/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.bluetooth;

import android.compat.annotation.UnsupportedAppUsage;
import android.net.LocalSocket;
import android.os.ParcelFileDescriptor;
import android.os.ParcelUuid;
import android.os.RemoteException;
import android.util.Log;

import java.io.Closeable;
import java.io.FileDescriptor;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Arrays;
import java.util.Locale;
import java.util.UUID;

/**
 * A connected or connecting Bluetooth socket.
 *
 * <p>The interface for Bluetooth Sockets is similar to that of TCP sockets:
 * {@link java.net.Socket} and {@link java.net.ServerSocket}. On the server
 * side, use a {@link BluetoothServerSocket} to create a listening server
 * socket. When a connection is accepted by the {@link BluetoothServerSocket},
 * it will return a new {@link BluetoothSocket} to manage the connection.
 * On the client side, use a single {@link BluetoothSocket} to both initiate
 * an outgoing connection and to manage the connection.
 *
 * <p>The most common type of Bluetooth socket is RFCOMM, which is the type
 * supported by the Android APIs. RFCOMM is a connection-oriented, streaming
 * transport over Bluetooth. It is also known as the Serial Port Profile (SPP).
 *
 * <p>To create a {@link BluetoothSocket} for connecting to a known device, use
 * {@link BluetoothDevice#createRfcommSocketToServiceRecord
 * BluetoothDevice.createRfcommSocketToServiceRecord()}.
 * Then call {@link #connect()} to attempt a connection to the remote device.
 * This call will block until a connection is established or the connection
 * fails.
 *
 * <p>To create a {@link BluetoothSocket} as a server (or "host"), see the
 * {@link BluetoothServerSocket} documentation.
 *
 * <p>Once the socket is connected, whether initiated as a client or accepted
 * as a server, open the IO streams by calling {@link #getInputStream} and
 * {@link #getOutputStream} in order to retrieve {@link java.io.InputStream}
 * and {@link java.io.OutputStream} objects, respectively, which are
 * automatically connected to the socket.
 *
 * <p>{@link BluetoothSocket} is thread
 * safe. In particular, {@link #close} will always immediately abort ongoing
 * operations and close the socket.
 *
 * <p class="note"><strong>Note:</strong>
 * Requires the {@link android.Manifest.permission#BLUETOOTH} permission.
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about using Bluetooth, read the
 * <a href="{@docRoot}guide/topics/connectivity/bluetooth.html">Bluetooth</a> developer guide.</p>
 * </div>
 *
 * {@see BluetoothServerSocket}
 * {@see java.io.InputStream}
 * {@see java.io.OutputStream}
 */
public final class BluetoothSocket implements Closeable {
    private static final String TAG = "BluetoothSocket";
    private static final boolean DBG = Log.isLoggable(TAG, Log.DEBUG);
    private static final boolean VDBG = Log.isLoggable(TAG, Log.VERBOSE);

    /** @hide */
    public static final int MAX_RFCOMM_CHANNEL = 30;
    /*package*/ static final int MAX_L2CAP_PACKAGE_SIZE = 0xFFFF;

    /** RFCOMM socket */
    public static final int TYPE_RFCOMM = 1;

    /** SCO socket */
    public static final int TYPE_SCO = 2;

    /** L2CAP socket */
    public static final int TYPE_L2CAP = 3;

    /** L2CAP socket on BR/EDR transport
     * @hide
     */
    public static final int TYPE_L2CAP_BREDR = TYPE_L2CAP;

    /** L2CAP socket on LE transport
     * @hide
     */
    public static final int TYPE_L2CAP_LE = 4;

    /*package*/ static final int EBADFD = 77;
    @UnsupportedAppUsage
    /*package*/ static final int EADDRINUSE = 98;

