IOException：读取失败，套接字可能已关闭 - Android 4.3 上的蓝牙

目前，我正在尝试在使用 Android 4.3（Build JWR66Y，我猜是第二个 4.3 更新）的 Nexus 7 (2012) 上打开 BluetoothSocket 时处理一个奇怪的异常。我看过一些相关的帖子（例如https://stackoverflow.com/questions/13648373/bluetoothsocket-connect- throwing-exception-read-failed），但似乎没有人提供解决此问题的方法。此外，正如这些线程中所建议的，重新配对没有帮助，并且不断尝试连接（通过愚蠢的循环）也没有效果。

我正在处理一个嵌入式设备（一个无名的 OBD-II 汽车适配器，类似于http://images04.olx.com/ui/15/53/76/1316534072_254254776_2-OBD-II-BLUTOOTH-ADAPTERSCLEAR-CHECK-ENGINE-LIGHTS-WITH-YOUR-PHONE-Oceanside.jpg）。我的 Android 2.3.7 手机没有任何连接问题，同事的 Xperia（Android 4.1.2）也可以使用。另一个 Google Nexus（我不知道是“One”还是“S”，但不是“4”）在 Android 4.3 上也失败了。

这是连接建立的片段。它在自己的线程中运行，该线程是在服务中创建的。

private class ConnectThread extends Thread {

    private static final UUID EMBEDDED_BOARD_SPP = UUID
        .fromString("00001101-0000-1000-8000-00805F9B34FB");

    private BluetoothAdapter adapter;
    private boolean secure;
    private BluetoothDevice device;
    private List<UUID> uuidCandidates;
    private int candidate;
    protected boolean started;

    public ConnectThread(BluetoothDevice device, boolean secure) {
        logger.info("initiliasing connection to device "+device.getName() +" / "+ device.getAddress());
        adapter = BluetoothAdapter.getDefaultAdapter();
        this.secure = secure;
        this.device = device;

        setName("BluetoothConnectThread");

        if (!startQueryingForUUIDs()) {
            this.uuidCandidates = Collections.singletonList(EMBEDDED_BOARD_SPP);
            this.start();
        } else{
            logger.info("Using UUID discovery mechanism.");
        }
        /*
         * it will start upon the broadcast receive otherwise
         */
    }

    private boolean startQueryingForUUIDs() {
        Class<?> cl = BluetoothDevice.class;

        Class<?>[] par = {};
        Method fetchUuidsWithSdpMethod;
        try {
            fetchUuidsWithSdpMethod = cl.getMethod("fetchUuidsWithSdp", par);
        } catch (NoSuchMethodException e) {
            logger.warn(e.getMessage());
            return false;
        }

        Object[] args = {};
        try {
            BroadcastReceiver receiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
                    BluetoothDevice deviceExtra = intent.getParcelableExtra("android.bluetooth.device.extra.DEVICE");
                    Parcelable[] uuidExtra = intent.getParcelableArrayExtra("android.bluetooth.device.extra.UUID");

                    uuidCandidates = new ArrayList<UUID>();
                    for (Parcelable uuid : uuidExtra) {
                        uuidCandidates.add(UUID.fromString(uuid.toString()));
                    }

                    synchronized (ConnectThread.this) {
                        if (!ConnectThread.this.started) {
                            ConnectThread.this.start();
                            ConnectThread.this.started = true;
                            unregisterReceiver(this);
                        }

                    }
                }

            };
            registerReceiver(receiver, new IntentFilter("android.bleutooth.device.action.UUID"));
            registerReceiver(receiver, new IntentFilter("android.bluetooth.device.action.UUID"));

            fetchUuidsWithSdpMethod.invoke(device, args);
        } catch (IllegalArgumentException e) {
            logger.warn(e.getMessage());
            return false;
        } catch (IllegalAccessException e) {
            logger.warn(e.getMessage());
            return false;
        } catch (InvocationTargetException e) {
            logger.warn(e.getMessage());
            return false;
        }           

        return true;
    }

    public void run() {
        boolean success = false;
        while (selectSocket()) {

            if (bluetoothSocket == null) {
                logger.warn("Socket is null! Cancelling!");
                deviceDisconnected();
                openTroubleshootingActivity(TroubleshootingActivity.BLUETOOTH_EXCEPTION);
            }

            // Always cancel discovery because it will slow down a connection
            adapter.cancelDiscovery();

