Android WifiDisplay分析二:Wifi display连接过程

这一章中我们来看Wifi Display连接过程的建立,包含P2P的部分和RTSP的部分,首先来大致看一下Wifi Display规范相关的东西。

Android WifiDisplay分析二:Wifi display连接过程_第1张图片


HIDC: Human Interface Device Class  (遵循HID标准的设备类)
UIBC: User Input Back Channel  (UIBC分为两种,一种是Generic,包含鼠标、键盘等;另一种是HIDC,HID是一个规范,只有遵循HID的标准,都可以叫做HID设备,包含USB鼠标、键盘、蓝牙、红外等)
PES: Packetized Elementary Stream (数字电视基本码流)
HDCP: High-bandwidth Digital Content Protection  (加密方式,用于加密传输的MPEG2-TS流)
MPEG2-TS: Moving Picture Experts Group 2 Transport Stream   (Wifi display之间传输的是MPEG2-TS流)
RTSP: Real-Time Streaming Protocol     (Wifi display通过RTSP协议来交互两边的能力)
RTP: Real-time Transport Protocol        (Wifi display通过RTP来传输MPEG2-TS流)
Wi-Fi P2P: Wi-Fi Direct
TDLS: Tunneled Direct Link Setup        (另一种方式建立两台设备之间的直连,与P2P类似,但要借助一台AP)


另一种比较重要的概念是在Wifi Display中分为Source和Sink两种角色,如下图。Source是用于encode并输出TS流;Sink用于decode并显示TS流。相当于Server/Client架构中,Source就是Server,用于提供服务;Sink就是Client。当然,我们这篇文章主要介绍在Android上Wifi display Source的流程。

Android WifiDisplay分析二:Wifi display连接过程_第2张图片


从上面的架构图我们可以看到,Wifi display是建立在TCP/UDP上面的应用层协议,L2链路层是通过P2P和TDLS两种方式建立,TDLS是optional的。在L2层建立连接后,Source就会在一个特定的port上listen,等待client的TCP连接。当与Client建立了TCP连接后,就会有M1~M7七个消息的交互,用户获取对方设备的能力,包括视频编码能力、Audio输出能力、是否支持HDCP加密等等。在获取这些能力之后,Source就会选择一种视频编码格式以及Audio格式用于这次会话当中。当一个RTSP会话建立后,双方就会决定出用于传输TS流的RTP port,RTP协议是基于UDP的。当这些都准备好后,Sink设备就会发送M7消息,也就是Play给Source,双方就可以开始传输数据了。

关于M1~M7是什么,我们后面再来介绍。首先我们来介绍在Android WifiDisplay中如何建立P2P的连接。


WifiDisplay之P2P的建立


通过我们之间关于Wifi display的service启动以及enable的分析,我们知道当扫描到可用的设备后,就会显示在WifiDisplaySettings这个页面上,当我们选择其中一个后,就会开始P2P的建立了,首先到WifiDisplaySettings中的代码分析:
    private void pairWifiDisplay(WifiDisplay display) {
        if (display.canConnect()) {
            mDisplayManager.connectWifiDisplay(display.getDeviceAddress());
        }
    }

WifiDisplaySettings通过AIDL调用到DisplayManagerService的connectWifiDisplay方法,关于AIDL的调用过程这里不讲了,直接到DisplayManagerService的connectWifiDisplay方法来看:
    public void connectWifiDisplay(String address) {
        if (address == null) {
            throw new IllegalArgumentException("address must not be null");
        }
        mContext.enforceCallingOrSelfPermission(Manifest.permission.CONFIGURE_WIFI_DISPLAY,
                "Permission required to connect to a wifi display");

        final long token = Binder.clearCallingIdentity();
        try {
            synchronized (mSyncRoot) {
                if (mWifiDisplayAdapter != null) {
                    mWifiDisplayAdapter.requestConnectLocked(address);
                }
            }
        } finally {
            Binder.restoreCallingIdentity(token);
        }
    }

首先做参数的检查,即MAC地址不能为空,然后做权限检查,调用这个方法的application必须要在manifest中声明有CONFIGURE_WIFI_DISPLAY权限,最后直接调用WifiDisplayAdapter的requestConnectLocked方法:
    public void requestConnectLocked(final String address) {
        if (DEBUG) {
            Slog.d(TAG, "requestConnectLocked: address=" + address);
        }

        getHandler().post(new Runnable() {
            @Override
            public void run() {
                if (mDisplayController != null) {
                    mDisplayController.requestConnect(address);
                }
            }
        });
    }

这里比较简单,直接调用WifiDisplayController的requestConnect方法。前面都是直接的调用,最终做事情的还是WifiDisplayController。
    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)) {
            if (DEBUG) {
                Slog.d(TAG, "connect: nothing to do, already connecting to "
                        + describeWifiP2pDevice(device));
            }
            return;
        }

        if (mConnectedDevice != null
                && !mConnectedDevice.deviceAddress.equals(device.deviceAddress)
                && mDesiredDevice == null) {
            if (DEBUG) {
                Slog.d(TAG, "connect: nothing to do, already connected to "
                        + describeWifiP2pDevice(device) + " and not part way through "
                        + "connecting to a different device.");
            }
            return;
        }

        if (!mWfdEnabled) {
            Slog.i(TAG, "Ignoring request to connect to Wifi display because the "
                    +" feature is currently disabled: " + device.deviceName);
            return;
        }

        mDesiredDevice = device;
        mConnectionRetriesLeft = CONNECT_MAX_RETRIES;
        updateConnection();
    }

requestConnect先从mAvaiableWifiDsiplayPeers中通过Mac地址找到所有连接的WifiP2pDevice,然后调用connect方法,在connect方法中会做一系列的判断,看首先是否有正在连接中或者断开中的设备,如果有就直接返回;再看有没有已经连接上的设备,如果有,也直接返回,然后赋值mDesiredDevice为这次要连接的设备,最后调用updateConnection来更新连接状态并发起连接。updateConnection的代码比较长,我们分段来分析:
    private void updateConnection() {
	//更新是否需要scan或者停止scan
        updateScanState();

