Android -- 网络管理分析

Android -- 网络管理分析

在当前网络成为必不可少的条件时，android系统也集成的wifi,bluetooth,eth,cablemodem等等，为了将其它网络加入进来，大致浏览一下网络管理的相关分析，重点看了wifi的管理，还是绕了很多弯弯的。

在 ConnectivityManager.java 中定义的有如下类型：

public static final int TYPE_MOBILE = 0;

public static final int TYPE_WIFI = 1;

public static final int TYPE_MOBILE_MMS = 2;

public static final int TYPE_MOBILE_SUPL = 3;

public static final int TYPE_MOBILE_DUN = 4;

public static final int TYPE_MOBILE_HIPRI = 5;

public static final int TYPE_WIMAX = 6;

/* 这是在机顶盒上为android系统添加的网络类型 */

public static final int TYPE_PPPOE = 7;

public static final int TYPE_ETHERNET = 8;

public static final int TYPE_CABLEMODEM = 9;

public static final int DEFAULT_NETWORK_PREFERENCE = TYPE_WIFI;

设置了默认的网络连接是TYPE_WIFI

而android系统中对众多的网络类型进行管理其整个流程是怎样的呢？下面就来分析一下吧。

系统中对网络的判断和选在是在 ConnectivityService.java 这个服务中来处理的，在系统启动的时候会启动这个系统服务，

而在系统启动完毕后，ConnectivityService在系统启动的时候就启动了。

用户操作的类是 ConnectivityManager.java 通过aidl访问 ConnectivityService.java提供的服务。

public class ConnectivityService extends IConnectivityManager.Stub

看定义就相当明确了。。

1、网络服务启动

SystemServer启动 ConnectivityService,ConnectivityService 服务中启动对网络的监视器

在SystemServer的run()函数中，启动 ConnectivityService 的代码：

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try {

Slog.i(TAG, "Connectivity Service");

connectivity = ConnectivityService.getInstance(context);

ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);

} catch (Throwable e) {

Slog.e(TAG, "Failure starting Connectivity Service", e);

}

f (connectivityF != null) connectivityF.systemReady();

2、增加定义网络类型

framework/base/core/res/res/values/config.xml中定义了网络的类型

类型定义如下：

<!-- This string array should be overridden by the device to present a list of network

attributes. This is used by the connectivity manager to decide which networks can coexist

based on the hardware -->

<!-- An Array of "[Connection name],[ConnectivityManager connection type],

[associated radio-type],[priority] -->

<string-array translatable="false" name="networkAttributes">

<item>"wifi,1,1,2"</item>

<item>"mobile,0,0,3"</item>

<item>"mobile_mms,2,0,4"</item>

<item>"mobile_supl,3,0,4"</item>

<item>"mobile_hipri,5,0,5"</item>

<item>"pppoe,7,7,1"</item>

<item>"ethernet,8,8,0"</item>

<item>"cablemodem,9,9,0"</item>

</string-array>

!!!!! 参考 NetworkAttributes 类定义即明白什么意思了

<!-- This string array should be overridden by the device to present a list of radio

attributes. This is used by the connectivity manager to decide which networks can coexist

based on the hardware -->

<!-- An Array of "[ConnectivityManager connectionType],

[# simultaneous connection types]" -->

<string-array translatable="false" name="radioAttributes">

<item>"9,1"</item>

<item>"8,1"</item>

<item>"7,1"</item>

<item>"1,1"</item>

<item>"0,1"</item>

</string-array>

!!!! 参考 RadioAttributes 类定义即明白什么意思了

这里代表什么含义呢？在 ConnectivityService内部，定义了两个类用于解析xml文件中内容。

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private static class NetworkAttributes {

/**

* Class for holding settings read from resources.

