Sometimes big HTTP messages are splitted between onOpen and onMessage
Hi, I don't have run extensive testing but noticed big HTTP messages are split between onOpen and onMessage, I observed those scenarios :

1. onOpen request has headers but body empty, following onMessage call brings also request body
2. onOpen request has headers and body
3. onOpen request has headers but body is empty, following onMessage call brings a request body part , last onMessage call brings final request body part.

We expose HTTP webhook with json payload , depending on message type the payload could be around 12KB, we needed to address packet re-assembly

Could you confirm this behaviour ? To obtain a complete packet under some conditions user need to code to assemble splitted messages ?

I can't find in variuos layers of Ratchet onion architecture a logic to packet reassembly , right ?


```php

// extract from Ratchet

class \Ratchet\Http\HttpServer implements MessageComponentInterface { 
    // ... 
    // ... 
    public function onMessage(ConnectionInterface $from, $msg) {
        if (true !== $from->httpHeadersReceived) {
            try {
                if (null === ($request = $this->_reqParser->onMessage($from, $msg))) {
                    return;
                }
            } catch (\OverflowException $oe) {
                return $this->close($from, 413);
            }
            $from->httpHeadersReceived = true;
            return $this->_httpServer->onOpen($from, $request);
        }
        $this->_httpServer->onMessage($from, $msg);
    }

```

## Solution

To solve the problem we keep track of connection between onOpen and onMessage and gather fragments in a buffer until content-length in header match buffer size


