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   /*
    * Copyright 2013 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 static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufHolder;
  
  /**
   * Default {@link MessageSizeEstimator} implementation which supports the estimation of the size of
   * {@link ByteBuf}, {@link ByteBufHolder} and {@link FileRegion}.
   */
  public final class DefaultMessageSizeEstimator implements MessageSizeEstimator {
  
      private static final class HandleImpl implements Handle {
          private final int unknownSize;
  
          private HandleImpl(int unknownSize) {
              this.unknownSize = unknownSize;
          }
  
          @Override
          public int size(Object msg) {
              if (msg instanceof ByteBuf) {
                  return ((ByteBuf) msg).readableBytes();
              }
              if (msg instanceof ByteBufHolder) {
                  return ((ByteBufHolder) msg).content().readableBytes();
              }
              if (msg instanceof FileRegion) {
                  return 0;
              }
              return unknownSize;
          }
      }
  
      /**
       * Return the default implementation which returns {@code 8} for unknown messages.
       */
      public static final MessageSizeEstimator DEFAULT = new DefaultMessageSizeEstimator(8);
  
      private final Handle handle;
  
      /**
       * Create a new instance
       *
       * @param unknownSize       The size which is returned for unknown messages.
       */
      public DefaultMessageSizeEstimator(int unknownSize) {
          checkPositiveOrZero(unknownSize, "unknownSize");
          handle = new HandleImpl(unknownSize);
      }
  
      @Override
      public Handle newHandle() {
          return handle;
      }
  }