Android -- Wifi热点的打开与关闭流程简介

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。