Merge "Add a NetworkAgent API to indicate that a network will be replaced."

framework/api/system-current.txt

@@ -236,6 +236,7 @@ package android.net {
   public abstract class NetworkAgent {
     ctor public NetworkAgent(@NonNull android.content.Context, @NonNull android.os.Looper, @NonNull String, @NonNull android.net.NetworkCapabilities, @NonNull android.net.LinkProperties, int, @NonNull android.net.NetworkAgentConfig, @Nullable android.net.NetworkProvider);
     ctor public NetworkAgent(@NonNull android.content.Context, @NonNull android.os.Looper, @NonNull String, @NonNull android.net.NetworkCapabilities, @NonNull android.net.LinkProperties, @NonNull android.net.NetworkScore, @NonNull android.net.NetworkAgentConfig, @Nullable android.net.NetworkProvider);
+    method public void destroyAndAwaitReplacement(@IntRange(from=0, to=0x1388) int);
     method @Nullable public android.net.Network getNetwork();
     method public void markConnected();
     method public void onAddKeepalivePacketFilter(int, @NonNull android.net.KeepalivePacketData);

framework/src/android/net/INetworkAgentRegistry.aidl

@@ -47,4 +47,5 @@ oneway interface INetworkAgentRegistry {
     void sendAddDscpPolicy(in DscpPolicy policy);
     void sendRemoveDscpPolicy(int policyId);
     void sendRemoveAllDscpPolicies();
+    void sendDestroyAndAwaitReplacement(int timeoutMillis);
 }

framework/src/android/net/NetworkAgent.java

@@ -434,6 +434,14 @@ public abstract class NetworkAgent {
      */
     public static final int CMD_DSCP_POLICY_STATUS = BASE + 28;
 
+    /**
+     * Sent by the NetworkAgent to ConnectivityService to notify that this network is expected to be
+     * replaced within the specified time by a similar network.
+     * arg1 = timeout in milliseconds
+     * @hide
+     */
+    public static final int EVENT_DESTROY_AND_AWAIT_REPLACEMENT = BASE + 29;
+
     private static NetworkInfo getLegacyNetworkInfo(final NetworkAgentConfig config) {
         final NetworkInfo ni = new NetworkInfo(config.legacyType, config.legacySubType,
                 config.legacyTypeName, config.legacySubTypeName);
@@ -942,6 +950,45 @@ public abstract class NetworkAgent {
         queueOrSendMessage(reg -> reg.sendTeardownDelayMs(teardownDelayMillis));
     }
 
+    /**
+     * Indicates that this agent will likely soon be replaced by another agent for a very similar
+     * network (e.g., same Wi-Fi SSID).
+     *
+     * If the network is not currently satisfying any {@link NetworkRequest}s, it will be torn down.
+     * If it is satisfying requests, then the native network corresponding to the agent will be
+     * destroyed immediately, but the agent will remain registered and will continue to satisfy
+     * requests until {@link #unregister} is called, the network is replaced by an equivalent or
+     * better network, or the specified timeout expires. During this time:
+     *
+     * <ul>
+     * <li>The agent may not send any further updates, for example by calling methods
+     *    such as {@link #sendNetworkCapabilities}, {@link #sendLinkProperties},
+     *    {@link #sendNetworkScore(NetworkScore)} and so on. Any such updates will be ignored.
+     * <li>The network will remain connected and continue to satisfy any requests that it would
+     *    otherwise satisfy (including, possibly, the default request).
+     * <li>The validation state of the network will not change, and calls to
+     *    {@link ConnectivityManager#reportNetworkConnectivity(Network, boolean)} will be ignored.
+     * </ul>
+     *
+     * Once this method is called, it is not possible to restore the agent to a functioning state.
+     * If a replacement network becomes available, then a new agent must be registered. When that
+     * replacement network is fully capable of replacing this network (including, possibly, being
+     * validated), this agent will no longer be needed and will be torn down. Otherwise, this agent
+     * can be disconnected by calling {@link #unregister}. If {@link #unregister} is not called,
+     * this agent will automatically be unregistered when the specified timeout expires. Any
+     * teardown delay previously set using{@link #setTeardownDelayMillis} is ignored.
+     *
+     * <p>This method has no effect if {@link #markConnected} has not yet been called.
+     * <p>This method may only be called once.
+     *
+     * @param timeoutMillis the timeout after which this network will be unregistered even if
+     *                      {@link #unregister} was not called.
+     */
+    public void destroyAndAwaitReplacement(
+            @IntRange(from = 0, to = MAX_TEARDOWN_DELAY_MS) int timeoutMillis) {
+        queueOrSendMessage(reg -> reg.sendDestroyAndAwaitReplacement(timeoutMillis));
+    }
+
     /**
      * Change the legacy subtype of this network agent.
      *

service/src/com/android/server/ConnectivityService.java

@@ -3503,6 +3503,12 @@ public class ConnectivityService extends IConnectivityManager.Stub
         return false;
     }
 
