Merge "minor change to keep it building"
diff --git a/core/java/android/app/usage/NetworkStatsManager.java b/core/java/android/app/usage/NetworkStatsManager.java
index 6bade90..9c4a8f4 100644
--- a/core/java/android/app/usage/NetworkStatsManager.java
+++ b/core/java/android/app/usage/NetworkStatsManager.java
@@ -16,19 +16,23 @@
 
 package android.app.usage;
 
-import static com.android.internal.util.Preconditions.checkNotNull;
-
+import android.annotation.NonNull;
 import android.annotation.Nullable;
+import android.annotation.RequiresPermission;
+import android.annotation.SystemApi;
 import android.annotation.SystemService;
 import android.annotation.TestApi;
-import android.annotation.UnsupportedAppUsage;
 import android.app.usage.NetworkStats.Bucket;
+import android.compat.annotation.UnsupportedAppUsage;
 import android.content.Context;
 import android.net.ConnectivityManager;
 import android.net.DataUsageRequest;
 import android.net.INetworkStatsService;
 import android.net.NetworkIdentity;
 import android.net.NetworkTemplate;
+import android.net.netstats.provider.AbstractNetworkStatsProvider;
+import android.net.netstats.provider.NetworkStatsProviderCallback;
+import android.net.netstats.provider.NetworkStatsProviderWrapper;
 import android.os.Binder;
 import android.os.Handler;
 import android.os.Looper;
@@ -42,6 +46,8 @@
 
 import com.android.internal.annotations.VisibleForTesting;
 
+import java.util.Objects;
+
 /**
  * Provides access to network usage history and statistics. Usage data is collected in
  * discrete bins of time called 'Buckets'. See {@link NetworkStats.Bucket} for details.
@@ -418,7 +424,7 @@
     /** @hide */
     public void registerUsageCallback(NetworkTemplate template, int networkType,
             long thresholdBytes, UsageCallback callback, @Nullable Handler handler) {
-        checkNotNull(callback, "UsageCallback cannot be null");
+        Objects.requireNonNull(callback, "UsageCallback cannot be null");
 
         final Looper looper;
         if (handler == null) {
@@ -519,6 +525,34 @@
         private DataUsageRequest request;
     }
 
+    /**
+     * Registers a custom provider of {@link android.net.NetworkStats} to combine the network
+     * statistics that cannot be seen by the kernel to system. To unregister, invoke
+     * {@link NetworkStatsProviderCallback#unregister()}.
+     *
+     * @param tag a human readable identifier of the custom network stats provider.
+     * @param provider a custom implementation of {@link AbstractNetworkStatsProvider} that needs to
+     *                 be registered to the system.
+     * @return a {@link NetworkStatsProviderCallback}, which can be used to report events to the
+     *         system.
+     * @hide
+     */
+    @SystemApi
+    @RequiresPermission(android.Manifest.permission.UPDATE_DEVICE_STATS)
+    @NonNull public NetworkStatsProviderCallback registerNetworkStatsProvider(
+            @NonNull String tag,
+            @NonNull AbstractNetworkStatsProvider provider) {
+        try {
+            final NetworkStatsProviderWrapper wrapper = new NetworkStatsProviderWrapper(provider);
+            return new NetworkStatsProviderCallback(
+                    mService.registerNetworkStatsProvider(tag, wrapper));
+        } catch (RemoteException e) {
+            e.rethrowAsRuntimeException();
+        }
+        // Unreachable code, but compiler doesn't know about it.
+        return null;
+    }
+
     private static NetworkTemplate createTemplate(int networkType, String subscriberId) {
         final NetworkTemplate template;
         switch (networkType) {
diff --git a/core/java/android/net/EthernetManager.java b/core/java/android/net/EthernetManager.java
index 7256502..fd015b4 100644
--- a/core/java/android/net/EthernetManager.java
+++ b/core/java/android/net/EthernetManager.java
@@ -17,7 +17,7 @@
 package android.net;
 
 import android.annotation.SystemService;
-import android.annotation.UnsupportedAppUsage;
+import android.compat.annotation.UnsupportedAppUsage;
 import android.content.Context;
 import android.os.Handler;
 import android.os.Message;
diff --git a/core/java/android/net/INetworkStatsService.aidl b/core/java/android/net/INetworkStatsService.aidl
index 9994f9f..5fa515a 100644
--- a/core/java/android/net/INetworkStatsService.aidl
+++ b/core/java/android/net/INetworkStatsService.aidl
@@ -23,6 +23,8 @@
 import android.net.NetworkStats;
 import android.net.NetworkStatsHistory;
 import android.net.NetworkTemplate;
+import android.net.netstats.provider.INetworkStatsProvider;
+import android.net.netstats.provider.INetworkStatsProviderCallback;
 import android.os.IBinder;
 import android.os.Messenger;
 import com.android.internal.net.VpnInfo;
@@ -89,4 +91,7 @@
     /** Get the total network stats information since boot */
     long getTotalStats(int type);
 
+    /** Registers a network stats provider */
+    INetworkStatsProviderCallback registerNetworkStatsProvider(String tag,
+            in INetworkStatsProvider provider);
 }
diff --git a/core/java/android/net/IpSecManager.java b/core/java/android/net/IpSecManager.java
index 45d0c73..09ec6c3 100644
--- a/core/java/android/net/IpSecManager.java
+++ b/core/java/android/net/IpSecManager.java
@@ -17,7 +17,6 @@
 
 import static com.android.internal.util.Preconditions.checkNotNull;
 
-import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.RequiresFeature;
 import android.annotation.RequiresPermission;
@@ -26,6 +25,7 @@
 import android.annotation.TestApi;
 import android.content.Context;
 import android.content.pm.PackageManager;
+import android.net.annotations.PolicyDirection;
 import android.os.Binder;
 import android.os.ParcelFileDescriptor;
 import android.os.RemoteException;
@@ -41,8 +41,6 @@
 
 import java.io.FileDescriptor;
 import java.io.IOException;
-import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
 import java.net.DatagramSocket;
 import java.net.InetAddress;
 import java.net.Socket;
@@ -78,11 +76,6 @@
      */
     public static final int DIRECTION_OUT = 1;
 
