Android -- Wifi热点的打开与关闭流程简介

在Android手机中，热点也是一个较为常用的功能。对于framework开发者来说，要开发、维护SoftAp，了解framework中热点开关的具体流程是非常有必要的。下面就对这部分内容做一些介绍，以供后续查阅。

一、SoftAp打开流程

当我们在设置中打开热点时，会调用WifiManager::setWifiApEnabled()，参数enabled为true；间接调用同名的WifiServiceImpl::setWifiApEnabled()：

/*** Start AccessPoint mode with the specified* configuration. If the radio is already running in* AP mode, update the new configuration* Note that starting in access point mode disables station* mode operation* @param wifiConfig SSID, security and channel details as*        part of WifiConfiguration* @return {@code true} if the operation succeeds, {@code false} otherwise** @hide Dont open up yet*/public boolean setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled) {try {mService.setWifiApEnabled(wifiConfig, enabled);return true;} catch (RemoteException e) {return false;}}

    /*** see {@link android.net.wifi.WifiManager#setWifiApEnabled(WifiConfiguration, boolean)}* @param wifiConfig SSID, security and channel details as*        part of WifiConfiguration* @param enabled true to enable and false to disable*/public void setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled) {enforceChangePermission();ConnectivityManager.enforceTetherChangePermission(mContext);if (mUserManager.hasUserRestriction(UserManager.DISALLOW_CONFIG_TETHERING)) {throw new SecurityException("DISALLOW_CONFIG_TETHERING is enabled for this user.");}// null wifiConfig is a meaningful input for CMD_SET_APif (wifiConfig == null || isValid(wifiConfig)) {mWifiController.obtainMessage(CMD_SET_AP, enabled ? 1 : 0, 0, wifiConfig).sendToTarget();} else {Slog.e(TAG, "Invalid WifiConfiguration");}}

参数中的wifiConfig对象保存了在Settings中操作时保留的热点信息，如热点名称、密钥和加密方式等等。与Wifi本身的打开和关闭类似，Wifi热点的打开流程也是通过WifiController状态机向WifiStateMachine转发消息的。与前面介绍的Wifi打开流程类似，CMD_SET_AP消息在ApStaDisabledState状态处理：

                case CMD_SET_AP:if (msg.arg1 == 1) {mWifiStateMachine.setHostApRunning((WifiConfiguration) msg.obj,true);transitionTo(mApEnabledState);//此时WifiController的状态停留在ApEnabledState}

由此转入WifiStateMachine进行打开流程：

    /*** TODO: doc*/public void setHostApRunning(WifiConfiguration wifiConfig, boolean enable) {if (enable) {sendMessage(CMD_START_AP, wifiConfig);} else {sendMessage(CMD_STOP_AP);}}

WifiStateMachine::InitialState会处理该消息：

case CMD_START_AP:if (mWifiNative.loadDriver() == false) {loge("Failed to load driver for softap");} else {if (enableSoftAp() == true) {setWifiApState(WIFI_AP_STATE_ENABLING, 0);//该函数中会发送广播，告知外界当前热点的启动阶段transitionTo(mSoftApStartingState);//切换状态} else {setWifiApState(WIFI_AP_STATE_FAILED,WifiManager.SAP_START_FAILURE_GENERAL);transitionTo(mInitialState);}}break;

首先肯定是先加载驱动，驱动加载成功后通过enableSoftAp()配置Wifi热点：

    /* SoftAP configuration */private boolean enableSoftAp() {if (WifiNative.getInterfaces() != 0) {if (!mWifiNative.toggleInterface(0)) {if (DBG) Log.e(TAG, "toggleInterface failed");return false;}} else {if (DBG) Log.d(TAG, "No interfaces to toggle");}try {mNwService.wifiFirmwareReload(mInterfaceName, "AP");//加载固件if (DBG) Log.d(TAG, "Firmware reloaded in AP mode");} catch (Exception e) {Log.e(TAG, "Failed to reload AP firmware " + e);}if (WifiNative.startHal() == false) {//启动HAL层/* starting HAL is optional */Log.e(TAG, "Failed to start HAL");}return true;}

