套接字初始化和报文收取

1. netlink_manager.cpp 中 NetlinkManager 类的 start 函数中通过 WatchSocket 将 async_netlink_fd_ 绑定到 netlink 套接字打开，并通过 SubscribeToEvents 订阅对应的广播事件（NL80211_MULTICAST_GROUP_REG 和 NL80211_MULTICAST_GROUP_SCAN），从而该套接字可以收到 SCAN 的广播报文；

2. 套接字的处理函数 ReceivePacketAndRunHandler 通过 read 报文进行收包处理，广播报文调用 BroadcastHandler 进行处理；

3. BroadcastHandler 中判断 command 类型，如果是 NL80211_CMD_NEW_SCAN_RESULTS 或者 NL80211_CMD_SCAN_ABORTED 则调用 OnScanReaultReady 进行向上回调广播

4. 需要特别关注 WatchSocket，将其打开的套接字文件描述放到 event_loop_ 的 event_poll 中等到事件触发报文收取，实际的操作在新的线程中发生；

5. OnScanResultsReady 中对报文进行处理，解析对应的 ssids 和 freqs 然后调用所有注册了相关事件的 handlers

回调事件注册过程

1. 在 netlink_manager.cpp 中 NetlinkManager 类的 OnScanResultsReady 中调用的回调实际上实在 ScannerImpl 类创建和初始化的时候由其构造函数调用了 scan_utils_ 的 SubscribeScanResultNotification 将其 OnScanResultsReady 注册进来的，因此其在此被调用；

2. 同样地 ScannerImpl 类地 OnScanResultsReady 处理过程为调用其 scan_event_handler_ 的 OnScanResultReady 方法；

3. scan_event_handler_ 的初始化是显式调用了 subscribeScanEvents 进行指针赋值的，其调用发生在 WifiNl80211Manager.java 中的 setupInterfaceForClientMode 接口中，其内部通过 wificondScanner 的 subscribeScanEvents 将 scanEventHandler 注册进来：

    /*** Set up an interface for client (STA) mode.** @param ifaceName Name of the interface to configure.* @param executor The Executor on which to execute the callbacks.* @param scanCallback A callback for framework initiated scans.* @param pnoScanCallback A callback for PNO (offloaded) scans.* @return true on success.*/public boolean setupInterfaceForClientMode(@NonNull String ifaceName,@NonNull @CallbackExecutor Executor executor,@NonNull ScanEventCallback scanCallback, @NonNull ScanEventCallback pnoScanCallback) {Log.d(TAG, "Setting up interface for client mode");if (!retrieveWificondAndRegisterForDeath()) {return false;}if (scanCallback == null || pnoScanCallback == null || executor == null) {Log.e(TAG, "setupInterfaceForClientMode invoked with null callbacks");return false;}IClientInterface clientInterface = null;try {clientInterface = mWificond.createClientInterface(ifaceName);} catch (RemoteException e1) {Log.e(TAG, "Failed to get IClientInterface due to remote exception");return false;}if (clientInterface == null) {Log.e(TAG, "Could not get IClientInterface instance from wificond");return false;}Binder.allowBlocking(clientInterface.asBinder());// Refresh HandlersmClientInterfaces.put(ifaceName, clientInterface);try {IWifiScannerImpl wificondScanner = clientInterface.getWifiScannerImpl();if (wificondScanner == null) {Log.e(TAG, "Failed to get WificondScannerImpl");return false;}mWificondScanners.put(ifaceName, wificondScanner);Binder.allowBlocking(wificondScanner.asBinder());ScanEventHandler scanEventHandler = new ScanEventHandler(executor, scanCallback);mScanEventHandlers.put(ifaceName,  scanEventHandler);wificondScanner.subscribeScanEvents(scanEventHandler);PnoScanEventHandler pnoScanEventHandler = new PnoScanEventHandler(executor,pnoScanCallback);mPnoScanEventHandlers.put(ifaceName,  pnoScanEventHandler);wificondScanner.subscribePnoScanEvents(pnoScanEventHandler);} catch (RemoteException e) {Log.e(TAG, "Failed to refresh wificond scanner due to remote exception");}return true;}