*/

public String mName;

public int mType;

public int mRadio;

public int mPriority;

public NetworkInfo.State mLastState;

public NetworkAttributes(String init) {

String fragments[] = init.split(",");

mName = fragments[0].toLowerCase();

mType = Integer.parseInt(fragments[1]);

mRadio = Integer.parseInt(fragments[2]);

mPriority = Integer.parseInt(fragments[3]);

mLastState = NetworkInfo.State.UNKNOWN;

}

public boolean isDefault() {

return (mType == mRadio);

}

}

private static class RadioAttributes {

public int mSimultaneity;

public int mType;

public RadioAttributes(String init) {

String fragments[] = init.split(",");

mType = Integer.parseInt(fragments[0]);

mSimultaneity = Integer.parseInt(fragments[1]);

}

}

网络有优先级之分，优先级高的先被执行，这是通过如下代码进行分配的：

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// high priority first

mPriorityList = new int[mNetworksDefined];

{

int insertionPoint = mNetworksDefined-1;

int currentLowest = 0;

int nextLowest = 0;

while (insertionPoint > -1) {

for (NetworkAttributes na : mNetAttributes) {

if (na == null) continue;

if (na.mPriority < currentLowest) continue;

if (na.mPriority > currentLowest) {

if (na.mPriority < nextLowest || nextLowest == 0) {

nextLowest = na.mPriority;

}

continue;

}

mPriorityList[insertionPoint--] = na.mType;

}

currentLowest = nextLowest;

nextLowest = 0;

}

}

其中，TYPE_MOBILE_HIPRI的优先级最高，其次为TYPE_MOBILE_MMS，TYPE_MOBILE_SUPL，TYPE_MOBILE_DUN，

优先级最低的为TYPE_WIFI，TYPE_MOBILE。TYPE_WIFI，TYPE_MOBILE两个网络类型中，TYPE_WIFI大于TYPE_MOBILE的优先级

在打开wifi的连接后，mobile网络会被关闭。wifi网络连接关闭后，mobile网络会重新连接.

在处理网络连接的Handler的代码中有处理：

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private void handleConnect(NetworkInfo info) {

int type = info.getType();

// snapshot isFailover, because sendConnectedBroadcast() resets it

boolean isFailover = info.isFailover();

NetworkStateTracker thisNet = mNetTrackers[type];

// if this is a default net and other default is running

// kill the one not preferred

if (mNetAttributes[type].isDefault()) {

if (mActiveDefaultNetwork != -1 && mActiveDefaultNetwork != type) {

if ((type != mNetworkPreference &&

mNetAttributes[mActiveDefaultNetwork].mPriority >

mNetAttributes[type].mPriority) ||

mNetworkPreference == mActiveDefaultNetwork) {

<span style="color:#3366FF;"> // don't accept this one

if (DBG) Slog.v(TAG, "Not broadcasting CONNECT_ACTION " +

"to torn down network " + info.getTypeName());

teardown(thisNet);</span>

return;

} else {

<span style="color:#3333FF;"> // tear down the other

NetworkStateTracker otherNet =

mNetTrackers[mActiveDefaultNetwork];

if (DBG) Slog.v(TAG, "Policy requires " +

otherNet.getNetworkInfo().getTypeName() +

" teardown");

if (!teardown(otherNet)) {

Slog.e(TAG, "Network declined teardown request");

return;

}

if (isFailover) {

otherNet.releaseWakeLock();

}</span>

}

}

mActiveDefaultNetwork = type;

// this will cause us to come up initially as unconnected and switching

// to connected after our normal pause unless somebody reports us as reall

// disconnected

mDefaultInetConditionPublished = 0;

mDefaultConnectionSequence++;

mInetConditionChangeInFlight = false;

// Don't do this - if we never sign in stay, grey

//reportNetworkCondition(mActiveDefaultNetwork, 100);

}

thisNet.setTeardownRequested(false);

thisNet.updateNetworkSettings();

handleConnectivityChange(type);

sendConnectedBroadcast(info);

}

因此请注意，由于WIFI优先级高于ETH网络，如果wifi被开启，可以eth就会被关闭掉，而如果我们想在

这两者同时存在，那么在调用teardown(NetworkStateTracker)函数前进行判定即可。

2、启个各类网络监控器服务代码,这里以wifi为例

在ConnectivityService的构造函数中启动网络监视器的代码

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/*

* Create the network state trackers for Wi-Fi and mobile

* data. Maybe this could be done with a factory class,

* but it's not clear that it's worth it, given that

* the number of different network types is not going

* to change very often.

