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

/*
 * Copyright (C) 2021 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;

import static android.net.ConnectivityManager.NETID_UNSET;
import static android.net.nsd.NsdManager.MDNS_DISCOVERY_MANAGER_EVENT;
import static android.net.nsd.NsdManager.MDNS_SERVICE_EVENT;
import static android.provider.DeviceConfig.NAMESPACE_CONNECTIVITY;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.INetd;
import android.net.InetAddresses;
import android.net.LinkProperties;
import android.net.Network;
import android.net.mdns.aidl.DiscoveryInfo;
import android.net.mdns.aidl.GetAddressInfo;
import android.net.mdns.aidl.IMDnsEventListener;
import android.net.mdns.aidl.RegistrationInfo;
import android.net.mdns.aidl.ResolutionInfo;
import android.net.nsd.INsdManager;
import android.net.nsd.INsdManagerCallback;
import android.net.nsd.INsdServiceConnector;
import android.net.nsd.MDnsManager;
import android.net.nsd.NsdManager;
import android.net.nsd.NsdServiceInfo;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;
import android.os.RemoteException;
import android.os.UserHandle;
import android.text.TextUtils;
import android.util.Log;
import android.util.Pair;
import android.util.SparseArray;
import android.util.SparseIntArray;

import com.android.internal.annotations.VisibleForTesting;
import com.android.internal.util.State;
import com.android.internal.util.StateMachine;
import com.android.net.module.util.DeviceConfigUtils;
import com.android.net.module.util.PermissionUtils;
import com.android.server.connectivity.mdns.ExecutorProvider;
import com.android.server.connectivity.mdns.MdnsAdvertiser;
import com.android.server.connectivity.mdns.MdnsDiscoveryManager;
import com.android.server.connectivity.mdns.MdnsMultinetworkSocketClient;
import com.android.server.connectivity.mdns.MdnsSearchOptions;
import com.android.server.connectivity.mdns.MdnsServiceBrowserListener;
import com.android.server.connectivity.mdns.MdnsServiceInfo;
import com.android.server.connectivity.mdns.MdnsSocketClientBase;
import com.android.server.connectivity.mdns.MdnsSocketProvider;

import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Network Service Discovery Service handles remote service discovery operation requests by
 * implementing the INsdManager interface.
 *
 * @hide
 */
public class NsdService extends INsdManager.Stub {
    private static final String TAG = "NsdService";
    private static final String MDNS_TAG = "mDnsConnector";
    /**
     * Enable discovery using the Java DiscoveryManager, instead of the legacy mdnsresponder
     * implementation.
     */
    private static final String MDNS_DISCOVERY_MANAGER_VERSION = "mdns_discovery_manager_version";
    private static final String LOCAL_DOMAIN_NAME = "local";
    // Max label length as per RFC 1034/1035
    private static final int MAX_LABEL_LENGTH = 63;

    /**
     * Enable advertising using the Java MdnsAdvertiser, instead of the legacy mdnsresponder
     * implementation.
     */
    private static final String MDNS_ADVERTISER_VERSION = "mdns_advertiser_version";

    public static final boolean DBG = Log.isLoggable(TAG, Log.DEBUG);
    private static final long CLEANUP_DELAY_MS = 10000;
    private static final int IFACE_IDX_ANY = 0;

    private final Context mContext;
    private final NsdStateMachine mNsdStateMachine;
    private final MDnsManager mMDnsManager;
    private final MDnsEventCallback mMDnsEventCallback;
    @Nullable
    private final MdnsMultinetworkSocketClient mMdnsSocketClient;
    @Nullable
    private final MdnsDiscoveryManager mMdnsDiscoveryManager;
    @Nullable
    private final MdnsSocketProvider mMdnsSocketProvider;
    @Nullable
    private final MdnsAdvertiser mAdvertiser;
    // WARNING : Accessing these values in any thread is not safe, it must only be changed in the
    // state machine thread. If change this outside state machine, it will need to introduce
    // synchronization.
    private boolean mIsDaemonStarted = false;
    private boolean mIsMonitoringSocketsStarted = false;

    /**
     * Clients receiving asynchronous messages
     */
    private final HashMap<NsdServiceConnector, ClientInfo> mClients = new HashMap<>();

    /* A map from unique id to client info */
    private final SparseArray<ClientInfo> mIdToClientInfoMap= new SparseArray<>();

    private final long mCleanupDelayMs;

    private static final int INVALID_ID = 0;
    private int mUniqueId = 1;
    // The count of the connected legacy clients.
    private int mLegacyClientCount = 0;

    private static class MdnsListener implements MdnsServiceBrowserListener {
        protected final int mClientId;
        protected final int mTransactionId;
        @NonNull
        protected final NsdServiceInfo mReqServiceInfo;
        @NonNull
        protected final String mListenedServiceType;

        MdnsListener(int clientId, int transactionId, @NonNull NsdServiceInfo reqServiceInfo,
                @NonNull String listenedServiceType) {
            mClientId = clientId;
            mTransactionId = transactionId;
            mReqServiceInfo = reqServiceInfo;
            mListenedServiceType = listenedServiceType;
        }

        @NonNull
        public String getListenedServiceType() {
            return mListenedServiceType;
        }

        @Override
        public void onServiceFound(@NonNull MdnsServiceInfo serviceInfo) { }

        @Override
        public void onServiceUpdated(@NonNull MdnsServiceInfo serviceInfo) { }

        @Override
        public void onServiceRemoved(@NonNull MdnsServiceInfo serviceInfo) { }

        @Override
        public void onServiceNameDiscovered(@NonNull MdnsServiceInfo serviceInfo) { }

        @Override
        public void onServiceNameRemoved(@NonNull MdnsServiceInfo serviceInfo) { }

        @Override
        public void onSearchStoppedWithError(int error) { }

        @Override
        public void onSearchFailedToStart() { }

        @Override
        public void onDiscoveryQuerySent(@NonNull List<String> subtypes, int transactionId) { }

        @Override
        public void onFailedToParseMdnsResponse(int receivedPacketNumber, int errorCode) { }
    }

    private class DiscoveryListener extends MdnsListener {

        DiscoveryListener(int clientId, int transactionId, @NonNull NsdServiceInfo reqServiceInfo,
                @NonNull String listenServiceType) {
            super(clientId, transactionId, reqServiceInfo, listenServiceType);
        }

        @Override
        public void onServiceNameDiscovered(@NonNull MdnsServiceInfo serviceInfo) {
            mNsdStateMachine.sendMessage(MDNS_DISCOVERY_MANAGER_EVENT, mTransactionId,
                    NsdManager.SERVICE_FOUND,
                    new MdnsEvent(mClientId, mReqServiceInfo.getServiceType(), serviceInfo));
        }

        @Override
        public void onServiceNameRemoved(@NonNull MdnsServiceInfo serviceInfo) {
            mNsdStateMachine.sendMessage(MDNS_DISCOVERY_MANAGER_EVENT, mTransactionId,
                    NsdManager.SERVICE_LOST,
                    new MdnsEvent(mClientId, mReqServiceInfo.getServiceType(), serviceInfo));
        }
    }

    private class ResolutionListener extends MdnsListener {

        ResolutionListener(int clientId, int transactionId, @NonNull NsdServiceInfo reqServiceInfo,
                @NonNull String listenServiceType) {
            super(clientId, transactionId, reqServiceInfo, listenServiceType);
        }

        @Override
        public void onServiceFound(MdnsServiceInfo serviceInfo) {
            mNsdStateMachine.sendMessage(MDNS_DISCOVERY_MANAGER_EVENT, mTransactionId,
                    NsdManager.RESOLVE_SERVICE_SUCCEEDED,
                    new MdnsEvent(mClientId, mReqServiceInfo.getServiceType(), serviceInfo));
        }
    }

