Motivation: The current DnsNameResolver fails to resolve an A+CNAME answer. For example: dig moose.rmq.cloudamqp.com ... ;; ANSWER SECTION: moose.rmq.cloudamqp.com. 1800 IN CNAME ec2-54-152-221-139.compute-1.amazonaws.com. ec2-54-152-221-139.compute-1.amazonaws.com. 583612 IN A 54.152.221.139 ... The resolver constructs a map of cnames but forgets the trailing "." in the values which lead to not resolve the A record. Modifications: Reuse the code of DefaltDnsRecordDecoder which correctly handles the trailing dot. Result: Correctly resolve.
188 lines
6.5 KiB
Java
188 lines
6.5 KiB
Java
/*
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* Copyright 2015 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.handler.codec.dns;
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import io.netty.buffer.ByteBuf;
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import io.netty.handler.codec.CorruptedFrameException;
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import io.netty.util.CharsetUtil;
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import io.netty.util.internal.UnstableApi;
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/**
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* The default {@link DnsRecordDecoder} implementation.
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*
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* @see DefaultDnsRecordEncoder
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*/
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@UnstableApi
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public class DefaultDnsRecordDecoder implements DnsRecordDecoder {
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static final String ROOT = ".";
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/**
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* Creates a new instance.
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*/
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protected DefaultDnsRecordDecoder() { }
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@Override
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public final DnsQuestion decodeQuestion(ByteBuf in) throws Exception {
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String name = decodeName(in);
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DnsRecordType type = DnsRecordType.valueOf(in.readUnsignedShort());
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int qClass = in.readUnsignedShort();
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return new DefaultDnsQuestion(name, type, qClass);
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}
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@Override
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public final <T extends DnsRecord> T decodeRecord(ByteBuf in) throws Exception {
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final int startOffset = in.readerIndex();
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final String name = decodeName(in);
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final int endOffset = in.writerIndex();
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if (endOffset - startOffset < 10) {
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// Not enough data
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in.readerIndex(startOffset);
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return null;
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}
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final DnsRecordType type = DnsRecordType.valueOf(in.readUnsignedShort());
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final int aClass = in.readUnsignedShort();
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final long ttl = in.readUnsignedInt();
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final int length = in.readUnsignedShort();
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final int offset = in.readerIndex();
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if (endOffset - offset < length) {
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// Not enough data
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in.readerIndex(startOffset);
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return null;
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}
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@SuppressWarnings("unchecked")
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T record = (T) decodeRecord(name, type, aClass, ttl, in, offset, length);
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in.readerIndex(offset + length);
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return record;
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}
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/**
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* Decodes a record from the information decoded so far by {@link #decodeRecord(ByteBuf)}.
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*
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* @param name the domain name of the record
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* @param type the type of the record
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* @param dnsClass the class of the record
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* @param timeToLive the TTL of the record
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* @param in the {@link ByteBuf} that contains the RDATA
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* @param offset the start offset of the RDATA in {@code in}
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* @param length the length of the RDATA
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*
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* @return a {@link DnsRawRecord}. Override this method to decode RDATA and return other record implementation.
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*/
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protected DnsRecord decodeRecord(
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String name, DnsRecordType type, int dnsClass, long timeToLive,
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ByteBuf in, int offset, int length) throws Exception {
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if (type == DnsRecordType.PTR) {
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in.setIndex(offset, offset + length);
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return new DefaultDnsPtrRecord(name, dnsClass, timeToLive, decodeName0(in));
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}
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return new DefaultDnsRawRecord(
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name, type, dnsClass, timeToLive, in.retainedDuplicate().setIndex(offset, offset + length));
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}
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/**
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* Retrieves a domain name given a buffer containing a DNS packet. If the
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* name contains a pointer, the position of the buffer will be set to
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* directly after the pointer's index after the name has been read.
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*
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* @param in the byte buffer containing the DNS packet
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* @return the domain name for an entry
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*/
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protected String decodeName0(ByteBuf in) {
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return decodeName(in);
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}
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/**
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* Retrieves a domain name given a buffer containing a DNS packet. If the
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* name contains a pointer, the position of the buffer will be set to
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* directly after the pointer's index after the name has been read.
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*
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* @param in the byte buffer containing the DNS packet
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* @return the domain name for an entry
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*/
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public static String decodeName(ByteBuf in) {
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int position = -1;
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int checked = 0;
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final int end = in.writerIndex();
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final int readable = in.readableBytes();
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// Looking at the spec we should always have at least enough readable bytes to read a byte here but it seems
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// some servers do not respect this for empty names. So just workaround this and return an empty name in this
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// case.
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//
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// See:
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// - https://github.com/netty/netty/issues/5014
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// - https://www.ietf.org/rfc/rfc1035.txt , Section 3.1
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if (readable == 0) {
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return ROOT;
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}
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final StringBuilder name = new StringBuilder(readable << 1);
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while (in.isReadable()) {
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final int len = in.readUnsignedByte();
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final boolean pointer = (len & 0xc0) == 0xc0;
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if (pointer) {
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if (position == -1) {
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position = in.readerIndex() + 1;
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}
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if (!in.isReadable()) {
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throw new CorruptedFrameException("truncated pointer in a name");
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}
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final int next = (len & 0x3f) << 8 | in.readUnsignedByte();
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if (next >= end) {
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throw new CorruptedFrameException("name has an out-of-range pointer");
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}
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in.readerIndex(next);
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// check for loops
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checked += 2;
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if (checked >= end) {
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throw new CorruptedFrameException("name contains a loop.");
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}
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} else if (len != 0) {
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if (!in.isReadable(len)) {
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throw new CorruptedFrameException("truncated label in a name");
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}
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name.append(in.toString(in.readerIndex(), len, CharsetUtil.UTF_8)).append('.');
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in.skipBytes(len);
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} else { // len == 0
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break;
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}
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}
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if (position != -1) {
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in.readerIndex(position);
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}
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if (name.length() == 0) {
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return ROOT;
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}
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if (name.charAt(name.length() - 1) != '.') {
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name.append('.');
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}
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return name.toString();
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}
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}
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