server/wifi/WifiConnectivityManager.java

/*
 * Copyright (C) 2016 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 com.android.server.wifi;

import static com.android.server.wifi.WifiStateMachine.WIFI_WORK_SOURCE;

import android.app.AlarmManager;
import android.content.Context;
import android.net.wifi.ScanResult;
import android.net.wifi.SupplicantState;
import android.net.wifi.WifiConfiguration;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiScanner;
import android.net.wifi.WifiScanner.PnoSettings;
import android.net.wifi.WifiScanner.ScanSettings;
import android.os.Handler;
import android.os.Looper;
import android.util.LocalLog;
import android.util.Log;

import com.android.internal.R;
import com.android.internal.annotations.VisibleForTesting;
import com.android.server.wifi.util.ScanResultUtil;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

/**
 * This class manages all the connectivity related scanning activities.
 *
 * When the screen is turned on or off, WiFi is connected or disconnected,
 * or on-demand, a scan is initiatiated and the scan results are passed
 * to WifiNetworkSelector for it to make a recommendation on which network
 * to connect to.
 */
public class WifiConnectivityManager {
    public static final String WATCHDOG_TIMER_TAG =
            "WifiConnectivityManager Schedule Watchdog Timer";
    public static final String PERIODIC_SCAN_TIMER_TAG =
            "WifiConnectivityManager Schedule Periodic Scan Timer";
    public static final String RESTART_SINGLE_SCAN_TIMER_TAG =
            "WifiConnectivityManager Restart Single Scan";
    public static final String RESTART_CONNECTIVITY_SCAN_TIMER_TAG =
            "WifiConnectivityManager Restart Scan";

    private static final String TAG = "WifiConnectivityManager";
    private static final long RESET_TIME_STAMP = Long.MIN_VALUE;
    // Constants to indicate whether a scan should start immediately or
    // it should comply to the minimum scan interval rule.
    private static final boolean SCAN_IMMEDIATELY = true;
    private static final boolean SCAN_ON_SCHEDULE = false;
    // Periodic scan interval in milli-seconds. This is the scan
    // performed when screen is on.
    @VisibleForTesting
    public static final int PERIODIC_SCAN_INTERVAL_MS = 20 * 1000; // 20 seconds
    // When screen is on and WiFi traffic is heavy, exponential backoff
    // connectivity scans are scheduled. This constant defines the maximum
    // scan interval in this scenario.
    @VisibleForTesting
    public static final int MAX_PERIODIC_SCAN_INTERVAL_MS = 160 * 1000; // 160 seconds
    // PNO scan interval in milli-seconds. This is the scan
    // performed when screen is off and disconnected.
    private static final int DISCONNECTED_PNO_SCAN_INTERVAL_MS = 20 * 1000; // 20 seconds
    // PNO scan interval in milli-seconds. This is the scan
    // performed when screen is off and connected.
    private static final int CONNECTED_PNO_SCAN_INTERVAL_MS = 160 * 1000; // 160 seconds
    // When a network is found by PNO scan but gets rejected by Wifi Network Selector due
    // to its low RSSI value, scan will be reschduled in an exponential back off manner.
    private static final int LOW_RSSI_NETWORK_RETRY_START_DELAY_MS = 20 * 1000; // 20 seconds
    private static final int LOW_RSSI_NETWORK_RETRY_MAX_DELAY_MS = 80 * 1000; // 80 seconds
    // Maximum number of retries when starting a scan failed
    @VisibleForTesting
    public static final int MAX_SCAN_RESTART_ALLOWED = 5;
    // Number of milli-seconds to delay before retry starting
    // a previously failed scan
    private static final int RESTART_SCAN_DELAY_MS = 2 * 1000; // 2 seconds
    // When in disconnected mode, a watchdog timer will be fired
    // every WATCHDOG_INTERVAL_MS to start a single scan. This is
    // to prevent caveat from things like PNO scan.
    private static final int WATCHDOG_INTERVAL_MS = 20 * 60 * 1000; // 20 minutes
    // Restricted channel list age out value.
    private static final int CHANNEL_LIST_AGE_MS = 60 * 60 * 1000; // 1 hour
    // This is the time interval for the connection attempt rate calculation. Connection attempt
    // timestamps beyond this interval is evicted from the list.
    public static final int MAX_CONNECTION_ATTEMPTS_TIME_INTERVAL_MS = 4 * 60 * 1000; // 4 mins
    // Max number of connection attempts in the above time interval.
    public static final int MAX_CONNECTION_ATTEMPTS_RATE = 6;
    // Packet tx/rx rates to determine if we want to do partial vs full scans.
    // TODO(b/31180330): Make these device configs.
    public static final int MAX_TX_PACKET_FOR_FULL_SCANS = 8;
    public static final int MAX_RX_PACKET_FOR_FULL_SCANS = 16;

    // WifiStateMachine has a bunch of states. From the
    // WifiConnectivityManager's perspective it only cares
    // if it is in Connected state, Disconnected state or in
    // transition between these two states.
    public static final int WIFI_STATE_UNKNOWN = 0;
    public static final int WIFI_STATE_CONNECTED = 1;
    public static final int WIFI_STATE_DISCONNECTED = 2;
    public static final int WIFI_STATE_TRANSITIONING = 3;