Wifi热点首先需要绑定端口信息，再以AP模式通过NetworkManagementService在wlan0端口下加载固件；同时热点功能也需要HAL层的支持。

setWifiApState()会发送广播，告知当前热点打开的过程信息；同理，也有setWifiState()，告知外界当前Wifi打开的过程信息；如果我们有必要知道当前热点打开的过程进行到什么阶段了，可以监听WifiManager.WIFI_AP_STATE_CHANGED_ACTION广播。最后状态切换到SoftApStartingState，如果流程有误，则会重新进入InitialState。

接着看SoftApStartingState::enter()：

        public void enter() {final Message message = getCurrentMessage();if (message.what == CMD_START_AP) {final WifiConfiguration config = (WifiConfiguration) message.obj;if (config == null) {mWifiApConfigChannel.sendMessage(CMD_REQUEST_AP_CONFIG);//1 - 获取先前或者默认的配置信息} else {mWifiApConfigChannel.sendMessage(CMD_SET_AP_CONFIG, config);//2 - 将上层传入的配置信息写到本地文件startSoftApWithConfig(config);//开启热点}} else {throw new RuntimeException("Illegal transition to SoftApStartingState: " + message);}}

首先会判断打开热点时传入的WifiConfiguration对象是否为null；如果为空，则会向WifiApConfigStore发送CMD_REQUEST_AP_CONFIG消息，请求一个热点配置信息

。我们一起介绍这两个分支过程。回过头看InitialState状态的enter()：

public void enter() {WifiNative.stopHal();mWifiNative.unloadDriver();if (mWifiP2pChannel == null) {mWifiP2pChannel = new AsyncChannel();mWifiP2pChannel.connect(mContext, getHandler(),mWifiP2pServiceImpl.getP2pStateMachineMessenger());}if (mWifiApConfigChannel == null) {mWifiApConfigChannel = new AsyncChannel();mWifiApConfigStore = WifiApConfigStore.makeWifiApConfigStore(mContext, getHandler());//WifiApConfigStore也是一个小的状态机，此时会构建mWifiApConfigStore对戏，并启动状态机mWifiApConfigStore.loadApConfiguration();//在WifiApConfigStore中加载默认的热点配置信息mWifiApConfigChannel.connectSync(mContext, getHandler(),mWifiApConfigStore.getMessenger());//创建AsyncChannel对象，以供向WifiApConfigStore发送消息}if (mWifiConfigStore.enableHalBasedPno.get()) {// make sure developer Settings are in sync with the config optionmHalBasedPnoEnableInDevSettings = true;}}

在创建完mWifiApConfigStore对象后，会调用mWifiApConfigStore.loadApConfiguration()加载热点配置信息：

    void loadApConfiguration() {DataInputStream in = null;try {WifiConfiguration config = new WifiConfiguration();in = new DataInputStream(new BufferedInputStream(new FileInputStream(AP_CONFIG_FILE)));int version = in.readInt();if ((version != 1) && (version != 2)) {Log.e(TAG, "Bad version on hotspot configuration file, set defaults");setDefaultApConfiguration();return;}config.SSID = in.readUTF();if (version >= 2) {config.apBand = in.readInt();config.apChannel = in.readInt();}int authType = in.readInt();config.allowedKeyManagement.set(authType);if (authType != KeyMgmt.NONE) {config.preSharedKey = in.readUTF();}mWifiApConfig = config;} catch (IOException ignore) {setDefaultApConfiguration();} finally {if (in != null) {try {in.close();} catch (IOException e) {}}}}

主要是从/misc/wifi/softap.conf文件中读取其中的信息，并赋给WifiApConfigStore的成员变量mWifiApConfig，这个变量保存的就是当前SoftAp的配置信息。该文件一开始会有默认的信息保存其中，如果我们从没配置过热点，拿到的就是系统默认的信息；如果，上层配置了热点；我们也会将新的配置信息更新到softap.conf中，以供下载再次加载。再看消息处理过程：

case WifiStateMachine.CMD_REQUEST_AP_CONFIG:mReplyChannel.replyToMessage(message,WifiStateMachine.CMD_RESPONSE_AP_CONFIG, mWifiApConfig);