            // Make a connection to the BluetoothSocket
            try {
                // This is a blocking call and will only return on a
                // successful connection or an exception
                bluetoothSocket.connect();
                success = true;
                break;

            } catch (IOException e) {
                // Close the socket
                try {
                    shutdownSocket();
                } catch (IOException e2) {
                    logger.warn(e2.getMessage(), e2);
                }
            }
        }

        if (success) {
            deviceConnected();
        } else {
            deviceDisconnected();
            openTroubleshootingActivity(TroubleshootingActivity.BLUETOOTH_EXCEPTION);
        }
    }

    private boolean selectSocket() {
        if (candidate >= uuidCandidates.size()) {
            return false;
        }

        BluetoothSocket tmp;
        UUID uuid = uuidCandidates.get(candidate++);
        logger.info("Attempting to connect to SDP "+ uuid);
        try {
            if (secure) {
                tmp = device.createRfcommSocketToServiceRecord(
                        uuid);
            } else {
                tmp = device.createInsecureRfcommSocketToServiceRecord(
                        uuid);
            }
            bluetoothSocket = tmp;
            return true;
        } catch (IOException e) {
            logger.warn(e.getMessage() ,e);
        }

        return false;
    }

}

代码失败于bluetoothSocket.connect()。我得到了java.io.IOException: read failed, socket might closed, read ret: -1。这是 GitHub 上的相应来源：https://github.com/android/platform_frameworks_base/blob/android-4.3_r2/core/java/android/bluetooth/BluetoothSocket.java#L504它是通过 readInt() 调用的，调用自https://github.com/android/platform_frameworks_base/blob/android-4.3_r2/core/java/android/bluetooth/BluetoothSocket.java#L319

所用套接字的一些元数据转储导致以下信息。这些在 Nexus 7 和我的 2.3.7 手机上完全相同。

Bluetooth Device 'OBDII'
Address: 11:22:33:DD:EE:FF
Bond state: 12 (bonded)
Type: 1
Class major version: 7936
Class minor version: 7936
Class Contents: 0
Contents: 0

我还有一些其他 OBD-II 适配器（更广泛），它们都可以工作。我是否有可能遗漏了某些东西，或者这可能是 Android 中的一个错误？

我终于找到了解决方法。魔法隐藏在引擎盖下BluetoothDevice类（参见https://github.com/android/platform_frameworks_base/blob/android-4.3_r2/core/java/android/bluetooth/BluetoothDevice.java#L1037).

现在，当我收到该异常时，我会实例化一个后备BluetoothSocket，类似于下面的源代码。正如你所看到的，调用隐藏方法createRfcommSocket通过反射。我不知道为什么这个方法被隐藏。源代码将其定义为public尽管...

Class<?> clazz = tmp.getRemoteDevice().getClass();
Class<?>[] paramTypes = new Class<?>[] {Integer.TYPE};

Method m = clazz.getMethod("createRfcommSocket", paramTypes);
Object[] params = new Object[] {Integer.valueOf(1)};

fallbackSocket = (BluetoothSocket) m.invoke(tmp.getRemoteDevice(), params);
fallbackSocket.connect();

connect()然后不再失败。我仍然遇到了一些问题。基本上，这有时会阻塞并失败。在这种情况下，重新启动 SPP 设备（拔掉/插入）会有所帮助。有时我还会收到另一个配对请求connect()即使设备已经绑定。

UPDATE:

这是一个完整的类，包含一些嵌套类。对于真正的实现，这些可以作为单独的类进行。

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Method;
import java.util.List;
import java.util.UUID;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.util.Log;

public class BluetoothConnector {

    private BluetoothSocketWrapper bluetoothSocket;
    private BluetoothDevice device;
    private boolean secure;
    private BluetoothAdapter adapter;
    private List<UUID> uuidCandidates;
    private int candidate;


