作者：mznewfacer 时间：2012年12月7日
在上一回我们一块分析了WifiDisplay有关设备发现的部分，这一回将主要针对设备连接和建立数据流展开分析。
首先，回顾下应用层，当用户在搜寻完设备后，可以选择设备进行连接，当然正在进行连接或已经连接配对的设备，再次点击配置后，会弹出对话框供用户选择断开连接。
packages/apps/Settings/src/com/android/settings/wfd/WifiDisplaySettings.java
public boolean onPreferenceTreeClick(PreferenceScreen preferenceScreen,
Preference preference) {
if (preference instanceof WifiDisplayPreference) {
WifiDisplayPreference p = (WifiDisplayPreference)preference;
WifiDisplay display = p.getDisplay();
if (display.equals(mWifiDisplayStatus.getActiveDisplay())) {
showDisconnectDialog(display);
} else {
mDisplayManager.connectWifiDisplay(display.getDeviceAddress());
}
}
return super.onPreferenceTreeClick(preferenceScreen, preference);
}如同设备发现的调用流程，当用户选择设备进行连接后，程序会调用DisplayManager的connectWifiDisplay()函数接口。该函数会进一步根据DisplayManagerGlobal提供的单实例对象调用AIDL提供的接口函数connectWifiDisplay()，这又是上一回已经提到过的调用模式。其实际的调用实现是Displaymanager service中提供的connectWifiDisplay()函数，
frameworks/base/services/java/com/android/server/display/DisplayManagerService.java
public void connectWifiDisplay(String address) {
if (address == null) {
throw new IllegalArgumentException("address must not be null");
}
final boolean trusted = canCallerConfigureWifiDisplay();
final long token = Binder.clearCallingIdentity();
try {
synchronized (mSyncRoot) {
if (mWifiDisplayAdapter != null) {
mWifiDisplayAdapter.requestConnectLocked(address, trusted);
}
}
} finally {
Binder.restoreCallingIdentity(token);
}
}
到此，我们容易发现连接WifiDisplay设备的函数调用流程与发现设备的流程一致，这里将不做多余解释（详见），在此会罗列出之后的基本流程。
frameworks/base/services/java/com/android/server/display/WifiDisplayAdapter.java
public void requestConnectLocked(final String address, final boolean trusted) {
if (DEBUG) {
Slog.d(TAG, "requestConnectLocked: address=" + address + ", trusted=" + trusted);
}
if (!trusted) {
synchronized (getSyncRoot()) {
if (!isRememberedDisplayLocked(address)) { //如果设备地址不在保存列表中则忽略不做处理
...
return;
}
}
}
getHandler().post(new Runnable() {
@Override
public void run() {
if (mDisplayController != null) {
mDisplayController.requestConnect(address);
}
}
});
}
frameworks/base/services/java/com/android/server/display/WifiDisplayController.java
public void requestConnect(String address) {
for (WifiP2pDevice device : mAvailableWifiDisplayPeers) {
if (device.deviceAddress.equals(address)) {
connect(device);
}
}
}
private void connect(final WifiP2pDevice device) {
if (mDesiredDevice != null
&& !mDesiredDevice.deviceAddress.equals(device.deviceAddress)) { //如果设备已经正在连接则返回
if (DEBUG) {
...
}
return;
}
if (mConnectedDevice != null
&& !mConnectedDevice.deviceAddress.equals(device.deviceAddress)
&& mDesiredDevice == null) {//如果设备已经连接则返回
if (DEBUG) {
...