-    /** @hide */
-    @IntDef(value = {DIRECTION_IN, DIRECTION_OUT})
-    @Retention(RetentionPolicy.SOURCE)
-    public @interface PolicyDirection {}
-
     /**
      * The Security Parameter Index (SPI) 0 indicates an unknown or invalid index.
      *
diff --git a/core/java/android/net/NetworkStats.java b/core/java/android/net/NetworkStats.java
index 6c7aa13..96d7a80 100644
--- a/core/java/android/net/NetworkStats.java
+++ b/core/java/android/net/NetworkStats.java
@@ -19,7 +19,10 @@
 import static android.os.Process.CLAT_UID;
 
 import android.annotation.NonNull;
-import android.annotation.UnsupportedAppUsage;
+import android.annotation.Nullable;
+import android.annotation.SuppressLint;
+import android.annotation.SystemApi;
+import android.compat.annotation.UnsupportedAppUsage;
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.os.SystemClock;
@@ -48,59 +51,104 @@
  * @hide
  */
 // @NotThreadSafe
-public class NetworkStats implements Parcelable {
+@SystemApi
+public final class NetworkStats implements Parcelable {
     private static final String TAG = "NetworkStats";
+
     /** {@link #iface} value when interface details unavailable. */
-    public static final String IFACE_ALL = null;
+    @SuppressLint("CompileTimeConstant")
+    @Nullable public static final String IFACE_ALL = null;
+    /**
+     * Virtual network interface for video telephony. This is for VT data usage counting
+     * purpose.
+     */
+    public static final String IFACE_VT = "vt_data0";
+
     /** {@link #uid} value when UID details unavailable. */
     public static final int UID_ALL = -1;
-    /** {@link #tag} value matching any tag. */
+    /** Special UID value for data usage by tethering. */
+    public static final int UID_TETHERING = -5;
+
+    /**
+     * {@link #tag} value matching any tag.
+     * @hide
+     */
     // TODO: Rename TAG_ALL to TAG_ANY.
     public static final int TAG_ALL = -1;
-    /** {@link #set} value for all sets combined, not including debug sets. */
+    /**
+     * {@link #set} value for all sets combined, not including debug sets.
+     * @hide
+     */
     public static final int SET_ALL = -1;
     /** {@link #set} value where background data is accounted. */
     public static final int SET_DEFAULT = 0;
     /** {@link #set} value where foreground data is accounted. */
     public static final int SET_FOREGROUND = 1;
-    /** All {@link #set} value greater than SET_DEBUG_START are debug {@link #set} values. */
+    /**
+     * All {@link #set} value greater than SET_DEBUG_START are debug {@link #set} values.
+     * @hide
+     */
     public static final int SET_DEBUG_START = 1000;
-    /** Debug {@link #set} value when the VPN stats are moved in. */
+    /**
+     * Debug {@link #set} value when the VPN stats are moved in.
+     * @hide
+     */
     public static final int SET_DBG_VPN_IN = 1001;
-    /** Debug {@link #set} value when the VPN stats are moved out of a vpn UID. */
+    /**
+     * Debug {@link #set} value when the VPN stats are moved out of a vpn UID.
+     * @hide
+     */
     public static final int SET_DBG_VPN_OUT = 1002;
 
-    /** Include all interfaces when filtering */
-    public static final String[] INTERFACES_ALL = null;
+    /**
+     * Include all interfaces when filtering
+     * @hide
+     */
+    public @Nullable static final String[] INTERFACES_ALL = null;
 
     /** {@link #tag} value for total data across all tags. */
     // TODO: Rename TAG_NONE to TAG_ALL.
     public static final int TAG_NONE = 0;
 
-    /** {@link #metered} value to account for all metered states. */
+    /**
+     * {@link #metered} value to account for all metered states.
+     * @hide
+     */
     public static final int METERED_ALL = -1;
     /** {@link #metered} value where native, unmetered data is accounted. */
     public static final int METERED_NO = 0;
     /** {@link #metered} value where metered data is accounted. */
     public static final int METERED_YES = 1;
 
-    /** {@link #roaming} value to account for all roaming states. */
+    /**
+     * {@link #roaming} value to account for all roaming states.
+     * @hide
+     */
     public static final int ROAMING_ALL = -1;
     /** {@link #roaming} value where native, non-roaming data is accounted. */
     public static final int ROAMING_NO = 0;
     /** {@link #roaming} value where roaming data is accounted. */
     public static final int ROAMING_YES = 1;
 
-    /** {@link #onDefaultNetwork} value to account for all default network states. */
+    /**
+     * {@link #onDefaultNetwork} value to account for all default network states.
+     * @hide
+     */
     public static final int DEFAULT_NETWORK_ALL = -1;
     /** {@link #onDefaultNetwork} value to account for usage while not the default network. */
     public static final int DEFAULT_NETWORK_NO = 0;
     /** {@link #onDefaultNetwork} value to account for usage while the default network. */
     public static final int DEFAULT_NETWORK_YES = 1;
 
-    /** Denotes a request for stats at the interface level. */
+    /**
+     * Denotes a request for stats at the interface level.
+     * @hide
+     */
     public static final int STATS_PER_IFACE = 0;
-    /** Denotes a request for stats at the interface and UID level. */
+    /**
+     * Denotes a request for stats at the interface and UID level.
+     * @hide
+     */
     public static final int STATS_PER_UID = 1;
 
     private static final String CLATD_INTERFACE_PREFIX = "v4-";
@@ -144,60 +192,78 @@
     @UnsupportedAppUsage
     private long[] operations;
 
+    /** @hide */
+    @SystemApi
     public static class Entry {
+        /** @hide */
         @UnsupportedAppUsage
         public String iface;
+        /** @hide */
         @UnsupportedAppUsage
         public int uid;
+        /** @hide */
         @UnsupportedAppUsage
         public int set;
+        /** @hide */
         @UnsupportedAppUsage
         public int tag;
         /**
          * Note that this is only populated w/ the default value when read from /proc or written
          * to disk. We merge in the correct value when reporting this value to clients of
          * getSummary().
+         * @hide
          */
         public int metered;
         /**
          * Note that this is only populated w/ the default value when read from /proc or written
          * to disk. We merge in the correct value when reporting this value to clients of
          * getSummary().
+         * @hide
          */
         public int roaming;
         /**
          * Note that this is only populated w/ the default value when read from /proc or written
          * to disk. We merge in the correct value when reporting this value to clients of
          * getSummary().
+         * @hide
          */
         public int defaultNetwork;
+        /** @hide */
         @UnsupportedAppUsage
         public long rxBytes;
+        /** @hide */
         @UnsupportedAppUsage
         public long rxPackets;
+        /** @hide */
         @UnsupportedAppUsage
         public long txBytes;
+        /** @hide */
         @UnsupportedAppUsage
         public long txPackets;
+        /** @hide */
+        @UnsupportedAppUsage
         public long operations;
 
+        /** @hide */
         @UnsupportedAppUsage
         public Entry() {
             this(IFACE_ALL, UID_ALL, SET_DEFAULT, TAG_NONE, 0L, 0L, 0L, 0L, 0L);
         }
 
+        /** @hide */
         public Entry(long rxBytes, long rxPackets, long txBytes, long txPackets, long operations) {
             this(IFACE_ALL, UID_ALL, SET_DEFAULT, TAG_NONE, rxBytes, rxPackets, txBytes, txPackets,
                     operations);
         }
 