    // Saved network evaluator priority
    private static final int SAVED_NETWORK_EVALUATOR_PRIORITY = 1;
    private static final int EXTERNAL_SCORE_EVALUATOR_PRIORITY = 2;

    private final WifiStateMachine mStateMachine;
    private final WifiScanner mScanner;
    private final WifiConfigManager mConfigManager;
    private final WifiInfo mWifiInfo;
    private final WifiNetworkSelector mNetworkSelector;
    private final WifiLastResortWatchdog mWifiLastResortWatchdog;
    private final WifiMetrics mWifiMetrics;
    private final AlarmManager mAlarmManager;
    private final Handler mEventHandler;
    private final Clock mClock;
    private final LocalLog mLocalLog;
    private final LinkedList<Long> mConnectionAttemptTimeStamps;

    private boolean mDbg = false;
    private boolean mWifiEnabled = false;
    private boolean mWifiConnectivityManagerEnabled = true;
    private boolean mScreenOn = false;
    private int mWifiState = WIFI_STATE_UNKNOWN;
    private boolean mUntrustedConnectionAllowed = false;
    private int mScanRestartCount = 0;
    private int mSingleScanRestartCount = 0;
    private int mTotalConnectivityAttemptsRateLimited = 0;
    private String mLastConnectionAttemptBssid = null;
    private int mPeriodicSingleScanInterval = PERIODIC_SCAN_INTERVAL_MS;
    private long mLastPeriodicSingleScanTimeStamp = RESET_TIME_STAMP;
    private boolean mPnoScanStarted = false;
    private boolean mPeriodicScanTimerSet = false;
    // Device configs
    private boolean mEnableAutoJoinWhenAssociated;
    private boolean mWaitForFullBandScanResults = false;

    // PNO settings
    private int mMin5GHzRssi;
    private int mMin24GHzRssi;
    private int mInitialScoreMax;
    private int mCurrentConnectionBonus;
    private int mSameNetworkBonus;
    private int mSecureBonus;
    private int mBand5GHzBonus;

    // A helper to log debugging information in the local log buffer, which can
    // be retrieved in bugreport.
    private void localLog(String log) {
        if (mLocalLog != null) {
            mLocalLog.log(log);
        }
    }

    // A periodic/PNO scan will be rescheduled up to MAX_SCAN_RESTART_ALLOWED times
    // if the start scan command failed. An timer is used here to make it a deferred retry.
    private final AlarmManager.OnAlarmListener mRestartScanListener =
            new AlarmManager.OnAlarmListener() {
                public void onAlarm() {
                    startConnectivityScan(SCAN_IMMEDIATELY);
                }
            };

    // A single scan will be rescheduled up to MAX_SCAN_RESTART_ALLOWED times
    // if the start scan command failed. An timer is used here to make it a deferred retry.
    private class RestartSingleScanListener implements AlarmManager.OnAlarmListener {
        private final boolean mIsFullBandScan;

        RestartSingleScanListener(boolean isFullBandScan) {
            mIsFullBandScan = isFullBandScan;
        }

        @Override
        public void onAlarm() {
            startSingleScan(mIsFullBandScan);
        }
    }

    // As a watchdog mechanism, a single scan will be scheduled every WATCHDOG_INTERVAL_MS
    // if it is in the WIFI_STATE_DISCONNECTED state.
    private final AlarmManager.OnAlarmListener mWatchdogListener =
            new AlarmManager.OnAlarmListener() {
                public void onAlarm() {
                    watchdogHandler();
                }
            };

    // Due to b/28020168, timer based single scan will be scheduled
    // to provide periodic scan in an exponential backoff fashion.
    private final AlarmManager.OnAlarmListener mPeriodicScanTimerListener =
            new AlarmManager.OnAlarmListener() {
                public void onAlarm() {
                    periodicScanTimerHandler();
                }
            };

    /**
     * Handles 'onResult' callbacks for the Periodic, Single & Pno ScanListener.
     * Executes selection of potential network candidates, initiation of connection attempt to that
     * network.
     *
     * @return true - if a candidate is selected by WifiNetworkSelector
     *         false - if no candidate is selected by WifiNetworkSelector
     */
    private boolean handleScanResults(List<ScanDetail> scanDetails, String listenerName) {
        if (mStateMachine.isLinkDebouncing() || mStateMachine.isSupplicantTransientState()) {
            localLog(listenerName + " onResults: No network selection because linkDebouncing is "
                    + mStateMachine.isLinkDebouncing() + " and supplicantTransient is "
                    + mStateMachine.isSupplicantTransientState());
            return false;
        }

        localLog(listenerName + " onResults: start network selection");

        WifiConfiguration candidate =
                mNetworkSelector.selectNetwork(scanDetails, mWifiInfo,
                mStateMachine.isConnected(), mStateMachine.isDisconnected(),
                mUntrustedConnectionAllowed);
        mWifiLastResortWatchdog.updateAvailableNetworks(
                mNetworkSelector.getFilteredScanDetails());
        mWifiMetrics.countScanResults(scanDetails);
        if (candidate != null) {
            localLog(listenerName + ":  WNS candidate-" + candidate.SSID);
            connectToNetwork(candidate);
            return true;
        } else {
            return false;
        }
    }

