while (ob_get_level()) { ob_end_flush(); }
flush();

<?php

namespace App\Controller;

use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\StreamedResponse;

class LegacyController
{
    private const STREAMED_SCRIPT_LIST = [
        'download.php',
    ];

    /**
     * @param string $requestPath
     * @param string $legacyScript
     * @return Response
     */
    public function loadLegacyScript(string $requestPath, string $legacyScript): Response
    {
        $scriptName = basename($legacyScript);

        // 1. For scripts handling large files, use StreamedResponse (Memory Protection)
        if (in_array($scriptName, self::STREAMED_SCRIPT_LIST, true)) {
            return new StreamedResponse(function () use ($requestPath, $legacyScript) {
                $this->prepareLegacyEnvironment($requestPath, $legacyScript);
                require $legacyScript; // Some of these scripts call exit;
            });
        }

        // 2. For standard APIs (including small file downloads)
        $this->prepareLegacyEnvironment($requestPath, $legacyScript);

        // Start output buffering to capture content and status codes
        ob_start();

        require $legacyScript;

        // If exit; was called inside the script, the following lines are NOT executed.
        $content = ob_get_clean();

        // Capture the status code set by the legacy script (default 200)
        $statusCode = http_response_code() ?: 200;

        $response = new Response($content, $statusCode);

        // Synchronize Content-Type from raw header() calls back to Symfony Response
        // to prevent Symfony from overwriting it with the default text/html.
        foreach (headers_list() as $h) {
            if (stripos($h, 'Content-Type:') === 0) {
                [, $value] = explode(':', $h, 2);
                $response->headers->set('Content-Type', trim($value));
            }
        }

        return $response;
    }

    /**
     * Setup environment variables and working directory for legacy compatibility.
     */
    private function prepareLegacyEnvironment(string $requestPath, string $legacyScript): void
    {
        $_SERVER['PHP_SELF'] = $requestPath;
        $_SERVER['SCRIPT_NAME'] = $requestPath;
        $_SERVER['SCRIPT_FILENAME'] = $legacyScript;

        // Resolve relative paths inside legacy scripts
        chdir(dirname($legacyScript));
    }
}