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   /*
    * Copyright 2019 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.handler.codec.dns;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandler;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.MessageToByteEncoder;
  import io.netty.util.internal.UnstableApi;
  
  @ChannelHandler.Sharable
  @UnstableApi
  public final class TcpDnsQueryEncoder extends MessageToByteEncoder<DnsQuery> {
  
      private final DnsQueryEncoder encoder;
  
      /**
       * Creates a new encoder with {@linkplain DnsRecordEncoder#DEFAULT the default record encoder}.
       */
      public TcpDnsQueryEncoder() {
          this(DnsRecordEncoder.DEFAULT);
      }
  
      /**
       * Creates a new encoder with the specified {@code recordEncoder}.
       */
      public TcpDnsQueryEncoder(DnsRecordEncoder recordEncoder) {
          this.encoder = new DnsQueryEncoder(recordEncoder);
      }
  
      @Override
      protected void encode(ChannelHandlerContext ctx, DnsQuery msg, ByteBuf out) throws Exception {
          // Length is two octets as defined by RFC-7766
          // See https://tools.ietf.org/html/rfc7766#section-8
          out.writerIndex(out.writerIndex() + 2);
          encoder.encode(msg, out);
  
          // Now fill in the correct length based on the amount of data that we wrote the ByteBuf.
          out.setShort(0, out.readableBytes() - 2);
      }
  
      @Override
      protected ByteBuf allocateBuffer(ChannelHandlerContext ctx, @SuppressWarnings("unused") DnsQuery msg,
                                       boolean preferDirect) {
          if (preferDirect) {
              return ctx.alloc().ioBuffer(1024);
          } else {
              return ctx.alloc().heapBuffer(1024);
          }
      }
  }