Merge pull request #3 from Flowdalic/androidagnostic

Make minidns Android agnostic

11 files changed, 1476 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;
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/DNSMessage.java b/src/main/java/de/measite/minidns/DNSMessage.java
new file mode 100644
index 00000000..14c8f04b
--- /dev/null
+++ b/src/main/java/de/measite/minidns/DNSMessage.java
@@ -0,0 +1,507 @@
+package de.measite.minidns;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.util.Arrays;
+
+/**
+ * A DNS message as defined by rfc1035. The message consists of a header and
+ * 4 sections: question, answer, nameserver and addition resource record
+ * section.
+ * A message can either be parsed ({@see #parse(byte[])}) or serialized
+ * ({@see #toArray()}).
+ */
+public class DNSMessage {
+
+    /**
+     * Possible DNS reply codes.
+     */
+    public static enum RESPONSE_CODE {
+        NO_ERROR(0), FORMAT_ERR(1), SERVER_FAIL(2), NX_DOMAIN(3),
+        NO_IMP(4), REFUSED(5), YXDOMAIN(6), YXRRSET(7),
+        NXRRSET(8), NOT_AUTH(9),NOT_ZONE(10);
+
+        /**
+         * Reverse lookup table for response codes.
+         */
+        private final static RESPONSE_CODE INVERSE_LUT[] = new RESPONSE_CODE[]{
+            NO_ERROR, FORMAT_ERR, SERVER_FAIL, NX_DOMAIN, NO_IMP,
+            REFUSED, YXDOMAIN, YXRRSET, NXRRSET, NOT_AUTH, NOT_ZONE,
+            null, null, null, null, null
+        };
+
+        /**
+         * The response code value.
+         */
+        private final byte value;
+
+        /**
+         * Create a new response code.
+         * @param value The response code value.
+         */
+        private RESPONSE_CODE(int value) {
+            this.value = (byte)value;
+        }
+
+        /**
+         * Retrieve the byte value of the response code.
+         * @return
+         */
+        public byte getValue() {
+            return (byte) value;
+        }
+
+        /**
+         * Retrieve the response code for a byte value.
+         * @param value The byte value.
+         * @return The symbolic response code or null.
+         * @throws IllegalArgumentException if the value is not in the range of
+         *         0..15.
+         */
+        public static RESPONSE_CODE getResponseCode(int value) {
+            if (value < 0 || value > 15) {
+                throw new IllegalArgumentException();
+            }
+            return INVERSE_LUT[value];
+        }
+
+    };
+
+    /**
+     * Symbolic DNS Opcode values.
+     */
+    public static enum OPCODE {
+        QUERY(0),
+        INVERSE_QUERY(1),
+        STATUS(2),
+        NOTIFY(4),
+        UPDATE(5);
+
+        /**
+         * Lookup table for for obcode reolution.
+         */
+        private final static OPCODE INVERSE_LUT[] = new OPCODE[]{
+            QUERY, INVERSE_QUERY, STATUS, null, NOTIFY, UPDATE, null,
+            null, null, null, null, null, null, null, null
+        };
+
+        /**
+         * The value of this opcode.
+         */
+        private final byte value;
+
+        /**
+         * Create a new opcode for a given byte value.
+         * @param value The byte value of the opcode.
+         */
+        private OPCODE(int value) {
+            this.value = (byte)value;
+        }
+
+        /**
+         * Retrieve the byte value of this opcode.
+         * @return The byte value of this opcode.
+         */
+        public byte getValue() {
+            return value;
+        }
+
+        /**
+         * Retrieve the symbolic name of an opcode byte.
+         * @param value The byte value of the opcode.
+         * @return The symbolic opcode or null.
+         * @throws IllegalArgumentException If the byte value is not in the
+         *         range 0..15.
+         */
+        public static OPCODE getOpcode(int value) {
+            if (value < 0 || value > 15) {
+                throw new IllegalArgumentException();
+            }
+            return INVERSE_LUT[value];
+        }
+
+    };
+
+    /**
+     * The DNS message id.
