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   /*
    * Copyright 2012 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;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelDuplexHandler;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  import io.netty.util.internal.TypeParameterMatcher;
  
  import java.util.List;
  
  /**
   * A Codec for on-the-fly encoding/decoding of bytes to messages and vise-versa.
   *
   * This can be thought of as a combination of {@link ByteToMessageDecoder} and {@link MessageToByteEncoder}.
   *
   * Be aware that sub-classes of {@link ByteToMessageCodec} <strong>MUST NOT</strong>
   * annotated with {@link @Sharable}.
   */
  public abstract class ByteToMessageCodec<I> extends ChannelDuplexHandler {
  
      private final TypeParameterMatcher outboundMsgMatcher;
      private final MessageToByteEncoder<I> encoder;
  
      private final ByteToMessageDecoder decoder = new ByteToMessageDecoder() {
          @Override
          public void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
              ByteToMessageCodec.this.decode(ctx, in, out);
          }
  
          @Override
          protected void decodeLast(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
              ByteToMessageCodec.this.decodeLast(ctx, in, out);
          }
      };
  
      /**
       * see {@link #ByteToMessageCodec(boolean)} with {@code true} as boolean parameter.
       */
      protected ByteToMessageCodec() {
          this(true);
      }
  
      /**
       * see {@link #ByteToMessageCodec(Class, boolean)} with {@code true} as boolean value.
       */
      protected ByteToMessageCodec(Class<? extends I> outboundMessageType) {
          this(outboundMessageType, true);
      }
  
      /**
       * Create a new instance which will try to detect the types to match out of the type parameter of the class.
       *
       * @param preferDirect          {@code true} if a direct {@link ByteBuf} should be tried to be used as target for
       *                              the encoded messages. If {@code false} is used it will allocate a heap
       *                              {@link ByteBuf}, which is backed by an byte array.
       */
      protected ByteToMessageCodec(boolean preferDirect) {
          ensureNotSharable();
          outboundMsgMatcher = TypeParameterMatcher.find(this, ByteToMessageCodec.class, "I");
          encoder = new Encoder(preferDirect);
      }
  
      /**
       * Create a new instance
       *
       * @param outboundMessageType   The type of messages to match
       * @param preferDirect          {@code true} if a direct {@link ByteBuf} should be tried to be used as target for
       *                              the encoded messages. If {@code false} is used it will allocate a heap
       *                              {@link ByteBuf}, which is backed by an byte array.
       */
      protected ByteToMessageCodec(Class<? extends I> outboundMessageType, boolean preferDirect) {
          ensureNotSharable();
          outboundMsgMatcher = TypeParameterMatcher.get(outboundMessageType);
          encoder = new Encoder(preferDirect);
      }
  
      /**
       * Returns {@code true} if and only if the specified message can be encoded by this codec.
       *
       * @param msg the message
       */
      public boolean acceptOutboundMessage(Object msg) throws Exception {
          return outboundMsgMatcher.match(msg);
      }
 
     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         decoder.channelRead(ctx, msg);
     }
 
     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
         encoder.write(ctx, msg, promise);
     }
 
     @Override
     public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
         decoder.channelReadComplete(ctx);
     }
 
     @Override
     public void channelInactive(ChannelHandlerContext ctx) throws Exception {
         decoder.channelInactive(ctx);
     }
 
     @Override
     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
         try {
             decoder.handlerAdded(ctx);
         } finally {
             encoder.handlerAdded(ctx);
         }
     }
 
     @Override
     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
         try {
             decoder.handlerRemoved(ctx);
         } finally {
             encoder.handlerRemoved(ctx);
         }
     }
 
     /**
      * @see MessageToByteEncoder#encode(ChannelHandlerContext, Object, ByteBuf)
      */
     protected abstract void encode(ChannelHandlerContext ctx, I msg, ByteBuf out) throws Exception;
 
     /**
      * @see ByteToMessageDecoder#decode(ChannelHandlerContext, ByteBuf, List)
      */
     protected abstract void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception;
 
     /**
      * @see ByteToMessageDecoder#decodeLast(ChannelHandlerContext, ByteBuf, List)
      */
     protected void decodeLast(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
         if (in.isReadable()) {
             // Only call decode() if there is something left in the buffer to decode.
             // See https://github.com/netty/netty/issues/4386
             decode(ctx, in, out);
         }
     }
 
     private final class Encoder extends MessageToByteEncoder<I> {
         Encoder(boolean preferDirect) {
             super(preferDirect);
         }
 
         @Override
         public boolean acceptOutboundMessage(Object msg) throws Exception {
             return ByteToMessageCodec.this.acceptOutboundMessage(msg);
         }
 
         @Override
         protected void encode(ChannelHandlerContext ctx, I msg, ByteBuf out) throws Exception {
             ByteToMessageCodec.this.encode(ctx, msg, out);
         }
     }
 }