向WifiStateMachine回复CMD_RESPONSE_AP_CONFIG消息，并附带mWifiApConfig对象。在SoftApStartingState::enter()中，如果config不为空，我们直接去调用startSoftApWithConfig()启动SoftAP；如果一开始config为null，通过处理CMD_RESPONSE_AP_CONFIG，获取到新的config对象，也应该去开启SoftAP了：

case WifiStateMachine.CMD_RESPONSE_AP_CONFIG:WifiConfiguration config = (WifiConfiguration) message.obj;if (config != null) {startSoftApWithConfig(config);} else {loge("Softap config is null!");//config依然为null，则热点打开失败sendMessage(CMD_START_AP_FAILURE, WifiManager.SAP_START_FAILURE_GENERAL);//SoftApStartingState处理，状态重新切换到InitialState}break;

如果一开始的config对象不为空，从代码可知我们会先发送CMD_SET_AP_CONFIG消息，通知WifiApConfigStore更新配置信息，看处理流程：

    class InactiveState extends State {public boolean processMessage(Message message) {switch (message.what) {case WifiStateMachine.CMD_SET_AP_CONFIG:WifiConfiguration config = (WifiConfiguration)message.obj;if (config.SSID != null) {mWifiApConfig = config;//将上层传入的配置信息先保存到成员变量中transitionTo(mActiveState);//切换状态} else {Log.e(TAG, "Try to setup AP config without SSID: " + message);}

首先将传入的配置对象保存到mWifiApConfig，接着切换状态：

    class ActiveState extends State {public void enter() {new Thread(new Runnable() {public void run() {writeApConfiguration(mWifiApConfig);//更新配置信息到本地sendMessage(WifiStateMachine.CMD_SET_AP_CONFIG_COMPLETED);//发送更新完成消息}}).start();}public boolean processMessage(Message message) {switch (message.what) {//TODO: have feedback to the user when we do this//to indicate the write is currently in progresscase WifiStateMachine.CMD_SET_AP_CONFIG:deferMessage(message);break;case WifiStateMachine.CMD_SET_AP_CONFIG_COMPLETED:transitionTo(mInactiveState);break;default:return NOT_HANDLED;}return HANDLED;}}

enter()函数中，会调用writeApConfiguration()将mWifiApConfig的信息更新到/misc/wifi/softap.conf文件中，供下次加载使用：

    private void writeApConfiguration(final WifiConfiguration config) {DataOutputStream out = null;try {out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(AP_CONFIG_FILE)));out.writeInt(AP_CONFIG_FILE_VERSION);out.writeUTF(config.SSID);out.writeInt(config.apBand);out.writeInt(config.apChannel);int authType = config.getAuthType();out.writeInt(authType);if(authType != KeyMgmt.NONE) {out.writeUTF(config.preSharedKey);}} catch (IOException e) {Log.e(TAG, "Error writing hotspot configuration" + e);} finally {if (out != null) {try {out.close();} catch (IOException e) {}}}}

处理比较简单，接着给自己发送CMD_SET_AP_CONFIG_COMPLETED消息，告知配置信息更新已经完毕，并重新进入InactiveState，重新等待下次配置信息的更新处理。

我们再返回到WifiStateMachine::SoftApStartingState处理CMD_RESPONSE_AP_CONFIG，如果再次获取后的config依然为null，则通知热点打开失败。接着就是真正开启热点的函数处理：

