HTTP header save-data

gistfile1.php

<?php
function getHttpRequestHeaders()
{
    $headers = [];
    foreach ($_SERVER as $key => $value) {
        if (substr($key, 0, 5) === 'HTTP_') {
            $headerKey           = str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($key, 5)))));
            $headers[$headerKey] = $value;
        }
    }

    return $headers;
}

function dataSavingMode()
{
    $headers = getHttpRequestHeaders();

    if (isset($headers['Save-Data']) && $headers['Save-Data'] === 'on') {
        return true;
    } else {
        return false;
    }
}
?>

use
<?php if(dataSavingMode()): ?>
<p>DATA</p>
<?php endif; ?>