home | career | drupal | java | mac | mysql | perl | scala | uml | unix

Android example source code file (WifiWatchdogService.java)

This example Android source code file (WifiWatchdogService.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

accesspoint, android, bssid, content, d, datagrampacket, internet, interruptedexception, invalid, net, network, override, ssid, string, util, v, wifiinfo, wifiwatchdoghandler, wifiwatchdogservice, wifiwatchdogthread

The WifiWatchdogService.java Android example source code

/*
 * Copyright (C) 2008 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;

import android.content.BroadcastReceiver;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.database.ContentObserver;
import android.net.NetworkInfo;
import android.net.DhcpInfo;
import android.net.wifi.ScanResult;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.net.wifi.WifiStateTracker;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.provider.Settings;
import android.text.TextUtils;
import android.util.Config;
import android.util.Slog;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.SocketTimeoutException;
import java.net.UnknownHostException;
import java.util.List;
import java.util.Random;

/**
 * {@link WifiWatchdogService} monitors the initial connection to a Wi-Fi
 * network with multiple access points. After the framework successfully
 * connects to an access point, the watchdog verifies whether the DNS server is
 * reachable. If not, the watchdog blacklists the current access point, leading
 * to a connection on another access point within the same network.
 * <p>
 * The watchdog has a few safeguards:
 * <ul>
 * <li>Only monitor networks with multiple access points
 * <li>Only check at most {@link #getMaxApChecks()} different access points
 * within the network before giving up
 * <p>
 * The watchdog checks for connectivity on an access point by ICMP pinging the
 * DNS. There are settings that allow disabling the watchdog, or tweaking the
 * acceptable packet loss (and other various parameters).
 * <p>
 * The core logic of the watchdog is done on the main watchdog thread. Wi-Fi
 * callbacks can come in on other threads, so we must queue messages to the main
 * watchdog thread's handler. Most (if not all) state is only written to from
 * the main thread.
 * 
 * {@hide}
 */
public class WifiWatchdogService {
    private static final String TAG = "WifiWatchdogService";
    private static final boolean V = false || Config.LOGV;
    private static final boolean D = true || Config.LOGD;
    
    private Context mContext;
    private ContentResolver mContentResolver;
    private WifiStateTracker mWifiStateTracker;
    private WifiManager mWifiManager;
    
    /**
     * The main watchdog thread.
     */
    private WifiWatchdogThread mThread;
    /**
     * The handler for the main watchdog thread.
     */
    private WifiWatchdogHandler mHandler;

    private ContentObserver mContentObserver;

    /**
     * The current watchdog state. Only written from the main thread!
     */
    private WatchdogState mState = WatchdogState.IDLE;
    /**
     * The SSID of the network that the watchdog is currently monitoring. Only
     * touched in the main thread!
     */
    private String mSsid;
    /**
     * The number of access points in the current network ({@link #mSsid}) that
     * have been checked. Only touched in the main thread!
     */
    private int mNumApsChecked;
    /** Whether the current AP check should be canceled. */
    private boolean mShouldCancel;
    
    WifiWatchdogService(Context context, WifiStateTracker wifiStateTracker) {
        mContext = context;
        mContentResolver = context.getContentResolver();
        mWifiStateTracker = wifiStateTracker;
        mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
        
        createThread();
        
        // The content observer to listen needs a handler, which createThread creates
        registerForSettingsChanges();
        if (isWatchdogEnabled()) {
            registerForWifiBroadcasts();
        }
        
        if (V) {
            myLogV("WifiWatchdogService: Created");
        }
    }

    /**
     * Observes the watchdog on/off setting, and takes action when changed.
     */
    private void registerForSettingsChanges() {
        ContentResolver contentResolver = mContext.getContentResolver();
        contentResolver.registerContentObserver(
                Settings.Secure.getUriFor(Settings.Secure.WIFI_WATCHDOG_ON), false,
                mContentObserver = new ContentObserver(mHandler) {
            @Override
            public void onChange(boolean selfChange) {
                if (isWatchdogEnabled()) {
                    registerForWifiBroadcasts();
                } else {
                    unregisterForWifiBroadcasts();
                    if (mHandler != null) {
                        mHandler.disableWatchdog();
                    }
                }
            }
        });
    }

    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_ON
     */
    private boolean isWatchdogEnabled() {
        return Settings.Secure.getInt(mContentResolver, Settings.Secure.WIFI_WATCHDOG_ON, 1) == 1;
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_AP_COUNT
     */
    private int getApCount() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_AP_COUNT, 2);
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_INITIAL_IGNORED_PING_COUNT
     */
    private int getInitialIgnoredPingCount() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_INITIAL_IGNORED_PING_COUNT , 2);
    }