    /*package*/ static final int SEC_FLAG_ENCRYPT = 1;
    /*package*/ static final int SEC_FLAG_AUTH = 1 << 1;
    /*package*/ static final int BTSOCK_FLAG_NO_SDP = 1 << 2;
    /*package*/ static final int SEC_FLAG_AUTH_MITM = 1 << 3;
    /*package*/ static final int SEC_FLAG_AUTH_16_DIGIT = 1 << 4;

    private final int mType;  /* one of TYPE_RFCOMM etc */
    private BluetoothDevice mDevice;    /* remote device */
    private String mAddress;    /* remote address */
    private final boolean mAuth;
    private final boolean mEncrypt;
    private final BluetoothInputStream mInputStream;
    private final BluetoothOutputStream mOutputStream;
    private final ParcelUuid mUuid;
    private boolean mExcludeSdp = false; /* when true no SPP SDP record will be created */
    private boolean mAuthMitm = false;   /* when true Man-in-the-middle protection will be enabled*/
    private boolean mMin16DigitPin = false; /* Minimum 16 digit pin for sec mode 2 connections */
    @UnsupportedAppUsage(publicAlternatives = "Use {@link BluetoothSocket} public API instead.")
    private ParcelFileDescriptor mPfd;
    @UnsupportedAppUsage
    private LocalSocket mSocket;
    private InputStream mSocketIS;
    private OutputStream mSocketOS;
    @UnsupportedAppUsage
    private int mPort;  /* RFCOMM channel or L2CAP psm */
    private int mFd;
    private String mServiceName;
    private static final int PROXY_CONNECTION_TIMEOUT = 5000;

    private static final int SOCK_SIGNAL_SIZE = 20;

    private ByteBuffer mL2capBuffer = null;
    private int mMaxTxPacketSize = 0; // The l2cap maximum packet size supported by the peer.
    private int mMaxRxPacketSize = 0; // The l2cap maximum packet size that can be received.

    private enum SocketState {
        INIT,
        CONNECTED,
        LISTENING,
        CLOSED,
    }

    /** prevents all native calls after destroyNative() */
    private volatile SocketState mSocketState;

    /** protects mSocketState */
    //private final ReentrantReadWriteLock mLock;

    /**
     * Construct a BluetoothSocket.
     *
     * @param type type of socket
     * @param fd fd to use for connected socket, or -1 for a new socket
     * @param auth require the remote device to be authenticated
     * @param encrypt require the connection to be encrypted
     * @param device remote device that this socket can connect to
     * @param port remote port
     * @param uuid SDP uuid
     * @throws IOException On error, for example Bluetooth not available, or insufficient
     * privileges
     */
    /*package*/ BluetoothSocket(int type, int fd, boolean auth, boolean encrypt,
            BluetoothDevice device, int port, ParcelUuid uuid) throws IOException {
        this(type, fd, auth, encrypt, device, port, uuid, false, false);
    }

    /**
     * Construct a BluetoothSocket.
     *
     * @param type type of socket
     * @param fd fd to use for connected socket, or -1 for a new socket
     * @param auth require the remote device to be authenticated
     * @param encrypt require the connection to be encrypted
     * @param device remote device that this socket can connect to
     * @param port remote port
     * @param uuid SDP uuid
     * @param mitm enforce man-in-the-middle protection.
     * @param min16DigitPin enforce a minimum length of 16 digits for a sec mode 2 connection
     * @throws IOException On error, for example Bluetooth not available, or insufficient
     * privileges
     */
    /*package*/ BluetoothSocket(int type, int fd, boolean auth, boolean encrypt,
            BluetoothDevice device, int port, ParcelUuid uuid, boolean mitm, boolean min16DigitPin)
            throws IOException {
        if (VDBG) Log.d(TAG, "Creating new BluetoothSocket of type: " + type);
        if (type == BluetoothSocket.TYPE_RFCOMM && uuid == null && fd == -1
                && port != BluetoothAdapter.SOCKET_CHANNEL_AUTO_STATIC_NO_SDP) {
            if (port < 1 || port > MAX_RFCOMM_CHANNEL) {
                throw new IOException("Invalid RFCOMM channel: " + port);
            }
        }
        if (uuid != null) {
            mUuid = uuid;
        } else {
            mUuid = new ParcelUuid(new UUID(0, 0));
        }
        mType = type;
        mAuth = auth;
        mAuthMitm = mitm;
        mMin16DigitPin = min16DigitPin;
        mEncrypt = encrypt;
        mDevice = device;
        mPort = port;
        mFd = fd;

        mSocketState = SocketState.INIT;