+    private boolean isDisconnectRequest(Message msg) {
+        if (msg.what != NetworkAgent.EVENT_NETWORK_INFO_CHANGED) return false;
+        final NetworkInfo info = (NetworkInfo) ((Pair) msg.obj).second;
+        return info.getState() == NetworkInfo.State.DISCONNECTED;
+    }
+
     // must be stateless - things change under us.
     private class NetworkStateTrackerHandler extends Handler {
         public NetworkStateTrackerHandler(Looper looper) {
@@ -3519,6 +3525,11 @@ public class ConnectivityService extends IConnectivityManager.Stub
                 return;
             }
 
+            // If the network has been destroyed, the only thing that it can do is disconnect.
+            if (nai.destroyed && !isDisconnectRequest(msg)) {
+                return;
+            }
+
             switch (msg.what) {
                 case NetworkAgent.EVENT_NETWORK_CAPABILITIES_CHANGED: {
                     final NetworkCapabilities networkCapabilities = new NetworkCapabilities(
@@ -3620,12 +3631,60 @@ public class ConnectivityService extends IConnectivityManager.Stub
                     }
                     break;
                 }
+                case NetworkAgent.EVENT_DESTROY_AND_AWAIT_REPLACEMENT: {
+                    // If nai is not yet created, or is already destroyed, ignore.
+                    if (!shouldDestroyNativeNetwork(nai)) break;
+
+                    final int timeoutMs = (int) arg.second;
+                    if (timeoutMs < 0 || timeoutMs > NetworkAgent.MAX_TEARDOWN_DELAY_MS) {
+                        Log.e(TAG, "Invalid network replacement timer " + timeoutMs
+                                + ", must be between 0 and " + NetworkAgent.MAX_TEARDOWN_DELAY_MS);
+                    }
+
+                    // Marking a network awaiting replacement is used to ensure that any requests
+                    // satisfied by the network do not switch to another network until a
+                    // replacement is available or the wait for a replacement times out.
+                    // If the network is inactive (i.e., nascent or lingering), then there are no
+                    // such requests, and there is no point keeping it. Just tear it down.
+                    // Note that setLingerDuration(0) cannot be used to do this because the network
+                    // could be nascent.
+                    nai.clearInactivityState();
+                    if (unneeded(nai, UnneededFor.TEARDOWN)) {
+                        Log.d(TAG, nai.toShortString()
+                                + " marked awaiting replacement is unneeded, tearing down instead");
+                        teardownUnneededNetwork(nai);
+                        break;
+                    }
+
+                    Log.d(TAG, "Marking " + nai.toShortString()
+                            + " destroyed, awaiting replacement within " + timeoutMs + "ms");
+                    destroyNativeNetwork(nai);
+
+                    // TODO: deduplicate this call with the one in disconnectAndDestroyNetwork.
+                    // This is not trivial because KeepaliveTracker#handleStartKeepalive does not
+                    // consider the fact that the network could already have disconnected or been
+                    // destroyed. Fix the code to send ERROR_INVALID_NETWORK when this happens
+                    // (taking care to ensure no dup'd FD leaks), then remove the code duplication
+                    // and move this code to a sensible location (destroyNativeNetwork perhaps?).
+                    mKeepaliveTracker.handleStopAllKeepalives(nai,
+                            SocketKeepalive.ERROR_INVALID_NETWORK);
+
+                    nai.updateScoreForNetworkAgentUpdate();
+                    // This rematch is almost certainly not going to result in any changes, because
+                    // the destroyed flag is only just above the "current satisfier wins"
+                    // tie-breaker. But technically anything that affects scoring should rematch.
+                    rematchAllNetworksAndRequests();
+                    mHandler.postDelayed(() -> nai.disconnect(), timeoutMs);
+                    break;
+                }
             }
         }
 
         private boolean maybeHandleNetworkMonitorMessage(Message msg) {
             final int netId = msg.arg2;
             final NetworkAgentInfo nai = getNetworkAgentInfoForNetId(netId);
+            // If a network has already been destroyed, all NetworkMonitor updates are ignored.
+            if (nai != null && nai.destroyed) return true;
             switch (msg.what) {
                 default:
                     return false;
@@ -4125,6 +4184,10 @@ public class ConnectivityService extends IConnectivityManager.Stub
         }
     }
 