*/

boolean noMobileData = !getMobileDataEnabled();

for (int netType : mPriorityList) {

switch (mNetAttributes[netType].mRadio) {

case ConnectivityManager.TYPE_WIFI:

if (DBG) Slog.v(TAG, "Starting Wifi Service.");

WifiStateTracker wst = new WifiStateTracker(context, mHandler);

WifiService wifiService = new WifiService(context, wst);

ServiceManager.addService(Context.WIFI_SERVICE, wifiService);

wifiService.startWifi();

mNetTrackers[ConnectivityManager.TYPE_WIFI] = wst;

wst.startMonitoring();

break;

在settings中可以设置网络连接，比如打开wifi，打开bluetooth,设置apn的连接等等，在设置完成后,设置的消息会存在一个数据库中保存，并发送系统消息来广播网络设置的变化。

在网络监视器中捕捉了settings中发出的相应的网络广播信息，网络监视器中注册了settings中网络变化的信息，有变化会做相应的处理，并将处理的结果存储在NetworkInfo类的一个对象中，在ConnectivityService中通过

public NetworkInfo getNetworkInfo(int networkType)方法可以得知当前networkType类型网络的连接情况。

3、
应用监控

在app中，我们可以通过 ConnectivityManager 来获取当前的网络信息，并能指定当前程序需要的网络类型：

ConnectivityManager mCnn = context.getSystemService(context.CONNECTIVITY_SERVICE);

NetworkInfo mNetinfo = mCnn.getActiveNetworkInfo();

mCnn.setNetworkPreference(int preference);//设定首选网络类型。

假如没有设定，网络类型为系统默认。在wifi，3G网络同时存在的情况下，系统会默认的调用wifi网络，加载wifi的驱动，走wifi网络。

4、下面详细分析一下wifi网络信息

wifi 图示层次：



ConnectivityService 的构造函数会将 WifiService 添加到 ServiceManager 中，使之需要服务者可以访问。

mWifiStateTracker = new WifiStateTracker(context, handler);

WifiService wifiService = new WifiService(context, mWifiStateTracker);

ServiceManager.addService(Context.WIFI_SERVICE, wifiService);

WifiStateTracker 会创建 WifiMonitor 接收来自底层的事件,WifiService 和 WifiMonitor
是整个模块的核心。

WifiService 负责启动关闭 wpa_supplicant、启动关闭 WifiMonitor 监视线程

和把命令下发给 wpa_supplicant,而 WifiMonitor 则负责从 wpa_supplicant 接收事件通知。

连接 AP:

1. 使能 WIFI

WirelessSettings 在初始化的时候配置了由 WifiEnabler 来处理 Wifi 按钮,

当用户按下 Wifi 按钮后, Android 会调用 WifiEnabler 的 onPreferenceChange,

再由 WifiEnabler 调用 WifiManager 的 setWifiEnabled 接口函数,通过 AIDL,实际调用的是 WifiService 的

setWifiEnabled 函数,WifiService 接着向自身发送一条 MESSAGE_ENABLE_WIFI 消息,

在处理该消息的代码中做真正的使能工作:

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@Override

public void handleMessage(Message msg) {

switch (msg.what) {

case MESSAGE_ENABLE_WIFI:

setWifiEnabledBlocking(true, msg.arg1 == 1, msg.arg2);

if (mWifiWatchdogService == null) {

mWifiWatchdogService = new WifiWatchdogService(mContext, mWifiStateTracker);

}

sWakeLock.release();

break;

首先装载 WIFI 内核模块(该模块的位置硬编码为"/system/lib/modules/wlan.ko" ), 然后启动 wpa_supplicant

(配置文件硬编码为"/data/misc/wifi/wpa_supplicant.conf") 再通过 WifiStateTracker 来启动

WifiMonitor 中的监视线程。

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private boolean setWifiEnabledBlocking(boolean enable, boolean persist, int uid) {

...

setWifiEnabledState(enable ? WIFI_STATE_ENABLING : WIFI_STATE_DISABLING, uid);

if (enable) {

if (!mWifiStateTracker.loadDriver()) {

Slog.e(TAG, "Failed to load Wi-Fi driver.");

setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);

return false;

}

if (!mWifiStateTracker.startSupplicant()) {

mWifiStateTracker.unloadDriver();

Slog.e(TAG, "Failed to start supplicant daemon.");

setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);

return false;

}

registerForBroadcasts();

mWifiStateTracker.startEventLoop();

}

当使能成功后,会广播发送 WIFI_STATE_CHANGED_ACTION 这个 Intent 通知外界 WIFI 已经成功使能了

// Broadcast

final Intent intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);

intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);

mContext.sendStickyBroadcast(intent);

WifiEnabler 创建的时候就会向 Android 注册接收

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/**

* Registers to receive the necessary Wi-Fi broadcasts.

