Merge "Add aggressive query mode" into main

service-t/src/com/android/server/NsdService.java

@@ -35,6 +35,7 @@ import static com.android.networkstack.apishim.ConstantsShim.REGISTER_NSD_OFFLOA
 import static com.android.server.connectivity.mdns.MdnsAdvertiser.AdvertiserMetrics;
 import static com.android.server.connectivity.mdns.MdnsConstants.NO_PACKET;
 import static com.android.server.connectivity.mdns.MdnsRecord.MAX_LABEL_LENGTH;
+import static com.android.server.connectivity.mdns.MdnsSearchOptions.AGGRESSIVE_QUERY_MODE;
 import static com.android.server.connectivity.mdns.MdnsSearchOptions.PASSIVE_QUERY_MODE;
 import static com.android.server.connectivity.mdns.util.MdnsUtils.Clock;
 
@@ -252,6 +253,8 @@ public class NsdService extends INsdManager.Stub {
 
     private final RemoteCallbackList<IOffloadEngine> mOffloadEngines =
             new RemoteCallbackList<>();
+    @NonNull
+    private final MdnsFeatureFlags mMdnsFeatureFlags;
 
     private static class OffloadEngineInfo {
         @NonNull final String mInterfaceName;
@@ -794,7 +797,10 @@ public class NsdService extends INsdManager.Stub {
                                     MdnsSearchOptions.newBuilder()
                                             .setNetwork(discoveryRequest.getNetwork())
                                             .setRemoveExpiredService(true)
-                                            .setQueryMode(PASSIVE_QUERY_MODE);
+                                            .setQueryMode(
+                                                    mMdnsFeatureFlags.isAggressiveQueryModeEnabled()
+                                                            ? AGGRESSIVE_QUERY_MODE
+                                                            : PASSIVE_QUERY_MODE);
                             if (subtype != null) {
                                 // checkSubtypeLabels() ensures that subtypes start with '_' but
                                 // MdnsSearchOptions expects the underscore to not be present.
@@ -1063,7 +1069,9 @@ public class NsdService extends INsdManager.Stub {
                                     transactionId, resolveServiceType);
                             final MdnsSearchOptions options = MdnsSearchOptions.newBuilder()
                                     .setNetwork(info.getNetwork())
-                                    .setQueryMode(PASSIVE_QUERY_MODE)
+                                    .setQueryMode(mMdnsFeatureFlags.isAggressiveQueryModeEnabled()
+                                            ? AGGRESSIVE_QUERY_MODE
+                                            : PASSIVE_QUERY_MODE)
                                     .setResolveInstanceName(info.getServiceName())
                                     .setRemoveExpiredService(true)
                                     .build();
@@ -1161,7 +1169,9 @@ public class NsdService extends INsdManager.Stub {
                                 transactionId, resolveServiceType);
                         final MdnsSearchOptions options = MdnsSearchOptions.newBuilder()
                                 .setNetwork(info.getNetwork())
-                                .setQueryMode(PASSIVE_QUERY_MODE)
+                                .setQueryMode(mMdnsFeatureFlags.isAggressiveQueryModeEnabled()
+                                        ? AGGRESSIVE_QUERY_MODE
+                                        : PASSIVE_QUERY_MODE)
                                 .setResolveInstanceName(info.getServiceName())
                                 .setRemoveExpiredService(true)
                                 .build();
@@ -1787,7 +1797,7 @@ public class NsdService extends INsdManager.Stub {
         am.addOnUidImportanceListener(new UidImportanceListener(handler),
                 mRunningAppActiveImportanceCutoff);
 
