Simple websocket server in PHP

I am developing a simple websocket server in PHP. I know there are quite a few existing implementations but I want to make my own so to learn the protocol better. I managed to do the handshaking fine and my clients connect to the server. I also managed to decode the data from the client but I have problems sending back messages. The client disconnects when it receives my response. Firefox says The connection to ws://localhost:12345/ was interrupted while the page was loading..

I used this answer as a guide.

Here is my code for wrapping the data:

private function wrap($msg = ""){
    $length = strlen($msg);
    $this->log("wrapping (" . $length . " bytes): " . $msg);

    $bytesFormatted = chr(129);
    if($length <= 125){
        $bytesFormatted .= chr($length);
    } else if($length >= 126 && $length <= 65535) {
        $bytesFormatted .= chr(126);
        $bytesFormatted .= chr(( $length  >> 8 ) & 255);
        $bytesFormatted .= chr(( $length       ) & 255);
    } else {
        $bytesFormatted .= chr(127);
        $bytesFormatted .= chr(( $length >> 56 ) & 255);
        $bytesFormatted .= chr(( $length >> 48 ) & 255);
        $bytesFormatted .= chr(( $length >> 40 ) & 255);
        $bytesFormatted .= chr(( $length >> 32 ) & 255);
        $bytesFormatted .= chr(( $length >> 24 ) & 255);
        $bytesFormatted .= chr(( $length >> 16 ) & 255);
        $bytesFormatted .= chr(( $length >>  8 ) & 255);
        $bytesFormatted .= chr(( $length       ) & 255);
    }

    $bytesFormatted .= $msg;
    $this->log("wrapped (" . strlen($bytesFormatted) . " bytes): " . $bytesFormatted);
    return $bytesFormatted;
}

UPDATE: I tried it with Chrome and I got the following e