nitrous.io websockets - Connection and Upgrade headers required

Question

I have a Ruby server using em-websocket for websockets.

From the browser, I'm using the following code to connect:

var ws       = new WebSocket('ws://' + window.location.host);
ws.onopen    = function()  { alert('websocket opened'); };

I know this is hitting the server because I see the server produce the following error:

EventMachine::WebSocket::HandshakeError - Connection and Upgrade headers required:

How can I ensure these headers are being sent by the client? I'm just using the standard browser websocket API.

Not sure if it changes anything that I'm running on Nitrous IO and I am binding the server to "0.0.0.0"