+     */
+    protected int id;
+
+    /**
+     * The DNS message opcode.
+     */
+    protected OPCODE opcode;
+
+    /**
+     * The response code of this dns message.
+     */
+    protected RESPONSE_CODE responseCode;
+
+    /**
+     * True if this is a query.
+     */
+    protected boolean query;
+
+    /**
+     * True if this is a authorative response.
+     */
+    protected boolean authoritativeAnswer;
+
+    /**
+     * True on truncate, tcp should be used.
+     */
+    protected boolean truncated;
+
+    /**
+     * True if the server should recurse.
+     */
+    protected boolean recursionDesired;
+
+    /**
+     * True if recursion is possible.
+     */
+    protected boolean recursionAvailable;
+
+    /**
+     * True if the server regarded the response as authentic.
+     */
+    protected boolean authenticData;
+
+    /**
+     * True if the server should not check the replies.
+     */
+    protected boolean checkDisabled;
+
+    /**
+     * The question section content.
+     */
+    protected Question questions[];
+
+    /**
+     * The answers section content.
+     */
+    protected Record answers[];
+
+    /**
+     * The nameserver records.
+     */
+    protected Record nameserverRecords[];
+
+    /**
+     * Additional resousrce records.
+     */
+    protected Record additionalResourceRecords[];
+
+    /**
+     * Retrieve the current DNS message id.
+     * @return The current DNS message id.
+     */
+    public int getId() {
+        return id;
+    }
+
+    /**
+     * Set the current DNS message id.
+     * @param id The new DNS message id.
+     */
+    public void setId(int id) {
+        this.id = id & 0xffff;
+    }
+
+    /**
+     * Retrieve the query type (true or false;
+     * @return True if this DNS message is a query.
+     */
+    public boolean isQuery() {
+        return query;
+    }
+
+    /**
+     * Set the query status of this message.
+     * @param query The new query status.
+     */
+    public void setQuery(boolean query) {
+        this.query = query;
+    }
+
+    /**
+     * True if the DNS message is an authoritative answer.
+     * @return True if this an authoritative DNS message.
+     */
+    public boolean isAuthoritativeAnswer() {
+        return authoritativeAnswer;
+    }
+
+    /**
+     * Set the authoritative answer flag.
+     * @param authoritativeAnswer Tge new authoritative answer value.
+     */
+    public void setAuthoritativeAnswer(boolean authoritativeAnswer) {
+        this.authoritativeAnswer = authoritativeAnswer;
+    }
+
+    /**
+     * Retrieve the truncation status of this message. True means that the
+     * client should try a tcp lookup.
+     * @return True if this message was truncated.
+     */
+    public boolean isTruncated() {
+        return truncated;
+    }
+
+    /**
+     * Set the truncation bit on this DNS message.
+     * @param truncated The new truncated bit status.
+     */
+    public void setTruncated(boolean truncated) {
+        this.truncated = truncated;
+    }
+
+    /**
+     * Check if this message preferes recursion.
+     * @return True if recursion is desired.
+     */
+    public boolean isRecursionDesired() {
+        return recursionDesired;
+    }
+
+    /**
+     * Set the recursion desired flag on this message.
+     * @param recursionDesired The new recusrion setting.
+     */
+    public void setRecursionDesired(boolean recursionDesired) {
+        this.recursionDesired = recursionDesired;
+    }
+
+    /**
+     * Retrieve the recursion available flag of this DNS message.
+     * @return The recursion available flag of this message.
+     */
+    public boolean isRecursionAvailable() {
+        return recursionAvailable;
+    }
+
+    /**
+     * Set the recursion available flog from this DNS message.
+     * @param recursionAvailable The new recursion available status.
+     */
+    public void setRecursionAvailable(boolean recursionAvailable) {
+        this.recursionAvailable = recursionAvailable;
+    }
+
+    /**
+     * Retrieve the authentic data flag of this message.
+     * @return The authentic data flag.
