WiFi 连接到网络的过程

在 WifiConnectivityManager 中收到扫描结果进行处理，选择相应的网络进行连接，发生在 connectToNetwork 接口中：

    /*** Attempt to connect to a network candidate.** Based on the currently connected network, this menthod determines whether we should* connect or roam to the network candidate recommended by WifiNetworkSelector.*/private void connectToNetwork(WifiConfiguration candidate) {ScanResult scanResultCandidate = candidate.getNetworkSelectionStatus().getCandidate();if (scanResultCandidate == null) {localLog("connectToNetwork: bad candidate - "  + candidate+ " scanResult: " + scanResultCandidate);return;}String targetBssid = scanResultCandidate.BSSID;String targetAssociationId = candidate.SSID + " : " + targetBssid;// Check if we are already connected or in the process of connecting to the target// BSSID. mWifiInfo.mBSSID tracks the currently connected BSSID. This is checked just// in case the firmware automatically roamed to a BSSID different from what// WifiNetworkSelector selected.if (targetBssid != null&& (targetBssid.equals(mLastConnectionAttemptBssid)|| targetBssid.equals(mWifiInfo.getBSSID()))&& SupplicantState.isConnecting(mWifiInfo.getSupplicantState())) {localLog("connectToNetwork: Either already connected "+ "or is connecting to " + targetAssociationId);return;}if (candidate.BSSID != null&& !candidate.BSSID.equals(ClientModeImpl.SUPPLICANT_BSSID_ANY)&& !candidate.BSSID.equals(targetBssid)) {localLog("connecToNetwork: target BSSID " + targetBssid + " does not match the "+ "config specified BSSID " + candidate.BSSID + ". Drop it!");return;}long elapsedTimeMillis = mClock.getElapsedSinceBootMillis();if (!mScreenOn && shouldSkipConnectionAttempt(elapsedTimeMillis)) {localLog("connectToNetwork: Too many connection attempts. Skipping this attempt!");mTotalConnectivityAttemptsRateLimited++;return;}noteConnectionAttempt(elapsedTimeMillis);mLastConnectionAttemptBssid = targetBssid;WifiConfiguration currentConnectedNetwork = mConfigManager.getConfiguredNetwork(mWifiInfo.getNetworkId());String currentAssociationId = (currentConnectedNetwork == null) ? "Disconnected" :(mWifiInfo.getSSID() + " : " + mWifiInfo.getBSSID());if (currentConnectedNetwork != null&& (currentConnectedNetwork.networkId == candidate.networkId//TODO(b/36788683): re-enable linked configuration check/* || currentConnectedNetwork.isLinked(candidate) */)) {// Framework initiates roaming only if firmware doesn't support// {@link android.net.wifi.WifiManager#WIFI_FEATURE_CONTROL_ROAMING}.if (mConnectivityHelper.isFirmwareRoamingSupported()) {// Keep this logging here for now to validate the firmware roaming behavior.localLog("connectToNetwork: Roaming candidate - " + targetAssociationId + "."+ " The actual roaming target is up to the firmware.");} else {localLog("connectToNetwork: Roaming to " + targetAssociationId + " from "+ currentAssociationId);mStateMachine.startRoamToNetwork(candidate.networkId, scanResultCandidate);}} else {// Framework specifies the connection target BSSID if firmware doesn't support// {@link android.net.wifi.WifiManager#WIFI_FEATURE_CONTROL_ROAMING} or the// candidate configuration contains a specified BSSID.if (mConnectivityHelper.isFirmwareRoamingSupported() && (candidate.BSSID == null|| candidate.BSSID.equals(ClientModeImpl.SUPPLICANT_BSSID_ANY))) {targetBssid = ClientModeImpl.SUPPLICANT_BSSID_ANY;localLog("connectToNetwork: Connect to " + candidate.SSID + ":" + targetBssid+ " from " + currentAssociationId);} else {localLog("connectToNetwork: Connect to " + targetAssociationId + " from "+ currentAssociationId);}mStateMachine.startConnectToNetwork(candidate.networkId, Process.WIFI_UID, targetBssid);}}