4. wificondScanner 则是在由 mWifiCond 通过 createClientInterface 创建的 clientInterface 通过其 getWifiScannerImpl 获取到的；

5. getWifiScannerImpl 通过 binder 机制透过 HIDL 调用到了 client_interface_impl.cpp 中 ClientInterfaceImpl 类的 GetScanner 方法，返回了对应的 scanner_;

6. scanner_ 的创建就是在 ClientInterfaceImpl 的构造函数中进行的，而其创建是在 mWifiCond 的 HIDL server 端通过 createClientInterface 中；

7. mWifiCond 则是在 retrieveWificondAndRegisterForDeath 中通过获取 HIDL 服务 WIFI_NL80211_SERVICE 而初始化的，同样发生在 setupInterfaceForClientMode 接口中；

8. 再回过头来看 scanEventHandler，其类型为 ScanEventHandler，通过传入的 executor 和 scanCallback 来进行初始化，scanCallback 的类型是 ScanEventCallback：

/* ScanEventCallback *//*** Interface used when waiting for scans to be completed (with results).*/public interface ScanEventCallback {/*** Called when scan results are available. Scans results should then be obtained from* {@link #getScanResults(String, int)}.*/void onScanResultReady();/*** Called when a scan has failed.*/void onScanFailed();}/* ScanEventHandler */private class ScanEventHandler extends IScanEvent.Stub {private Executor mExecutor;private ScanEventCallback mCallback;ScanEventHandler(@NonNull Executor executor, @NonNull ScanEventCallback callback) {mExecutor = executor;mCallback = callback;}@Overridepublic void OnScanResultReady() {Log.d(TAG, "Scan result ready event");Binder.clearCallingIdentity();mExecutor.execute(() -> mCallback.onScanResultReady());}@Overridepublic void OnScanFailed() {Log.d(TAG, "Scan failed event");Binder.clearCallingIdentity();mExecutor.execute(() -> mCallback.onScanFailed());}}

通过对比可以发现其实 ScanEventHandler 就是再 ScanEventCallback 的基础之上加入了 executor 线程，将 callback 调用过程放到该线程中执行，将二者进行了绑定而已；

9. 在 WifiNative.java 的 WifiNative 类中通过 setupInterfaceForClientInScanMode 或者 setupInterfaceForClientInConnectivityMode 而调用了 WifiCondManager 类的 setupInterfaceForClientMode 接口，其内部以接口名为参数新创建 NormalScanEventCallback 作为回调参数传入：

    private class NormalScanEventCallback implements WifiNl80211Manager.ScanEventCallback {private String mIfaceName;NormalScanEventCallback(String ifaceName) {mIfaceName = ifaceName;}@Overridepublic void onScanResultReady() {Log.d(TAG, "Scan result ready event");mWifiMonitor.broadcastScanResultEvent(mIfaceName);}@Overridepublic void onScanFailed() {Log.d(TAG, "Scan failed event");mWifiMonitor.broadcastScanFailedEvent(mIfaceName);}}

10. 如上面所示，NormalScanEventCallback 实际上以类初始化时传入的接口为参数，均调用了 WifiMonitor 类的广播处理函数 broadcastScanResultEvent 和 broadcastScanFailedEvent 进行广播处理；

11. broadcastScanResultEvent 接口调用sendMessage 将 SCAN_RESULTS_EVENT 消息发送出去，最终的发送其实是在 mHandlerMap 中查找每个 iface 对应的 Handler 对象，将消息发给 Target：

