在过去的几周里，Android 的 NSD 实现让我抓狂：
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发现彼此。如果我启动我的NsdManager基于应用程序，如果只涉及两个设备，它或多或少可以工作。如果第三个设备加入，它很少会发现前两个，前两个不会看到第三个。如果我退出应用程序（它们优雅地取消注册 NSD 侦听器）并以不同的顺序重新启动它们，则发现模式不完全相同，但相似。
在我的家庭网络中，发现的设备的IP解析基本上按预期工作。在工作中，有时即使只使用两个设备（A 和 B），设备A将通过A的IP地址和B的端口解析设备B的服务反之亦然。因此，不知何故，IP 地址和服务名称似乎在较低级别（可能是 NsdManager）混淆了。
我现在已经为此提交了关于 Google 代码的错误报告（）。我也将其发布在这里，希望得到更多反馈；也许我的 Nsd 帮助类中的某些内容是错误的。
首先，经过无休止的调试，我现在在logcat中发现了Android底层的提示NsdService其本身可能出现故障，而 MDnsDS 似乎工作正常。但我不确定...
以下是一些说明问题的日志输出（为了可读性而过滤了一些消息）：
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 }
关于上下文的一些注释：
- 我的 NSD 服务类型是_tusync._tcp。
- 我以以下格式为所有节点创建唯一的服务名称TuSync-0.[本地端口号]以防止命名冲突并简化调试。
- 在此测试场景中，共有三台设备。日志设备的IP为10.0.0.4，端口57392。
日志显示，底层MDnsDS守护进程正确发现并解析所有节点。但是，那NsdService以上并没有传播所有这些的决议。 16:57:04.627 似乎存在 ID 冲突，设备的两个对等点（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解释机制） 。这discoveryListener我注册了NsdManager在发现两个节点时收到通知，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
我还经历过其他案例，在NsdService在日志中发出“SERVICE_FOUND Raw”消息，我的发现监听器没有收到通知。示例日志（经过严格过滤；与上面相同的测试设置）：
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，发现的对等点 10.0.0.5（端口 36230）不会触发 discoveryListener 通知。在最后一条日志消息之后，没有任何反应。所以我的日志节点 10.0.0.4 只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，这让我想知道我是否是唯一遇到这些问题的人，或者 NsdManager 是否完全不稳定并且没有人使用它？
作为参考，这里是我的助手类的代码 - 它类似于 Android NSD 聊天教程，但我尝试改进它，因为该教程似乎引发了一些其他错误。
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 ([email protected] /cdn-cgi/l/email-protection)
*/
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。然而，将其设置为 1 不起作用，因为有时正在进行的解决既不成功也不失败；这会导致信号量无法释放，并且 NsdManager 线程永久卡在下一个解析请求上。
还有其他人遇到这样的问题吗？如果成功使用 NsdManager 的人也能发表评论，我会很高兴 - 这至少意味着我面临着一个可以解决的问题:)
我已经考虑放弃 NSD 并实现我自己的广播/多播发现机制。理论上这可能是一件轻而易举的事，但我读到 Android 上的多播也是一个 PITA，因为某些设备阻止了它......