+        /** @hide */
         public Entry(String iface, int uid, int set, int tag, long rxBytes, long rxPackets,
                 long txBytes, long txPackets, long operations) {
             this(iface, uid, set, tag, METERED_NO, ROAMING_NO, DEFAULT_NETWORK_NO,
                     rxBytes, rxPackets, txBytes, txPackets, operations);
         }
 
-        public Entry(String iface, int uid, int set, int tag, int metered, int roaming,
+        public Entry(@Nullable String iface, int uid, int set, int tag, int metered, int roaming,
                  int defaultNetwork, long rxBytes, long rxPackets, long txBytes, long txPackets,
                  long operations) {
             this.iface = iface;
@@ -214,15 +280,18 @@
             this.operations = operations;
         }
 
+        /** @hide */
         public boolean isNegative() {
             return rxBytes < 0 || rxPackets < 0 || txBytes < 0 || txPackets < 0 || operations < 0;
         }
 
+        /** @hide */
         public boolean isEmpty() {
             return rxBytes == 0 && rxPackets == 0 && txBytes == 0 && txPackets == 0
                     && operations == 0;
         }
 
+        /** @hide */
         public void add(Entry another) {
             this.rxBytes += another.rxBytes;
             this.rxPackets += another.rxPackets;
@@ -249,6 +318,7 @@
             return builder.toString();
         }
 
+        /** @hide */
         @Override
         public boolean equals(Object o) {
             if (o instanceof Entry) {
@@ -262,13 +332,13 @@
             return false;
         }
 
+        /** @hide */
         @Override
         public int hashCode() {
             return Objects.hash(uid, set, tag, metered, roaming, defaultNetwork, iface);
         }
     }
 
-    @UnsupportedAppUsage
     public NetworkStats(long elapsedRealtime, int initialSize) {
         this.elapsedRealtime = elapsedRealtime;
         this.size = 0;
@@ -292,6 +362,7 @@
         }
     }
 
+    /** @hide */
     @UnsupportedAppUsage
     public NetworkStats(Parcel parcel) {
         elapsedRealtime = parcel.readLong();
@@ -312,7 +383,7 @@
     }
 
     @Override
-    public void writeToParcel(Parcel dest, int flags) {
+    public void writeToParcel(@NonNull Parcel dest, int flags) {
         dest.writeLong(elapsedRealtime);
         dest.writeInt(size);
         dest.writeInt(capacity);
@@ -330,19 +401,23 @@
         dest.writeLongArray(operations);
     }
 
+    /**
+     * @hide
+     */
     @Override
     public NetworkStats clone() {
         final NetworkStats clone = new NetworkStats(elapsedRealtime, size);
         NetworkStats.Entry entry = null;
         for (int i = 0; i < size; i++) {
             entry = getValues(i, entry);
-            clone.addValues(entry);
+            clone.addEntry(entry);
         }
         return clone;
     }
 
     /**
      * Clear all data stored in this object.
+     * @hide
      */
     public void clear() {
         this.capacity = 0;
@@ -360,25 +435,28 @@
         this.operations = EmptyArray.LONG;
     }
 
+    /** @hide */
     @VisibleForTesting
     public NetworkStats addIfaceValues(
             String iface, long rxBytes, long rxPackets, long txBytes, long txPackets) {
-        return addValues(
+        return addEntry(
                 iface, UID_ALL, SET_DEFAULT, TAG_NONE, rxBytes, rxPackets, txBytes, txPackets, 0L);
     }
 
+    /** @hide */
     @VisibleForTesting
-    public NetworkStats addValues(String iface, int uid, int set, int tag, long rxBytes,
+    public NetworkStats addEntry(String iface, int uid, int set, int tag, long rxBytes,
             long rxPackets, long txBytes, long txPackets, long operations) {
-        return addValues(new Entry(
+        return addEntry(new Entry(
                 iface, uid, set, tag, rxBytes, rxPackets, txBytes, txPackets, operations));
     }
 
+    /** @hide */
     @VisibleForTesting
-    public NetworkStats addValues(String iface, int uid, int set, int tag, int metered, int roaming,
+    public NetworkStats addEntry(String iface, int uid, int set, int tag, int metered, int roaming,
             int defaultNetwork, long rxBytes, long rxPackets, long txBytes, long txPackets,
             long operations) {
-        return addValues(new Entry(
+        return addEntry(new Entry(
                 iface, uid, set, tag, metered, roaming, defaultNetwork, rxBytes, rxPackets,
                 txBytes, txPackets, operations));
     }
@@ -386,8 +464,9 @@
     /**
      * Add new stats entry, copying from given {@link Entry}. The {@link Entry}
      * object can be recycled across multiple calls.
+     * @hide
      */
-    public NetworkStats addValues(Entry entry) {
+    public NetworkStats addEntry(Entry entry) {
         if (size >= capacity) {
             final int newLength = Math.max(size, 10) * 3 / 2;
             iface = Arrays.copyOf(iface, newLength);
@@ -428,6 +507,7 @@
 
     /**
      * Return specific stats entry.
+     * @hide
      */
     @UnsupportedAppUsage
     public Entry getValues(int i, Entry recycle) {
@@ -467,10 +547,12 @@
         operations[dest] = operations[src];
     }
 
+    /** @hide */
     public long getElapsedRealtime() {
         return elapsedRealtime;
     }
 
+    /** @hide */
     public void setElapsedRealtime(long time) {
         elapsedRealtime = time;
     }
@@ -478,21 +560,25 @@
     /**
      * Return age of this {@link NetworkStats} object with respect to
      * {@link SystemClock#elapsedRealtime()}.
+     * @hide
      */
     public long getElapsedRealtimeAge() {
         return SystemClock.elapsedRealtime() - elapsedRealtime;
     }
 
+    /** @hide */
     @UnsupportedAppUsage
     public int size() {
         return size;
     }
 
+    /** @hide */
     @VisibleForTesting
     public int internalSize() {
         return capacity;
     }
 
+    /** @hide */
     @Deprecated
     public NetworkStats combineValues(String iface, int uid, int tag, long rxBytes, long rxPackets,
             long txBytes, long txPackets, long operations) {
@@ -501,6 +587,7 @@
                 txPackets, operations);
     }
 
+    /** @hide */
     public NetworkStats combineValues(String iface, int uid, int set, int tag,
             long rxBytes, long rxPackets, long txBytes, long txPackets, long operations) {
         return combineValues(new Entry(
@@ -509,16 +596,20 @@
 
     /**
      * Combine given values with an existing row, or create a new row if
-     * {@link #findIndex(String, int, int, int, int)} is unable to find match. Can
-     * also be used to subtract values from existing rows.
+     * {@link #findIndex(String, int, int, int, int, int, int)} is unable to find match. Can
+     * also be used to subtract values from existing rows. This method mutates the referencing
+     * {@link NetworkStats} object.
+     *
+     * @param entry the {@link Entry} to combine.
+     * @return a reference to this mutated {@link NetworkStats} object.
+     * @hide
      */
-    @UnsupportedAppUsage
-    public NetworkStats combineValues(Entry entry) {
+    public @NonNull NetworkStats combineValues(@NonNull Entry entry) {
         final int i = findIndex(entry.iface, entry.uid, entry.set, entry.tag, entry.metered,
                 entry.roaming, entry.defaultNetwork);
         if (i == -1) {
             // only create new entry when positive contribution
-            addValues(entry);
+            addEntry(entry);
         } else {
             rxBytes[i] += entry.rxBytes;
             rxPackets[i] += entry.rxPackets;
@@ -530,10 +621,33 @@
     }
 
