android - Android，NSD/DNS-SD : NsdManager unreliable discovery and IP resolution

Question

在过去的几周中，Android的NSD实现让我发疯了:

从用户的角度来看，会出现以下问题:

设备以完全不确定的方式相互发现。如果我启动基于NsdManager的应用程序，则只要涉及两个设备，它就会或多或少地起作用。 如果加入了第三个设备，则很少会发现前两个，而前两个将看不到第三个。如果我退出这些应用程序(它们正常注销了NSD监听器)并以不同的顺序重新启动它们，则发现模式并不完全相同，而是相似的。

在我的家庭网络中，发现的设备的IP分辨率基本上可以按预期工作。在工作中，有时即使仅使用两个设备(A和B)，设备A也会使用A的IP地址和B的端口解析设备B的服务，反之亦然。因此，IP地址和服务名称似乎以某种方式在较低级别(可能是NsdManager)混合在一起。

现在，我已经针对此(https://code.google.com/p/android/issues/detail?id=201314&thanks=201314&ts=1455814995)在Google代码上提交了错误报告。我也将其发布在这里，希望能获得更多反馈。也许我的Nsd帮助器类中出现错误。

首先，经过无休止的调试，现在我在日志猫中发现了一些提示，即Android的基础NsdService本身可能正在发生故障，而MDnsDS似乎可以正常工作。但是我不确定...

这是一些说明问题的日志输出(已过滤某些消息以提高可读性):