+    private static boolean shouldDestroyNativeNetwork(@NonNull NetworkAgentInfo nai) {
+        return nai.created && !nai.destroyed;
+    }
+
     private void handleNetworkAgentDisconnected(Message msg) {
         NetworkAgentInfo nai = (NetworkAgentInfo) msg.obj;
         disconnectAndDestroyNetwork(nai);
@@ -4231,7 +4294,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
     }
 
     private void destroyNetwork(NetworkAgentInfo nai) {
-        if (nai.created) {
+        if (shouldDestroyNativeNetwork(nai)) {
             // Tell netd to clean up the configuration for this network
             // (routing rules, DNS, etc).
             // This may be slow as it requires a lot of netd shelling out to ip and
@@ -4240,15 +4303,15 @@ public class ConnectivityService extends IConnectivityManager.Stub
             // network or service a new request from an app), so network traffic isn't interrupted
             // for an unnecessarily long time.
             destroyNativeNetwork(nai);
-            mDnsManager.removeNetwork(nai.network);
-
-            // clean up tc police filters on interface.
-            if (nai.everConnected && canNetworkBeRateLimited(nai) && mIngressRateLimit >= 0) {
-                mDeps.disableIngressRateLimit(nai.linkProperties.getInterfaceName());
         }
+        if (!nai.created && !SdkLevel.isAtLeastT()) {
+            // Backwards compatibility: send onNetworkDestroyed even if network was never created.
+            // This can never run if the code above runs because shouldDestroyNativeNetwork is
+            // false if the network was never created.
+            // TODO: delete when S is no longer supported.
+            nai.onNetworkDestroyed();
         }
         mNetIdManager.releaseNetId(nai.network.getNetId());
-        nai.onNetworkDestroyed();
     }
 
     private boolean createNativeNetwork(@NonNull NetworkAgentInfo nai) {
@@ -4291,6 +4354,18 @@ public class ConnectivityService extends IConnectivityManager.Stub
         } catch (RemoteException | ServiceSpecificException e) {
             loge("Exception destroying network: " + e);
         }
+        // TODO: defer calling this until the network is removed from mNetworkAgentInfos.
+        // Otherwise, a private DNS configuration update for a destroyed network, or one that never
+        // gets created, could add data to DnsManager data structures that will never get deleted.
+        mDnsManager.removeNetwork(nai.network);
+
+        // clean up tc police filters on interface.
+        if (nai.everConnected && canNetworkBeRateLimited(nai) && mIngressRateLimit >= 0) {
+            mDeps.disableIngressRateLimit(nai.linkProperties.getInterfaceName());
+        }
+
+        nai.destroyed = true;
+        nai.onNetworkDestroyed();
     }
 
     // If this method proves to be too slow then we can maintain a separate
@@ -8543,11 +8618,19 @@ public class ConnectivityService extends IConnectivityManager.Stub
                     log("   accepting network in place of " + previousSatisfier.toShortString());
                 }
                 previousSatisfier.removeRequest(previousRequest.requestId);
-                if (canSupportGracefulNetworkSwitch(previousSatisfier, newSatisfier)) {
+                if (canSupportGracefulNetworkSwitch(previousSatisfier, newSatisfier)
+                        && !previousSatisfier.destroyed) {
                     // If this network switch can't be supported gracefully, the request is not
                     // lingered. This allows letting go of the network sooner to reclaim some
                     // performance on the new network, since the radio can't do both at the same
                     // time while preserving good performance.
+                    //
+                    // Also don't linger the request if the old network has been destroyed.
+                    // A destroyed network does not provide actual network connectivity, so
+                    // lingering it is not useful. In particular this ensures that a destroyed
+                    // network is outscored by its replacement,
+                    // then it is torn down immediately instead of being lingered, and any apps that
+                    // were using it immediately get onLost and can connect using the new network.
                     previousSatisfier.lingerRequest(previousRequest.requestId, now);
                 }
             } else {

service/src/com/android/server/connectivity/Nat464Xlat.java

@@ -132,7 +132,7 @@ public class Nat464Xlat {
         final boolean skip464xlat = (nai.netAgentConfig() != null)
                 && nai.netAgentConfig().skip464xlat;
 