    /* Current design is to not set the config on a running hostapd but instead* stop and start tethering when user changes config on a running access point** TODO: Add control channel setup through hostapd that allows changing config* on a running daemon*/private void startSoftApWithConfig(final WifiConfiguration configuration) {// set channelfinal WifiConfiguration config = new WifiConfiguration(configuration);if (DBG) {Log.d(TAG, "SoftAp config channel is: " + config.apChannel);}//We need HAL support to set country code and get available channel list, if HAL is//not available, like razor, we regress to original implementaion (2GHz, channel 6)if (mWifiNative.isHalStarted()) {//因为SoftAp需要HAL层的支持，所有首先要进行确定，再继续配置//set country code through HAL Hereif (mSetCountryCode != null) {if (!mWifiNative.setCountryCodeHal(mSetCountryCode.toUpperCase(Locale.ROOT))) {if (config.apBand != 0) {Log.e(TAG, "Fail to set country code. Can not setup Softap on 5GHz");//countrycode is mandatory for 5GHzsendMessage(CMD_START_AP_FAILURE, WifiManager.SAP_START_FAILURE_GENERAL);return;}}} else {if (config.apBand != 0) {//countrycode is mandatory for 5GHzLog.e(TAG, "Can not setup softAp on 5GHz without country code!");sendMessage(CMD_START_AP_FAILURE, WifiManager.SAP_START_FAILURE_GENERAL);return;}}if (config.apChannel == 0) {config.apChannel = chooseApChannel(config.apBand);if (config.apChannel == 0) {if(mWifiNative.isGetChannelsForBandSupported()) {//fail to get available channelsendMessage(CMD_START_AP_FAILURE, WifiManager.SAP_START_FAILURE_NO_CHANNEL);return;} else {//for some old device, wifiHal may not be supportedget valid channels are not//supportedconfig.apBand = 0;config.apChannel = 6;}}}} else {//for some old device, wifiHal may not be supportedconfig.apBand = 0;config.apChannel = 6;}// Start hostapd on a separate threadnew Thread(new Runnable() {//开启一个新线程，来启动hostapd；我们支持wpa_s是支持Wifi的，hostapd则是支持SoftAP的public void run() {try {mNwService.startAccessPoint(config, mInterfaceName);//通过NetworkManagerService，在无线端口上，按传入的配置信息开启SoftAP；} catch (Exception e) {loge("Exception in softap start " + e);try {mNwService.stopAccessPoint(mInterfaceName);mNwService.startAccessPoint(config, mInterfaceName);} catch (Exception e1) {loge("Exception in softap re-start " + e1);sendMessage(CMD_START_AP_FAILURE, WifiManager.SAP_START_FAILURE_GENERAL);//打开失败,状态会重新切换到InitialState；等待下一次过程return;}}if (DBG) log("Soft AP start successful");sendMessage(CMD_START_AP_SUCCESS);//打开成功}}).start();}

如果最后热点打开成功，发送CMD_START_AP_SUCCESS，看处理过程，SoftApStartingState：

                case CMD_START_AP_SUCCESS:setWifiApState(WIFI_AP_STATE_ENABLED, 0);//发送广播，告知SoftAp已经成功打开transitionTo(mSoftApStartedState);//切换状态break;case CMD_START_AP_FAILURE:setWifiApState(WIFI_AP_STATE_FAILED, message.arg1);//发送广播，告知SoftAp未成功打开transitionTo(mInitialState);//切换到初始状态

最终状态在SoftApStartedState：

    class SoftApStartedState extends State {@Overridepublic boolean processMessage(Message message) {logStateAndMessage(message, getClass().getSimpleName());switch(message.what) {case CMD_STOP_AP:if (DBG) log("Stopping Soft AP");/* We have not tethered at this point, so we just shutdown soft Ap */try {mNwService.stopAccessPoint(mInterfaceName);} catch(Exception e) {loge("Exception in stopAccessPoint()");}setWifiApState(WIFI_AP_STATE_DISABLED, 0);transitionTo(mInitialState);break;case CMD_START_AP:// Ignore a start on a running access pointbreak;// Fail client mode operation when soft AP is enabledcase CMD_START_SUPPLICANT:loge("Cannot start supplicant with a running soft AP");setWifiState(WIFI_STATE_UNKNOWN);break;case CMD_TETHER_STATE_CHANGE:TetherStateChange stateChange = (TetherStateChange) message.obj;if (startTethering(stateChange.available)) {transitionTo(mTetheringState);}break;default:return NOT_HANDLED;}return HANDLED;}