        if (device == null) {
            // Server socket
            mAddress = BluetoothAdapter.getDefaultAdapter().getAddress();
        } else {
            // Remote socket
            mAddress = device.getAddress();
        }
        mInputStream = new BluetoothInputStream(this);
        mOutputStream = new BluetoothOutputStream(this);
    }

    private BluetoothSocket(BluetoothSocket s) {
        if (VDBG) Log.d(TAG, "Creating new Private BluetoothSocket of type: " + s.mType);
        mUuid = s.mUuid;
        mType = s.mType;
        mAuth = s.mAuth;
        mEncrypt = s.mEncrypt;
        mPort = s.mPort;
        mInputStream = new BluetoothInputStream(this);
        mOutputStream = new BluetoothOutputStream(this);
        mMaxRxPacketSize = s.mMaxRxPacketSize;
        mMaxTxPacketSize = s.mMaxTxPacketSize;

        mServiceName = s.mServiceName;
        mExcludeSdp = s.mExcludeSdp;
        mAuthMitm = s.mAuthMitm;
        mMin16DigitPin = s.mMin16DigitPin;
    }

    private BluetoothSocket acceptSocket(String remoteAddr) throws IOException {
        BluetoothSocket as = new BluetoothSocket(this);
        as.mSocketState = SocketState.CONNECTED;
        FileDescriptor[] fds = mSocket.getAncillaryFileDescriptors();
        if (DBG) Log.d(TAG, "socket fd passed by stack fds: " + Arrays.toString(fds));
        if (fds == null || fds.length != 1) {
            Log.e(TAG, "socket fd passed from stack failed, fds: " + Arrays.toString(fds));
            as.close();
            throw new IOException("bt socket acept failed");
        }

        as.mPfd = new ParcelFileDescriptor(fds[0]);
        as.mSocket = LocalSocket.createConnectedLocalSocket(fds[0]);
        as.mSocketIS = as.mSocket.getInputStream();
        as.mSocketOS = as.mSocket.getOutputStream();
        as.mAddress = remoteAddr;
        as.mDevice = BluetoothAdapter.getDefaultAdapter().getRemoteDevice(remoteAddr);
        return as;
    }

    /**
     * Construct a BluetoothSocket from address. Used by native code.
     *
     * @param type type of socket
     * @param fd fd to use for connected socket, or -1 for a new socket
     * @param auth require the remote device to be authenticated
     * @param encrypt require the connection to be encrypted
     * @param address remote device that this socket can connect to
     * @param port remote port
     * @throws IOException On error, for example Bluetooth not available, or insufficient
     * privileges
     */
    private BluetoothSocket(int type, int fd, boolean auth, boolean encrypt, String address,
            int port) throws IOException {
        this(type, fd, auth, encrypt, new BluetoothDevice(address), port, null, false, false);
    }

    /** @hide */
    @Override
    protected void finalize() throws Throwable {
        try {
            close();
        } finally {
            super.finalize();
        }
    }

    private int getSecurityFlags() {
        int flags = 0;
        if (mAuth) {
            flags |= SEC_FLAG_AUTH;
        }
        if (mEncrypt) {
            flags |= SEC_FLAG_ENCRYPT;
        }
        if (mExcludeSdp) {
            flags |= BTSOCK_FLAG_NO_SDP;
        }
        if (mAuthMitm) {
            flags |= SEC_FLAG_AUTH_MITM;
        }
        if (mMin16DigitPin) {
            flags |= SEC_FLAG_AUTH_16_DIGIT;
        }
        return flags;
    }

    /**
     * Get the remote device this socket is connecting, or connected, to.
     *
     * @return remote device
     */
    public BluetoothDevice getRemoteDevice() {
        return mDevice;
    }

    /**
     * Get the input stream associated with this socket.
     * <p>The input stream will be returned even if the socket is not yet
     * connected, but operations on that stream will throw IOException until
     * the associated socket is connected.
     *
     * @return InputStream
     */
    public InputStream getInputStream() throws IOException {
        return mInputStream;
    }

    /**
     * Get the output stream associated with this socket.
     * <p>The output stream will be returned even if the socket is not yet
     * connected, but operations on that stream will throw IOException until
     * the associated socket is connected.
     *
     * @return OutputStream
     */
    public OutputStream getOutputStream() throws IOException {
        return mOutputStream;
    }

