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_AP
if (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 option
mHalBasedPnoEnableInDevSettings = 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 progress
case 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 channel
final 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 Here
if (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 5GHz
sendMessage(CMD_START_AP_FAILURE, WifiManager.SAP_START_FAILURE_GENERAL);
return;
}
}
} else {
if (config.apBand != 0) {
//countrycode is mandatory for 5GHz
Log.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 channel
sendMessage(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
//supported
config.apBand = 0;
config.apChannel = 6;
}
}
}
} else {
//for some old device, wifiHal may not be supported
config.apBand = 0;
config.apChannel = 6;
}
// Start hostapd on a separate thread
new 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 {
@Override
public 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 point
break;
// Fail client mode operation when soft AP is enabled
case 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 option
mHalBasedPnoEnableInDevSettings = 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。
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