DnsPinger.java revision 26a8d71413f107603ad68f4fa80cf2bf3da9dab1 
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 " + newActivePing.internalId +
151                                " to " + dnsAddress.getHostAddress()
152                                + " with packetId " + newActivePing.packetId + ".");
153                    }
154
155                    newActivePing.socket.send(packet);
156                    mActivePings.add(newActivePing);
157                    mEventCounter++;
158                    sendMessageDelayed(obtainMessage(ACTION_LISTEN_FOR_RESPONSE, mEventCounter, 0),
159                            RECEIVE_POLL_INTERVAL_MS);
160                } catch (IOException e) {
161                    sendResponse(msg.arg1, -9999, SOCKET_EXCEPTION);
162                }
163                break;
164            case ACTION_LISTEN_FOR_RESPONSE:
165                if (msg.arg1 != mEventCounter) {
166                    break;
167                }
168                for (ActivePing curPing : mActivePings) {
169                    try {
170                        /** Each socket will block for {@link #SOCKET_TIMEOUT_MS} in receive() */
171                        byte[] responseBuf = new byte[2];
172                        DatagramPacket replyPacket = new DatagramPacket(responseBuf, 2);
173                        curPing.socket.receive(replyPacket);
174                        // Check that ID field matches (we're throwing out the rest of the packet)
175                        if (responseBuf[0] == (byte) (curPing.packetId >> 8) &&
176                                responseBuf[1] == (byte) curPing.packetId) {
177                            curPing.result =
178                                    (int) (SystemClock.elapsedRealtime() - curPing.start);
179                        } else {
180                            if (V) {
181                                Slog.v(TAG, "response ID didn't match, ignoring packet");
182                            }
183                        }
184                    } catch (SocketTimeoutException e) {
185                        // A timeout here doesn't mean anything - squelsh this exception
186                    } catch (Exception e) {
187                        if (V) {
188                            Slog.v(TAG, "DnsPinger.pingDns got socket exception: ", e);
189                        }
190                        curPing.result = SOCKET_EXCEPTION;
191                    }
192                }
193                Iterator<ActivePing> iter = mActivePings.iterator();
194                while (iter.hasNext()) {
195                   ActivePing curPing = iter.next();
196                   if (curPing.result != null) {
197                       sendResponse(curPing.internalId, curPing.packetId, curPing.result);
198                       curPing.socket.close();
199                       iter.remove();
200                   } else if (SystemClock.elapsedRealtime() >
201                                  curPing.start + curPing.timeout) {
202                       sendResponse(curPing.internalId, curPing.packetId, TIMEOUT);
203                       curPing.socket.close();
204                       iter.remove();
205                   }
206                }
207                if (!mActivePings.isEmpty()) {
208                    sendMessageDelayed(obtainMessage(ACTION_LISTEN_FOR_RESPONSE, mEventCounter, 0),
209                            RECEIVE_POLL_INTERVAL_MS);
210                }
211                break;
212            case ACTION_CANCEL_ALL_PINGS:
213                for (ActivePing activePing : mActivePings)
214                    activePing.socket.close();
215                mActivePings.clear();
216                removeMessages(ACTION_PING_DNS);
217                break;
218        }
219    }
220
221    /**
222     * @return The first DNS in the link properties of the specified connection
223     *         type or the default system DNS if the link properties has null
224     *         dns set. Should not be null.
225     */
226    public InetAddress getDns() {
227        LinkProperties curLinkProps = getCurrentLinkProperties();
228        if (curLinkProps == null) {
229            Slog.e(TAG, "getCurLinkProperties:: LP for type" + mConnectionType + " is null!");
230            return mDefaultDns;
231        }
232
233        Collection<InetAddress> dnses = curLinkProps.getDnses();
234        if (dnses == null || dnses.size() == 0) {
235            Slog.v(TAG, "getDns::LinkProps has null dns - returning default");
236            return mDefaultDns;
237        }
238
239        return dnses.iterator().next();
240    }
241
242    /**
243     * Send a ping.  The response will come via a {@link #DNS_PING_RESULT} to the handler
244     * specified at creation.
245     * @param dns address of dns server to ping
246     * @param timeout timeout for ping
247     * @return an ID field, which will also be included in the {@link #DNS_PING_RESULT} message.
248     */
249    public int pingDnsAsync(InetAddress dns, int timeout, int delay) {
250        int id = sCounter.incrementAndGet();
251        sendMessageDelayed(obtainMessage(ACTION_PING_DNS, id, timeout, dns), delay);
252        return id;
253    }
254
255    public void cancelPings() {
256        obtainMessage(ACTION_CANCEL_ALL_PINGS).sendToTarget();
257    }
258
259    private void sendResponse(int internalId, int externalId, int responseVal) {
260        if(V) {
261            Slog.d(TAG, "Responding to packet " + internalId +
262                    " externalId " + externalId +
263                    " and val " + responseVal);
264        }
265        mTarget.sendMessage(obtainMessage(DNS_PING_RESULT, internalId, responseVal));
266    }
267
268    private LinkProperties getCurrentLinkProperties() {
269        if (mConnectivityManager == null) {
270            mConnectivityManager = (ConnectivityManager) mContext.getSystemService(
271                    Context.CONNECTIVITY_SERVICE);
272        }
273
274        return mConnectivityManager.getLinkProperties(mConnectionType);
275    }
276
277    private InetAddress getDefaultDns() {
278        String dns = Settings.Secure.getString(mContext.getContentResolver(),
279                Settings.Secure.DEFAULT_DNS_SERVER);
280        if (dns == null || dns.length() == 0) {
281            dns = mContext.getResources().getString(
282                    com.android.internal.R.string.config_default_dns_server);
283        }
284        try {
285            return NetworkUtils.numericToInetAddress(dns);
286        } catch (IllegalArgumentException e) {
287            Slog.w(TAG, "getDefaultDns::malformed default dns address");
288            return null;
289        }
290    }
291
292    private static final byte[] mDnsQuery = new byte[] {
293        0, 0, // [0-1] is for ID (will set each time)
294        1, 0, // [2-3] are flags.  Set byte[2] = 1 for recursion desired (RD) on.  Currently on.
295        0, 1, // [4-5] bytes are for number of queries (QCOUNT)
296        0, 0, // [6-7] unused count field for dns response packets
297        0, 0, // [8-9] unused count field for dns response packets
298        0, 0, // [10-11] unused count field for dns response packets
299        3, 'w', 'w', 'w',
300        6, 'g', 'o', 'o', 'g', 'l', 'e',
301        3, 'c', 'o', 'm',
302        0,    // null terminator of address (also called empty TLD)
303        0, 1, // QTYPE, set to 1 = A (host address)
304        0, 1  // QCLASS, set to 1 = IN (internet)
305    };
306}
307