package server import ( "heckel.io/ntfy/log" "math/rand" "sync" ) // topic represents a channel to which subscribers can subscribe, and publishers // can publish a message type topic struct { ID string subscribers map[int]*topicSubscriber mu sync.Mutex } type topicSubscriber struct { userID string // User ID associated with this subscription, may be empty subscriber subscriber cancel func() } // subscriber is a function that is called for every new message on a topic type subscriber func(v *visitor, msg *message) error // newTopic creates a new topic func newTopic(id string) *topic { return &topic{ ID: id, subscribers: make(map[int]*topicSubscriber), } } // 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() t.subscribers[subscriberID] = &topicSubscriber{ userID: userID, // May be empty subscriber: s, cancel: cancel, } return subscriberID } // Unsubscribe removes the subscription from the list of subscribers func (t *topic) Unsubscribe(id int) { t.mu.Lock() defer t.mu.Unlock() delete(t.subscribers, id) } // Publish asynchronously publishes to all subscribers func (t *topic) Publish(v *visitor, m *message) error { go func() { // We want to lock the topic as short as possible, so we make a shallow copy of the // subscribers map here. Actually sending out the messages then doesn't have to lock. subscribers := t.subscribersCopy() if len(subscribers) > 0 { log.Debug("%s Forwarding to %d subscriber(s)", logMessagePrefix(v, m), len(subscribers)) for _, s := range subscribers { // We call the subscriber functions in their own Go routines because they are blocking, and // we don't want individual slow subscribers to be able to block others. go func(s subscriber) { if err := s(v, m); err != nil { log.Warn("%s Error forwarding to subscriber", logMessagePrefix(v, m)) } }(s.subscriber) } } else { log.Trace("%s No stream or WebSocket subscribers, not forwarding", logMessagePrefix(v, m)) } }() return nil } // SubscribersCount returns the number of subscribers to this topic func (t *topic) SubscribersCount() int { t.mu.Lock() defer t.mu.Unlock() return len(t.subscribers) } // CancelSubscribers calls the cancel function for all subscribers, forcing func (t *topic) CancelSubscribers(exceptUserID string) { t.mu.Lock() defer t.mu.Unlock() for _, s := range t.subscribers { if s.userID != exceptUserID { log.Trace("Canceling subscriber %s", s.userID) s.cancel() } } } // subscribersCopy returns a shallow copy of the subscribers map func (t *topic) subscribersCopy() map[int]*topicSubscriber { t.mu.Lock() defer t.mu.Unlock() subscribers := make(map[int]*topicSubscriber) for k, sub := range t.subscribers { subscribers[k] = &topicSubscriber{ userID: sub.userID, subscriber: sub.subscriber, cancel: sub.cancel, } } return subscribers }