to get headers sent

get_header.php

<?php 

$result = "";

foreach($_SERVER as $K => $V){

  $a = explode('_' , $K);

  if(array_shift($a) == 'HTTP'){

    array_walk($a, function(&$v){
      $v = ucfirst(strtolower($v));
    });

    $result .= join('-',$a).": ".$V."<br>";
  }
  
}

 echo $result;