Hide a xiag (dev) domain from Google

index.php

<?php

$app->get('/robots.txt', function () {
    return new Response(
        (
            (stripos($_SERVER['HTTP_HOST'], 'xiag') !== false) ?
            "User-agent: *\nDisallow: /\n" :
            "User-agent: *\n"
        ),

        200,
        ['Content-Type' => 'text/plain']
    );
});