    /**
     * Data class of mdns service callback information.
     */
    private static class MdnsEvent {
        final int mClientId;
        @NonNull
        final String mRequestedServiceType;
        @NonNull
        final MdnsServiceInfo mMdnsServiceInfo;

        MdnsEvent(int clientId, @NonNull String requestedServiceType,
                @NonNull MdnsServiceInfo mdnsServiceInfo) {
            mClientId = clientId;
            mRequestedServiceType = requestedServiceType;
            mMdnsServiceInfo = mdnsServiceInfo;
        }
    }

    private class NsdStateMachine extends StateMachine {

        private final DefaultState mDefaultState = new DefaultState();
        private final EnabledState mEnabledState = new EnabledState();

        @Override
        protected String getWhatToString(int what) {
            return NsdManager.nameOf(what);
        }

        private void maybeStartDaemon() {
            if (mIsDaemonStarted) {
                if (DBG) Log.d(TAG, "Daemon is already started.");
                return;
            }
            mMDnsManager.registerEventListener(mMDnsEventCallback);
            mMDnsManager.startDaemon();
            mIsDaemonStarted = true;
            maybeScheduleStop();
        }

        private void maybeStopDaemon() {
            if (!mIsDaemonStarted) {
                if (DBG) Log.d(TAG, "Daemon has not been started.");
                return;
            }
            mMDnsManager.unregisterEventListener(mMDnsEventCallback);
            mMDnsManager.stopDaemon();
            mIsDaemonStarted = false;
        }

        private boolean isAnyRequestActive() {
            return mIdToClientInfoMap.size() != 0;
        }

        private void scheduleStop() {
            sendMessageDelayed(NsdManager.DAEMON_CLEANUP, mCleanupDelayMs);
        }
        private void maybeScheduleStop() {
            // The native daemon should stay alive and can't be cleanup
            // if any legacy client connected.
            if (!isAnyRequestActive() && mLegacyClientCount == 0) {
                scheduleStop();
            }
        }

        private void cancelStop() {
            this.removeMessages(NsdManager.DAEMON_CLEANUP);
        }

        private void maybeStartMonitoringSockets() {
            if (mIsMonitoringSocketsStarted) {
                if (DBG) Log.d(TAG, "Socket monitoring is already started.");
                return;
            }

            mMdnsSocketProvider.startMonitoringSockets();
            mIsMonitoringSocketsStarted = true;
        }

        private void maybeStopMonitoringSockets() {
            if (!mIsMonitoringSocketsStarted) {
                if (DBG) Log.d(TAG, "Socket monitoring has not been started.");
                return;
            }
            mMdnsSocketProvider.stopMonitoringSockets();
            mIsMonitoringSocketsStarted = false;
        }

        private void maybeStopMonitoringSocketsIfNoActiveRequest() {
            if (!isAnyRequestActive()) {
                maybeStopMonitoringSockets();
            }
        }

        NsdStateMachine(String name, Handler handler) {
            super(name, handler);
            addState(mDefaultState);
                addState(mEnabledState, mDefaultState);
            State initialState = mEnabledState;
            setInitialState(initialState);
            setLogRecSize(25);
        }

        class DefaultState extends State {
            @Override
            public boolean processMessage(Message msg) {
                final ClientInfo cInfo;
                final int clientId = msg.arg2;
                switch (msg.what) {
                    case NsdManager.REGISTER_CLIENT:
                        final Pair<NsdServiceConnector, INsdManagerCallback> arg =
                                (Pair<NsdServiceConnector, INsdManagerCallback>) msg.obj;
                        final INsdManagerCallback cb = arg.second;
                        try {
                            cb.asBinder().linkToDeath(arg.first, 0);
                            cInfo = new ClientInfo(cb);
                            mClients.put(arg.first, cInfo);
                        } catch (RemoteException e) {
                            Log.w(TAG, "Client " + clientId + " has already died");
                        }
                        break;
                    case NsdManager.UNREGISTER_CLIENT:
                        final NsdServiceConnector connector = (NsdServiceConnector) msg.obj;
                        cInfo = mClients.remove(connector);
                        if (cInfo != null) {
                            if (mMdnsDiscoveryManager != null) {
                                cInfo.unregisterAllListeners();
                            }
                            cInfo.expungeAllRequests();
                            if (cInfo.isLegacy()) {
                                mLegacyClientCount -= 1;
                            }
                        }
                        if (mMdnsDiscoveryManager != null || mAdvertiser != null) {
                            maybeStopMonitoringSocketsIfNoActiveRequest();
                        }
                        maybeScheduleStop();
                        break;
                    case NsdManager.DISCOVER_SERVICES:
                        cInfo = getClientInfoForReply(msg);
                        if (cInfo != null) {
                            cInfo.onDiscoverServicesFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        }
                       break;
                    case NsdManager.STOP_DISCOVERY:
                        cInfo = getClientInfoForReply(msg);
                        if (cInfo != null) {
                            cInfo.onStopDiscoveryFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        }
                        break;
                    case NsdManager.REGISTER_SERVICE:
                        cInfo = getClientInfoForReply(msg);
                        if (cInfo != null) {
                            cInfo.onRegisterServiceFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        }
                        break;
                    case NsdManager.UNREGISTER_SERVICE:
                        cInfo = getClientInfoForReply(msg);
                        if (cInfo != null) {
                            cInfo.onUnregisterServiceFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        }
                        break;
                    case NsdManager.RESOLVE_SERVICE:
                        cInfo = getClientInfoForReply(msg);
                        if (cInfo != null) {
                            cInfo.onResolveServiceFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        }
                        break;
                    case NsdManager.STOP_RESOLUTION:
                        cInfo = getClientInfoForReply(msg);
                        if (cInfo != null) {
                            cInfo.onStopResolutionFailed(
                                    clientId, NsdManager.FAILURE_OPERATION_NOT_RUNNING);
                        }
                        break;
                    case NsdManager.DAEMON_CLEANUP:
                        maybeStopDaemon();
                        break;
                    // This event should be only sent by the legacy (target SDK < S) clients.
                    // Mark the sending client as legacy.
                    case NsdManager.DAEMON_STARTUP:
                        cInfo = getClientInfoForReply(msg);
                        if (cInfo != null) {
                            cancelStop();
                            cInfo.setLegacy();
                            mLegacyClientCount += 1;
                            maybeStartDaemon();
                        }
                        break;
                    default:
                        Log.e(TAG, "Unhandled " + msg);
                        return NOT_HANDLED;
                }
                return HANDLED;
            }

            private ClientInfo getClientInfoForReply(Message msg) {
                final ListenerArgs args = (ListenerArgs) msg.obj;
                return mClients.get(args.connector);
            }
        }

        class EnabledState extends State {
            @Override
            public void enter() {
                sendNsdStateChangeBroadcast(true);
            }