	//如果有已经连接上的RemoteDisplay,先断开。这里先不看
        if (mRemoteDisplay != null && mConnectedDevice != mDesiredDevice) {
            
        }

        // 接上面的一步,段开这个group
        if (mDisconnectingDevice != null) {
            return; // wait for asynchronous callback
        }
        if (mConnectedDevice != null && mConnectedDevice != mDesiredDevice) {

        }

        // 如果有正在连接的设备,先停止连接之前的设备
        if (mCancelingDevice != null) {
            return; // wait for asynchronous callback
        }
        if (mConnectingDevice != null && mConnectingDevice != mDesiredDevice) {
            
        }

        // 当断开之前的连接或者启动匿名GROUP时,这里就结束了
        if (mDesiredDevice == null) {

        }

        // 开始连接,这是我们要看的重点
        if (mConnectedDevice == null && mConnectingDevice == null) {
            Slog.i(TAG, "Connecting to Wifi display: " + mDesiredDevice.deviceName);

            mConnectingDevice = mDesiredDevice;
            WifiP2pConfig config = new WifiP2pConfig();
            WpsInfo wps = new WpsInfo();
            if (mWifiDisplayWpsConfig != WpsInfo.INVALID) {
                wps.setup = mWifiDisplayWpsConfig;
            } else if (mConnectingDevice.wpsPbcSupported()) {
                wps.setup = WpsInfo.PBC;
            } else if (mConnectingDevice.wpsDisplaySupported()) {
                wps.setup = WpsInfo.KEYPAD;
            } else {
                wps.setup = WpsInfo.DISPLAY;
            }
            config.wps = wps;
            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() {
                @Override
                public void onSuccess() {
                    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; 
        }   

这段函数比较长,我们先看我们需要的,剩下的后面再来分析。首先赋值给mConnectingDevice表示当前正在连接的设备,然后构造一个WifiP2pConfig对象,这个对象包含这次连接的设备的Mac地址、wps方式以及我们自己的GROUP_OWNER intent值,然后调用advertieseDisplay方法来通知WifiDisplayAdapter相关状态的改变,WifiDisplayAdapter会发送相应的broadcast出来,这是WifiDisplaySettings可以接收这些broadcast,然后在UI上更新相应的状态。关于advertieseDisplay的实现,我们后面再来分析。

接着看updateConnection,调用WifiP2pManager的connect方法去实现两台设备的P2P连接,具体过程可以参考前面介绍的P2P连接的文章。这里的onSuccess()并不是表示P2P已经建立成功,而只是表示这个发送命令到wpa_supplicant成功,所以在这里设置了一个连接超时的timeout,为30秒。当连接成功后,会发送WIFI_P2P_CONNECTION_CHANGED_ACTION的广播出来,接着回到WifiDisplayController看如何处理连接成功的broadcast:
            } else if (action.equals(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION)) {
                NetworkInfo networkInfo = (NetworkInfo)intent.getParcelableExtra(
                        WifiP2pManager.EXTRA_NETWORK_INFO);
                if (DEBUG) {
                    Slog.d(TAG, "Received WIFI_P2P_CONNECTION_CHANGED_ACTION: networkInfo="
                            + networkInfo);
                }

                handleConnectionChanged(networkInfo);

    private void handleConnectionChanged(NetworkInfo networkInfo) {
        mNetworkInfo = networkInfo;
        if (mWfdEnabled && networkInfo.isConnected()) {
            if (mDesiredDevice != null || mWifiDisplayCertMode) {
                mWifiP2pManager.requestGroupInfo(mWifiP2pChannel, new GroupInfoListener() {
                    @Override
                    public void onGroupInfoAvailable(WifiP2pGroup info) {
                        if (DEBUG) {
                            Slog.d(TAG, "Received group info: " + describeWifiP2pGroup(info));
                        }

                        if (mConnectingDevice != null && !info.contains(mConnectingDevice)) {
                            Slog.i(TAG, "Aborting connection to Wifi display because "
                                    + "the current P2P group does not contain the device "
                                    + "we expected to find: " + mConnectingDevice.deviceName
                                    + ", group info was: " + describeWifiP2pGroup(info));
                            handleConnectionFailure(false);
                            return;
                        }

                        if (mDesiredDevice != null && !info.contains(mDesiredDevice)) {
                            disconnect();
                            return;
                        }

                        if (mConnectingDevice != null && mConnectingDevice == mDesiredDevice) {
                            Slog.i(TAG, "Connected to Wifi display: "
                                    + mConnectingDevice.deviceName);

                            mHandler.removeCallbacks(mConnectionTimeout);
                            mConnectedDeviceGroupInfo = info;
                            mConnectedDevice = mConnectingDevice;
                            mConnectingDevice = null;
                            updateConnection();
                        }
                    }
                });
            }
        }

