functions.php

<?php

function handleSessionWriteRequest(Request $request, Response $response) {
  $session = yield (new Session($request))->open();
  
  $something = $session->get("something");
  $session->set("something", "{$something}-else");
  
  yield $session->save();
  
  $response->send("Content: $something");
}

function handleSessionReadOnlyRequest(Request $request, Response $response) {
  $session = (new Session($request))->read();
  $something = $session->get("...");
  
  $response->send("Content: $something");
}