Internal API for system apps to determine default network for other apps

Callers with CONNECTIVITY_INTERNAL permission can read off the netId
that an application is assigned to by default.

Necessary for making connections as the default network for a client
app eg. when downloading stuff on its behalf.

Bug: 27074270
Change-Id: I8d35e8e99126875f55f3c545090326f3e9be43fb

core/java/android/net/ConnectivityManager.java

@@ -766,6 +766,28 @@ public class ConnectivityManager {
         }
     }
 
+    /**
+     * Returns a {@link Network} object corresponding to the currently active
+     * default data network for a specific UID.  In the event that the default data
+     * network disconnects, the returned {@code Network} object will no longer
+     * be usable.  This will return {@code null} when there is no default
+     * network for the UID.
+     * <p>This method requires the caller to hold the permission
+     * {@link android.Manifest.permission#CONNECTIVITY_INTERNAL}.
+     *
+     * @return a {@link Network} object for the current default network for the
+     *         given UID or {@code null} if no default network is currently active
+     *
+     * @hide
+     */
+    public Network getActiveNetworkForUid(int uid) {
+        try {
+            return mService.getActiveNetworkForUid(uid);
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
+
     /**
      * Configures an always-on VPN connection through a specific application.
      * This connection is automatically granted and persisted after a reboot.

core/java/android/net/IConnectivityManager.aidl

@@ -44,6 +44,7 @@ import com.android.internal.net.VpnProfile;
 interface IConnectivityManager
 {
     Network getActiveNetwork();
+    Network getActiveNetworkForUid(int uid);
     NetworkInfo getActiveNetworkInfo();
     NetworkInfo getActiveNetworkInfoForUid(int uid);
     NetworkInfo getNetworkInfo(int networkType);

services/core/java/com/android/server/ConnectivityService.java

@@ -1006,7 +1006,16 @@ public class ConnectivityService extends IConnectivityManager.Stub
     @Override
     public Network getActiveNetwork() {
         enforceAccessPermission();
-        final int uid = Binder.getCallingUid();
+        return getActiveNetworkForUidInternal(Binder.getCallingUid());
+    }
+
+    @Override
+    public Network getActiveNetworkForUid(int uid) {
+        enforceConnectivityInternalPermission();
+        return getActiveNetworkForUidInternal(uid);
+    }
+
+    private Network getActiveNetworkForUidInternal(final int uid) {
         final int user = UserHandle.getUserId(uid);
         int vpnNetId = NETID_UNSET;
         synchronized (mVpns) {

services/tests/servicestests/src/com/android/server/ConnectivityServiceTest.java

@@ -59,6 +59,7 @@ import android.os.Message;
 import android.os.MessageQueue;
 import android.os.Messenger;
 import android.os.MessageQueue.IdleHandler;
+import android.os.Process;
 import android.os.SystemClock;
 import android.test.AndroidTestCase;
 import android.test.suitebuilder.annotation.LargeTest;
@@ -690,6 +691,7 @@ public class ConnectivityServiceTest extends AndroidTestCase {
         assertEquals(transportToLegacyType(transport), mCm.getActiveNetworkInfo().getType());
         // Test getActiveNetwork()
         assertNotNull(mCm.getActiveNetwork());
+        assertEquals(mCm.getActiveNetwork(), mCm.getActiveNetworkForUid(Process.myUid()));
         switch (transport) {
             case TRANSPORT_WIFI:
                 assertEquals(mCm.getActiveNetwork(), mWiFiNetworkAgent.getNetwork());
@@ -713,6 +715,7 @@ public class ConnectivityServiceTest extends AndroidTestCase {
         assertNull(mCm.getActiveNetworkInfo());
         // Test getActiveNetwork()
         assertNull(mCm.getActiveNetwork());
+        assertNull(mCm.getActiveNetworkForUid(Process.myUid()));
         // Test getAllNetworks()
         assertEquals(0, mCm.getAllNetworks().length);
     }