1 /*
2 * Copyright 2019 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package io.netty.handler.codec.dns;
17
18 import io.netty.buffer.ByteBuf;
19 import io.netty.handler.codec.CorruptedFrameException;
20
21 import java.net.SocketAddress;
22
23 import static io.netty.util.internal.ObjectUtil.checkNotNull;
24
25 abstract class DnsResponseDecoder<A extends SocketAddress> {
26
27 private final DnsRecordDecoder recordDecoder;
28
29 /**
30 * Creates a new decoder with the specified {@code recordDecoder}.
31 */
32 DnsResponseDecoder(DnsRecordDecoder recordDecoder) {
33 this.recordDecoder = checkNotNull(recordDecoder, "recordDecoder");
34 }
35
36 final DnsResponse decode(A sender, A recipient, ByteBuf buffer) throws Exception {
37 final int id = buffer.readUnsignedShort();
38
39 final int flags = buffer.readUnsignedShort();
40 if (flags >> 15 == 0) {
41 throw new CorruptedFrameException("not a response");
42 }
43
44 final DnsResponse response = newResponse(
45 sender,
46 recipient,
47 id,
48 DnsOpCode.valueOf((byte) (flags >> 11 & 0xf)), DnsResponseCode.valueOf((byte) (flags & 0xf)));
49
50 response.setRecursionDesired((flags >> 8 & 1) == 1);
51 response.setAuthoritativeAnswer((flags >> 10 & 1) == 1);
52 response.setTruncated((flags >> 9 & 1) == 1);
53 response.setRecursionAvailable((flags >> 7 & 1) == 1);
54 response.setZ(flags >> 4 & 0x7);
55
56 boolean success = false;
57 try {
58 final int questionCount = buffer.readUnsignedShort();
59 final int answerCount = buffer.readUnsignedShort();
60 final int authorityRecordCount = buffer.readUnsignedShort();
61 final int additionalRecordCount = buffer.readUnsignedShort();
62
63 decodeQuestions(response, buffer, questionCount);
64 if (!decodeRecords(response, DnsSection.ANSWER, buffer, answerCount)) {
65 success = true;
66 return response;
67 }
68 if (!decodeRecords(response, DnsSection.AUTHORITY, buffer, authorityRecordCount)) {
69 success = true;
70 return response;
71 }
72
73 decodeRecords(response, DnsSection.ADDITIONAL, buffer, additionalRecordCount);
74 success = true;
75 return response;
76 } finally {
77 if (!success) {
78 response.release();
79 }
80 }
81 }
82
83 protected abstract DnsResponse newResponse(A sender, A recipient, int id,
84 DnsOpCode opCode, DnsResponseCode responseCode) throws Exception;
85
86 private void decodeQuestions(DnsResponse response, ByteBuf buf, int questionCount) throws Exception {
87 for (int i = questionCount; i > 0; i --) {
88 response.addRecord(DnsSection.QUESTION, recordDecoder.decodeQuestion(buf));
89 }
90 }
91
92 private boolean decodeRecords(
93 DnsResponse response, DnsSection section, ByteBuf buf, int count) throws Exception {
94 for (int i = count; i > 0; i --) {
95 final DnsRecord r = recordDecoder.decodeRecord(buf);
96 if (r == null) {
97 // Truncated response
98 return false;
99 }
100
101 response.addRecord(section, r);
102 }
103 return true;
104 }
105 }
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