// SendAsync sends `req` to the other end and calls callback on the response.
func (cnv *Conversation) SendAsync(req *wire.Request, callback transfer.AsyncFunc) error {
cnv.Lock()
defer cnv.Unlock()
// Add a nonce so that the same message is guaranteed to result
// in a different ciphertext:
req.Nonce = rand.Int63()
// Broadcast messages usually do not register a callback.
// (it wouldn't have been called anyways)
if callback != nil {
cnv.notifees[req.ID] = callback
}
return cnv.proto.Send(req)
}
