DnsPinger.java revision d2fe04b71a89a0608eb7c67065dead2a1f540122 
1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.net;
18
19import android.content.Context;
20import android.os.Handler;
21import android.os.Looper;
22import android.os.Message;
23import android.os.SystemClock;
24import android.provider.Settings;
25import android.util.Slog;
26
27import com.android.internal.util.Protocol;
28
29import java.io.IOException;
30import java.net.DatagramPacket;
31import java.net.DatagramSocket;
32import java.net.InetAddress;
33import java.net.NetworkInterface;
34import java.net.SocketTimeoutException;
35import java.util.ArrayList;
36import java.util.Collection;
37import java.util.Iterator;
38import java.util.List;
39import java.util.Random;
40import java.util.concurrent.atomic.AtomicInteger;
41
42/**
43 * Performs a simple DNS "ping" by sending a "server status" query packet to the
44 * DNS server. As long as the server replies, we consider it a success.
45 * <p>
46 * We do not use a simple hostname lookup because that could be cached and the
47 * API may not differentiate between a time out and a failure lookup (which we
48 * really care about).
49 * <p>
50 *
51 * @hide
52 */
53public final class DnsPinger extends Handler {
54    private static final boolean V = true;
55
56    private static final int RECEIVE_POLL_INTERVAL_MS = 30;
57    private static final int DNS_PORT = 53;
58
59    /** Short socket timeout so we don't block one any 'receive' call */
60    private static final int SOCKET_TIMEOUT_MS = 1;
61
62    /** Used to generate IDs */
63    private static final Random sRandom = new Random();
64    private static final AtomicInteger sCounter = new AtomicInteger();
65
66    private ConnectivityManager mConnectivityManager = null;
67    private final Context mContext;
68    private final int mConnectionType;
69    private final Handler mTarget;
70    private final InetAddress mDefaultDns;
71    private String TAG;
72
73    private static final int BASE = Protocol.BASE_DNS_PINGER;
74
75    /**
76     * Async response packet for dns pings.
77     * arg1 is the ID of the ping, also returned by {@link #pingDnsAsync(InetAddress, int, int)}
78     * arg2 is the delay, or is negative on error.
79     */
80    public static final int DNS_PING_RESULT = BASE;
81    /** An error code for a {@link #DNS_PING_RESULT} packet */
82    public static final int TIMEOUT = -1;
83    /** An error code for a {@link #DNS_PING_RESULT} packet */
84    public static final int SOCKET_EXCEPTION = -2;
85
86    /**
87     * Send a new ping via a socket.  arg1 is ID, arg2 is timeout, obj is InetAddress to ping
88     */
89    private static final int ACTION_PING_DNS = BASE + 1;
90    private static final int ACTION_LISTEN_FOR_RESPONSE = BASE + 2;
91    private static final int ACTION_CANCEL_ALL_PINGS = BASE + 3;
92
93    private List<ActivePing> mActivePings = new ArrayList<ActivePing>();
94    private int mEventCounter;
95
96    private class ActivePing {
97        DatagramSocket socket;
98        int internalId;
99        short packetId;
100        int timeout;
101        Integer result;
102        long start = SystemClock.elapsedRealtime();
103    }
104
105    public DnsPinger(Context context, String TAG, Looper looper,
106            Handler target, int connectionType) {
107        super(looper);
108        this.TAG = TAG;
109        mContext = context;
110        mTarget = target;
111        mConnectionType = connectionType;
112        if (!ConnectivityManager.isNetworkTypeValid(connectionType)) {
113            throw new IllegalArgumentException("Invalid connectionType in constructor: "
114                    + connectionType);
115        }
116        mDefaultDns = getDefaultDns();
117        mEventCounter = 0;
118    }
119
120    @Override
121    public void handleMessage(Message msg) {
122        switch (msg.what) {
123            case ACTION_PING_DNS:
124                try {
125                    ActivePing newActivePing = new ActivePing();
126                    InetAddress dnsAddress = (InetAddress) msg.obj;
127                    newActivePing.internalId = msg.arg1;
128                    newActivePing.timeout = msg.arg2;
129                    newActivePing.socket = new DatagramSocket();
130                    // Set some socket properties
131                    newActivePing.socket.setSoTimeout(SOCKET_TIMEOUT_MS);
132
133                    // Try to bind but continue ping if bind fails
134                    try {
135                        newActivePing.socket.setNetworkInterface(NetworkInterface.getByName(