-        final MdnsFeatureFlags flags = new MdnsFeatureFlags.Builder()
+        mMdnsFeatureFlags = new MdnsFeatureFlags.Builder()
                 .setIsMdnsOffloadFeatureEnabled(mDeps.isTetheringFeatureNotChickenedOut(
                         mContext, MdnsFeatureFlags.NSD_FORCE_DISABLE_MDNS_OFFLOAD))
                 .setIncludeInetAddressRecordsInProbing(mDeps.isFeatureEnabled(
@@ -1800,18 +1810,21 @@ public class NsdService extends INsdManager.Stub {
                         mContext, MdnsFeatureFlags.NSD_KNOWN_ANSWER_SUPPRESSION))
                 .setIsUnicastReplyEnabled(mDeps.isFeatureEnabled(
                         mContext, MdnsFeatureFlags.NSD_UNICAST_REPLY_ENABLED))
+                .setIsAggressiveQueryModeEnabled(mDeps.isFeatureEnabled(
+                        mContext, MdnsFeatureFlags.NSD_AGGRESSIVE_QUERY_MODE))
                 .setOverrideProvider(flag -> mDeps.isFeatureEnabled(
                         mContext, FORCE_ENABLE_FLAG_FOR_TEST_PREFIX + flag))
                 .build();
         mMdnsSocketClient =
                 new MdnsMultinetworkSocketClient(handler.getLooper(), mMdnsSocketProvider,
-                        LOGGER.forSubComponent("MdnsMultinetworkSocketClient"), flags);
+                        LOGGER.forSubComponent("MdnsMultinetworkSocketClient"), mMdnsFeatureFlags);
         mMdnsDiscoveryManager = deps.makeMdnsDiscoveryManager(new ExecutorProvider(),
-                mMdnsSocketClient, LOGGER.forSubComponent("MdnsDiscoveryManager"), flags);
+                mMdnsSocketClient, LOGGER.forSubComponent("MdnsDiscoveryManager"),
+                mMdnsFeatureFlags);
         handler.post(() -> mMdnsSocketClient.setCallback(mMdnsDiscoveryManager));
         mAdvertiser = deps.makeMdnsAdvertiser(handler.getLooper(), mMdnsSocketProvider,
-                new AdvertiserCallback(), LOGGER.forSubComponent("MdnsAdvertiser"), flags,
+                new AdvertiserCallback(), LOGGER.forSubComponent("MdnsAdvertiser"),
-                mContext);
+                mMdnsFeatureFlags, mContext);
         mClock = deps.makeClock();
     }
 

service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java

@@ -57,6 +57,11 @@ public class MdnsFeatureFlags {
      */
     public static final String NSD_UNICAST_REPLY_ENABLED = "nsd_unicast_reply_enabled";
 
+    /**
+     * A feature flag to control whether the aggressive query mode should be enabled.
+     */
+    public static final String NSD_AGGRESSIVE_QUERY_MODE = "nsd_aggressive_query_mode";
+
     // Flag for offload feature
     public final boolean mIsMdnsOffloadFeatureEnabled;
 
@@ -75,6 +80,9 @@ public class MdnsFeatureFlags {
     // Flag to enable replying unicast to queries requesting unicast replies
     public final boolean mIsUnicastReplyEnabled;
 
+    // Flag for aggressive query mode
+    public final boolean mIsAggressiveQueryModeEnabled;
+
     @Nullable
     private final FlagOverrideProvider mOverrideProvider;
 
@@ -102,6 +110,13 @@ public class MdnsFeatureFlags {
         return mIsUnicastReplyEnabled || isForceEnabledForTest(NSD_UNICAST_REPLY_ENABLED);
     }
 