-        return supported && connected && isIpv6OnlyNetwork && !skip464xlat
+        return supported && connected && isIpv6OnlyNetwork && !skip464xlat && !nai.destroyed
                 && (nai.networkCapabilities.hasTransport(TRANSPORT_CELLULAR)
                 ? isCellular464XlatEnabled() : true);
     }

service/src/com/android/server/connectivity/NetworkAgentInfo.java

@@ -732,6 +732,12 @@ public class NetworkAgentInfo implements Comparable<NetworkAgentInfo>, NetworkRa
             mHandler.obtainMessage(NetworkAgent.EVENT_REMOVE_ALL_DSCP_POLICIES,
                     new Pair<>(NetworkAgentInfo.this, null)).sendToTarget();
         }
+
+        @Override
+        public void sendDestroyAndAwaitReplacement(final int timeoutMillis) {
+            mHandler.obtainMessage(NetworkAgent.EVENT_DESTROY_AND_AWAIT_REPLACEMENT,
+                    new Pair<>(NetworkAgentInfo.this, timeoutMillis)).sendToTarget();
+        }
     }
 
     /**
@@ -976,7 +982,7 @@ public class NetworkAgentInfo implements Comparable<NetworkAgentInfo>, NetworkRa
     /**
      * Update the ConnectivityService-managed bits in the score.
      *
-     * Call this after updating the network agent config.
+     * Call this after changing any data that might affect the score (e.g., agent config).
      */
     public void updateScoreForNetworkAgentUpdate() {
         mScore = mScore.mixInScore(networkCapabilities, networkAgentConfig,
@@ -1256,6 +1262,8 @@ public class NetworkAgentInfo implements Comparable<NetworkAgentInfo>, NetworkRa
                 + "network{" + network + "}  handle{" + network.getNetworkHandle() + "}  ni{"
                 + networkInfo.toShortString() + "} "
                 + mScore + " "
+                + (created ? " created" : "")
+                + (destroyed ? " destroyed" : "")
                 + (isNascent() ? " nascent" : (isLingering() ? " lingering" : ""))
                 + (everValidated ? " everValidated" : "")
                 + (lastValidated ? " lastValidated" : "")

tests/cts/net/src/android/net/cts/NetworkAgentTest.kt

@@ -19,6 +19,7 @@ import android.Manifest.permission.NETWORK_SETTINGS
 import android.app.Instrumentation
 import android.content.Context
 import android.net.ConnectivityManager
+import android.net.EthernetNetworkSpecifier
 import android.net.INetworkAgent
 import android.net.INetworkAgentRegistry
 import android.net.InetAddresses
@@ -35,6 +36,7 @@ import android.net.NetworkCapabilities
 import android.net.NetworkCapabilities.NET_CAPABILITY_INTERNET
 import android.net.NetworkCapabilities.NET_CAPABILITY_NOT_CONGESTED
 import android.net.NetworkCapabilities.NET_CAPABILITY_NOT_METERED
+import android.net.NetworkCapabilities.NET_CAPABILITY_NOT_RESTRICTED
 import android.net.NetworkCapabilities.NET_CAPABILITY_NOT_ROAMING
 import android.net.NetworkCapabilities.NET_CAPABILITY_NOT_SUSPENDED
 import android.net.NetworkCapabilities.NET_CAPABILITY_NOT_VCN_MANAGED
@@ -42,7 +44,9 @@ import android.net.NetworkCapabilities.NET_CAPABILITY_NOT_VPN
 import android.net.NetworkCapabilities.NET_CAPABILITY_TEMPORARILY_NOT_METERED
 import android.net.NetworkCapabilities.NET_CAPABILITY_TRUSTED
 import android.net.NetworkCapabilities.NET_CAPABILITY_VALIDATED
+import android.net.NetworkCapabilities.TRANSPORT_CELLULAR
 import android.net.NetworkCapabilities.TRANSPORT_TEST
+import android.net.NetworkCapabilities.TRANSPORT_WIFI
 import android.net.NetworkCapabilities.TRANSPORT_VPN
 import android.net.NetworkInfo
 import android.net.NetworkProvider
@@ -100,6 +104,7 @@ import com.android.testutils.TestableNetworkAgent.CallbackEntry.OnStopSocketKeep
 import com.android.testutils.TestableNetworkAgent.CallbackEntry.OnUnregisterQosCallback
 import com.android.testutils.TestableNetworkAgent.CallbackEntry.OnValidationStatus
 import com.android.testutils.TestableNetworkCallback
+import com.android.testutils.assertThrows
 import org.junit.After
 import org.junit.Assume.assumeFalse
 import org.junit.Before
@@ -112,6 +117,8 @@ import org.mockito.Mockito.doReturn
 import org.mockito.Mockito.mock
 import org.mockito.Mockito.timeout
 import org.mockito.Mockito.verify
+import java.io.IOException
+import java.net.DatagramSocket
 import java.net.InetAddress
 import java.net.InetSocketAddress
 import java.net.Socket
@@ -249,14 +256,10 @@ class NetworkAgentTest {
                 .build()
     }
 