136                                getCurrentLinkProperties().getInterfaceName()));
137                    } catch (Exception e) {
138                        Slog.w(TAG,"sendDnsPing::Error binding to socket", e);
139                    }
140
141                    newActivePing.packetId = (short) sRandom.nextInt();
142                    byte[] buf = mDnsQuery.clone();
143                    buf[0] = (byte) (newActivePing.packetId >> 8);
144                    buf[1] = (byte) newActivePing.packetId;
145
146                    // Send the DNS query
147                    DatagramPacket packet = new DatagramPacket(buf,
148                            buf.length, dnsAddress, DNS_PORT);
149                    if (V) {
150                        Slog.v(TAG, "Sending a ping to " + dnsAddress.getHostAddress()
151                                + " with ID " + newActivePing.packetId + ".");
152                    }
153
154                    newActivePing.socket.send(packet);
155                    mActivePings.add(newActivePing);
156                    mEventCounter++;
157                    sendMessageDelayed(obtainMessage(ACTION_LISTEN_FOR_RESPONSE, mEventCounter, 0),
158                            RECEIVE_POLL_INTERVAL_MS);
159                } catch (IOException e) {
160                    sendResponse((short) msg.arg1, SOCKET_EXCEPTION);
161                }
162                break;
163            case ACTION_LISTEN_FOR_RESPONSE:
164                if (msg.arg1 != mEventCounter) {
165                    break;
166                }
167                for (ActivePing curPing : mActivePings) {
168                    try {
169                        /** Each socket will block for {@link #SOCKET_TIMEOUT_MS} in receive() */
170                        byte[] responseBuf = new byte[2];
171                        DatagramPacket replyPacket = new DatagramPacket(responseBuf, 2);
172                        curPing.socket.receive(replyPacket);
173                        // Check that ID field matches (we're throwing out the rest of the packet)
174                        if (responseBuf[0] == (byte) (curPing.packetId >> 8) &&
175                                responseBuf[1] == (byte) curPing.packetId) {
176                            curPing.result =
177                                    (int) (SystemClock.elapsedRealtime() - curPing.start);
178                        } else {
179                            if (V) {
180                                Slog.v(TAG, "response ID didn't match, ignoring packet");
181                            }
182                        }
183                    } catch (SocketTimeoutException e) {
184                        // A timeout here doesn't mean anything - squelsh this exception
185                    } catch (Exception e) {
186                        if (V) {
187                            Slog.v(TAG, "DnsPinger.pingDns got socket exception: ", e);
188                        }
189                        curPing.result = SOCKET_EXCEPTION;
190                    }
191                }
192                Iterator<ActivePing> iter = mActivePings.iterator();
193                while (iter.hasNext()) {
194                   ActivePing curPing = iter.next();
195                   if (curPing.result != null) {
196                       sendResponse(curPing.internalId, curPing.result);
197                       curPing.socket.close();
198                       iter.remove();
199                   } else if (SystemClock.elapsedRealtime() >
200                                  curPing.start + curPing.timeout) {
201                       sendResponse(curPing.internalId, TIMEOUT);
202                       curPing.socket.close();
203                       iter.remove();
204                   }
205                }
206                if (!mActivePings.isEmpty()) {
207                    sendMessageDelayed(obtainMessage(ACTION_LISTEN_FOR_RESPONSE, mEventCounter, 0),
208                            RECEIVE_POLL_INTERVAL_MS);
209                }
210                break;
211            case ACTION_CANCEL_ALL_PINGS:
212                for (ActivePing activePing : mActivePings)
213                    activePing.socket.close();
214                mActivePings.clear();
215                removeMessages(ACTION_PING_DNS);
216                break;
217        }
218    }
219
220    /**
221     * @return The first DNS in the link properties of the specified connection
222     *         type or the default system DNS if the link properties has null
223     *         dns set. Should not be null.
