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.nio.ByteBuffer;
30 import java.nio.file.Paths;
31 import java.util.ArrayList;
32 import java.util.Arrays;
33 import java.util.List;
34 import java.util.Scanner;
35 import java.util.regex.MatchResult;
36
37 /*
38 * A dummy DNS server.
39 *
40 * Loads a sequence of DNS messages from a capture file into its cache.
41 * It listens for DNS UDP requests, finds match request in cache and sends the
42 * corresponding DNS responses.
43 *
44 * The capture file contains an DNS protocol exchange in the hexadecimal
45 * dump format emitted by HexDumpEncoder:
46 *
47 * xxxx: 00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff ................
48 *
49 * Typically, DNS protocol exchange is generated by DNSTracer who captures
50 * communication messages between DNS application program and real DNS server
51 */
52 public class DNSServer implements Runnable {
53
54 public class Pair<F, S> {
55 private F first;
56 private S second;
57
58 public Pair(F first, S second) {
59 this.first = first;
60 this.second = second;
61 }
62
63 public void setFirst(F first) {
64 this.first = first;
65 }
66
67 public void setSecond(S second) {
68 this.second = second;
69 }
70
71 public F getFirst() {
72 return first;
73 }
74
75 public S getSecond() {
76 return second;
77 }
78 }
79
80 public static final int DNS_HEADER_SIZE = 12;
81 public static final int DNS_PACKET_SIZE = 512;
82
83 static HexDumpEncoder encoder = new HexDumpEncoder();
84
85 private DatagramSocket socket;
86 private String filename;
87 private boolean loop;
88 private final List<Pair<byte[], byte[]>> cache = new ArrayList<>();
89 private ByteBuffer reqBuffer = ByteBuffer.allocate(DNS_PACKET_SIZE);
90
91 public DNSServer(DatagramSocket socket, String filename) {
92 this(socket, filename, false);
93 }
94
95 public DNSServer(DatagramSocket socket, String filename, boolean loop) {
96 this.socket = socket;
97 this.filename = filename;
98 this.loop = loop;
99 }
100
101 public void run() {
102 try {
103 System.out.println(
104 "DNSServer: Loading DNS cache data from : " + filename);
105 loadCaptureFile(filename);
106
107 System.out.println(
108 "DNSServer: listening on port " + socket.getLocalPort());
109
110 System.out.println("DNSServer: loop playback: " + loop);
111
112 int playbackIndex = 0;
113
114 while (playbackIndex < cache.size()) {
115 DatagramPacket reqPacket = new DatagramPacket(reqBuffer.array(),
116 reqBuffer.array().length);
117 socket.receive(reqPacket);
118
119 System.out.println(
120 "DNSServer: received query message from " + reqPacket
121 .getSocketAddress());
122
123 if (!verifyRequestMsg(reqPacket, playbackIndex)) {
124 throw new RuntimeException(
125 "DNSServer: Error: Failed to verify DNS request. "
126 + "Not identical request message : \n"
127 + encoder.encodeBuffer(
128 Arrays.copyOf(reqPacket.getData(),
129 reqPacket.getLength())));
130 }
131
132 byte[] payload = generateResponsePayload(reqPacket,
133 playbackIndex);
134 socket.send(new DatagramPacket(payload, payload.length,
135 reqPacket.getSocketAddress()));
136 System.out.println(
137 "DNSServer: send response message to " + reqPacket
138 .getSocketAddress());
139
140 playbackIndex++;
141 if (loop && playbackIndex >= cache.size()) {
142 playbackIndex = 0;
143 }
144 }
145
146 System.out.println(
147 "DNSServer: Done for all cached messages playback");
148 } catch (Exception e) {
149 System.err.println("DNSServer: Error: " + e);
150 }
151 }
152
153 /*
154 * Load a capture file containing an DNS protocol exchange in the
155 * hexadecimal dump format emitted by sun.misc.HexDumpEncoder:
156 *
157 * xxxx: 00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff ................