    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_PING_COUNT
     */
    private int getPingCount() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_PING_COUNT, 4);
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_PING_TIMEOUT_MS
     */
    private int getPingTimeoutMs() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_PING_TIMEOUT_MS, 500);
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_PING_DELAY_MS
     */
    private int getPingDelayMs() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_PING_DELAY_MS, 250);
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_ACCEPTABLE_PACKET_LOSS_PERCENTAGE
     */
    private int getAcceptablePacketLossPercentage() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_ACCEPTABLE_PACKET_LOSS_PERCENTAGE, 25);
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_MAX_AP_CHECKS
     */
    private int getMaxApChecks() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_MAX_AP_CHECKS, 7);
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_BACKGROUND_CHECK_ENABLED
     */
    private boolean isBackgroundCheckEnabled() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_BACKGROUND_CHECK_ENABLED, 1) == 1;
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_BACKGROUND_CHECK_DELAY_MS
     */
    private int getBackgroundCheckDelayMs() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_BACKGROUND_CHECK_DELAY_MS, 60000);
    }
    
    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_BACKGROUND_CHECK_TIMEOUT_MS
     */
    private int getBackgroundCheckTimeoutMs() {
        return Settings.Secure.getInt(mContentResolver,
            Settings.Secure.WIFI_WATCHDOG_BACKGROUND_CHECK_TIMEOUT_MS, 1000);
    }

    /**
     * @see android.provider.Settings.Secure#WIFI_WATCHDOG_WATCH_LIST
     * @return the comma-separated list of SSIDs
     */
    private String getWatchList() {
        return Settings.Secure.getString(mContentResolver,
                Settings.Secure.WIFI_WATCHDOG_WATCH_LIST);
    }
    
    /**
     * Registers to receive the necessary Wi-Fi broadcasts.
     */
    private void registerForWifiBroadcasts() {
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
        intentFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);
        mContext.registerReceiver(mReceiver, intentFilter);
    }

    /**
     * Unregisters from receiving the Wi-Fi broadcasts.
     */
    private void unregisterForWifiBroadcasts() {
        mContext.unregisterReceiver(mReceiver);
    }

    /**
     * Creates the main watchdog thread, including waiting for the handler to be
     * created.
     */
    private void createThread() {
        mThread = new WifiWatchdogThread();
        mThread.start();
        waitForHandlerCreation();
    }

    /**
     * Unregister broadcasts and quit the watchdog thread
     */
    private void quit() {
        unregisterForWifiBroadcasts();
        mContext.getContentResolver().unregisterContentObserver(mContentObserver);
        mHandler.removeAllActions();
        mHandler.getLooper().quit();
    }

    /**
     * Waits for the main watchdog thread to create the handler.
     */
    private void waitForHandlerCreation() {
        synchronized(this) {
            while (mHandler == null) {
                try {
                    // Wait for the handler to be set by the other thread
                    wait();
                } catch (InterruptedException e) {
                    Slog.e(TAG, "Interrupted while waiting on handler.");
                }
            }
        }
    }

    // Utility methods
    
    /**
     * Logs with the current thread.
     */
    private static void myLogV(String message) {
        Slog.v(TAG, "(" + Thread.currentThread().getName() + ") " + message);
    }
    
    private static void myLogD(String message) {
        Slog.d(TAG, "(" + Thread.currentThread().getName() + ") " + message);
    }
    
    /**
     * Gets the DNS of the current AP.
     * 
     * @return The DNS of the current AP.
     */
    private int getDns() {
        DhcpInfo addressInfo = mWifiManager.getDhcpInfo();
        if (addressInfo != null) {
            return addressInfo.dns1;
        } else {
            return -1;
        }
    }
    
    /**
     * Checks whether the DNS can be reached using multiple attempts according
     * to the current setting values.
     * 
     * @return Whether the DNS is reachable
     */
    private boolean checkDnsConnectivity() {
        int dns = getDns();
        if (dns == -1) {
            if (V) {
                myLogV("checkDnsConnectivity: Invalid DNS, returning false");
            }
            return false;
        }
        
        if (V) {
            myLogV("checkDnsConnectivity: Checking 0x" +
                    Integer.toHexString(Integer.reverseBytes(dns)) + " for connectivity");
        }

        int numInitialIgnoredPings = getInitialIgnoredPingCount();
        int numPings = getPingCount();
        int pingDelay = getPingDelayMs();
        int acceptableLoss = getAcceptablePacketLossPercentage();
        
        /** See {@link Secure#WIFI_WATCHDOG_INITIAL_IGNORED_PING_COUNT} */
        int ignoredPingCounter = 0;
        int pingCounter = 0;
        int successCounter = 0;
        
        // No connectivity check needed
        if (numPings == 0) {
            return true;
        }

