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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.compression;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.ByteToMessageDecoder;
  
  import java.util.List;
  import java.util.zip.Adler32;
  import java.util.zip.Checksum;
  
  import static io.netty.handler.codec.compression.FastLz.BLOCK_TYPE_COMPRESSED;
  import static io.netty.handler.codec.compression.FastLz.BLOCK_WITH_CHECKSUM;
  import static io.netty.handler.codec.compression.FastLz.MAGIC_NUMBER;
  import static io.netty.handler.codec.compression.FastLz.decompress;
  
  /**
   * Uncompresses a {@link ByteBuf} encoded by {@link FastLzFrameEncoder} using the FastLZ algorithm.
   *
   * See <a href="https://github.com/netty/netty/issues/2750">FastLZ format</a>.
   */
  public class FastLzFrameDecoder extends ByteToMessageDecoder {
      /**
       * Current state of decompression.
       */
      private enum State {
          INIT_BLOCK,
          INIT_BLOCK_PARAMS,
          DECOMPRESS_DATA,
          CORRUPTED
      }
  
      private State currentState = State.INIT_BLOCK;
  
      /**
       * Underlying checksum calculator in use.
       */
      private final ByteBufChecksum checksum;
  
      /**
       * Length of current received chunk of data.
       */
      private int chunkLength;
  
      /**
       * Original of current received chunk of data.
       * It is equal to {@link #chunkLength} for non compressed chunks.
       */
      private int originalLength;
  
      /**
       * Indicates is this chunk compressed or not.
       */
      private boolean isCompressed;
  
      /**
       * Indicates is this chunk has checksum or not.
       */
      private boolean hasChecksum;
  
      /**
       * Checksum value of current received chunk of data which has checksum.
       */
      private int currentChecksum;
  
      /**
       * Creates the fastest FastLZ decoder without checksum calculation.
       */
      public FastLzFrameDecoder() {
          this(false);
      }
  
      /**
       * Creates a FastLZ decoder with calculation of checksums as specified.
       *
       * @param validateChecksums
       *        If true, the checksum field will be validated against the actual
       *        uncompressed data, and if the checksums do not match, a suitable
       *        {@link DecompressionException} will be thrown.
       *        Note, that in this case decoder will use {@link java.util.zip.Adler32}
       *        as a default checksum calculator.
       */
      public FastLzFrameDecoder(boolean validateChecksums) {
          this(validateChecksums ? new Adler32() : null);
      }
 
     /**
      * Creates a FastLZ decoder with specified checksum calculator.
      *
      * @param checksum
      *        the {@link Checksum} instance to use to check data for integrity.
      *        You may set {@code null} if you do not want to validate checksum of each block.
      */
     public FastLzFrameDecoder(Checksum checksum) {
         this.checksum = checksum == null ? null : ByteBufChecksum.wrapChecksum(checksum);
     }
 
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
         try {
             switch (currentState) {
             case INIT_BLOCK:
                 if (in.readableBytes() < 4) {
                     break;
                 }
 
                 final int magic = in.readUnsignedMedium();
                 if (magic != MAGIC_NUMBER) {
                     throw new DecompressionException("unexpected block identifier");
                 }
 
                 final byte options = in.readByte();
                 isCompressed = (options & 0x01) == BLOCK_TYPE_COMPRESSED;
                 hasChecksum = (options & 0x10) == BLOCK_WITH_CHECKSUM;
 
                 currentState = State.INIT_BLOCK_PARAMS;
                 // fall through
             case INIT_BLOCK_PARAMS:
                 if (in.readableBytes() < 2 + (isCompressed ? 2 : 0) + (hasChecksum ? 4 : 0)) {
                     break;
                 }
                 currentChecksum = hasChecksum ? in.readInt() : 0;
                 chunkLength = in.readUnsignedShort();
                 originalLength = isCompressed ? in.readUnsignedShort() : chunkLength;
 
                 currentState = State.DECOMPRESS_DATA;
                 // fall through
             case DECOMPRESS_DATA:
                 final int chunkLength = this.chunkLength;
                 if (in.readableBytes() < chunkLength) {
                     break;
                 }
 
                 final int idx = in.readerIndex();
                 final int originalLength = this.originalLength;
 
                 ByteBuf output = null;
 
                 try {
                     if (isCompressed) {
 
                         output = ctx.alloc().buffer(originalLength);
                         int outputOffset = output.writerIndex();
                         final int decompressedBytes = decompress(in, idx, chunkLength,
                                 output, outputOffset, originalLength);
                         if (originalLength != decompressedBytes) {
                             throw new DecompressionException(String.format(
                                     "stream corrupted: originalLength(%d) and actual length(%d) mismatch",
                                     originalLength, decompressedBytes));
                         }
                         output.writerIndex(output.writerIndex() + decompressedBytes);
                     } else {
                         output = in.retainedSlice(idx, chunkLength);
                     }
 
                     final ByteBufChecksum checksum = this.checksum;
                     if (hasChecksum && checksum != null) {
                         checksum.reset();
                         checksum.update(output, output.readerIndex(), output.readableBytes());
                         final int checksumResult = (int) checksum.getValue();
                         if (checksumResult != currentChecksum) {
                             throw new DecompressionException(String.format(
                                     "stream corrupted: mismatching checksum: %d (expected: %d)",
                                     checksumResult, currentChecksum));
                         }
                     }
 
                     if (output.readableBytes() > 0) {
                         out.add(output);
                     } else {
                         output.release();
                     }
                     output = null;
                     in.skipBytes(chunkLength);
 
                     currentState = State.INIT_BLOCK;
                 } finally {
                     if (output != null) {
                         output.release();
                     }
                 }
                 break;
             case CORRUPTED:
                 in.skipBytes(in.readableBytes());
                 break;
             default:
                 throw new IllegalStateException();
             }
         } catch (Exception e) {
             currentState = State.CORRUPTED;
             throw e;
         }
     }
 }