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.
85 lines
2.8 KiB
Java
85 lines
2.8 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.channel.AddressedEnvelope;
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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.channel.socket.DatagramPacket;
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import io.netty.handler.codec.MessageToMessageEncoder;
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import io.netty.util.internal.UnstableApi;
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import java.net.InetSocketAddress;
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import java.util.List;
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/**
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* Encodes a {@link DatagramDnsQuery} (or an {@link AddressedEnvelope} of {@link DnsQuery}} into a
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* {@link DatagramPacket}.
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*/
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@UnstableApi
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@ChannelHandler.Sharable
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public class DatagramDnsQueryEncoder extends MessageToMessageEncoder<AddressedEnvelope<DnsQuery, InetSocketAddress>> {
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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 DatagramDnsQueryEncoder() {
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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 DatagramDnsQueryEncoder(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(
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ChannelHandlerContext ctx,
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AddressedEnvelope<DnsQuery, InetSocketAddress> in, List<Object> out) throws Exception {
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final InetSocketAddress recipient = in.recipient();
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final DnsQuery query = in.content();
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final ByteBuf buf = allocateBuffer(ctx, in);
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boolean success = false;
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try {
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encoder.encode(query, buf);
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success = true;
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} finally {
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if (!success) {
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buf.release();
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}
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}
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out.add(new DatagramPacket(buf, recipient, null));
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}
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/**
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* Allocate a {@link ByteBuf} which will be used for constructing a datagram packet.
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* Sub-classes may override this method to return a {@link ByteBuf} with a perfect matching initial capacity.
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*/
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protected ByteBuf allocateBuffer(
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ChannelHandlerContext ctx,
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@SuppressWarnings("unused") AddressedEnvelope<DnsQuery, InetSocketAddress> msg) throws Exception {
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return ctx.alloc().ioBuffer(1024);
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}
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}
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