    /**
     * Get the connection status of this socket, ie, whether there is an active connection with
     * remote device.
     *
     * @return true if connected false if not connected
     */
    public boolean isConnected() {
        return mSocketState == SocketState.CONNECTED;
    }

    /*package*/ void setServiceName(String name) {
        mServiceName = name;
    }

    /**
     * Attempt to connect to a remote device.
     * <p>This method will block until a connection is made or the connection
     * fails. If this method returns without an exception then this socket
     * is now connected.
     * <p>Creating new connections to
     * remote Bluetooth devices should not be attempted while device discovery
     * is in progress. Device discovery is a heavyweight procedure on the
     * Bluetooth adapter and will significantly slow a device connection.
     * Use {@link BluetoothAdapter#cancelDiscovery()} to cancel an ongoing
     * discovery. Discovery is not managed by the Activity,
     * but is run as a system service, so an application should always call
     * {@link BluetoothAdapter#cancelDiscovery()} even if it
     * did not directly request a discovery, just to be sure.
     * <p>{@link #close} can be used to abort this call from another thread.
     *
     * @throws IOException on error, for example connection failure
     */
    public void connect() throws IOException {
        if (mDevice == null) throw new IOException("Connect is called on null device");

        try {
            if (mSocketState == SocketState.CLOSED) throw new IOException("socket closed");
            IBluetooth bluetoothProxy =
                    BluetoothAdapter.getDefaultAdapter().getBluetoothService(null);
            if (bluetoothProxy == null) throw new IOException("Bluetooth is off");
            mPfd = bluetoothProxy.getSocketManager().connectSocket(mDevice, mType,
                    mUuid, mPort, getSecurityFlags());
            synchronized (this) {
                if (DBG) Log.d(TAG, "connect(), SocketState: " + mSocketState + ", mPfd: " + mPfd);
                if (mSocketState == SocketState.CLOSED) throw new IOException("socket closed");
                if (mPfd == null) throw new IOException("bt socket connect failed");
                FileDescriptor fd = mPfd.getFileDescriptor();
                mSocket = LocalSocket.createConnectedLocalSocket(fd);
                mSocketIS = mSocket.getInputStream();
                mSocketOS = mSocket.getOutputStream();
            }
            int channel = readInt(mSocketIS);
            if (channel <= 0) {
                throw new IOException("bt socket connect failed");
            }
            mPort = channel;
            waitSocketSignal(mSocketIS);
            synchronized (this) {
                if (mSocketState == SocketState.CLOSED) {
                    throw new IOException("bt socket closed");
                }
                mSocketState = SocketState.CONNECTED;
            }
        } catch (RemoteException e) {
            Log.e(TAG, Log.getStackTraceString(new Throwable()));
            throw new IOException("unable to send RPC: " + e.getMessage());
        }
    }

    /**
     * Currently returns unix errno instead of throwing IOException,
     * so that BluetoothAdapter can check the error code for EADDRINUSE
     */
    /*package*/ int bindListen() {
        int ret;
        if (mSocketState == SocketState.CLOSED) return EBADFD;
        IBluetooth bluetoothProxy = BluetoothAdapter.getDefaultAdapter().getBluetoothService(null);
        if (bluetoothProxy == null) {
            Log.e(TAG, "bindListen fail, reason: bluetooth is off");
            return -1;
        }
        try {
            if (DBG) Log.d(TAG, "bindListen(): mPort=" + mPort + ", mType=" + mType);
            mPfd = bluetoothProxy.getSocketManager().createSocketChannel(mType, mServiceName,
                    mUuid, mPort, getSecurityFlags());
        } catch (RemoteException e) {
            Log.e(TAG, Log.getStackTraceString(new Throwable()));
            return -1;
        }

