android/bluetooth/BluetoothAdapter.java

/*
 * Copyright (C) 2009 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.annotation.SdkConstant;
import android.annotation.SdkConstant.SdkConstantType;
import android.os.Binder;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.ParcelUuid;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.util.Log;

import java.io.IOException;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Random;
import java.util.Set;
import java.util.UUID;

/**
 * Represents the local device Bluetooth adapter. The {@link BluetoothAdapter}
 * lets you perform fundamental Bluetooth tasks, such as initiate
 * device discovery, query a list of bonded (paired) devices,
 * instantiate a {@link BluetoothDevice} using a known MAC address, and create
 * a {@link BluetoothServerSocket} to listen for connection requests from other
 * devices.
 *
 * <p>To get a {@link BluetoothAdapter} representing the local Bluetooth
 * adapter, call the static {@link #getDefaultAdapter} method.
 * Fundamentally, this is your starting point for all
 * Bluetooth actions. Once you have the local adapter, you can get a set of
 * {@link BluetoothDevice} objects representing all paired devices with
 * {@link #getBondedDevices()}; start device discovery with
 * {@link #startDiscovery()}; or create a {@link BluetoothServerSocket} to
 * listen for incoming connection requests with
 * {@link #listenUsingRfcommWithServiceRecord(String,UUID)}.
 *
 * <p class="note"><strong>Note:</strong>
 * Most methods require the {@link android.Manifest.permission#BLUETOOTH}
 * permission and some also require the
 * {@link android.Manifest.permission#BLUETOOTH_ADMIN} permission.
 *
 * {@see BluetoothDevice}
 * {@see BluetoothServerSocket}
 */
public final class BluetoothAdapter {
    private static final String TAG = "BluetoothAdapter";
    private static final boolean DBG = false;

    /**
     * Sentinel error value for this class. Guaranteed to not equal any other
     * integer constant in this class. Provided as a convenience for functions
     * that require a sentinel error value, for example:
     * <p><code>Intent.getIntExtra(BluetoothAdapter.EXTRA_STATE,
     * BluetoothAdapter.ERROR)</code>
     */
    public static final int ERROR = Integer.MIN_VALUE;

    /**
     * Broadcast Action: The state of the local Bluetooth adapter has been
     * changed.
     * <p>For example, Bluetooth has been turned on or off.
     * <p>Always contains the extra fields {@link #EXTRA_STATE} and {@link
     * #EXTRA_PREVIOUS_STATE} containing the new and old states
     * respectively.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH} to receive.
     */
    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)
    public static final String ACTION_STATE_CHANGED =
            "android.bluetooth.adapter.action.STATE_CHANGED";

    /**
     * Used as an int extra field in {@link #ACTION_STATE_CHANGED}
     * intents to request the current power state. Possible values are:
     * {@link #STATE_OFF},
     * {@link #STATE_TURNING_ON},
     * {@link #STATE_ON},
     * {@link #STATE_TURNING_OFF},
     */
    public static final String EXTRA_STATE =
            "android.bluetooth.adapter.extra.STATE";
    /**
     * Used as an int extra field in {@link #ACTION_STATE_CHANGED}
     * intents to request the previous power state. Possible values are:
     * {@link #STATE_OFF},
     * {@link #STATE_TURNING_ON},
     * {@link #STATE_ON},
     * {@link #STATE_TURNING_OFF},
     */
    public static final String EXTRA_PREVIOUS_STATE =
            "android.bluetooth.adapter.extra.PREVIOUS_STATE";

    /**
     * Indicates the local Bluetooth adapter is off.
     */
    public static final int STATE_OFF = 10;
    /**
     * Indicates the local Bluetooth adapter is turning on. However local
     * clients should wait for {@link #STATE_ON} before attempting to
     * use the adapter.
     */
    public static final int STATE_TURNING_ON = 11;
    /**
     * Indicates the local Bluetooth adapter is on, and ready for use.
     */
    public static final int STATE_ON = 12;
    /**
     * Indicates the local Bluetooth adapter is turning off. Local clients
     * should immediately attempt graceful disconnection of any remote links.
     */
    public static final int STATE_TURNING_OFF = 13;

