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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.MessageToByteEncoder;
  
  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_TYPE_NON_COMPRESSED;
  import static io.netty.handler.codec.compression.FastLz.BLOCK_WITHOUT_CHECKSUM;
  import static io.netty.handler.codec.compression.FastLz.BLOCK_WITH_CHECKSUM;
  import static io.netty.handler.codec.compression.FastLz.CHECKSUM_OFFSET;
  import static io.netty.handler.codec.compression.FastLz.LEVEL_1;
  import static io.netty.handler.codec.compression.FastLz.LEVEL_2;
  import static io.netty.handler.codec.compression.FastLz.LEVEL_AUTO;
  import static io.netty.handler.codec.compression.FastLz.MAGIC_NUMBER;
  import static io.netty.handler.codec.compression.FastLz.MAX_CHUNK_LENGTH;
  import static io.netty.handler.codec.compression.FastLz.MIN_LENGTH_TO_COMPRESSION;
  import static io.netty.handler.codec.compression.FastLz.OPTIONS_OFFSET;
  import static io.netty.handler.codec.compression.FastLz.calculateOutputBufferLength;
  import static io.netty.handler.codec.compression.FastLz.compress;
  
  /**
   * Compresses a {@link ByteBuf} using the FastLZ algorithm.
   *
   * See <a href="https://github.com/netty/netty/issues/2750">FastLZ format</a>.
   */
  public class FastLzFrameEncoder extends MessageToByteEncoder<ByteBuf> {
      /**
       * Compression level.
       */
      private final int level;
  
      /**
       * Underlying checksum calculator in use.
       */
      private final ByteBufChecksum checksum;
  
      /**
       * Creates a FastLZ encoder without checksum calculator and with auto detection of compression level.
       */
      public FastLzFrameEncoder() {
          this(LEVEL_AUTO, null);
      }
  
      /**
       * Creates a FastLZ encoder with specified compression level and without checksum calculator.
       *
       * @param level supports only these values:
       *        0 - Encoder will choose level automatically depending on the length of the input buffer.
       *        1 - Level 1 is the fastest compression and generally useful for short data.
       *        2 - Level 2 is slightly slower but it gives better compression ratio.
       */
      public FastLzFrameEncoder(int level) {
          this(level, null);
      }
  
      /**
       * Creates a FastLZ encoder with auto detection of compression
       * level and calculation of checksums as specified.
       *
       * @param validateChecksums
       *        If true, the checksum of each block will be calculated and this value
       *        will be added to the header of block.
       *        By default {@link FastLzFrameEncoder} uses {@link java.util.zip.Adler32}
       *        for checksum calculation.
       */
      public FastLzFrameEncoder(boolean validateChecksums) {
          this(LEVEL_AUTO, validateChecksums ? new Adler32() : null);
      }
  
      /**
       * Creates a FastLZ encoder with specified compression level and checksum calculator.
       *
       * @param level supports only these values:
       *        0 - Encoder will choose level automatically depending on the length of the input buffer.
       *        1 - Level 1 is the fastest compression and generally useful for short data.
       *        2 - Level 2 is slightly slower but it gives better compression ratio.
       * @param checksum
       *        the {@link Checksum} instance to use to check data for integrity.
       *        You may set {@code null} if you don't want to validate checksum of each block.
       */
     public FastLzFrameEncoder(int level, Checksum checksum) {
         if (level != LEVEL_AUTO && level != LEVEL_1 && level != LEVEL_2) {
             throw new IllegalArgumentException(String.format(
                     "level: %d (expected: %d or %d or %d)", level, LEVEL_AUTO, LEVEL_1, LEVEL_2));
         }
         this.level = level;
         this.checksum = checksum == null ? null : ByteBufChecksum.wrapChecksum(checksum);
     }
 
     @Override
     protected void encode(ChannelHandlerContext ctx, ByteBuf in, ByteBuf out) throws Exception {
         final ByteBufChecksum checksum = this.checksum;
 
         for (;;) {
             if (!in.isReadable()) {
                 return;
             }
             final int idx = in.readerIndex();
             final int length = Math.min(in.readableBytes(), MAX_CHUNK_LENGTH);
 
             final int outputIdx = out.writerIndex();
             out.setMedium(outputIdx, MAGIC_NUMBER);
             int outputOffset = outputIdx + CHECKSUM_OFFSET + (checksum != null ? 4 : 0);
 
             final byte blockType;
             final int chunkLength;
             if (length < MIN_LENGTH_TO_COMPRESSION) {
                 blockType = BLOCK_TYPE_NON_COMPRESSED;
 
                 out.ensureWritable(outputOffset + 2 + length);
                 final int outputPtr = outputOffset + 2;
 
                 if (checksum != null) {
                     checksum.reset();
                     checksum.update(in, idx, length);
                     out.setInt(outputIdx + CHECKSUM_OFFSET, (int) checksum.getValue());
                 }
                 out.setBytes(outputPtr, in, idx, length);
                 chunkLength = length;
             } else {
                 // try to compress
                 if (checksum != null) {
                     checksum.reset();
                     checksum.update(in, idx, length);
                     out.setInt(outputIdx + CHECKSUM_OFFSET, (int) checksum.getValue());
                 }
 
                 final int maxOutputLength = calculateOutputBufferLength(length);
                 out.ensureWritable(outputOffset + 4 + maxOutputLength);
                 final int outputPtr = outputOffset + 4;
                 final int compressedLength = compress(in, in.readerIndex(), length, out, outputPtr, level);
 
                 if (compressedLength < length) {
                     blockType = BLOCK_TYPE_COMPRESSED;
                     chunkLength = compressedLength;
 
                     out.setShort(outputOffset, chunkLength);
                     outputOffset += 2;
                 } else {
                     blockType = BLOCK_TYPE_NON_COMPRESSED;
                     out.setBytes(outputOffset + 2, in, idx, length);
                     chunkLength = length;
                 }
             }
             out.setShort(outputOffset, length);
 
             out.setByte(outputIdx + OPTIONS_OFFSET,
                     blockType | (checksum != null ? BLOCK_WITH_CHECKSUM : BLOCK_WITHOUT_CHECKSUM));
             out.writerIndex(outputOffset + 2 + chunkLength);
             in.skipBytes(length);
         }
     }
 }