            @Override
            public void exit() {
                // TODO: it is incorrect to stop the daemon without expunging all requests
                // and sending error callbacks to clients.
                scheduleStop();
            }

            private boolean requestLimitReached(ClientInfo clientInfo) {
                if (clientInfo.mClientIds.size() >= ClientInfo.MAX_LIMIT) {
                    if (DBG) Log.d(TAG, "Exceeded max outstanding requests " + clientInfo);
                    return true;
                }
                return false;
            }

            private void storeRequestMap(int clientId, int globalId, ClientInfo clientInfo, int what) {
                clientInfo.mClientIds.put(clientId, globalId);
                clientInfo.mClientRequests.put(clientId, what);
                mIdToClientInfoMap.put(globalId, clientInfo);
                // Remove the cleanup event because here comes a new request.
                cancelStop();
            }

            private void removeRequestMap(int clientId, int globalId, ClientInfo clientInfo) {
                clientInfo.mClientIds.delete(clientId);
                clientInfo.mClientRequests.delete(clientId);
                mIdToClientInfoMap.remove(globalId);
                maybeScheduleStop();
                maybeStopMonitoringSocketsIfNoActiveRequest();
            }

            private void storeListenerMap(int clientId, int transactionId, MdnsListener listener,
                    ClientInfo clientInfo) {
                clientInfo.mClientIds.put(clientId, transactionId);
                clientInfo.mListeners.put(clientId, listener);
                mIdToClientInfoMap.put(transactionId, clientInfo);
            }

            private void removeListenerMap(int clientId, int transactionId, ClientInfo clientInfo) {
                clientInfo.mClientIds.delete(clientId);
                clientInfo.mListeners.delete(clientId);
                mIdToClientInfoMap.remove(transactionId);
                maybeStopMonitoringSocketsIfNoActiveRequest();
            }

            /**
             * Check the given service type is valid and construct it to a service type
             * which can use for discovery / resolution service.
             *
             * <p> The valid service type should be 2 labels, or 3 labels if the query is for a
             * subtype (see RFC6763 7.1). Each label is up to 63 characters and must start with an
             * underscore; they are alphanumerical characters or dashes or underscore, except the
             * last one that is just alphanumerical. The last label must be _tcp or _udp.
             *
             * @param serviceType the request service type for discovery / resolution service
             * @return constructed service type or null if the given service type is invalid.
             */
            @Nullable
            private String constructServiceType(String serviceType) {
                if (TextUtils.isEmpty(serviceType)) return null;

                final Pattern serviceTypePattern = Pattern.compile(
                        "^(_[a-zA-Z0-9-_]{1,61}[a-zA-Z0-9]\\.)?"
                                + "(_[a-zA-Z0-9-_]{1,61}[a-zA-Z0-9]\\._(?:tcp|udp))$");
                final Matcher matcher = serviceTypePattern.matcher(serviceType);
                if (!matcher.matches()) return null;
                return matcher.group(1) == null
                        ? serviceType
                        : matcher.group(1) + "_sub." + matcher.group(2);
            }

            /**
             * Truncate a service name to up to 63 UTF-8 bytes.
             *
             * See RFC6763 4.1.1: service instance names are UTF-8 and up to 63 bytes. Truncating
             * names used in registerService follows historical behavior (see mdnsresponder
             * handle_regservice_request).
             */
            @NonNull
            private String truncateServiceName(@NonNull String originalName) {
                // UTF-8 is at most 4 bytes per character; return early in the common case where
                // the name can't possibly be over the limit given its string length.
                if (originalName.length() <= MAX_LABEL_LENGTH / 4) return originalName;

                final Charset utf8 = StandardCharsets.UTF_8;
                final CharsetEncoder encoder = utf8.newEncoder();
                final ByteBuffer out = ByteBuffer.allocate(MAX_LABEL_LENGTH);
                // encode will write as many characters as possible to the out buffer, and just
                // return an overflow code if there were too many characters (no need to check the
                // return code here, this method truncates the name on purpose).
                encoder.encode(CharBuffer.wrap(originalName), out, true /* endOfInput */);
                return new String(out.array(), 0, out.position(), utf8);
            }

            @Override
            public boolean processMessage(Message msg) {
                final ClientInfo clientInfo;
                final int id;
                final int clientId = msg.arg2;
                final ListenerArgs args;
                switch (msg.what) {
                    case NsdManager.DISCOVER_SERVICES: {
                        if (DBG) Log.d(TAG, "Discover services");
                        args = (ListenerArgs) msg.obj;
                        clientInfo = mClients.get(args.connector);
                        // If the binder death notification for a INsdManagerCallback was received
                        // before any calls are received by NsdService, the clientInfo would be
                        // cleared and cause NPE. Add a null check here to prevent this corner case.
                        if (clientInfo == null) {
                            Log.e(TAG, "Unknown connector in discovery");
                            break;
                        }

                        if (requestLimitReached(clientInfo)) {
                            clientInfo.onDiscoverServicesFailed(
                                    clientId, NsdManager.FAILURE_MAX_LIMIT);
                            break;
                        }

                        final NsdServiceInfo info = args.serviceInfo;
                        id = getUniqueId();
                        if (mMdnsDiscoveryManager != null) {
                            final String serviceType = constructServiceType(info.getServiceType());
                            if (serviceType == null) {
                                clientInfo.onDiscoverServicesFailed(clientId,
                                        NsdManager.FAILURE_INTERNAL_ERROR);
                                break;
                            }

                            final String listenServiceType = serviceType + ".local";
                            maybeStartMonitoringSockets();
                            final MdnsListener listener =
                                    new DiscoveryListener(clientId, id, info, listenServiceType);
                            final MdnsSearchOptions options = MdnsSearchOptions.newBuilder()
                                    .setNetwork(info.getNetwork())
                                    .setIsPassiveMode(true)
                                    .build();
                            mMdnsDiscoveryManager.registerListener(
                                    listenServiceType, listener, options);
                            storeListenerMap(clientId, id, listener, clientInfo);
                            clientInfo.onDiscoverServicesStarted(clientId, info);
                        } else {
                            maybeStartDaemon();
                            if (discoverServices(id, info)) {
                                if (DBG) {
                                    Log.d(TAG, "Discover " + msg.arg2 + " " + id
                                            + info.getServiceType());
                                }
                                storeRequestMap(clientId, id, clientInfo, msg.what);
                                clientInfo.onDiscoverServicesStarted(clientId, info);
                            } else {
                                stopServiceDiscovery(id);
                                clientInfo.onDiscoverServicesFailed(clientId,
                                        NsdManager.FAILURE_INTERNAL_ERROR);
                            }
                        }
                        break;
                    }
                    case NsdManager.STOP_DISCOVERY:
                        if (DBG) Log.d(TAG, "Stop service discovery");
                        args = (ListenerArgs) msg.obj;
                        clientInfo = mClients.get(args.connector);
                        // If the binder death notification for a INsdManagerCallback was received
                        // before any calls are received by NsdService, the clientInfo would be
                        // cleared and cause NPE. Add a null check here to prevent this corner case.
                        if (clientInfo == null) {
                            Log.e(TAG, "Unknown connector in stop discovery");
                            break;
                        }

                        try {
                            id = clientInfo.mClientIds.get(clientId);
                        } catch (NullPointerException e) {
                            clientInfo.onStopDiscoveryFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                            break;
                        }
                        if (mMdnsDiscoveryManager != null) {
                            final MdnsListener listener = clientInfo.mListeners.get(clientId);
                            if (listener == null) {
                                clientInfo.onStopDiscoveryFailed(
                                        clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                                break;
                            }
                            mMdnsDiscoveryManager.unregisterListener(
                                    listener.getListenedServiceType(), listener);
                            removeListenerMap(clientId, id, clientInfo);
                            clientInfo.onStopDiscoverySucceeded(clientId);
                        } else {
                            removeRequestMap(clientId, id, clientInfo);
                            if (stopServiceDiscovery(id)) {
                                clientInfo.onStopDiscoverySucceeded(clientId);
                            } else {
                                clientInfo.onStopDiscoveryFailed(
                                        clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                            }
                        }
                        break;
                    case NsdManager.REGISTER_SERVICE:
                        if (DBG) Log.d(TAG, "Register service");
                        args = (ListenerArgs) msg.obj;
                        clientInfo = mClients.get(args.connector);
                        // If the binder death notification for a INsdManagerCallback was received
                        // before any calls are received by NsdService, the clientInfo would be
                        // cleared and cause NPE. Add a null check here to prevent this corner case.
                        if (clientInfo == null) {
                            Log.e(TAG, "Unknown connector in registration");
                            break;
                        }