+     */
+    public boolean isAuthenticData() {
+        return authenticData;
+    }
+
+    /**
+     * Set the authentic data flag on this DNS message.
+     * @param authenticData The new authentic data flag value.
+     */
+    public void setAuthenticData(boolean authenticData) {
+        this.authenticData = authenticData;
+    }
+
+    /**
+     * Check if checks are disabled.
+     * @return The status of the CheckDisabled flag.
+     */
+    public boolean isCheckDisabled() {
+        return checkDisabled;
+    }
+
+    /**
+     * Change the check status of this packet.
+     * @param checkDisabled
+     */
+    public void setCheckDisabled(boolean checkDisabled) {
+        this.checkDisabled = checkDisabled;
+    }
+
+    /**
+     * Generate a binary dns packet out of this message.
+     * @return byte[] the binary representation.
+     * @throws IOException Should never happen.
+     */
+    public byte[] toArray() throws IOException {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream(512);
+        DataOutputStream dos = new DataOutputStream(baos);
+        int header = 0;
+        if (query) {
+            header += 1 << 15;
+        }
+        if (opcode != null) {
+            header += opcode.getValue() << 11;
+        }
+        if (authoritativeAnswer) {
+            header += 1 << 10;
+        }
+        if (truncated) {
+            header += 1 << 9;
+        }
+        if (recursionDesired) {
+            header += 1 << 8;
+        }
+        if (recursionAvailable) {
+            header += 1 << 7;
+        }
+        if (authenticData) {
+            header += 1 << 5;
+        }
+        if (checkDisabled) {
+            header += 1 << 4;
+        }
+        if (responseCode != null) {
+            header += responseCode.getValue();
+        }
+        dos.writeShort((short)id);
+        dos.writeShort((short)header);
+        if (questions == null) {
+            dos.writeShort(0);
+        } else {
+            dos.writeShort((short)questions.length);
+        }
+        if (answers == null) {
+            dos.writeShort(0);
+        } else {
+            dos.writeShort((short)answers.length);
+        }
+        if (nameserverRecords == null) {
+            dos.writeShort(0);
+        } else {
+            dos.writeShort((short)nameserverRecords.length);
+        }
+        if (additionalResourceRecords == null) {
+            dos.writeShort(0);
+        } else {
+            dos.writeShort((short)additionalResourceRecords.length);
+        }
+        for (Question question: questions) {
+            dos.write(question.toByteArray());
+        }
+        dos.flush();
+        return baos.toByteArray();
+    }
+
+    /**
+     * Build a DNS Message based on a binary DNS message.
+     * @param data The DNS message data.
+     * @return Parsed DNSMessage message.
+     * @throws IOException On read errors.
+     */
+    public static DNSMessage parse(byte data[]) throws IOException {
+        ByteArrayInputStream bis = new ByteArrayInputStream(data);
+        DataInputStream dis = new DataInputStream(bis);
+        DNSMessage message = new DNSMessage();
+        message.id = dis.readUnsignedShort();
+        int header = dis.readUnsignedShort();
+        message.query = ((header >> 15) & 1) == 0;
+        message.opcode = OPCODE.getOpcode((header >> 11) & 0xf);
+        message.authoritativeAnswer = ((header >> 10) & 1) == 1;
+        message.truncated = ((header >> 9) & 1) == 1;
+        message.recursionDesired = ((header >> 8) & 1) == 1;
+        message.recursionAvailable = ((header >> 7) & 1) == 1;
+        message.authenticData = ((header >> 5) & 1) == 1;
+        message.checkDisabled = ((header >> 4) & 1) == 1;
+        message.responseCode = RESPONSE_CODE.getResponseCode(header & 0xf);
+        int questionCount = dis.readUnsignedShort();
+        int answerCount = dis.readUnsignedShort();
+        int nameserverCount = dis.readUnsignedShort();
+        int additionalResourceRecordCount = dis.readUnsignedShort();
+        message.questions = new Question[questionCount];
+        while (questionCount-- > 0) {
+            Question q = new Question();
+            q.parse(dis, data);
+            message.questions[questionCount] = q;
+        }
+        message.answers = new Record[answerCount];
+        while (answerCount-- > 0) {
+            Record rr = new Record();
+            rr.parse(dis, data);
+            message.answers[answerCount] = rr;
+        }
+        message.nameserverRecords = new Record[nameserverCount];
+        while (nameserverCount-- > 0) {
+            Record rr = new Record();
+            rr.parse(dis, data);
+            message.nameserverRecords[nameserverCount] = rr;
+        }
+        message.additionalResourceRecords =
+                                    new Record[additionalResourceRecordCount];
+        while (additionalResourceRecordCount-- > 0) {
+            Record rr = new Record();
+            rr.parse(dis, data);
+            message.additionalResourceRecords[additionalResourceRecordCount] =
+                    rr;
+        }
+        return message;
+    }
+
+    /**
+     * Set the question part of this message.