当WifiDisplayController收到WIFI_P2P_CONNECTION_CHANGED_ACTION广播后,会调用handleConnectionChanged来获取当前P2P Group相关的信息,如果获取到的P2P Group信息里面没有mConnectingDevice或者mDesiredDevice的信息,则表示连接出错了,直接退出。如果当前连接信息与前面设置的mConnectingDevice一直,则表示连接P2P成功,这里首先会移除前面设置的连接timeout的callback,然后设置mConnectedDevice为当前连接的设备,并设置mConnectingDevice为空,最后调用updateConnection来更新连接状态信息。我们又回到updateConnection这个函数了,但这次进入的分支与之前连接请求的分支又不同了,我们来看代码:
   private void updateConnection() {
        // 更新是否需要scan或者停止scan
        updateScanState();

        // 如果有连接上的RemoteDisplay,这里先断开
        if (mRemoteDisplay != null && mConnectedDevice != mDesiredDevice) {

        }

        // 接着上面的一步,先断开之前连接的设备
        if (mDisconnectingDevice != null) {
            return; // wait for asynchronous callback
        }
        if (mConnectedDevice != null && mConnectedDevice != mDesiredDevice) {
  
        }

        // 如果有正在连接的设备,先断开之前连接的设备
        if (mCancelingDevice != null) {
            return; // wait for asynchronous callback
        }
        if (mConnectingDevice != null && mConnectingDevice != mDesiredDevice) {
 
        }

        // 当断开之前的连接或者匿名GO时,这里就结束了
        if (mDesiredDevice == null) {

        }

        // 如果有连接请求,则进入此
        if (mConnectedDevice == null && mConnectingDevice == null) {

        }

        // 当连接上P2P后,就进入到此
        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
            }

            mWifiP2pManager.setMiracastMode(WifiP2pManager.MIRACAST_SOURCE);

            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() {
                @Override
                public void onDisplayConnected(Surface surface,
                        int width, int height, int flags, int session) {
                    if (mConnectedDevice == oldDevice && !mRemoteDisplayConnected) {
                        Slog.i(TAG, "Opened RTSP connection with Wifi display: "
                                + mConnectedDevice.deviceName);
                        mRemoteDisplayConnected = true;
                        mHandler.removeCallbacks(mRtspTimeout);

                        if (mWifiDisplayCertMode) {
                            mListener.onDisplaySessionInfo(
                                    getSessionInfo(mConnectedDeviceGroupInfo, session));
                        }

                        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);

            // Use extended timeout value for certification, as some tests require user inputs
            int rtspTimeout = mWifiDisplayCertMode ?
                    RTSP_TIMEOUT_SECONDS_CERT_MODE : RTSP_TIMEOUT_SECONDS;

            mHandler.postDelayed(mRtspTimeout, rtspTimeout * 1000);
        }
    }

到这里P2P的连接就算建立成功了,接下来就是RTSP的部分了

WifiDisplay之RTSP server的创建

这里首先设置MiracastMode,博主认为这部分应该放在enable WifiDisplay时,不知道Google为什么放在这里? 然后从GroupInfo中取出对方设备的IP地址,利用默认的CONTROL PORT构建mRemoteDisplayInterface,接着调用RemoteDisplay的listen方法去listen指定的IP和端口上面的TCP连接请求。最后会设置Rtsp的连接请求的timeout,当用于Miracast认证时是120秒,正常的使用中是30秒,如果在这么长的时间内没有收到Sink的TCP请求,则表示失败了。下面来看RemoteDisplay的listen的实现:
    public static RemoteDisplay listen(String iface, Listener listener, Handler handler) {
        if (iface == null) {
            throw new IllegalArgumentException("iface must not be null");
        }
        if (listener == null) {
            throw new IllegalArgumentException("listener must not be null");
        }
        if (handler == null) {
            throw new IllegalArgumentException("handler must not be null");
        }

        RemoteDisplay display = new RemoteDisplay(listener, handler);
        display.startListening(iface);
        return display;
    }

这里首先进行参数的检查,然后创建一个RemoteDisplay对象(这里不能直接创建RemoteDisplay对象,因为它的构造函数是private的),接着调用RemoteDisplay的startListening方法:
    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");
    }

nativeListen会调用JNI中的实现,相关代码在android_media_RemoteDisplay.cpp中。注意上面的mGuard是CloseGuard对象,是一种用于显示释放一些资源的机制。
static jint nativeListen(JNIEnv* env, jobject remoteDisplayObj, jstring ifaceStr) {
    ScopedUtfChars iface(env, ifaceStr);

    sp<IServiceManager> sm = defaultServiceManager();
    sp<IMediaPlayerService> service = interface_cast<IMediaPlayerService>(
            sm->getService(String16("media.player")));
    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()));
    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);
}

上面的代码中先从ServiceManager中获取MediaPlayerService的Bpbinder引用,然后由传入的第二个参数remoteDisplayObj,也就是RemoteDisplay对象构造一个NativeRemoteDisplayClient,在framework中,我们经常看到像这样的用法,类似于设计模式中的包装模式,例如在framework中对Java层的BnBinder也是做了一层封装JavaBBinder。在NativeRemoteDisplayClient中通过JNI的反向调用,就可以直接回调RemoteDisplay中的一些函数,实现回调方法了,下面来看它的实现:
class NativeRemoteDisplayClient : public BnRemoteDisplayClient {
public:
    NativeRemoteDisplayClient(JNIEnv* env, jobject remoteDisplayObj) :
            mRemoteDisplayObjGlobal(env->NewGlobalRef(remoteDisplayObj)) {
    }