}
return;
}
mDesiredDevice = device;
mConnectionRetriesLeft = CONNECT_MAX_RETRIES; //尝试连接最大次数
updateConnection();
}
接下来，我们将重点看一看updateConnection()函数，此函数是建立Wifidisplay连接，监听RTSP连接的核心实现函数。
private void updateConnection() {
//在尝试连接到新设备时，需要通知系统这里已经与旧的设备断开连接
if (mRemoteDisplay != null && mConnectedDevice != mDesiredDevice) {
...
mRemoteDisplay.dispose(); //释放NativeRemoteDisplay资源停止监听
mRemoteDisplay = null; //监听返回对象置为空
mRemoteDisplayInterface = null; //监听端口置为空
mRemoteDisplayConnected = false; //连接标识为未连接
mHandler.removeCallbacks(mRtspTimeout);//将挂起的mRtspTimeout线程从消息队列中移除
setRemoteSubmixOn(false); //关闭远程混音重建模式
unadvertiseDisplay();
}
if (mConnectedDevice != null && mConnectedDevice != mDesiredDevice) {
...
unadvertiseDisplay();
final WifiP2pDevice oldDevice = mConnectedDevice;
mWifiP2pManager.removeGroup(mWifiP2pChannel, new ActionListener() {
@Override
public void onSuccess() {
...
next();
}
@Override
public void onFailure(int reason) {
...
next();
}
private void next() {
if (mConnectedDevice == oldDevice) { //确保连接设备已经不是旧的设备否则递归调用该函数
mConnectedDevice = null;
updateConnection();
}
}
});
return;
}
if (mConnectingDevice != null && mConnectingDevice != mDesiredDevice) {
...
unadvertiseDisplay();
mHandler.removeCallbacks(mConnectionTimeout);
final WifiP2pDevice oldDevice = mConnectingDevice;
mWifiP2pManager.cancelConnect(mWifiP2pChannel, new ActionListener() { //在尝试连接到新设备之前，取消正在进行的p2p连接
@Override
public void onSuccess() {
...
next();
}
@Override
public void onFailure(int reason) {
...
next();
}
private void next() {
if (mConnectingDevice == oldDevice) {
mConnectingDevice = null;
updateConnection();
}
}
});
return;
}
// 如果想断开连接，则任务结束
if (mDesiredDevice == null) {
unadvertiseDisplay();
return;
}
if (mConnectedDevice == null && mConnectingDevice == null) {
Slog.i(TAG, "Connecting to Wifi display: " + mDesiredDevice.deviceName);
mConnectingDevice = mDesiredDevice;
WifiP2pConfig config = new WifiP2pConfig();
config.deviceAddress = mConnectingDevice.deviceAddress;
config.groupOwnerIntent = WifiP2pConfig.MIN_GROUP_OWNER_INTENT;
WifiDisplay display = createWifiDisplay(mConnectingDevice);
advertiseDisplay(display, null, 0, 0, 0);
final WifiP2pDevice newDevice = mDesiredDevice;
mWifiP2pManager.connect(mWifiP2pChannel, config, new ActionListener() {
//以特定的配置信息开启P2P连接，如果当前设备不是P2P组的一部分，会建立P2P小组并发起连接请求；如果当前设备是现存P2P组的一部分，则加入该组的邀请会发送至该配对设备。
@Override
public void onSuccess() {
//为了防止连接还没有建立成功，这里设定了等待处理函数，如果在定长时间内还没有接受到WIFI_P2P_CONNECTION_CHANGED_ACTION广播，则按照handleConnectionFailure（true）处理。
Slog.i(TAG, "Initiated connection to Wifi display: " + newDevice.deviceName);
mHandler.postDelayed(mConnectionTimeout, CONNECTION_TIMEOUT_SECONDS * 1000);
}
@Override
public void onFailure(int reason) {
if (mConnectingDevice == newDevice) {
