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   /*
    * Copyright 2017 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.util.internal.ObjectUtil;
  
  abstract class PendingBytesTracker implements MessageSizeEstimator.Handle {
      private final MessageSizeEstimator.Handle estimatorHandle;
  
      private PendingBytesTracker(MessageSizeEstimator.Handle estimatorHandle) {
          this.estimatorHandle = ObjectUtil.checkNotNull(estimatorHandle, "estimatorHandle");
      }
  
      @Override
      public final int size(Object msg) {
          return estimatorHandle.size(msg);
      }
  
      public abstract void incrementPendingOutboundBytes(long bytes);
      public abstract void decrementPendingOutboundBytes(long bytes);
  
      static PendingBytesTracker newTracker(Channel channel) {
          if (channel.pipeline() instanceof DefaultChannelPipeline) {
              return new DefaultChannelPipelinePendingBytesTracker((DefaultChannelPipeline) channel.pipeline());
          } else {
              ChannelOutboundBuffer buffer = channel.unsafe().outboundBuffer();
              MessageSizeEstimator.Handle handle = channel.config().getMessageSizeEstimator().newHandle();
              // We need to guard against null as channel.unsafe().outboundBuffer() may returned null
              // if the channel was already closed when constructing the PendingBytesTracker.
              // See https://github.com/netty/netty/issues/3967
              return buffer == null ?
                      new NoopPendingBytesTracker(handle) : new ChannelOutboundBufferPendingBytesTracker(buffer, handle);
          }
      }
  
      private static final class DefaultChannelPipelinePendingBytesTracker extends PendingBytesTracker {
          private final DefaultChannelPipeline pipeline;
  
          DefaultChannelPipelinePendingBytesTracker(DefaultChannelPipeline pipeline) {
              super(pipeline.estimatorHandle());
              this.pipeline = pipeline;
          }
  
          @Override
          public void incrementPendingOutboundBytes(long bytes) {
              pipeline.incrementPendingOutboundBytes(bytes);
          }
  
          @Override
          public void decrementPendingOutboundBytes(long bytes) {
              pipeline.decrementPendingOutboundBytes(bytes);
          }
      }
  
      private static final class ChannelOutboundBufferPendingBytesTracker extends PendingBytesTracker {
          private final ChannelOutboundBuffer buffer;
  
          ChannelOutboundBufferPendingBytesTracker(
                  ChannelOutboundBuffer buffer, MessageSizeEstimator.Handle estimatorHandle) {
              super(estimatorHandle);
              this.buffer = buffer;
          }
  
          @Override
          public void incrementPendingOutboundBytes(long bytes) {
              buffer.incrementPendingOutboundBytes(bytes);
          }
  
          @Override
          public void decrementPendingOutboundBytes(long bytes) {
              buffer.decrementPendingOutboundBytes(bytes);
          }
      }
  
      private static final class NoopPendingBytesTracker extends PendingBytesTracker {
  
          NoopPendingBytesTracker(MessageSizeEstimator.Handle estimatorHandle) {
              super(estimatorHandle);
          }
  
          @Override
          public void incrementPendingOutboundBytes(long bytes) {
              // Noop
          }
  
          @Override
         public void decrementPendingOutboundBytes(long bytes) {
             // Noop
         }
     }
 }