protected:
    ~NativeRemoteDisplayClient() {
        JNIEnv* env = AndroidRuntime::getJNIEnv();
        env->DeleteGlobalRef(mRemoteDisplayObjGlobal);
    }

public:
    virtual void onDisplayConnected(const sp<IGraphicBufferProducer>& bufferProducer,
            uint32_t width, uint32_t height, uint32_t flags, uint32_t session) {
        env->CallVoidMethod(mRemoteDisplayObjGlobal,
                gRemoteDisplayClassInfo.notifyDisplayConnected,
                surfaceObj, width, height, flags, session);
    }

    virtual void onDisplayDisconnected() {

    }

    virtual void onDisplayError(int32_t error) {

    }

private:
    jobject mRemoteDisplayObjGlobal;

    static void checkAndClearExceptionFromCallback(JNIEnv* env, const char* methodName) {

        }
    }
};

在NativeRemoteDisplayClient的构造函数中,把RemoteDisplay对象先保存到mRemoteDisplayObjGlobal中,可以看到上面主要实现了三个回调函数,onDisplayConnected、onDisplayDisconnected、onDisplayError,这三个回调函数对应到RemoteDisplay类的notifyDisplayConnected、notifyDisplayDisconnected和notifyDisplayError三个方法。接着回到nativeListen中,接着会调用MediaPlayerService的listenForRemoteDisplay方法去监听socket连接,这个方法是返回一个RemoteDisplay对象,当然经过binder的调用,最终返回到nativeListen的是BpRemoteDisplay对象,然后会由这个BpRemoteDisplay对象构造一个NativeRemoteDisplay对象并把它的指针地址返回给上层RemoteDisplay使用。
class NativeRemoteDisplay {
public:
    NativeRemoteDisplay(const sp<IRemoteDisplay>& display,
            const sp<NativeRemoteDisplayClient>& client) :
            mDisplay(display), mClient(client) {
    }

    ~NativeRemoteDisplay() {
        mDisplay->dispose();
    }

    void pause() {
        mDisplay->pause();
    }

    void resume() {
        mDisplay->resume();
    }

private:
    sp<IRemoteDisplay> mDisplay;
    sp<NativeRemoteDisplayClient> mClient;
};

来看一下这时Java层的RemoteDisplay和Native层RemoteDisplay之间的关系:
Android WifiDisplay分析二:Wifi display连接过程_第3张图片
WifiDisplayController通过左边的一条线路关系去控制WifiDisplaySource,而WifiDisplaySource又通过右边一条线路关系去回调WifiDisplayController的一些方法。

接着来看MediaPlayerService的listenForRemoteDisplay方法:
sp<IRemoteDisplay> MediaPlayerService::listenForRemoteDisplay(
        const sp<IRemoteDisplayClient>& client, const String8& iface) {
    if (!checkPermission("android.permission.CONTROL_WIFI_DISPLAY")) {
        return NULL;
    }

    return new RemoteDisplay(client, iface.string());
}

首先进行权限的检查,然后创建一个RemoteDisplay对象(注意现在已经在C++层了),这里看RemoteDisplay.cpp文件。RemoteDisplay继承于BnRemoteDisplay,并实现BnRemoteDisplay中的一些方法,有兴趣的可以去看一下IRemoteDisplay的实现。接下来来看RemoteDisplay的构造函数:
RemoteDisplay::RemoteDisplay(
        const sp<IRemoteDisplayClient> &client,
        const char *iface)
    : mLooper(new ALooper),
      mNetSession(new ANetworkSession) {
    mLooper->setName("wfd_looper");

    mSource = new WifiDisplaySource(mNetSession, client);
    mLooper->registerHandler(mSource);

    mNetSession->start();
    mLooper->start();

    mSource->start(iface);
}

RemoteDisplay类包含三个比较重要的元素:ALooper、ANetworkSession、WifiDisplaySource。首先来看一下在Native层的类图:
Android WifiDisplay分析二:Wifi display连接过程_第4张图片

ALooper中会创建一个Thread,并且不断的进行Looper循环去收消息,并dispatch给WifiDisplaySource去处理消息。首先来看它的构造函数和setName以及registerHandler这三个方法:
ALooper::ALooper()
    : mRunningLocally(false) {
}

void ALooper::setName(const char *name) {
    mName = name;
}

ALooper::handler_id ALooper::registerHandler(const sp<AHandler> &handler) {
    return gLooperRoster.registerHandler(this, handler);
}

这三个方法都比较简单,我们看LooperRoster的registerHandler方法:
ALooper::handler_id ALooperRoster::registerHandler(
        const sp<ALooper> looper, const sp<AHandler> &handler) {
    Mutex::Autolock autoLock(mLock);

    if (handler->id() != 0) {
        CHECK(!"A handler must only be registered once.");
        return INVALID_OPERATION;
    }

    HandlerInfo info;
    info.mLooper = looper;
    info.mHandler = handler;
    ALooper::handler_id handlerID = mNextHandlerID++;
    mHandlers.add(handlerID, info);

    handler->setID(handlerID);

    return handlerID;
}

这里为每一个注册的AHandler分配一个handlerID,并且把注册的AHandler保存在mHandlers列表中,后面使用时,就可以快速的通过HandlerID找到对应的AHandler以及ALooper了。注意这里HandlerInfo结构中的mLooper和mHander都是是wp,是一个弱引用,在使用中必须调用其promote方法获取sp指针才能使用。再回到RemoteDisplay的构造函数中看ALooper的start方法:
status_t ALooper::start(
        bool runOnCallingThread, bool canCallJava, int32_t priority) {
    if (runOnCallingThread) {