    /*** Similar functions to Handler#sendMessage that send the message to the registered handler* for the given interface and message what.* All of these should be called with the WifiMonitor class lock*/private void sendMessage(String iface, int what) {sendMessage(iface, Message.obtain(null, what));}private void sendMessage(String iface, int what, Object obj) {sendMessage(iface, Message.obtain(null, what, obj));}private void sendMessage(String iface, int what, int arg1) {sendMessage(iface, Message.obtain(null, what, arg1, 0));}private void sendMessage(String iface, int what, int arg1, int arg2) {sendMessage(iface, Message.obtain(null, what, arg1, arg2));}private void sendMessage(String iface, int what, int arg1, int arg2, Object obj) {sendMessage(iface, Message.obtain(null, what, arg1, arg2, obj));}private void sendMessage(String iface, Message message) {SparseArray<Set<Handler>> ifaceHandlers = mHandlerMap.get(iface);if (iface != null && ifaceHandlers != null) {if (isMonitoring(iface)) {Set<Handler> ifaceWhatHandlers = ifaceHandlers.get(message.what);if (ifaceWhatHandlers != null) {for (Handler handler : ifaceWhatHandlers) {if (handler != null) {sendMessage(handler, Message.obtain(message));}}}} else {if (mVerboseLoggingEnabled) {Log.d(TAG, "Dropping event because (" + iface + ") is stopped");}}} else {if (mVerboseLoggingEnabled) {Log.d(TAG, "Sending to all monitors because there's no matching iface");}for (Map.Entry<String, SparseArray<Set<Handler>>> entry : mHandlerMap.entrySet()) {if (isMonitoring(entry.getKey())) {Set<Handler> ifaceWhatHandlers = entry.getValue().get(message.what);for (Handler handler : ifaceWhatHandlers) {if (handler != null) {sendMessage(handler, Message.obtain(message));}}}}}message.recycle();}private void sendMessage(Handler handler, Message message) {message.setTarget(handler);message.sendToTarget();}

最终在 message.sendToTarget 中其实调用了 Handler 的 sendMessage 接口进行消息发送

Handler 的源头

12. 在 WifiCondScannerImpl 的构造函数中通过 wifiMonitor 的 registerHandler 接口将 mEventHandler 注册到 WifiMonitor 类的对象中，而 mEventHandler 则是新创建的 Handler 对象，其中 Looper 对象则由调用者传入；

13. Looper 是在 WifiScannerImpl 类的创建过程中传入的，WifiScannerImpl 类有两个继承类，实际上为 WificondScannerImpl 和 HalWifiScannerImpl 类，根据 wifiNative 的 getBgScanCapabilities 类型区分，其实际创建过程发生在 WifiScanningServiceImpl.java 中，WifiScanningServiceImpl 类的 setupScannerImpls 中通过 wifiNative 获取到 ifaces，针对每个 iface 创建对应的 Scanner，Looper 对象为其自身的 mLooper 成员；

14. mLooper 的初始化发生在 WifiScanningServiceImpl 类的初始化构造函数中，由入参 looper 进行初始化，在 WifiScanningService 类的初始化过程中新创建了 HandlerThread，由其对应的 Looper 成员来进行初始化，实际上为专门用于 Scanning 服务的 Looper 成员；

Message 的处理

15. Message 实际上最终是在 Looper 类的 loop 函数中处理，如果 Handler 在构建过程中有传入 callback 对象且其 handleMessage 方法不为空，则会调用该接口进行处理，这里 WificondScannerImpl 类实现了 Handler.Callback 接口，其内部实现了 handleMessage 方法，因此该方法被调用进行处理：

    @Overridepublic boolean handleMessage(Message msg) {switch(msg.what) {case WifiMonitor.SCAN_FAILED_EVENT:Log.w(TAG, "Scan failed");cancelScanTimeout();reportScanFailure();break;case WifiMonitor.PNO_SCAN_RESULTS_EVENT:pollLatestScanDataForPno();break;case WifiMonitor.SCAN_RESULTS_EVENT:cancelScanTimeout();pollLatestScanData();break;default:// ignore unknown event}return true;}

16. pollLatestScanData 接口被调用，如果发现设置变更，scanning 被取消，则直接返回，否则首先调用 WifiNative 的 getScanResults 方法进行扫描结果的获取；