    /**
     * Activity Action: Show a system activity that requests discoverable mode.
     * This activity will also request the user to turn on Bluetooth if it
     * is not currently enabled.
     * <p>Discoverable mode is equivalent to {@link
     * #SCAN_MODE_CONNECTABLE_DISCOVERABLE}. It allows remote devices to see
     * this Bluetooth adapter when they perform a discovery.
     * <p>For privacy, Android is not discoverable by default.
     * <p>The sender of this Intent can optionally use extra field {@link
     * #EXTRA_DISCOVERABLE_DURATION} to request the duration of
     * discoverability. Currently the default duration is 120 seconds, and
     * maximum duration is capped at 300 seconds for each request.
     * <p>Notification of the result of this activity is posted using the
     * {@link android.app.Activity#onActivityResult} callback. The
     * <code>resultCode</code>
     * will be the duration (in seconds) of discoverability, or a negative
     * value if the user rejected discoverability.
     * <p>Applications can also listen for {@link #ACTION_SCAN_MODE_CHANGED}
     * for global notification whenever the scan mode changes. For example, an
     * application can be notified when the device has ended discoverability.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     */
    @SdkConstant(SdkConstantType.ACTIVITY_INTENT_ACTION)
    public static final String ACTION_REQUEST_DISCOVERABLE =
            "android.bluetooth.adapter.action.REQUEST_DISCOVERABLE";

    /**
     * Used as an optional int extra field in {@link
     * #ACTION_REQUEST_DISCOVERABLE} intents to request a specific duration
     * for discoverability in seconds. The current default is 120 seconds, and
     * requests over 300 seconds will be capped. These values could change.
     */
    public static final String EXTRA_DISCOVERABLE_DURATION =
            "android.bluetooth.adapter.extra.DISCOVERABLE_DURATION";

    /**
     * Activity Action: Show a system activity that allows the user to turn on
     * Bluetooth.
     * <p>This system activity will return once Bluetooth has completed turning
     * on, or the user has decided not to turn Bluetooth on.
     * <p>Notification of the result of this activity is posted using the
     * {@link android.app.Activity#onActivityResult} callback. The
     * <code>resultCode</code>
     * will be negative if the user did not turn on Bluetooth, and non-negative
     * if Bluetooth has been turned on.
     * <p>Applications can also listen for {@link #ACTION_STATE_CHANGED}
     * for global notification whenever Bluetooth is turned on or off.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     */
    @SdkConstant(SdkConstantType.ACTIVITY_INTENT_ACTION)
    public static final String ACTION_REQUEST_ENABLE =
            "android.bluetooth.adapter.action.REQUEST_ENABLE";

    /**
     * Broadcast Action: Indicates the Bluetooth scan mode of the local Adapter
     * has changed.
     * <p>Always contains the extra fields {@link #EXTRA_SCAN_MODE} and {@link
     * #EXTRA_PREVIOUS_SCAN_MODE} containing the new and old scan modes
     * respectively.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     */
    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)
    public static final String ACTION_SCAN_MODE_CHANGED =
            "android.bluetooth.adapter.action.SCAN_MODE_CHANGED";

    /**
     * Used as an int extra field in {@link #ACTION_SCAN_MODE_CHANGED}
     * intents to request the current scan mode. Possible values are:
     * {@link #SCAN_MODE_NONE},
     * {@link #SCAN_MODE_CONNECTABLE},
     * {@link #SCAN_MODE_CONNECTABLE_DISCOVERABLE},
     */
    public static final String EXTRA_SCAN_MODE = "android.bluetooth.adapter.extra.SCAN_MODE";
    /**
     * Used as an int extra field in {@link #ACTION_SCAN_MODE_CHANGED}
     * intents to request the previous scan mode. Possible values are:
     * {@link #SCAN_MODE_NONE},
     * {@link #SCAN_MODE_CONNECTABLE},
     * {@link #SCAN_MODE_CONNECTABLE_DISCOVERABLE},
     */
    public static final String EXTRA_PREVIOUS_SCAN_MODE =
            "android.bluetooth.adapter.extra.PREVIOUS_SCAN_MODE";

    /**
     * Indicates that both inquiry scan and page scan are disabled on the local
     * Bluetooth adapter. Therefore this device is neither discoverable
     * nor connectable from remote Bluetooth devices.
     */
    public static final int SCAN_MODE_NONE = 20;
    /**
     * Indicates that inquiry scan is disabled, but page scan is enabled on the
     * local Bluetooth adapter. Therefore this device is not discoverable from
     * remote Bluetooth devices, but is connectable from remote devices that
     * have previously discovered this device.
     */
    public static final int SCAN_MODE_CONNECTABLE = 21;
    /**
     * Indicates that both inquiry scan and page scan are enabled on the local
     * Bluetooth adapter. Therefore this device is both discoverable and
     * connectable from remote Bluetooth devices.
     */
    public static final int SCAN_MODE_CONNECTABLE_DISCOVERABLE = 23;


