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   /*
    * Copyright 2015 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.channel;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.buffer.CompositeByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.util.internal.ObjectUtil;
  
  /**
   * A FIFO queue of bytes where producers add bytes by repeatedly adding {@link ByteBuf} and consumers take bytes in
   * arbitrary lengths. This allows producers to add lots of small buffers and the consumer to take all the bytes
   * out in a single buffer. Conversely the producer may add larger buffers and the consumer could take the bytes in
   * many small buffers.
   *
   * <p>Bytes are added and removed with promises. If the last byte of a buffer added with a promise is removed then
   * that promise will complete when the promise passed to {@link #remove} completes.
   *
   * <p>This functionality is useful for aggregating or partitioning writes into fixed size buffers for framing protocols
   * such as HTTP2.
   */
  public final class CoalescingBufferQueue extends AbstractCoalescingBufferQueue {
      private final Channel channel;
  
      public CoalescingBufferQueue(Channel channel) {
          this(channel, 4);
      }
  
      public CoalescingBufferQueue(Channel channel, int initSize) {
          this(channel, initSize, false);
      }
  
      public CoalescingBufferQueue(Channel channel, int initSize, boolean updateWritability) {
          super(updateWritability ? channel : null, initSize);
          this.channel = ObjectUtil.checkNotNull(channel, "channel");
      }
  
      /**
       * Remove a {@link ByteBuf} from the queue with the specified number of bytes. Any added buffer who's bytes are
       * fully consumed during removal will have it's promise completed when the passed aggregate {@link ChannelPromise}
       * completes.
       *
       * @param bytes the maximum number of readable bytes in the returned {@link ByteBuf}, if {@code bytes} is greater
       *              than {@link #readableBytes} then a buffer of length {@link #readableBytes} is returned.
       * @param aggregatePromise used to aggregate the promises and listeners for the constituent buffers.
       * @return a {@link ByteBuf} composed of the enqueued buffers.
       */
      public ByteBuf remove(int bytes, ChannelPromise aggregatePromise) {
          return remove(channel.alloc(), bytes, aggregatePromise);
      }
  
      /**
       *  Release all buffers in the queue and complete all listeners and promises.
       */
      public void releaseAndFailAll(Throwable cause) {
          releaseAndFailAll(channel, cause);
      }
  
      @Override
      protected ByteBuf compose(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf next) {
          if (cumulation instanceof CompositeByteBuf) {
              CompositeByteBuf composite = (CompositeByteBuf) cumulation;
              composite.addComponent(true, next);
              return composite;
          }
          return composeIntoComposite(alloc, cumulation, next);
      }
  
      @Override
      protected ByteBuf removeEmptyValue() {
          return Unpooled.EMPTY_BUFFER;
      }
  }