    // All single scan results listener.
    //
    // Note: This is the listener for all the available single scan results,
    //       including the ones initiated by WifiConnectivityManager and
    //       other modules.
    private class AllSingleScanListener implements WifiScanner.ScanListener {
        private List<ScanDetail> mScanDetails = new ArrayList<ScanDetail>();

        public void clearScanDetails() {
            mScanDetails.clear();
        }

        @Override
        public void onSuccess() {
            localLog("registerScanListener onSuccess");
        }

        @Override
        public void onFailure(int reason, String description) {
            Log.e(TAG, "registerScanListener onFailure:"
                          + " reason: " + reason
                          + " description: " + description);
        }

        @Override
        public void onPeriodChanged(int periodInMs) {
        }

        @Override
        public void onResults(WifiScanner.ScanData[] results) {
            if (!mWifiEnabled || !mWifiConnectivityManagerEnabled) {
                clearScanDetails();
                mWaitForFullBandScanResults = false;
                return;
            }

            // Full band scan results only.
            if (mWaitForFullBandScanResults) {
                if (!results[0].isAllChannelsScanned()) {
                    localLog("AllSingleScanListener waiting for full band scan results.");
                    clearScanDetails();
                    return;
                } else {
                    mWaitForFullBandScanResults = false;
                }
            }

            boolean wasConnectAttempted = handleScanResults(mScanDetails, "AllSingleScanListener");
            clearScanDetails();

            // Update metrics to see if a single scan detected a valid network
            // while PNO scan didn't.
            // Note: We don't update the background scan metrics any more as it is
            //       not in use.
            if (mPnoScanStarted) {
                if (wasConnectAttempted) {
                    mWifiMetrics.incrementNumConnectivityWatchdogPnoBad();
                } else {
                    mWifiMetrics.incrementNumConnectivityWatchdogPnoGood();
                }
            }
        }

        @Override
        public void onFullResult(ScanResult fullScanResult) {
            if (!mWifiEnabled || !mWifiConnectivityManagerEnabled) {
                return;
            }

            if (mDbg) {
                localLog("AllSingleScanListener onFullResult: "
                            + fullScanResult.SSID + " capabilities "
                            + fullScanResult.capabilities);
            }

            mScanDetails.add(ScanResultUtil.toScanDetail(fullScanResult));
        }
    }

    private final AllSingleScanListener mAllSingleScanListener = new AllSingleScanListener();

    // Single scan results listener. A single scan is initiated when
    // DisconnectedPNO scan found a valid network and woke up
    // the system, or by the watchdog timer, or to form the timer based
    // periodic scan.
    //
    // Note: This is the listener for the single scans initiated by the
    //        WifiConnectivityManager.
    private class SingleScanListener implements WifiScanner.ScanListener {
        private final boolean mIsFullBandScan;

        SingleScanListener(boolean isFullBandScan) {
            mIsFullBandScan = isFullBandScan;
        }

        @Override
        public void onSuccess() {
            localLog("SingleScanListener onSuccess");
        }

        @Override
        public void onFailure(int reason, String description) {
            Log.e(TAG, "SingleScanListener onFailure:"
                          + " reason: " + reason
                          + " description: " + description);

            // reschedule the scan
            if (mSingleScanRestartCount++ < MAX_SCAN_RESTART_ALLOWED) {
                scheduleDelayedSingleScan(mIsFullBandScan);
            } else {
                mSingleScanRestartCount = 0;
                Log.e(TAG, "Failed to successfully start single scan for "
                          + MAX_SCAN_RESTART_ALLOWED + " times");
            }
        }

        @Override
        public void onPeriodChanged(int periodInMs) {
            localLog("SingleScanListener onPeriodChanged: "
                          + "actual scan period " + periodInMs + "ms");
        }

        @Override
        public void onResults(WifiScanner.ScanData[] results) {
        }

        @Override
        public void onFullResult(ScanResult fullScanResult) {
        }
    }

    // PNO scan results listener for both disconected and connected PNO scanning.
    // A PNO scan is initiated when screen is off.
    private class PnoScanListener implements WifiScanner.PnoScanListener {
        private List<ScanDetail> mScanDetails = new ArrayList<ScanDetail>();
        private int mLowRssiNetworkRetryDelay =
                LOW_RSSI_NETWORK_RETRY_START_DELAY_MS;

        public void clearScanDetails() {
            mScanDetails.clear();
        }

        // Reset to the start value when either a non-PNO scan is started or
        // WifiNetworkSelector selects a candidate from the PNO scan results.
        public void resetLowRssiNetworkRetryDelay() {
            mLowRssiNetworkRetryDelay = LOW_RSSI_NETWORK_RETRY_START_DELAY_MS;
        }

        @VisibleForTesting
        public int getLowRssiNetworkRetryDelay() {
            return mLowRssiNetworkRetryDelay;
        }