158 */
159 private void loadCaptureFile(String filename) throws IOException {
160 StringBuilder hexString = new StringBuilder();
161 String pattern = "(....): (..) (..) (..) (..) (..) (..) (..) (..) "
162 + "(..) (..) (..) (..) (..) (..) (..) (..).*";
163
164 try (Scanner fileScanner = new Scanner(Paths.get(filename))) {
165 while (fileScanner.hasNextLine()) {
166
167 try (Scanner lineScanner = new Scanner(
168 fileScanner.nextLine())) {
169 if (lineScanner.findInLine(pattern) == null) {
170 continue;
171 }
172 MatchResult result = lineScanner.match();
173 for (int i = 1; i <= result.groupCount(); i++) {
174 String digits = result.group(i);
175 if (digits.length() == 4) {
176 if (digits.equals("0000")) { // start-of-message
177 if (hexString.length() > 0) {
178 addToCache(hexString.toString());
179 hexString.delete(0, hexString.length());
180 }
181 }
182 continue;
183 } else if (digits.equals(" ")) { // short message
184 continue;
185 }
186 hexString.append(digits);
187 }
188 }
189 }
190 }
191 addToCache(hexString.toString());
192 }
193
194 /*
195 * Add an DNS encoding to the cache (by request message key).
196 */
197 private void addToCache(String hexString) {
198 byte[] encoding = parseHexBinary(hexString);
199 if (encoding.length < DNS_HEADER_SIZE) {
200 throw new RuntimeException("Invalid DNS message : " + hexString);
201 }
202
203 if (getQR(encoding) == 0) {
204 // a query message, create entry in cache
205 cache.add(new Pair<>(encoding, null));
206 System.out.println(
207 " adding DNS query message with ID " + getID(encoding)
208 + " to the cache");
209 } else {
210 // a response message, attach it to the query entry
211 if (!cache.isEmpty() && (getID(getLatestCacheEntry().getFirst())
212 == getID(encoding))) {
213 getLatestCacheEntry().setSecond(encoding);
214 System.out.println(
215 " adding DNS response message associated to ID "
216 + getID(encoding) + " in the cache");
217 } else {
218 throw new RuntimeException(
219 "Invalid DNS message : " + hexString);
220 }
221 }
222 }
223
224 /*
225 * ID: A 16 bit identifier assigned by the program that generates any
226 * kind of query. This identifier is copied the corresponding reply and
227 * can be used by the requester to match up replies to outstanding queries.
228 */
229 private static int getID(byte[] encoding) {
230 return ByteBuffer.wrap(encoding, 0, 2).getShort();
231 }
232
233 /*
234 * QR: A one bit field that specifies whether this message is
235 * a query (0), or a response (1) after ID
236 */
237 private static int getQR(byte[] encoding) {
238 return encoding[2] & (0x01 << 7);
239 }
240
241 private Pair<byte[], byte[]> getLatestCacheEntry() {
242 return cache.get(cache.size() - 1);
243 }
244
245 private boolean verifyRequestMsg(DatagramPacket packet, int playbackIndex) {
246 byte[] cachedRequest = cache.get(playbackIndex).getFirst();
247 return Arrays.equals(Arrays
248 .copyOfRange(packet.getData(), 2, packet.getLength()),
249 Arrays.copyOfRange(cachedRequest, 2, cachedRequest.length));
250 }
251
252 private byte[] generateResponsePayload(DatagramPacket packet,
253 int playbackIndex) {
254 byte[] resMsg = cache.get(playbackIndex).getSecond();
255 byte[] payload = Arrays.copyOf(resMsg, resMsg.length);
256
257 // replace the ID with same with real request
258 payload[0] = packet.getData()[0];
259 payload[1] = packet.getData()[1];
260
261 return payload;
262 }
263
264 public static byte[] parseHexBinary(String s) {
265
266 final int len = s.length();
267
268 // "111" is not a valid hex encoding.
269 if (len % 2 != 0) {
270 throw new IllegalArgumentException(
271 "hexBinary needs to be even-length: " + s);
272 }
273
274 byte[] out = new byte[len / 2];
275
276 for (int i = 0; i < len; i += 2) {
277 int h = hexToBin(s.charAt(i));
278 int l = hexToBin(s.charAt(i + 1));
279 if (h == -1 || l == -1) {
280 throw new IllegalArgumentException(
281 "contains illegal character for hexBinary: " + s);
282 }
283
284 out[i / 2] = (byte) (h * 16 + l);
285 }
286
287 return out;
288 }
289
290 private static int hexToBin(char ch) {
291 if ('0' <= ch && ch <= '9') {
292 return ch - '0';
293 }
294 if ('A' <= ch && ch <= 'F') {
295 return ch - 'A' + 10;
296 }
297 if ('a' <= ch && ch <= 'f') {
298 return ch - 'a' + 10;
299 }
300 return -1;
301 }
302 }