到这里，一个完整的SoftAp打开流程就结束了。

二、SoftAp关闭流程

关闭SoftAp的方法调用与打开SoftAp一致，不过enabled此时是为false：

public boolean setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled)

由第一部分的内容可知WifiController状态机在处理完SoftAp打开后，停在ApEnabledState状态，那么我们看它是怎么处理CMD_SET_AP的：

 case CMD_SET_AP:if (msg.arg1 == 0) {mWifiStateMachine.setHostApRunning(null, false);//在WifiStateMachine中开始热点关闭流程transitionTo(mApStaDisabledState);//切换到初始状态}break;

有前述可知，如果参数enabled为false，mag.arg1就应该为0，调用setHostApRunning()走关闭流程，并将WifiController中的状态重置为ApStaDisabledState，等待下一次流程的开始。看setHostApRunning()：

    /*** TODO: doc*/public void setHostApRunning(WifiConfiguration wifiConfig, boolean enable) {if (enable) {sendMessage(CMD_START_AP, wifiConfig);} else {sendMessage(CMD_STOP_AP);}}

发送CMD_STOP_AP消息；已知SoftAp成功打开后，WifiStateMachine停留在SoftApStartedState，看其处理：

                case CMD_STOP_AP:if (DBG) log("Stopping Soft AP");/* We have not tethered at this point, so we just shutdown soft Ap */try {mNwService.stopAccessPoint(mInterfaceName);//直接关闭SoftAp} catch(Exception e) {loge("Exception in stopAccessPoint()");}setWifiApState(WIFI_AP_STATE_DISABLED, 0);//发送广播，告知外界SoftAp的状态transitionTo(mInitialState);//切换到初始状态

首先，通过NetworkManagermentService关闭SoftAp，并发送广播通知SoftAp的状态改变；最后WifiStateMachine切换到InitialState：

public void enter() {WifiNative.stopHal();mWifiNative.unloadDriver();if (mWifiP2pChannel == null) {mWifiP2pChannel = new AsyncChannel();mWifiP2pChannel.connect(mContext, getHandler(),mWifiP2pServiceImpl.getP2pStateMachineMessenger());}if (mWifiApConfigChannel == null) {mWifiApConfigChannel = new AsyncChannel();mWifiApConfigStore = WifiApConfigStore.makeWifiApConfigStore(mContext, getHandler());mWifiApConfigStore.loadApConfiguration();mWifiApConfigChannel.connectSync(mContext, getHandler(),mWifiApConfigStore.getMessenger());}if (mWifiConfigStore.enableHalBasedPno.get()) {// make sure developer Settings are in sync with the config optionmHalBasedPnoEnableInDevSettings = true;}}

停掉HAL层，卸载驱动；重新等待下一次Wifi/SoftAp的启动过程。到此，热点关闭的动作就结束了。

PS：

WifiManager中提供了两个关于SoftAp的操作函数：

1、设置SoftAP的配置信息

    /*** Sets the Wi-Fi AP Configuration.* @return {@code true} if the operation succeeded, {@code false} otherwise** @hide Dont open yet*/public boolean setWifiApConfiguration(WifiConfiguration wifiConfig) {try {mService.setWifiApConfiguration(wifiConfig);return true;} catch (RemoteException e) {return false;}}

设置Wi-Fi AP的配置信息，它真正的处理过程是向WifiApConfigStore发送CMD_SET_AP_CONFIG消息，告知其要更新配置信息了。这一部分处理在第一部分已经分析过。

2、获取当前SoftAp正在使用的配置信息

    /*** Gets the Wi-Fi AP Configuration.* @return AP details in WifiConfiguration** @hide Dont open yet*/public WifiConfiguration getWifiApConfiguration() {try {return mService.getWifiApConfiguration();} catch (RemoteException e) {return null;}}

它真正的处理过程是向WifiApConfigStore发送CMD_REQUEST_AP_CONFIG消息，请求WifiApConfigStore::mWifiApConfig成员，第一部分也已经说过，该变量保存的就是当前SoftAp正在使用的配置信息。