consumer/async.go
func (c *Consumer) SetOnConnectCallback(cb func()) {
	c.callbackLock.Lock()
	defer c.callbackLock.Unlock()
	c.callback = cb
}
func (c *Consumer) SetOnConnectCallback(cb func()) {
	c.callbackLock.Lock()
	defer c.callbackLock.Unlock()
	c.callback = cb
}
// SetOnConnectCallback sets a callback function to be called with the
// websocket connection is established.