+    /**
+     * Indicates whether {@link #NSD_AGGRESSIVE_QUERY_MODE} is enabled, including for testing.
+     */
+    public boolean isAggressiveQueryModeEnabled() {
+        return mIsAggressiveQueryModeEnabled || isForceEnabledForTest(NSD_AGGRESSIVE_QUERY_MODE);
+    }
+
     /**
      * The constructor for {@link MdnsFeatureFlags}.
      */
@@ -111,6 +126,7 @@ public class MdnsFeatureFlags {
             boolean isLabelCountLimitEnabled,
             boolean isKnownAnswerSuppressionEnabled,
             boolean isUnicastReplyEnabled,
+            boolean isAggressiveQueryModeEnabled,
             @Nullable FlagOverrideProvider overrideProvider) {
         mIsMdnsOffloadFeatureEnabled = isOffloadFeatureEnabled;
         mIncludeInetAddressRecordsInProbing = includeInetAddressRecordsInProbing;
@@ -118,6 +134,7 @@ public class MdnsFeatureFlags {
         mIsLabelCountLimitEnabled = isLabelCountLimitEnabled;
         mIsKnownAnswerSuppressionEnabled = isKnownAnswerSuppressionEnabled;
         mIsUnicastReplyEnabled = isUnicastReplyEnabled;
+        mIsAggressiveQueryModeEnabled = isAggressiveQueryModeEnabled;
         mOverrideProvider = overrideProvider;
     }
 
@@ -136,6 +153,7 @@ public class MdnsFeatureFlags {
         private boolean mIsLabelCountLimitEnabled;
         private boolean mIsKnownAnswerSuppressionEnabled;
         private boolean mIsUnicastReplyEnabled;
+        private boolean mIsAggressiveQueryModeEnabled;
         private FlagOverrideProvider mOverrideProvider;
 
         /**
@@ -148,6 +166,7 @@ public class MdnsFeatureFlags {
             mIsLabelCountLimitEnabled = true; // Default enabled.
             mIsKnownAnswerSuppressionEnabled = false;
             mIsUnicastReplyEnabled = true;
+            mIsAggressiveQueryModeEnabled = false;
             mOverrideProvider = null;
         }
 
@@ -223,6 +242,16 @@ public class MdnsFeatureFlags {
             return this;
         }
 
+        /**
+         * Set whether the aggressive query mode is enabled.
+         *
+         * @see #NSD_AGGRESSIVE_QUERY_MODE
+         */
+        public Builder setIsAggressiveQueryModeEnabled(boolean isAggressiveQueryModeEnabled) {
+            mIsAggressiveQueryModeEnabled = isAggressiveQueryModeEnabled;
+            return this;
+        }
+
         /**
          * Builds a {@link MdnsFeatureFlags} with the arguments supplied to this builder.
          */
@@ -233,6 +262,7 @@ public class MdnsFeatureFlags {
                     mIsLabelCountLimitEnabled,
                     mIsKnownAnswerSuppressionEnabled,
                     mIsUnicastReplyEnabled,
+                    mIsAggressiveQueryModeEnabled,
                     mOverrideProvider);
         }
     }

service-t/src/com/android/server/connectivity/mdns/MdnsSearchOptions.java

@@ -44,6 +44,10 @@ public class MdnsSearchOptions implements Parcelable {
     public static final int PASSIVE_QUERY_MODE = 0;
     // Active query mode scans frequently.
     public static final int ACTIVE_QUERY_MODE = 1;
+    // Aggressive query mode scans more frequently than the active mode at first, and sends both
+    // unicast and multicast queries simultaneously, but in long sessions it eventually sends as
+    // many queries as the PASSIVE mode.
+    public static final int AGGRESSIVE_QUERY_MODE = 2;
 
     /** @hide */
     public static final Parcelable.Creator<MdnsSearchOptions> CREATOR =

service-t/src/com/android/server/connectivity/mdns/QueryTaskConfig.java

@@ -16,6 +16,7 @@
 
 package com.android.server.connectivity.mdns;
 