总体来讲该函数获取当前的连接状态，包括已经配置的网络信息，与即将准备连接的网络进行对比，如果相同并且支持 roaming，则进行漫游连接操作，如果不同，进行连接操作，调用了 mStateMachine 的 startConnectToNetwork 方法进行连接

mStateMachine 实际上是 ClientModeImpl 类对象，在 WifiConnectivityManager 类对象初始化的时候传入，它是 ClientMode 的实现类，实现了 Client Mode 的事件处理逻辑，它是 StateMachine 的子类，连接方法非常简单，就是发送 CMD_START_CONNECT 消息进行连接：

    /*** Automatically connect to the network specified** @param networkId ID of the network to connect to* @param uid UID of the app triggering the connection.* @param bssid BSSID of the network*/public void startConnectToNetwork(int networkId, int uid, String bssid) {sendMessage(CMD_START_CONNECT, networkId, uid, bssid);}

CMD_START_CONNECT 消息在状态机中由两个状态会处理，分别是 DefaultState 和 ConnectModeState，他们之间的关系如下：

        addState(mDefaultState);addState(mConnectModeState, mDefaultState);addState(mL2ConnectedState, mConnectModeState);addState(mObtainingIpState, mL2ConnectedState);addState(mConnectedState, mL2ConnectedState);addState(mRoamingState, mL2ConnectedState);addState(mDisconnectingState, mConnectModeState);addState(mDisconnectedState, mConnectModeState);setInitialState(mDefaultState);

因此由 ConnectModeState 进行处理，截取其 processMessage 片段如下：

                case CMD_START_CONNECT:/* connect command coming from auto-join */netId = message.arg1;int uid = message.arg2;bssid = (String) message.obj;mSentHLPs = false;if (!hasConnectionRequests()) {if (mNetworkAgent == null) {loge("CMD_START_CONNECT but no requests and not connected,"+ " bailing");break;} else if (!mWifiPermissionsUtil.checkNetworkSettingsPermission(uid)) {loge("CMD_START_CONNECT but no requests and connected, but app "+ "does not have sufficient permissions, bailing");break;}}config = mWifiConfigManager.getConfiguredNetworkWithoutMasking(netId);logd("CMD_START_CONNECT "+ " my state " + getCurrentState().getName()+ " nid=" + Integer.toString(netId)+ " roam=" + Boolean.toString(mIsAutoRoaming));if (config == null) {loge("CMD_START_CONNECT and no config, bail out...");break;}mTargetNetworkId = netId;// Update scorecard while there is still state from existing connectionint scanRssi = mWifiConfigManager.findScanRssi(netId,mWifiHealthMonitor.getScanRssiValidTimeMs());mWifiScoreCard.noteConnectionAttempt(mWifiInfo, scanRssi, config.SSID);mBssidBlocklistMonitor.updateFirmwareRoamingConfiguration(config.SSID);updateWifiConfigOnStartConnection(config, bssid);reportConnectionAttemptStart(config, mTargetBssid,WifiMetricsProto.ConnectionEvent.ROAM_UNRELATED);String currentMacAddress = mWifiNative.getMacAddress(mInterfaceName);mWifiInfo.setMacAddress(currentMacAddress);Log.i(TAG, "Connecting with " + currentMacAddress + " as the mac address");mTargetWifiConfiguration = config;/* Check for FILS configuration again after updating the config */if (config.allowedKeyManagement.get(WifiConfiguration.KeyMgmt.FILS_SHA256)|| config.allowedKeyManagement.get(WifiConfiguration.KeyMgmt.FILS_SHA384)) {boolean isIpClientStarted = startIpClient(config, true);if (isIpClientStarted) {mIpClientWithPreConnection = true;break;}}connectToNetwork(config);break;

处理过程分析如下：

1. 判断是否存在连接请求，通过 hasConnectionRequests 方法，最终调用了 mNetworkFactory 和 mUntrackedNetworkFactory 的 hasConnectionRequests 方法进行判断，关于连接请求的添加另外分析；

2. 判断 mNetworkAgent 是否为空，NetworkAgent 是每个网络连接模块与系统网络管理模块交互的接口，对于 WiFi 连接，采用了 WifiNetworkAgent 类进行了封装，注册到系统中；

3. 获取当前 netId 对应的网络配置信息，该请求通过 WifiConfigManager 的 getConfiguredNetworkWithoutMasking 进行，而配置在什么地方如何设置到 Configuration 中在后面分析，这里如果没有查找到配置信息，则不会继续进行连接过程（网络配置的保存发生在调用 connectToNetwork 的 WifiConnectivityManager 类的回调 handleScanResults 中，在 connectToNetwork 之前调用，通过 NetworkSelector 类的 selectNetwork 方法，调用 updateChosenPasspointNetwork 方法，接着调用了 WifiConfigManager 的 addOrUpdateNetwork 方法将配置保存下来，内部调用了 addOrUpdateNetworkInternal 方法）；