-    private fun createNetworkAgent(
+    private fun makeTestNetworkCapabilities(
-        context: Context = realContext,
         specifier: String? = null,
-        initialNc: NetworkCapabilities? = null,
+        transports: IntArray = intArrayOf()
-        initialLp: LinkProperties? = null,
+    ) = NetworkCapabilities().apply {
-        initialConfig: NetworkAgentConfig? = null
-    ): TestableNetworkAgent {
-        val nc = initialNc ?: NetworkCapabilities().apply {
         addTransportType(TRANSPORT_TEST)
         removeCapability(NET_CAPABILITY_TRUSTED)
         removeCapability(NET_CAPABILITY_INTERNET)
@@ -269,7 +272,20 @@ class NetworkAgentTest {
         if (null != specifier) {
             setNetworkSpecifier(CompatUtil.makeEthernetNetworkSpecifier(specifier))
         }
+        for (t in transports) { addTransportType(t) }
+        // Most transports are not allowed on test networks unless the network is marked restricted.
+        // This test does not need
+        if (transports.size > 0) removeCapability(NET_CAPABILITY_NOT_RESTRICTED)
     }
+
+    private fun createNetworkAgent(
+        context: Context = realContext,
+        specifier: String? = null,
+        initialNc: NetworkCapabilities? = null,
+        initialLp: LinkProperties? = null,
+        initialConfig: NetworkAgentConfig? = null
+    ): TestableNetworkAgent {
+        val nc = initialNc ?: makeTestNetworkCapabilities(specifier)
         val lp = initialLp ?: LinkProperties().apply {
             addLinkAddress(LinkAddress(LOCAL_IPV4_ADDRESS, 32))
             addRoute(RouteInfo(IpPrefix("0.0.0.0/0"), null, null))
@@ -284,12 +300,14 @@ class NetworkAgentTest {
         context: Context = realContext,
         specifier: String? = UUID.randomUUID().toString(),
         initialConfig: NetworkAgentConfig? = null,
-        expectedInitSignalStrengthThresholds: IntArray? = intArrayOf()
+        expectedInitSignalStrengthThresholds: IntArray? = intArrayOf(),
+        transports: IntArray = intArrayOf()
     ): Pair<TestableNetworkAgent, TestableNetworkCallback> {
         val callback = TestableNetworkCallback()
         // Ensure this NetworkAgent is never unneeded by filing a request with its specifier.
         requestNetwork(makeTestNetworkRequest(specifier = specifier), callback)
-        val agent = createNetworkAgent(context, specifier, initialConfig = initialConfig)
+        val nc = makeTestNetworkCapabilities(specifier, transports)
+        val agent = createNetworkAgent(context, initialConfig = initialConfig, initialNc = nc)
         agent.setTeardownDelayMillis(0)
         // Connect the agent and verify initial status callbacks.
         agent.register()
@@ -301,6 +319,15 @@ class NetworkAgentTest {
         return agent to callback
     }
 