    /**
     * Broadcast Action: The local Bluetooth adapter has started the remote
     * device discovery process.
     * <p>This usually involves an inquiry scan of about 12 seconds, followed
     * by a page scan of each new device to retrieve its Bluetooth name.
     * <p>Register for {@link BluetoothDevice#ACTION_FOUND} to be notified as
     * remote Bluetooth devices are found.
     * <p>Device discovery is a heavyweight procedure. New connections to
     * remote Bluetooth devices should not be attempted while discovery is in
     * progress, and existing connections will experience limited bandwidth
     * and high latency. Use {@link #cancelDiscovery()} to cancel an ongoing
     * discovery.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH} to receive.
     */
    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)
    public static final String ACTION_DISCOVERY_STARTED =
            "android.bluetooth.adapter.action.DISCOVERY_STARTED";
    /**
     * Broadcast Action: The local Bluetooth adapter has finished the device
     * discovery process.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH} to receive.
     */
    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)
    public static final String ACTION_DISCOVERY_FINISHED =
            "android.bluetooth.adapter.action.DISCOVERY_FINISHED";

    /**
     * Broadcast Action: The local Bluetooth adapter has changed its friendly
     * Bluetooth name.
     * <p>This name is visible to remote Bluetooth devices.
     * <p>Always contains the extra field {@link #EXTRA_LOCAL_NAME} containing
     * the name.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH} to receive.
     */
    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)
    public static final String ACTION_LOCAL_NAME_CHANGED =
            "android.bluetooth.adapter.action.LOCAL_NAME_CHANGED";
    /**
     * Used as a String extra field in {@link #ACTION_LOCAL_NAME_CHANGED}
     * intents to request the local Bluetooth name.
     */
    public static final String EXTRA_LOCAL_NAME = "android.bluetooth.adapter.extra.LOCAL_NAME";

    /** @hide */
    public static final String BLUETOOTH_SERVICE = "bluetooth";

    private static final int ADDRESS_LENGTH = 17;

    /**
     * Lazyily initialized singleton. Guaranteed final after first object
     * constructed.
     */
    private static BluetoothAdapter sAdapter;

    private final IBluetooth mService;

    /**
     * Get a handle to the default local Bluetooth adapter.
     * <p>Currently Android only supports one Bluetooth adapter, but the API
     * could be extended to support more. This will always return the default
     * adapter.
     * @return the default local adapter, or null if Bluetooth is not supported
     *         on this hardware platform
     */
    public static synchronized BluetoothAdapter getDefaultAdapter() {
        if (sAdapter == null) {
            IBinder b = ServiceManager.getService(BluetoothAdapter.BLUETOOTH_SERVICE);
            if (b != null) {
                IBluetooth service = IBluetooth.Stub.asInterface(b);
                sAdapter = new BluetoothAdapter(service);
            }
        }
        return sAdapter;
    }

    /**
     * Use {@link #getDefaultAdapter} to get the BluetoothAdapter instance.
     * @hide
     */
    public BluetoothAdapter(IBluetooth service) {
        if (service == null) {
            throw new IllegalArgumentException("service is null");
        }
        mService = service;
    }

    /**
     * Get a {@link BluetoothDevice} object for the given Bluetooth hardware
     * address.
     * <p>Valid Bluetooth hardware addresses must be upper case, in a format
     * such as "00:11:22:33:AA:BB". The helper {@link #checkBluetoothAddress} is
     * available to validate a Bluetooth address.
     * <p>A {@link BluetoothDevice} will always be returned for a valid
     * hardware address, even if this adapter has never seen that device.
     *
     * @param address valid Bluetooth MAC address
     * @throws IllegalArgumentException if address is invalid
     */
    public BluetoothDevice getRemoteDevice(String address) {
        return new BluetoothDevice(address);
    }

