1 /*
2 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24 import sun.security.util.HexDumpEncoder;
25
26 import java.io.IOException;
27 import java.net.DatagramPacket;
28 import java.net.DatagramSocket;
29 import java.net.InetAddress;
30 import java.net.SocketException;
31 import java.nio.ByteBuffer;
32 import java.nio.file.Paths;
33 import java.util.ArrayList;
34 import java.util.Arrays;
35 import java.util.List;
36 import java.util.Scanner;
37 import java.util.regex.MatchResult;
38
39 /*
40 * A dummy DNS server.
41 *
42 * Loads a sequence of DNS messages from a capture file into its cache.
43 * It listens for DNS UDP requests, finds match request in cache and sends the
44 * corresponding DNS responses.
45 *
46 * The capture file contains an DNS protocol exchange in the hexadecimal
47 * dump format emitted by HexDumpEncoder:
48 *
49 * xxxx: 00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff ................
50 *
51 * Typically, DNS protocol exchange is generated by DNSTracer who captures
52 * communication messages between DNS application program and real DNS server
53 */
54 public class DNSServer extends Thread implements Server {
55
56 public class Pair<F, S> {
57 private F first;
58 private S second;
59
60 public Pair(F first, S second) {
61 this.first = first;
62 this.second = second;
63 }
64
65 public void setFirst(F first) {
66 this.first = first;
67 }
68
69 public void setSecond(S second) {
70 this.second = second;
71 }
72
73 public F getFirst() {
74 return first;
75 }
76
77 public S getSecond() {
78 return second;
79 }
80 }
81
82 public static final int DNS_HEADER_SIZE = 12;
83 public static final int DNS_PACKET_SIZE = 512;
84
85 static HexDumpEncoder encoder = new HexDumpEncoder();
86
87 private DatagramSocket socket;
88 private String filename;
89 private boolean loop;
90 private final List<Pair<byte[], byte[]>> cache = new ArrayList<>();
91 private ByteBuffer reqBuffer = ByteBuffer.allocate(DNS_PACKET_SIZE);
92 private volatile boolean isRunning;
93
94 public DNSServer(String filename) throws SocketException {
95 this(filename, false);
96 }
97
98 public DNSServer(String filename, boolean loop) throws SocketException {
99 this.socket = new DatagramSocket(0, InetAddress.getLoopbackAddress());
100 this.filename = filename;
101 this.loop = loop;
102 }
103
104 public void run() {
105 try {
106 isRunning = true;
107 System.out.println(
108 "DNSServer: Loading DNS cache data from : " + filename);
109 loadCaptureFile(filename);
110
111 System.out.println(
112 "DNSServer: listening on port " + socket.getLocalPort());
113
114 System.out.println("DNSServer: loop playback: " + loop);
115
116 int playbackIndex = 0;
117
118 while (playbackIndex < cache.size()) {
119 DatagramPacket reqPacket = receiveQuery();
120
121 if (!verifyRequestMsg(reqPacket, playbackIndex)) {
122 if (playbackIndex > 0 && verifyRequestMsg(reqPacket,
123 playbackIndex - 1)) {
124 System.out.println(
125 "DNSServer: received retry query, resend");
126 playbackIndex--;
127 } else {
128 throw new RuntimeException(
129 "DNSServer: Error: Failed to verify DNS request. "
130 + "Not identical request message : \n"
131 + encoder.encodeBuffer(
132 Arrays.copyOf(reqPacket.getData(),
133 reqPacket.getLength())));
134 }
135 }
136
137 sendResponse(reqPacket, playbackIndex);
138
139 playbackIndex++;
140 if (loop && playbackIndex >= cache.size()) {
141 playbackIndex = 0;
142 }
143 }
144
145 System.out.println(
146 "DNSServer: Done for all cached messages playback");
147
148 System.out.println(
149 "DNSServer: Still listening for possible retry query");
150 while (true) {
151 DatagramPacket reqPacket = receiveQuery();
152
153 // here we only handle the retry query for last one
154 if (!verifyRequestMsg(reqPacket, playbackIndex - 1)) {
155 throw new RuntimeException(
156 "DNSServer: Error: Failed to verify DNS request. "
157 + "Not identical request message : \n"
158 + encoder.encodeBuffer(
159 Arrays.copyOf(reqPacket.getData(),
160 reqPacket.getLength())));
161 }
162
163 sendResponse(reqPacket, playbackIndex - 1);
164 }
165 } catch (Exception e) {
166 if (isRunning) {
167 System.err.println("DNSServer: Error: " + e);
168 e.printStackTrace();
169 } else {
170 System.out.println("DNSServer: Exit");
171 }
172 }
173 }
174
175 private DatagramPacket receiveQuery() throws IOException {
176 DatagramPacket reqPacket = new DatagramPacket(reqBuffer.array(),
177 reqBuffer.array().length);
178 socket.receive(reqPacket);
179
180 System.out.println("DNSServer: received query message from " + reqPacket
181 .getSocketAddress());
182
183 return reqPacket;
184 }
185
186 private void sendResponse(DatagramPacket reqPacket, int playbackIndex)
187 throws IOException {
188 byte[] payload = generateResponsePayload(reqPacket, playbackIndex);
189 socket.send(new DatagramPacket(payload, payload.length,
190 reqPacket.getSocketAddress()));
191 System.out.println("DNSServer: send response message to " + reqPacket
192 .getSocketAddress());
193 }
194
195 /*
196 * Load a capture file containing an DNS protocol exchange in the
197 * hexadecimal dump format emitted by sun.misc.HexDumpEncoder:
198 *
199 * xxxx: 00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff ................
