/*
    * Copyright 2015 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.AddressedEnvelope;
  import io.netty.channel.ChannelHandler;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.socket.DatagramPacket;
  import io.netty.handler.codec.MessageToMessageEncoder;
  import io.netty.util.internal.UnstableApi;
  
  import java.net.InetSocketAddress;
  import java.util.List;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * Encodes a {@link DatagramDnsResponse} (or an {@link AddressedEnvelope} of {@link DnsResponse}} into a
   * {@link DatagramPacket}.
   */
  @UnstableApi
  @ChannelHandler.Sharable
  public class DatagramDnsResponseEncoder
      extends MessageToMessageEncoder<AddressedEnvelope<DnsResponse, InetSocketAddress>> {
  
      private final DnsRecordEncoder recordEncoder;
  
      /**
       * Creates a new encoder with {@linkplain DnsRecordEncoder#DEFAULT the default record encoder}.
       */
      public DatagramDnsResponseEncoder() {
          this(DnsRecordEncoder.DEFAULT);
      }
  
      /**
       * Creates a new encoder with the specified {@code recordEncoder}.
       */
      public DatagramDnsResponseEncoder(DnsRecordEncoder recordEncoder) {
          this.recordEncoder = checkNotNull(recordEncoder, "recordEncoder");
      }
  
      @Override
      protected void encode(ChannelHandlerContext ctx,
                            AddressedEnvelope<DnsResponse, InetSocketAddress> in, List<Object> out) throws Exception {
  
          final InetSocketAddress recipient = in.recipient();
          final DnsResponse response = in.content();
          final ByteBuf buf = allocateBuffer(ctx, in);
  
          DnsMessageUtil.encodeDnsResponse(recordEncoder, response, buf);
  
          out.add(new DatagramPacket(buf, recipient, null));
      }
  
      /**
       * Allocate a {@link ByteBuf} which will be used for constructing a datagram packet.
       * Sub-classes may override this method to return a {@link ByteBuf} with a perfect matching initial capacity.
       */
      protected ByteBuf allocateBuffer(
          ChannelHandlerContext ctx,
          @SuppressWarnings("unused") AddressedEnvelope<DnsResponse, InetSocketAddress> msg) throws Exception {
          return ctx.alloc().ioBuffer(1024);
      }
  }