        // Do the initial pings that we ignore
        for (; ignoredPingCounter < numInitialIgnoredPings; ignoredPingCounter++) {
            if (shouldCancel()) return false;

            boolean dnsAlive = DnsPinger.isDnsReachable(dns, getPingTimeoutMs());
            if (dnsAlive) {
                /*
                 * Successful "ignored" pings are *not* ignored (they count in the total number
                 * of pings), but failures are really ignored.
                 */
                pingCounter++;
                successCounter++;
            }
            
            if (V) {
                Slog.v(TAG, (dnsAlive ? "  +" : "  Ignored: -"));
            }

            if (shouldCancel()) return false;
            
            try {
                Thread.sleep(pingDelay);
            } catch (InterruptedException e) {
                Slog.w(TAG, "Interrupted while pausing between pings", e);
            }
        }
        
        // Do the pings that we use to measure packet loss
        for (; pingCounter < numPings; pingCounter++) {
            if (shouldCancel()) return false;

            if (DnsPinger.isDnsReachable(dns, getPingTimeoutMs())) {
                successCounter++;
                if (V) {
                    Slog.v(TAG, "  +");
                }
            } else {
                if (V) {
                    Slog.v(TAG, "  -");
                }
            }

            if (shouldCancel()) return false;
            
            try {
                Thread.sleep(pingDelay);
            } catch (InterruptedException e) {
                Slog.w(TAG, "Interrupted while pausing between pings", e);
            }
        }
        
        int packetLossPercentage = 100 * (numPings - successCounter) / numPings;
        if (D) {
            Slog.d(TAG, packetLossPercentage
                    + "% packet loss (acceptable is " + acceptableLoss + "%)");
        }
        
        return !shouldCancel() && (packetLossPercentage <= acceptableLoss);
    }

    private boolean backgroundCheckDnsConnectivity() {
        int dns = getDns();
        if (false && V) {
            myLogV("backgroundCheckDnsConnectivity: Background checking " + dns +
                    " for connectivity");
        }
        
        if (dns == -1) {
            if (V) {
                myLogV("backgroundCheckDnsConnectivity: DNS is empty, returning false");
            }
            return false;
        }
        
        return DnsPinger.isDnsReachable(dns, getBackgroundCheckTimeoutMs());
    }
    
    /**
     * Signals the current action to cancel.
     */
    private void cancelCurrentAction() {
        mShouldCancel = true;
    }
    
    /**
     * Helper to check whether to cancel. 
     * 
     * @return Whether to cancel processing the action.
     */
    private boolean shouldCancel() {
        if (V && mShouldCancel) {
            myLogV("shouldCancel: Cancelling");
        }
        
        return mShouldCancel;
    }
    
    // Wi-Fi initiated callbacks (could be executed in another thread)

    /**
     * Called when connected to an AP (this can be the next AP in line, or
     * it can be a completely different network).
     * 
     * @param ssid The SSID of the access point.
     * @param bssid The BSSID of the access point.
     */
    private void onConnected(String ssid, String bssid) {
        if (V) {
            myLogV("onConnected: SSID: " + ssid + ", BSSID: " + bssid);
        }

        /*
         * The current action being processed by the main watchdog thread is now
         * stale, so cancel it.
         */
        cancelCurrentAction();
        
        if ((mSsid == null) || !mSsid.equals(ssid)) {
            /*
             * This is a different network than what the main watchdog thread is
             * processing, dispatch the network change message on the main thread.
             */
            mHandler.dispatchNetworkChanged(ssid);
        }
        
        if (requiresWatchdog(ssid, bssid)) {
            if (D) {
                myLogD(ssid + " (" + bssid + ") requires the watchdog");
            }

            // This access point requires a watchdog, so queue the check on the main thread
            mHandler.checkAp(new AccessPoint(ssid, bssid));
            
        } else {
            if (D) {
                myLogD(ssid + " (" + bssid + ") does not require the watchdog");
            }

            // This access point does not require a watchdog, so queue idle on the main thread
            mHandler.idle();
        }
    }
    
    /**
     * Called when Wi-Fi is enabled.
     */
    private void onEnabled() {
        cancelCurrentAction();
        // Queue a hard-reset of the state on the main thread
        mHandler.reset();
    }
    
    /**
     * Called when disconnected (or some other event similar to being disconnected).
     */
    private void onDisconnected() {
        if (V) {
            myLogV("onDisconnected");
        }
        
        /*
         * Disconnected from an access point, the action being processed by the
         * watchdog thread is now stale, so cancel it.
         */
        cancelCurrentAction();
        // Dispatch the disconnected to the main watchdog thread
        mHandler.dispatchDisconnected();
        // Queue the action to go idle
        mHandler.idle();
    }

