Android BluetoothSocket连接失败：read failed，socket可能关闭或超时

按照Android官方蓝牙设备连接指引，尝试连接Allflex LPR RFID Reader（型号"LPR_64980"），已完成设备发现并获取到BluetoothDevice对象存储在this.rfidreader中，使用官方示例的ConnectThread发起连接：

public void tappedConnectLPR() {
        new ConnectThread(rfidreader).start();
}

可正常创建BluetoothSocket，但调用mmSocket.connect()时，阻塞约20秒后抛出IOException，错误信息：

exception: read failed, socket might closed or timeout, read ret: -1

Logcat相关日志：

13:38:12.789  D  close() this: android.bluetooth.BluetoothSocket@7eb866e, channel: -1, mSocketIS: android.net.LocalSocketImpl$SocketInputStream@951f10f, mSocketOS: android.net.LocalSocketImpl$SocketOutputStream@ff0659c, mSocket: android.net.LocalSocket@af8fba5
                 impl:android.net.LocalSocketImpl@f4d9b7a fd:java.io.FileDescriptor@3c68f2b, mSocketState: INIT

补充说明：iPhone可正常连接该设备，已断开iPhone与设备的连接并让iPhone忽略该设备，排除干扰。

ConnectThread完整代码：

private class ConnectThread extends Thread {
    private static final UUID bluetoothServiceUUID = UUID.fromString("5cb6b8e2-b944-44b3-b806-a92d4587123c");

    private final BluetoothSocket mmSocket;
    private final BluetoothDevice mmDevice;

    @SuppressLint("MissingPermission")
    public ConnectThread(BluetoothDevice device) {
        BluetoothSocket tmp = null;
        mmDevice = device;

        try {
            Log.d("MA", "about to create rfcomm socket...");
            tmp = device.createRfcommSocketToServiceRecord(bluetoothServiceUUID);

        } catch (IOException e) {
            Log.e("MA", "Socket's create() method failed", e);
        }
        mmSocket = tmp;
        Log.d("MA", "got rfcomm socket...");
    }

    @SuppressLint("MissingPermission")
    public void run() {
        Log.d("MA", "stopping discovery, just in case");
        bluetoothAdapter.cancelDiscovery();

        try {
            Log.d("MA", "trying to connect");
            mmSocket.connect();
            Log.d("MA", "connected?");

        } catch (IOException connectException) {
            Log.d("MA", "exception: "+connectException.getMessage());

            try {
                mmSocket.close();
            } catch (IOException closeException) {
                Log.e("MA", "Could not close the client socket", closeException);
            }
            return;
        }

        manageMyConnectedSocket(mmSocket);
    }

    public void cancel() {
        try {
            mmSocket.close();
        } catch (IOException e) {
            Log.e("MA", "Could not close the client socket", e);
        }
    }
}

解决方案 #

1. 验证UUID正确性 #

当前使用的UUID可能与设备实际服务UUID不匹配，可通过以下方式获取设备广播的UUID：

@SuppressLint("MissingPermission")
UUID[] uuids = rfidreader.getUuids();
if (uuids != null) {
    for (UUID uuid : uuids) {
        Log.d("MA", "设备服务UUID: " + uuid.toString());
    }
}

若设备未广播UUID，可尝试通用SPP协议UUID：00001101-0000-1000-8000-00805F9B34FB

2. 尝试反射指定RFCOMM通道连接 #

部分设备不支持通过Service Record创建Socket，可直接指定RFCOMM通道（常用通道为1，可尝试1-30范围）：

// 替换原createRfcommSocketToServiceRecord的调用
try {
    Method m = device.getClass().getMethod("createRfcommSocket", new Class[] {int.class});
    tmp = (BluetoothSocket) m.invoke(device, 1);
} catch (Exception e) {
    Log.e("MA", "反射创建Socket失败", e);
}

3. 检查蓝牙权限 #

确保已申请对应Android版本的蓝牙权限：

• Android 12+：BLUETOOTH_SCAN、BLUETOOTH_CONNECT
• Android 11及以下：BLUETOOTH、BLUETOOTH_ADMIN、ACCESS_FINE_LOCATION

4. 重置蓝牙状态 #

重启Android设备和RFID阅读器的蓝牙模块，清除双方配对记录后重新尝试配对连接。

5. 避免扫描时连接 #

确保设备发现完成后再发起连接，避免扫描过程中资源冲突导致连接超时。

内容的提问来源于stack exchange，提问作者Kenny Wyland