        // read out port number
        try {
            synchronized (this) {
                if (DBG) {
                    Log.d(TAG, "bindListen(), SocketState: " + mSocketState + ", mPfd: " + mPfd);
                }
                if (mSocketState != SocketState.INIT) return EBADFD;
                if (mPfd == null) return -1;
                FileDescriptor fd = mPfd.getFileDescriptor();
                if (fd == null) {
                    Log.e(TAG, "bindListen(), null file descriptor");
                    return -1;
                }

                if (DBG) Log.d(TAG, "bindListen(), Create LocalSocket");
                mSocket = LocalSocket.createConnectedLocalSocket(fd);
                if (DBG) Log.d(TAG, "bindListen(), new LocalSocket.getInputStream()");
                mSocketIS = mSocket.getInputStream();
                mSocketOS = mSocket.getOutputStream();
            }
            if (DBG) Log.d(TAG, "bindListen(), readInt mSocketIS: " + mSocketIS);
            int channel = readInt(mSocketIS);
            synchronized (this) {
                if (mSocketState == SocketState.INIT) {
                    mSocketState = SocketState.LISTENING;
                }
            }
            if (DBG) Log.d(TAG, "bindListen(): channel=" + channel + ", mPort=" + mPort);
            if (mPort <= -1) {
                mPort = channel;
            } // else ASSERT(mPort == channel)
            ret = 0;
        } catch (IOException e) {
            if (mPfd != null) {
                try {
                    mPfd.close();
                } catch (IOException e1) {
                    Log.e(TAG, "bindListen, close mPfd: " + e1);
                }
                mPfd = null;
            }
            Log.e(TAG, "bindListen, fail to get port number, exception: " + e);
            return -1;
        }
        return ret;
    }

    /*package*/ BluetoothSocket accept(int timeout) throws IOException {
        BluetoothSocket acceptedSocket;
        if (mSocketState != SocketState.LISTENING) {
            throw new IOException("bt socket is not in listen state");
        }
        if (timeout > 0) {
            Log.d(TAG, "accept() set timeout (ms):" + timeout);
            mSocket.setSoTimeout(timeout);
        }
        String RemoteAddr = waitSocketSignal(mSocketIS);
        if (timeout > 0) {
            mSocket.setSoTimeout(0);
        }
        synchronized (this) {
            if (mSocketState != SocketState.LISTENING) {
                throw new IOException("bt socket is not in listen state");
            }
            acceptedSocket = acceptSocket(RemoteAddr);
            //quick drop the reference of the file handle
        }
        return acceptedSocket;
    }

    /*package*/ int available() throws IOException {
        if (VDBG) Log.d(TAG, "available: " + mSocketIS);
        return mSocketIS.available();
    }

    /*package*/ int read(byte[] b, int offset, int length) throws IOException {
        int ret = 0;
        if (VDBG) Log.d(TAG, "read in:  " + mSocketIS + " len: " + length);
        if ((mType == TYPE_L2CAP) || (mType == TYPE_L2CAP_LE)) {
            int bytesToRead = length;
            if (VDBG) {
                Log.v(TAG, "l2cap: read(): offset: " + offset + " length:" + length
                        + "mL2capBuffer= " + mL2capBuffer);
            }
            if (mL2capBuffer == null) {
                createL2capRxBuffer();
            }
            if (mL2capBuffer.remaining() == 0) {
                if (VDBG) Log.v(TAG, "l2cap buffer empty, refilling...");
                if (fillL2capRxBuffer() == -1) {
                    return -1;
                }
            }
            if (bytesToRead > mL2capBuffer.remaining()) {
                bytesToRead = mL2capBuffer.remaining();
            }
            if (VDBG) {
                Log.v(TAG, "get(): offset: " + offset
                        + " bytesToRead: " + bytesToRead);
            }
            mL2capBuffer.get(b, offset, bytesToRead);
            ret = bytesToRead;
        } else {
            if (VDBG) Log.v(TAG, "default: read(): offset: " + offset + " length:" + length);
            ret = mSocketIS.read(b, offset, length);
        }
        if (ret < 0) {
            throw new IOException("bt socket closed, read return: " + ret);
        }
        if (VDBG) Log.d(TAG, "read out:  " + mSocketIS + " ret: " + ret);
        return ret;
    }

