編輯：關於Android編程
在Android手機中，熱點也是一個較為常用的功能。對於framework開發者來說，要開發、維護SoftAp，了解framework中熱點開關的具體流程是非常有必要的。下面就對這部分內容做一些介紹，以供後續查閱。
當我們在設置中打開熱點時，會調用WifiManager::setWifiApEnabled()，參數enabled為true；間接調用同名的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");
}
}
參數中的wifiConfig對象保存了在Settings中操作時保留的熱點信息，如熱點名稱、密鑰和加密方式等等。與Wifi本身的打開和關閉類似，Wifi熱點的打開流程也是通過WifiController狀態機向WifiStateMachine轉發消息的。與前面介紹的Wifi打開流程類似，CMD_SET_AP消息在ApStaDisabledState狀態處理：
case CMD_SET_AP:
if (msg.arg1 == 1) {
mWifiStateMachine.setHostApRunning((WifiConfiguration) msg.obj,
true);
transitionTo(mApEnabledState);//此時WifiController的狀態停留在ApEnabledState
}
由此轉入WifiStateMachine進行打開流程：
/**
* TODO: doc
*/
public void setHostApRunning(WifiConfiguration wifiConfig, boolean enable) {
if (enable) {
sendMessage(CMD_START_AP, wifiConfig);
} else {
sendMessage(CMD_STOP_AP);
}
}
WifiStateMachine::InitialState會處理該消息：
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);//該函數中會發送廣播，告知外界當前熱點的啟動階段
transitionTo(mSoftApStartingState);//切換狀態
} else {
setWifiApState(WIFI_AP_STATE_FAILED,
WifiManager.SAP_START_FAILURE_GENERAL);
transitionTo(mInitialState);
}
}
break;
首先肯定是先加載驅動，驅動加載成功後通過enableSoftAp()配置Wifi熱點：
/* 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");//加載固件
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) {//啟動HAL層
/* starting HAL is optional */
Log.e(TAG, "Failed to start HAL");
}
return true;
}
Wifi熱點首先需要綁定端口信息，再以AP模式通過NetworkManagementService在wlan0端口下加載固件；同時熱點功能也需要HAL層的支持。
setWifiApState()會發送廣播，告知當前熱點打開的過程信息；同理，也有setWifiState()，告知外界當前Wifi打開的過程信息；如果我們有必要知道當前熱點打開的過程進行到什麼階段了，可以監聽WifiManager.WIFI_AP_STATE_CHANGED_ACTION廣播。最後狀態切換到SoftApStartingState，如果流程有誤，則會重新進入InitialState。
接著看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 - 獲取先前或者默認的配置信息
} else {
mWifiApConfigChannel.sendMessage(CMD_SET_AP_CONFIG, config);//2 - 將上層傳入的配置信息寫到本地文件
startSoftApWithConfig(config);//開啟熱點
}
} else {
throw new RuntimeException("Illegal transition to SoftApStartingState: " + message);
}
}
首先會判斷打開熱點時傳入的WifiConfiguration對象是否為null；如果為空，則會向WifiApConfigStore發送CMD_REQUEST_AP_CONFIG消息，請求一個熱點配置信息
。我們一起介紹這兩個分支過程。回過頭看InitialState狀態的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也是一個小的狀態機，此時會構建mWifiApConfigStore對戲，並啟動狀態機
mWifiApConfigStore.loadApConfiguration();//在WifiApConfigStore中加載默認的熱點配置信息
mWifiApConfigChannel.connectSync(mContext, getHandler(),
mWifiApConfigStore.getMessenger());//創建AsyncChannel對象，以供向WifiApConfigStore發送消息
}
if (mWifiConfigStore.enableHalBasedPno.get()) {
// make sure developer Settings are in sync with the config option
mHalBasedPnoEnableInDevSettings = true;
}
}
在創建完mWifiApConfigStore對象後，會調用mWifiApConfigStore.loadApConfiguration()加載熱點配置信息：
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) {}
}
}
}
主要是從/misc/wifi/softap.conf文件中讀取其中的信息，並賦給WifiApConfigStore的成員變量mWifiApConfig，這個變量保存的就是當前SoftAp的配置信息。該文件一開始會有默認的信息保存其中，如果我們從沒配置過熱點，拿到的就是系統默認的信息；如果，上層配置了熱點；我們也會將新的配置信息更新到softap.conf中，以供下載再次加載。再看消息處理過程：
case WifiStateMachine.CMD_REQUEST_AP_CONFIG:
mReplyChannel.replyToMessage(message,
WifiStateMachine.CMD_RESPONSE_AP_CONFIG, mWifiApConfig);
向WifiStateMachine回復CMD_RESPONSE_AP_CONFIG消息，並附帶mWifiApConfig對象。在SoftApStartingState::enter()中，如果config不為空，我們直接去調用startSoftApWithConfig()啟動SoftAP；如果一開始config為null，通過處理CMD_RESPONSE_AP_CONFIG，獲取到新的config對象，也應該去開啟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依然為null，則熱點打開失敗
sendMessage(CMD_START_AP_FAILURE, WifiManager.SAP_START_FAILURE_GENERAL);//SoftApStartingState處理，狀態重新切換到InitialState