+    private fun connectNetwork(vararg transports: Int): Pair<TestableNetworkAgent, Network> {
+        val (agent, callback) = createConnectedNetworkAgent(transports = transports)
+        val network = agent.network!!
+        // createConnectedNetworkAgent internally files a request; release it so that the network
+        // will be torn down if unneeded.
+        mCM.unregisterNetworkCallback(callback)
+        return agent to network
+    }
+
     private fun createNetworkAgentWithFakeCS() = createNetworkAgent().also {
         mFakeConnectivityService.connect(it.registerForTest(Network(FAKE_NET_ID)))
     }
@@ -1123,4 +1150,138 @@ class NetworkAgentTest {
                 remoteAddresses
         )
     }
+
+    @Test
+    fun testDestroyAndAwaitReplacement() {
+        // Keeps an eye on all test networks.
+        val matchAllCallback = TestableNetworkCallback(timeoutMs = DEFAULT_TIMEOUT_MS)
+        registerNetworkCallback(makeTestNetworkRequest(), matchAllCallback)
+
+        // File a request that matches and keeps up the best-scoring test network.
+        val testCallback = TestableNetworkCallback(timeoutMs = DEFAULT_TIMEOUT_MS)
+        requestNetwork(makeTestNetworkRequest(), testCallback)
+
+        // Connect the first network. This should satisfy the request.
+        val (agent1, network1) = connectNetwork()
+        matchAllCallback.expectAvailableThenValidatedCallbacks(network1)
+        testCallback.expectAvailableThenValidatedCallbacks(network1)
+        // Check that network1 exists by binding a socket to it and getting no exceptions.
+        network1.bindSocket(DatagramSocket())
+
+        // Connect a second agent. network1 is preferred because it was already registered, so
+        // testCallback will not see any events. agent2 is be torn down because it has no requests.
+        val (agent2, network2) = connectNetwork()
+        matchAllCallback.expectAvailableThenValidatedCallbacks(network2)
+        matchAllCallback.expectCallback<Lost>(network2)
+        agent2.expectCallback<OnNetworkUnwanted>()
+        agent2.expectCallback<OnNetworkDestroyed>()
+        assertNull(mCM.getLinkProperties(network2))
+
+        // Mark the first network as awaiting replacement. This should destroy the underlying
+        // native network and send onNetworkDestroyed, but will not send any NetworkCallbacks,
+        // because for callback and scoring purposes network1 is still connected.
+        agent1.destroyAndAwaitReplacement(5_000 /* timeoutMillis */)
+        agent1.expectCallback<OnNetworkDestroyed>()
+        assertThrows(IOException::class.java) { network1.bindSocket(DatagramSocket()) }
+        assertNotNull(mCM.getLinkProperties(network1))
+
+        // Calling destroyAndAwaitReplacement more than once has no effect.
+        // If it did, this test would fail because the 1ms timeout means that the network would be
+        // torn down before the replacement arrives.
+        agent1.destroyAndAwaitReplacement(1 /* timeoutMillis */)
+
+        // Connect a third network. Because network1 is awaiting replacement, network3 is preferred
+        // as soon as it validates (until then, it is outscored by network1).
+        // The fact that the first events seen by matchAllCallback is the connection of network3
+        // implicitly ensures that no callbacks are sent since network1 was lost.
+        val (agent3, network3) = connectNetwork()
+        matchAllCallback.expectAvailableThenValidatedCallbacks(network3)
+        testCallback.expectAvailableDoubleValidatedCallbacks(network3)
+
+        // As soon as the replacement arrives, network1 is disconnected.
+        // Check that this happens before the replacement timeout (5 seconds) fires.
+        matchAllCallback.expectCallback<Lost>(network1, 2_000 /* timeoutMs */)
+        agent1.expectCallback<OnNetworkUnwanted>()
+
+        // Test lingering:
+        // - Connect a higher-scoring network and check that network3 starts lingering.
+        // - Mark network3 awaiting replacement.
+        // - Check that network3 is torn down immediately without waiting for the linger timer or
+        //   the replacement timer to fire. This is a regular teardown, so it results in
+        //   onNetworkUnwanted before onNetworkDestroyed.
