server/topic.Subscribe can produce duplicate subscriber IDs

[peterbourgon]

ntfy/server/topic.go

Line 50 in 6ad3b2e

subscriberID := rand.Int()

// Subscribe subscribes to this topic
func (t *topic) Subscribe(s subscriber, userID string, cancel func()) int {
	t.mu.Lock()
	defer t.mu.Unlock()
	subscriberID := rand.Int() // <---- here
	t.subscribers[subscriberID] = &topicSubscriber{
		userID:     userID, // May be empty
		subscriber: s,
		cancel:     cancel,
	}
	t.lastAccess = time.Now()
	return subscriberID
}

Nothing prevents subscriberID := rand.Int() from producing an integer which is already present in the t.subscribers map. In that case, the previous subscriber is over-written.

[dropdevrahul]

can I pick this up?

[binwiederhier]

Sure thing

[dropdevrahul]

@binwiederhier tried a fix with #713

[dropdevrahul]

Please note Just added a simple retry mechanism and added a test case to catch the edge case

[binwiederhier]

Thanks to you both. The best effort retry should be enough.