private function createServerProcess(SymfonyStyle $io, $address, $documentRoot, $router)
    {
        $finder = new PhpExecutableFinder();
        if (false === $binary = $finder->find()) {
            $io->error('Unable to find PHP binary to start server.');

            return;
        }

        $script = implode(' ', array_map(array('Symfony\Component\Process\ProcessUtils', 'escapeArgument'), array(
            $binary,
            '-S',
            $address,
            $router,
        )));

        return new Process('exec '.$script, $documentRoot, null, null, null);
    }