     /**
-     * Combine all values from another {@link NetworkStats} into this object.
+     * Add given values with an existing row, or create a new row if
+     * {@link #findIndex(String, int, int, int, int, int, int)} is unable to find match. Can
+     * also be used to subtract values from existing rows.
+     *
+     * @param entry the {@link Entry} to add.
+     * @return a new constructed {@link NetworkStats} object that contains the result.
      */
-    @UnsupportedAppUsage
-    public void combineAllValues(NetworkStats another) {
+    public @NonNull NetworkStats addValues(@NonNull Entry entry) {
+        return this.clone().combineValues(entry);
+    }
+
+    /**
+     * Add the given {@link NetworkStats} objects.
+     *
+     * @return the sum of two objects.
+     */
+    public @NonNull NetworkStats add(@NonNull NetworkStats another) {
+        final NetworkStats ret = this.clone();
+        ret.combineAllValues(another);
+        return ret;
+    }
+
+    /**
+     * Combine all values from another {@link NetworkStats} into this object.
+     * @hide
+     */
+    public void combineAllValues(@NonNull NetworkStats another) {
         NetworkStats.Entry entry = null;
         for (int i = 0; i < another.size; i++) {
             entry = another.getValues(i, entry);
@@ -543,6 +657,7 @@
 
     /**
      * Find first stats index that matches the requested parameters.
+     * @hide
      */
     public int findIndex(String iface, int uid, int set, int tag, int metered, int roaming,
             int defaultNetwork) {
@@ -560,6 +675,7 @@
     /**
      * Find first stats index that matches the requested parameters, starting
      * search around the hinted index as an optimization.
+     * @hide
      */
     @VisibleForTesting
     public int findIndexHinted(String iface, int uid, int set, int tag, int metered, int roaming,
@@ -589,6 +705,7 @@
      * Splice in {@link #operations} from the given {@link NetworkStats} based
      * on matching {@link #uid} and {@link #tag} rows. Ignores {@link #iface},
      * since operation counts are at data layer.
+     * @hide
      */
     public void spliceOperationsFrom(NetworkStats stats) {
         for (int i = 0; i < size; i++) {
@@ -604,6 +721,7 @@
 
     /**
      * Return list of unique interfaces known by this data structure.
+     * @hide
      */
     public String[] getUniqueIfaces() {
         final HashSet<String> ifaces = new HashSet<String>();
@@ -617,6 +735,7 @@
 
     /**
      * Return list of unique UIDs known by this data structure.
+     * @hide
      */
     @UnsupportedAppUsage
     public int[] getUniqueUids() {
@@ -636,6 +755,7 @@
     /**
      * Return total bytes represented by this snapshot object, usually used when
      * checking if a {@link #subtract(NetworkStats)} delta passes a threshold.
+     * @hide
      */
     @UnsupportedAppUsage
     public long getTotalBytes() {
@@ -645,6 +765,7 @@
 
     /**
      * Return total of all fields represented by this snapshot object.
+     * @hide
      */
     @UnsupportedAppUsage
     public Entry getTotal(Entry recycle) {
@@ -654,6 +775,7 @@
     /**
      * Return total of all fields represented by this snapshot object matching
      * the requested {@link #uid}.
+     * @hide
      */
     @UnsupportedAppUsage
     public Entry getTotal(Entry recycle, int limitUid) {
@@ -663,11 +785,13 @@
     /**
      * Return total of all fields represented by this snapshot object matching
      * the requested {@link #iface}.
+     * @hide
      */
     public Entry getTotal(Entry recycle, HashSet<String> limitIface) {
         return getTotal(recycle, limitIface, UID_ALL, false);
     }
 
+    /** @hide */
     @UnsupportedAppUsage
     public Entry getTotalIncludingTags(Entry recycle) {
         return getTotal(recycle, null, UID_ALL, true);
@@ -717,6 +841,7 @@
 
     /**
      * Fast path for battery stats.
+     * @hide
      */
     public long getTotalPackets() {
         long total = 0;
@@ -729,9 +854,12 @@
     /**
      * Subtract the given {@link NetworkStats}, effectively leaving the delta
      * between two snapshots in time. Assumes that statistics rows collect over
-     * time, and that none of them have disappeared.
+     * time, and that none of them have disappeared. This method does not mutate
+     * the referencing object.
+     *
+     * @return the delta between two objects.
      */
-    public NetworkStats subtract(NetworkStats right) {
+    public @NonNull NetworkStats subtract(@NonNull NetworkStats right) {
         return subtract(this, right, null, null);
     }
 
@@ -742,6 +870,7 @@
      * <p>
      * If counters have rolled backwards, they are clamped to {@code 0} and
      * reported to the given {@link NonMonotonicObserver}.
+     * @hide
      */
     public static <C> NetworkStats subtract(NetworkStats left, NetworkStats right,
             NonMonotonicObserver<C> observer, C cookie) {
@@ -759,6 +888,7 @@
      * If <var>recycle</var> is supplied, this NetworkStats object will be
      * reused (and returned) as the result if it is large enough to contain
      * the data.
+     * @hide
      */
     public static <C> NetworkStats subtract(NetworkStats left, NetworkStats right,
             NonMonotonicObserver<C> observer, C cookie, NetworkStats recycle) {
@@ -817,7 +947,7 @@
                 entry.operations = Math.max(entry.operations, 0);
             }
 
-            result.addValues(entry);
+            result.addEntry(entry);
         }
 
         return result;
@@ -847,6 +977,7 @@
      * @param stackedTraffic Stats with traffic stacked on top of our ifaces. Will also be mutated.
      * @param stackedIfaces Mapping ipv6if -> ipv4if interface where traffic is counted on both.
      * @param useBpfStats True if eBPF is in use.
+     * @hide
      */
     public static void apply464xlatAdjustments(NetworkStats baseTraffic,
             NetworkStats stackedTraffic, Map<String, String> stackedIfaces, boolean useBpfStats) {
@@ -899,6 +1030,7 @@
      * {@link #apply464xlatAdjustments(NetworkStats, NetworkStats, Map)} with {@code this} as
      * base and stacked traffic.
      * @param stackedIfaces Mapping ipv6if -> ipv4if interface where traffic is counted on both.
+     * @hide
      */
     public void apply464xlatAdjustments(Map<String, String> stackedIfaces, boolean useBpfStats) {
         apply464xlatAdjustments(this, this, stackedIfaces, useBpfStats);
@@ -907,6 +1039,7 @@
     /**
      * Return total statistics grouped by {@link #iface}; doesn't mutate the
      * original structure.
+     * @hide
      */
     public NetworkStats groupedByIface() {
         final NetworkStats stats = new NetworkStats(elapsedRealtime, 10);
@@ -938,6 +1071,7 @@
     /**
      * Return total statistics grouped by {@link #uid}; doesn't mutate the
      * original structure.
+     * @hide
      */
     public NetworkStats groupedByUid() {
         final NetworkStats stats = new NetworkStats(elapsedRealtime, 10);
@@ -968,6 +1102,7 @@
 