4. 回到 handleScanResults 处理过程，紧接着调用了 WifiConnectivityManager 中的 connectToNetwork，它内部继续调用了 mStateMachine 也就是 ClientModeImpl 类的 startConnectToNetwork 方法，其内部处理很简单，发出一个 CMD_START_CONNECT 消息由状态机进行处理，这里的处理过程发生在 ConnectModeState，在进行连接前更新配置息 updateWifiConfigOnStartConnection；

5. 通过 reportConnectionAttemptStart 方法通知系统其他组件网络开始进行连接；

6. 通过 startIpClient 启动 IP 配置功能，可能为 STATIC 或者 DHCP；

7. 通过 connectToNetwork 接口开始连接，代码如下：

    void connectToNetwork(WifiConfiguration config) {if ((config != null) && mWifiNative.connectToNetwork(mInterfaceName, config)) {mWifiInjector.getWifiLastResortWatchdog().noteStartConnectTime();mWifiMetrics.logStaEvent(StaEvent.TYPE_CMD_START_CONNECT, config);mLastConnectAttemptTimestamp = mClock.getWallClockMillis();mIsAutoRoaming = false;if (getCurrentState() != mDisconnectedState) {transitionTo(mDisconnectingState);}} else {loge("CMD_START_CONNECT Failed to start connection to network " + config);mTargetWifiConfiguration = null;stopIpClient();reportConnectionAttemptEnd(WifiMetrics.ConnectionEvent.FAILURE_CONNECT_NETWORK_FAILED,WifiMetricsProto.ConnectionEvent.HLF_NONE,WifiMetricsProto.ConnectionEvent.FAILURE_REASON_UNKNOWN);}}

处理过程较简单，判断 config 非空的情况下调用 WifiNative 的 connectToNetwork 进行连接，成功返回 true，然后更新时间戳和记录状态等，判断状态信息是否正确，如果当前不是处于 mDisconnectedState 则需要切换到该状态；而如果 WifiNative 的 connectToNetwork 返回了 false 则停止 IP 配置功能，记录状态信息。

WifiNative 的 connectToNetwork 如下：

    /*** Add the provided network configuration to wpa_supplicant and initiate connection to it.* This method does the following:* 1. Abort any ongoing scan to unblock the connection request.* 2. Remove any existing network in wpa_supplicant(This implicitly triggers disconnect).* 3. Add a new network to wpa_supplicant.* 4. Save the provided configuration to wpa_supplicant.* 5. Select the new network in wpa_supplicant.* 6. Triggers reconnect command to wpa_supplicant.** @param ifaceName Name of the interface.* @param configuration WifiConfiguration parameters for the provided network.* @return {@code true} if it succeeds, {@code false} otherwise*/public boolean connectToNetwork(@NonNull String ifaceName, WifiConfiguration configuration) {// Abort ongoing scan before connect() to unblock connection request.mWifiCondManager.abortScan(ifaceName);return mSupplicantStaIfaceHal.connectToNetwork(ifaceName, configuration);}

首先通过 WifiCondManager 的 abortScan 方法停止对应接口的扫描动作，然后调用 SupplicantStaIfaceHal 的 connectToNetwork 方法进行连接。abortScan 实际上调用到具体的 ScannerImpl 实现中对应的同名接口实现，SupplicantStaIfaceHal 的 connectToNetwork 方法如下：

