Android(安卓)BLE Gatt实现原理解析（未完）

BluetoothManagerService是Android的系统service，是在SystemServer中初始化的，如下：

public static void main(String[] args) {    .............    ServerThread thr = new ServerThread();    thr.initAndLoop();}class ServerThread {    public void initAndLoop() {        ..........        BluetoothManagerService bluetooth = null;        ..........        bluetooth = new BluetoothManagerService(context);        ServiceManager.addService(BluetoothAdapter.BLUETOOTH_MANAGER_SERVICE, bluetooth);        ..........    }}

那么这个Service是从哪里取出的呢？在BluetoothAdapter中，如下：

public static synchronized BluetoothAdapter getDefaultAdapter() {        if (sAdapter == null) {            IBinder b = ServiceManager.getService(BLUETOOTH_MANAGER_SERVICE);            if (b != null) {                IBluetoothManager managerService = IBluetoothManager.Stub.asInterface(b);                sAdapter = new BluetoothAdapter(managerService);            } else {                Log.e(TAG, "Bluetooth binder is null");            }        }        return sAdapter;    }

我们再来看看当绑定到BluetoothManagerService时会做什么？

private class BluetoothServiceConnection implements ServiceConnection {        public void onServiceConnected(ComponentName className, IBinder service) {            Message msg = mHandler.obtainMessage(MESSAGE_BLUETOOTH_SERVICE_CONNECTED);            if (className.getClassName().equals("com.android.bluetooth.btservice.AdapterService")) {                msg.arg1 = SERVICE_IBLUETOOTH;                // } else if (className.getClassName().equals(IBluetoothGatt.class.getName())) {            } else if (className.getClassName().equals("com.android.bluetooth.gatt.GattService")) {                msg.arg1 = SERVICE_IBLUETOOTHGATT;            } else {                return;            }            msg.obj = service;            mHandler.sendMessage(msg);        }        public void onServiceDisconnected(ComponentName className) {            // Called if we unexpected disconnected.            Message msg = mHandler.obtainMessage(MESSAGE_BLUETOOTH_SERVICE_DISCONNECTED);            if (className.getClassName().equals("com.android.bluetooth.btservice.AdapterService")) {                msg.arg1 = SERVICE_IBLUETOOTH;            } else if (className.getClassName().equals("com.android.bluetooth.gatt.GattService")) {                msg.arg1 = SERVICE_IBLUETOOTHGATT;            } else {                return;            }            mHandler.sendMessage(msg);        }    }

在Handler中，只是将这个service转化成IBluetoothGatt的stub。

接下来我们看看BluetoothDevice.connectGatt的实现：

 public BluetoothGatt connectGatt(Context context, boolean autoConnect,                                     BluetoothGattCallback callback) {        BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();        IBluetoothManager managerService = adapter.getBluetoothManager();        try {            IBluetoothGatt iGatt = managerService.getBluetoothGatt();            BluetoothGatt gatt = new BluetoothGatt(context, iGatt, this);            gatt.connect(autoConnect, callback);            return gatt;        } catch (RemoteException e) {Log.e(TAG, "", e);}        return null;    }

这个adapter.getBluetoothManager()返回的就是BluetoothManagerService的stub，

而这个gatt.connect函数其实调用的是registerApp，如下：

boolean connect(Boolean autoConnect, BluetoothGattCallback callback) {    registerApp(callback)}private boolean registerApp(BluetoothGattCallback callback) {    mCallback = callback;    UUID uuid = UUID.randomUUID();    mService.registerClient(new ParcelUuid(uuid), mBluetoothGattCallback);}

这个registerClient是在哪里实现的呢，是在GattService中，如下：

private static class BluetoothGattBinder extends IBluetoothGatt.Stub implements IProfileServiceBinder {    private GattService mService;    public BluetoothGattBinder(GattService svc) {        mService = svc;    }    public void registerClient(ParcelUuid uuid, IBluetoothGattCallback callback) {        mService.registerClient(uuid.getUuid(), callback);    }    ..........}

真正的实现如下：

void registerClient(UUID uuid, IBluetoothGattCallback callback) {        mClientMap.add(uuid, callback);        gattClientRegisterAppNative(uuid.getLeastSignificantBits(), uuid.getMostSignificantBits());    }

这里又调到了一个native函数，实现在com_android_bluetooth_gatt.cpp中，如下：

static void gattClientRegisterAppNative(JNIEnv* env, jobject object, jlong app_uuid_lsb, jlong app_uuid_msb ){    bt_uuid_t uuid;    set_uuid(uuid.uu, app_uuid_msb, app_uuid_lsb);    sGattIf->client->register_client(&uuid);}

接下来我们重点看看这个sGattIf是何方神圣？

com_android:bluetooth_gatt.cpp中initializeNative中会初始化sGattIf，如下：

static void initializeNative(JNIEnv *env, jobject object) {    btIf = getBluetoothInterface();    sGattIf = (btgatt_interface_t *) btIf->get_profile_interface(BT_PROFILE_GATT_ID);    sGattIf->init(&sGattCallbacks);    mCallbacksObj = env->NewGlobalRef(object);}

这个get_profile_interface的实现在bluetooth.c中，返回的是

static const btgatt_interface_t btgattInterface = {    sizeof(btgattInterface),    btif_gatt_init,    btif_gatt_cleanup,    &btgattClientInterface,    &btgattServerInterface,};typedef struct {    /** Set to sizeof(btgatt_interface_t) */    size_t          size;    /** * Initializes the interface and provides callback routines */    bt_status_t (*init)( const btgatt_callbacks_t* callbacks );    /** Closes the interface */    void (*cleanup)( void );    /** Pointer to the GATT client interface methods.*/    const btgatt_client_interface_t* client;    /** Pointer to the GATT server interface methods.*/    const btgatt_server_interface_t* server;} btgatt_interface_t;

可见这里对应着四个值，init，cleanup，gattClient和gattServer的接口。

我们来看看btif_gatt_init的实现：

static bt_status_t btif_gatt_init( const btgatt_callbacks_t* callbacks ){    bt_gatt_callbacks = callbacks;    return BT_STATUS_SUCCESS;}

只是简单地保留回调而已。

手机端通常是作为client端，所以我们看看client端的接口，定义在btif_gatt_client.c中

const btgatt_client_interface_t btgattClientInterface = {    btif_gattc_register_app,    btif_gattc_unregister_app,    btif_gattc_scan,    btif_gattc_open,    btif_gattc_close,    btif_gattc_listen,    btif_gattc_refresh,    btif_gattc_search_service,    btif_gattc_get_included_service,    btif_gattc_get_characteristic,    btif_gattc_get_descriptor,    btif_gattc_read_char,    btif_gattc_write_char,    btif_gattc_read_char_descr,    btif_gattc_write_char_descr,    btif_gattc_execute_write,    btif_gattc_reg_for_notification,    btif_gattc_dereg_for_notification,    btif_gattc_read_remote_rssi,    btif_gattc_get_device_type,    btif_gattc_set_adv_data,    btif_gattc_test_command};

所以sGattIf->client->register_client(&uuid);调的其实就是btif_gattc_register_app函数，如下

// btif_gatt_client.cstatic bt_status_t btif_gattc_register_app(bt_uuid_t *uuid){    btif_gattc_cb_t btif_cb;    memcpy(&btif_cb.uuid, uuid, sizeof(bt_uuid_t));    return btif_transfer_context(btgattc_handle_event, BTIF_GATTC_REGISTER_APP,                                 (char*) &btif_cb, sizeof(btif_gattc_cb_t), NULL);}

今天先到此为止，剩下的改天再研究。

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