The assertions are actually there to signal a problem in your code, don't turn them off.
In your case, the code that's wrong is this:
let future = newAsyncHttpClient().getContent(url)
future.withTimeout(timeout).addCallback(proc() =
future.fail(newException(OSError, "HTTP timed out.")))
Run
You're completing a future that has already been completed from what I can
tell. You cannot call `fail` on a future that has been completed already.
