def call_reply(msg, call_return):
    """Construct message used by CtrlServer when replying to API calls.

    :param msg: Description of API call.
    :type msg: string
    :param call_return: Return value of API call.
    :type call_return: string
    :returns: Constructed call_reply dict, ready to be sent over the wire.

    """
    return {"type": "call_reply", "msg": msg, "call_return": call_return}