    /*package*/ int write(byte[] b, int offset, int length) throws IOException {

        //TODO: Since bindings can exist between the SDU size and the
        //      protocol, we might need to throw an exception instead of just
        //      splitting the write into multiple smaller writes.
        //      Rfcomm uses dynamic allocation, and should not have any bindings
        //      to the actual message length.
        if (VDBG) Log.d(TAG, "write: " + mSocketOS + " length: " + length);
        if ((mType == TYPE_L2CAP) || (mType == TYPE_L2CAP_LE)) {
            if (length <= mMaxTxPacketSize) {
                mSocketOS.write(b, offset, length);
            } else {
                if (DBG) {
                    Log.w(TAG, "WARNING: Write buffer larger than L2CAP packet size!\n"
                            + "Packet will be divided into SDU packets of size "
                            + mMaxTxPacketSize);
                }
                int tmpOffset = offset;
                int bytesToWrite = length;
                while (bytesToWrite > 0) {
                    int tmpLength = (bytesToWrite > mMaxTxPacketSize)
                            ? mMaxTxPacketSize
                            : bytesToWrite;
                    mSocketOS.write(b, tmpOffset, tmpLength);
                    tmpOffset += tmpLength;
                    bytesToWrite -= tmpLength;
                }
            }
        } else {
            mSocketOS.write(b, offset, length);
        }
        // There is no good way to confirm since the entire process is asynchronous anyway
        if (VDBG) Log.d(TAG, "write out: " + mSocketOS + " length: " + length);
        return length;
    }

    @Override
    public void close() throws IOException {
        Log.d(TAG, "close() this: " + this + ", channel: " + mPort + ", mSocketIS: " + mSocketIS
                + ", mSocketOS: " + mSocketOS + "mSocket: " + mSocket + ", mSocketState: "
                + mSocketState);
        if (mSocketState == SocketState.CLOSED) {
            return;
        } else {
            synchronized (this) {
                if (mSocketState == SocketState.CLOSED) {
                    return;
                }
                mSocketState = SocketState.CLOSED;
                if (mSocket != null) {
                    if (DBG) Log.d(TAG, "Closing mSocket: " + mSocket);
                    mSocket.shutdownInput();
                    mSocket.shutdownOutput();
                    mSocket.close();
                    mSocket = null;
                }
                if (mPfd != null) {
                    mPfd.close();
                    mPfd = null;
                }
            }
        }
    }

    /*package */ void removeChannel() {
    }

    /*package */ int getPort() {
        return mPort;
    }

    /**
     * Get the maximum supported Transmit packet size for the underlying transport.
     * Use this to optimize the writes done to the output socket, to avoid sending
     * half full packets.
     *
     * @return the maximum supported Transmit packet size for the underlying transport.
     */
    public int getMaxTransmitPacketSize() {
        return mMaxTxPacketSize;
    }

    /**
     * Get the maximum supported Receive packet size for the underlying transport.
     * Use this to optimize the reads done on the input stream, as any call to read
     * will return a maximum of this amount of bytes - or for some transports a
     * multiple of this value.
     *
     * @return the maximum supported Receive packet size for the underlying transport.
     */
    public int getMaxReceivePacketSize() {
        return mMaxRxPacketSize;
    }

    /**
     * Get the type of the underlying connection.
     *
     * @return one of {@link #TYPE_RFCOMM}, {@link #TYPE_SCO} or {@link #TYPE_L2CAP}
     */
    public int getConnectionType() {
        if (mType == TYPE_L2CAP_LE) {
            // Treat the LE CoC to be the same type as L2CAP.
            return TYPE_L2CAP;
        }
        return mType;
    }

    /**
     * Change if a SDP entry should be automatically created.
     * Must be called before calling .bind, for the call to have any effect.
     *
     * @param excludeSdp <li>TRUE - do not auto generate SDP record. <li>FALSE - default - auto
     * generate SPP SDP record.
     * @hide
     */
    public void setExcludeSdp(boolean excludeSdp) {
        mExcludeSdp = excludeSdp;
    }

    /**
     * Set the LE Transmit Data Length to be the maximum that the BT Controller is capable of. This
     * parameter is used by the BT Controller to set the maximum transmission packet size on this
     * connection. This function is currently used for testing only.
     * @hide
     */
    public void requestMaximumTxDataLength() throws IOException {
        if (mDevice == null) {
            throw new IOException("requestMaximumTxDataLength is called on null device");
        }

        try {
            if (mSocketState == SocketState.CLOSED) {
                throw new IOException("socket closed");
            }
            IBluetooth bluetoothProxy =
                    BluetoothAdapter.getDefaultAdapter().getBluetoothService(null);
            if (bluetoothProxy == null) {
                throw new IOException("Bluetooth is off");
            }

