Aerys\Websocket\Handshake::flush PHP Method

    public function flush()
    {
        if ($this->status === 101) {
            throw new \DomainException("Cannot flush(); entity body content disallowed for Switching Protocols Response");
        }
        // We don't assign websocket headers in flush() because calling
        // this method before Response output starts is an error and will
        // throw when invoked on the wrapped Response.
        $this->response->flush();
        return $this;
    }