legEntries.keySet()) {
-            final NetworkStatsHistory legHistory = legEntries.get(legKey);
-            final NetworkStatsHistory migHistory = migEntries.get(legKey);
-
-            if (migHistory == null && couldKeyChangeOnImport(legKey)) {
-                unmatchedLegKeys.remove(legKey);
-                continue;
-            }
-
-            if (migHistory == null) {
-                return "Missing migrated history for legacy key " + str(legKey)
-                        + ", legacy history was " + legHistory;
-            }
-            if (!migHistory.isSameAs(legHistory)) {
-                return "Difference in history for key " + legKey + "; legacy history " + legHistory
-                        + ", migrated history " + migHistory;
-            }
-            unmatchedLegKeys.remove(legKey);
-        }
-
-        if (!unmatchedLegKeys.isEmpty()) {
-            final NetworkStatsHistory first = legEntries.get(unmatchedLegKeys.valueAt(0));
-            return "Found unmatched legacy keys: count=" + unmatchedLegKeys.size()
-                    + ", first unmatched collection " + first;
-        }
-
-        if (migrated.getStartMillis() != legacy.getStartMillis()
-                || migrated.getEndMillis() != legacy.getEndMillis()) {
-            return "Start / end of the collections "
-                    + migrated.getStartMillis() + "/" + legacy.getStartMillis() + " and "
-                    + migrated.getEndMillis() + "/" + legacy.getEndMillis()
-                    + " don't match";
-        }
-
-        if (migrated.getTotalBytes() != legacy.getTotalBytes()) {
-            return "Total bytes " + migrated.getTotalBytes() + " and " + legacy.getTotalBytes()
-                    + " don't match for collections with start/end "
-                    + migrated.getStartMillis()
-                    + "/" + legacy.getStartMillis();
-        }
-
-        return null;
-    }
-
     @GuardedBy("mStatsLock")
     @NonNull
     private NetworkStatsCollection readPlatformCollectionForRecorder(