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   /*
    * Copyright 2016 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.kqueue;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.channel.ChannelConfig;
  import io.netty.channel.RecvByteBufAllocator.DelegatingHandle;
  import io.netty.channel.RecvByteBufAllocator.ExtendedHandle;
  import io.netty.channel.unix.PreferredDirectByteBufAllocator;
  import io.netty.util.UncheckedBooleanSupplier;
  
  import static java.lang.Math.max;
  import static java.lang.Math.min;
  
  final class KQueueRecvByteAllocatorHandle extends DelegatingHandle implements ExtendedHandle {
      private final PreferredDirectByteBufAllocator preferredDirectByteBufAllocator =
              new PreferredDirectByteBufAllocator();
  
      private final UncheckedBooleanSupplier defaultMaybeMoreDataSupplier = new UncheckedBooleanSupplier() {
          @Override
          public boolean get() {
              return maybeMoreDataToRead();
          }
      };
      private boolean overrideGuess;
      private boolean readEOF;
      private long numberBytesPending;
  
      KQueueRecvByteAllocatorHandle(ExtendedHandle handle) {
          super(handle);
      }
  
      @Override
      public int guess() {
          return overrideGuess ? guess0() : delegate().guess();
      }
  
      @Override
      public void reset(ChannelConfig config) {
          overrideGuess = ((KQueueChannelConfig) config).getRcvAllocTransportProvidesGuess();
          delegate().reset(config);
      }
  
      @Override
      public ByteBuf allocate(ByteBufAllocator alloc) {
          // We need to ensure we always allocate a direct ByteBuf as we can only use a direct buffer to read via JNI.
          preferredDirectByteBufAllocator.updateAllocator(alloc);
          return overrideGuess ? preferredDirectByteBufAllocator.ioBuffer(guess0()) :
                  delegate().allocate(preferredDirectByteBufAllocator);
      }
  
      @Override
      public void lastBytesRead(int bytes) {
          numberBytesPending = bytes < 0 ? 0 : max(0, numberBytesPending - bytes);
          delegate().lastBytesRead(bytes);
      }
  
      @Override
      public boolean continueReading(UncheckedBooleanSupplier maybeMoreDataSupplier) {
          return ((ExtendedHandle) delegate()).continueReading(maybeMoreDataSupplier);
      }
  
      @Override
      public boolean continueReading() {
          // We must override the supplier which determines if there maybe more data to read.
          return continueReading(defaultMaybeMoreDataSupplier);
      }
  
      void readEOF() {
          readEOF = true;
      }
  
      boolean isReadEOF() {
          return readEOF;
      }
  
      void numberBytesPending(long numberBytesPending) {
          this.numberBytesPending = numberBytesPending;
      }
  
      boolean maybeMoreDataToRead() {
          /**
           * kqueue with EV_CLEAR flag set requires that we read until we consume "data" bytes
           * (see <a href="https://www.freebsd.org/cgi/man.cgi?kqueue">kqueue man</a>). However in order to
           * respect auto read we supporting reading to stop if auto read is off. If auto read is on we force reading to
          * continue to avoid a {@link StackOverflowError} between channelReadComplete and reading from the
          * channel. It is expected that the {@link #KQueueSocketChannel} implementations will track if all data was not
          * read, and will force a EVFILT_READ ready event.
          *
          * It is assumed EOF is handled externally by checking {@link #isReadEOF()}.
          */
         return numberBytesPending != 0;
     }
 
     private int guess0() {
         return (int) min(numberBytesPending, Integer.MAX_VALUE);
     }
 }