                        if (requestLimitReached(clientInfo)) {
                            clientInfo.onRegisterServiceFailed(
                                    clientId, NsdManager.FAILURE_MAX_LIMIT);
                            break;
                        }

                        id = getUniqueId();
                        if (mAdvertiser != null) {
                            final NsdServiceInfo serviceInfo = args.serviceInfo;
                            final String serviceType = serviceInfo.getServiceType();
                            final String registerServiceType = constructServiceType(serviceType);
                            if (registerServiceType == null) {
                                Log.e(TAG, "Invalid service type: " + serviceType);
                                clientInfo.onRegisterServiceFailed(clientId,
                                        NsdManager.FAILURE_INTERNAL_ERROR);
                                break;
                            }
                            serviceInfo.setServiceType(registerServiceType);
                            serviceInfo.setServiceName(truncateServiceName(
                                    serviceInfo.getServiceName()));

                            maybeStartMonitoringSockets();
                            mAdvertiser.addService(id, serviceInfo);
                            storeRequestMap(clientId, id, clientInfo, msg.what);
                        } else {
                            maybeStartDaemon();
                            if (registerService(id, args.serviceInfo)) {
                                if (DBG) Log.d(TAG, "Register " + clientId + " " + id);
                                storeRequestMap(clientId, id, clientInfo, msg.what);
                                // Return success after mDns reports success
                            } else {
                                unregisterService(id);
                                clientInfo.onRegisterServiceFailed(
                                        clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                            }

                        }
                        break;
                    case NsdManager.UNREGISTER_SERVICE:
                        if (DBG) Log.d(TAG, "unregister service");
                        args = (ListenerArgs) msg.obj;
                        clientInfo = mClients.get(args.connector);
                        // If the binder death notification for a INsdManagerCallback was received
                        // before any calls are received by NsdService, the clientInfo would be
                        // cleared and cause NPE. Add a null check here to prevent this corner case.
                        if (clientInfo == null) {
                            Log.e(TAG, "Unknown connector in unregistration");
                            break;
                        }
                        id = clientInfo.mClientIds.get(clientId);
                        removeRequestMap(clientId, id, clientInfo);

                        if (mAdvertiser != null) {
                            mAdvertiser.removeService(id);
                            clientInfo.onUnregisterServiceSucceeded(clientId);
                        } else {
                            if (unregisterService(id)) {
                                clientInfo.onUnregisterServiceSucceeded(clientId);
                            } else {
                                clientInfo.onUnregisterServiceFailed(
                                        clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                            }
                        }
                        break;
                    case NsdManager.RESOLVE_SERVICE: {
                        if (DBG) Log.d(TAG, "Resolve service");
                        args = (ListenerArgs) msg.obj;
                        clientInfo = mClients.get(args.connector);
                        // If the binder death notification for a INsdManagerCallback was received
                        // before any calls are received by NsdService, the clientInfo would be
                        // cleared and cause NPE. Add a null check here to prevent this corner case.
                        if (clientInfo == null) {
                            Log.e(TAG, "Unknown connector in resolution");
                            break;
                        }

                        final NsdServiceInfo info = args.serviceInfo;
                        id = getUniqueId();
                        if (mMdnsDiscoveryManager != null) {
                            final String serviceType = constructServiceType(info.getServiceType());
                            if (serviceType == null) {
                                clientInfo.onResolveServiceFailed(clientId,
                                        NsdManager.FAILURE_INTERNAL_ERROR);
                                break;
                            }
                            final String resolveServiceType = serviceType + ".local";

                            maybeStartMonitoringSockets();
                            final MdnsListener listener =
                                    new ResolutionListener(clientId, id, info, resolveServiceType);
                            final MdnsSearchOptions options = MdnsSearchOptions.newBuilder()
                                    .setNetwork(info.getNetwork())
                                    .setIsPassiveMode(true)
                                    .build();
                            mMdnsDiscoveryManager.registerListener(
                                    resolveServiceType, listener, options);
                            storeListenerMap(clientId, id, listener, clientInfo);
                        } else {
                            if (clientInfo.mResolvedService != null) {
                                clientInfo.onResolveServiceFailed(
                                        clientId, NsdManager.FAILURE_ALREADY_ACTIVE);
                                break;
                            }

                            maybeStartDaemon();
                            if (resolveService(id, args.serviceInfo)) {
                                clientInfo.mResolvedService = new NsdServiceInfo();
                                storeRequestMap(clientId, id, clientInfo, msg.what);
                            } else {
                                clientInfo.onResolveServiceFailed(
                                        clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                            }
                        }
                        break;
                    }
                    case NsdManager.STOP_RESOLUTION:
                        if (DBG) Log.d(TAG, "Stop service resolution");
                        args = (ListenerArgs) msg.obj;
                        clientInfo = mClients.get(args.connector);
                        // If the binder death notification for a INsdManagerCallback was received
                        // before any calls are received by NsdService, the clientInfo would be
                        // cleared and cause NPE. Add a null check here to prevent this corner case.
                        if (clientInfo == null) {
                            Log.e(TAG, "Unknown connector in stop resolution");
                            break;
                        }

                        id = clientInfo.mClientIds.get(clientId);
                        removeRequestMap(clientId, id, clientInfo);
                        if (stopResolveService(id)) {
                            clientInfo.onStopResolutionSucceeded(clientId);
                        } else {
                            clientInfo.onStopResolutionFailed(
                                    clientId, NsdManager.FAILURE_OPERATION_NOT_RUNNING);
                        }
                        clientInfo.mResolvedService = null;
                        // TODO: Implement the stop resolution with MdnsDiscoveryManager.
                        break;
                    case MDNS_SERVICE_EVENT:
                        if (!handleMDnsServiceEvent(msg.arg1, msg.arg2, msg.obj)) {
                            return NOT_HANDLED;
                        }
                        break;
                    case MDNS_DISCOVERY_MANAGER_EVENT:
                        if (!handleMdnsDiscoveryManagerEvent(msg.arg1, msg.arg2, msg.obj)) {
                            return NOT_HANDLED;
                        }
                        break;
                    default:
                        return NOT_HANDLED;
                }
                return HANDLED;
            }

            private boolean handleMDnsServiceEvent(int code, int id, Object obj) {
                NsdServiceInfo servInfo;
                ClientInfo clientInfo = mIdToClientInfoMap.get(id);
                if (clientInfo == null) {
                    Log.e(TAG, String.format("id %d for %d has no client mapping", id, code));
                    return false;
                }

