@Override
	public void produce(DataStreamChannel channel) throws IOException {
		if (isBegin.compareAndSet(false, true)) {
			channel.write(ByteBuffer.wrap(multipartHeader.getBytes()));
		}

		DelegateDataStreamChannel delegateChannel = DelegateDataStreamChannel.from(channel);
		fileEntityProducer.produce(delegateChannel);

		if (delegateChannel.isEnd()) {
			channel.write(ByteBuffer.wrap(NEWLINE.getBytes()));
			remaining = false;
		}
	}
A part of file for multipart form data entity.
<p>
This entity writes multipart header to {@link DataStreamChannel} and
internally delegates {@link #produce(DataStreamChannel)} to {@link FileEntityProducer}.
ngrinder-runtime/src/main/java/org/ngrinder/http/multipart/FileMultipartEntity.java