private function readPartContent($handle, PartBuilder $partBuilder)
    {
        $partBuilder->setStreamContentStartPos(ftell($handle));
        $this->findContentBoundary($handle, $partBuilder);
        if ($partBuilder->isMultiPart()) {
            while (!$partBuilder->isParentBoundaryFound()) {
                $child = $this->partBuilderFactory->newPartBuilder(
                    $this->partFactoryService->getMimePartFactory()
                );
                $partBuilder->addChild($child);
                $this->readPart($handle, $child);
            }
        }
    }