224     */
225    public InetAddress getDns() {
226        LinkProperties curLinkProps = getCurrentLinkProperties();
227        if (curLinkProps == null) {
228            Slog.e(TAG, "getCurLinkProperties:: LP for type" + mConnectionType + " is null!");
229            return mDefaultDns;
230        }
231
232        Collection<InetAddress> dnses = curLinkProps.getDnses();
233        if (dnses == null || dnses.size() == 0) {
234            Slog.v(TAG, "getDns::LinkProps has null dns - returning default");
235            return mDefaultDns;
236        }
237
238        return dnses.iterator().next();
239    }
240
241    /**
242     * Send a ping.  The response will come via a {@link #DNS_PING_RESULT} to the handler
243     * specified at creation.
244     * @param dns address of dns server to ping
245     * @param timeout timeout for ping
246     * @return an ID field, which will also be included in the {@link #DNS_PING_RESULT} message.
247     */
248    public int pingDnsAsync(InetAddress dns, int timeout, int delay) {
249        int id = sCounter.incrementAndGet();
250        sendMessageDelayed(obtainMessage(ACTION_PING_DNS, id, timeout, dns), delay);
251        return id;
252    }
253
254    public void cancelPings() {
255        obtainMessage(ACTION_CANCEL_ALL_PINGS).sendToTarget();
256    }
257
258    private void sendResponse(int internalId, int responseVal) {
259        if(V) {
260            Slog.v(TAG, "Responding with id " + internalId + " and val " + responseVal);
261        }
262        mTarget.sendMessage(obtainMessage(DNS_PING_RESULT, internalId, responseVal));
263    }
264
265    private LinkProperties getCurrentLinkProperties() {
266        if (mConnectivityManager == null) {
267            mConnectivityManager = (ConnectivityManager) mContext.getSystemService(
268                    Context.CONNECTIVITY_SERVICE);
269        }
270
271        return mConnectivityManager.getLinkProperties(mConnectionType);
272    }
273
274    private InetAddress getDefaultDns() {
275        String dns = Settings.Secure.getString(mContext.getContentResolver(),
276                Settings.Secure.DEFAULT_DNS_SERVER);
277        if (dns == null || dns.length() == 0) {
278            dns = mContext.getResources().getString(
279                    com.android.internal.R.string.config_default_dns_server);
280        }
281        try {
282            return NetworkUtils.numericToInetAddress(dns);
283        } catch (IllegalArgumentException e) {
284            Slog.w(TAG, "getDefaultDns::malformed default dns address");
285            return null;
286        }
287    }
288
289    private static final byte[] mDnsQuery = new byte[] {
290        0, 0, // [0-1] is for ID (will set each time)
291        0, 0, // [2-3] are flags.  Set byte[2] = 1 for recursion desired (RD) on.  Currently off.
292        0, 1, // [4-5] bytes are for number of queries (QCOUNT)
293        0, 0, // [6-7] unused count field for dns response packets
294        0, 0, // [8-9] unused count field for dns response packets
295        0, 0, // [10-11] unused count field for dns response packets
296        3, 'w', 'w', 'w',
297        6, 'g', 'o', 'o', 'g', 'l', 'e',
298        3, 'c', 'o', 'm',
299        0,    // null terminator of address (also called empty TLD)
300        0, 1, // QTYPE, set to 1 = A (host address)
301        0, 1  // QCLASS, set to 1 = IN (internet)
302    };
303}
304