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; /** * The internal DNS cache. */ protected DNSCache cache; /** * Create a new DNS client with the given DNS cache. * @param cache The backend DNS cache. */ public Client(DNSCache cache) { try { random = SecureRandom.getInstance("SHA1PRNG"); } catch (NoSuchAlgorithmException e1) { random = new SecureRandom(); } this.cache = cache; } /** * Create a new DNS client. */ public Client() { this(null); } /** * 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(name, type, clazz); 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(name, type, clazz); 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(name, type, clazz); 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 dnsMessage = (cache == null) ? null : cache.get(q); if (dnsMessage != null) { return dnsMessage; } 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.parse(packet.getData()); if (dnsMessage.getId() != message.getId()) { return null; } for (Record record : dnsMessage.getAnswers()) { if (record.isAnswer(q)) { if (cache != null) { cache.put(q, dnsMessage); } break; } } return dnsMessage; } } /** * Query the system DNS server for one entry. * @param q The question section of the DNS query. */ public DNSMessage query(Question q) { // While this query method does in fact re-use query(Question, String) // we still do a cache lookup here in order to avoid unnecessary // findDNS()calls, which are expensive on Android. Note that we do not // put the results back into the Cache, as this is already done by // query(Question, String). DNSMessage message = cache.get(q); if (message != null) { return message; } String dnsServer[] = findDNS(); for (String dns : dnsServer) { try { 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 server = new HashSet(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 servers = new ArrayList(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; } }