        @Override
        public void onSuccess() {
            localLog("PnoScanListener onSuccess");
        }

        @Override
        public void onFailure(int reason, String description) {
            Log.e(TAG, "PnoScanListener onFailure:"
                          + " reason: " + reason
                          + " description: " + description);

            // reschedule the scan
            if (mScanRestartCount++ < MAX_SCAN_RESTART_ALLOWED) {
                scheduleDelayedConnectivityScan(RESTART_SCAN_DELAY_MS);
            } else {
                mScanRestartCount = 0;
                Log.e(TAG, "Failed to successfully start PNO scan for "
                          + MAX_SCAN_RESTART_ALLOWED + " times");
            }
        }

        @Override
        public void onPeriodChanged(int periodInMs) {
            localLog("PnoScanListener onPeriodChanged: "
                          + "actual scan period " + periodInMs + "ms");
        }

        // Currently the PNO scan results doesn't include IE,
        // which contains information required by WifiNetworkSelector. Ignore them
        // for now.
        @Override
        public void onResults(WifiScanner.ScanData[] results) {
        }

        @Override
        public void onFullResult(ScanResult fullScanResult) {
        }

        @Override
        public void onPnoNetworkFound(ScanResult[] results) {
            localLog("PnoScanListener: onPnoNetworkFound: results len = " + results.length);

            for (ScanResult result: results) {
                mScanDetails.add(ScanResultUtil.toScanDetail(result));
            }

            boolean wasConnectAttempted;
            wasConnectAttempted = handleScanResults(mScanDetails, "PnoScanListener");
            clearScanDetails();
            mScanRestartCount = 0;

            if (!wasConnectAttempted) {
                // The scan results were rejected by WifiNetworkSelector due to low RSSI values
                if (mLowRssiNetworkRetryDelay > LOW_RSSI_NETWORK_RETRY_MAX_DELAY_MS) {
                    mLowRssiNetworkRetryDelay = LOW_RSSI_NETWORK_RETRY_MAX_DELAY_MS;
                }
                scheduleDelayedConnectivityScan(mLowRssiNetworkRetryDelay);

                // Set up the delay value for next retry.
                mLowRssiNetworkRetryDelay *= 2;
            } else {
                resetLowRssiNetworkRetryDelay();
            }
        }
    }

    private final PnoScanListener mPnoScanListener = new PnoScanListener();

    /**
     * WifiConnectivityManager constructor
     */
    WifiConnectivityManager(Context context, WifiStateMachine stateMachine,
                WifiScanner scanner, WifiConfigManager configManager, WifiInfo wifiInfo,
                WifiNetworkSelector networkSelector, WifiInjector wifiInjector, Looper looper,
                boolean enable) {
        mStateMachine = stateMachine;
        mScanner = scanner;
        mConfigManager = configManager;
        mWifiInfo = wifiInfo;
        mNetworkSelector = networkSelector;
        mLocalLog = networkSelector.getLocalLog();
        mWifiLastResortWatchdog = wifiInjector.getWifiLastResortWatchdog();
        mWifiMetrics = wifiInjector.getWifiMetrics();
        mAlarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
        mEventHandler = new Handler(looper);
        mClock = wifiInjector.getClock();
        mConnectionAttemptTimeStamps = new LinkedList<>();

        mMin5GHzRssi = context.getResources().getInteger(
                R.integer.config_wifi_framework_wifi_score_bad_rssi_threshold_5GHz);
        mMin24GHzRssi = context.getResources().getInteger(
                R.integer.config_wifi_framework_wifi_score_bad_rssi_threshold_24GHz);
        mBand5GHzBonus = context.getResources().getInteger(
                R.integer.config_wifi_framework_5GHz_preference_boost_factor);
        mCurrentConnectionBonus = context.getResources().getInteger(
                R.integer.config_wifi_framework_current_network_boost);
        mSameNetworkBonus = context.getResources().getInteger(
                R.integer.config_wifi_framework_SAME_BSSID_AWARD);
        mSecureBonus = context.getResources().getInteger(
                R.integer.config_wifi_framework_SECURITY_AWARD);
        int thresholdSaturatedRssi24 = context.getResources().getInteger(
                R.integer.config_wifi_framework_wifi_score_good_rssi_threshold_24GHz);
        mEnableAutoJoinWhenAssociated = context.getResources().getBoolean(
                R.bool.config_wifi_framework_enable_associated_network_selection);
        mInitialScoreMax = (context.getResources().getInteger(
                R.integer.config_wifi_framework_wifi_score_good_rssi_threshold_24GHz)
                    + context.getResources().getInteger(
                            R.integer.config_wifi_framework_RSSI_SCORE_OFFSET))
                * context.getResources().getInteger(
                        R.integer.config_wifi_framework_RSSI_SCORE_SLOPE);

        Log.i(TAG, "PNO settings:" + " min5GHzRssi " + mMin5GHzRssi
                    + " min24GHzRssi " + mMin24GHzRssi
                    + " currentConnectionBonus " + mCurrentConnectionBonus
                    + " sameNetworkBonus " + mSameNetworkBonus
                    + " secureNetworkBonus " + mSecureBonus
                    + " initialScoreMax " + mInitialScoreMax);