    /**
     * Checks whether an access point requires watchdog monitoring.
     * 
     * @param ssid The SSID of the access point.
     * @param bssid The BSSID of the access point.
     * @return Whether the access point/network should be monitored by the
     *         watchdog.
     */
    private boolean requiresWatchdog(String ssid, String bssid) {
        if (V) {
            myLogV("requiresWatchdog: SSID: " + ssid + ", BSSID: " + bssid);
        }
        
        WifiInfo info = null;
        if (ssid == null) {
            /*
             * This is called from a Wi-Fi callback, so assume the WifiInfo does
             * not have stale data.
             */
            info = mWifiManager.getConnectionInfo();
            ssid = info.getSSID();
            if (ssid == null) {
                // It's still null, give up
                if (V) {
                    Slog.v(TAG, "  Invalid SSID, returning false");
                }
                return false;
            }
        }
        
        if (TextUtils.isEmpty(bssid)) {
            // Similar as above
            if (info == null) {
                info = mWifiManager.getConnectionInfo();
            }
            bssid = info.getBSSID();
            if (TextUtils.isEmpty(bssid)) {
                // It's still null, give up
                if (V) {
                    Slog.v(TAG, "  Invalid BSSID, returning false");
                }
                return false;
            }
        }

        if (!isOnWatchList(ssid)) {
            if (V) {
                Slog.v(TAG, "  SSID not on watch list, returning false");
            }
            return false;
        }

        // The watchdog only monitors networks with multiple APs
        if (!hasRequiredNumberOfAps(ssid)) {
            return false;
        }

        return true;
    }

    private boolean isOnWatchList(String ssid) {
        String watchList;

        if (ssid == null || (watchList = getWatchList()) == null) {
            return false;
        }

        String[] list = watchList.split(" *, *");

        for (String name : list) {
            if (ssid.equals(name)) {
                return true;
            }
        }

        return false;
    }
    
    /**
     * Checks if the current scan results have multiple access points with an SSID.
     * 
     * @param ssid The SSID to check.
     * @return Whether the SSID has multiple access points.
     */
    private boolean hasRequiredNumberOfAps(String ssid) {
        List<ScanResult> results = mWifiManager.getScanResults();
        if (results == null) {
            if (V) {
                myLogV("hasRequiredNumberOfAps: Got null scan results, returning false");
            }
            return false;
        }
        
        int numApsRequired = getApCount();
        int numApsFound = 0;
        int resultsSize = results.size();
        for (int i = 0; i < resultsSize; i++) {
            ScanResult result = results.get(i);
            if (result == null) continue;
            if (result.SSID == null) continue;
            
            if (result.SSID.equals(ssid)) {
                numApsFound++;
                
                if (numApsFound >= numApsRequired) {
                    if (V) {
                        myLogV("hasRequiredNumberOfAps: SSID: " + ssid + ", returning true");
                    }
                    return true;
                }
            }
        }
        
        if (V) {
            myLogV("hasRequiredNumberOfAps: SSID: " + ssid + ", returning false");
        }
        return false;
    }
    
    // Watchdog logic (assume all of these methods will be in our main thread)
    
    /**
     * Handles a Wi-Fi network change (for example, from networkA to networkB).
     */
    private void handleNetworkChanged(String ssid) {
        // Set the SSID being monitored to the new SSID 
        mSsid = ssid;
        // Set various state to that when being idle 
        setIdleState(true);
    }
    
    /**
     * Handles checking whether an AP is a "good" AP.  If not, it will be blacklisted.
     * 
     * @param ap The access point to check.
     */
    private void handleCheckAp(AccessPoint ap) {
        // Reset the cancel state since this is the entry point of this action
        mShouldCancel = false;
        
        if (V) {
            myLogV("handleCheckAp: AccessPoint: " + ap);
        }
        
        // Make sure we are not sleeping
        if (mState == WatchdogState.SLEEP) {
            if (V) {
                Slog.v(TAG, "  Sleeping (in " + mSsid + "), so returning");
            }
            return;
        }
        
        mState = WatchdogState.CHECKING_AP;
        
        /*
         * Checks to make sure we haven't exceeded the max number of checks
         * we're allowed per network
         */
        mNumApsChecked++;
        if (mNumApsChecked > getMaxApChecks()) {
            if (V) {
                Slog.v(TAG, "  Passed the max attempts (" + getMaxApChecks()
                        + "), going to sleep for " + mSsid);
            }
            mHandler.sleep(mSsid);
            return;
        }

        // Do the check
        boolean isApAlive = checkDnsConnectivity();
        
        if (V) {
            Slog.v(TAG, "  Is it alive: " + isApAlive);
        }

        // Take action based on results
        if (isApAlive) {
            handleApAlive(ap);
        } else {
            handleApUnresponsive(ap);
        }
    }

