Avoid overlapping NetIDs in ConnectivityServiceTest with real NetIDs

Overlapping the NetIDs can cause the ConnectivityService instance under test
to inadvertently use real networks, for example when NetworkMonitor attempts
to validate a network.  This fixes test hangs when run on devices with
active internet connections.

Change-Id: I5e1898953f0117b9f75beccac4a52ae2db173567

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

@@ -100,6 +100,7 @@ import android.util.Xml;
 
 import com.android.internal.R;
 import com.android.internal.annotations.GuardedBy;
+import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.app.IBatteryStats;
 import com.android.internal.net.LegacyVpnInfo;
 import com.android.internal.net.NetworkStatsFactory;
@@ -767,7 +768,8 @@ public class ConnectivityService extends IConnectivityManager.Stub
         return mNextNetworkRequestId++;
     }
 
-    private int reserveNetId() {
+    @VisibleForTesting
+    protected int reserveNetId() {
         synchronized (mNetworkForNetId) {
             for (int i = MIN_NET_ID; i <= MAX_NET_ID; i++) {
                 int netId = mNextNetId;
@@ -1664,6 +1666,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
     private static final String DEFAULT_TCP_RWND_KEY = "net.tcp.default_init_rwnd";
 
     // Overridden for testing purposes to avoid writing to SystemProperties.
+    @VisibleForTesting
     protected int getDefaultTcpRwnd() {
         return SystemProperties.getInt(DEFAULT_TCP_RWND_KEY, 0);
     }

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

@@ -235,6 +235,27 @@ public class ConnectivityServiceTest extends AndroidTestCase {
             // Prevent wrapped ConnectivityService from trying to write to SystemProperties.
             return 0;
         }
+
+        @Override
+        protected int reserveNetId() {
+            while (true) {
+                final int netId = super.reserveNetId();
+
+                // Don't overlap test NetIDs with real NetIDs as binding sockets to real networks
+                // can have odd side-effects, like network validations succeeding.
+                final Network[] networks = ConnectivityManager.from(getContext()).getAllNetworks();
+                boolean overlaps = false;
+                for (Network network : networks) {
+                    if (netId == network.netId) {
+                        overlaps = true;
+                        break;
+                    }
+                }
+                if (overlaps) continue;
+
+                return netId;
+            }
+        }
     }
 
     @Override