    /**
     * Return true if Bluetooth is currently enabled and ready for use.
     * <p>Equivalent to:
     * <code>getBluetoothState() == STATE_ON</code>
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     *
     * @return true if the local adapter is turned on
     */
    public boolean isEnabled() {
        try {
            return mService.isEnabled();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /**
     * Get the current state of the local Bluetooth adapter.
     * <p>Possible return values are
     * {@link #STATE_OFF},
     * {@link #STATE_TURNING_ON},
     * {@link #STATE_ON},
     * {@link #STATE_TURNING_OFF}.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     *
     * @return current state of Bluetooth adapter
     */
    public int getState() {
        try {
            return mService.getBluetoothState();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return STATE_OFF;
    }

    /**
     * Turn on the local Bluetooth adapter.
     * <p>This powers on the underlying Bluetooth hardware, and starts all
     * Bluetooth system services.
     * <p>This is an asynchronous call: it will return immediately, and
     * clients should listen for {@link #ACTION_STATE_CHANGED}
     * to be notified of subsequent adapter state changes. If this call returns
     * true, then the adapter state will immediately transition from {@link
     * #STATE_OFF} to {@link #STATE_TURNING_ON}, and some time
     * later transition to either {@link #STATE_OFF} or {@link
     * #STATE_ON}. If this call returns false then there was an
     * immediate problem that will prevent the adapter from being turned on -
     * such as Airplane mode, or the adapter is already turned on.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH_ADMIN}
     *
     * @return true to indicate adapter startup has begun, or false on
     *         immediate error
     */
    public boolean enable() {
        try {
            return mService.enable();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /**
     * Turn off the local Bluetooth adapter.
     * <p>This gracefully shuts down all Bluetooth connections, stops Bluetooth
     * system services, and powers down the underlying Bluetooth hardware.
     * <p>This is an asynchronous call: it will return immediately, and
     * clients should listen for {@link #ACTION_STATE_CHANGED}
     * to be notified of subsequent adapter state changes. If this call returns
     * true, then the adapter state will immediately transition from {@link
     * #STATE_ON} to {@link #STATE_TURNING_OFF}, and some time
     * later transition to either {@link #STATE_OFF} or {@link
     * #STATE_ON}. If this call returns false then there was an
     * immediate problem that will prevent the adapter from being turned off -
     * such as the adapter already being turned off.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH_ADMIN}
     *
     * @return true to indicate adapter shutdown has begun, or false on
     *         immediate error
     */
    public boolean disable() {
        try {
            return mService.disable(true);
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /**
     * Returns the hardware address of the local Bluetooth adapter.
     * <p>For example, "00:11:22:AA:BB:CC".
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     *
     * @return Bluetooth hardware address as string
     */
    public String getAddress() {
        try {
            return mService.getAddress();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return null;
    }

    /**
     * Get the friendly Bluetooth name of the local Bluetooth adapter.
     * <p>This name is visible to remote Bluetooth devices.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     *
     * @return the Bluetooth name, or null on error
     */
    public String getName() {
        try {
            return mService.getName();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return null;
    }

    /**
     * Set the friendly Bluetooth name of the local Bluetoth adapter.
     * <p>This name is visible to remote Bluetooth devices.
     * <p>Valid Bluetooth names are a maximum of 248 UTF-8 characters, however
     * many remote devices can only display the first 40 characters, and some
     * may be limited to just 20.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH_ADMIN}
     *
     * @param name a valid Bluetooth name
     * @return     true if the name was set, false otherwise
     */
    public boolean setName(String name) {
        try {
            return mService.setName(name);
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /**
     * Get the current Bluetooth scan mode of the local Bluetooth adaper.
     * <p>The Bluetooth scan mode determines if the local adapter is
     * connectable and/or discoverable from remote Bluetooth devices.
     * <p>Possible values are:
     * {@link #SCAN_MODE_NONE},
     * {@link #SCAN_MODE_CONNECTABLE},
     * {@link #SCAN_MODE_CONNECTABLE_DISCOVERABLE}.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     *
     * @return scan mode
     */
    public int getScanMode() {
        try {
            return mService.getScanMode();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return SCAN_MODE_NONE;
    }

