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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 java.util.logging.Level;
+import java.util.logging.Logger;
+
+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 {
+
+ private static final Logger LOGGER = Logger.getLogger(Client.class.getName());
+
+ /**
+ * The internal random class for sequence generation.
+ */
+ protected Random random;
+
+ /**
+ * The buffer size for dns replies.
+ */
+ protected int bufferSize = 1500;
+
+ /**
+ * DNS timeout.
+ */
+ protected int timeout = 5000;
+
+ /**
+ * 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.
+ * @param port The DNS server port.
+ * @return
+ * @throws IOException On IO Errors.
+ */
+ public DNSMessage query(String name, TYPE type, CLASS clazz, String host, int port)
+ throws IOException
+ {
+ Question q = new Question();
+ q.setClazz(clazz);
+ q.setType(type);
+ q.setName(name);
+ return query(q, host, port);
+ }
+
+ /**
+ * 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 {
+ return query(q, host, 53);
+ }
+
+ /**
+ * Query a specific server for one entry.
+ * @param q The question section of the DNS query.
+ * @param host The dns server host.
+ * @param port the dns port.
+ * @throws IOException On IOErrors.
+ */
+ public DNSMessage query(Question q, String host, int port) throws IOException {
+ DNSMessage message = new DNSMessage();
+ message.setQuestions(new Question[]{q});
+ message.setRecursionDesired(true);
+ message.setId(random.nextInt());
+ byte[] buf = message.toArray();
+ try (DatagramSocket socket = new DatagramSocket()) {
+ DatagramPacket packet = new DatagramPacket(buf, buf.length,
+ InetAddress.getByName(host), port);
+ socket.setSoTimeout(timeout);
+ socket.send(packet);
+ packet = new DatagramPacket(new byte[bufferSize], bufferSize);
+ 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) {
+ LOGGER.log(Level.FINE, "IOException in query", ioe);
+ }
+ }
+ return null;
+ }
+
+ /**
+ * Retrieve a list of currently configured DNS servers.
+ * @return The server array.
+ */
+ public String[] findDNS() {
+ String[] result = findDNSByReflection();
+ if (result != null) {
+ LOGGER.fine("Got DNS servers via reflection: " + Arrays.toString(result));
+ return result;
+ }
+
+ result = findDNSByExec();
+ if (result != null) {
+ LOGGER.fine("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
+ LOGGER.fine("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) {
+ LOGGER.log(Level.WARNING, "Exception in findDNSByExec", e);
+ }
+ 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
+ LOGGER.log(Level.WARNING, "Exception in findDNSByReflection", e);
+ }
+ return null;
+ }
+
+}