02-18 16:57:02.327: D/NsdService(628): startMDnsDaemon
02-18 16:57:02.327: D/MDnsDS(187): Starting MDNSD
02-18 16:57:02.529: D/NsdService(628): New client listening to asynchronous messages
02-18 16:57:02.529: D/NsdService(628): New client, channel: com.android.internal.util.AsyncChannel@1fa188ce messenger: android.os.Messenger@cca33ef
02-18 16:57:02.532: D/NsdService(628): Register service
02-18 16:57:02.532: D/NsdService(628): registerService: 106 name: TuSync-0.57392, type: _tusync._tcp., host: /::, port: 57392
02-18 16:57:02.533: D/MDnsDS(187): serviceRegister(106, (null), TuSync-0.57392, _tusync._tcp., (null), (null), 57392, 0, <binary>)
02-18 16:57:02.533: D/MDnsDS(187): serviceRegister successful
02-18 16:57:02.534: D/NsdService(628): Register 1 106
02-18 16:57:04.083: D/MDnsDS(187): register succeeded for 106 as TuSync-0.57392
02-18 16:57:04.087: D/NsdService(628): SERVICE_REGISTERED Raw: 606 106 "TuSync-0.57392"
02-18 16:57:04.109: D/NsdService(628): Discover services
02-18 16:57:04.109: D/NsdService(628): discoverServices: 107 _tusync._tcp.
02-18 16:57:04.110: D/MDnsDS(187): discover((null), _tusync._tcp., (null), 107, 0)
02-18 16:57:04.110: D/MDnsDS(187): discover successful
02-18 16:57:04.110: D/NsdService(628): Discover 2 107_tusync._tcp.
02-18 16:57:04.333: D/MDnsDS(187): Discover found new serviceName TuSync-0.57392, regType _tusync._tcp. and domain local. for 107
02-18 16:57:04.334: D/NsdService(628): SERVICE_FOUND Raw: 603 107 "TuSync-0.57392" _tusync._tcp. local.
02-18 16:57:04.338: D/NsdService(628): Resolve service
02-18 16:57:04.338: D/NsdService(628): resolveService: 108 name: TuSync-0.57392, type: _tusync._tcp., host: null, port: 0
02-18 16:57:04.339: D/MDnsDS(187): resolveService(108, (null), TuSync-0.57392, _tusync._tcp., local.)
02-18 16:57:04.345: D/MDnsDS(187): startMonitoring 108
02-18 16:57:04.345: D/MDnsDS(187): resolveService successful
02-18 16:57:04.346: D/MDnsDS(187): resolve succeeded for 108 finding TuSync-0\.57392._tusync._tcp.local. at Android-3.local.:57392 with txtLen 1
02-18 16:57:04.347: D/NsdService(628): SERVICE_RESOLVED Raw: 608 108 "TuSync-0\\.57392._tusync._tcp.local." "Android-3.local." 57392 1
02-18 16:57:04.347: D/NsdService(628): stopResolveService: 108
02-18 16:57:04.347: D/MDnsDS(187): Stopping resolve with ref 0xb5c4734c
02-18 16:57:04.349: D/NsdService(628): getAdddrInfo: 109
02-18 16:57:04.349: D/MDnsDS(187): getAddrInfo(109, (null) 0, Android-3.local.)
02-18 16:57:04.350: D/MDnsDS(187): getAddrInfo successful
02-18 16:57:04.352: D/MDnsDS(187): getAddrInfo succeeded for 109: 109 "Android-3.local." 120 10.0.0.4
02-18 16:57:04.352: D/MDnsDS(187): getAddrInfo succeeded for 109: 109 "Android-3.local." 120 fe80::204:4bff:fe2c:6c87
02-18 16:57:04.354: D/NsdService(628): SERVICE_GET_ADDR_SUCCESS Raw: 612 109 "Android-3.local." 120 10.0.0.4
02-18 16:57:04.354: D/NsdService(628): stopGetAdddrInfo: 109
02-18 16:57:04.355: D/MDnsDS(187): Stopping getaddrinfo with ref 0xb5c472d4
02-18 16:57:04.364: E/NsdService(628): Unique id with no client mapping: 109
02-18 16:57:04.364: E/NsdService(628): Unhandled { when=-10ms what=393242 obj=com.android.server.NsdService$NativeEvent@86af300 target=com.android.internal.util.StateMachine$SmHandler }
02-18 16:57:04.627: D/MDnsDS(187): Discover found new serviceName TuSync-0.36230, regType _tusync._tcp. and domain local. for 107
02-18 16:57:04.632: D/MDnsDS(187): Discover found new serviceName TuSync-0.60493, regType _tusync._tcp. and domain local. for 107
02-18 16:57:04.633: D/NsdService(628): SERVICE_FOUND Raw: 603 107 "TuSync-0.36230" _tusync._tcp. local.
02-18 16:57:04.634: D/NsdService(628): SERVICE_FOUND Raw: 603 107 "TuSync-0.60493" _tusync._tcp. local.
02-18 16:57:04.635: D/NsdService(628): Resolve service
02-18 16:57:04.635: D/NsdService(628): resolveService: 110 name: TuSync-0.36230, type: _tusync._tcp., host: null, port: 0
02-18 16:57:04.636: D/MDnsDS(187): resolveService(110, (null), TuSync-0.36230, _tusync._tcp., local.)
02-18 16:57:04.637: D/MDnsDS(187): resolve succeeded for 110 finding TuSync-0\.36230._tusync._tcp.local. at Android.local.:36230 with txtLen 1
02-18 16:57:04.638: D/NsdService(628): Resolve service
02-18 16:57:04.638: D/NsdService(628): SERVICE_RESOLVED Raw: 608 110 "TuSync-0\\.36230._tusync._tcp.local." "Android.local." 36230 1
02-18 16:57:04.639: D/NsdService(628): stopResolveService: 110
02-18 16:57:04.639: D/MDnsDS(187): Stopping resolve with ref 0xb5c473c4
02-18 16:57:04.643: D/MDnsDS(187): getAddrInfo succeeded for 111: 111 "Android.local." 120 10.0.0.5
02-18 16:57:04.643: D/MDnsDS(187): getAddrInfo succeeded for 111: 111 "Android.local." 120 fe80::204:4bff:fe26:8483
02-18 16:57:04.644: D/NsdService(628): SERVICE_GET_ADDR_SUCCESS Raw: 612 111 "Android.local." 120 10.0.0.5
02-18 16:57:04.644: D/NsdService(628): stopGetAdddrInfo: 111
02-18 16:57:04.645: D/MDnsDS(187): Stopping getaddrinfo with ref 0xb5c47364
02-18 16:57:04.645: D/MDnsDS(187): Going to poll with pollCount 3
02-18 16:57:04.658: E/NsdService(628): Unique id with no client mapping: 111
02-18 16:57:04.658: E/NsdService(628): Unhandled { when=-14ms what=393242 obj=com.android.server.NsdService$NativeEvent@1d93a739 target=com.android.internal.util.StateMachine$SmHandler }

有关上下文的一些说明:

