Note, header_size include "\r\n\r\n". So if you use CURLOPT_FOLLOWLOCATION>0, CURLOPT_HEADER=true, CURLOPT_RETURNTRANSFER=true right way splite header/body:
$response = curl_exec($ch);
$curl_info = curl_getinfo($ch);
curl_close($ch);
$header_size = $curl_info['header_size'];
$header = substr($response, 0, $header_size);
$body = substr($response, $header_size);