ntfy/server/topic.go

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package server
import (
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"heckel.io/ntfy/log"
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"math/rand"
"sync"
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)
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// topic represents a channel to which subscribers can subscribe, and publishers
// can publish a message
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type topic struct {
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ID string
subscribers map[int]*topicSubscriber
rateVisitor *visitor
mu sync.RWMutex
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}
type topicSubscriber struct {
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userID string // User ID associated with this subscription, may be empty
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subscriber subscriber
cancel func()
}
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// subscriber is a function that is called for every new message on a topic
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type subscriber func(v *visitor, msg *message) error
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// newTopic creates a new topic
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func newTopic(id string) *topic {
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return &topic{
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ID: id,
subscribers: make(map[int]*topicSubscriber),
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}
}
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// Subscribe subscribes to this topic
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func (t *topic) Subscribe(s subscriber, userID string, cancel func()) int {
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t.mu.Lock()
defer t.mu.Unlock()
subscriberID := rand.Int()
t.subscribers[subscriberID] = &topicSubscriber{
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userID: userID, // May be empty
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subscriber: s,
cancel: cancel,
}
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return subscriberID
}
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func (t *topic) Stale() bool {
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t.mu.Lock()
defer t.mu.Unlock()
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if t.rateVisitor != nil && !t.rateVisitor.Stale() {
return false
}
return len(t.subscribers) == 0
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}
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func (t *topic) SetRateVisitor(v *visitor) {
t.mu.Lock()
defer t.mu.Unlock()
t.rateVisitor = v
}
func (t *topic) RateVisitor() *visitor {
t.mu.Lock()
defer t.mu.Unlock()
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if t.rateVisitor != nil && t.rateVisitor.Stale() {
t.rateVisitor = nil
}
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return t.rateVisitor
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}
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// Unsubscribe removes the subscription from the list of subscribers
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func (t *topic) Unsubscribe(id int) {
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t.mu.Lock()
defer t.mu.Unlock()
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delete(t.subscribers, id)
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}
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// Publish asynchronously publishes to all subscribers
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func (t *topic) Publish(v *visitor, m *message) error {
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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 {
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logvm(v, m).Tag(tagPublish).Debug("Forwarding to %d subscriber(s)", 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 {
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logvm(v, m).Tag(tagPublish).Err(err).Warn("Error forwarding to subscriber")
}
}(s.subscriber)
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}
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} else {
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logvm(v, m).Tag(tagPublish).Trace("No stream or WebSocket subscribers, not forwarding")
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}
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}()
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return nil
}
// SubscribersCount returns the number of subscribers to this topic
func (t *topic) SubscribersCount() int {
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t.mu.RLock()
defer t.mu.RUnlock()
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return len(t.subscribers)
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}
// 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 {
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if s.userID != exceptUserID {
log.
Tag(tagSubscribe).
Fields(log.Context{
"message_topic": t.ID,
"user_id": s.userID,
}).
Debug("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{
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userID: sub.userID,
subscriber: sub.subscriber,
cancel: sub.cancel,
}
}
return subscribers
}