        // Register the network evaluators
        SavedNetworkEvaluator savedNetworkEvaluator = new SavedNetworkEvaluator(context,
                mConfigManager, mClock, mLocalLog);
        mNetworkSelector.registerNetworkEvaluator(savedNetworkEvaluator,
                    SAVED_NETWORK_EVALUATOR_PRIORITY);

        ExternalScoreEvaluator externalScoreEvaluator = new ExternalScoreEvaluator(context,
                mConfigManager, mClock, mLocalLog);
        mNetworkSelector.registerNetworkEvaluator(externalScoreEvaluator,
                    EXTERNAL_SCORE_EVALUATOR_PRIORITY);

        // Register for all single scan results
        mScanner.registerScanListener(mAllSingleScanListener);

        mWifiConnectivityManagerEnabled = enable;

        Log.i(TAG, "ConnectivityScanManager initialized and "
                + (enable ? "enabled" : "disabled"));
    }

    /**
     * This checks the connection attempt rate and recommends whether the connection attempt
     * should be skipped or not. This attempts to rate limit the rate of connections to
     * prevent us from flapping between networks and draining battery rapidly.
     */
    private boolean shouldSkipConnectionAttempt(Long timeMillis) {
        Iterator<Long> attemptIter = mConnectionAttemptTimeStamps.iterator();
        // First evict old entries from the queue.
        while (attemptIter.hasNext()) {
            Long connectionAttemptTimeMillis = attemptIter.next();
            if ((timeMillis - connectionAttemptTimeMillis)
                    > MAX_CONNECTION_ATTEMPTS_TIME_INTERVAL_MS) {
                attemptIter.remove();
            } else {
                // This list is sorted by timestamps, so we can skip any more checks
                break;
            }
        }
        // If we've reached the max connection attempt rate, skip this connection attempt
        return (mConnectionAttemptTimeStamps.size() >= MAX_CONNECTION_ATTEMPTS_RATE);
    }

    /**
     * Add the current connection attempt timestamp to our queue of connection attempts.
     */
    private void noteConnectionAttempt(Long timeMillis) {
        mConnectionAttemptTimeStamps.addLast(timeMillis);
    }

    /**
     * This is used to clear the connection attempt rate limiter. This is done when the user
     * explicitly tries to connect to a specified network.
     */
    private void clearConnectionAttemptTimeStamps() {
        mConnectionAttemptTimeStamps.clear();
    }

    /**
     * Attempt to connect to a network candidate.
     *
     * Based on the currently connected network, this menthod determines whether we should
     * connect or roam to the network candidate recommended by WifiNetworkSelector.
     */
    private void connectToNetwork(WifiConfiguration candidate) {
        ScanResult scanResultCandidate = candidate.getNetworkSelectionStatus().getCandidate();
        if (scanResultCandidate == null) {
            Log.e(TAG, "connectToNetwork: bad candidate - "  + candidate
                    + " scanResult: " + scanResultCandidate);
            return;
        }

        String targetBssid = scanResultCandidate.BSSID;
        String targetAssociationId = candidate.SSID + " : " + targetBssid;

        // Check if we are already connected or in the process of connecting to the target
        // BSSID. mWifiInfo.mBSSID tracks the currently connected BSSID. This is checked just
        // in case the firmware automatically roamed to a BSSID different from what
        // WifiNetworkSelector selected.
        if (targetBssid != null
                && (targetBssid.equals(mLastConnectionAttemptBssid)
                    || targetBssid.equals(mWifiInfo.getBSSID()))
                && SupplicantState.isConnecting(mWifiInfo.getSupplicantState())) {
            localLog("connectToNetwork: Either already connected "
                    + "or is connecting to " + targetAssociationId);
            return;
        }

        Long elapsedTimeMillis = mClock.getElapsedSinceBootMillis();
        if (!mScreenOn && shouldSkipConnectionAttempt(elapsedTimeMillis)) {
            localLog("connectToNetwork: Too many connection attempts. Skipping this attempt!");
            mTotalConnectivityAttemptsRateLimited++;
            return;
        }
        noteConnectionAttempt(elapsedTimeMillis);

        mLastConnectionAttemptBssid = targetBssid;

        WifiConfiguration currentConnectedNetwork = mConfigManager
                .getConfiguredNetwork(mWifiInfo.getNetworkId());
        String currentAssociationId = (currentConnectedNetwork == null) ? "Disconnected" :
                (mWifiInfo.getSSID() + " : " + mWifiInfo.getBSSID());

        if (currentConnectedNetwork != null
                && (currentConnectedNetwork.networkId == candidate.networkId
                || currentConnectedNetwork.isLinked(candidate))) {
            localLog("connectToNetwork: Roaming from " + currentAssociationId + " to "
                        + targetAssociationId);
            mStateMachine.startRoamToNetwork(candidate.networkId, scanResultCandidate);
        } else {
            localLog("connectToNetwork: Reconnect from " + currentAssociationId + " to "
                        + targetAssociationId);
            mStateMachine.startConnectToNetwork(candidate.networkId, scanResultCandidate.BSSID);
        }
    }

