A simple echo page in PHP

echo.php

<?php
/** A simple echo page in PHP
 *
 * It just outputs the request it received back, including HTTP headers.
 */

if (!function_exists('getallheaders')) {
    // Polyfill for PHP<7.3
    function getallheaders()
    {
        $headers = '';
        foreach ($_SERVER as $key => $value) {
            if (strpos($key, 'HTTP_') === 0) {
                $chunks = explode('_', $key);
                $header = '';
                for ($i = 1; $y = sizeof($chunks) - 1, $i < $y; $i++) {
                    $header .= ucfirst(strtolower($chunks[$i])).'-';
                }
                $header .= ucfirst(strtolower($chunks[$i])).': '.$value;
                $headers .= $header . PHP_EOL;
            }
        }
        return $headers;
    }
}

header("Content-Type: text/plain");

echo "{$_SERVER['REQUEST_METHOD']} {$_SERVER['REQUEST_URI']} {$_SERVER['SERVER_PROTOCOL']}" . PHP_EOL;

echo getallheaders();
echo PHP_EOL;
echo file_get_contents('php://input');