Slog.i(TAG, "Failed to initiate connection to Wifi display: "
+ newDevice.deviceName + ", reason=" + reason);
mConnectingDevice = null;
handleConnectionFailure(false);
}
}
});
return;
}
// 根据连接的网络地址和端口号监听Rtsp流连接
if (mConnectedDevice != null && mRemoteDisplay == null) {
Inet4Address addr = getInterfaceAddress(mConnectedDeviceGroupInfo);
if (addr == null) {
Slog.i(TAG, "Failed to get local interface address for communicating "
+ "with Wifi display: " + mConnectedDevice.deviceName);
handleConnectionFailure(false);
return; // done
}
setRemoteSubmixOn(true);
final WifiP2pDevice oldDevice = mConnectedDevice;
final int port = getPortNumber(mConnectedDevice);
final String iface = addr.getHostAddress() + ":" + port;
mRemoteDisplayInterface = iface;
Slog.i(TAG, "Listening for RTSP connection on " + iface
+ " from Wifi display: " + mConnectedDevice.deviceName);
mRemoteDisplay = RemoteDisplay.listen(iface, new RemoteDisplay.Listener() {
//开始监听连接上的接口
@Override
public void onDisplayConnected(Surface surface,
int width, int height, int flags) {
if (mConnectedDevice == oldDevice && !mRemoteDisplayConnected) {
Slog.i(TAG, "Opened RTSP connection with Wifi display: "
+ mConnectedDevice.deviceName);
mRemoteDisplayConnected = true;
mHandler.removeCallbacks(mRtspTimeout);
final WifiDisplay display = createWifiDisplay(mConnectedDevice);
advertiseDisplay(display, surface, width, height, flags);
}
}
@Override
public void onDisplayDisconnected() {
if (mConnectedDevice == oldDevice) {
Slog.i(TAG, "Closed RTSP connection with Wifi display: "
+ mConnectedDevice.deviceName);
mHandler.removeCallbacks(mRtspTimeout);
disconnect();
}
}
@Override
public void onDisplayError(int error) {
if (mConnectedDevice == oldDevice) {
Slog.i(TAG, "Lost RTSP connection with Wifi display due to error "
+ error + ": " + mConnectedDevice.deviceName);
mHandler.removeCallbacks(mRtspTimeout);
handleConnectionFailure(false);
}
}
}, mHandler);
mHandler.postDelayed(mRtspTimeout, RTSP_TIMEOUT_SECONDS * 1000);
}
}
至此，我们已经了解了建立WifiDisplay连接的基本流程，当然可以继续向底层深入，只要用户选择尝试连接并且已经确认处于连接断开的状态，则会调用WifiP2pManager中的connect()接口函数，该函数会向Channel中发送CONNECT信号，并注册监听器监听相应结果。在进入P2pStateMachine状态机后，WifiP2pService会分为两种情况进行处理。如果当前的设备不是P2P组的成员，WifiP2pService会调用WifiNative类中的p2pConnect()函数，该函数会继续向底层调用，最终会调用wifi.cwifi_send_command()命令，把groupnegotiation请求发送至wpa_supplicant供其处理；如果这个设备已经是P2P组的成员，或者自己通过WifiNative类中的p2pGroupAdd()函数创建了一个组，那么会进入GroupCreatedState，进一步会调用WifiNative类中的p2pInvite()函数向设备发送邀请请求。具体的有关wpa_supplicant同底层驱动的交互，以及wpa_supplicant同WifiMonitor与WifiP2pService状态机之间的调用流程以后有机会再讨论。
在本文的最后，还想继续讨论一下监听RTSP连接的核心实现函数RemoteDisplay.listen(...)，
frameworks/base/media/java/android/media/RemoteDisplay.java
public static RemoteDisplay listen(String iface, Listener listener, Handler handler) {
...