我的NSD服务类型是_tusync._tcp。

我以TuSync-0。[本地端口号]的格式为所有节点创建唯一的服务名称，以防止命名冲突并简化调试。

在此测试方案中，有三个设备。记录设备的IP为10.0.0.4，端口为57392。

日志显示，底层MDnsDS守护程序正确发现并解析了所有节点。但是，上面的NsdService不会传播所有分辨率。在16:57:04.627似乎存在ID冲突，在该设备的两个对等方(TuSync-0.36230和TuSync-0.60493)都被分配了内部ID 107(如果我仅通过查看日志正确地解释了机制) 。发现两个节点后，我会通知我在discoveryListener中注册的NsdManager，但是，解析仅适用于其中一个，另一个会触发错误:

02-18 16:57:04.638: E/NsdHelper(6370): Resolve failed with error code:
3. Service: name: TuSync-0.60493, type: _tusync._tcp., host: null, port: 0

我还遇到了其他情况，即NsdService在日志中发出“SERVICE_FOUND Raw”消息后，未通知我的发现监听器。示例日志(经过大量过滤；与上述测试设置相同):

02-18 17:54:06.692: D/MDnsDS(187): Starting MDNSD
02-18 17:54:06.896: D/NsdService(628): registerService: 112 name: TuSync-0.57392, type: _tusync._tcp., host: /::, port: 57392
02-18 17:54:06.896: D/MDnsDS(187): serviceRegister(112, (null), TuSync-0.57392, _tusync._tcp., (null), (null), 57392, 0, <binary>)
02-18 17:54:06.896: D/MDnsDS(187): serviceRegister successful
02-18 17:54:08.802: D/NsdService(628): SERVICE_REGISTERED Raw: 606 112 "TuSync-0.57392"
02-18 17:54:08.820: D/NsdService(628): Discover services
02-18 17:54:09.050: D/MDnsDS(187): Discover found new serviceName TuSync-0.57392, regType _tusync._tcp. and domain local. for 113
02-18 17:54:09.050: D/NsdService(628): SERVICE_FOUND Raw: 603 113 "TuSync-0.57392" _tusync._tcp. local.
02-18 17:54:09.211: D/MDnsDS(187): Discover found new serviceName TuSync-0.60493, regType _tusync._tcp. and domain local. for 113
02-18 17:54:09.212: D/NsdService(628): SERVICE_FOUND Raw: 603 113 "TuSync-0.60493" _tusync._tcp. local.
02-18 17:54:09.215: D/NsdService(628): resolveService: 116 name: TuSync-0.60493, type: _tusync._tcp., host: null, port: 0
02-18 17:54:09.216: D/MDnsDS(187): resolveService(116, (null), TuSync-0.60493, _tusync._tcp., local.)
02-18 17:54:09.217: D/MDnsDS(187): resolve succeeded for 116 finding TuSync-0\.60493._tusync._tcp.local. at Android-2.local.:60493 with txtLen 1
02-18 17:54:09.219: D/NsdService(628): SERVICE_RESOLVED Raw: 608 116 "TuSync-0\\.60493._tusync._tcp.local." "Android-2.local." 60493 1
02-18 17:54:09.228: D/MDnsDS(187): getAddrInfo succeeded for 117: 117 "Android-2.local." 120 10.0.0.6
02-18 17:54:09.228: D/MDnsDS(187): getAddrInfo succeeded for 117: 117 "Android-2.local." 120 fe80::c643:8fff:fec5:5648
02-18 17:54:09.229: D/NsdService(628): SERVICE_GET_ADDR_SUCCESS Raw: 612 117 "Android-2.local." 120 10.0.0.6
02-18 17:54:09.244: D/MDnsDS(187): Discover found new serviceName TuSync-0.36230, regType _tusync._tcp. and domain local. for 113
02-18 17:54:09.251: E/NsdService(628): Unique id with no client mapping: 117
02-18 17:54:09.251: E/NsdService(628): Unhandled { when=-22ms what=393242 obj=com.android.server.NsdService$NativeEvent@1e992653 target=com.android.internal.util.StateMachine$SmHandler }
02-18 17:54:09.255: D/NsdService(628): SERVICE_FOUND Raw: 603 113 "TuSync-0.36230" _tusync._tcp. local.