+import static com.android.server.connectivity.mdns.MdnsSearchOptions.AGGRESSIVE_QUERY_MODE;
 import static com.android.server.connectivity.mdns.MdnsSearchOptions.PASSIVE_QUERY_MODE;
 
 import android.annotation.NonNull;
@@ -35,13 +36,23 @@ public class QueryTaskConfig {
 
     private static final int INITIAL_TIME_BETWEEN_BURSTS_MS =
             (int) MdnsConfigs.initialTimeBetweenBurstsMs();
-    private static final int TIME_BETWEEN_BURSTS_MS = (int) MdnsConfigs.timeBetweenBurstsMs();
+    private static final int MAX_TIME_BETWEEN_ACTIVE_PASSIVE_BURSTS_MS =
+            (int) MdnsConfigs.timeBetweenBurstsMs();
     private static final int QUERIES_PER_BURST = (int) MdnsConfigs.queriesPerBurst();
     private static final int TIME_BETWEEN_QUERIES_IN_BURST_MS =
             (int) MdnsConfigs.timeBetweenQueriesInBurstMs();
     private static final int QUERIES_PER_BURST_PASSIVE_MODE =
             (int) MdnsConfigs.queriesPerBurstPassive();
     private static final int UNSIGNED_SHORT_MAX_VALUE = 65536;
+    @VisibleForTesting
+    // RFC 6762 5.2: The interval between the first two queries MUST be at least one second.
+    static final int INITIAL_AGGRESSIVE_TIME_BETWEEN_BURSTS_MS = 1000;
+    @VisibleForTesting
+    // Basically this tries to send one query per typical DTIM interval 100ms, to maximize the
+    // chances that a query will be received if devices are using a DTIM multiplier (in which case
+    // they only listen once every [multiplier] DTIM intervals).
+    static final int TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS = 100;
+    static final int MAX_TIME_BETWEEN_AGGRESSIVE_BURSTS_MS = 60000;
     // The following fields are used by QueryTask so we need to test them.
     @VisibleForTesting
     final List<String> subtypes;
@@ -81,6 +92,7 @@ public class QueryTaskConfig {
         this.queryCount = queryCount;
         this.socketKey = other.socketKey;
     }
+
     QueryTaskConfig(@NonNull Collection<String> subtypes,
             int queryMode,
             boolean onlyUseIpv6OnIpv6OnlyNetworks,
@@ -96,21 +108,59 @@ public class QueryTaskConfig {
         this.expectUnicastResponse = true;
         this.isFirstBurst = true;
         // Config the scan frequency based on the scan mode.
-        if (this.queryMode == PASSIVE_QUERY_MODE) {
+        if (this.queryMode == AGGRESSIVE_QUERY_MODE) {
+            this.timeBetweenBurstsInMs = INITIAL_AGGRESSIVE_TIME_BETWEEN_BURSTS_MS;
+            this.delayUntilNextTaskWithoutBackoffMs =
+                    TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS;
+        } else if (this.queryMode == PASSIVE_QUERY_MODE) {
             // In passive scan mode, sends a single burst of QUERIES_PER_BURST queries, and then
             // in each TIME_BETWEEN_BURSTS interval, sends QUERIES_PER_BURST_PASSIVE_MODE
             // queries.
-            this.timeBetweenBurstsInMs = TIME_BETWEEN_BURSTS_MS;
+            this.timeBetweenBurstsInMs = MAX_TIME_BETWEEN_ACTIVE_PASSIVE_BURSTS_MS;
+            this.delayUntilNextTaskWithoutBackoffMs = TIME_BETWEEN_QUERIES_IN_BURST_MS;
         } else {
             // In active scan mode, sends a burst of QUERIES_PER_BURST queries,
             // TIME_BETWEEN_QUERIES_IN_BURST_MS apart, then waits for the scan interval, and
             // then repeats. The scan interval starts as INITIAL_TIME_BETWEEN_BURSTS_MS and
             // doubles until it maxes out at TIME_BETWEEN_BURSTS_MS.
             this.timeBetweenBurstsInMs = INITIAL_TIME_BETWEEN_BURSTS_MS;
+            this.delayUntilNextTaskWithoutBackoffMs = TIME_BETWEEN_QUERIES_IN_BURST_MS;
         }
         this.socketKey = socketKey;
         this.queryCount = 0;
-        this.delayUntilNextTaskWithoutBackoffMs = TIME_BETWEEN_QUERIES_IN_BURST_MS;
+    }
+
+    long getDelayUntilNextTaskWithoutBackoff(boolean isFirstQueryInBurst,
+            boolean isLastQueryInBurst) {
+        if (isFirstQueryInBurst && queryMode == AGGRESSIVE_QUERY_MODE) {
+            return 0;
+        }
+        if (isLastQueryInBurst) {
+            return timeBetweenBurstsInMs;
+        }
+        return queryMode == AGGRESSIVE_QUERY_MODE
+                ? TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS
+                : TIME_BETWEEN_QUERIES_IN_BURST_MS;
+    }
+
+    boolean getNextExpectUnicastResponse(boolean isLastQueryInBurst) {
+        if (!isLastQueryInBurst) {
+            return false;
+        }
+        if (queryMode == AGGRESSIVE_QUERY_MODE) {
+            return true;
+        }
+        return alwaysAskForUnicastResponse;
+    }
+
+    int getNextTimeBetweenBurstsMs(boolean isLastQueryInBurst) {
+        if (!isLastQueryInBurst) {
+            return timeBetweenBurstsInMs;
+        }
+        final int maxTimeBetweenBursts = queryMode == AGGRESSIVE_QUERY_MODE
+                ? MAX_TIME_BETWEEN_AGGRESSIVE_BURSTS_MS : MAX_TIME_BETWEEN_ACTIVE_PASSIVE_BURSTS_MS;
+        return timeBetweenBurstsInMs < maxTimeBetweenBursts
+                ? Math.min(timeBetweenBurstsInMs * 2, maxTimeBetweenBursts) : timeBetweenBurstsInMs;
     }
 