    /*** Add the provided network configuration to wpa_supplicant and initiate connection to it.* This method does the following:* 1. If |config| is different to the current supplicant network, removes all supplicant* networks and saves |config|.* 2. Select the new network in wpa_supplicant.** @param ifaceName Name of the interface.* @param config WifiConfiguration parameters for the provided network.* @return {@code true} if it succeeds, {@code false} otherwise*/public boolean connectToNetwork(@NonNull String ifaceName, @NonNull WifiConfiguration config) {synchronized (mLock) {logd("connectToNetwork " + config.getKey());WifiConfiguration currentConfig = getCurrentNetworkLocalConfig(ifaceName);if (WifiConfigurationUtil.isSameNetwork(config, currentConfig)) {String networkSelectionBSSID = config.getNetworkSelectionStatus().getNetworkSelectionBSSID();String networkSelectionBSSIDCurrent =currentConfig.getNetworkSelectionStatus().getNetworkSelectionBSSID();if (Objects.equals(networkSelectionBSSID, networkSelectionBSSIDCurrent)) {logd("Network is already saved, will not trigger remove and add operation.");} else {logd("Network is already saved, but need to update BSSID.");if (!setCurrentNetworkBssid(ifaceName,config.getNetworkSelectionStatus().getNetworkSelectionBSSID())) {loge("Failed to set current network BSSID.");return false;}mCurrentNetworkLocalConfigs.put(ifaceName, new WifiConfiguration(config));}} else {mCurrentNetworkRemoteHandles.remove(ifaceName);mCurrentNetworkLocalConfigs.remove(ifaceName);if (!removeAllNetworks(ifaceName)) {loge("Failed to remove existing networks");return false;}Pair<SupplicantStaNetworkHal, WifiConfiguration> pair =addNetworkAndSaveConfig(ifaceName, config);if (pair == null) {loge("Failed to add/save network configuration: " + config.getKey());return false;}mCurrentNetworkRemoteHandles.put(ifaceName, pair.first);mCurrentNetworkLocalConfigs.put(ifaceName, pair.second);}SupplicantStaNetworkHal networkHandle =checkSupplicantStaNetworkAndLogFailure(ifaceName, "connectToNetwork");if (networkHandle == null) {loge("No valid remote network handle for network configuration: "+ config.getKey());return false;}PmkCacheStoreData pmkData = mPmkCacheEntries.get(config.networkId);if (pmkData != null&& !WifiConfigurationUtil.isConfigForPskNetwork(config)&& pmkData.expirationTimeInSec > mClock.getElapsedSinceBootMillis() / 1000) {logi("Set PMK cache for config id " + config.networkId);if (networkHandle.setPmkCache(pmkData.data)) {mWifiMetrics.setConnectionPmkCache(true);}}if (!networkHandle.select()) {loge("Failed to select network configuration: " + config.getKey());return false;}return true;}}

它完成两件事情，首先将当前网络配置信息添加到 wpa_supplicant 中，如果当前 supplicant 网络不是该 config 对应的网络则清除当前网络，并在 wpa_supplicant 中选择 config 对应的网络进行连接。

这里 SupplicantStaIfaceHal 自身通过 HashMap<String, WifiConfiguration> 类型对象 mCurrentNetworkLocalConfigs 保存了配置信息，如果发现 isSameNetwork 则进行对应的配置更新操作，否则会网络不同则：

1. 删除掉 mCurrentNetworkRemoteHandles 中保存的对应信息，即底层 HIDL 端的 SupplicantStaNetworkHal 信息；

2. 删除掉 mCurrentNetworkLocalConfigs 中保存的对应信息，实际就是 WifiConfiguration 配置内容；

3. 通过 removeAllNetworks 将所有 ifaceName 对应的 networks 全部删除，实际调用了 listNetworks 取得对应的 network id 列表，并通过 removeNetwork 将其删除；对应的接口以及一个 ifaceName 为何可以对应多个 networks 在后面分析；

4. 通过 addNetworkAndSaveConfig 添加网络以及保存配置，首先其调用 addNetwork 获取到 SupplicantStaNetworkHal 对象 network，紧接着通过 network 的 saveWifiConfiguration 方法设定配置信息；

5. 最终通过 checkSupplicantStaNetworkAndLogFailure 查询确认添加是否成功；

6. 如果添加成功，则进行缓存更新，并且调用 networkHandle 的 select 方法选择对应的网络进行连接，networkHandle 就是 SupplicantStaNetworkHal 类，select 方法其实就是调用到了 HIDL 中对应服务的 select 方法:

    /*** Trigger a connection to this network.** @return true if it succeeds, false otherwise.*/public boolean select() {synchronized (mLock) {final String methodStr = "select";if (!checkISupplicantStaNetworkAndLogFailure(methodStr)) return false;try {SupplicantStatus status = mISupplicantStaNetwork.select();return checkStatusAndLogFailure(status, methodStr);} catch (RemoteException e) {handleRemoteException(e, methodStr);return false;}}}

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