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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.example.mqtt.heartBeat;
  
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandlerAdapter;
  import io.netty.handler.codec.mqtt.MqttConnAckMessage;
  import io.netty.handler.codec.mqtt.MqttConnAckVariableHeader;
  import io.netty.handler.codec.mqtt.MqttConnectReturnCode;
  import io.netty.handler.codec.mqtt.MqttFixedHeader;
  import io.netty.handler.codec.mqtt.MqttMessage;
  import io.netty.handler.codec.mqtt.MqttMessageType;
  import io.netty.handler.codec.mqtt.MqttQoS;
  import io.netty.handler.timeout.IdleState;
  import io.netty.handler.timeout.IdleStateEvent;
  import io.netty.util.ReferenceCountUtil;
  
  @Sharable
  public final class MqttHeartBeatBrokerHandler extends ChannelInboundHandlerAdapter {
  
      public static final MqttHeartBeatBrokerHandler INSTANCE = new MqttHeartBeatBrokerHandler();
  
      private MqttHeartBeatBrokerHandler() {
      }
  
      @Override
      public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
          MqttMessage mqttMessage = (MqttMessage) msg;
          System.out.println("Received MQTT message: " + mqttMessage);
          switch (mqttMessage.fixedHeader().messageType()) {
          case CONNECT:
              MqttFixedHeader connackFixedHeader =
                      new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0);
              MqttConnAckVariableHeader mqttConnAckVariableHeader =
                      new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_ACCEPTED, false);
              MqttConnAckMessage connack = new MqttConnAckMessage(connackFixedHeader, mqttConnAckVariableHeader);
              ctx.writeAndFlush(connack);
              break;
          case PINGREQ:
              MqttFixedHeader pingreqFixedHeader = new MqttFixedHeader(MqttMessageType.PINGRESP, false,
                                                                       MqttQoS.AT_MOST_ONCE, false, 0);
              MqttMessage pingResp = new MqttMessage(pingreqFixedHeader);
              ctx.writeAndFlush(pingResp);
              break;
          case DISCONNECT:
              ctx.close();
              break;
          default:
              System.out.println("Unexpected message type: " + mqttMessage.fixedHeader().messageType());
              ReferenceCountUtil.release(msg);
              ctx.close();
          }
      }
  
      @Override
      public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
          System.out.println("Channel heartBeat lost");
          if (evt instanceof IdleStateEvent && IdleState.READER_IDLE == ((IdleStateEvent) evt).state()) {
              ctx.close();
          }
      }
  
      @Override
      public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
          cause.printStackTrace();
          ctx.close();
      }
  }