status-go/vendor/github.com/libp2p/go-libp2p-pubsub/subscription.go

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package pubsub
import (
"context"
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"sync"
)
// Subscription handles the details of a particular Topic subscription.
// There may be many subscriptions for a given Topic.
type Subscription struct {
topic string
ch chan *Message
cancelCh chan<- *Subscription
ctx context.Context
err error
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once sync.Once
}
// Topic returns the topic string associated with the Subscription
func (sub *Subscription) Topic() string {
return sub.topic
}
// Next returns the next message in our subscription
func (sub *Subscription) Next(ctx context.Context) (*Message, error) {
select {
case msg, ok := <-sub.ch:
if !ok {
return msg, sub.err
}
return msg, nil
case <-ctx.Done():
return nil, ctx.Err()
}
}
// Cancel closes the subscription. If this is the last active subscription then pubsub will send an unsubscribe
// announcement to the network.
func (sub *Subscription) Cancel() {
select {
case sub.cancelCh <- sub:
case <-sub.ctx.Done():
}
}
func (sub *Subscription) close() {
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sub.once.Do(func() {
close(sub.ch)
})
}