1 files changed, 293 insertions, 0 deletions
diff --git a/src/main/java/de/measite/minidns/Client.java b/src/main/java/de/measite/minidns/Client.java
new file mode 100644
index 00000000..cad3902a
--- /dev/null
+++ b/src/main/java/de/measite/minidns/Client.java
@@ -0,0 +1,293 @@
+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;
+    }
+
+}