                /* This goes in response as msg.arg2 */
                int clientId = clientInfo.getClientId(id);
                if (clientId < 0) {
                    // This can happen because of race conditions. For example,
                    // SERVICE_FOUND may race with STOP_SERVICE_DISCOVERY,
                    // and we may get in this situation.
                    Log.d(TAG, String.format("%d for listener id %d that is no longer active",
                            code, id));
                    return false;
                }
                if (DBG) {
                    Log.d(TAG, String.format("MDns service event code:%d id=%d", code, id));
                }
                switch (code) {
                    case IMDnsEventListener.SERVICE_FOUND: {
                        final DiscoveryInfo info = (DiscoveryInfo) obj;
                        final String name = info.serviceName;
                        final String type = info.registrationType;
                        servInfo = new NsdServiceInfo(name, type);
                        final int foundNetId = info.netId;
                        if (foundNetId == 0L) {
                            // Ignore services that do not have a Network: they are not usable
                            // by apps, as they would need privileged permissions to use
                            // interfaces that do not have an associated Network.
                            break;
                        }
                        if (foundNetId == INetd.DUMMY_NET_ID) {
                            // Ignore services on the dummy0 interface: they are only seen when
                            // discovering locally advertised services, and are not reachable
                            // through that interface.
                            break;
                        }
                        setServiceNetworkForCallback(servInfo, info.netId, info.interfaceIdx);
                        clientInfo.onServiceFound(clientId, servInfo);
                        break;
                    }
                    case IMDnsEventListener.SERVICE_LOST: {
                        final DiscoveryInfo info = (DiscoveryInfo) obj;
                        final String name = info.serviceName;
                        final String type = info.registrationType;
                        final int lostNetId = info.netId;
                        servInfo = new NsdServiceInfo(name, type);
                        // The network could be set to null (netId 0) if it was torn down when the
                        // service is lost
                        // TODO: avoid returning null in that case, possibly by remembering
                        // found services on the same interface index and their network at the time
                        setServiceNetworkForCallback(servInfo, lostNetId, info.interfaceIdx);
                        clientInfo.onServiceLost(clientId, servInfo);
                        break;
                    }
                    case IMDnsEventListener.SERVICE_DISCOVERY_FAILED:
                        clientInfo.onDiscoverServicesFailed(
                                clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        break;
                    case IMDnsEventListener.SERVICE_REGISTERED: {
                        final RegistrationInfo info = (RegistrationInfo) obj;
                        final String name = info.serviceName;
                        servInfo = new NsdServiceInfo(name, null /* serviceType */);
                        clientInfo.onRegisterServiceSucceeded(clientId, servInfo);
                        break;
                    }
                    case IMDnsEventListener.SERVICE_REGISTRATION_FAILED:
                        clientInfo.onRegisterServiceFailed(
                                clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        break;
                    case IMDnsEventListener.SERVICE_RESOLVED: {
                        final ResolutionInfo info = (ResolutionInfo) obj;
                        int index = 0;
                        final String fullName = info.serviceFullName;
                        while (index < fullName.length() && fullName.charAt(index) != '.') {
                            if (fullName.charAt(index) == '\\') {
                                ++index;
                            }
                            ++index;
                        }
                        if (index >= fullName.length()) {
                            Log.e(TAG, "Invalid service found " + fullName);
                            break;
                        }

                        String name = unescape(fullName.substring(0, index));
                        String rest = fullName.substring(index);
                        String type = rest.replace(".local.", "");

                        clientInfo.mResolvedService.setServiceName(name);
                        clientInfo.mResolvedService.setServiceType(type);
                        clientInfo.mResolvedService.setPort(info.port);
                        clientInfo.mResolvedService.setTxtRecords(info.txtRecord);
                        // Network will be added after SERVICE_GET_ADDR_SUCCESS

                        stopResolveService(id);
                        removeRequestMap(clientId, id, clientInfo);

                        final int id2 = getUniqueId();
                        if (getAddrInfo(id2, info.hostname, info.interfaceIdx)) {
                            storeRequestMap(clientId, id2, clientInfo, NsdManager.RESOLVE_SERVICE);
                        } else {
                            clientInfo.onResolveServiceFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                            clientInfo.mResolvedService = null;
                        }
                        break;
                    }
                    case IMDnsEventListener.SERVICE_RESOLUTION_FAILED:
                        /* NNN resolveId errorCode */
                        stopResolveService(id);
                        removeRequestMap(clientId, id, clientInfo);
                        clientInfo.mResolvedService = null;
                        clientInfo.onResolveServiceFailed(
                                clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        break;
                    case IMDnsEventListener.SERVICE_GET_ADDR_FAILED:
                        /* NNN resolveId errorCode */
                        stopGetAddrInfo(id);
                        removeRequestMap(clientId, id, clientInfo);
                        clientInfo.mResolvedService = null;
                        clientInfo.onResolveServiceFailed(
                                clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        break;
                    case IMDnsEventListener.SERVICE_GET_ADDR_SUCCESS: {
                        /* NNN resolveId hostname ttl addr interfaceIdx netId */
                        final GetAddressInfo info = (GetAddressInfo) obj;
                        final String address = info.address;
                        final int netId = info.netId;
                        InetAddress serviceHost = null;
                        try {
                            serviceHost = InetAddress.getByName(address);
                        } catch (UnknownHostException e) {
                            Log.wtf(TAG, "Invalid host in GET_ADDR_SUCCESS", e);
                        }

                        // If the resolved service is on an interface without a network, consider it
                        // as a failure: it would not be usable by apps as they would need
                        // privileged permissions.
                        if (netId != NETID_UNSET && serviceHost != null) {
                            clientInfo.mResolvedService.setHost(serviceHost);
                            setServiceNetworkForCallback(clientInfo.mResolvedService,
                                    netId, info.interfaceIdx);
                            clientInfo.onResolveServiceSucceeded(
                                    clientId, clientInfo.mResolvedService);
                        } else {
                            clientInfo.onResolveServiceFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        }
                        stopGetAddrInfo(id);
                        removeRequestMap(clientId, id, clientInfo);
                        clientInfo.mResolvedService = null;
                        break;
                    }
                    default:
                        return false;
                }
                return true;
            }

            private NsdServiceInfo buildNsdServiceInfoFromMdnsEvent(final MdnsEvent event) {
                final MdnsServiceInfo serviceInfo = event.mMdnsServiceInfo;
                final String serviceType = event.mRequestedServiceType;
                final String serviceName = serviceInfo.getServiceInstanceName();
                final NsdServiceInfo servInfo = new NsdServiceInfo(serviceName, serviceType);
                final Network network = serviceInfo.getNetwork();
                setServiceNetworkForCallback(
                        servInfo,
                        network == null ? NETID_UNSET : network.netId,
                        serviceInfo.getInterfaceIndex());
                return servInfo;
            }

            private boolean handleMdnsDiscoveryManagerEvent(
                    int transactionId, int code, Object obj) {
                final ClientInfo clientInfo = mIdToClientInfoMap.get(transactionId);
                if (clientInfo == null) {
                    Log.e(TAG, String.format(
                            "id %d for %d has no client mapping", transactionId, code));
                    return false;
                }

                final MdnsEvent event = (MdnsEvent) obj;
                final int clientId = event.mClientId;
                final NsdServiceInfo info = buildNsdServiceInfoFromMdnsEvent(event);
                if (DBG) {
                    Log.d(TAG, String.format("MdnsDiscoveryManager event code=%s transactionId=%d",
                            NsdManager.nameOf(code), transactionId));
                }
                switch (code) {
                    case NsdManager.SERVICE_FOUND:
                        clientInfo.onServiceFound(clientId, info);
                        break;
                    case NsdManager.SERVICE_LOST:
                        clientInfo.onServiceLost(clientId, info);
                        break;
                    case NsdManager.RESOLVE_SERVICE_SUCCEEDED: {
                        final MdnsServiceInfo serviceInfo = event.mMdnsServiceInfo;
                        // Add '.' in front of the service type that aligns with historical behavior
                        info.setServiceType("." + event.mRequestedServiceType);
                        info.setPort(serviceInfo.getPort());

                        Map<String, String> attrs = serviceInfo.getAttributes();
                        for (Map.Entry<String, String> kv : attrs.entrySet()) {
                            final String key = kv.getKey();
                            try {
                                info.setAttribute(key, serviceInfo.getAttributeAsBytes(key));
                            } catch (IllegalArgumentException e) {
                                Log.e(TAG, "Invalid attribute", e);
                            }
                        }
                        try {
                            if (serviceInfo.getIpv4Address() != null) {
                                info.setHost(InetAddresses.parseNumericAddress(
                                        serviceInfo.getIpv4Address()));
                            } else {
                                info.setHost(InetAddresses.parseNumericAddress(
                                        serviceInfo.getIpv6Address()));
                            }
                            clientInfo.onResolveServiceSucceeded(clientId, info);
                        } catch (IllegalArgumentException e) {
                            Log.wtf(TAG, "Invalid address in RESOLVE_SERVICE_SUCCEEDED", e);
                            clientInfo.onResolveServiceFailed(
                                    clientId, NsdManager.FAILURE_INTERNAL_ERROR);
                        }