    }

    Mutex::Autolock autoLock(mLock);

    mThread = new LooperThread(this, canCallJava);

    status_t err = mThread->run(
            mName.empty() ? "ALooper" : mName.c_str(), priority);
    if (err != OK) {
        mThread.clear();
    }

    return err;
}

这里的runOnCallingThread会根据默认形参为false,所以会新建一个LooperThread来不断的做循环,LooperThread是继承于Thread,并实现它的readyToRun和threadLoop方法,在threadLoop方法中去调用ALooper的loop方法,代码如下:
    virtual bool threadLoop() {
        return mLooper->loop();
    }

bool ALooper::loop() {
    Event event;

    {
        Mutex::Autolock autoLock(mLock);
 
        if (mEventQueue.empty()) {
            mQueueChangedCondition.wait(mLock);
            return true;
        }
        int64_t whenUs = (*mEventQueue.begin()).mWhenUs;
        int64_t nowUs = GetNowUs();

        if (whenUs > nowUs) {
            int64_t delayUs = whenUs - nowUs;
            mQueueChangedCondition.waitRelative(mLock, delayUs * 1000ll);

            return true;
        }

        event = *mEventQueue.begin();
        mEventQueue.erase(mEventQueue.begin());
    }

    gLooperRoster.deliverMessage(event.mMessage);

    return true;
}

在loop方法中,不断的从mEventQueue取出消息,并dispatch给LooperRoster处理,mEventQueue是一个list链表,其元素都是Event结构,Event结构又包含消息处理的时间以及消息本身AMessage。再来看ALooperRoster的deliverMessage方法:
void ALooperRoster::deliverMessage(const sp<AMessage> &msg) {
    sp<AHandler> handler;

    {
        Mutex::Autolock autoLock(mLock);

        ssize_t index = mHandlers.indexOfKey(msg->target());

        if (index < 0) {
            ALOGW("failed to deliver message. Target handler not registered.");
            return;
        }

        const HandlerInfo &info = mHandlers.valueAt(index);
        handler = info.mHandler.promote();

        if (handler == NULL) {
            ALOGW("failed to deliver message. "
                 "Target handler %d registered, but object gone.",
                 msg->target());

            mHandlers.removeItemsAt(index);
            return;
        }
    }

    handler->onMessageReceived(msg);
}

这里首先通过AMessage的target找到需要哪个AHandler处理,然后调用这个AHandler的onMessageReceived去处理这个消息。注意前面的info.mHandler.promote()用于当前AHandler的强引用指针,也可以用来判断当前AHandler是否还存活在。由前面的知识我们知道,这里会调用到WifiDisplaySource的onMessageReceived方法,至于这些消息如何被处理,我们后面再来分析。再回到RemoteDisplay的构造函数中,ANetworkSession用于处理与网络请求相关的工作,比如创建socket,从socket中收发数据,当然这些工作都是由WifiDisplaySource控制的,我们先来看ANetworkSession的构造方法和start方法:
ANetworkSession::ANetworkSession()
    : mNextSessionID(1) {
    mPipeFd[0] = mPipeFd[1] = -1;
}

status_t ANetworkSession::start() {
    if (mThread != NULL) {
        return INVALID_OPERATION;
    }

    int res = pipe(mPipeFd);
    if (res != 0) {
        mPipeFd[0] = mPipeFd[1] = -1;
        return -errno;
    }

    mThread = new NetworkThread(this);

    status_t err = mThread->run("ANetworkSession", ANDROID_PRIORITY_AUDIO);

    if (err != OK) {
        mThread.clear();

        close(mPipeFd[0]);
        close(mPipeFd[1]);
        mPipeFd[0] = mPipeFd[1] = -1;

        return err;
    }

    return OK;
}

在start方法中,首先创建一个管道,这里创建的管理主要用于让ANetworkSession不断的做select循环,当有事务要处理时,就从select中跳出来处理,我们后面会分析到具体的代码。接着创建一个NetworkThread,NetworkThread也是继承于Thread,并实现threadLoop方法,在threadLoop方法中只是简单的调用ANetworkSession的threadLoop方法,我们来分析threadLoop方法:
void ANetworkSession::threadLoop() {
    fd_set rs, ws;
    FD_ZERO(&rs);
    FD_ZERO(&ws);

    FD_SET(mPipeFd[0], &rs);
    int maxFd = mPipeFd[0];

    {
        Mutex::Autolock autoLock(mLock);

        for (size_t i = 0; i < mSessions.size(); ++i) {
            const sp<Session> &session = mSessions.valueAt(i);

            int s = session->socket();

            if (s < 0) {
                continue;
            }

            if (session->wantsToRead()) {
                FD_SET(s, &rs);
                if (s > maxFd) {
                    maxFd = s;
                }
            }

            if (session->wantsToWrite()) {
                FD_SET(s, &ws);
                if (s > maxFd) {
                    maxFd = s;
                }
            }
        }
    }

    int res = select(maxFd + 1, &rs, &ws, NULL, NULL /* tv */);

    if (res == 0) {
        return;
    }

    if (res < 0) {
        if (errno == EINTR) {
            return;
        }

        ALOGE("select failed w/ error %d (%s)", errno, strerror(errno));
        return;
    }