在这种情况下，发现的对等体10.0.0.5(端口36230)不会触发DiscoveryDiscovery通知。在最后一条日志消息之后，什么都没有发生。因此，我的日志记录节点10.0.0.4仅发现了另一个对等节点10.0.0.6:60493。

类似错误报告的数量很少，让我想知道我是否是仅有的出现这些问题的人，或者NsdManager是否完全不稳定并且没有人使用它？

作为引用，这是我的帮助程序类的代码-与Android NSD聊天教程相似，但是由于该教程似乎会引起一些其他错误，因此我尝试对其进行改进。

public final class NsdHelper {

    public static final String TAG = "NsdHelper";

    private final Context mContext;

    private final NsdManager mNsdManager;

    private final String mBaseServiceName; // Base component of the service name, e.g. "service_xy"
    private String mServiceName; // Service name of the local node, may be updated upon peer detection with service name conflicts, e.g. to "service_xy (2)"
    private final String mServiceType;

    private final NsdHandler mNsdHandler;

    private MyRegistrationListener mRegistrationListener;
    private final Object mRegistrationLock = new Object();

    private MyDiscoveryListener mDiscoveryListener;
    private final Object mDiscoveryLock = new Object();

    private final Object mResolveLock = new Object();
    private final Semaphore mResolveSemaphore;

    public NsdHelper(Context context, String baseServiceName, String serviceName, String serviceType, NsdHandler nsdHandler) {
        mContext = context;
        mNsdManager = (NsdManager) context.getSystemService(Context.NSD_SERVICE);
        mNsdHandler = nsdHandler;
        mBaseServiceName = baseServiceName;
        mServiceName = serviceName;
        mServiceType = serviceType;

        mResolveSemaphore = new Semaphore(10, true);
    }

    /*********************
     * Lifecycle methods *
     *********************/

    public void registerLocalService(final int port) {

        NsdServiceInfo localServiceInfo = new NsdServiceInfo();
        localServiceInfo.setServiceName(mServiceName);
        localServiceInfo.setServiceType(mServiceType);
        localServiceInfo.setPort(port);

        synchronized (mRegistrationLock) {
            if (mRegistrationListener == null) {
                mRegistrationListener = new MyRegistrationListener();
                // try {
                mNsdManager.registerService(
                        localServiceInfo, NsdManager.PROTOCOL_DNS_SD, mRegistrationListener);

                /*} catch (Exception e) {
                    MLog.e(TAG, "Exception registering service; trying to unregister.", e);
                    unregisterLocalService();

                    mNsdHandler.onRegistrationFailed(localServiceInfo, 0);
                }*/
            } else {
                MLog.w(TAG, "registerLocalService called while service registration already in progress or service already registered.");
            }
        }
    }

    public void unregisterLocalService() {
        synchronized (mRegistrationLock) {
            if (mRegistrationListener != null) {
                // try {
                    mNsdManager.unregisterService(mRegistrationListener);
                /*} catch (IllegalArgumentException e) {
                    MLog.w(TAG, "Exception trying to unregister registrationListener.");
                }*/
                mRegistrationListener = null;
            } else {
                MLog.w(TAG, "unregisterLocalService called while service not yet registered or already unregistered.");
            }
        }
    }

    public void startDiscovery() {
        synchronized(mDiscoveryLock) {
            if(mDiscoveryListener == null) {
                mDiscoveryListener = new MyDiscoveryListener();
                mNsdManager.discoverServices(
                        mServiceType, NsdManager.PROTOCOL_DNS_SD, mDiscoveryListener);
            } else {
                MLog.w(TAG, "StartDiscovery called while discovery is already in progress.");
            }
        }
    }

    public void stopDiscovery() {
        synchronized (mDiscoveryLock) {
            if (mDiscoveryListener != null) {
                mNsdManager.stopServiceDiscovery(mDiscoveryListener);
                mDiscoveryListener = null;
            } else {
                MLog.w(TAG, "StopDiscovery called while no discovery is in progress.");
            }
        }
    }

    public void tearDown() {
        MLog.v(TAG, "NsdHelper: tearDown()");
        stopDiscovery();
        unregisterLocalService(); // TODO this causes an exception, when the listener is already unregistered
    }

    /**
     * Returns the current service name of the service.
     * @return
     */
    public String getServiceName() {
        return mServiceName;
    }

    /**
     * Convenience method to initiate service resolution
     * @param serviceInfo NsdServiceInfo object for the service to be resolved
     */
    private void resolveService(NsdServiceInfo serviceInfo) {
        try {
            MLog.vv(TAG, "Resolving service: acquiring semaphore.");
            mResolveSemaphore.acquire();
            MLog.vv(TAG, "Resolving service: semaphore acquired.");
        } catch (InterruptedException e) {
            MLog.w(TAG, "resolveService: Waiting for acquisition of semaphore interrupted.");
        }
        mNsdManager.resolveService(serviceInfo, new MyResolveListener(serviceInfo.getServiceName()));
    }