RemoteDisplay display = new RemoteDisplay(listener, handler);
display.startListening(iface);
return display;
}
可以看到该监听函数会调用以下函数，并把监听端口作为参数进行传递，
private void startListening(String iface) {
mPtr = nativeListen(iface);
if (mPtr == 0) {
throw new IllegalStateException("Could not start listening for "
+ "remote display connection on \"" + iface + "\"");
}
mGuard.open("dispose");
}以上函数最终会调用JNI层的接口函数nativeListen()进行监听。至于CloseGuardmGuard.open()，不理解的话，我们就把它看作是Android提供的一种资源清理机制。
接下来，可以具体看一下RemoteDisplay在JNI层的接口实现，
frameworks/base/core/jni/android_media_RemoteDisplay.cpp
static jint nativeListen(JNIEnv* env, jobject remoteDisplayObj, jstring ifaceStr) {
ScopedUtfChars iface(env, ifaceStr); //通过智能指针的方式将string类型转化为只读的UTF chars类型
sp<IServiceManager> sm = defaultServiceManager();
sp<IMediaPlayerService> service = interface_cast<IMediaPlayerService>(
sm->getService(String16("media.player")));
//用service manager获得 media player服务的代理实例，即通过interface_cast将其转化成BpMediaPlayerService （Bridge模式）
if (service == NULL) {
ALOGE("Could not obtain IMediaPlayerService from service manager");
return 0;
}
sp<NativeRemoteDisplayClient> client(new NativeRemoteDisplayClient(env, remoteDisplayObj));
sp<IRemoteDisplay> display = service->listenForRemoteDisplay(
client, String8(iface.c_str()));
//调用BpMediaPlayerService提供的接口函数，与服务端BnMediaPlayerService进行通讯
if (display == NULL) {
ALOGE("Media player service rejected request to listen for remote display '%s'.",
iface.c_str());
return 0;
}
NativeRemoteDisplay* wrapper = new NativeRemoteDisplay(display, client);
return reinterpret_cast<jint>(wrapper);
}
这里采用了Binder通信机制，BpMediaPlayerService继承BpInterface<IMediaPlayerService>作为代理端，采用Bridge模式调用listenForRemoteDisplay()接口函数将上层的监听接口以及实例化的NativeRemoteDisplayClient代理对象传递至服务端BnMediaPlayerService进行处理。
/frameworks/av/media/libmedia/IMediaPlayerService.cpp
class BpMediaPlayerService: public BpInterface<IMediaPlayerService>
{
public:
…
virtual sp<IRemoteDisplay> listenForRemoteDisplay(const sp<IRemoteDisplayClient>& client,
const String8& iface)
{
Parcel data, reply;
data.writeInterfaceToken(IMediaPlayerService::getInterfaceDescriptor());
data.writeStrongBinder(client->asBinder());
data.writeString8(iface);
remote()->transact(LISTEN_FOR_REMOTE_DISPLAY, data, &reply); //向服务端BnMediaPlayerService发送LISTEN_FOR_REMOTE_DISPLAY 处理命令
return interface_cast<IRemoteDisplay>(reply.readStrongBinder());
}
};
进一步可以看到，NativeRemoteDisplayClient继承于BnRemoteDisplayClient，其实这是IRemoteDisplayClient接口的服务端实现。该类提供了三个接口函数onDisplayConnected()、onDisplayDisconnected()、onDisplayError()是frameworks/base/media/java/android/media/RemoteDisplay.java中RemoteDisplay.Listener{}的三个监听函数在JNI层的实现，特别的，对于onDisplayConnected()函数而言，调用android_view_Surface_createFromISurfaceTexture()函数创建surfaceObj并将其向RemoteDisplay中注册的监听线程传递并进行回调。
frameworks/base/core/jni/android_media_RemoteDisplay.cpp
virtual void onDisplayConnected(const sp<ISurfaceTexture>& surfaceTexture,
uint32_t width, uint32_t height, uint32_t flags) {
JNIEnv* env = AndroidRuntime::getJNIEnv();
jobject surfaceObj = android_view_Surface_createFromISurfaceTexture(env, surfaceTexture);
//跟据当前获取的media server的surface texture来创建Surface对象
if (surfaceObj == NULL) {
...