}

这个函数比较长,我们分段来看,首先看select前半段部分,首先将mPipeFd[0]作为select监听的一个fd。然后循环的从mSessions中取出各个子Session(Session即为一个回话,在RTSP中当双方连接好TCP连接,并交互完Setup以后,就表示一个回话建立成功了,在RTSP中,可以在一对Server & Client之间建立多个回话,用于传输不同的数据),并通过socket类型添加到ReadFd和WirteFd中,最后调用select去等待是否有可读或者可写的事件发生。mSessions是一个KeyedVector,保存所有的Session及其SessionID,方便查找。关于Session何时创建,如何创建,我们后面再来分析。

接着回到RemoteDisplay的构造函数,再来分析WifiDisplaySource,WifiDisplaySource继承于AHandler,并实现其中的onMessageReceived方法用于处理消息。先来看WifiDisplaySource的构造函数:
WifiDisplaySource::WifiDisplaySource(
        const sp<ANetworkSession> &netSession,
        const sp<IRemoteDisplayClient> &client,
        const char *path)
    : mState(INITIALIZED),
      mNetSession(netSession),
      mClient(client),
      mSessionID(0),
      mStopReplyID(0),
      mChosenRTPPort(-1),
      mUsingPCMAudio(false),
      mClientSessionID(0),
      mReaperPending(false),
      mNextCSeq(1),
      mUsingHDCP(false),
      mIsHDCP2_0(false),
      mHDCPPort(0),
      mHDCPInitializationComplete(false),
      mSetupTriggerDeferred(false),
      mPlaybackSessionEstablished(false) {
    if (path != NULL) {
        mMediaPath.setTo(path);
    }

    mSupportedSourceVideoFormats.disableAll();

    mSupportedSourceVideoFormats.setNativeResolution(
            VideoFormats::RESOLUTION_CEA, 5);  // 1280x720 p30

    // Enable all resolutions up to 1280x720p30
    mSupportedSourceVideoFormats.enableResolutionUpto(
            VideoFormats::RESOLUTION_CEA, 5,
            VideoFormats::PROFILE_CHP,  // Constrained High Profile
            VideoFormats::LEVEL_32);    // Level 3.2
}

首先给一些变量出初始化处理,由默认形参我们知道path为空。接着去清空VideoFormats中所有的设置,并把1280*720p以上的所有分辨率打开。VideoFormats是用于与Sink回复的M3作比对用的,可以快速找出我们和Sink支持的分辨率以及帧率,作为回复M4消息用,也用作后续传输TS数据的格式。首先来看VideoFormats的构造函数:
VideoFormats::VideoFormats() {
    memcpy(mConfigs, mResolutionTable, sizeof(mConfigs));

    for (size_t i = 0; i < kNumResolutionTypes; ++i) {
        mResolutionEnabled[i] = 0;
    }

    setNativeResolution(RESOLUTION_CEA, 0);  // default to 640x480 p60
}

mResolutionTable是按照Wifi Display 规范定义好的一个3*32数组,里面的元素是config_t类型:
    struct config_t {
        size_t width, height, framesPerSecond;
        bool interlaced;
        unsigned char profile, level;
    };

config_t包含了长、宽、帧率、隔行视频、profile和H.264 level。然后在构造函数中,对mResolutionEnabled[]数组全部置为0,mResolutionEnabled数组有三个元素,分别对应CEA、VESA、HH被选取的位,如果在mConfigs数组中相应的格式被选取,就会置mResolutionEnabled对应的位为1;相反取消支持一种格式时,相应的位就被置为0。在来看setNativeResolution:
void VideoFormats::setNativeResolution(ResolutionType type, size_t index) {
    CHECK_LT(type, kNumResolutionTypes);
    CHECK(GetConfiguration(type, index, NULL, NULL, NULL, NULL));

    mNativeType = type;
    mNativeIndex = index;

    setResolutionEnabled(type, index);
}

首先做参数检查,检查输入的type和index是否合法,然后调用setResolutionEnabled去设置mResolutionEnabled和mConfigs中的相应的值:
void VideoFormats::setResolutionEnabled(
        ResolutionType type, size_t index, bool enabled) {
    CHECK_LT(type, kNumResolutionTypes);
    CHECK(GetConfiguration(type, index, NULL, NULL, NULL, NULL));

    if (enabled) {
        mResolutionEnabled[type] |= (1ul << index);
        mConfigs[type][index].profile = (1ul << PROFILE_CBP);
        mConfigs[type][index].level = (1ul << LEVEL_31);
    } else {
        mResolutionEnabled[type] &= ~(1ul << index);
        mConfigs[type][index].profile = 0;
        mConfigs[type][index].level = 0;
    }
}

这里首先还是做参数的检查,由默认形参我们知道,enable是true,则设置mResolutionEnabled相应type中的对应格式为1,并设置mConfigs中的profile和level值为CBP和Level 3.1。这里设置640*480 p60是因为在Wifi Display规范中,这个格式是必须要强制支持的,在Miracast认证中,这种格式也会被测试到。然后回到WifiDisplaySource的构造函数中,接下来会调用setNativeResolution去设置当前系统支持的默认格式为1280*720 p30,并调用enableResolutionUpto去将1280*720 p30以上的格式都设置为支持:
void VideoFormats::enableResolutionUpto(
        ResolutionType type, size_t index,
        ProfileType profile, LevelType level) {
    size_t width, height, fps, score;
    bool interlaced;
    if (!GetConfiguration(type, index, &width, &height,
            &fps, &interlaced)) {
        ALOGE("Maximum resolution not found!");
        return;
    }
    score = width * height * fps * (!interlaced + 1);
    for (size_t i = 0; i < kNumResolutionTypes; ++i) {
        for (size_t j = 0; j < 32; j++) {
            if (GetConfiguration((ResolutionType)i, j,
                    &width, &height, &fps, &interlaced)
                    && score >= width * height * fps * (!interlaced + 1)) {
                setResolutionEnabled((ResolutionType)i, j);
                setProfileLevel((ResolutionType)i, j, profile, level);
            }
        }
    }
}