    // Helper for selecting the band for connectivity scan
    private int getScanBand() {
        return getScanBand(true);
    }

    private int getScanBand(boolean isFullBandScan) {
        if (isFullBandScan) {
            return WifiScanner.WIFI_BAND_BOTH_WITH_DFS;
        } else {
            // Use channel list instead.
            return WifiScanner.WIFI_BAND_UNSPECIFIED;
        }
    }

    // Helper for setting the channels for connectivity scan when band is unspecified. Returns
    // false if we can't retrieve the info.
    private boolean setScanChannels(ScanSettings settings) {
        WifiConfiguration config = mStateMachine.getCurrentWifiConfiguration();

        if (config == null) {
            return false;
        }

        Set<Integer> freqs =
                mConfigManager.fetchChannelSetForNetworkForPartialScan(
                        config.networkId, CHANNEL_LIST_AGE_MS);

        if (freqs != null && freqs.size() != 0) {
            int index = 0;
            settings.channels = new WifiScanner.ChannelSpec[freqs.size()];
            for (Integer freq : freqs) {
                settings.channels[index++] = new WifiScanner.ChannelSpec(freq);
            }
            return true;
        } else {
            localLog("No scan channels for " + config.configKey() + ". Perform full band scan");
            return false;
        }
    }

    // Watchdog timer handler
    private void watchdogHandler() {
        localLog("watchdogHandler");

        // Schedule the next timer and start a single scan if we are in disconnected state.
        // Otherwise, the watchdog timer will be scheduled when entering disconnected
        // state.
        if (mWifiState == WIFI_STATE_DISCONNECTED) {
            localLog("start a single scan from watchdogHandler");

            scheduleWatchdogTimer();
            startSingleScan(true);
        }
    }

    // Start a single scan and set up the interval for next single scan.
    private void startPeriodicSingleScan() {
        long currentTimeStamp = mClock.getElapsedSinceBootMillis();

        if (mLastPeriodicSingleScanTimeStamp != RESET_TIME_STAMP) {
            long msSinceLastScan = currentTimeStamp - mLastPeriodicSingleScanTimeStamp;
            if (msSinceLastScan < PERIODIC_SCAN_INTERVAL_MS) {
                localLog("Last periodic single scan started " + msSinceLastScan
                        + "ms ago, defer this new scan request.");
                schedulePeriodicScanTimer(PERIODIC_SCAN_INTERVAL_MS - (int) msSinceLastScan);
                return;
            }
        }

        boolean isFullBandScan = true;

        // If the WiFi traffic is heavy, only partial scan is initiated.
        if (mWifiState == WIFI_STATE_CONNECTED
                && (mWifiInfo.txSuccessRate > MAX_TX_PACKET_FOR_FULL_SCANS
                    || mWifiInfo.rxSuccessRate > MAX_RX_PACKET_FOR_FULL_SCANS)) {
            localLog("No full band scan due to heavy traffic, txSuccessRate="
                        + mWifiInfo.txSuccessRate + " rxSuccessRate="
                        + mWifiInfo.rxSuccessRate);
            isFullBandScan = false;
        }

        mLastPeriodicSingleScanTimeStamp = currentTimeStamp;
        startSingleScan(isFullBandScan);
        schedulePeriodicScanTimer(mPeriodicSingleScanInterval);

        // Set up the next scan interval in an exponential backoff fashion.
        mPeriodicSingleScanInterval *= 2;
        if (mPeriodicSingleScanInterval >  MAX_PERIODIC_SCAN_INTERVAL_MS) {
            mPeriodicSingleScanInterval = MAX_PERIODIC_SCAN_INTERVAL_MS;
        }
    }

    // Reset the last periodic single scan time stamp so that the next periodic single
    // scan can start immediately.
    private void resetLastPeriodicSingleScanTimeStamp() {
        mLastPeriodicSingleScanTimeStamp = RESET_TIME_STAMP;
    }

    // Periodic scan timer handler
    private void periodicScanTimerHandler() {
        localLog("periodicScanTimerHandler");

        // Schedule the next timer and start a single scan if screen is on.
        if (mScreenOn) {
            startPeriodicSingleScan();
        }
    }

    // Start a single scan
    private void startSingleScan(boolean isFullBandScan) {
        if (!mWifiEnabled || !mWifiConnectivityManagerEnabled) {
            return;
        }

        mPnoScanListener.resetLowRssiNetworkRetryDelay();

        ScanSettings settings = new ScanSettings();
        if (!isFullBandScan) {
            if (!setScanChannels(settings)) {
                isFullBandScan = true;
            }
        }
        settings.band = getScanBand(isFullBandScan);
        settings.reportEvents = WifiScanner.REPORT_EVENT_FULL_SCAN_RESULT
                            | WifiScanner.REPORT_EVENT_AFTER_EACH_SCAN;
        settings.numBssidsPerScan = 0;

        List<ScanSettings.HiddenNetwork> hiddenNetworkList =
                mConfigManager.retrieveHiddenNetworkList();
        settings.hiddenNetworks =
                hiddenNetworkList.toArray(new ScanSettings.HiddenNetwork[hiddenNetworkList.size()]);

