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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.stream;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.FileRegion;
  import io.netty.util.internal.ObjectUtil;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.nio.channels.ClosedChannelException;
  import java.nio.channels.FileChannel;
  
  /**
   * A {@link ChunkedInput} that fetches data from a file chunk by chunk using
   * NIO {@link FileChannel}.
   * <p>
   * If your operating system supports
   * <a href="https://en.wikipedia.org/wiki/Zero-copy">zero-copy file transfer</a>
   * such as {@code sendfile()}, you might want to use {@link FileRegion} instead.
   */
  public class ChunkedNioFile implements ChunkedInput<ByteBuf> {
  
      private final FileChannel in;
      private final long startOffset;
      private final long endOffset;
      private final int chunkSize;
      private long offset;
  
      /**
       * Creates a new instance that fetches data from the specified file.
       */
      public ChunkedNioFile(File in) throws IOException {
          this(new RandomAccessFile(in, "r").getChannel());
      }
  
      /**
       * Creates a new instance that fetches data from the specified file.
       *
       * @param chunkSize the number of bytes to fetch on each
       *                  {@link #readChunk(ChannelHandlerContext)} call
       */
      public ChunkedNioFile(File in, int chunkSize) throws IOException {
          this(new RandomAccessFile(in, "r").getChannel(), chunkSize);
      }
  
      /**
       * Creates a new instance that fetches data from the specified file.
       */
      public ChunkedNioFile(FileChannel in) throws IOException {
          this(in, ChunkedStream.DEFAULT_CHUNK_SIZE);
      }
  
      /**
       * Creates a new instance that fetches data from the specified file.
       *
       * @param chunkSize the number of bytes to fetch on each
       *                  {@link #readChunk(ChannelHandlerContext)} call
       */
      public ChunkedNioFile(FileChannel in, int chunkSize) throws IOException {
          this(in, 0, in.size(), chunkSize);
      }
  
      /**
       * Creates a new instance that fetches data from the specified file.
       *
       * @param offset the offset of the file where the transfer begins
       * @param length the number of bytes to transfer
       * @param chunkSize the number of bytes to fetch on each
       *                  {@link #readChunk(ChannelHandlerContext)} call
       */
      public ChunkedNioFile(FileChannel in, long offset, long length, int chunkSize)
              throws IOException {
          ObjectUtil.checkNotNull(in, "in");
          ObjectUtil.checkPositiveOrZero(offset, "offset");
          ObjectUtil.checkPositiveOrZero(length, "length");
          ObjectUtil.checkPositive(chunkSize, "chunkSize");
          if (!in.isOpen()) {
              throw new ClosedChannelException();
          }
          this.in = in;
          this.chunkSize = chunkSize;
          this.offset = startOffset = offset;
         endOffset = offset + length;
     }
 
     /**
      * Returns the offset in the file where the transfer began.
      */
     public long startOffset() {
         return startOffset;
     }
 
     /**
      * Returns the offset in the file where the transfer will end.
      */
     public long endOffset() {
         return endOffset;
     }
 
     /**
      * Returns the offset in the file where the transfer is happening currently.
      */
     public long currentOffset() {
         return offset;
     }
 
     @Override
     public boolean isEndOfInput() throws Exception {
         return !(offset < endOffset && in.isOpen());
     }
 
     @Override
     public void close() throws Exception {
         in.close();
     }
 
     @Deprecated
     @Override
     public ByteBuf readChunk(ChannelHandlerContext ctx) throws Exception {
         return readChunk(ctx.alloc());
     }
 
     @Override
     public ByteBuf readChunk(ByteBufAllocator allocator) throws Exception {
         long offset = this.offset;
         if (offset >= endOffset) {
             return null;
         }
 
         int chunkSize = (int) Math.min(this.chunkSize, endOffset - offset);
         ByteBuf buffer = allocator.buffer(chunkSize);
         boolean release = true;
         try {
             int readBytes = 0;
             for (;;) {
                 int localReadBytes = buffer.writeBytes(in, offset + readBytes, chunkSize - readBytes);
                 if (localReadBytes < 0) {
                     break;
                 }
                 readBytes += localReadBytes;
                 if (readBytes == chunkSize) {
                     break;
                 }
             }
             this.offset += readBytes;
             release = false;
             return buffer;
         } finally {
             if (release) {
                 buffer.release();
             }
         }
     }
 
     @Override
     public long length() {
         return endOffset - startOffset;
     }
 
     @Override
     public long progress() {
         return offset - startOffset;
     }
 }