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   /*
    * Copyright 2014 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.http.websocketx.extensions.compression;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.CompositeByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.embedded.EmbeddedChannel;
  import io.netty.handler.codec.CodecException;
  import io.netty.handler.codec.compression.ZlibCodecFactory;
  import io.netty.handler.codec.compression.ZlibWrapper;
  import io.netty.handler.codec.http.websocketx.BinaryWebSocketFrame;
  import io.netty.handler.codec.http.websocketx.ContinuationWebSocketFrame;
  import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
  import io.netty.handler.codec.http.websocketx.WebSocketFrame;
  import io.netty.handler.codec.http.websocketx.extensions.WebSocketExtensionDecoder;
  import io.netty.handler.codec.http.websocketx.extensions.WebSocketExtensionFilter;
  
  import java.util.List;
  
  import static io.netty.util.internal.ObjectUtil.*;
  
  /**
   * Deflate implementation of a payload decompressor for
   * <tt>io.netty.handler.codec.http.websocketx.WebSocketFrame</tt>.
   */
  abstract class DeflateDecoder extends WebSocketExtensionDecoder {
  
      static final ByteBuf FRAME_TAIL = Unpooled.unreleasableBuffer(
              Unpooled.wrappedBuffer(new byte[] {0x00, 0x00, (byte) 0xff, (byte) 0xff}))
              .asReadOnly();
  
      static final ByteBuf EMPTY_DEFLATE_BLOCK = Unpooled.unreleasableBuffer(
              Unpooled.wrappedBuffer(new byte[] { 0x00 }))
              .asReadOnly();
  
      private final boolean noContext;
      private final WebSocketExtensionFilter extensionDecoderFilter;
  
      private EmbeddedChannel decoder;
  
      /**
       * Constructor
       *
       * @param noContext true to disable context takeover.
       * @param extensionDecoderFilter extension decoder filter.
       */
      DeflateDecoder(boolean noContext, WebSocketExtensionFilter extensionDecoderFilter) {
          this.noContext = noContext;
          this.extensionDecoderFilter = checkNotNull(extensionDecoderFilter, "extensionDecoderFilter");
      }
  
      /**
       * Returns the extension decoder filter.
       */
      protected WebSocketExtensionFilter extensionDecoderFilter() {
          return extensionDecoderFilter;
      }
  
      protected abstract boolean appendFrameTail(WebSocketFrame msg);
  
      protected abstract int newRsv(WebSocketFrame msg);
  
      @Override
      protected void decode(ChannelHandlerContext ctx, WebSocketFrame msg, List<Object> out) throws Exception {
          final ByteBuf decompressedContent = decompressContent(ctx, msg);
  
          final WebSocketFrame outMsg;
          if (msg instanceof TextWebSocketFrame) {
              outMsg = new TextWebSocketFrame(msg.isFinalFragment(), newRsv(msg), decompressedContent);
          } else if (msg instanceof BinaryWebSocketFrame) {
              outMsg = new BinaryWebSocketFrame(msg.isFinalFragment(), newRsv(msg), decompressedContent);
          } else if (msg instanceof ContinuationWebSocketFrame) {
              outMsg = new ContinuationWebSocketFrame(msg.isFinalFragment(), newRsv(msg), decompressedContent);
          } else {
              throw new CodecException("unexpected frame type: " + msg.getClass().getName());
          }
  
          out.add(outMsg);
      }
  
      @Override
      public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
          cleanup();
          super.handlerRemoved(ctx);
     }
 
     @Override
     public void channelInactive(ChannelHandlerContext ctx) throws Exception {
         cleanup();
         super.channelInactive(ctx);
     }
 
     private ByteBuf decompressContent(ChannelHandlerContext ctx, WebSocketFrame msg) {
         if (decoder == null) {
             if (!(msg instanceof TextWebSocketFrame) && !(msg instanceof BinaryWebSocketFrame)) {
                 throw new CodecException("unexpected initial frame type: " + msg.getClass().getName());
             }
             decoder = new EmbeddedChannel(ZlibCodecFactory.newZlibDecoder(ZlibWrapper.NONE));
         }
 
         boolean readable = msg.content().isReadable();
         boolean emptyDeflateBlock = EMPTY_DEFLATE_BLOCK.equals(msg.content());
 
         decoder.writeInbound(msg.content().retain());
         if (appendFrameTail(msg)) {
             decoder.writeInbound(FRAME_TAIL.duplicate());
         }
 
         CompositeByteBuf compositeDecompressedContent = ctx.alloc().compositeBuffer();
         for (;;) {
             ByteBuf partUncompressedContent = decoder.readInbound();
             if (partUncompressedContent == null) {
                 break;
             }
             if (!partUncompressedContent.isReadable()) {
                 partUncompressedContent.release();
                 continue;
             }
             compositeDecompressedContent.addComponent(true, partUncompressedContent);
         }
         // Correctly handle empty frames
         // See https://github.com/netty/netty/issues/4348
         if (!emptyDeflateBlock && readable && compositeDecompressedContent.numComponents() <= 0) {
             // Sometimes after fragmentation the last frame
             // May contain left-over data that doesn't affect decompression
             if (!(msg instanceof ContinuationWebSocketFrame)) {
                 compositeDecompressedContent.release();
                 throw new CodecException("cannot read uncompressed buffer");
             }
         }
 
         if (msg.isFinalFragment() && noContext) {
             cleanup();
         }
 
         return compositeDecompressedContent;
     }
 
     private void cleanup() {
         if (decoder != null) {
             // Clean-up the previous encoder if not cleaned up correctly.
             decoder.finishAndReleaseAll();
             decoder = null;
         }
     }
 }