        SingleScanListener singleScanListener =
                new SingleScanListener(isFullBandScan);
        mScanner.startScan(settings, singleScanListener, WIFI_WORK_SOURCE);
    }

    // Start a periodic scan when screen is on
    private void startPeriodicScan(boolean scanImmediately) {
        mPnoScanListener.resetLowRssiNetworkRetryDelay();

        // No connectivity scan if auto roaming is disabled.
        if (mWifiState == WIFI_STATE_CONNECTED && !mEnableAutoJoinWhenAssociated) {
            return;
        }

        // Due to b/28020168, timer based single scan will be scheduled
        // to provide periodic scan in an exponential backoff fashion.
        if (scanImmediately) {
            resetLastPeriodicSingleScanTimeStamp();
        }
        mPeriodicSingleScanInterval = PERIODIC_SCAN_INTERVAL_MS;
        startPeriodicSingleScan();
    }

    // Start a DisconnectedPNO scan when screen is off and Wifi is disconnected
    private void startDisconnectedPnoScan() {
        // TODO(b/29503772): Need to change this interface.

        // Initialize PNO settings
        PnoSettings pnoSettings = new PnoSettings();
        List<PnoSettings.PnoNetwork> pnoNetworkList = mConfigManager.retrievePnoNetworkList();
        int listSize = pnoNetworkList.size();

        if (listSize == 0) {
            // No saved network
            localLog("No saved network for starting disconnected PNO.");
            return;
        }

        pnoSettings.networkList = new PnoSettings.PnoNetwork[listSize];
        pnoSettings.networkList = pnoNetworkList.toArray(pnoSettings.networkList);
        pnoSettings.min5GHzRssi = mMin5GHzRssi;
        pnoSettings.min24GHzRssi = mMin24GHzRssi;
        pnoSettings.initialScoreMax = mInitialScoreMax;
        pnoSettings.currentConnectionBonus = mCurrentConnectionBonus;
        pnoSettings.sameNetworkBonus = mSameNetworkBonus;
        pnoSettings.secureBonus = mSecureBonus;
        pnoSettings.band5GHzBonus = mBand5GHzBonus;

        // Initialize scan settings
        ScanSettings scanSettings = new ScanSettings();
        scanSettings.band = getScanBand();
        scanSettings.reportEvents = WifiScanner.REPORT_EVENT_NO_BATCH;
        scanSettings.numBssidsPerScan = 0;
        scanSettings.periodInMs = DISCONNECTED_PNO_SCAN_INTERVAL_MS;

        mPnoScanListener.clearScanDetails();

        mScanner.startDisconnectedPnoScan(scanSettings, pnoSettings, mPnoScanListener);
        mPnoScanStarted = true;
    }

    // Stop PNO scan.
    private void stopPnoScan() {
        if (mPnoScanStarted) {
            mScanner.stopPnoScan(mPnoScanListener);
        }

        mPnoScanStarted = false;
    }

    // Set up watchdog timer
    private void scheduleWatchdogTimer() {
        localLog("scheduleWatchdogTimer");

        mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                            mClock.getElapsedSinceBootMillis() + WATCHDOG_INTERVAL_MS,
                            WATCHDOG_TIMER_TAG,
                            mWatchdogListener, mEventHandler);
    }

    // Set up periodic scan timer
    private void schedulePeriodicScanTimer(int intervalMs) {
        mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                            mClock.getElapsedSinceBootMillis() + intervalMs,
                            PERIODIC_SCAN_TIMER_TAG,
                            mPeriodicScanTimerListener, mEventHandler);
        mPeriodicScanTimerSet = true;
    }

    // Cancel periodic scan timer
    private void cancelPeriodicScanTimer() {
        if (mPeriodicScanTimerSet) {
            mAlarmManager.cancel(mPeriodicScanTimerListener);
            mPeriodicScanTimerSet = false;
        }
    }

    // Set up timer to start a delayed single scan after RESTART_SCAN_DELAY_MS
    private void scheduleDelayedSingleScan(boolean isFullBandScan) {
        localLog("scheduleDelayedSingleScan");

        RestartSingleScanListener restartSingleScanListener =
                new RestartSingleScanListener(isFullBandScan);
        mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                            mClock.getElapsedSinceBootMillis() + RESTART_SCAN_DELAY_MS,
                            RESTART_SINGLE_SCAN_TIMER_TAG,
                            restartSingleScanListener, mEventHandler);
    }

    // Set up timer to start a delayed scan after msFromNow milli-seconds
    private void scheduleDelayedConnectivityScan(int msFromNow) {
        localLog("scheduleDelayedConnectivityScan");

        mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                            mClock.getElapsedSinceBootMillis() + msFromNow,
                            RESTART_CONNECTIVITY_SCAN_TIMER_TAG,
                            mRestartScanListener, mEventHandler);