+     * @param questions The questions.
+     */
+    public void setQuestions(Question ... questions) {
+        this.questions = questions;
+    }
+
+    /**
+     * Retrieve the opcode of this message.
+     * @return The opcode of this message.
+     */
+    public OPCODE getOpcode() {
+        return opcode;
+    }
+
+    /**
+     * Retrieve the response code of this message.
+     * @return The response code.
+     */
+    public RESPONSE_CODE getResponseCode() {
+        return responseCode;
+    }
+
+    /**
+     * Retrieve the question section of this message.
+     * @return The DNS question section.
+     */
+    public Question[] getQuestions() {
+        return questions;
+    }
+
+    /**
+     * Retrieve the answer records of this DNS message.
+     * @return The answer section of this DNS message.
+     */
+    public Record[] getAnswers() {
+        return answers;
+    }
+
+    /**
+     * Retrieve the nameserver records of this DNS message.
+     * @return The nameserver section of this DNS message.
+     */
+    public Record[] getNameserverRecords() {
+        return nameserverRecords;
+    }
+
+    /**
+     * Retrieve the additional resource records attached to this DNS message.
+     * @return The additional resource record section of this DNS message.
+     */
+    public Record[] getAdditionalResourceRecords() {
+        return additionalResourceRecords;
+    }
+
+    public String toString() {
+        return "-- DNSMessage " + id + " --\n" +
+               Arrays.toString(answers);
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/Question.java b/src/main/java/de/measite/minidns/Question.java
new file mode 100644
index 00000000..9d1e3f56
--- /dev/null
+++ b/src/main/java/de/measite/minidns/Question.java
@@ -0,0 +1,62 @@
+package de.measite.minidns;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+
+import de.measite.minidns.Record.CLASS;
+import de.measite.minidns.Record.TYPE;
+import de.measite.minidns.util.NameUtil;
+
+public class Question {
+
+    private String name;
+
+    private TYPE type;
+
+    private CLASS clazz = CLASS.IN;
+
+    public TYPE getType() {
+        return type;
+    }
+
+    public void setType(TYPE type) {
+        this.type = type;
+    }
+
+    public CLASS getClazz() {
+        return clazz;
+    }
+
+    public void setClazz(CLASS clazz) {
+        this.clazz = clazz;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public void parse(DataInputStream dis, byte[] data) throws IOException {
+        this.name = NameUtil.parse(dis, data);
+        this.type = TYPE.getType(dis.readUnsignedShort());
+        this.clazz = CLASS.getClass(dis.readUnsignedShort());
+    }
+
+    public byte[] toByteArray() throws IOException {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream(512);
+        DataOutputStream dos = new DataOutputStream(baos);
+
+        dos.write(NameUtil.toByteArray(this.name));
+        dos.writeShort(type.getValue());
+        dos.writeShort(clazz.getValue());
+
+        dos.flush();
+        return baos.toByteArray();
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/Record.java b/src/main/java/de/measite/minidns/Record.java
new file mode 100644
index 00000000..fb0b5d5f
--- /dev/null
+++ b/src/main/java/de/measite/minidns/Record.java
@@ -0,0 +1,297 @@
+package de.measite.minidns;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+import java.util.HashMap;
+
+import de.measite.minidns.record.A;
+import de.measite.minidns.record.AAAA;
+import de.measite.minidns.record.CNAME;
+import de.measite.minidns.record.Data;
+import de.measite.minidns.record.NS;
+import de.measite.minidns.record.SRV;
+import de.measite.minidns.util.NameUtil;
+
+/**
+ * A generic DNS record.