            if (DBG) Log.d(TAG, "requestMaximumTxDataLength");
            bluetoothProxy.getSocketManager().requestMaximumTxDataLength(mDevice);
        } catch (RemoteException e) {
            Log.e(TAG, Log.getStackTraceString(new Throwable()));
            throw new IOException("unable to send RPC: " + e.getMessage());
        }
    }

    private String convertAddr(final byte[] addr) {
        return String.format(Locale.US, "%02X:%02X:%02X:%02X:%02X:%02X",
                addr[0], addr[1], addr[2], addr[3], addr[4], addr[5]);
    }

    private String waitSocketSignal(InputStream is) throws IOException {
        byte[] sig = new byte[SOCK_SIGNAL_SIZE];
        int ret = readAll(is, sig);
        if (VDBG) {
            Log.d(TAG, "waitSocketSignal read " + SOCK_SIGNAL_SIZE + " bytes signal ret: " + ret);
        }
        ByteBuffer bb = ByteBuffer.wrap(sig);
        /* the struct in native is decorated with __attribute__((packed)), hence this is possible */
        bb.order(ByteOrder.nativeOrder());
        int size = bb.getShort();
        if (size != SOCK_SIGNAL_SIZE) {
            throw new IOException("Connection failure, wrong signal size: " + size);
        }
        byte[] addr = new byte[6];
        bb.get(addr);
        int channel = bb.getInt();
        int status = bb.getInt();
        mMaxTxPacketSize = (bb.getShort() & 0xffff); // Convert to unsigned value
        mMaxRxPacketSize = (bb.getShort() & 0xffff); // Convert to unsigned value
        String RemoteAddr = convertAddr(addr);
        if (VDBG) {
            Log.d(TAG, "waitSocketSignal: sig size: " + size + ", remote addr: "
                    + RemoteAddr + ", channel: " + channel + ", status: " + status
                    + " MaxRxPktSize: " + mMaxRxPacketSize + " MaxTxPktSize: " + mMaxTxPacketSize);
        }
        if (status != 0) {
            throw new IOException("Connection failure, status: " + status);
        }
        return RemoteAddr;
    }

    private void createL2capRxBuffer() {
        if ((mType == TYPE_L2CAP) || (mType == TYPE_L2CAP_LE)) {
            // Allocate the buffer to use for reads.
            if (VDBG) Log.v(TAG, "  Creating mL2capBuffer: mMaxPacketSize: " + mMaxRxPacketSize);
            mL2capBuffer = ByteBuffer.wrap(new byte[mMaxRxPacketSize]);
            if (VDBG) Log.v(TAG, "mL2capBuffer.remaining()" + mL2capBuffer.remaining());
            mL2capBuffer.limit(0); // Ensure we do a real read at the first read-request
            if (VDBG) {
                Log.v(TAG, "mL2capBuffer.remaining() after limit(0):" + mL2capBuffer.remaining());
            }
        }
    }

    private int readAll(InputStream is, byte[] b) throws IOException {
        int left = b.length;
        while (left > 0) {
            int ret = is.read(b, b.length - left, left);
            if (ret <= 0) {
                throw new IOException("read failed, socket might closed or timeout, read ret: "
                        + ret);
            }
            left -= ret;
            if (left != 0) {
                Log.w(TAG, "readAll() looping, read partial size: " + (b.length - left)
                        + ", expect size: " + b.length);
            }
        }
        return b.length;
    }

    private int readInt(InputStream is) throws IOException {
        byte[] ibytes = new byte[4];
        int ret = readAll(is, ibytes);
        if (VDBG) Log.d(TAG, "inputStream.read ret: " + ret);
        ByteBuffer bb = ByteBuffer.wrap(ibytes);
        bb.order(ByteOrder.nativeOrder());
        return bb.getInt();
    }

    private int fillL2capRxBuffer() throws IOException {
        mL2capBuffer.rewind();
        int ret = mSocketIS.read(mL2capBuffer.array());
        if (ret == -1) {
            // reached end of stream - return -1
            mL2capBuffer.limit(0);
            return -1;
        }
        mL2capBuffer.limit(ret);
        return ret;
    }


}