*/

private void registerForWifiBroadcasts() {

IntentFilter intentFilter = new IntentFilter();

intentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);

intentFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);

mContext.registerReceiver(mReceiver, intentFilter);

}

WIFI_STATE_CHANGED_ACTION,因此它会收到该 Intent,从而开始扫描。

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/**

* see {@link android.net.wifi.WifiManager#startScan()}

*/

public void startScan(boolean forceActive) {

enforceChangePermission();

if (mWifiHandler == null) return;

Message.obtain(mWifiHandler, MESSAGE_START_SCAN, forceActive ? 1 : 0, 0).sendToTarget();

}

2. 查找 AP

扫描的入口函数是 WifiService 的 startScan,它其实也就是往 wpa_supplicant 发送 SCAN 命令。

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static jboolean android_net_wifi_scanCommand(JNIEnv* env, jobject clazz, jboolean forceActive)

{

jboolean result;

// Ignore any error from setting the scan mode.

// The scan will still work.

if (forceActive && !sScanModeActive)

doSetScanMode(true);

result = doBooleanCommand("SCAN", "OK");

if (forceActive && !sScanModeActive)

doSetScanMode(sScanModeActive);

return result;

}

当 wpa_supplicant 处理完 SCAN 命令后,它会向控制通道发送事件通知扫描完成,从而wifi_wait_for_event 函数会接收到该事件,由此 WifiMonitor 中的 MonitorThread 会被执行来出来这个事件

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static jstring android_net_wifi_waitForEvent(JNIEnv* env, jobject clazz)

{

char buf[256];

int nread = ::wifi_wait_for_event(buf, sizeof buf);

if (nread > 0) {

return env->NewStringUTF(buf);

} else {

return env->NewStringUTF(NULL);

}

}

void handleEvent(int event, String remainder) {

case SCAN_RESULTS:

mWifiStateTracker.notifyScanResultsAvailable();

break;

WifiStateTracker 则接着广播发送 SCAN_RESULTS_AVAILABLE_ACTION 这个 Intent

case EVENT_SCAN_RESULTS_AVAILABLE:

mContext.sendBroadcast(new Intent(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));

WifiLayer 注册了接收 SCAN_RESULTS_AVAILABLE_ACTION 这个 Intent,所以它的相关

处理函数 handleScanResultsAvailable 会被调用,在该函数中,先会去拿到 SCAN 的结果

(最终是往 wpa_supplicant 发送 SCAN_RESULT 命令并读取返回值来实现的) ,

List<ScanResult> list = mWifiManager.getScanResults();

对每一个扫描返回的 AP,WifiLayer 会调用 WifiSettings 的 onAccessPointSetChanged 函数,

从而最终把该 AP 加到 GUI 显示列表中。

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public void onAccessPointSetChanged(AccessPointState ap, boolean added) {

AccessPointPreference pref = mAps.get(ap);

if (added) {

if (pref == null) {

pref = new AccessPointPreference(this, ap);

mAps.put(ap, pref);

} else {

pref.setEnabled(true);

}

mApCategory.addPreference(pref);

}

}

3. 配置 AP 参数

当用户在 WifiSettings 界面上选择了一个 AP 后,会显示配置 AP 参数的一个对话框,

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public boolean onPreferenceTreeClick(PreferenceScreen preferenceScreen, Preference

preference) {

if (preference instanceof AccessPointPreference) {

AccessPointState state=((AccessPointPreference)preference).getAccessPointState();

showAccessPointDialog(state, AccessPointDialog.MODE_INFO);

}

}

4. 连接

当用户在 AcessPointDialog 中选择好加密方式和输入密钥之后,再点击连接按钮,Android就会去连接这个 AP。

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private void handleConnect() {