return;
}
env->CallVoidMethod(mRemoteDisplayObjGlobal,
gRemoteDisplayClassInfo.notifyDisplayConnected,
surfaceObj, width, height, flags); //将Suface对象作为参数传递至notifyDisplayConnected函数用于监听函数的回调
env->DeleteLocalRef(surfaceObj);
checkAndClearExceptionFromCallback(env, "notifyDisplayConnected");
}接下来，我们继续来看服务端BnMediaPlayerService的实现，其中onTransact函数用于接收来自BpMediaPlayerService发送的命令，如果命令为LISTEN_FOR_REMOTE_DISPLAY，则会读取相应数据并作为参数进行传递。这里的listenForRemoteDisplay()函数是纯虚函数，其实现是由派生类MediaPlayerService来完成的。
status_t BnMediaPlayerService::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
switch (code) {
…
case LISTEN_FOR_REMOTE_DISPLAY: {
CHECK_INTERFACE(IMediaPlayerService, data, reply);
sp<IRemoteDisplayClient> client(
interface_cast<IRemoteDisplayClient>(data.readStrongBinder()));
String8 iface(data.readString8());
sp<IRemoteDisplay> display(listenForRemoteDisplay(client, iface));//调用纯虚函数接口，运行时实际调用派生类MediaPlayerService的函数实现
reply->writeStrongBinder(display->asBinder());
return NO_ERROR;
} break;
default:
return BBinder::onTransact(code, data, reply, flags);
}
}
最后，来看一看该函数的实际实现，
frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp
sp<IRemoteDisplay> MediaPlayerService::listenForRemoteDisplay(
const sp<IRemoteDisplayClient>& client, const String8& iface) {
if (!checkPermission("android.permission.CONTROL_WIFI_DISPLAY")) {
//检查是否有WIFI Display权限
return NULL;
}
return new RemoteDisplay(client, iface.string()); //直接调用 RemoteDisplay构造函数来开启Wifi display source端
}
其中，RemoteDisplay继承于BnRemoteDisplay，也采取了Binder通信机制,代理端BpRemoteDisplay与服务端BnRemoteDisplay的接口实现详见frameworks/av/media/libmedia/IRemoteDisplay.cpp。这里，值得一提的是，函数listenForRemoteDisplay()假设在同一时刻连接到指定网络端口iface的remotedisplay设备最多只有一个。换句话说，在同一时刻只有一个设备能作为WifiDisplay source端设备进行播放。
最后，我们来看一看开启Wifidisplay source端的这个构造函数，
frameworks/av/media/libmediaplayerservice/RemoteDisplay.cpp
RemoteDisplay::RemoteDisplay(
const sp<IRemoteDisplayClient> &client, const char *iface)
: mLooper(new ALooper),
mNetSession(new ANetworkSession),
mSource(new WifiDisplaySource(mNetSession, client)) {
mLooper->setName("wfd_looper");
mLooper->registerHandler(mSource); //注册了Wifi display 处理线程
mNetSession->start(); //初始化数据管道，启动NetworkThread线程，进入threadLoop中监听数据流变化等待处理
mLooper->start(); //开启消息处理管理线程
mSource->start(iface); //将网络端口作为消息载体进行传递处理，并等待响应结果，完成与Wifi Display source端开启播放的相关工作
}
其中mLooper,mNetSession, mSource分别为sp<ALooper>mLooper，sp<ANetworkSession>mNetSession以及sp<WifiDisplaySource>mSource等三个强指针，对强指针概念不清的请见此。此处是利用构造函数的初始化列表将这三个强指针指向这三个new出来的对象。之后便是利用这三个指针，调用类中的方法以开启Wifidisplay source端进行播放。这里，ALooper是关于线程以及消息队列等待处理管理相关的一个类。ANetworkSessions是管理所有与数据报文和数据流相关socket的一个单线程帮助类。在此处，该类负责管理与WifiDisplay播放相关的socket，其中相关的数据传递和消息返回通过AMessage类对象和方法进行。WifiDisplaySource光看命名就知道，其主要负责WifiDisplaysource端的开启关闭，以及与其相关的建立Rtsp服务器，管理所有支持的协议连接、数据流传递以及各个状态之间转换处理等内容。此外，该类还定义了关闭WifiDisplay source端，停止相关线程、关闭socket以及释放资源等内容。
至此，有关WifiDisplay设备连接和建立数据流的流程已经交代清楚了，可以看到应用层建立的连接是与source端相关的。Sink端的主程序在frameworks/av/media/libstagefright/wifi-display/wfd.cpp中，与sink端实现相关的程序在frameworks/av/media/libstagefright/wifi-display/sink目录下面。关于source如何建立rtsp连接，开始通信，各个状态之间的转换以及与sink端的交互将在下回介绍。
