content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF 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
   *
   *    http://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 org.apache.spark.network.protocol;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.channels.WritableByteChannel;
  import javax.annotation.Nullable;
  
  import com.google.common.base.Preconditions;
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.FileRegion;
  import io.netty.util.AbstractReferenceCounted;
  import io.netty.util.ReferenceCountUtil;
  
  import org.apache.spark.network.buffer.ManagedBuffer;
  
  /**
   * A wrapper message that holds two separate pieces (a header and a body).
   *
   * The header must be a ByteBuf, while the body can be a ByteBuf or a FileRegion.
   */
  class MessageWithHeader extends AbstractReferenceCounted implements FileRegion {
  
    @Nullable private final ManagedBuffer managedBuffer;
    private final ByteBuf header;
    private final int headerLength;
    private final Object body;
    private final long bodyLength;
    private long totalBytesTransferred;
  
    /**
     * When the write buffer size is larger than this limit, I/O will be done in chunks of this size.
     * The size should not be too large as it will waste underlying memory copy. e.g. If network
     * avaliable buffer is smaller than this limit, the data cannot be sent within one single write
     * operation while it still will make memory copy with this size.
     */
    private static final int NIO_BUFFER_LIMIT = 256 * 1024;
  
    /**
     * Construct a new MessageWithHeader.
     *
     * @param managedBuffer the {@link ManagedBuffer} that the message body came from. This needs to
     *                      be passed in so that the buffer can be freed when this message is
     *                      deallocated. Ownership of the caller's reference to this buffer is
     *                      transferred to this class, so if the caller wants to continue to use the
     *                      ManagedBuffer in other messages then they will need to call retain() on
     *                      it before passing it to this constructor. This may be null if and only if
     *                      `body` is a {@link FileRegion}.
     * @param header the message header.
     * @param body the message body. Must be either a {@link ByteBuf} or a {@link FileRegion}.
     * @param bodyLength the length of the message body, in bytes.
       */
    MessageWithHeader(
        @Nullable ManagedBuffer managedBuffer,
        ByteBuf header,
        Object body,
        long bodyLength) {
      Preconditions.checkArgument(body instanceof ByteBuf || body instanceof FileRegion,
        "Body must be a ByteBuf or a FileRegion.");
      this.managedBuffer = managedBuffer;
      this.header = header;
      this.headerLength = header.readableBytes();
      this.body = body;
      this.bodyLength = bodyLength;
    }
  
    @Override
    public long count() {
      return headerLength + bodyLength;
    }
  
    @Override
    public long position() {
      return 0;
    }
  
    @Override
    public long transfered() {
      return totalBytesTransferred;
    }
  
    /**
     * This code is more complicated than you would think because we might require multiple
     * transferTo invocations in order to transfer a single MessageWithHeader to avoid busy waiting.
     *
     * The contract is that the caller will ensure position is properly set to the total number
     * of bytes transferred so far (i.e. value returned by transfered()).
     */
    @Override
    public long transferTo(final WritableByteChannel target, final long position) throws IOException {
      Preconditions.checkArgument(position == totalBytesTransferred, "Invalid position.");
      // Bytes written for header in this call.
      long writtenHeader = 0;
      if (header.readableBytes() > 0) {
        writtenHeader = copyByteBuf(header, target);
        totalBytesTransferred += writtenHeader;
        if (header.readableBytes() > 0) {
          return writtenHeader;
        }
      }
  
      // Bytes written for body in this call.
      long writtenBody = 0;
      if (body instanceof FileRegion) {
        writtenBody = ((FileRegion) body).transferTo(target, totalBytesTransferred - headerLength);
      } else if (body instanceof ByteBuf) {
        writtenBody = copyByteBuf((ByteBuf) body, target);
      }
      totalBytesTransferred += writtenBody;
  
      return writtenHeader + writtenBody;
    }
  
    @Override
    protected void deallocate() {
      header.release();
      ReferenceCountUtil.release(body);
      if (managedBuffer != null) {
        managedBuffer.release();
      }
    }
  
    private int copyByteBuf(ByteBuf buf, WritableByteChannel target) throws IOException {
      ByteBuffer buffer = buf.nioBuffer();
      int written = (buffer.remaining() <= NIO_BUFFER_LIMIT) ?
        target.write(buffer) : writeNioBuffer(target, buffer);
      buf.skipBytes(written);
      return written;
    }
  
    private int writeNioBuffer(
        WritableByteChannel writeCh,
        ByteBuffer buf) throws IOException {
      int originalLimit = buf.limit();
      int ret = 0;
  
      try {
        int ioSize = Math.min(buf.remaining(), NIO_BUFFER_LIMIT);
        buf.limit(buf.position() + ioSize);
        ret = writeCh.write(buf);
      } finally {
        buf.limit(originalLimit);
      }
  
      return ret;
    }
  }
  