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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 static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  final class DnsQueryEncoder {
  
      private final DnsRecordEncoder recordEncoder;
  
      /**
       * Creates a new encoder with the specified {@code recordEncoder}.
       */
      DnsQueryEncoder(DnsRecordEncoder recordEncoder) {
          this.recordEncoder = checkNotNull(recordEncoder, "recordEncoder");
      }
  
      /**
       * Encodes the given {@link DnsQuery} into a {@link ByteBuf}.
       */
      void encode(DnsQuery query, ByteBuf out) throws Exception {
          encodeHeader(query, out);
          encodeQuestions(query, out);
          encodeRecords(query, DnsSection.ADDITIONAL, out);
      }
  
      /**
       * Encodes the header that is always 12 bytes long.
       *
       * @param query the query header being encoded
       * @param buf   the buffer the encoded data should be written to
       */
      private static void encodeHeader(DnsQuery query, ByteBuf buf) {
          buf.writeShort(query.id());
          int flags = 0;
          flags |= (query.opCode().byteValue() & 0xFF) << 14;
          if (query.isRecursionDesired()) {
              flags |= 1 << 8;
          }
          buf.writeShort(flags);
          buf.writeShort(query.count(DnsSection.QUESTION));
          buf.writeShort(0); // answerCount
          buf.writeShort(0); // authorityResourceCount
          buf.writeShort(query.count(DnsSection.ADDITIONAL));
      }
  
      private void encodeQuestions(DnsQuery query, ByteBuf buf) throws Exception {
          final int count = query.count(DnsSection.QUESTION);
          for (int i = 0; i < count; i++) {
              recordEncoder.encodeQuestion((DnsQuestion) query.recordAt(DnsSection.QUESTION, i), buf);
          }
      }
  
      private void encodeRecords(DnsQuery query, DnsSection section, ByteBuf buf) throws Exception {
          final int count = query.count(section);
          for (int i = 0; i < count; i++) {
              recordEncoder.encodeRecord(query.recordAt(section, i), buf);
          }
      }
  }