+ */
+public class Record {
+
+    /**
+     * The record type.
+     * {@see http://www.iana.org/assignments/dns-parameters}
+     */
+    public static enum TYPE {
+        A(1),
+        NS(2),
+        MD(3),
+        MF(4),
+        CNAME(5),
+        SOA(6),
+        MB(7),
+        MG(8),
+        MR(9),
+        NULL(10),
+        WKS(11),
+        PTR(12),
+        HINFO(13),
+        MINFO(14),
+        MX(15),
+        TXT(16),
+        RP(17),
+        AFSDB(18),
+        X25(19),
+        ISDN(20),
+        RT(21),
+        NSAP(22),
+        NSAP_PTR(23),
+        SIG(24),
+        KEY(25),
+        PX(26),
+        GPOS(27),
+        AAAA(28),
+        LOC(29),
+        NXT(30),
+        EID(31),
+        NIMLOC(32),
+        SRV(33),
+        ATMA(34),
+        NAPTR(35),
+        KX(36),
+        CERT(37),
+        A6(38),
+        DNAME(39),
+        SINK(40),
+        OPT(41),
+        APL(42),
+        DS(43),
+        SSHFP(44),
+        IPSECKEY(45),
+        RRSIG(46),
+        NSEC(47),
+        DNSKEY(48),
+        DHCID(49),
+        NSEC3(50),
+        NSEC3PARAM(51),
+        HIP(55),
+        NINFO(56),
+        RKEY(57),
+        TALINK(58),
+        SPF(99),
+        UINFO(100),
+        UID(101),
+        GID(102),
+        TKEY(249),
+        TSIG(250),
+        IXFR(251),
+        AXFR(252),
+        MAILB(253),
+        MAILA(254),
+        ANY(255),
+        TA(32768),
+        DLV(32769);
+
+        /**
+         * The value of this DNS record type.
+         */
+        private final int value;
+
+        /**
+         * Internal lookup table to map values to types.
+         */
+        private final static HashMap<Integer, TYPE> INVERSE_LUT =
+                                        new HashMap<Integer, TYPE>();
+
+        /**
+         * Initialize the reverse lookup table.
+         */
+        static {
+            for(TYPE t: TYPE.values()) {
+                INVERSE_LUT.put(t.getValue(), t);
+            }
+        }
+
+        /**
+         * Create a new record type.
+         * @param value The binary value of this type.
+         */
+        private TYPE(int value) {
+            this.value = value;
+        }
+
+        /**
+         * Retrieve the binary value of this type.
+         * @return The binary value.
+         */
+        public int getValue() {
+            return value;
+        }
+
+        /**
+         * Retrieve the symbolic type of the binary value.
+         * @param value The binary type value.
+         * @return The symbolic tpye.
+         */
+        public static TYPE getType(int value) {
+            return INVERSE_LUT.get(value);
+        }
+    };
+
+    /**
+     * The symbolic class of a DNS record (usually IN for Internet).
+     */
+    public static enum CLASS {
+        IN(1),
+        CH(3),
+        HS(4),
+        NONE(254),
+        ANY(255);
+
+        /**
+         * Internal reverse lookup table to map binary class values to symbolic
+         * names.
+         */
+        private final static HashMap<Integer, CLASS> INVERSE_LUT =
+                                            new HashMap<Integer, CLASS>();
+
+        /**
+         * Initialize the interal reverse lookup table.
+         */
+        static {
+            for(CLASS c: CLASS.values()) {
+                INVERSE_LUT.put(c.getValue(), c);
+            }
+        }
+
+        /**
+         * The binary value of this dns class.