    }

    // Start a connectivity scan. The scan method is chosen according to
    // the current screen state and WiFi state.
    private void startConnectivityScan(boolean scanImmediately) {
        localLog("startConnectivityScan: screenOn=" + mScreenOn
                        + " wifiState=" + mWifiState
                        + " scanImmediately=" + scanImmediately
                        + " wifiEnabled=" + mWifiEnabled
                        + " wifiConnectivityManagerEnabled="
                        + mWifiConnectivityManagerEnabled);

        if (!mWifiEnabled || !mWifiConnectivityManagerEnabled) {
            return;
        }

        // Always stop outstanding connecivity scan if there is any
        stopConnectivityScan();

        // Don't start a connectivity scan while Wifi is in the transition
        // between connected and disconnected states.
        if (mWifiState != WIFI_STATE_CONNECTED && mWifiState != WIFI_STATE_DISCONNECTED) {
            return;
        }

        if (mScreenOn) {
            startPeriodicScan(scanImmediately);
        } else { // screenOff
            if (mWifiState == WIFI_STATE_DISCONNECTED) {
                startDisconnectedPnoScan();
            }
        }
    }

    // Stop connectivity scan if there is any.
    private void stopConnectivityScan() {
        // Due to b/28020168, timer based single scan will be scheduled
        // to provide periodic scan in an exponential backoff fashion.
        cancelPeriodicScanTimer();
        stopPnoScan();
        mScanRestartCount = 0;
    }

    /**
     * Handler for screen state (on/off) changes
     */
    public void handleScreenStateChanged(boolean screenOn) {
        localLog("handleScreenStateChanged: screenOn=" + screenOn);

        mScreenOn = screenOn;

        startConnectivityScan(SCAN_ON_SCHEDULE);
    }

    /**
     * Handler for WiFi state (connected/disconnected) changes
     */
    public void handleConnectionStateChanged(int state) {
        localLog("handleConnectionStateChanged: state=" + state);

        mWifiState = state;

        // Reset BSSID of last connection attempt and kick off
        // the watchdog timer if entering disconnected state.
        if (mWifiState == WIFI_STATE_DISCONNECTED) {
            mLastConnectionAttemptBssid = null;
            scheduleWatchdogTimer();
        }

        startConnectivityScan(SCAN_ON_SCHEDULE);
    }

    /**
     * Handler when user toggles whether untrusted connection is allowed
     */
    public void setUntrustedConnectionAllowed(boolean allowed) {
        localLog("setUntrustedConnectionAllowed: allowed=" + allowed);

        if (mUntrustedConnectionAllowed != allowed) {
            mUntrustedConnectionAllowed = allowed;
            startConnectivityScan(SCAN_IMMEDIATELY);
        }
    }

    /**
     * Handler when user specifies a particular network to connect to
     */
    public void setUserConnectChoice(int netId) {
        localLog("setUserConnectChoice: netId=" + netId);

        mNetworkSelector.setUserConnectChoice(netId);
        clearConnectionAttemptTimeStamps();
    }

    /**
     * Handler for on-demand connectivity scan
     */
    public void forceConnectivityScan() {
        localLog("forceConnectivityScan");

        mWaitForFullBandScanResults = true;
        startSingleScan(true);
    }

    /**
     * Track whether a BSSID should be enabled or disabled for WifiNetworkSelector
     */
    public boolean trackBssid(String bssid, boolean enable) {
        localLog("trackBssid: " + (enable ? "enable " : "disable ") + bssid);

        boolean ret = mNetworkSelector
                            .enableBssidForNetworkSelection(bssid, enable);

        if (ret && !enable) {
            // Disabling a BSSID can happen when the AP candidate to connect to has
            // no capacity for new stations. We start another scan immediately so that
            // WifiNetworkSelector can give us another candidate to connect to.
            startConnectivityScan(SCAN_IMMEDIATELY);
        }

        return ret;
    }

    /**
     * Inform WiFi is enabled for connection or not
     */
    public void setWifiEnabled(boolean enable) {
        localLog("Set WiFi " + (enable ? "enabled" : "disabled"));

        mWifiEnabled = enable;

        if (!mWifiEnabled) {
            stopConnectivityScan();
            resetLastPeriodicSingleScanTimeStamp();
            mLastConnectionAttemptBssid = null;
            mWaitForFullBandScanResults = false;
        } else if (mWifiConnectivityManagerEnabled) {
            startConnectivityScan(SCAN_IMMEDIATELY);
        }
    }

    /**
     * Turn on/off the WifiConnectivityMangager at runtime
     */
    public void enable(boolean enable) {
        localLog("Set WiFiConnectivityManager " + (enable ? "enabled" : "disabled"));

        mWifiConnectivityManagerEnabled = enable;

        if (!mWifiConnectivityManagerEnabled) {
            stopConnectivityScan();
            resetLastPeriodicSingleScanTimeStamp();
            mLastConnectionAttemptBssid = null;
            mWaitForFullBandScanResults = false;
        } else if (mWifiEnabled) {
            startConnectivityScan(SCAN_IMMEDIATELY);
        }
    }

    @VisibleForTesting
    int getLowRssiNetworkRetryDelay() {
        return mPnoScanListener.getLowRssiNetworkRetryDelay();
    }

    @VisibleForTesting
    long getLastPeriodicSingleScanTimeStamp() {
        return mLastPeriodicSingleScanTimeStamp;
    }
}