     /**
      * Remove all rows that match one of specified UIDs.
+     * @hide
      */
     public void removeUids(int[] uids) {
         int nextOutputEntry = 0;
@@ -989,6 +1124,7 @@
      * @param limitUid UID to filter for, or {@link #UID_ALL}.
      * @param limitIfaces Interfaces to filter for, or {@link #INTERFACES_ALL}.
      * @param limitTag Tag to filter for, or {@link #TAG_ALL}.
+     * @hide
      */
     public void filter(int limitUid, String[] limitIfaces, int limitTag) {
         if (limitUid == UID_ALL && limitTag == TAG_ALL && limitIfaces == INTERFACES_ALL) {
@@ -1004,6 +1140,7 @@
      * Only keep entries with {@link #set} value less than {@link #SET_DEBUG_START}.
      *
      * <p>This mutates the original structure in place.
+     * @hide
      */
     public void filterDebugEntries() {
         filter(e -> e.set < SET_DEBUG_START);
@@ -1024,6 +1161,7 @@
         size = nextOutputEntry;
     }
 
+    /** @hide */
     public void dump(String prefix, PrintWriter pw) {
         pw.print(prefix);
         pw.print("NetworkStats: elapsedRealtime="); pw.println(elapsedRealtime);
@@ -1047,6 +1185,7 @@
 
     /**
      * Return text description of {@link #set} value.
+     * @hide
      */
     public static String setToString(int set) {
         switch (set) {
@@ -1067,6 +1206,7 @@
 
     /**
      * Return text description of {@link #set} value.
+     * @hide
      */
     public static String setToCheckinString(int set) {
         switch (set) {
@@ -1087,6 +1227,7 @@
 
     /**
      * @return true if the querySet matches the dataSet.
+     * @hide
      */
     public static boolean setMatches(int querySet, int dataSet) {
         if (querySet == dataSet) {
@@ -1098,6 +1239,7 @@
 
     /**
      * Return text description of {@link #tag} value.
+     * @hide
      */
     public static String tagToString(int tag) {
         return "0x" + Integer.toHexString(tag);
@@ -1105,6 +1247,7 @@
 
     /**
      * Return text description of {@link #metered} value.
+     * @hide
      */
     public static String meteredToString(int metered) {
         switch (metered) {
@@ -1121,6 +1264,7 @@
 
     /**
      * Return text description of {@link #roaming} value.
+     * @hide
      */
     public static String roamingToString(int roaming) {
         switch (roaming) {
@@ -1137,6 +1281,7 @@
 
     /**
      * Return text description of {@link #defaultNetwork} value.
+     * @hide
      */
     public static String defaultNetworkToString(int defaultNetwork) {
         switch (defaultNetwork) {
@@ -1151,6 +1296,7 @@
         }
     }
 
+    /** @hide */
     @Override
     public String toString() {
         final CharArrayWriter writer = new CharArrayWriter();
@@ -1163,8 +1309,7 @@
         return 0;
     }
 
-    @UnsupportedAppUsage
-    public static final @android.annotation.NonNull Creator<NetworkStats> CREATOR = new Creator<NetworkStats>() {
+    public static final @NonNull Creator<NetworkStats> CREATOR = new Creator<NetworkStats>() {
         @Override
         public NetworkStats createFromParcel(Parcel in) {
             return new NetworkStats(in);
@@ -1176,6 +1321,7 @@
         }
     };
 
+    /** @hide */
     public interface NonMonotonicObserver<C> {
         public void foundNonMonotonic(
                 NetworkStats left, int leftIndex, NetworkStats right, int rightIndex, C cookie);
@@ -1195,6 +1341,7 @@
      * @param tunUid uid of the VPN application
      * @param tunIface iface of the vpn tunnel
      * @param underlyingIfaces underlying network ifaces used by the VPN application
+     * @hide
      */
     public void migrateTun(int tunUid, @NonNull String tunIface,
             @NonNull String[] underlyingIfaces) {
diff --git a/core/java/android/net/NetworkStatsHistory.java b/core/java/android/net/NetworkStatsHistory.java
index f61260e..7b799e2 100644
--- a/core/java/android/net/NetworkStatsHistory.java
+++ b/core/java/android/net/NetworkStatsHistory.java
@@ -30,7 +30,7 @@
 
 import static com.android.internal.util.ArrayUtils.total;
 
-import android.annotation.UnsupportedAppUsage;
+import android.compat.annotation.UnsupportedAppUsage;
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.service.NetworkStatsHistoryBucketProto;
diff --git a/core/java/android/net/NetworkTemplate.java b/core/java/android/net/NetworkTemplate.java
index 87c7118..5e6c47a 100644
--- a/core/java/android/net/NetworkTemplate.java
+++ b/core/java/android/net/NetworkTemplate.java
@@ -34,7 +34,7 @@
 import static android.net.NetworkStats.ROAMING_YES;
 import static android.net.wifi.WifiInfo.removeDoubleQuotes;
 
-import android.annotation.UnsupportedAppUsage;
+import android.compat.annotation.UnsupportedAppUsage;
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.util.BackupUtils;
diff --git a/core/java/android/net/TrafficStats.java b/core/java/android/net/TrafficStats.java
index bf4884a..8108cf0 100644
--- a/core/java/android/net/TrafficStats.java
+++ b/core/java/android/net/TrafficStats.java
@@ -20,10 +20,10 @@
 import android.annotation.SuppressLint;
 import android.annotation.SystemApi;
 import android.annotation.TestApi;
-import android.annotation.UnsupportedAppUsage;
 import android.app.DownloadManager;
 import android.app.backup.BackupManager;
 import android.app.usage.NetworkStatsManager;
+import android.compat.annotation.UnsupportedAppUsage;
 import android.content.Context;
 import android.media.MediaPlayer;
 import android.os.Build;
@@ -89,7 +89,7 @@
      *
      * @hide
      */
-    public static final int UID_TETHERING = -5;
+    public static final int UID_TETHERING = NetworkStats.UID_TETHERING;
 