    /*************
     * Listeners *
     *************/

    private class MyDiscoveryListener implements NsdManager.DiscoveryListener {

        @Override
        public void onDiscoveryStarted(String regType) {
            MLog.d(TAG, "Service discovery started");
            mNsdHandler.onDiscoveryStarted();
        }

        @Override
        public void onServiceFound(NsdServiceInfo serviceInfo) {
            MLog.d(TAG, "Discovered service: " + serviceInfo);

            // Protocol matches?
            if (!serviceInfo.getServiceType().equals(mServiceType)) {
                MLog.v(TAG, "Discovered: other serviceType: " + serviceInfo.getServiceType());
            }
            // Make sure, that service name matches, and just resolve remote host
            else if (serviceInfo.getServiceName().contains(mBaseServiceName)){
                MLog.d(TAG, "Discovered: correct serviceType: " + mBaseServiceName);
                resolveService(serviceInfo);
            }
            else {
                // Other service name, log anyway
                MLog.d(TAG, "Discovered: service with different serviceName: " + serviceInfo.getServiceName() + ". Ignoring.");
            }
        }

        @Override
        public void onServiceLost(NsdServiceInfo service) {
            MLog.e(TAG, "Service lost: " + service);
            mNsdHandler.onRemotePeerLost(service);
        }

        @Override
        public void onDiscoveryStopped(String serviceType) {
            MLog.v(TAG, "Discovery stopped: " + serviceType);
            mNsdHandler.onDiscoveryStopped();
        }

        @Override
        public void onStartDiscoveryFailed(String serviceType, int errorCode) {
            MLog.e(TAG, "Discovery starting failed. Error code: " + errorCode);
            synchronized (mDiscoveryLock) {
                mDiscoveryListener = null;  // just throw away the discovery listener, explicit stopping of the discovery should not be needed according to
                                            // https://code.google.com/p/android/issues/detail?id=99510&q=nsd&colspec=ID%20Type%20Status%20Owner%20Summary%20Stars
            }
        }

        @Override
        public void onStopDiscoveryFailed(String serviceType, int errorCode) {
            MLog.e(TAG, "Discovery stopping failed. Error code: " + errorCode);
            // try again
            // mNsdManager.stopServiceDiscovery(this); // This should not be needed according to https://code.google.com/p/android/issues/detail?id=99510&q=nsd&colspec=ID%20Type%20Status%20Owner%20Summary%20Stars
        }
    };

    private class MyRegistrationListener implements NsdManager.RegistrationListener {

        @Override
        public void onServiceRegistered(NsdServiceInfo nsdServiceInfo) {
            MLog.d(TAG, "Service registered. NsdServiceInfo: " + nsdServiceInfo);

            boolean nameChanged = false;

            // Update service name of this node (might change due to automatic conflict resolution!)
            if(!mServiceName.equals(nsdServiceInfo.getServiceName())){
                mServiceName = nsdServiceInfo.getServiceName();

                nameChanged = true;
                MLog.d(TAG, "Local service name updated to: " + mServiceName);
            }

            // Notify
            if (mNsdHandler != null) {
                mNsdHandler.onRegistrationSuccess(nsdServiceInfo);

                if (nameChanged) {
                mNsdHandler.onLocalServiceNameChanged(mServiceName);
                }
            } else {
                MLog.w(TAG, "onServiceRegistered: NsdHandler is null.");
            }
        }

        @Override
        public void onRegistrationFailed(NsdServiceInfo arg0, int arg1) {
            MLog.w(TAG, "Service registration failed with error code " + arg1 + ".");

            if (mNsdHandler == null) {
                MLog.w(TAG, "onRegistrationFailed: NsdHandler is null.");
                return;
            }

            mNsdHandler.onRegistrationFailed(arg0, arg1);
        }

        @Override
        public void onServiceUnregistered(NsdServiceInfo arg0) {
            MLog.d(TAG, "Service unregistered.");

            if (mNsdHandler == null) {
                MLog.w(TAG, "onServiceUnRegistered: NsdHandler is null.");
                return;
            }
        }