+         */
+        private final int value;
+
+        /**
+         * Create a new DNS class based on a binary value.
+         * @param value The binary value of this DNS class.
+         */
+        private CLASS(int value) {
+            this.value = value;
+        }
+
+        /**
+         * Retrieve the binary value of this DNS class.
+         * @return The binary value of this DNS class.
+         */
+        public int getValue() {
+            return value;
+        }
+
+        /**
+         * Retrieve the symbolic DNS class for a binary class value.
+         * @param value The binary DNS class value.
+         * @return The symbolic class instance.
+         */
+        public static CLASS getClass(int value) {
+            return INVERSE_LUT.get(value);
+        }
+
+    }
+
+    /**
+     * The generic name of this record.
+     */
+    protected String name;
+
+    /**
+     * The type (and payload type) of this record.
+     */
+    protected TYPE type;
+
+    /**
+     * The record class (usually CLASS.IN).
+     */
+    protected CLASS clazz;
+
+    /**
+     * The ttl of this record.
+     */
+    protected long ttl;
+
+    /**
+     * The payload object of this record.
+     */
+    protected Data payloadData;
+
+    /**
+     * Parse a given record based on the full message data and the current
+     * stream position.
+     * @param dis The DataInputStream positioned at the first record byte.
+     * @param data The full message data.
+     * @throws IOException In case of malformed replies.
+     */
+    public void parse(DataInputStream dis, byte[] data) throws IOException {
+        this.name = NameUtil.parse(dis, data);
+        this.type = TYPE.getType(dis.readUnsignedShort());
+        this.clazz = CLASS.getClass(dis.readUnsignedShort());
+        this.ttl = (((long)dis.readUnsignedShort()) << 32) +
+                   dis.readUnsignedShort();
+        int payloadLength = dis.readUnsignedShort();
+        switch (this.type) {
+        case SRV:
+            this.payloadData = new SRV();
+            break;
+        case AAAA:
+            this.payloadData = new AAAA();
+            break;
+        case A:
+            this.payloadData = new A();
+            break;
+        case NS:
+            this.payloadData = new NS();
+            break;
+        case CNAME:
+            this.payloadData = new CNAME();
+            break;
+        default:
+            System.out.println("Unparsed type " + type);
+            this.payloadData = null;
+            for (int i = 0; i < payloadLength; i++) {
+                dis.readByte();
+            }
+            break;
+        }
+        if (this.payloadData != null) {
+            this.payloadData.parse(dis, data, payloadLength);
+        }
+    }
+
+    /**
+     * Retrieve a textual representation of this resource record.
+     * @return String
+     */
+    @Override
+    public String toString() {
+        if (payloadData == null) {
+            return "RR " + type + "/" + clazz;
+        }
+        return "RR " + type + "/" + clazz + ": " + payloadData.toString();
+    };
+
+    /**
+     * Check if this record answers a given query.
+     * @param q The query.
+     * @return True if this record is a valid answer.