     /**
@@ -122,43 +172,28 @@ public class QueryTaskConfig {
         if (newTransactionId > UNSIGNED_SHORT_MAX_VALUE) {
             newTransactionId = 1;
         }
-        boolean newExpectUnicastResponse = false;
         boolean newIsFirstBurst = isFirstBurst;
         int newQueriesPerBurst = queriesPerBurst;
         int newBurstCounter = burstCounter + 1;
-        long newDelayUntilNextTaskWithoutBackoffMs = delayUntilNextTaskWithoutBackoffMs;
+        final boolean isFirstQueryInBurst = newBurstCounter == 1;
-        int newTimeBetweenBurstsInMs = timeBetweenBurstsInMs;
+        final boolean isLastQueryInBurst = newBurstCounter == queriesPerBurst;
-        // Only the first query expects uni-cast response.
+        if (isLastQueryInBurst) {
-        if (newBurstCounter == queriesPerBurst) {
             newBurstCounter = 0;
-
-            if (alwaysAskForUnicastResponse) {
-                newExpectUnicastResponse = true;
-            }
-            // In passive scan mode, sends a single burst of QUERIES_PER_BURST queries, and
-            // then in each TIME_BETWEEN_BURSTS interval, sends QUERIES_PER_BURST_PASSIVE_MODE
-            // queries.
             if (isFirstBurst) {
                 newIsFirstBurst = false;
+                // In passive scan mode, sends a single burst of QUERIES_PER_BURST queries, and
+                // then in each TIME_BETWEEN_BURSTS interval, sends QUERIES_PER_BURST_PASSIVE_MODE
+                // queries.
                 if (queryMode == PASSIVE_QUERY_MODE) {
                     newQueriesPerBurst = QUERIES_PER_BURST_PASSIVE_MODE;
                 }
             }
-            // In active scan mode, sends a burst of QUERIES_PER_BURST queries,
-            // TIME_BETWEEN_QUERIES_IN_BURST_MS apart, then waits for the scan interval, and
-            // then repeats. The scan interval starts as INITIAL_TIME_BETWEEN_BURSTS_MS and
-            // doubles until it maxes out at TIME_BETWEEN_BURSTS_MS.
-            newDelayUntilNextTaskWithoutBackoffMs = timeBetweenBurstsInMs;
-            if (timeBetweenBurstsInMs < TIME_BETWEEN_BURSTS_MS) {
-                newTimeBetweenBurstsInMs = Math.min(timeBetweenBurstsInMs * 2,
-                        TIME_BETWEEN_BURSTS_MS);
-            }
-        } else {
-            newDelayUntilNextTaskWithoutBackoffMs = TIME_BETWEEN_QUERIES_IN_BURST_MS;
         }
+
         return new QueryTaskConfig(this, newQueryCount, newTransactionId,
-                newExpectUnicastResponse, newIsFirstBurst, newBurstCounter, newQueriesPerBurst,
+                getNextExpectUnicastResponse(isLastQueryInBurst), newIsFirstBurst, newBurstCounter,
-                newTimeBetweenBurstsInMs, newDelayUntilNextTaskWithoutBackoffMs);
+                newQueriesPerBurst, getNextTimeBetweenBurstsMs(isLastQueryInBurst),
+                getDelayUntilNextTaskWithoutBackoff(isFirstQueryInBurst, isLastQueryInBurst));
     }
 