String password = getEnteredPassword();

if (!TextUtils.isEmpty(password)) {

mState.setPassword(password);

}

mWifiLayer.connectToNetwork(mState);

}

WifiLayer 会先检测这个 AP 是不是之前被配置过,这个是通过向 wpa_supplicant 发送LIST_NETWORK 命令并且比较返回值来实现的,

// Need WifiConfiguration for the AP

WifiConfiguration config = findConfiguredNetwork(state);

如果 wpa_supplicant 没有这个 AP 的配置信息则会向 wpa_supplicant 发送 ADD_NETWORK 命令来添加该 AP,

if (config == null) {

// Connecting for the first time, need to create it

config = addConfiguration(state,ADD_CONFIGURATION_ENABLE|ADD_CONFIGURATION_SAVE);

}

ADD_NETWORK 命 令 会 返 回 一 个 ID , WifiLayer 再 用 这 个 返 回 的 ID 作 为 参 数 向

wpa_supplicant 发送 ENABLE_NETWORK 命令,从而让 wpa_supplicant 去连接该 AP。

// Make sure that network is enabled, and disable others

mReenableApsOnNetworkStateChange = true;

if (!mWifiManager.enableNetwork(state.networkId, true)) {

Log.e(TAG, "Could not enable network ID " + state.networkId);

error(R.string.error_connecting);

return false;

}

5. 配置 IP 地址

当 wpa_supplicant 成功连接上 AP 之后,它会向控制通道发送事件通知连接上 AP 了,从而

wifi_wait_for_event 函数会接收到该事件,由此 WifiMonitor 中的 MonitorThread 会被执行来

出来这个事件,

void handleEvent(int event, String remainder) {

case CONNECTED:

handleNetworkStateChange(NetworkInfo.DetailedState.CONNECTED,remainder);

break;

WifiMonitor 再调用 WifiStateTracker 的 notifyStateChange,WifiStateTracker 则接着会往自身

发送 EVENT_DHCP_START 消息来启动 DHCP 去获取 IP 地址,

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private void handleConnectedState() {

setPollTimer();

mLastSignalLevel = -1;

if (!mHaveIPAddress && !mObtainingIPAddress) {

mObtainingIPAddress = true;

mDhcpTarget.obtainMessage(EVENT_DHCP_START).sendToTarget();

}

}

然后再广播发送 NETWORK_STATE_CHANGED_ACTION 这个 Intent

case EVENT_NETWORK_STATE_CHANGED:

if (result.state != DetailedState.DISCONNECTED || !mDisconnectPending) {

intent = new Intent(WifiManager.NETWORK_STATE_CHANGED_ACTION);

intent.putExtra(WifiManager.EXTRA_NETWORK_INFO,mNetworkInfo);

if (result.BSSID != null)

intent.putExtra(WifiManager.EXTRA_BSSID,
result.BSSID);

mContext.sendStickyBroadcast(intent);

}

break;

WifiLayer 注册了接收 NETWORK_STATE_CHANGED_ACTION 这个 Intent,所以它的相关处理函数 handleNetworkStateChanged 会被调用,

当 DHCP 拿到 IP 地址之后,会再发送 EVENT_DHCP_SUCCEEDED 消息,

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private class DhcpHandler extends Handler {

public void handleMessage(Message msg) {

switch (msg.what) {

case EVENT_DHCP_START:

if (NetworkUtils.runDhcp(mInterfaceName, mDhcpInfo)) {

event = EVENT_DHCP_SUCCEEDED;

}

WifiLayer 处 理 EVENT_DHCP_SUCCEEDED 消息 , 会再次广播发送NETWORK_STATE_CHANGED_ACTION 这个 Intent,这次带上完整的 IP 地址信息。

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case EVENT_DHCP_SUCCEEDED:

mWifiInfo.setIpAddress(mDhcpInfo.ipAddress);

setDetailedState(DetailedState.CONNECTED);

intent =new Intent(WifiManager.NETWORK_STATE_CHANGED_ACTION);

intent.putExtra(WifiManager.EXTRA_NETWORK_INFO, mNetworkInfo);

mContext.sendStickyBroadcast(intent);

break;

至此为止,整个连接过程完成。