OutgoingEventManager::prepareBatchItem

private function prepareBatchItem(
	string $boundary,
	SyncEvent $syncEvent,
	array $vendorEvent,
	string $methodHeader
): string
{
	$data = '--' . $boundary . self::LINE_SEPARATOR;

	$data .= 'Content-Type: application/http' . self::LINE_SEPARATOR;

	$id = $syncEvent->getEvent()->getId();
	$data .= "Content-ID: item{$id}:{$id}" . self::LINE_SEPARATOR . self::LINE_SEPARATOR;

	$content = Json::encode($vendorEvent, JSON_UNESCAPED_SLASHES);

	$data .= $methodHeader;
	$data .= 'Content-type: application/json' . self::LINE_SEPARATOR;
	$data .= 'Content-Length: ' . mb_strlen($content) . self::LINE_SEPARATOR . self::LINE_SEPARATOR;

	$data .= $content;
	$data .= self::LINE_SEPARATOR . self::LINE_SEPARATOR;

	return $data;
}