                        // Unregister the listener immediately like IMDnsEventListener design
                        final MdnsListener listener = clientInfo.mListeners.get(clientId);
                        mMdnsDiscoveryManager.unregisterListener(
                                listener.getListenedServiceType(), listener);
                        removeListenerMap(clientId, transactionId, clientInfo);
                        break;
                    }
                    default:
                        return false;
                }
                return true;
            }
       }
    }

    private static void setServiceNetworkForCallback(NsdServiceInfo info, int netId, int ifaceIdx) {
        switch (netId) {
            case NETID_UNSET:
                info.setNetwork(null);
                break;
            case INetd.LOCAL_NET_ID:
                // Special case for LOCAL_NET_ID: Networks on netId 99 are not generally
                // visible / usable for apps, so do not return it. Store the interface
                // index instead, so at least if the client tries to resolve the service
                // with that NsdServiceInfo, it will be done on the same interface.
                // If they recreate the NsdServiceInfo themselves, resolution would be
                // done on all interfaces as before T, which should also work.
                info.setNetwork(null);
                info.setInterfaceIndex(ifaceIdx);
                break;
            default:
                info.setNetwork(new Network(netId));
        }
    }

    // The full service name is escaped from standard DNS rules on mdnsresponder, making it suitable
    // for passing to standard system DNS APIs such as res_query() . Thus, make the service name
    // unescape for getting right service address. See "Notes on DNS Name Escaping" on
    // external/mdnsresponder/mDNSShared/dns_sd.h for more details.
    private String unescape(String s) {
        StringBuilder sb = new StringBuilder(s.length());
        for (int i = 0; i < s.length(); ++i) {
            char c = s.charAt(i);
            if (c == '\\') {
                if (++i >= s.length()) {
                    Log.e(TAG, "Unexpected end of escape sequence in: " + s);
                    break;
                }
                c = s.charAt(i);
                if (c != '.' && c != '\\') {
                    if (i + 2 >= s.length()) {
                        Log.e(TAG, "Unexpected end of escape sequence in: " + s);
                        break;
                    }
                    c = (char) ((c - '0') * 100 + (s.charAt(i + 1) - '0') * 10
                            + (s.charAt(i + 2) - '0'));
                    i += 2;
                }
            }
            sb.append(c);
        }
        return sb.toString();
    }

    @VisibleForTesting
    NsdService(Context ctx, Handler handler, long cleanupDelayMs) {
        this(ctx, handler, cleanupDelayMs, new Dependencies());
    }

    @VisibleForTesting
    NsdService(Context ctx, Handler handler, long cleanupDelayMs, Dependencies deps) {
        mCleanupDelayMs = cleanupDelayMs;
        mContext = ctx;
        mNsdStateMachine = new NsdStateMachine(TAG, handler);
        mNsdStateMachine.start();
        mMDnsManager = ctx.getSystemService(MDnsManager.class);
        mMDnsEventCallback = new MDnsEventCallback(mNsdStateMachine);

        final boolean discoveryManagerEnabled = deps.isMdnsDiscoveryManagerEnabled(ctx);
        final boolean advertiserEnabled = deps.isMdnsAdvertiserEnabled(ctx);
        if (discoveryManagerEnabled || advertiserEnabled) {
            mMdnsSocketProvider = deps.makeMdnsSocketProvider(ctx, handler.getLooper());
        } else {
            mMdnsSocketProvider = null;
        }

        if (discoveryManagerEnabled) {
            mMdnsSocketClient =
                    new MdnsMultinetworkSocketClient(handler.getLooper(), mMdnsSocketProvider);
            mMdnsDiscoveryManager =
                    deps.makeMdnsDiscoveryManager(new ExecutorProvider(), mMdnsSocketClient);
            handler.post(() -> mMdnsSocketClient.setCallback(mMdnsDiscoveryManager));
        } else {
            mMdnsSocketClient = null;
            mMdnsDiscoveryManager = null;
        }

        if (advertiserEnabled) {
            mAdvertiser = deps.makeMdnsAdvertiser(handler.getLooper(), mMdnsSocketProvider,
                    new AdvertiserCallback());
        } else {
            mAdvertiser = null;
        }
    }

    /**
     * Dependencies of NsdService, for injection in tests.
     */
    @VisibleForTesting
    public static class Dependencies {
        /**
         * Check whether the MdnsDiscoveryManager feature is enabled.
         *
         * @param context The global context information about an app environment.
         * @return true if the MdnsDiscoveryManager feature is enabled.
         */
        public boolean isMdnsDiscoveryManagerEnabled(Context context) {
            return DeviceConfigUtils.isFeatureEnabled(context, NAMESPACE_CONNECTIVITY,
                    MDNS_DISCOVERY_MANAGER_VERSION, false /* defaultEnabled */);
        }

        /**
         * Check whether the MdnsAdvertiser feature is enabled.
         *
         * @param context The global context information about an app environment.
         * @return true if the MdnsAdvertiser feature is enabled.
         */
        public boolean isMdnsAdvertiserEnabled(Context context) {
            return DeviceConfigUtils.isFeatureEnabled(context, NAMESPACE_CONNECTIVITY,
                    MDNS_ADVERTISER_VERSION, false /* defaultEnabled */);
        }

        /**
         * @see MdnsDiscoveryManager
         */
        public MdnsDiscoveryManager makeMdnsDiscoveryManager(
                ExecutorProvider executorProvider, MdnsSocketClientBase socketClient) {
            return new MdnsDiscoveryManager(executorProvider, socketClient);
        }

        /**
         * @see MdnsAdvertiser
         */
        public MdnsAdvertiser makeMdnsAdvertiser(
                @NonNull Looper looper, @NonNull MdnsSocketProvider socketProvider,
                @NonNull MdnsAdvertiser.AdvertiserCallback cb) {
            return new MdnsAdvertiser(looper, socketProvider, cb);
        }

        /**
         * @see MdnsSocketProvider
         */
        public MdnsSocketProvider makeMdnsSocketProvider(Context context, Looper looper) {
            return new MdnsSocketProvider(context, looper);
        }
    }

    public static NsdService create(Context context) {
        HandlerThread thread = new HandlerThread(TAG);
        thread.start();
        Handler handler = new Handler(thread.getLooper());
        NsdService service = new NsdService(context, handler, CLEANUP_DELAY_MS);
        return service;
    }

    private static class MDnsEventCallback extends IMDnsEventListener.Stub {
        private final StateMachine mStateMachine;

        MDnsEventCallback(StateMachine sm) {
            mStateMachine = sm;
        }

        @Override
        public void onServiceRegistrationStatus(final RegistrationInfo status) {
            mStateMachine.sendMessage(
                    MDNS_SERVICE_EVENT, status.result, status.id, status);
        }

        @Override
        public void onServiceDiscoveryStatus(final DiscoveryInfo status) {
            mStateMachine.sendMessage(
                    MDNS_SERVICE_EVENT, status.result, status.id, status);
        }

        @Override
        public void onServiceResolutionStatus(final ResolutionInfo status) {
            mStateMachine.sendMessage(
                    MDNS_SERVICE_EVENT, status.result, status.id, status);
        }

