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   /*
    * Copyright 2020 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.stomp.websocket;
  
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.MessageToMessageCodec;
  import io.netty.handler.codec.http.websocketx.BinaryWebSocketFrame;
  import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
  import io.netty.handler.codec.http.websocketx.WebSocketFrame;
  import io.netty.handler.codec.http.websocketx.WebSocketFrameAggregator;
  import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
  import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler.HandshakeComplete;
  import io.netty.handler.codec.stomp.StompSubframe;
  import io.netty.handler.codec.stomp.StompSubframeAggregator;
  import io.netty.handler.codec.stomp.StompSubframeDecoder;
  
  import java.util.List;
  
  @Sharable
  public class StompWebSocketProtocolCodec extends MessageToMessageCodec<WebSocketFrame, StompSubframe> {
  
      private final StompChatHandler stompChatHandler = new StompChatHandler();
      private final StompWebSocketFrameEncoder stompWebSocketFrameEncoder = new StompWebSocketFrameEncoder();
  
      @Override
      public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
          if (evt instanceof WebSocketServerProtocolHandler.HandshakeComplete) {
              StompVersion stompVersion = StompVersion.findBySubProtocol(((HandshakeComplete) evt).selectedSubprotocol());
              ctx.channel().attr(StompVersion.CHANNEL_ATTRIBUTE_KEY).set(stompVersion);
              ctx.pipeline()
                 .addLast(new WebSocketFrameAggregator(65536))
                 .addLast(new StompSubframeDecoder())
                 .addLast(new StompSubframeAggregator(65536))
                 .addLast(stompChatHandler)
                 .remove(StompWebSocketClientPageHandler.INSTANCE);
          } else {
              super.userEventTriggered(ctx, evt);
          }
      }
  
      @Override
      protected void encode(ChannelHandlerContext ctx, StompSubframe stompFrame, List<Object> out) throws Exception {
          stompWebSocketFrameEncoder.encode(ctx, stompFrame, out);
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, WebSocketFrame webSocketFrame, List<Object> out) {
          if (webSocketFrame instanceof TextWebSocketFrame || webSocketFrame instanceof BinaryWebSocketFrame) {
              out.add(webSocketFrame.content().retain());
          } else {
              ctx.close();
          }
      }
  }