1672b6d12c
Motivation: Sometimes DNS responses can be very large which mean they will not fit in a UDP packet. When this is happening the DNS server will set the TC flag (truncated flag) to tell the resolver that the response was truncated. When a truncated response was received we should allow to retry via TCP and use the received response (if possible) as a replacement for the truncated one. See https://tools.ietf.org/html/rfc7766. Modifications: - Add support for TCP fallback by allow to specify a socketChannelFactory / socketChannelType on the DnsNameResolverBuilder. If this is set to something different then null we will try to fallback to TCP. - Add decoder / encoder for TCP - Add unit tests Result: Support for TCP fallback as defined by https://tools.ietf.org/html/rfc7766 when using DnsNameResolver.
65 lines
2.2 KiB
Java
65 lines
2.2 KiB
Java
/*
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* Copyright 2019 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.channel.ChannelHandler;
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import io.netty.channel.ChannelHandlerContext;
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import io.netty.handler.codec.MessageToByteEncoder;
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import io.netty.util.internal.UnstableApi;
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@ChannelHandler.Sharable
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@UnstableApi
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public final class TcpDnsQueryEncoder extends MessageToByteEncoder<DnsQuery> {
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private final DnsQueryEncoder encoder;
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/**
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* Creates a new encoder with {@linkplain DnsRecordEncoder#DEFAULT the default record encoder}.
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*/
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public TcpDnsQueryEncoder() {
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this(DnsRecordEncoder.DEFAULT);
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}
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/**
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* Creates a new encoder with the specified {@code recordEncoder}.
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*/
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public TcpDnsQueryEncoder(DnsRecordEncoder recordEncoder) {
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this.encoder = new DnsQueryEncoder(recordEncoder);
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}
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@Override
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protected void encode(ChannelHandlerContext ctx, DnsQuery msg, ByteBuf out) throws Exception {
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// Length is two octets as defined by RFC-7766
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// See https://tools.ietf.org/html/rfc7766#section-8
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out.writerIndex(out.writerIndex() + 2);
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encoder.encode(msg, out);
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// Now fill in the correct length based on the amount of data that we wrote the ByteBuf.
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out.setShort(0, out.readableBytes() - 2);
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}
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@Override
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protected ByteBuf allocateBuffer(ChannelHandlerContext ctx, @SuppressWarnings("unused") DnsQuery msg,
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boolean preferDirect) {
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if (preferDirect) {
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return ctx.alloc().ioBuffer(1024);
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} else {
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return ctx.alloc().heapBuffer(1024);
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}
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}
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}
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