    /**
     * Set the Bluetooth scan mode of the local Bluetooth adapter.
     * <p>The Bluetooth scan mode determines if the local adapter is
     * connectable and/or discoverable from remote Bluetooth devices.
     * <p>For privacy reasons, discoverable mode is automatically turned off
     * after <code>duration</code> seconds. For example, 120 seconds should be
     * enough for a remote device to initiate and complete its discovery
     * process.
     * <p>Valid scan mode values are:
     * {@link #SCAN_MODE_NONE},
     * {@link #SCAN_MODE_CONNECTABLE},
     * {@link #SCAN_MODE_CONNECTABLE_DISCOVERABLE}.
     * <p>Requires {@link android.Manifest.permission#WRITE_SECURE_SETTINGS}
     * <p>Applications cannot set the scan mode. They should use
     * <code>startActivityForResult(
     * BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE})
     * </code>instead.
     *
     * @param mode valid scan mode
     * @param duration time in seconds to apply scan mode, only used for
     *                 {@link #SCAN_MODE_CONNECTABLE_DISCOVERABLE}
     * @return     true if the scan mode was set, false otherwise
     * @hide
     */
    public boolean setScanMode(int mode, int duration) {
        try {
            return mService.setScanMode(mode, duration);
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /** @hide */
    public boolean setScanMode(int mode) {
        return setScanMode(mode, 120);
    }

    /** @hide */
    public int getDiscoverableTimeout() {
        try {
            return mService.getDiscoverableTimeout();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return -1;
    }

    /** @hide */
    public void setDiscoverableTimeout(int timeout) {
        try {
            mService.setDiscoverableTimeout(timeout);
        } catch (RemoteException e) {Log.e(TAG, "", e);}
    }

    /**
     * Start the remote device discovery process.
     * <p>The discovery process usually involves an inquiry scan of about 12
     * seconds, followed by a page scan of each new device to retrieve its
     * Bluetooth name.
     * <p>This is an asynchronous call, it will return immediately. Register
     * for {@link #ACTION_DISCOVERY_STARTED} and {@link
     * #ACTION_DISCOVERY_FINISHED} intents to determine exactly when the
     * discovery starts and completes. Register for {@link
     * BluetoothDevice#ACTION_FOUND} to be notified as remote Bluetooth devices
     * are found.
     * <p>Device discovery is a heavyweight procedure. New connections to
     * remote Bluetooth devices should not be attempted while discovery is in
     * progress, and existing connections will experience limited bandwidth
     * and high latency. Use {@link #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>Device discovery will only find remote devices that are currently
     * <i>discoverable</i> (inquiry scan enabled). Many Bluetooth devices are
     * not discoverable by default, and need to be entered into a special mode.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH_ADMIN}.
     *
     * @return true on success, false on error
     */
    public boolean startDiscovery() {
        try {
            return mService.startDiscovery();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /**
     * Cancel the current device discovery process.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH_ADMIN}.
     * <p>Because discovery is a heavyweight precedure for the Bluetooth
     * adapter, this method should always be called before attempting to connect
     * to a remote device with {@link
     * android.bluetooth.BluetoothSocket#connect()}. Discovery is not managed by
     * the  Activity, but is run as a system service, so an application should
     * always call cancel discovery even if it did not directly request a
     * discovery, just to be sure.
     *
     * @return true on success, false on error
     */
    public boolean cancelDiscovery() {
        try {
            mService.cancelDiscovery();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /**
     * Return true if the local Bluetooth adapter is currently in the device
     * discovery process.
     * <p>Device discovery is a heavyweight procedure. New connections to
     * remote Bluetooth devices should not be attempted while discovery is in
     * progress, and existing connections will experience limited bandwidth
     * and high latency. Use {@link #cancelDiscovery()} to cancel an ongoing
     * discovery.
     * <p>Applications can also register for {@link #ACTION_DISCOVERY_STARTED}
     * or {@link #ACTION_DISCOVERY_FINISHED} to be notified when discovery
     * starts or completes.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}.
     *
     * @return true if discovering
     */
    public boolean isDiscovering() {
        try {
            return mService.isDiscovering();
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return false;
    }

    /**
     * Return the set of {@link BluetoothDevice} objects that are bonded
     * (paired) to the local adapter.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}.
     *
     * @return unmodifiable set of {@link BluetoothDevice}, or null on error
     */
    public Set<BluetoothDevice> getBondedDevices() {
        try {
            return toDeviceSet(mService.listBonds());
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        return null;
    }