这里采用width * height * fps * (!interlaced + 1)的方式去计算一个score值,然后遍历所有的mResolutionTable中的值去检查是否计算到的值比当前score要高,如果大于当前score值,就将这种分辨率enable,并设置mConfigs中对应分辨率的profile和H.264 level为CHP和Level 3.2。到这里WifiDisplaySource的构造函数分析完了,接着回到RemoteDisplay构造函数中,它会调用WifiDisplaySource的start方法,参数是的"ip:rtspPort":
status_t WifiDisplaySource::start(const char *iface) {
    CHECK_EQ(mState, INITIALIZED);

    sp<AMessage> msg = new AMessage(kWhatStart, id());
    msg->setString("iface", iface);

    sp<AMessage> response;
    return PostAndAwaitResponse(msg, &response);
}

static status_t PostAndAwaitResponse(
        const sp<AMessage> &msg, sp<AMessage> *response) {
    status_t err = msg->postAndAwaitResponse(response);

    if (err != OK) {
        return err;
    }

    if (response == NULL || !(*response)->findInt32("err", &err)) {
        err = OK;
    }

    return err;
}

在start函数中,构造一个AMessage,消息种类是kWhatStart,id()返回在ALooperRoster注册的handlerID值,ALooperRoster通过handlerID值可以快速找到对应的AHandler,我们知道,这里的id()返回WifiDisplaySource这个AHander的id值,这个消息最终也会被WifiDisplaySource的onMessageReceived方法处理。首先来看AMessage的postAndAwaitResponse方法:
status_t AMessage::postAndAwaitResponse(sp<AMessage> *response) {
    return gLooperRoster.postAndAwaitResponse(this, response);
}

这里直接调用LooperRoster的postAndAwaitResponse方法,这里比较重要的是gLooperRoster在这里只是被extern引用:extern ALooperRoster gLooperRoster,其最终的声明和定义是在我们前面讲到的ALooper中。接着去看LooperRoster的postAndAwaitResponse方法:
status_t ALooperRoster::postAndAwaitResponse(
        const sp<AMessage> &msg, sp<AMessage> *response) {
    Mutex::Autolock autoLock(mLock);

    uint32_t replyID = mNextReplyID++;

    msg->setInt32("replyID", replyID);

    status_t err = postMessage_l(msg, 0 /* delayUs */);

    if (err != OK) {
        response->clear();
        return err;
    }

    ssize_t index;
    while ((index = mReplies.indexOfKey(replyID)) < 0) {
        mRepliesCondition.wait(mLock);
    }

    *response = mReplies.valueAt(index);
    mReplies.removeItemsAt(index);

    return OK;
}

首先会为每个需要reply的消息赋予一个replyID,后面会根据这个replyID去mReplies找到对应的response。再来看postMessage_l的实现:
status_t ALooperRoster::postMessage_l(
        const sp<AMessage> &msg, int64_t delayUs) {
    ssize_t index = mHandlers.indexOfKey(msg->target());

    if (index < 0) {
        ALOGW("failed to post message '%s'. Target handler not registered.",
              msg->debugString().c_str());
        return -ENOENT;
    }

    const HandlerInfo &info = mHandlers.valueAt(index);

    sp<ALooper> looper = info.mLooper.promote();

    if (looper == NULL) {
        ALOGW("failed to post message. "
             "Target handler %d still registered, but object gone.",
             msg->target());

        mHandlers.removeItemsAt(index);
        return -ENOENT;
    }

    looper->post(msg, delayUs);

    return OK;
}

首先从mHandler数组中找到当前AMessage对应的ALooper,然后调用ALooper的post方法,来看一下实现:
void ALooper::post(const sp<AMessage> &msg, int64_t delayUs) {
    Mutex::Autolock autoLock(mLock);

    int64_t whenUs;
    if (delayUs > 0) {
        whenUs = GetNowUs() + delayUs;
    } else {
        whenUs = GetNowUs();
    }

    List<Event>::iterator it = mEventQueue.begin();
    while (it != mEventQueue.end() && (*it).mWhenUs <= whenUs) {
        ++it;
    }

    Event event;
    event.mWhenUs = whenUs;
    event.mMessage = msg;

    if (it == mEventQueue.begin()) {
        mQueueChangedCondition.signal();
    }

    mEventQueue.insert(it, event);
}

delayUs用于做延时消息使用,会加上当前时间作为消息应该被处理的时间。然后依次比较mEventQueue链表中的所有消息,并把当前消息插入到比whenUs大的前面一个位置。如果这是mEventQueue中的第一个消息,则发出一个signal通知等待的线程。前面我们知道在ALooper的loop方法中会循环的从mEventQueue获取消息并dispatch出去给WifiDisplaySource的onMessageReceived去处理,我们接着来看这部分的实现。这里绕这么大一圈,最后WifiDisplaySource发送的消息还是给自己处理,主要是为了避开主线程处理的事务太多,通过消息机制,让更多的繁杂的活都在Thread中去完成。
void WifiDisplaySource::onMessageReceived(const sp<AMessage> &msg) {
    switch (msg->what()) {
        case kWhatStart:
        {
            uint32_t replyID;
            CHECK(msg->senderAwaitsResponse(&replyID));