     /**

tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceTypeClientTests.java

@@ -17,8 +17,12 @@
 package com.android.server.connectivity.mdns;
 
 import static com.android.server.connectivity.mdns.MdnsSearchOptions.ACTIVE_QUERY_MODE;
+import static com.android.server.connectivity.mdns.MdnsSearchOptions.AGGRESSIVE_QUERY_MODE;
 import static com.android.server.connectivity.mdns.MdnsSearchOptions.PASSIVE_QUERY_MODE;
 import static com.android.server.connectivity.mdns.MdnsServiceTypeClient.EVENT_START_QUERYTASK;
+import static com.android.server.connectivity.mdns.QueryTaskConfig.INITIAL_AGGRESSIVE_TIME_BETWEEN_BURSTS_MS;
+import static com.android.server.connectivity.mdns.QueryTaskConfig.MAX_TIME_BETWEEN_AGGRESSIVE_BURSTS_MS;
+import static com.android.server.connectivity.mdns.QueryTaskConfig.TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS;
 import static com.android.testutils.DevSdkIgnoreRuleKt.SC_V2;
 
 import static org.junit.Assert.assertArrayEquals;
@@ -147,8 +151,8 @@ public class MdnsServiceTypeClientTests {
         MockitoAnnotations.initMocks(this);
         doReturn(TEST_ELAPSED_REALTIME).when(mockDecoderClock).elapsedRealtime();
 
-        expectedIPv4Packets = new DatagramPacket[16];
+        expectedIPv4Packets = new DatagramPacket[24];
-        expectedIPv6Packets = new DatagramPacket[16];
+        expectedIPv6Packets = new DatagramPacket[24];
         socketKey = new SocketKey(mockNetwork, INTERFACE_INDEX);
 
         for (int i = 0; i < expectedIPv4Packets.length; ++i) {
@@ -173,7 +177,15 @@ public class MdnsServiceTypeClientTests {
                 .thenReturn(expectedIPv4Packets[12])
                 .thenReturn(expectedIPv4Packets[13])
                 .thenReturn(expectedIPv4Packets[14])
-                .thenReturn(expectedIPv4Packets[15]);
+                .thenReturn(expectedIPv4Packets[15])
+                .thenReturn(expectedIPv4Packets[16])
+                .thenReturn(expectedIPv4Packets[17])
+                .thenReturn(expectedIPv4Packets[18])
+                .thenReturn(expectedIPv4Packets[19])
+                .thenReturn(expectedIPv4Packets[20])
+                .thenReturn(expectedIPv4Packets[21])
+                .thenReturn(expectedIPv4Packets[22])
+                .thenReturn(expectedIPv4Packets[23]);
 