        @Override
        public void onUnregistrationFailed(NsdServiceInfo serviceInfo, int errorCode) {
            MLog.w(TAG, "Service unregistering failed.");

            if (mNsdHandler == null) {
                MLog.w(TAG, "onUnRegistrationFailed: NsdHandler is null.");
                return;
            }
        }

    };

    private class MyResolveListener implements NsdManager.ResolveListener {

        private final String mServiceName;

        public MyResolveListener(String serviceName) {
            mServiceName = serviceName;
        }

        @Override
        public void onResolveFailed(final NsdServiceInfo serviceInfo, int errorCode) {
            // Release resource
            mResolveSemaphore.release();

            MLog.e(TAG, "Resolve failed with error code: " + errorCode + ". Service: " + serviceInfo);
            if((serviceInfo.getServiceName() != null) && (!serviceInfo.getServiceName().equals(mServiceName))) {
                MLog.e(TAG, "Service name changed: " + mServiceName + " => " + serviceInfo.getServiceName());
            }
        }

        @Override
        public void onServiceResolved(final NsdServiceInfo serviceInfo) {
            // Release resource
            mResolveSemaphore.release();

            MLog.v(TAG, "Resolve succeeded. Service: " + serviceInfo + ", Address: " + serviceInfo.getHost().getHostAddress() + ":" + serviceInfo.getPort());
            if((serviceInfo.getServiceName() != null) && (!serviceInfo.getServiceName().equals(mServiceName))) {
                MLog.w(TAG, "Service name changed: " + mServiceName + " => " + serviceInfo.getServiceName());
            }

            mNsdHandler.onNewRemotePeerResolved(serviceInfo);
        }
    };



    /**
     * Interface for handlers that deal just with essential NSD events.
     * @author Alexander Fischl (alexander.fischl@semeion.net)
     */
    public interface NsdHandler {

        /**
         * Called, when the NSD manager registered the service successfully.
         * @param nsdServiceInfo
         */
        public void onRegistrationSuccess(final NsdServiceInfo nsdServiceInfo);

        /**
         * Called, when the NSD registration was unsuccessful.
         */
        public void onRegistrationFailed(final NsdServiceInfo nsdServiceInfo, final int errorCode);


        /**
         * Called, when the NSD manager discovers a new peer. Services registered on the
         * local machine DO NOT trigger this call!
         * @param nsdServiceInfo
         */
        public void onNewRemotePeerDiscovered(final NsdServiceInfo nsdServiceInfo);

        /**
         * Called, when the NSD manager resolves a new peer, yielding the connection data.
         * Services registered on the local machine DO NOT trigger this call!
         * @param nsdServiceInfo
         */
        public void onNewRemotePeerResolved(final NsdServiceInfo nsdServiceInfo);

        /**
         * Called, when the NSD manager loses an already discovered peer.
         * @param nsdServiceInfo
         */
        public void onRemotePeerLost(final NsdServiceInfo nsdServiceInfo);

        /**
         * Called, when the local service name needs to be updated (e.g. due to
         * conflict resolution when the local service is registered, and the chosen service
         * name is already taken by another node in the network.)
         * @param newLocalServiceName
         */
        public void onLocalServiceNameChanged(String newLocalServiceName);

        /**
         * Called, when the service discovery has successfully started.
         */
        public void onDiscoveryStarted();

        /**
         * Called, when the service discovery was halted.
         */
        public void onDiscoveryStopped();
    }
}

请注意，我什至实现了一个可以设置为1的信号量，以防止并行解析多个服务，因为其他人报告了并行解析的问题。但是，将其设置为1无效，因为有时正在进行的解析既不会成功也不会失败。这将导致信号量不被释放，并且NsdManager线程将永久卡在下一个解析请求中。

还有其他人遇到这样的问题吗？ 如果能够成功使用NsdManager的人也发表评论，我会很高兴-这至少意味着我遇到了可以解决的问题:)

我已经考虑放弃NSD并实现自己的广播/多播发现机制。从理论上讲这可能很容易，但是我已经读到Android上的多播也是PITA，因为某些设备阻止了它。

Answer 1

与Android NSD仍然没有区别。我一直在使用棉花糖版本的Android，而NSD实际上仍然不可靠。我用RxDNSSD(https://github.com/andriydruk/RxDNSSD)替换了NSD。到目前为止，很少有类轮代码可以完美运行。

我测试了NSD和RXDNSSD，当RXDNSSD一直工作时，NSD能够发现服务，但无法解析IP地址。

希望对其他用户有帮助。