[NS B09] Create NetworkRanker

Bug: 113554781
Test: FrameworksNetTests
Change-Id: Ia534247144f479fe896e1a6e05b906103cd10005

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

@@ -194,6 +194,7 @@ import com.android.server.connectivity.NetworkAgentInfo;
 import com.android.server.connectivity.NetworkDiagnostics;
 import com.android.server.connectivity.NetworkNotificationManager;
 import com.android.server.connectivity.NetworkNotificationManager.NotificationType;
+import com.android.server.connectivity.NetworkRanker;
 import com.android.server.connectivity.PermissionMonitor;
 import com.android.server.connectivity.ProxyTracker;
 import com.android.server.connectivity.Vpn;
@@ -579,6 +580,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
     final ConnectivityDiagnosticsHandler mConnectivityDiagnosticsHandler;
 
     private final DnsManager mDnsManager;
+    private final NetworkRanker mNetworkRanker;
 
     private boolean mSystemReady;
     private Intent mInitialBroadcast;
@@ -958,6 +960,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
 
         mMetricsLog = logger;
         mDefaultRequest = createDefaultInternetRequestForTransport(-1, NetworkRequest.Type.REQUEST);
+        mNetworkRanker = new NetworkRanker();
         NetworkRequestInfo defaultNRI = new NetworkRequestInfo(null, mDefaultRequest, new Binder());
         mNetworkRequests.put(mDefaultRequest, defaultNRI);
         mNetworkRequestInfoLogs.log("REGISTER " + defaultNRI);
@@ -6660,24 +6663,12 @@ public class ConnectivityService extends IConnectivityManager.Stub
             changes.addRematchedNetwork(new NetworkReassignment.NetworkBgStatePair(nai,
                     nai.isBackgroundNetwork()));
         }
-        Collections.sort(nais);
 
         for (final NetworkRequestInfo nri : mNetworkRequests.values()) {
             if (nri.request.isListen()) continue;
-            // Find the top scoring network satisfying this request.
+            final NetworkAgentInfo bestNetwork = mNetworkRanker.getBestNetwork(nri.request, nais);
-            NetworkAgentInfo bestNetwork = null;
+            if (bestNetwork != nri.mSatisfier) {
-            for (final NetworkAgentInfo nai : nais) {
+                // bestNetwork may be null if no network can satisfy this request.
-                if (!nai.satisfies(nri.request)) continue;
-                bestNetwork = nai;
-                // As the nais are sorted by score, this is the top-scoring network that can
-                // satisfy this request. The best network for this request has been found,
-                // go process the next NRI
-                break;
-            }
-            // If no NAI satisfies this request, bestNetwork is still null. That's fine : it
-            // means no network can satisfy the request. If nri.mSatisfier is not null, it just
-            // means the network that used to satisfy the request stopped satisfying it.
-            if (nri.mSatisfier != bestNetwork) {
                 changes.addRequestReassignment(new NetworkReassignment.RequestReassignment(
                         nri, nri.mSatisfier, bestNetwork));
             }

services/core/java/com/android/server/connectivity/NetworkRanker.java

@@ -0,0 +1,50 @@
+/*
+ * 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 com.android.server.connectivity;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.net.NetworkRequest;
+
+import java.util.Collection;
+
+/**
+ * A class that knows how to find the best network matching a request out of a list of networks.
+ */
+public class NetworkRanker {
+    public NetworkRanker() { }
+
+    /**
+     * Find the best network satisfying this request among the list of passed networks.
+     */
+    // Almost equivalent to Collections.max(nais), but allows returning null if no network
+    // satisfies the request.
+    @Nullable
+    public NetworkAgentInfo getBestNetwork(@NonNull final NetworkRequest request,
+            @NonNull final Collection<NetworkAgentInfo> nais) {
+        NetworkAgentInfo bestNetwork = null;
+        int bestScore = Integer.MIN_VALUE;
+        for (final NetworkAgentInfo nai : nais) {
+            if (!nai.satisfies(request)) continue;
+            if (nai.getCurrentScore() > bestScore) {
+                bestNetwork = nai;
+                bestScore = nai.getCurrentScore();
+            }
+        }
+        return bestNetwork;
+    }
+}

tests/net/java/com/android/server/connectivity/NetworkRankerTest.kt

@@ -0,0 +1,84 @@
+/*
+ * 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 com.android.server.connectivity
+
+import android.net.NetworkRequest
+import androidx.test.filters.SmallTest
+import androidx.test.runner.AndroidJUnit4
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.ArgumentMatchers.any
+import org.mockito.Mockito.doReturn
+import org.mockito.Mockito.mock
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+@RunWith(AndroidJUnit4::class)
+@SmallTest
+class NetworkRankerTest {
+    private val ranker = NetworkRanker()
+
+    private fun makeNai(satisfy: Boolean, score: Int) = mock(NetworkAgentInfo::class.java).also {
+        doReturn(satisfy).`when`(it).satisfies(any())
+        doReturn(score).`when`(it).currentScore
+    }
+
+    @Test
+    fun testGetBestNetwork() {
+        val scores = listOf(20, 50, 90, 60, 23, 68)
+        val nais = scores.map { makeNai(true, it) }
+        val bestNetwork = nais[2] // The one with the top score
+        val someRequest = mock(NetworkRequest::class.java)
+        assertEquals(bestNetwork, ranker.getBestNetwork(someRequest, nais))
+    }
+
+    @Test
+    fun testIgnoreNonSatisfying() {
+        val nais = listOf(makeNai(true, 20), makeNai(true, 50), makeNai(false, 90),
+                makeNai(false, 60), makeNai(true, 23), makeNai(false, 68))
+        val bestNetwork = nais[1] // Top score that's satisfying
+        val someRequest = mock(NetworkRequest::class.java)
+        assertEquals(bestNetwork, ranker.getBestNetwork(someRequest, nais))
+    }
+
+    @Test
+    fun testNoMatch() {
+        val nais = listOf(makeNai(false, 20), makeNai(false, 50), makeNai(false, 90))
+        val someRequest = mock(NetworkRequest::class.java)
+        assertNull(ranker.getBestNetwork(someRequest, nais))
+    }
+
+    @Test
+    fun testEmpty() {
+        val someRequest = mock(NetworkRequest::class.java)
+        assertNull(ranker.getBestNetwork(someRequest, emptyList()))
+    }
+
+    // Make sure the ranker is "stable" (as in stable sort), that is, it always returns the FIRST
+    // network satisfying the request if multiple of them have the same score.
+    @Test
+    fun testStable() {
+        val nais1 = listOf(makeNai(true, 30), makeNai(true, 30), makeNai(true, 30),
+                makeNai(true, 30), makeNai(true, 30), makeNai(true, 30))
+        val someRequest = mock(NetworkRequest::class.java)
+        assertEquals(nais1[0], ranker.getBestNetwork(someRequest, nais1))
+
+        val nais2 = listOf(makeNai(true, 30), makeNai(true, 50), makeNai(true, 20),
+                makeNai(true, 50), makeNai(true, 50), makeNai(true, 40))
+        assertEquals(nais2[1], ranker.getBestNetwork(someRequest, nais2))
+    }
+}