     /**
      * Tag values in this range are reserved for the network stack. The network stack is
diff --git a/core/java/android/net/netstats/provider/INetworkStatsProvider.aidl b/core/java/android/net/netstats/provider/INetworkStatsProvider.aidl
new file mode 100644
index 0000000..55b3d4e
--- /dev/null
+++ b/core/java/android/net/netstats/provider/INetworkStatsProvider.aidl
@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2020 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.provider;
+
+/**
+ * Interface for NetworkStatsService to query network statistics and set data limits.
+ *
+ * @hide
+ */
+oneway interface INetworkStatsProvider {
+    void requestStatsUpdate(int token);
+    void setLimit(String iface, long quotaBytes);
+    void setAlert(long quotaBytes);
+}
diff --git a/core/java/android/net/netstats/provider/INetworkStatsProviderCallback.aidl b/core/java/android/net/netstats/provider/INetworkStatsProviderCallback.aidl
new file mode 100644
index 0000000..3ea9318
--- /dev/null
+++ b/core/java/android/net/netstats/provider/INetworkStatsProviderCallback.aidl
@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2020 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.provider;
+
+import android.net.NetworkStats;
+
+/**
+ * Interface for implementor of {@link INetworkStatsProviderCallback} to push events
+ * such as network statistics update or notify limit reached.
+ * @hide
+ */
+oneway interface INetworkStatsProviderCallback {
+    void onStatsUpdated(int token, in NetworkStats ifaceStats, in NetworkStats uidStats);
+    void onAlertReached();
+    void onLimitReached();
+    void unregister();
+}
diff --git a/core/java/android/net/nsd/NsdServiceInfo.java b/core/java/android/net/nsd/NsdServiceInfo.java
index 459b140..0946499 100644
--- a/core/java/android/net/nsd/NsdServiceInfo.java
+++ b/core/java/android/net/nsd/NsdServiceInfo.java
@@ -17,13 +17,13 @@
 package android.net.nsd;
 
 import android.annotation.NonNull;
-import android.annotation.UnsupportedAppUsage;
-import android.os.Parcelable;
+import android.compat.annotation.UnsupportedAppUsage;
 import android.os.Parcel;
+import android.os.Parcelable;
 import android.text.TextUtils;
+import android.util.ArrayMap;
 import android.util.Base64;
 import android.util.Log;
-import android.util.ArrayMap;
 
 import java.io.UnsupportedEncodingException;
 import java.net.InetAddress;
diff --git a/packages/Tethering/src/android/net/util/TetheringMessageBase.java b/packages/Tethering/src/android/net/util/TetheringMessageBase.java
new file mode 100644
index 0000000..1b763ce
--- /dev/null
+++ b/packages/Tethering/src/android/net/util/TetheringMessageBase.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2020 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.util;
+
+/**
+ * This class defines Message.what base addresses for various state machine.
+ */
+public class TetheringMessageBase {
+    public static final int BASE_MASTER   = 0;
+    public static final int BASE_IPSERVER = 100;
+
+}
diff --git a/services/core/java/com/android/server/net/NetworkStatsFactory.java b/services/core/java/com/android/server/net/NetworkStatsFactory.java
index 3ca1803..22b01be 100644
--- a/services/core/java/com/android/server/net/NetworkStatsFactory.java
+++ b/services/core/java/com/android/server/net/NetworkStatsFactory.java
@@ -229,7 +229,7 @@
                     entry.txPackets += reader.nextLong();
                 }
 
-                stats.addValues(entry);
+                stats.addEntry(entry);
                 reader.finishLine();
             }
         } catch (NullPointerException|NumberFormatException e) {
@@ -279,7 +279,7 @@
                 entry.txBytes = reader.nextLong();
                 entry.txPackets = reader.nextLong();
 
-                stats.addValues(entry);
+                stats.addEntry(entry);
                 reader.finishLine();
             }
         } catch (NullPointerException|NumberFormatException e) {
@@ -439,7 +439,7 @@
                 if ((limitIfaces == null || ArrayUtils.contains(limitIfaces, entry.iface))
                         && (limitUid == UID_ALL || limitUid == entry.uid)
                         && (limitTag == TAG_ALL || limitTag == entry.tag)) {
-                    stats.addValues(entry);
+                    stats.addEntry(entry);
                 }
 
                 reader.finishLine();
diff --git a/services/core/java/com/android/server/net/NetworkStatsService.java b/services/core/java/com/android/server/net/NetworkStatsService.java
index a41fb7d..fc39a25 100644
--- a/services/core/java/com/android/server/net/NetworkStatsService.java
+++ b/services/core/java/com/android/server/net/NetworkStatsService.java
@@ -18,6 +18,7 @@
 
 import static android.Manifest.permission.ACCESS_NETWORK_STATE;
 import static android.Manifest.permission.READ_NETWORK_USAGE_HISTORY;
+import static android.Manifest.permission.UPDATE_DEVICE_STATS;
 import static android.content.Intent.ACTION_SHUTDOWN;
 import static android.content.Intent.ACTION_UID_REMOVED;
 import static android.content.Intent.ACTION_USER_REMOVED;
@@ -27,6 +28,7 @@
 import static android.net.NetworkStack.checkNetworkStackPermission;
 import static android.net.NetworkStats.DEFAULT_NETWORK_ALL;
 import static android.net.NetworkStats.IFACE_ALL;
+import static android.net.NetworkStats.IFACE_VT;
 import static android.net.NetworkStats.INTERFACES_ALL;
 import static android.net.NetworkStats.METERED_ALL;
 import static android.net.NetworkStats.ROAMING_ALL;
@@ -70,6 +72,7 @@
 import static com.android.server.NetworkManagementSocketTagger.setKernelCounterSet;
 
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.app.AlarmManager;
 import android.app.PendingIntent;
 import android.app.usage.NetworkStatsManager;
@@ -96,6 +99,9 @@
 import android.net.NetworkStatsHistory;
 import android.net.NetworkTemplate;
 import android.net.TrafficStats;
+import android.net.netstats.provider.INetworkStatsProvider;
+import android.net.netstats.provider.INetworkStatsProviderCallback;
+import android.net.netstats.provider.NetworkStatsProviderCallback;
 import android.os.BestClock;
 import android.os.Binder;
 import android.os.DropBoxManager;
@@ -108,6 +114,7 @@
 import android.os.Message;
 import android.os.Messenger;
 import android.os.PowerManager;
+import android.os.RemoteCallbackList;
 import android.os.RemoteException;
 import android.os.SystemClock;
 import android.os.Trace;
@@ -175,7 +182,7 @@
      * This avoids firing the global alert too often on devices with high transfer speeds and
      * high quota.
      */
-    private static final int PERFORM_POLL_DELAY_MS = 1000;
+    private static final int DEFAULT_PERFORM_POLL_DELAY_MS = 1000;
 
     private static final String TAG_NETSTATS_ERROR = "netstats_error";
 
@@ -211,13 +218,15 @@
     /**
      * Virtual network interface for video telephony. This is for VT data usage counting purpose.
      */
-    public static final String VT_INTERFACE = "vt_data0";
+    // TODO: Remove this after no one is using it.
+    public static final String VT_INTERFACE = NetworkStats.IFACE_VT;
 