            AString iface;
            CHECK(msg->findString("iface", &iface));

            status_t err = OK;

            ssize_t colonPos = iface.find(":");

            unsigned long port;

            if (colonPos >= 0) {
                const char *s = iface.c_str() + colonPos + 1;

                char *end;
                port = strtoul(s, &end, 10);

                if (end == s || *end != '\0' || port > 65535) {
                    err = -EINVAL;
                } else {
                    iface.erase(colonPos, iface.size() - colonPos);
                }
            } else {
                port = kWifiDisplayDefaultPort;
            }

            if (err == OK) {
                if (inet_aton(iface.c_str(), &mInterfaceAddr) != 0) {
                    sp<AMessage> notify = new AMessage(kWhatRTSPNotify, id());

                    err = mNetSession->createRTSPServer(
                            mInterfaceAddr, port, notify, &mSessionID);
                } else {
                    err = -EINVAL;
                }
            }

            mState = AWAITING_CLIENT_CONNECTION;

            sp<AMessage> response = new AMessage;
            response->setInt32("err", err);
            response->postReply(replyID);
            break;
        }

首先通过AMessage获取到replayID和iface,然后把iface分割成ip和port,分别保存在mInterfaceAddr和port中。在调用ANetSession的createRTSPServer去创建一个RTSP server,最后构造一个response对象并返回。我们先来看createRTSPServer方法:
status_t ANetworkSession::createRTSPServer(
        const struct in_addr &addr, unsigned port,
        const sp<AMessage> ¬ify, int32_t *sessionID) {
    return createClientOrServer(
            kModeCreateRTSPServer,
            &addr,
            port,
            NULL /* remoteHost */,
            0 /* remotePort */,
            notify,
            sessionID);
}

status_t ANetworkSession::createClientOrServer(
        Mode mode,
        const struct in_addr *localAddr,
        unsigned port,
        const char *remoteHost,
        unsigned remotePort,
        const sp<AMessage> ¬ify,
        int32_t *sessionID) {
    Mutex::Autolock autoLock(mLock);

    *sessionID = 0;
    status_t err = OK;
    int s, res;
    sp<Session> session;

    s = socket(
            AF_INET,
            (mode == kModeCreateUDPSession) ? SOCK_DGRAM : SOCK_STREAM,
            0);

    if (s < 0) {
        err = -errno;
        goto bail;
    }

    if (mode == kModeCreateRTSPServer
            || mode == kModeCreateTCPDatagramSessionPassive) {
        const int yes = 1;
        res = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));

        if (res < 0) {
            err = -errno;
            goto bail2;
        }
    }

    err = MakeSocketNonBlocking(s);

    if (err != OK) {
        goto bail2;
    }

    struct sockaddr_in addr;
    memset(addr.sin_zero, 0, sizeof(addr.sin_zero));
    addr.sin_family = AF_INET;
    } else if (localAddr != NULL) {
        addr.sin_addr = *localAddr;
        addr.sin_port = htons(port);

        res = bind(s, (const struct sockaddr *)&addr, sizeof(addr));

        if (res == 0) {
            if (mode == kModeCreateRTSPServer
                    || mode == kModeCreateTCPDatagramSessionPassive) {
                res = listen(s, 4);
            } else {


    if (res < 0) {
        err = -errno;
        goto bail2;
    }

    Session::State state;
    switch (mode) {

        case kModeCreateRTSPServer:
            state = Session::LISTENING_RTSP;
            break;

        default:
            CHECK_EQ(mode, kModeCreateUDPSession);
            state = Session::DATAGRAM;
            break;
    }

    session = new Session(
            mNextSessionID++,
            state,
            s,
            notify);


    mSessions.add(session->sessionID(), session);

    interrupt();

    *sessionID = session->sessionID();

    goto bail;

bail2:
    close(s);
    s = -1;

bail:
    return err;
}

createRTSPServer直接调用createClientOrServer,第一个参数是kModeCreateRTSPServer表示要创建一个RTSP server。createClientOrServer的代码比较长,上面是精简后的代码,其它没看到的代码我们以后遇到的过程中再来分析。上面的代码中首先创建一个socket,然后设置一下socket的reuse和no-block属性,接着bind到指定的IP和port上,然后再此socket上开始listen。接下来置当前ANetworkSession的状态是LISTENING_RTSP。然后创建一个Session会话对象,在构造函数中会传入notify作为参数,notify是一个kWhatRTSPNotify的AMessag,后面会看到如何使用它。然后添加到mSessions数组当中。接着调用interrupt方法,让ANetworkSession的NetworkThread线程跳出select语句,并重新计算readFd和writeFd用于select监听的文件句柄。
void ANetworkSession::interrupt() {
    static const char dummy = 0;

    ssize_t n;
    do {
        n = write(mPipeFd[1], &dummy, 1);
    } while (n < 0 && errno == EINTR);

    if (n < 0) {
        ALOGW("Error writing to pipe (%s)", strerror(errno));
    }
}

interrupt方法向pipe中写入一个空消息,前面我们已经介绍过threadLoop了,这里就会把刚刚创建的socket加入到监听的readFd中。到这里,关于WifiDisplay连接的建立就讲完了,后面会再从收到Sink的TCP连接请求开始讲起。最后贴一份从WifiDisplaySettings到ANetworkSession如何创建socket的时序图:
Android WifiDisplay分析二:Wifi display连接过程_第5张图片

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