    /**
     * Picks RFCOMM channels until none are left.
     * Avoids reserved channels.
     * Ideally we would pick random channels, but in the current implementation
     * we start with the channel that is the hash of the UUID, and try every
     * available channel from there. This means that in most cases a given
     * uuid will use the same channel. This is a workaround for a Bluez SDP
     * bug where we are not updating the cache when the channel changes for a
     * uuid.
     * TODO: Fix the Bluez SDP caching bug, and go back to random channel
     * selection
     */
    private static class RfcommChannelPicker {
        private static final int[] RESERVED_RFCOMM_CHANNELS =  new int[] {
            10,  // HFAG
            11,  // HSAG
            12,  // OPUSH
            19,  // PBAP
        };
        private static LinkedList<Integer> sChannels;  // master list of non-reserved channels
        private static Random sRandom;

        private final LinkedList<Integer> mChannels;  // local list of channels left to try

        private final UUID mUuid;

        public RfcommChannelPicker(UUID uuid) {
            synchronized (RfcommChannelPicker.class) {
                if (sChannels == null) {
                    // lazy initialization of non-reserved rfcomm channels
                    sChannels = new LinkedList<Integer>();
                    for (int i = 1; i <= BluetoothSocket.MAX_RFCOMM_CHANNEL; i++) {
                        sChannels.addLast(new Integer(i));
                    }
                    for (int reserved : RESERVED_RFCOMM_CHANNELS) {
                        sChannels.remove(new Integer(reserved));
                    }
                    sRandom = new Random();
                }
                mChannels = (LinkedList<Integer>)sChannels.clone();
            }
            mUuid = uuid;
        }
        /* Returns next channel, or -1 if we're out */
        public int nextChannel() {
            int channel = mUuid.hashCode();  // always pick the same channel to try first
            Integer channelInt;
            while (mChannels.size() > 0) {
                channelInt = new Integer(channel);
                if (mChannels.remove(channelInt)) {
                    return channel;
                }
                channel = (channel % BluetoothSocket.MAX_RFCOMM_CHANNEL) + 1;
            }

            return -1;
        }
    }

    /**
     * Create a listening, secure RFCOMM Bluetooth socket.
     * <p>A remote device connecting to this socket will be authenticated and
     * communication on this socket will be encrypted.
     * <p>Use {@link BluetoothServerSocket#accept} to retrieve incoming
     * connections from a listening {@link BluetoothServerSocket}.
     * <p>Valid RFCOMM channels are in range 1 to 30.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH_ADMIN}
     * @param channel RFCOMM channel to listen on
     * @return a listening RFCOMM BluetoothServerSocket
     * @throws IOException on error, for example Bluetooth not available, or
     *                     insufficient permissions, or channel in use.
     * @hide
     */
    public BluetoothServerSocket listenUsingRfcommOn(int channel) throws IOException {
        BluetoothServerSocket socket = new BluetoothServerSocket(
                BluetoothSocket.TYPE_RFCOMM, true, true, channel);
        int errno = socket.mSocket.bindListen();
        if (errno != 0) {
            try {
                socket.close();
            } catch (IOException e) {}
            socket.mSocket.throwErrnoNative(errno);
        }
        return socket;
    }

    /**
     * Create a listening, secure RFCOMM Bluetooth socket with Service Record.
     * <p>A remote device connecting to this socket will be authenticated and
     * communication on this socket will be encrypted.
     * <p>Use {@link BluetoothServerSocket#accept} to retrieve incoming
     * connections from a listening {@link BluetoothServerSocket}.
     * <p>The system will assign an unused RFCOMM channel to listen on.
     * <p>The system will also register a Service Discovery
     * Protocol (SDP) record with the local SDP server containing the specified
     * UUID, service name, and auto-assigned channel. Remote Bluetooth devices
     * can use the same UUID to query our SDP server and discover which channel
     * to connect to. This SDP record will be removed when this socket is
     * closed, or if this application closes unexpectedly.
     * <p>Use {@link BluetoothDevice#createRfcommSocketToServiceRecord} to
     * connect to this socket from another device using the same {@link UUID}.
     * <p>Requires {@link android.Manifest.permission#BLUETOOTH}
     * @param name service name for SDP record
     * @param uuid uuid for SDP record
     * @return a listening RFCOMM BluetoothServerSocket
     * @throws IOException on error, for example Bluetooth not available, or
     *                     insufficient permissions, or channel in use.
     */
    public BluetoothServerSocket listenUsingRfcommWithServiceRecord(String name, UUID uuid)
            throws IOException {
        RfcommChannelPicker picker = new RfcommChannelPicker(uuid);