     /**
      * Settings that can be changed externally.
      */
     public interface NetworkStatsSettings {
         public long getPollInterval();
+        public long getPollDelay();
         public boolean getSampleEnabled();
         public boolean getAugmentEnabled();
 
@@ -246,6 +255,7 @@
     }
 
     private final Object mStatsLock = new Object();
+    private final Object mStatsProviderLock = new Object();
 
     /** Set of currently active ifaces. */
     @GuardedBy("mStatsLock")
@@ -270,6 +280,9 @@
     private final DropBoxNonMonotonicObserver mNonMonotonicObserver =
             new DropBoxNonMonotonicObserver();
 
+    private final RemoteCallbackList<NetworkStatsProviderCallbackImpl> mStatsProviderCbList =
+            new RemoteCallbackList<>();
+
     @GuardedBy("mStatsLock")
     private NetworkStatsRecorder mDevRecorder;
     @GuardedBy("mStatsLock")
@@ -500,9 +513,9 @@
     }
 
     /**
-     * Register for a global alert that is delivered through
-     * {@link INetworkManagementEventObserver} once a threshold amount of data
-     * has been transferred.
+     * Register for a global alert that is delivered through {@link INetworkManagementEventObserver}
+     * or {@link NetworkStatsProviderCallback#onAlertReached()} once a threshold amount of data has
+     * been transferred.
      */
     private void registerGlobalAlert() {
         try {
@@ -512,6 +525,7 @@
         } catch (RemoteException e) {
             // ignored; service lives in system_server
         }
+        invokeForAllStatsProviderCallbacks((cb) -> cb.mProvider.setAlert(mGlobalAlertBytes));
     }
 
     @Override
@@ -712,7 +726,7 @@
         final NetworkStatsHistory.Entry entry = history.getValues(start, end, now, null);
 
         final NetworkStats stats = new NetworkStats(end - start, 1);
-        stats.addValues(new NetworkStats.Entry(IFACE_ALL, UID_ALL, SET_ALL, TAG_NONE,
+        stats.addEntry(new NetworkStats.Entry(IFACE_ALL, UID_ALL, SET_ALL, TAG_NONE,
                 METERED_ALL, ROAMING_ALL, DEFAULT_NETWORK_ALL, entry.rxBytes, entry.rxPackets,
                 entry.txBytes, entry.txPackets, entry.operations));
         return stats;
@@ -801,8 +815,7 @@
     @Override
     public void incrementOperationCount(int uid, int tag, int operationCount) {
         if (Binder.getCallingUid() != uid) {
-            mContext.enforceCallingOrSelfPermission(
-                    android.Manifest.permission.UPDATE_DEVICE_STATS, TAG);
+            mContext.enforceCallingOrSelfPermission(UPDATE_DEVICE_STATS, TAG);
         }
 
         if (operationCount < 0) {
@@ -1093,7 +1106,7 @@
     /**
      * Observer that watches for {@link INetworkManagementService} alerts.
      */
-    private INetworkManagementEventObserver mAlertObserver = new BaseNetworkObserver() {
+    private final INetworkManagementEventObserver mAlertObserver = new BaseNetworkObserver() {
         @Override
         public void limitReached(String limitName, String iface) {
             // only someone like NMS should be calling us
@@ -1104,7 +1117,7 @@
                 // such a call pending; UID stats are handled during normal polling interval.
                 if (!mHandler.hasMessages(MSG_PERFORM_POLL_REGISTER_ALERT)) {
                     mHandler.sendEmptyMessageDelayed(MSG_PERFORM_POLL_REGISTER_ALERT,
-                            PERFORM_POLL_DELAY_MS);
+                            mSettings.getPollDelay());
                 }
             }
         }
@@ -1179,8 +1192,8 @@
                                 ident.getSubType(), ident.getSubscriberId(), ident.getNetworkId(),
                                 ident.getRoaming(), true /* metered */,
                                 true /* onDefaultNetwork */);
-                        findOrCreateNetworkIdentitySet(mActiveIfaces, VT_INTERFACE).add(vtIdent);
-                        findOrCreateNetworkIdentitySet(mActiveUidIfaces, VT_INTERFACE).add(vtIdent);
+                        findOrCreateNetworkIdentitySet(mActiveIfaces, IFACE_VT).add(vtIdent);
+                        findOrCreateNetworkIdentitySet(mActiveUidIfaces, IFACE_VT).add(vtIdent);
                     }
 
                     if (isMobile) {
@@ -1250,6 +1263,14 @@
         xtSnapshot.combineAllValues(tetherSnapshot);
         devSnapshot.combineAllValues(tetherSnapshot);
 
+        // Snapshot for dev/xt stats from all custom stats providers. Counts per-interface data
+        // from stats providers that isn't already counted by dev and XT stats.
+        Trace.traceBegin(TRACE_TAG_NETWORK, "snapshotStatsProvider");
+        final NetworkStats providersnapshot = getNetworkStatsFromProviders(STATS_PER_IFACE);
+        Trace.traceEnd(TRACE_TAG_NETWORK);
+        xtSnapshot.combineAllValues(providersnapshot);
+        devSnapshot.combineAllValues(providersnapshot);
+
         // For xt/dev, we pass a null VPN array because usage is aggregated by UID, so VPN traffic
         // can't be reattributed to responsible apps.
         Trace.traceBegin(TRACE_TAG_NETWORK, "recordDev");
@@ -1353,6 +1374,10 @@
             performSampleLocked();
         }
 
+        // request asynchronous stats update from all providers for next poll.
+        // TODO: request with a valid token.
+        invokeForAllStatsProviderCallbacks((cb) -> cb.mProvider.requestStatsUpdate(0 /* unused */));
+
         // finally, dispatch updated event to any listeners
         final Intent updatedIntent = new Intent(ACTION_NETWORK_STATS_UPDATED);
         updatedIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
@@ -1474,6 +1499,12 @@
         public void forceUpdate() {
             NetworkStatsService.this.forceUpdate();
         }
+
+        @Override
+        public void setStatsProviderLimit(@NonNull String iface, long quota) {
+            Slog.v(TAG, "setStatsProviderLimit(" + iface + "," + quota + ")");
+            invokeForAllStatsProviderCallbacks((cb) -> cb.mProvider.setLimit(iface, quota));
+        }
     }
 
     @Override
@@ -1688,6 +1719,12 @@
             uidSnapshot.combineAllValues(vtStats);
         }
 