         when(mockPacketWriter.getPacket(IPV6_ADDRESS))
                 .thenReturn(expectedIPv6Packets[0])
@@ -191,7 +203,15 @@ public class MdnsServiceTypeClientTests {
                 .thenReturn(expectedIPv6Packets[12])
                 .thenReturn(expectedIPv6Packets[13])
                 .thenReturn(expectedIPv6Packets[14])
-                .thenReturn(expectedIPv6Packets[15]);
+                .thenReturn(expectedIPv6Packets[15])
+                .thenReturn(expectedIPv6Packets[16])
+                .thenReturn(expectedIPv6Packets[17])
+                .thenReturn(expectedIPv6Packets[18])
+                .thenReturn(expectedIPv6Packets[19])
+                .thenReturn(expectedIPv6Packets[20])
+                .thenReturn(expectedIPv6Packets[21])
+                .thenReturn(expectedIPv6Packets[22])
+                .thenReturn(expectedIPv6Packets[23]);
 
         thread = new HandlerThread("MdnsServiceTypeClientTests");
         thread.start();
@@ -1672,6 +1692,118 @@ public class MdnsServiceTypeClientTests {
                 socketKey);
     }
 
+    private int getBetweenBurstTime(int burstCounter, int currentBetweenTime, int maxBetweenTime,
+            int initialBetweenTime) {
+        return currentBetweenTime < maxBetweenTime
+                ? Math.min(initialBetweenTime * (int) Math.pow(2, burstCounter), maxBetweenTime)
+                : currentBetweenTime;
+    }
+
+    @Test
+    public void sendQueries_aggressiveScanMode() {
+        final MdnsSearchOptions searchOptions = MdnsSearchOptions.newBuilder()
+                .addSubtype(SUBTYPE).setQueryMode(AGGRESSIVE_QUERY_MODE).build();
+        startSendAndReceive(mockListenerOne, searchOptions);
+        // Always try to remove the task.
+        verify(mockDeps, times(1)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+
+        int burstCounter = 0;
+        int betweenBurstTime = 0;
+        for (int i = 0; i < expectedIPv4Packets.length; i += 3) {
+            verifyAndSendQuery(i, betweenBurstTime, /* expectsUnicastResponse= */ true);
+            verifyAndSendQuery(i + 1, /* timeInMs= */ 0, /* expectsUnicastResponse= */ false);
+            verifyAndSendQuery(i + 2, TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS,
+                    /* expectsUnicastResponse= */ false);
+            betweenBurstTime = getBetweenBurstTime(burstCounter, betweenBurstTime,
+                    MAX_TIME_BETWEEN_AGGRESSIVE_BURSTS_MS,
+                    INITIAL_AGGRESSIVE_TIME_BETWEEN_BURSTS_MS);
+            burstCounter++;
+        }
+        // Verify that Task is not removed before stopSendAndReceive was called.
+        verify(mockDeps, times(1)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+
+        // Stop sending packets.
+        stopSendAndReceive(mockListenerOne);
+        verify(mockDeps, times(2)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+    }
+
+    @Test
+    public void sendQueries_reentry_aggressiveScanMode() {
+        final MdnsSearchOptions searchOptions = MdnsSearchOptions.newBuilder()
+                .addSubtype(SUBTYPE).setQueryMode(AGGRESSIVE_QUERY_MODE).build();
+        startSendAndReceive(mockListenerOne, searchOptions);
+        // Always try to remove the task.
+        verify(mockDeps, times(1)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+
+        // First burst, first query is sent.
+        verifyAndSendQuery(0, /* timeInMs= */ 0, /* expectsUnicastResponse= */ true);
+
+        // After the first query is sent, change the subtypes, and restart.
+        final MdnsSearchOptions searchOptions2 = MdnsSearchOptions.newBuilder().addSubtype(SUBTYPE)
+                .addSubtype("_subtype2").setQueryMode(AGGRESSIVE_QUERY_MODE).build();