+     */
+    public boolean isAnswer(Question q) {
+        return ((q.getType() == type) || (q.getType() == TYPE.ANY)) &&
+               ((q.getClazz() == clazz) || (q.getClazz() == CLASS.ANY)) &&
+               (q.getName().equals(name));
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public Data getPayload() {
+        return payloadData;
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/record/A.java b/src/main/java/de/measite/minidns/record/A.java
new file mode 100644
index 00000000..a85a7af0
--- /dev/null
+++ b/src/main/java/de/measite/minidns/record/A.java
@@ -0,0 +1,37 @@
+package de.measite.minidns.record;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+
+import de.measite.minidns.Record.TYPE;
+
+public class A implements Data {
+
+    private byte[] ip;
+
+    @Override
+    public TYPE getType() {
+        return TYPE.A;
+    }
+
+    @Override
+    public byte[] toByteArray() {
+        return ip;
+    }
+
+    @Override
+    public void parse(DataInputStream dis, byte[] data, int length)
+            throws IOException {
+        ip = new byte[4];
+        dis.readFully(ip);
+    }
+
+    @Override
+    public String toString() {
+        return Integer.toString(ip[0] & 0xff) + "." +
+               Integer.toString(ip[1] & 0xff) + "." +
+               Integer.toString(ip[2] & 0xff) + "." +
+               Integer.toString(ip[3] & 0xff);
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/record/AAAA.java b/src/main/java/de/measite/minidns/record/AAAA.java
new file mode 100644
index 00000000..d89147b2
--- /dev/null
+++ b/src/main/java/de/measite/minidns/record/AAAA.java
@@ -0,0 +1,43 @@
+package de.measite.minidns.record;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+
+import de.measite.minidns.Record.TYPE;
+
+public class AAAA implements Data {
+
+    private byte[] ip;
+
+    @Override
+    public TYPE getType() {
+        return TYPE.AAAA;
+    }
+
+    @Override
+    public byte[] toByteArray() {
+        return ip;
+    }
+
+    @Override
+    public void parse(DataInputStream dis, byte[] data, int length)
+            throws IOException {
+        ip = new byte[16];
+        dis.readFully(ip);
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < ip.length; i += 2) {
+            if (i != 0) {
+                sb.append(':');
+            }
+            sb.append(Integer.toHexString(
+                ((ip[i] & 0xff) << 8) + (ip[i + 1] & 0xff)
+            ));
+        }
+        return sb.toString();
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/record/CNAME.java b/src/main/java/de/measite/minidns/record/CNAME.java
new file mode 100644
index 00000000..4657b4a5
--- /dev/null
+++ b/src/main/java/de/measite/minidns/record/CNAME.java
@@ -0,0 +1,44 @@
+package de.measite.minidns.record;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+
+import de.measite.minidns.Record.TYPE;
+import de.measite.minidns.util.NameUtil;
+
+public class CNAME implements Data {
+
+    protected String name;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public byte[] toByteArray() {
+        // TODO Auto-generated method stub
+        return null;
+    }
+
+    @Override
+    public void parse(DataInputStream dis, byte[] data, int length)
+        throws IOException
+    {
+        this.name = NameUtil.parse(dis, data);
+    }
+
+    @Override
+    public TYPE getType() {
+        return TYPE.CNAME;
+    }
+
+    @Override
+    public String toString() {
+        return "to \"" + name + "\"";
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/record/Data.java b/src/main/java/de/measite/minidns/record/Data.java
new file mode 100644
index 00000000..9cb80374
--- /dev/null
+++ b/src/main/java/de/measite/minidns/record/Data.java
@@ -0,0 +1,16 @@
+package de.measite.minidns.record;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+
+import de.measite.minidns.Record.TYPE;
+
+public interface Data {
+
+    TYPE getType();
+
+    byte[] toByteArray();
+
+    void parse(DataInputStream dis, byte data[], int length) throws IOException;
+
+}
diff --git a/src/main/java/de/measite/minidns/record/NS.java b/src/main/java/de/measite/minidns/record/NS.java
new file mode 100644
index 00000000..bf07e8c4
--- /dev/null
+++ b/src/main/java/de/measite/minidns/record/NS.java
@@ -0,0 +1,12 @@
+package de.measite.minidns.record;
+
+import de.measite.minidns.Record.TYPE;
+
+public class NS extends CNAME {
+
+    @Override
+    public TYPE getType() {
+        return TYPE.NS;
