PingAction.php

<?php

namespace App\Action;

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Zend\Diactoros\Response\JsonResponse;

class PingAction
{
    const ROUTE_NAME = 'api.ping';
    const ROUTE_PATH = '/api/ping';
    const ROUTE_METHODS = ['GET'];

    public function __invoke(ServerRequestInterface $request, ResponseInterface $response, callable $next = null)
    {
        return new JsonResponse(['ack' => time()]);
    }
}