stream csv file lumen

gistfile1.txt

<?php

namespace App\Http\Controllers;

use App\Result;
use Illuminate\Http\Request;
use Symfony\Component\HttpFoundation\StreamedResponse;

class ExportController extends Controller
{


    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
    }

    public function index()
    {
        $results = Result::all()->toArray();

        $headers = $this->getFileResponseHeaders('export.csv');

        return $this->streamFile(function () use ($results) {
            $output = fopen('php://output', 'w');
            foreach ($results as $row) {
                fputcsv($output, $row);
            }
            fclose($output);
        }, $headers);
    }

    protected function streamFile($callback, $headers)
    {
        $response = new StreamedResponse($callback, 200, $headers);
        $response->send();
    }

    protected function getFileResponseHeaders($filename)
    {
        return [
            'Cache-Control'       => 'must-revalidate, post-check=0, pre-check=0',
            'Content-type'        => 'text/csv',
            'Content-Disposition' => 'attachment; filename='.$filename,
            'Expires'             => '0',
            'Pragma'              => 'public'
        ];
    }
}