public HandshakeRequest(string uriString)
{
_uri = uriString.ToUri ();
_rawUrl = _uri.IsAbsoluteUri ? _uri.PathAndQuery : uriString;
_method = "GET";
var headers = Headers;
headers ["User-Agent"] = "websocket-sharp/1.0";
headers ["Upgrade"] = "websocket";
headers ["Connection"] = "Upgrade";
}