How to get the base URL of a Drupal 9 site

My goal was to get the base URL and compare it with the URL of the link.  Was it an internal or external link?  You can get the hostname, "{your_domain}", directly from the getHost() request:

$host = \Drupal::request()->getHost();

However, if you need the schema as well, such as https://{your_domain}

$host = \Drupal::request()->getSchemeAndHttpHost();

In my situation, I needed to redirect the page to an external site and count the page.  So

$cache = \Drupal::cache();
$cache->deleteAll();

$url = $this->helper->getField(
    $this->node, 'field_document_link'
);

$redirect = new TrustedRedirectResponse($url);
return $redirect->send();

Finally, the redirect would only kick in if the link was external.  Which I wrote separately.