}
break;
如果一開始的config對象不為空，從代碼可知我們會先發送CMD_SET_AP_CONFIG消息，通知WifiApConfigStore更新配置信息，看處理流程：
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;//將上層傳入的配置信息先保存到成員變量中
transitionTo(mActiveState);//切換狀態
} else {
Log.e(TAG, "Try to setup AP config without SSID: " + message);
}
首先將傳入的配置對象保存到mWifiApConfig，接著切換狀態：
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);//發送更新完成消息
}
}).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()函數中，會調用writeApConfiguration()將mWifiApConfig的信息更新到/misc/wifi/softap.conf文件中，供下次加載使用：
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) {}
}
}
}
處理比較簡單，接著給自己發送CMD_SET_AP_CONFIG_COMPLETED消息，告知配置信息更新已經完畢，並重新進入InactiveState，重新等待下次配置信息的更新處理。
我們再返回到WifiStateMachine::SoftApStartingState處理CMD_RESPONSE_AP_CONFIG，如果再次獲取後的config依然為null，則通知熱點打開失敗。接著就是真正開啟熱點的函數處理：
/* 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()) {//因為SoftAp需要HAL層的支持，所有首先要進行確定，再繼續配置
//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() {//開啟一個新線程，來啟動hostapd；我們支持wpa_s是支持Wifi的，hostapd則是支持SoftAP的
public void run() {
try {
mNwService.startAccessPoint(config, mInterfaceName);//通過NetworkManagerService，在無線端口上，按傳入的配置信息開啟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);//打開失敗,狀態會重新切換到InitialState；等待下一次過程
return;
}
}
if (DBG) log("Soft AP start successful");
sendMessage(CMD_START_AP_SUCCESS);//打開成功
}
}).start();
}
如果最後熱點打開成功，發送CMD_START_AP_SUCCESS，看處理過程，SoftApStartingState：
case CMD_START_AP_SUCCESS:
setWifiApState(WIFI_AP_STATE_ENABLED, 0);//發送廣播，告知SoftAp已經成功打開
transitionTo(mSoftApStartedState);//切換狀態
break;
case CMD_START_AP_FAILURE:
setWifiApState(WIFI_AP_STATE_FAILED, message.arg1);//發送廣播，告知SoftAp未成功打開
transitionTo(mInitialState);//切換到初始狀態
最終狀態在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;
}
到這裡，一個完整的SoftAp打開流程就結束了。
關閉SoftAp的方法調用與打開SoftAp一致，不過enabled此時是為false：
public boolean setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled)由第一部分的內容可知WifiController狀態機在處理完SoftAp打開後，停在ApEnabledState狀態，那麼我們看它是怎麼處理CMD_SET_AP的：
case CMD_SET_AP:
if (msg.arg1 == 0) {
mWifiStateMachine.setHostApRunning(null, false);//在WifiStateMachine中開始熱點關閉流程
transitionTo(mApStaDisabledState);//切換到初始狀態
}
break;
有前述可知，如果參數enabled為false，mag.arg1就應該為0，調用setHostApRunning()走關閉流程，並將WifiController中的狀態重置為ApStaDisabledState，等待下一次流程的開始。看setHostApRunning()：
/**
* TODO: doc
*/
public void setHostApRunning(WifiConfiguration wifiConfig, boolean enable) {
if (enable) {
sendMessage(CMD_START_AP, wifiConfig);
} else {
sendMessage(CMD_STOP_AP);
}
}
發送CMD_STOP_AP消息；已知SoftAp成功打開後，WifiStateMachine停留在SoftApStartedState，看其處理：
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);//直接關閉SoftAp
} catch(Exception e) {
loge("Exception in stopAccessPoint()");
}
setWifiApState(WIFI_AP_STATE_DISABLED, 0);//發送廣播，告知外界SoftAp的狀態
transitionTo(mInitialState);//切換到初始狀態
首先，通過NetworkManagermentService關閉SoftAp，並發送廣播通知SoftAp的狀態改變；最後WifiStateMachine切換到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層，卸載驅動；重新等待下一次Wifi/SoftAp的啟動過程。到此，熱點關閉的動作就結束了。
PS：
WifiManager中提供了兩個關於SoftAp的操作函數：
1、設置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;
}
}
設置Wi-Fi AP的配置信息，它真正的處理過程是向WifiApConfigStore發送CMD_SET_AP_CONFIG消息，告知其要更新配置信息了。這一部分處理在第一部分已經分析過。
2、獲取當前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;
}
}
它真正的處理過程是向WifiApConfigStore發送CMD_REQUEST_AP_CONFIG消息，請求WifiApConfigStore::mWifiApConfig成員，第一部分也已經說過，該變量保存的就是當前SoftAp正在使用的配置信息。
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