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/record/SRV.java b/src/main/java/de/measite/minidns/record/SRV.java
new file mode 100644
index 00000000..32b70c4d
--- /dev/null
+++ b/src/main/java/de/measite/minidns/record/SRV.java
@@ -0,0 +1,74 @@
+package de.measite.minidns.record;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+
+import de.measite.minidns.Record.TYPE;
+import de.measite.minidns.util.NameUtil;
+
+public class SRV implements Data {
+
+    protected int priority;
+    protected int weight;
+    protected int port;
+    protected String name;
+
+    public int getPriority() {
+        return priority;
+    }
+
+    public void setPriority(int priority) {
+        this.priority = priority;
+    }
+
+    public int getWeight() {
+        return weight;
+    }
+
+    public void setWeight(int weight) {
+        this.weight = weight;
+    }
+
+    public int getPort() {
+        return port;
+    }
+
+    public void setPort(int port) {
+        this.port = port;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public byte[] toByteArray() {
+        // TODO Auto-generated method stub
+        return null;
+    }
+
+    @Override
+    public void parse(DataInputStream dis, byte[] data, int length)
+        throws IOException
+    {
+        this.priority = dis.readUnsignedShort();
+        this.weight = dis.readUnsignedShort();
+        this.port = dis.readUnsignedShort();
+        this.name = NameUtil.parse(dis, data);
+    }
+
+    @Override
+    public String toString() {
+        return "SRV " + name + ":" + port + " p:" + priority + " w:" + weight;
+    }
+
+    @Override
+    public TYPE getType() {
+        return TYPE.SRV;
+    }
+
+}
diff --git a/src/main/java/de/measite/minidns/util/NameUtil.java b/src/main/java/de/measite/minidns/util/NameUtil.java
new file mode 100644
index 00000000..91a6649d
--- /dev/null
+++ b/src/main/java/de/measite/minidns/util/NameUtil.java
@@ -0,0 +1,91 @@
+package de.measite.minidns.util;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.net.IDN;
+import java.util.HashSet;
+import java.util.Arrays;
+
+public class NameUtil {
+
+    public static int size(String name) {
+        return name.length() + 2;
+    }
+
+    public static boolean idnEquals(String name1, String name2) {
+        if (name1 == name2) return true; // catches null, null
+        if (name1 == null) return false;
+        if (name2 == null) return false;
+        if (name1.equals(name2)) return true;
+
+        try {
+            return Arrays.equals(toByteArray(name1),toByteArray(name2));
+        } catch (IOException e) {
+            return false; // impossible
+        }
+    }
+
+    public static byte[] toByteArray(String name) throws IOException {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream(64);
+        DataOutputStream dos = new DataOutputStream(baos);
+        for (String s: name.split("[.\u3002\uFF0E\uFF61]")) {
+            byte[] buffer = IDN.toASCII(s).getBytes();
+            dos.writeByte(buffer.length);
+            dos.write(buffer);
+        }
+        dos.writeByte(0);
+        dos.flush();
+        return baos.toByteArray();
+    }   
+
+    public static String parse(DataInputStream dis, byte data[]) 
+        throws IOException
+    {
+        int c = dis.readUnsignedByte();
+        if ((c & 0xc0) == 0xc0) {
+            c = ((c & 0x3f) << 8) + dis.readUnsignedByte();
+            HashSet<Integer> jumps = new HashSet<Integer>();
+            jumps.add(c);
+            return parse(data, c, jumps);
+        }
+        if (c == 0) {
+            return "";
+        }
+        byte b[] = new byte[c];
+        dis.readFully(b);
+        String s = IDN.toUnicode(new String(b));
+        String t = parse(dis, data);
+        if (t.length() > 0) {
+            s = s + "." + t;
+        }
+        return s;
+    }
+
+    public static String parse(
+        byte data[],
+        int offset,
+        HashSet<Integer> jumps
+    ) {
+        int c = data[offset] & 0xff;
+        if ((c & 0xc0) == 0xc0) {
+            c = ((c & 0x3f) << 8) + (data[offset + 1] & 0xff);
+            if (jumps.contains(c)) {
+                throw new IllegalStateException("Cyclic offsets detected.");
+            }
+            jumps.add(c);
+            return parse(data, c, jumps);
+        }
+        if (c == 0) {
+            return "";
+        }
+        String s = new String(data,offset + 1, c);
+        String t = parse(data, offset + 1 + c, jumps);
+        if (t.length() > 0) {
+            s = s + "." + t;
+        }
+        return s;
+    }
+
+}