        @Override
        public void onGettingServiceAddressStatus(final GetAddressInfo status) {
            mStateMachine.sendMessage(
                    MDNS_SERVICE_EVENT, status.result, status.id, status);
        }

        @Override
        public int getInterfaceVersion() throws RemoteException {
            return this.VERSION;
        }

        @Override
        public String getInterfaceHash() throws RemoteException {
            return this.HASH;
        }
    }

    private class AdvertiserCallback implements MdnsAdvertiser.AdvertiserCallback {
        @Override
        public void onRegisterServiceSucceeded(int serviceId, NsdServiceInfo registeredInfo) {
            final ClientInfo clientInfo = getClientInfoOrLog(serviceId);
            if (clientInfo == null) return;

            final int clientId = getClientIdOrLog(clientInfo, serviceId);
            if (clientId < 0) return;

            // onRegisterServiceSucceeded only has the service name in its info. This aligns with
            // historical behavior.
            final NsdServiceInfo cbInfo = new NsdServiceInfo(registeredInfo.getServiceName(), null);
            clientInfo.onRegisterServiceSucceeded(clientId, cbInfo);
        }

        @Override
        public void onRegisterServiceFailed(int serviceId, int errorCode) {
            final ClientInfo clientInfo = getClientInfoOrLog(serviceId);
            if (clientInfo == null) return;

            final int clientId = getClientIdOrLog(clientInfo, serviceId);
            if (clientId < 0) return;

            clientInfo.onRegisterServiceFailed(clientId, errorCode);
        }

        private ClientInfo getClientInfoOrLog(int serviceId) {
            final ClientInfo clientInfo = mIdToClientInfoMap.get(serviceId);
            if (clientInfo == null) {
                Log.e(TAG, String.format("Callback for service %d has no client", serviceId));
            }
            return clientInfo;
        }

        private int getClientIdOrLog(@NonNull ClientInfo info, int serviceId) {
            final int clientId = info.getClientId(serviceId);
            if (clientId < 0) {
                Log.e(TAG, String.format("Client ID not found for service %d", serviceId));
            }
            return clientId;
        }
    }

    @Override
    public INsdServiceConnector connect(INsdManagerCallback cb) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.INTERNET, "NsdService");
        final INsdServiceConnector connector = new NsdServiceConnector();
        mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                NsdManager.REGISTER_CLIENT, new Pair<>(connector, cb)));
        return connector;
    }

    private static class ListenerArgs {
        public final NsdServiceConnector connector;
        public final NsdServiceInfo serviceInfo;
        ListenerArgs(NsdServiceConnector connector, NsdServiceInfo serviceInfo) {
            this.connector = connector;
            this.serviceInfo = serviceInfo;
        }
    }

    private class NsdServiceConnector extends INsdServiceConnector.Stub
            implements IBinder.DeathRecipient  {
        @Override
        public void registerService(int listenerKey, NsdServiceInfo serviceInfo) {
            mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                    NsdManager.REGISTER_SERVICE, 0, listenerKey,
                    new ListenerArgs(this, serviceInfo)));
        }

        @Override
        public void unregisterService(int listenerKey) {
            mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                    NsdManager.UNREGISTER_SERVICE, 0, listenerKey,
                    new ListenerArgs(this, null)));
        }

        @Override
        public void discoverServices(int listenerKey, NsdServiceInfo serviceInfo) {
            mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                    NsdManager.DISCOVER_SERVICES, 0, listenerKey,
                    new ListenerArgs(this, serviceInfo)));
        }

        @Override
        public void stopDiscovery(int listenerKey) {
            mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                    NsdManager.STOP_DISCOVERY, 0, listenerKey, new ListenerArgs(this, null)));
        }

        @Override
        public void resolveService(int listenerKey, NsdServiceInfo serviceInfo) {
            mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                    NsdManager.RESOLVE_SERVICE, 0, listenerKey,
                    new ListenerArgs(this, serviceInfo)));
        }

        @Override
        public void stopResolution(int listenerKey) {
            mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                    NsdManager.STOP_RESOLUTION, 0, listenerKey, new ListenerArgs(this, null)));
        }

        @Override
        public void startDaemon() {
            mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(
                    NsdManager.DAEMON_STARTUP, new ListenerArgs(this, null)));
        }

        @Override
        public void binderDied() {
            mNsdStateMachine.sendMessage(
                    mNsdStateMachine.obtainMessage(NsdManager.UNREGISTER_CLIENT, this));
        }
    }

    private void sendNsdStateChangeBroadcast(boolean isEnabled) {
        final Intent intent = new Intent(NsdManager.ACTION_NSD_STATE_CHANGED);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
        int nsdState = isEnabled ? NsdManager.NSD_STATE_ENABLED : NsdManager.NSD_STATE_DISABLED;
        intent.putExtra(NsdManager.EXTRA_NSD_STATE, nsdState);
        mContext.sendStickyBroadcastAsUser(intent, UserHandle.ALL);
    }

    private int getUniqueId() {
        if (++mUniqueId == INVALID_ID) return ++mUniqueId;
        return mUniqueId;
    }

    private boolean registerService(int regId, NsdServiceInfo service) {
        if (DBG) {
            Log.d(TAG, "registerService: " + regId + " " + service);
        }
        String name = service.getServiceName();
        String type = service.getServiceType();
        int port = service.getPort();
        byte[] textRecord = service.getTxtRecord();
        final int registerInterface = getNetworkInterfaceIndex(service);
        if (service.getNetwork() != null && registerInterface == IFACE_IDX_ANY) {
            Log.e(TAG, "Interface to register service on not found");
            return false;
        }
        return mMDnsManager.registerService(regId, name, type, port, textRecord, registerInterface);
    }

    private boolean unregisterService(int regId) {
        return mMDnsManager.stopOperation(regId);
    }

    private boolean discoverServices(int discoveryId, NsdServiceInfo serviceInfo) {
        final String type = serviceInfo.getServiceType();
        final int discoverInterface = getNetworkInterfaceIndex(serviceInfo);
        if (serviceInfo.getNetwork() != null && discoverInterface == IFACE_IDX_ANY) {
            Log.e(TAG, "Interface to discover service on not found");
            return false;
        }
        return mMDnsManager.discover(discoveryId, type, discoverInterface);
    }

    private boolean stopServiceDiscovery(int discoveryId) {
        return mMDnsManager.stopOperation(discoveryId);
    }

    private boolean resolveService(int resolveId, NsdServiceInfo service) {
        final String name = service.getServiceName();
        final String type = service.getServiceType();
        final int resolveInterface = getNetworkInterfaceIndex(service);
        if (service.getNetwork() != null && resolveInterface == IFACE_IDX_ANY) {
            Log.e(TAG, "Interface to resolve service on not found");
            return false;
        }
        return mMDnsManager.resolve(resolveId, name, type, "local.", resolveInterface);
    }

    /**
     * Guess the interface to use to resolve or discover a service on a specific network.
     *
     * This is an imperfect guess, as for example the network may be gone or not yet fully
     * registered. This is fine as failing is correct if the network is gone, and a client
     * attempting to resolve/discover on a network not yet setup would have a bad time anyway; also
     * this is to support the legacy mdnsresponder implementation, which historically resolved
     * services on an unspecified network.
     */
    private int getNetworkInterfaceIndex(NsdServiceInfo serviceInfo) {
        final Network network = serviceInfo.getNetwork();
        if (network == null) {
            // Fallback to getInterfaceIndex if present (typically if the NsdServiceInfo was
            // provided by NsdService from discovery results, and the service was found on an
            // interface that has no app-usable Network).
            if (serviceInfo.getInterfaceIndex() != 0) {
                return serviceInfo.getInterfaceIndex();
            }
            return IFACE_IDX_ANY;
        }

        final ConnectivityManager cm = mContext.getSystemService(ConnectivityManager.class);
        if (cm == null) {
            Log.wtf(TAG, "No ConnectivityManager for resolveService");
            return IFACE_IDX_ANY;
        }
        final LinkProperties lp = cm.getLinkProperties(network);
        if (lp == null) return IFACE_IDX_ANY;