200 */
201 private void loadCaptureFile(String filename) throws IOException {
202 StringBuilder hexString = new StringBuilder();
203 String pattern = "(....): (..) (..) (..) (..) (..) (..) (..) (..) "
204 + "(..) (..) (..) (..) (..) (..) (..) (..).*";
205
206 try (Scanner fileScanner = new Scanner(Paths.get(filename))) {
207 while (fileScanner.hasNextLine()) {
208
209 try (Scanner lineScanner = new Scanner(
210 fileScanner.nextLine())) {
211 if (lineScanner.findInLine(pattern) == null) {
212 continue;
213 }
214 MatchResult result = lineScanner.match();
215 for (int i = 1; i <= result.groupCount(); i++) {
216 String digits = result.group(i);
217 if (digits.length() == 4) {
218 if (digits.equals("0000")) { // start-of-message
219 if (hexString.length() > 0) {
220 addToCache(hexString.toString());
221 hexString.delete(0, hexString.length());
222 }
223 }
224 continue;
225 } else if (digits.equals(" ")) { // short message
226 continue;
227 }
228 hexString.append(digits);
229 }
230 }
231 }
232 }
233 addToCache(hexString.toString());
234 }
235
236 /*
237 * Add an DNS encoding to the cache (by request message key).
238 */
239 private void addToCache(String hexString) {
240 byte[] encoding = parseHexBinary(hexString);
241 if (encoding.length < DNS_HEADER_SIZE) {
242 throw new RuntimeException("Invalid DNS message : " + hexString);
243 }
244
245 if (getQR(encoding) == 0) {
246 // a query message, create entry in cache
247 cache.add(new Pair<>(encoding, null));
248 System.out.println(
249 " adding DNS query message with ID " + getID(encoding)
250 + " to the cache");
251 } else {
252 // a response message, attach it to the query entry
253 if (!cache.isEmpty() && (getID(getLatestCacheEntry().getFirst())
254 == getID(encoding))) {
255 getLatestCacheEntry().setSecond(encoding);
256 System.out.println(
257 " adding DNS response message associated to ID "
258 + getID(encoding) + " in the cache");
259 } else {
260 throw new RuntimeException(
261 "Invalid DNS message : " + hexString);
262 }
263 }
264 }
265
266 /*
267 * ID: A 16 bit identifier assigned by the program that generates any
268 * kind of query. This identifier is copied the corresponding reply and
269 * can be used by the requester to match up replies to outstanding queries.
270 */
271 private static int getID(byte[] encoding) {
272 return ByteBuffer.wrap(encoding, 0, 2).getShort();
273 }
274
275 /*
276 * QR: A one bit field that specifies whether this message is
277 * a query (0), or a response (1) after ID
278 */
279 private static int getQR(byte[] encoding) {
280 return encoding[2] & (0x01 << 7);
281 }
282
283 private Pair<byte[], byte[]> getLatestCacheEntry() {
284 return cache.get(cache.size() - 1);
285 }
286
287 private boolean verifyRequestMsg(DatagramPacket packet, int playbackIndex) {
288 byte[] cachedRequest = cache.get(playbackIndex).getFirst();
289 return Arrays.equals(Arrays
290 .copyOfRange(packet.getData(), 2, packet.getLength()),
291 Arrays.copyOfRange(cachedRequest, 2, cachedRequest.length));
292 }
293
294 private byte[] generateResponsePayload(DatagramPacket packet,
295 int playbackIndex) {
296 byte[] resMsg = cache.get(playbackIndex).getSecond();
297 byte[] payload = Arrays.copyOf(resMsg, resMsg.length);
298
299 // replace the ID with same with real request
300 payload[0] = packet.getData()[0];
301 payload[1] = packet.getData()[1];
302
303 return payload;
304 }
305
306 public static byte[] parseHexBinary(String s) {
307
308 final int len = s.length();
309
310 // "111" is not a valid hex encoding.
311 if (len % 2 != 0) {
312 throw new IllegalArgumentException(
313 "hexBinary needs to be even-length: " + s);
314 }
315
316 byte[] out = new byte[len / 2];
317
318 for (int i = 0; i < len; i += 2) {
319 int h = hexToBin(s.charAt(i));
320 int l = hexToBin(s.charAt(i + 1));
321 if (h == -1 || l == -1) {
322 throw new IllegalArgumentException(
323 "contains illegal character for hexBinary: " + s);
324 }
325
326 out[i / 2] = (byte) (h * 16 + l);
327 }
328
329 return out;
330 }
331
332 private static int hexToBin(char ch) {
333 if ('0' <= ch && ch <= '9') {
334 return ch - '0';
335 }
336 if ('A' <= ch && ch <= 'F') {
337 return ch - 'A' + 10;
338 }
339 if ('a' <= ch && ch <= 'f') {
340 return ch - 'a' + 10;
341 }
342 return -1;
343 }
344
345 @Override public void stopServer() {
346 isRunning = false;
347 if (socket != null) {
348 try {
349 socket.close();
350 } catch (Exception e) {
351 // ignore
352 }
353 }
354 }
355
356 @Override public int getPort() {
357 if (socket != null) {
358 return socket.getLocalPort();
359 } else {
360 return -1;
361 }
362 }
363 }