    /**
     * Handles the case when an access point is alive.
     * 
     * @param ap The access point.
     */
    private void handleApAlive(AccessPoint ap) {
        // Check whether we are stale and should cancel
        if (shouldCancel()) return;
        // We're satisfied with this AP, so go idle
        setIdleState(false);
        
        if (D) {
            myLogD("AP is alive: " + ap.toString());
        }
        
        // Queue the next action to be a background check
        mHandler.backgroundCheckAp(ap);
    }
    
    /**
     * Handles an unresponsive AP by blacklisting it.
     * 
     * @param ap The access point.
     */
    private void handleApUnresponsive(AccessPoint ap) {
        // Check whether we are stale and should cancel
        if (shouldCancel()) return;
        // This AP is "bad", switch to another
        mState = WatchdogState.SWITCHING_AP;

        if (D) {
            myLogD("AP is dead: " + ap.toString());
        }
        
        // Black list this "bad" AP, this will cause an attempt to connect to another
        blacklistAp(ap.bssid);
        // Initiate an association to an alternate AP
        mWifiStateTracker.reassociate();
    }

    private void blacklistAp(String bssid) {
        if (TextUtils.isEmpty(bssid)) {
            return;
        }
        
        // Before taking action, make sure we should not cancel our processing
        if (shouldCancel()) return;
        
        if (!mWifiStateTracker.addToBlacklist(bssid)) {
            // There's a known bug where this method returns failure on success
            //Slog.e(TAG, "Blacklisting " + bssid + " failed");
        }

        if (D) {
            myLogD("Blacklisting " + bssid);
        }
    }

    /**
     * Handles a single background check. If it fails, it should trigger a
     * normal check. If it succeeds, it should queue another background check.
     * 
     * @param ap The access point to do a background check for. If this is no
     *        longer the current AP, it is okay to return without any
     *        processing.
     */
    private void handleBackgroundCheckAp(AccessPoint ap) {
        // Reset the cancel state since this is the entry point of this action
        mShouldCancel = false;
        
        if (false && V) {
            myLogV("handleBackgroundCheckAp: AccessPoint: " + ap);
        }
        
        // Make sure we are not sleeping
        if (mState == WatchdogState.SLEEP) {
            if (V) {
                Slog.v(TAG, "  handleBackgroundCheckAp: Sleeping (in " + mSsid + "), so returning");
            }
            return;
        }
        
        // Make sure the AP we're supposed to be background checking is still the active one
        WifiInfo info = mWifiManager.getConnectionInfo();
        if (info.getSSID() == null || !info.getSSID().equals(ap.ssid)) {
            if (V) {
                myLogV("handleBackgroundCheckAp: We are no longer connected to "
                        + ap + ", and instead are on " + info);
            }
            return;
        }
        
        if (info.getBSSID() == null || !info.getBSSID().equals(ap.bssid)) {
            if (V) {
                myLogV("handleBackgroundCheckAp: We are no longer connected to "
                        + ap + ", and instead are on " + info);
            }
            return;
        }

        // Do the check
        boolean isApAlive = backgroundCheckDnsConnectivity();
        
        if (V && !isApAlive) {
            Slog.v(TAG, "  handleBackgroundCheckAp: Is it alive: " + isApAlive);
        }

        if (shouldCancel()) {
            return;
        }
        
        // Take action based on results
        if (isApAlive) {
            // Queue another background check
            mHandler.backgroundCheckAp(ap);
            
        } else {
            if (D) {
                myLogD("Background check failed for " + ap.toString());
            }
            
            // Queue a normal check, so it can take proper action
            mHandler.checkAp(ap);
        }
    }
    
    /**
     * Handles going to sleep for this network. Going to sleep means we will not
     * monitor this network anymore.
     * 
     * @param ssid The network that will not be monitored anymore.
     */
    private void handleSleep(String ssid) {
        // Make sure the network we're trying to sleep in is still the current network
        if (ssid != null && ssid.equals(mSsid)) {
            mState = WatchdogState.SLEEP;

            if (D) {
                myLogD("Going to sleep for " + ssid);
            }
            
            /*
             * Before deciding to go to sleep, we may have checked a few APs
             * (and blacklisted them). Clear the blacklist so the AP with best
             * signal is chosen.
             */
            if (!mWifiStateTracker.clearBlacklist()) {
                // There's a known bug where this method returns failure on success
                //Slog.e(TAG, "Clearing blacklist failed");
            }
            
            if (V) {
                myLogV("handleSleep: Set state to SLEEP and cleared blacklist");
            }
        }
    }

