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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.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.WebSocketExtensionEncoder;
  import io.netty.handler.codec.http.websocketx.extensions.WebSocketExtensionFilter;
  
  import java.util.List;
  
  import static io.netty.handler.codec.http.websocketx.extensions.compression.PerMessageDeflateDecoder.*;
  import static io.netty.util.internal.ObjectUtil.*;
  
  /**
   * Deflate implementation of a payload compressor for
   * <tt>io.netty.handler.codec.http.websocketx.WebSocketFrame</tt>.
   */
  abstract class DeflateEncoder extends WebSocketExtensionEncoder {
  
      private final int compressionLevel;
      private final int windowSize;
      private final boolean noContext;
      private final WebSocketExtensionFilter extensionEncoderFilter;
  
      private EmbeddedChannel encoder;
  
      /**
       * Constructor
       * @param compressionLevel compression level of the compressor.
       * @param windowSize maximum size of the window compressor buffer.
       * @param noContext true to disable context takeover.
       * @param extensionEncoderFilter extension encoder filter.
       */
      DeflateEncoder(int compressionLevel, int windowSize, boolean noContext,
                     WebSocketExtensionFilter extensionEncoderFilter) {
          this.compressionLevel = compressionLevel;
          this.windowSize = windowSize;
          this.noContext = noContext;
          this.extensionEncoderFilter = checkNotNull(extensionEncoderFilter, "extensionEncoderFilter");
      }
  
      /**
       * Returns the extension encoder filter.
       */
      protected WebSocketExtensionFilter extensionEncoderFilter() {
          return extensionEncoderFilter;
      }
  
      /**
       * @param msg the current frame.
       * @return the rsv bits to set in the compressed frame.
       */
      protected abstract int rsv(WebSocketFrame msg);
  
      /**
       * @param msg the current frame.
       * @return true if compressed payload tail needs to be removed.
       */
      protected abstract boolean removeFrameTail(WebSocketFrame msg);
  
      @Override
      protected void encode(ChannelHandlerContext ctx, WebSocketFrame msg, List<Object> out) throws Exception {
          final ByteBuf compressedContent;
          if (msg.content().isReadable()) {
              compressedContent = compressContent(ctx, msg);
          } else if (msg.isFinalFragment()) {
              // Set empty DEFLATE block manually for unknown buffer size
              // https://tools.ietf.org/html/rfc7692#section-7.2.3.6
              compressedContent = EMPTY_DEFLATE_BLOCK.duplicate();
          } else {
              throw new CodecException("cannot compress content buffer");
          }
  
          final WebSocketFrame outMsg;
          if (msg instanceof TextWebSocketFrame) {
              outMsg = new TextWebSocketFrame(msg.isFinalFragment(), rsv(msg), compressedContent);
         } else if (msg instanceof BinaryWebSocketFrame) {
             outMsg = new BinaryWebSocketFrame(msg.isFinalFragment(), rsv(msg), compressedContent);
         } else if (msg instanceof ContinuationWebSocketFrame) {
             outMsg = new ContinuationWebSocketFrame(msg.isFinalFragment(), rsv(msg), compressedContent);
         } 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);
     }
 
     private ByteBuf compressContent(ChannelHandlerContext ctx, WebSocketFrame msg) {
         if (encoder == null) {
             encoder = new EmbeddedChannel(ZlibCodecFactory.newZlibEncoder(
                     ZlibWrapper.NONE, compressionLevel, windowSize, 8));
         }
 
         encoder.writeOutbound(msg.content().retain());
 
         CompositeByteBuf fullCompressedContent = ctx.alloc().compositeBuffer();
         for (;;) {
             ByteBuf partCompressedContent = encoder.readOutbound();
             if (partCompressedContent == null) {
                 break;
             }
             if (!partCompressedContent.isReadable()) {
                 partCompressedContent.release();
                 continue;
             }
             fullCompressedContent.addComponent(true, partCompressedContent);
         }
 
         if (fullCompressedContent.numComponents() <= 0) {
             fullCompressedContent.release();
             throw new CodecException("cannot read compressed buffer");
         }
 
         if (msg.isFinalFragment() && noContext) {
             cleanup();
         }
 
         ByteBuf compressedContent;
         if (removeFrameTail(msg)) {
             int realLength = fullCompressedContent.readableBytes() - FRAME_TAIL.readableBytes();
             compressedContent = fullCompressedContent.slice(0, realLength);
         } else {
             compressedContent = fullCompressedContent;
         }
 
         return compressedContent;
     }
 
     private void cleanup() {
         if (encoder != null) {
             // Clean-up the previous encoder if not cleaned up correctly.
             encoder.finishAndReleaseAll();
             encoder = null;
         }
     }
 }