GoogleApiTransport::getId

private function getId ($headers): ?int
{
	$id = null;
	foreach (explode("n", $headers) as $k => $header)
	{
		if(mb_strpos($header, ':') !== false)
		{
			[$headerName, $headerValue] = explode(':', $header, 2);
			if(mb_strtolower($headerName) === 'content-id')
			{
				$part = explode(':', $headerValue);
				$id = rtrim($part[1], ">");
			}
		}
	}

	return (int)$id;
}