    /**
     * Handles an access point disconnection.
     */
    private void handleDisconnected() {
        /*
         * We purposefully do not change mSsid to null. This is to handle
         * disconnected followed by connected better (even if there is some
         * duration in between). For example, if the watchdog went to sleep in a
         * network, and then the phone goes to sleep, when the phone wakes up we
         * still want to be in the sleeping state. When the phone went to sleep,
         * we would have gotten a disconnected event which would then set mSsid
         * = null. This is bad, since the following connect would cause us to do
         * the "network is good?" check all over again. */
        
        /* 
         * Set the state as if we were idle (don't come out of sleep, only
         * hard reset and network changed should do that.
         */
        setIdleState(false);
    }

    /**
     * Handles going idle. Idle means we are satisfied with the current state of
     * things, but if a new connection occurs we'll re-evaluate.
     */
    private void handleIdle() {
        // Reset the cancel state since this is the entry point for this action
        mShouldCancel = false;
        
        if (V) {
            myLogV("handleSwitchToIdle");
        }
        
        // If we're sleeping, don't do anything
        if (mState == WatchdogState.SLEEP) {
            Slog.v(TAG, "  Sleeping (in " + mSsid + "), so returning");
            return;
        }
        
        // Set the idle state
        setIdleState(false);
        
        if (V) {
            Slog.v(TAG, "  Set state to IDLE");
        }
    }
    
    /**
     * Sets the state as if we are going idle.
     */
    private void setIdleState(boolean forceIdleState) {
        // Setting idle state does not kick us out of sleep unless the forceIdleState is set
        if (forceIdleState || (mState != WatchdogState.SLEEP)) {
            mState = WatchdogState.IDLE;
        }
        mNumApsChecked = 0;
    }

    /**
     * Handles a hard reset. A hard reset is rarely used, but when used it
     * should revert anything done by the watchdog monitoring.
     */
    private void handleReset() {
        mWifiStateTracker.clearBlacklist();
        setIdleState(true);
    }
    
    // Inner classes

    /**
     * Possible states for the watchdog to be in.
     */
    private static enum WatchdogState {
        /** The watchdog is currently idle, but it is still responsive to future AP checks in this network. */
        IDLE,
        /** The watchdog is sleeping, so it will not try any AP checks for the network. */
        SLEEP,
        /** The watchdog is currently checking an AP for connectivity. */
        CHECKING_AP,
        /** The watchdog is switching to another AP in the network. */
        SWITCHING_AP
    }

    /**
     * The main thread for the watchdog monitoring. This will be turned into a
     * {@link Looper} thread.
     */
    private class WifiWatchdogThread extends Thread {
        WifiWatchdogThread() {
            super("WifiWatchdogThread");
        }
        
        @Override
        public void run() {
            // Set this thread up so the handler will work on it
            Looper.prepare();
            
            synchronized(WifiWatchdogService.this) {
                mHandler = new WifiWatchdogHandler();

                // Notify that the handler has been created
                WifiWatchdogService.this.notify();
            }
            
            // Listen for messages to the handler
            Looper.loop();
        }
    }

    /**
     * The main thread's handler. There are 'actions', and just general 
     * 'messages'. There should only ever be one 'action' in the queue (aside
     * from the one being processed, if any). There may be multiple messages in
     * the queue. So, actions are replaced by more recent actions, where as
     * messages will be executed for sure. Messages end up being used to just
     * change some state, and not really take any action.
     * <p>
     * There is little logic inside this class, instead methods of the form
     * "handle___" are called in the main {@link WifiWatchdogService}.
     */
    private class WifiWatchdogHandler extends Handler {
        /** Check whether the AP is "good".  The object will be an {@link AccessPoint}. */
        static final int ACTION_CHECK_AP = 1;
        /** Go into the idle state. */
        static final int ACTION_IDLE = 2;
        /**
         * Performs a periodic background check whether the AP is still "good".
         * The object will be an {@link AccessPoint}.
         */
        static final int ACTION_BACKGROUND_CHECK_AP = 3;

        /**
         * Go to sleep for the current network. We are conservative with making
         * this a message rather than action. We want to make sure our main
         * thread sees this message, but if it were an action it could be
         * removed from the queue and replaced by another action. The main
         * thread will ensure when it sees the message that the state is still
         * valid for going to sleep.
         * <p>
         * For an explanation of sleep, see {@link android.provider.Settings.Secure#WIFI_WATCHDOG_MAX_AP_CHECKS}.
         */
        static final int MESSAGE_SLEEP = 101;
        /** Disables the watchdog. */
        static final int MESSAGE_DISABLE_WATCHDOG = 102;
        /** The network has changed. */
        static final int MESSAGE_NETWORK_CHANGED = 103;
        /** The current access point has disconnected. */
        static final int MESSAGE_DISCONNECTED = 104;
        /** Performs a hard-reset on the watchdog state. */
        static final int MESSAGE_RESET = 105;
        
