services.yml

Base service definitions to enable Symfony to route requests, resolve controllers etc.

Most important lines:

event_dispatcher:
  # ...
  calls:
    # ...
    - [ addListener, [ kernel.view, [ App\PromiseResponse, wrapPromise ] ] ]

PromiseResponse allows Symfony to return something. That something is a promise of the actual response.

RunCommand.php

Starts HTTP server that converts ReactPHP requests to Symfony requests and then Symfony responses to ReactPHP responses.

IndexController.php

An example controller. indexAction returns immediately response. promiseAction responds after X seconds waiting.

Run with:

$ ./app.php run