@Override
	public long getContentLength() {
		return fileEntityProducer.getContentLength() + multipartHeader.length();
	}
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