        void checkAp(AccessPoint ap) {
            removeAllActions();
            sendMessage(obtainMessage(ACTION_CHECK_AP, ap));
        }
        
        void backgroundCheckAp(AccessPoint ap) {
            if (!isBackgroundCheckEnabled()) return;
            
            removeAllActions();
            sendMessageDelayed(obtainMessage(ACTION_BACKGROUND_CHECK_AP, ap),
                    getBackgroundCheckDelayMs());
        }
        
        void idle() {
            removeAllActions();
            sendMessage(obtainMessage(ACTION_IDLE));
        }
        
        void sleep(String ssid) {
            removeAllActions();
            sendMessage(obtainMessage(MESSAGE_SLEEP, ssid));
        }
        
        void disableWatchdog() {
            removeAllActions();
            sendMessage(obtainMessage(MESSAGE_DISABLE_WATCHDOG));
        }
        
        void dispatchNetworkChanged(String ssid) {
            removeAllActions();
            sendMessage(obtainMessage(MESSAGE_NETWORK_CHANGED, ssid));
        }

        void dispatchDisconnected() {
            removeAllActions();
            sendMessage(obtainMessage(MESSAGE_DISCONNECTED));
        }

        void reset() {
            removeAllActions();
            sendMessage(obtainMessage(MESSAGE_RESET));
        }
        
        private void removeAllActions() {
            removeMessages(ACTION_CHECK_AP);
            removeMessages(ACTION_IDLE);
            removeMessages(ACTION_BACKGROUND_CHECK_AP);
        }
        
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MESSAGE_NETWORK_CHANGED:
                    handleNetworkChanged((String) msg.obj);
                    break;
                case ACTION_CHECK_AP:
                    handleCheckAp((AccessPoint) msg.obj);
                    break;
                case ACTION_BACKGROUND_CHECK_AP:
                    handleBackgroundCheckAp((AccessPoint) msg.obj);
                    break;
                case MESSAGE_SLEEP:
                    handleSleep((String) msg.obj);
                    break;
                case ACTION_IDLE:
                    handleIdle();
                    break;
                case MESSAGE_DISABLE_WATCHDOG:
                    handleIdle();
                    break;
                case MESSAGE_DISCONNECTED:
                    handleDisconnected();
                    break;
                case MESSAGE_RESET:
                    handleReset();
                    break;
            }
        }
    }

    /**
     * Receives Wi-Fi broadcasts.
     * <p>
     * There is little logic in this class, instead methods of the form "on___"
     * are called in the {@link WifiWatchdogService}.
     */
    private BroadcastReceiver mReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
            if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) {
                handleNetworkStateChanged(
                        (NetworkInfo) intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO));
            } else if (action.equals(WifiManager.WIFI_STATE_CHANGED_ACTION)) {
                handleWifiStateChanged(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                        WifiManager.WIFI_STATE_UNKNOWN));
            }
        }

        private void handleNetworkStateChanged(NetworkInfo info) {
            if (V) {
                myLogV("Receiver.handleNetworkStateChanged: NetworkInfo: "
                        + info);
            }
            
            switch (info.getState()) {
                case CONNECTED:
                    WifiInfo wifiInfo = mWifiManager.getConnectionInfo();
                    if (wifiInfo.getSSID() == null || wifiInfo.getBSSID() == null) {
                        if (V) {
                            myLogV("handleNetworkStateChanged: Got connected event but SSID or BSSID are null. SSID: "
                                + wifiInfo.getSSID()
                                + ", BSSID: "
                                + wifiInfo.getBSSID() + ", ignoring event");
                        }
                        return;
                    }
                    onConnected(wifiInfo.getSSID(), wifiInfo.getBSSID());
                    break;

                case DISCONNECTED:
                    onDisconnected();
                    break;
            }
        }

        private void handleWifiStateChanged(int wifiState) {
            if (wifiState == WifiManager.WIFI_STATE_DISABLED) {
                quit();
            } else if (wifiState == WifiManager.WIFI_STATE_ENABLED) {
                onEnabled();
            }
        }
    };

    /**
     * Describes an access point by its SSID and BSSID.
     */
    private static class AccessPoint {
        String ssid;
        String bssid;
        
        AccessPoint(String ssid, String bssid) {
            this.ssid = ssid;
            this.bssid = bssid;
        }

        private boolean hasNull() {
            return ssid == null || bssid == null;
        }
        
        @Override
        public boolean equals(Object o) {
            if (!(o instanceof AccessPoint)) return false;
            AccessPoint otherAp = (AccessPoint) o;
            boolean iHaveNull = hasNull();
            // Either we both have a null, or our SSIDs and BSSIDs are equal
            return (iHaveNull && otherAp.hasNull()) || 
                    (otherAp.bssid != null && ssid.equals(otherAp.ssid)
                    && bssid.equals(otherAp.bssid));
        }
        
