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package de.measite.minidns;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import java.lang.reflect.Method;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Random;
import android.util.Log;
import de.measite.minidns.Record.CLASS;
import de.measite.minidns.Record.TYPE;
/**
* A minimal DNS client for SRV/A/AAAA/NS and CNAME lookups, with IDN support.
* This circumvents the missing javax.naming package on android.
*/
public class Client {
/**
* The internal random class for sequence generation.
*/
protected Random random;
/**
* Create a new DNS client.
*/
public Client() {
try {
random = SecureRandom.getInstance("SHA1PRNG");
} catch (NoSuchAlgorithmException e1) {
random = new SecureRandom();
}
}
/**
* Query a nameserver for a single entry.
* @param name The DNS name to request.
* @param type The DNS type to request (SRV, A, AAAA, ...).
* @param clazz The class of the request (usually IN for Internet).
* @param host The DNS server host.
* @return
* @throws IOException On IO Errors.
*/
public DNSMessage query(String name, TYPE type, CLASS clazz, String host)
throws IOException
{
Question q = new Question();
q.setClazz(clazz);
q.setType(type);
q.setName(name);
return query(q, host);
}
/**
* Query the system nameserver for a single entry.
* @param name The DNS name to request.
* @param type The DNS type to request (SRV, A, AAAA, ...).
* @param clazz The class of the request (usually IN for Internet).
* @return The DNSMessage reply or null.
*/
public DNSMessage query(String name, TYPE type, CLASS clazz)
{
Question q = new Question();
q.setClazz(clazz);
q.setType(type);
q.setName(name);
return query(q);
}
/**
* Query a specific server for one entry.
* @param q The question section of the DNS query.
* @param host The dns server host.
* @throws IOException On IOErrors.
*/
public DNSMessage query(Question q, String host) throws IOException {
DNSMessage message = new DNSMessage();
message.setQuestions(new Question[]{q});
message.setRecursionDesired(true);
message.setId(random.nextInt());
byte[] buf = message.toArray();
DatagramSocket socket = new DatagramSocket();
DatagramPacket packet = new DatagramPacket(
buf, buf.length, InetAddress.getByName(host), 53);
socket.setSoTimeout(5000);
socket.send(packet);
packet = new DatagramPacket(new byte[513], 513);
socket.receive(packet);
DNSMessage dnsMessage = DNSMessage.parse(packet.getData());
if (dnsMessage.getId() != message.getId()) {
return null;
}
return dnsMessage;
}
/**
* Query the system DNS server for one entry.
* @param q The question section of the DNS query.
*/
public DNSMessage query(Question q) {
String dnsServer[] = findDNS();
for (String dns : dnsServer) {
try {
DNSMessage message = query(q, dns);
if (message == null) {
continue;
}
if (message.getResponseCode() !=
DNSMessage.RESPONSE_CODE.NO_ERROR) {
continue;
}
for (Record record: message.getAnswers()) {
if (record.isAnswer(q)) {
return message;
}
}
} catch (IOException ioe) {
}
}
return null;
}
/**
* Retrieve a list of currently configured DNS servers.
* @return The server array.
*/
public String[] findDNS() {
String[] result = findDNSByReflection();
if (result != null) {
Log.d("minidns/client",
"Got DNS servers via reflection: " + Arrays.toString(result));
return result;
}
result = findDNSByExec();
if (result != null) {
Log.d("minidns/client",
"Got DNS servers via exec: " + Arrays.toString(result));
return result;
}
// fallback for ipv4 and ipv6 connectivity
// see https://developers.google.com/speed/public-dns/docs/using
Log.d("minidns/client",
"No DNS found? Using fallback [8.8.8.8, [2001:4860:4860::8888]]");
return new String[]{"8.8.8.8", "[2001:4860:4860::8888]"};
}
/**
* Try to retrieve the list of dns server by executing getprop.
* @return Array of servers, or null on failure.
*/
protected String[] findDNSByExec() {
try {
Process process = Runtime.getRuntime().exec("getprop");
InputStream inputStream = process.getInputStream();
LineNumberReader lnr = new LineNumberReader(
new InputStreamReader(inputStream));
String line = null;
HashSet<String> server = new HashSet<String>(6);
while ((line = lnr.readLine()) != null) {
int split = line.indexOf("]: [");
if (split == -1) {
continue;
}
String property = line.substring(1, split);
String value = line.substring(split + 4, line.length() - 1);
if (property.endsWith(".dns") || property.endsWith(".dns1") ||
property.endsWith(".dns2") || property.endsWith(".dns3") ||
property.endsWith(".dns4")) {
// normalize the address
InetAddress ip = InetAddress.getByName(value);
if (ip == null) continue;
value = ip.getHostAddress();
if (value == null) continue;
if (value.length() == 0) continue;
server.add(value);
}
}
if (server.size() > 0) {
return server.toArray(new String[server.size()]);
}
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
/**
* Try to retrieve the list of dns server by calling SystemProperties.
* @return Array of servers, or null on failure.
*/
protected String[] findDNSByReflection() {
try {
Class<?> SystemProperties =
Class.forName("android.os.SystemProperties");
Method method = SystemProperties.getMethod("get",
new Class[] { String.class });
ArrayList<String> servers = new ArrayList<String>(5);
for (String propKey : new String[] {
"net.dns1", "net.dns2", "net.dns3", "net.dns4"}) {
String value = (String)method.invoke(null, propKey);
if (value == null) continue;
if (value.length() == 0) continue;
if (servers.contains(value)) continue;
InetAddress ip = InetAddress.getByName(value);
if (ip == null) continue;
value = ip.getHostAddress();
if (value == null) continue;
if (value.length() == 0) continue;
if (servers.contains(value)) continue;
servers.add(value);
}
if (servers.size() > 0) {
return servers.toArray(new String[servers.size()]);
}
} catch (Exception e) {
// we might trigger some problems this way
e.printStackTrace();
}
return null;
}
}
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