code: func (o *ClientOptions) SetBinaryWill(topic string, payload []byte, qos byte, retained bool) *ClientOptions {
  	o.WillEnabled = true
  	o.WillTopic = topic
  	o.WillPayload = payload
  	o.WillQos = qos
  	o.WillRetained = retained
  	return o
  }
docs: // SetBinaryWill accepts a []byte will message to be set. When the client connects,
  // it will give this will message to the broker, which will then publish the
  // provided payload (the will) to any clients that are subscribed to the provided
  // topic.