17. 进而调用了 WifiCondManager 的 getScanResults 方法进行扫描结果的获取：

    /*** Fetch the latest scan results of the indicated type for the specified interface. Note that* this method fetches the latest results - it does not initiate a scan. Initiating a scan can* be done using {@link #startScan(String, int, Set, List)} or* {@link #startPnoScan(String, PnoSettings, Executor, PnoScanRequestCallback)}.** Note: The interface must have been already set up using* {@link #setupInterfaceForClientMode(String, Executor, ScanEventCallback, ScanEventCallback)}* or {@link #setupInterfaceForSoftApMode(String)}.** @param ifaceName Name of the interface.* @param scanType The type of scan result to be returned, can be* {@link #SCAN_TYPE_SINGLE_SCAN} or {@link #SCAN_TYPE_PNO_SCAN}.* @return Returns an array of {@link NativeScanResult} or an empty array on failure (e.g. when* called before the interface has been set up).*/@NonNull public List<NativeScanResult> getScanResults(@NonNull String ifaceName,@ScanResultType int scanType) {IWifiScannerImpl scannerImpl = getScannerImpl(ifaceName);if (scannerImpl == null) {Log.e(TAG, "No valid wificond scanner interface handler");return new ArrayList<>();}List<NativeScanResult> results = null;try {if (scanType == SCAN_TYPE_SINGLE_SCAN) {results = Arrays.asList(scannerImpl.getScanResults());} else {results = Arrays.asList(scannerImpl.getPnoScanResults());}} catch (RemoteException e1) {Log.e(TAG, "Failed to create ScanDetail ArrayList");}if (results == null) {results = new ArrayList<>();}if (mVerboseLoggingEnabled) {Log.d(TAG, "get " + results.size() + " scan results from wificond");}return results;}

18. 根据接口查找到对应的 WifiScannerImpl 对象，调用其方法 getScanResults 进行扫描结果查询，实际上走到了 HIDL 后面 scanner_impl.cpp 中 ScannerImpl 类实现方法 getScanResults：

Status ScannerImpl::getScanResults(vector<NativeScanResult>* out_scan_results) {if (!CheckIsValid()) {return Status::ok();}if (!scan_utils_->GetScanResult(interface_index_, out_scan_results)) {LOG(ERROR) << "Failed to get scan results via NL80211";}return Status::ok();
}

19. 进而调用了 scan_utils_ 的 GetScanResult 方法获取扫描结果：

bool ScanUtils::GetScanResult(uint32_t interface_index,vector<NativeScanResult>* out_scan_results) {NL80211Packet get_scan(netlink_manager_->GetFamilyId(),NL80211_CMD_GET_SCAN,netlink_manager_->GetSequenceNumber(),getpid());get_scan.AddFlag(NLM_F_DUMP);NL80211Attr<uint32_t> ifindex(NL80211_ATTR_IFINDEX, interface_index);get_scan.AddAttribute(ifindex);vector<unique_ptr<const NL80211Packet>> response;if (!netlink_manager_->SendMessageAndGetResponses(get_scan, &response))  {LOG(ERROR) << "NL80211_CMD_GET_SCAN dump failed";return false;}if (response.empty()) {LOG(INFO) << "Unexpected empty scan result!";return true;}for (auto& packet : response) {if (packet->GetMessageType() == NLMSG_ERROR) {LOG(ERROR) << "Receive ERROR message: "<< strerror(packet->GetErrorCode());continue;}if (packet->GetMessageType() != netlink_manager_->GetFamilyId()) {LOG(ERROR) << "Wrong message type: "<< packet->GetMessageType();continue;}uint32_t if_index;if (!packet->GetAttributeValue(NL80211_ATTR_IFINDEX, &if_index)) {LOG(ERROR) << "No interface index in scan result.";continue;}if (if_index != interface_index) {LOG(WARNING) << "Uninteresting scan result for interface: " << if_index;continue;}NativeScanResult scan_result;if (!ParseScanResult(std::move(packet), &scan_result)) {LOG(DEBUG) << "Ignore invalid scan result";continue;}out_scan_results->push_back(std::move(scan_result));}return true;
}

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WiFi 扫描结果的通知过程

套接字初始化和报文收取

回调事件注册过程

Handler 的源头

Message 的处理

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