        // Only resolve on non-stacked interfaces
        final NetworkInterface iface;
        try {
            iface = NetworkInterface.getByName(lp.getInterfaceName());
        } catch (SocketException e) {
            Log.e(TAG, "Error querying interface", e);
            return IFACE_IDX_ANY;
        }

        if (iface == null) {
            Log.e(TAG, "Interface not found: " + lp.getInterfaceName());
            return IFACE_IDX_ANY;
        }

        return iface.getIndex();
    }

    private boolean stopResolveService(int resolveId) {
        return mMDnsManager.stopOperation(resolveId);
    }

    private boolean getAddrInfo(int resolveId, String hostname, int interfaceIdx) {
        return mMDnsManager.getServiceAddress(resolveId, hostname, interfaceIdx);
    }

    private boolean stopGetAddrInfo(int resolveId) {
        return mMDnsManager.stopOperation(resolveId);
    }

    @Override
    public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
        if (!PermissionUtils.checkDumpPermission(mContext, TAG, pw)) return;

        for (ClientInfo client : mClients.values()) {
            pw.println("Client Info");
            pw.println(client);
        }

        mNsdStateMachine.dump(fd, pw, args);
    }

    /* Information tracked per client */
    private class ClientInfo {

        private static final int MAX_LIMIT = 10;
        private final INsdManagerCallback mCb;
        /* Remembers a resolved service until getaddrinfo completes */
        private NsdServiceInfo mResolvedService;

        /* A map from client id to unique id sent to mDns */
        private final SparseIntArray mClientIds = new SparseIntArray();

        /* A map from client id to the type of the request we had received */
        private final SparseIntArray mClientRequests = new SparseIntArray();

        /* A map from client id to the MdnsListener */
        private final SparseArray<MdnsListener> mListeners = new SparseArray<>();

        // The target SDK of this client < Build.VERSION_CODES.S
        private boolean mIsLegacy = false;

        private ClientInfo(INsdManagerCallback cb) {
            mCb = cb;
            if (DBG) Log.d(TAG, "New client");
        }

        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder();
            sb.append("mResolvedService ").append(mResolvedService).append("\n");
            sb.append("mIsLegacy ").append(mIsLegacy).append("\n");
            for(int i = 0; i< mClientIds.size(); i++) {
                int clientID = mClientIds.keyAt(i);
                sb.append("clientId ").append(clientID).
                    append(" mDnsId ").append(mClientIds.valueAt(i)).
                    append(" type ").append(mClientRequests.get(clientID)).append("\n");
            }
            return sb.toString();
        }

        private boolean isLegacy() {
            return mIsLegacy;
        }

        private void setLegacy() {
            mIsLegacy = true;
        }

        // Remove any pending requests from the global map when we get rid of a client,
        // and send cancellations to the daemon.
        private void expungeAllRequests() {
            int globalId, clientId, i;
            // TODO: to keep handler responsive, do not clean all requests for that client at once.
            for (i = 0; i < mClientIds.size(); i++) {
                clientId = mClientIds.keyAt(i);
                globalId = mClientIds.valueAt(i);
                mIdToClientInfoMap.remove(globalId);
                if (DBG) {
                    Log.d(TAG, "Terminating client-ID " + clientId
                            + " global-ID " + globalId + " type " + mClientRequests.get(clientId));
                }
                switch (mClientRequests.get(clientId)) {
                    case NsdManager.DISCOVER_SERVICES:
                        stopServiceDiscovery(globalId);
                        break;
                    case NsdManager.RESOLVE_SERVICE:
                        stopResolveService(globalId);
                        break;
                    case NsdManager.REGISTER_SERVICE:
                        if (mAdvertiser != null) {
                            mAdvertiser.removeService(globalId);
                        } else {
                            unregisterService(globalId);
                        }
                        break;
                    default:
                        break;
                }
            }
            mClientIds.clear();
            mClientRequests.clear();
        }

        void unregisterAllListeners() {
            for (int i = 0; i < mListeners.size(); i++) {
                final MdnsListener listener = mListeners.valueAt(i);
                mMdnsDiscoveryManager.unregisterListener(
                        listener.getListenedServiceType(), listener);
            }
            mListeners.clear();
        }

        // mClientIds is a sparse array of listener id -> mDnsClient id.  For a given mDnsClient id,
        // return the corresponding listener id.  mDnsClient id is also called a global id.
        private int getClientId(final int globalId) {
            int idx = mClientIds.indexOfValue(globalId);
            if (idx < 0) {
                return idx;
            }
            return mClientIds.keyAt(idx);
        }

        void onDiscoverServicesStarted(int listenerKey, NsdServiceInfo info) {
            try {
                mCb.onDiscoverServicesStarted(listenerKey, info);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onDiscoverServicesStarted", e);
            }
        }

        void onDiscoverServicesFailed(int listenerKey, int error) {
            try {
                mCb.onDiscoverServicesFailed(listenerKey, error);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onDiscoverServicesFailed", e);
            }
        }

        void onServiceFound(int listenerKey, NsdServiceInfo info) {
            try {
                mCb.onServiceFound(listenerKey, info);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onServiceFound(", e);
            }
        }

        void onServiceLost(int listenerKey, NsdServiceInfo info) {
            try {
                mCb.onServiceLost(listenerKey, info);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onServiceLost(", e);
            }
        }

        void onStopDiscoveryFailed(int listenerKey, int error) {
            try {
                mCb.onStopDiscoveryFailed(listenerKey, error);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onStopDiscoveryFailed", e);
            }
        }

        void onStopDiscoverySucceeded(int listenerKey) {
            try {
                mCb.onStopDiscoverySucceeded(listenerKey);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onStopDiscoverySucceeded", e);
            }
        }

        void onRegisterServiceFailed(int listenerKey, int error) {
            try {
                mCb.onRegisterServiceFailed(listenerKey, error);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onRegisterServiceFailed", e);
            }
        }

        void onRegisterServiceSucceeded(int listenerKey, NsdServiceInfo info) {
            try {
                mCb.onRegisterServiceSucceeded(listenerKey, info);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onRegisterServiceSucceeded", e);
            }
        }

        void onUnregisterServiceFailed(int listenerKey, int error) {
            try {
                mCb.onUnregisterServiceFailed(listenerKey, error);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onUnregisterServiceFailed", e);
            }
        }

        void onUnregisterServiceSucceeded(int listenerKey) {
            try {
                mCb.onUnregisterServiceSucceeded(listenerKey);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onUnregisterServiceSucceeded", e);
            }
        }

        void onResolveServiceFailed(int listenerKey, int error) {
            try {
                mCb.onResolveServiceFailed(listenerKey, error);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onResolveServiceFailed", e);
            }
        }

        void onResolveServiceSucceeded(int listenerKey, NsdServiceInfo info) {
            try {
                mCb.onResolveServiceSucceeded(listenerKey, info);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onResolveServiceSucceeded", e);
            }
        }

        void onStopResolutionFailed(int listenerKey, int error) {
            try {
                mCb.onStopResolutionFailed(listenerKey, error);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onStopResolutionFailed", e);
            }
        }

        void onStopResolutionSucceeded(int listenerKey) {
            try {
                mCb.onStopResolutionSucceeded(listenerKey);
            } catch (RemoteException e) {
                Log.e(TAG, "Error calling onStopResolutionSucceeded", e);
            }
        }
    }
}