        BluetoothServerSocket socket;
        int channel;
        int errno;
        while (true) {
            channel = picker.nextChannel();

            if (channel == -1) {
                throw new IOException("No available channels");
            }

            socket = new BluetoothServerSocket(
                    BluetoothSocket.TYPE_RFCOMM, true, true, channel);
            errno = socket.mSocket.bindListen();
            if (errno == 0) {
                if (DBG) Log.d(TAG, "listening on RFCOMM channel " + channel);
                break;  // success
            } else if (errno == BluetoothSocket.EADDRINUSE) {
                if (DBG) Log.d(TAG, "RFCOMM channel " + channel + " in use");
                try {
                    socket.close();
                } catch (IOException e) {}
                continue;  // try another channel
            } else {
                try {
                    socket.close();
                } catch (IOException e) {}
                socket.mSocket.throwErrnoNative(errno);  // Exception as a result of bindListen()
            }
        }

        int handle = -1;
        try {
            handle = mService.addRfcommServiceRecord(name, new ParcelUuid(uuid), channel,
                    new Binder());
        } catch (RemoteException e) {Log.e(TAG, "", e);}
        if (handle == -1) {
            try {
                socket.close();
            } catch (IOException e) {}
            throw new IOException("Not able to register SDP record for " + name);
        }
        socket.setCloseHandler(mHandler, handle);
        return socket;
    }

    /**
     * Construct an unencrypted, unauthenticated, RFCOMM server socket.
     * Call #accept to retrieve connections to this socket.
     * @return An RFCOMM BluetoothServerSocket
     * @throws IOException On error, for example Bluetooth not available, or
     *                     insufficient permissions.
     * @hide
     */
    public BluetoothServerSocket listenUsingInsecureRfcommOn(int port) throws IOException {
        BluetoothServerSocket socket = new BluetoothServerSocket(
                BluetoothSocket.TYPE_RFCOMM, false, false, port);
        int errno = socket.mSocket.bindListen();
        if (errno != 0) {
            try {
                socket.close();
            } catch (IOException e) {}
            socket.mSocket.throwErrnoNative(errno);
        }
        return socket;
    }

    /**
     * Construct a SCO server socket.
     * Call #accept to retrieve connections to this socket.
     * @return A SCO BluetoothServerSocket
     * @throws IOException On error, for example Bluetooth not available, or
     *                     insufficient permissions.
     * @hide
     */
    public static BluetoothServerSocket listenUsingScoOn() throws IOException {
        BluetoothServerSocket socket = new BluetoothServerSocket(
                BluetoothSocket.TYPE_SCO, false, false, -1);
        int errno = socket.mSocket.bindListen();
        if (errno != 0) {
            try {
                socket.close();
            } catch (IOException e) {}
            socket.mSocket.throwErrnoNative(errno);
        }
        return socket;
    }

    private Set<BluetoothDevice> toDeviceSet(String[] addresses) {
        Set<BluetoothDevice> devices = new HashSet<BluetoothDevice>(addresses.length);
        for (int i = 0; i < addresses.length; i++) {
            devices.add(getRemoteDevice(addresses[i]));
        }
        return Collections.unmodifiableSet(devices);
    }

    private Handler mHandler = new Handler() {
        public void handleMessage(Message msg) {
            /* handle socket closing */
            int handle = msg.what;
            try {
                if (DBG) Log.d(TAG, "Removing service record " + Integer.toHexString(handle));
                mService.removeServiceRecord(handle);
            } catch (RemoteException e) {Log.e(TAG, "", e);}
        }
    };

    /**
     * Validate a Bluetooth address, such as "00:43:A8:23:10:F0"
     * <p>Alphabetic characters must be uppercase to be valid.
     *
     * @param address Bluetooth address as string
     * @return true if the address is valid, false otherwise
     */
    public static boolean checkBluetoothAddress(String address) {
        if (address == null || address.length() != ADDRESS_LENGTH) {
            return false;
        }
        for (int i = 0; i < ADDRESS_LENGTH; i++) {
            char c = address.charAt(i);
            switch (i % 3) {
            case 0:
            case 1:
                if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'F')) {
                    // hex character, OK
                    break;
                }
                return false;
            case 2:
                if (c == ':') {
                    break;  // OK
                }
                return false;
            }
        }
        return true;
    }
}