    /**
     * @param device the device
     * @param secure if connection should be done via a secure socket
     * @param adapter the Android BT adapter
     * @param uuidCandidates a list of UUIDs. if null or empty, the Serial PP id is used
     */
    public BluetoothConnector(BluetoothDevice device, boolean secure, BluetoothAdapter adapter,
            List<UUID> uuidCandidates) {
        this.device = device;
        this.secure = secure;
        this.adapter = adapter;
        this.uuidCandidates = uuidCandidates;

        if (this.uuidCandidates == null || this.uuidCandidates.isEmpty()) {
            this.uuidCandidates = new ArrayList<UUID>();
            this.uuidCandidates.add(UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));
        }
    }

    public BluetoothSocketWrapper connect() throws IOException {
        boolean success = false;
        while (selectSocket()) {
            adapter.cancelDiscovery();

            try {
                bluetoothSocket.connect();
                success = true;
                break;
            } catch (IOException e) {
                //try the fallback
                try {
                    bluetoothSocket = new FallbackBluetoothSocket(bluetoothSocket.getUnderlyingSocket());
                    Thread.sleep(500);                  
                    bluetoothSocket.connect();
                    success = true;
                    break;  
                } catch (FallbackException e1) {
                    Log.w("BT", "Could not initialize FallbackBluetoothSocket classes.", e);
                } catch (InterruptedException e1) {
                    Log.w("BT", e1.getMessage(), e1);
                } catch (IOException e1) {
                    Log.w("BT", "Fallback failed. Cancelling.", e1);
                }
            }
        }

        if (!success) {
            throw new IOException("Could not connect to device: "+ device.getAddress());
        }

        return bluetoothSocket;
    }

    private boolean selectSocket() throws IOException {
        if (candidate >= uuidCandidates.size()) {
            return false;
        }

        BluetoothSocket tmp;
        UUID uuid = uuidCandidates.get(candidate++);

        Log.i("BT", "Attempting to connect to Protocol: "+ uuid);
        if (secure) {
            tmp = device.createRfcommSocketToServiceRecord(uuid);
        } else {
            tmp = device.createInsecureRfcommSocketToServiceRecord(uuid);
        }
        bluetoothSocket = new NativeBluetoothSocket(tmp);

        return true;
    }

    public static interface BluetoothSocketWrapper {

        InputStream getInputStream() throws IOException;

        OutputStream getOutputStream() throws IOException;

        String getRemoteDeviceName();

        void connect() throws IOException;

        String getRemoteDeviceAddress();

        void close() throws IOException;

        BluetoothSocket getUnderlyingSocket();

    }


    public static class NativeBluetoothSocket implements BluetoothSocketWrapper {

        private BluetoothSocket socket;

        public NativeBluetoothSocket(BluetoothSocket tmp) {
            this.socket = tmp;
        }

        @Override
        public InputStream getInputStream() throws IOException {
            return socket.getInputStream();
        }

        @Override
        public OutputStream getOutputStream() throws IOException {
            return socket.getOutputStream();
        }

        @Override
        public String getRemoteDeviceName() {
            return socket.getRemoteDevice().getName();
        }

        @Override
        public void connect() throws IOException {
            socket.connect();
        }

        @Override
        public String getRemoteDeviceAddress() {
            return socket.getRemoteDevice().getAddress();
        }

        @Override
        public void close() throws IOException {
            socket.close();
        }

        @Override
        public BluetoothSocket getUnderlyingSocket() {
            return socket;
        }

    }

    public class FallbackBluetoothSocket extends NativeBluetoothSocket {

        private BluetoothSocket fallbackSocket;

        public FallbackBluetoothSocket(BluetoothSocket tmp) throws FallbackException {
            super(tmp);
            try
            {
              Class<?> clazz = tmp.getRemoteDevice().getClass();
              Class<?>[] paramTypes = new Class<?>[] {Integer.TYPE};
              Method m = clazz.getMethod("createRfcommSocket", paramTypes);
              Object[] params = new Object[] {Integer.valueOf(1)};
              fallbackSocket = (BluetoothSocket) m.invoke(tmp.getRemoteDevice(), params);
            }
            catch (Exception e)
            {
                throw new FallbackException(e);
            }
        }

        @Override
        public InputStream getInputStream() throws IOException {
            return fallbackSocket.getInputStream();
        }

        @Override
        public OutputStream getOutputStream() throws IOException {
            return fallbackSocket.getOutputStream();
        }


        @Override
        public void connect() throws IOException {
            fallbackSocket.connect();
        }


        @Override
        public void close() throws IOException {
            fallbackSocket.close();
        }

    }

    public static class FallbackException extends Exception {

        /**
         * 
         */
        private static final long serialVersionUID = 1L;

        public FallbackException(Exception e) {
            super(e);
        }

    }
}