+        startSendAndReceive(mockListenerOne, searchOptions2);
+        // The previous scheduled task should be canceled.
+        verify(mockDeps, times(2)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+
+        // Queries should continue to be sent.
+        verifyAndSendQuery(1, /* timeInMs= */ 0, /* expectsUnicastResponse= */ true);
+        verifyAndSendQuery(2, /* timeInMs= */ 0, /* expectsUnicastResponse= */ false);
+        verifyAndSendQuery(3, TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS,
+                /* expectsUnicastResponse= */ false);
+
+        // Stop sending packets.
+        stopSendAndReceive(mockListenerOne);
+        verify(mockDeps, times(3)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+    }
+
+    @Test
+    public void sendQueries_blendScanWithQueryBackoff() {
+        final int numOfQueriesBeforeBackoff = 11;
+        final MdnsSearchOptions searchOptions = MdnsSearchOptions.newBuilder()
+                .addSubtype(SUBTYPE)
+                .setQueryMode(AGGRESSIVE_QUERY_MODE)
+                .setNumOfQueriesBeforeBackoff(numOfQueriesBeforeBackoff)
+                .build();
+        startSendAndReceive(mockListenerOne, searchOptions);
+        // Always try to remove the task.
+        verify(mockDeps, times(1)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+
+        int burstCounter = 0;
+        int betweenBurstTime = 0;
+        for (int i = 0; i < numOfQueriesBeforeBackoff; i += 3) {
+            verifyAndSendQuery(i, betweenBurstTime, /* expectsUnicastResponse= */ true);
+            verifyAndSendQuery(i + 1, /* timeInMs= */ 0, /* expectsUnicastResponse= */ false);
+            verifyAndSendQuery(i + 2, TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS,
+                    /* expectsUnicastResponse= */ false);
+            betweenBurstTime = getBetweenBurstTime(burstCounter, betweenBurstTime,
+                    MAX_TIME_BETWEEN_AGGRESSIVE_BURSTS_MS,
+                    INITIAL_AGGRESSIVE_TIME_BETWEEN_BURSTS_MS);
+            burstCounter++;
+        }
+        // In backoff mode, the current scheduled task will be canceled and reschedule if the
+        // 0.8 * smallestRemainingTtl is larger than time to next run.
+        long currentTime = TEST_TTL / 2 + TEST_ELAPSED_REALTIME;
+        doReturn(currentTime).when(mockDecoderClock).elapsedRealtime();
+        doReturn(true).when(mockDeps).hasMessages(any(), eq(EVENT_START_QUERYTASK));
+        processResponse(createResponse(
+                "service-instance-1", "192.0.2.123", 5353,
+                SERVICE_TYPE_LABELS,
+                Collections.emptyMap(), TEST_TTL), socketKey);
+        verify(mockDeps, times(2)).removeMessages(any(), eq(EVENT_START_QUERYTASK));
+        assertNotNull(delayMessage);
+        verifyAndSendQuery(12 /* index */, (long) (TEST_TTL / 2 * 0.8) /* timeInMs */,
+                true /* expectsUnicastResponse */, true /* multipleSocketDiscovery */,
+                14 /* scheduledCount */);
+        currentTime += (long) (TEST_TTL / 2 * 0.8);
+        doReturn(currentTime).when(mockDecoderClock).elapsedRealtime();
+        verifyAndSendQuery(13 /* index */, 0 /* timeInMs */,
+                false /* expectsUnicastResponse */, true /* multipleSocketDiscovery */,
+                15 /* scheduledCount */);
+        verifyAndSendQuery(14 /* index */, TIME_BETWEEN_RETRANSMISSION_QUERIES_IN_BURST_MS,
+                false /* expectsUnicastResponse */, true /* multipleSocketDiscovery */,
+                16 /* scheduledCount */);
+    }
+
     private static MdnsServiceInfo matchServiceName(String name) {
         return argThat(info -> info.getServiceInstanceName().equals(name));
     }