+        // get a stale copy of uid stats snapshot provided by providers.
+        final NetworkStats providerStats = getNetworkStatsFromProviders(STATS_PER_UID);
+        providerStats.filter(UID_ALL, ifaces, TAG_ALL);
+        mStatsFactory.apply464xlatAdjustments(uidSnapshot, providerStats, mUseBpfTrafficStats);
+        uidSnapshot.combineAllValues(providerStats);
+
         uidSnapshot.combineAllValues(mUidOperations);
 
         return uidSnapshot;
@@ -1724,6 +1761,152 @@
         }
     }
 
+    /**
+     * Registers a custom provider of {@link android.net.NetworkStats} to combine the network
+     * statistics that cannot be seen by the kernel to system. To unregister, invoke the
+     * {@code unregister()} of the returned callback.
+     *
+     * @param tag a human readable identifier of the custom network stats provider.
+     * @param provider the binder interface of
+     *                 {@link android.net.netstats.provider.AbstractNetworkStatsProvider} that
+     *                 needs to be registered to the system.
+     *
+     * @return a binder interface of
+     *         {@link android.net.netstats.provider.NetworkStatsProviderCallback}, which can be
+     *         used to report events to the system.
+     */
+    public @NonNull INetworkStatsProviderCallback registerNetworkStatsProvider(
+            @NonNull String tag, @NonNull INetworkStatsProvider provider) {
+        mContext.enforceCallingOrSelfPermission(UPDATE_DEVICE_STATS, TAG);
+        Objects.requireNonNull(provider, "provider is null");
+        Objects.requireNonNull(tag, "tag is null");
+        try {
+            NetworkStatsProviderCallbackImpl callback = new NetworkStatsProviderCallbackImpl(
+                            tag, provider, mAlertObserver, mStatsProviderCbList);
+            mStatsProviderCbList.register(callback);
+            Log.d(TAG, "registerNetworkStatsProvider from " + callback.mTag + " uid/pid="
+                    + getCallingUid() + "/" + getCallingPid());
+            return callback;
+        } catch (RemoteException e) {
+            Log.e(TAG, "registerNetworkStatsProvider failed", e);
+        }
+        return null;
+    }
+
+    // Collect stats from local cache of providers.
+    private @NonNull NetworkStats getNetworkStatsFromProviders(int how) {
+        final NetworkStats ret = new NetworkStats(0L, 0);
+        invokeForAllStatsProviderCallbacks((cb) -> ret.combineAllValues(cb.getCachedStats(how)));
+        return ret;
+    }
+
+    @FunctionalInterface
+    private interface ThrowingConsumer<S, T extends Throwable> {
+        void accept(S s) throws T;
+    }
+
+    private void invokeForAllStatsProviderCallbacks(
+            @NonNull ThrowingConsumer<NetworkStatsProviderCallbackImpl, RemoteException> task) {
+        synchronized (mStatsProviderCbList) {
+            final int length = mStatsProviderCbList.beginBroadcast();
+            try {
+                for (int i = 0; i < length; i++) {
+                    final NetworkStatsProviderCallbackImpl cb =
+                            mStatsProviderCbList.getBroadcastItem(i);
+                    try {
+                        task.accept(cb);
+                    } catch (RemoteException e) {
+                        Log.e(TAG, "Fail to broadcast to provider: " + cb.mTag, e);
+                    }
+                }
+            } finally {
+                mStatsProviderCbList.finishBroadcast();
+            }
+        }
+    }
+
+    private static class NetworkStatsProviderCallbackImpl extends INetworkStatsProviderCallback.Stub
+            implements IBinder.DeathRecipient {
+        @NonNull final String mTag;
+        @NonNull private final Object mProviderStatsLock = new Object();
+        @NonNull final INetworkStatsProvider mProvider;
+        @NonNull final INetworkManagementEventObserver mAlertObserver;
+        @NonNull final RemoteCallbackList<NetworkStatsProviderCallbackImpl> mStatsProviderCbList;
+
+        @GuardedBy("mProviderStatsLock")
+        // STATS_PER_IFACE and STATS_PER_UID
+        private final NetworkStats mIfaceStats = new NetworkStats(0L, 0);
+        @GuardedBy("mProviderStatsLock")
+        private final NetworkStats mUidStats = new NetworkStats(0L, 0);
+
+        NetworkStatsProviderCallbackImpl(
+                @NonNull String tag, @NonNull INetworkStatsProvider provider,
+                @NonNull INetworkManagementEventObserver alertObserver,
+                @NonNull RemoteCallbackList<NetworkStatsProviderCallbackImpl> cbList)
+                throws RemoteException {
+            mTag = tag;
+            mProvider = provider;
+            mProvider.asBinder().linkToDeath(this, 0);
+            mAlertObserver = alertObserver;
+            mStatsProviderCbList = cbList;
+        }
+
+        @NonNull
+        public NetworkStats getCachedStats(int how) {
+            synchronized (mProviderStatsLock) {
+                NetworkStats stats;
+                switch (how) {
+                    case STATS_PER_IFACE:
+                        stats = mIfaceStats;
+                        break;
+                    case STATS_PER_UID:
+                        stats = mUidStats;
+                        break;
+                    default:
+                        throw new IllegalArgumentException("Invalid type: " + how);
+                }
+                // Return a defensive copy instead of local reference.
+                return stats.clone();
+            }
+        }
+
+        @Override
+        public void onStatsUpdated(int token, @Nullable NetworkStats ifaceStats,
+                @Nullable NetworkStats uidStats) {
+            // TODO: 1. Use token to map ifaces to correct NetworkIdentity.
+            //       2. Store the difference and store it directly to the recorder.
+            synchronized (mProviderStatsLock) {
+                if (ifaceStats != null) mIfaceStats.combineAllValues(ifaceStats);
+                if (uidStats != null) mUidStats.combineAllValues(uidStats);
+            }
+        }
+
+        @Override
+        public void onAlertReached() throws RemoteException {
+            mAlertObserver.limitReached(LIMIT_GLOBAL_ALERT, null /* unused */);
+        }
+
+        @Override
+        public void onLimitReached() {
+            Log.d(TAG, mTag + ": onLimitReached");
+            LocalServices.getService(NetworkPolicyManagerInternal.class)
+                    .onStatsProviderLimitReached(mTag);
+        }
+
+        @Override
+        public void binderDied() {
+            Log.d(TAG, mTag + ": binderDied");
+            mStatsProviderCbList.unregister(this);
+        }
+
+        @Override
+        public void unregister() {
+            Log.d(TAG, mTag + ": unregister");
+            mStatsProviderCbList.unregister(this);
+        }
+
+    }
+
     @VisibleForTesting
     static class HandlerCallback implements Handler.Callback {
         private final NetworkStatsService mService;
@@ -1813,6 +1996,10 @@
             return getGlobalLong(NETSTATS_POLL_INTERVAL, 30 * MINUTE_IN_MILLIS);
         }
         @Override
+        public long getPollDelay() {
+            return DEFAULT_PERFORM_POLL_DELAY_MS;
+        }
+        @Override
         public long getGlobalAlertBytes(long def) {
             return getGlobalLong(NETSTATS_GLOBAL_ALERT_BYTES, def);
         }