<?php
use Psr\Http\Message\ServerRequestInterface as Request;
use Psr\Http\Message\ResponseInterface as Response;
use HomoChecker\Model\Check;
use HomoChecker\View\ServerSentEventView;

require __DIR__ . '/../../../vendor/autoload.php';

$app = new \Slim\App([
    'settings' => [
        'outputBuffering'        => false,
        'addContentLengthHeader' => false,
    ],
]);
$app->get('/check[/{name}]', function (Request $request, Response $response, array $args) {
    $view = new ServerSentEventView('response');
    $checker = new Check;
    $checker->execute($args['name'] ?? null, [$view, 'render']);
    $view->close();
});
$app->run();

<?php
use Psr\Http\Message\ServerRequestInterface as Request;
use Psr\Http\Message\ResponseInterface as Response;
use HomoChecker\Model\Check;
use HomoChecker\View\ServerSentEventView;

require __DIR__ . '/../../../vendor/autoload.php';

$app = new \Slim\App([
    'settings' => [
        'outputBuffering' => false,
    ],
]);
$app->get('/check[/{name}]', function (Request $request, Response $response, array $args) {
    $view = new ServerSentEventView('response');
    $checker = new Check;
    $checker->execute($args['name'] ?? null, [$view, 'render']);
    $view->close();
});
$app->run();

--- 
+++ 
@@ -8,7 +8,8 @@
 
 $app = new \Slim\App([
     'settings' => [
-        'outputBuffering' => false,
+        'outputBuffering'        => false,
+        'addContentLengthHeader' => false,
     ],
 ]);
 $app->get('/check[/{name}]', function (Request $request, Response $response, array $args) {
Disable attempts for Content-Length in order not to output error