        @Override
        public int hashCode() {
            if (ssid == null || bssid == null) return 0;
            return ssid.hashCode() + bssid.hashCode();
        }

        @Override
        public String toString() {
            return ssid + " (" + bssid + ")";
        }
    }

    /**
     * Performs a simple DNS "ping" by sending a "server status" query packet to
     * the DNS server. As long as the server replies, we consider it a success.
     * <p>
     * We do not use a simple hostname lookup because that could be cached and
     * the API may not differentiate between a time out and a failure lookup
     * (which we really care about).
     */
    private static class DnsPinger {
        
        /** Number of bytes for the query */
        private static final int DNS_QUERY_BASE_SIZE = 33;
        
        /** The DNS port */
        private static final int DNS_PORT = 53;
        
        /** Used to generate IDs */
        private static Random sRandom = new Random();
        
        static boolean isDnsReachable(int dns, int timeout) {
            DatagramSocket socket = null;
            try {
                socket = new DatagramSocket();
                
                // Set some socket properties
                socket.setSoTimeout(timeout);
                
                byte[] buf = new byte[DNS_QUERY_BASE_SIZE];
                fillQuery(buf);
                
                // Send the DNS query
                byte parts[] = new byte[4];
                parts[0] = (byte)(dns & 0xff);
                parts[1] = (byte)((dns >> 8) & 0xff);
                parts[2] = (byte)((dns >> 16) & 0xff);
                parts[3] = (byte)((dns >> 24) & 0xff);

                InetAddress dnsAddress = InetAddress.getByAddress(parts);
                DatagramPacket packet = new DatagramPacket(buf,
                        buf.length, dnsAddress, DNS_PORT);
                socket.send(packet);
                
                // Wait for reply (blocks for the above timeout)
                DatagramPacket replyPacket = new DatagramPacket(buf, buf.length);
                socket.receive(replyPacket);

                // If a timeout occurred, an exception would have been thrown.  We got a reply!
                return true;
                
            } catch (SocketException e) {
                if (V) {
                    Slog.v(TAG, "DnsPinger.isReachable received SocketException", e);
                }
                return false;
                
            } catch (UnknownHostException e) {
                if (V) {
                    Slog.v(TAG, "DnsPinger.isReachable is unable to resolve the DNS host", e);
                }
                return false;

            } catch (SocketTimeoutException e) {
                return false;
                
            } catch (IOException e) {
                if (V) {
                    Slog.v(TAG, "DnsPinger.isReachable got an IOException", e);
                }
                return false;
                
            } catch (Exception e) {
                if (V || Config.LOGD) {
                    Slog.d(TAG, "DnsPinger.isReachable got an unknown exception", e);
                }
                return false;
            } finally {
                if (socket != null) {
                    socket.close();
                }
            }
        }
        
        private static void fillQuery(byte[] buf) {

            /*
             * See RFC2929 (though the bit tables in there are misleading for
             * us. For example, the recursion desired bit is the 0th bit for us,
             * but looking there it would appear as the 7th bit of the byte
             */

            // Make sure it's all zeroed out
            for (int i = 0; i < buf.length; i++) buf[i] = 0;

            // Form a query for www.android.com
            
            // [0-1] bytes are an ID, generate random ID for this query
            buf[0] = (byte) sRandom.nextInt(256); 
            buf[1] = (byte) sRandom.nextInt(256); 
            
            // [2-3] bytes are for flags.
            buf[2] = 1; // Recursion desired

            // [4-5] bytes are for the query count
            buf[5] = 1; // One query 
            
            // [6-7] [8-9] [10-11] are all counts of other fields we don't use

            // [12-15] for www
            writeString(buf, 12, "www");
            
            // [16-23] for android
            writeString(buf, 16, "android");
            
            // [24-27] for com
            writeString(buf, 24, "com");
            
            // [29-30] bytes are for QTYPE, set to 1 
            buf[30] = 1;

            // [31-32] bytes are for QCLASS, set to 1 
            buf[32] = 1;
        }
        
        private static void writeString(byte[] buf, int startPos, String string) {
            int pos = startPos;
            
            // Write the length first
            buf[pos++] = (byte) string.length();
            for (int i = 0; i < string.length(); i++) {
                buf[pos++] = (byte) string.charAt(i);
            }
        }
    }
}

Other Android examples (source code examples)

Here is a short list of links related to this Android WifiWatchdogService.java source code file:

new blog posts

 

Copyright 1998-2014 Alvin Alexander, alvinalexander.com
All Rights Reserved.