Bear in mind this special variable is somehow protected and not populated in some situation when the peer server close the connection early on (ssl reset)

=> Undefined variable: http_response_header



A code like this one:

$response = @file_get_contents($url);

empty($http_response_header) && $http_response_header = array('HTTP/1.1 400 Bad request');



Will return a cryptic error message:

Fatal error: Call to undefined function array() on line 2



--

Should you want to cope with this situation:

$hdrs = array('HTTP/1.1 400 Bad request');

!empty($htp_response_header) && $hdrs = $http_response_headers;



Now use $hdrs in place of $http_response_header