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/*
* Copyright (C) 2011 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.ContentResolver;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.LinkProperties;
import android.os.SystemClock;
import android.util.Slog;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketTimeoutException;
import java.util.Collection;
import java.util.Random;
/**
* 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).
* <p>
* TODO : More general API. Wifi is currently hard coded
* TODO : Choice of DNS query location - current looks up www.android.com
*
* @hide
*/
public final class DnsPinger {
private static final boolean V = true;
/** 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();
private ConnectivityManager mConnectivityManager = null;
private ContentResolver mContentResolver;
private Context mContext;
private String TAG;
public DnsPinger(String TAG, Context context) {
mContext = context;
mContentResolver = context.getContentResolver();
this.TAG = TAG;
}
/**
* Gets the first DNS of the current Wifi AP.
* @return The first DNS of the current AP.
*/
public InetAddress getDns() {
if (mConnectivityManager == null) {
mConnectivityManager = (ConnectivityManager) mContext.getSystemService(
Context.CONNECTIVITY_SERVICE);
}
LinkProperties linkProperties = mConnectivityManager.getLinkProperties(
ConnectivityManager.TYPE_WIFI);
if (linkProperties == null)
return null;
Collection<InetAddress> dnses = linkProperties.getDnses();
if (dnses == null || dnses.size() == 0)
return null;
return dnses.iterator().next();
}
/**
* @return time to response. Negative value on error.
*/
public long pingDns(InetAddress dnsAddress, 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
DatagramPacket packet = new DatagramPacket(buf,
buf.length, dnsAddress, DNS_PORT);
long start = SystemClock.elapsedRealtime();
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 SystemClock.elapsedRealtime() - start;
} catch (SocketTimeoutException e) {
// Squelch this exception.
return -1;
} catch (Exception e) {
if (V) {
Slog.v(TAG, "DnsPinger.pingDns got socket exception: ", e);
}
return -2;
} 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);
}
}
}
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