how to trigger onMessage function from server-side ?
in my project , i want to send data to some clients automatically , without receiving any request from clients.but i cant access to clients from out side of `MessageComponentInterface` class object. i prefer to tell to `MessageComponentInterface` class ; send to alive clients a message. so i need to trigger onMessage function from server-side , how can i do it ?
here is my WebSocketCon class :
```php
<?php 
use Ratchet\MessageComponentInterface;
use Ratchet\ConnectionInterface;

class WebSocketCon implements MessageComponentInterface {
    protected $clients;
    public $users;
	
    public function __construct() {
        $this->clients = new \SplObjectStorage; 
        $this->users = [];
    }

    public function onOpen(ConnectionInterface $conn) {
        $this->clients->attach($conn);
        echo "New connection! ({$conn->resourceId})\n";
    }

    public function onMessage(ConnectionInterface $from, $msg) {
        $data = json_decode($msg);
        if($data->command=="subscribe"){
            $this->users[(int)$data->uid] = $from;
            echo "New subscribe! ({$data->uid})\n";
        }
    }

    public function sendMessageToAll($msg){
        foreach ($this->clients as $client) {
            if ($from !== $client) {
                $client->send($msg);
            }
        }
    }
	
    public function sendMessageTo($idusers,$msg){
        foreach ($idusers as $idu) {
            $idu = (int) $idu;
            if(array_key_exists($idu,$this->users)){
                $this->users[$idu]->send($msg);
            }
        }
    }
	
    public function onClose(ConnectionInterface $conn) {
        $this->clients->detach($conn); 
            if (($key = array_search($conn, $this->users)) !== false) {
                unset($this->users[$key]);
            }
        echo "Connection {$conn->resourceId} has disconnected\n";
    }

    public function onError(ConnectionInterface $conn, \Exception $e) {
        echo "An error has occurred: {$e->getMessage()}\n";

        $conn->close();
    }
}
```
and here is my cmd.php :

```php
<?php
require 'vendor/autoload.php';

use Ratchet\Server\IoServer;
use Ratchet\Http\HttpServer;
use Ratchet\WebSocket\WsServer; 
require 'classes/WebSocketCon.php';

$server = IoServer::factory(
    new HttpServer(
        new WsServer(
            new WebSocketCon()
        )
    ),
    8081
);

$server->run();
?>
```