+        val (agent4, agent4callback) = createConnectedNetworkAgent()
+        val network4 = agent4.network!!
+        matchAllCallback.expectAvailableThenValidatedCallbacks(network4)
+        agent4.sendNetworkScore(NetworkScore.Builder().setTransportPrimary(true).build())
+        matchAllCallback.expectCallback<Losing>(network3)
+        testCallback.expectAvailableCallbacks(network4, validated = true)
+        mCM.unregisterNetworkCallback(agent4callback)
+        agent3.destroyAndAwaitReplacement(5_000)
+        agent3.expectCallback<OnNetworkUnwanted>()
+        matchAllCallback.expectCallback<Lost>(network3, 1000L)
+        agent3.expectCallback<OnNetworkDestroyed>()
+
+        // Now mark network4 awaiting replacement with a low timeout, and check that if no
+        // replacement arrives, it is torn down.
+        agent4.destroyAndAwaitReplacement(100 /* timeoutMillis */)
+        matchAllCallback.expectCallback<Lost>(network4, 1000L /* timeoutMs */)
+        testCallback.expectCallback<Lost>(network4, 1000L /* timeoutMs */)
+        agent4.expectCallback<OnNetworkDestroyed>()
+        agent4.expectCallback<OnNetworkUnwanted>()
+
+        // If a network that is awaiting replacement is unregistered, it disconnects immediately,
+        // before the replacement timeout fires.
+        val (agent5, network5) = connectNetwork()
+        matchAllCallback.expectAvailableThenValidatedCallbacks(network5)
+        testCallback.expectAvailableThenValidatedCallbacks(network5)
+        agent5.destroyAndAwaitReplacement(5_000 /* timeoutMillis */)
+        agent5.unregister()
+        matchAllCallback.expectCallback<Lost>(network5, 1000L /* timeoutMs */)
+        testCallback.expectCallback<Lost>(network5, 1000L /* timeoutMs */)
+        agent5.expectCallback<OnNetworkDestroyed>()
+        agent5.expectCallback<OnNetworkUnwanted>()
+
+        // If wifi is replaced within the timeout, the device does not switch to cellular.
+        val (cellAgent, cellNetwork) = connectNetwork(TRANSPORT_CELLULAR)
+        testCallback.expectAvailableThenValidatedCallbacks(cellNetwork)
+        matchAllCallback.expectAvailableThenValidatedCallbacks(cellNetwork)
+
+        val (wifiAgent, wifiNetwork) = connectNetwork(TRANSPORT_WIFI)
+        testCallback.expectAvailableCallbacks(wifiNetwork, validated = true)
+        testCallback.expectCapabilitiesThat(wifiNetwork) {
+            it.hasCapability(NET_CAPABILITY_VALIDATED)
+        }
+        matchAllCallback.expectAvailableCallbacks(wifiNetwork, validated = false)
+        matchAllCallback.expectCallback<Losing>(cellNetwork)
+        matchAllCallback.expectCapabilitiesThat(wifiNetwork) {
+            it.hasCapability(NET_CAPABILITY_VALIDATED)
+        }
+
+        wifiAgent.destroyAndAwaitReplacement(5_000 /* timeoutMillis */)
+        wifiAgent.expectCallback<OnNetworkDestroyed>()
+
+        // Once the network is awaiting replacement, changing LinkProperties, NetworkCapabilities or
+        // score, or calling reportNetworkConnectivity, have no effect.
+        val wifiSpecifier = mCM.getNetworkCapabilities(wifiNetwork)!!.networkSpecifier
+        assertNotNull(wifiSpecifier)
+        assertTrue(wifiSpecifier is EthernetNetworkSpecifier)
+
+        val wifiNc = makeTestNetworkCapabilities(wifiSpecifier.interfaceName,
+                intArrayOf(TRANSPORT_WIFI))
+        wifiAgent.sendNetworkCapabilities(wifiNc)
+        val wifiLp = mCM.getLinkProperties(wifiNetwork)!!
+        val newRoute = RouteInfo(IpPrefix("192.0.2.42/24"))
+        assertFalse(wifiLp.getRoutes().contains(newRoute))
+        wifiLp.addRoute(newRoute)
+        wifiAgent.sendLinkProperties(wifiLp)
+        mCM.reportNetworkConnectivity(wifiNetwork, false)
+        // The test implicitly checks that no callbacks are sent here, because the next events seen
+        // by the callbacks are for the new network connecting.
+
+        val (newWifiAgent, newWifiNetwork) = connectNetwork(TRANSPORT_WIFI)
+        testCallback.expectAvailableCallbacks(newWifiNetwork, validated = true)
+        matchAllCallback.expectAvailableThenValidatedCallbacks(newWifiNetwork)
+        matchAllCallback.expectCallback<Lost>(wifiNetwork)
+        wifiAgent.expectCallback<OnNetworkUnwanted>()
+    }
 }