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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.compression;
  
  import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.ByteToMessageDecoder;
  
  /**
   * Decompresses a {@link ByteBuf} using the deflate algorithm.
   */
  public abstract class ZlibDecoder extends ByteToMessageDecoder {
  
      /**
       * Maximum allowed size of the decompression buffer.
       */
      protected final int maxAllocation;
  
      /**
       * Same as {@link #ZlibDecoder(int)} with maxAllocation = 0.
       */
      public ZlibDecoder() {
          this(0);
      }
  
      /**
       * Construct a new ZlibDecoder.
       * @param maxAllocation
       *          Maximum size of the decompression buffer. Must be >= 0.
       *          If zero, maximum size is decided by the {@link ByteBufAllocator}.
       */
      public ZlibDecoder(int maxAllocation) {
          this.maxAllocation = checkPositiveOrZero(maxAllocation, "maxAllocation");
      }
  
      /**
       * Returns {@code true} if and only if the end of the compressed stream
       * has been reached.
       */
      public abstract boolean isClosed();
  
      /**
       * Allocate or expand the decompression buffer, without exceeding the maximum allocation.
       * Calls {@link #decompressionBufferExhausted(ByteBuf)} if the buffer is full and cannot be expanded further.
       */
      protected ByteBuf prepareDecompressBuffer(ChannelHandlerContext ctx, ByteBuf buffer, int preferredSize) {
          if (buffer == null) {
              if (maxAllocation == 0) {
                  return ctx.alloc().heapBuffer(preferredSize);
              }
  
              return ctx.alloc().heapBuffer(Math.min(preferredSize, maxAllocation), maxAllocation);
          }
  
          // this always expands the buffer if possible, even if the expansion is less than preferredSize
          // we throw the exception only if the buffer could not be expanded at all
          // this means that one final attempt to deserialize will always be made with the buffer at maxAllocation
          if (buffer.ensureWritable(preferredSize, true) == 1) {
              // buffer must be consumed so subclasses don't add it to output
              // we therefore duplicate it when calling decompressionBufferExhausted() to guarantee non-interference
              // but wait until after to consume it so the subclass can tell how much output is really in the buffer
              decompressionBufferExhausted(buffer.duplicate());
              buffer.skipBytes(buffer.readableBytes());
              throw new DecompressionException("Decompression buffer has reached maximum size: " + buffer.maxCapacity());
          }
  
          return buffer;
      }
  
      /**
       * Called when the decompression buffer cannot be expanded further.
       * Default implementation is a no-op, but subclasses can override in case they want to
       * do something before the {@link DecompressionException} is thrown, such as log the
       * data that was decompressed so far.
       */
      protected void decompressionBufferExhausted(ByteBuf buffer) {
      }
  
  }