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subscription.go
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subscription.go
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package events
import (
"context"
)
func newSubconf(opts ...SubOpt) *subconf {
conf := &subconf{buffer: 1 << 10}
for _, opt := range opts {
opt(conf)
}
return conf
}
type subconf struct {
buffer int
}
// SubOpt for changing subscribe options.
type SubOpt func(*subconf)
// WithBuffer changes subscription buffer size.
func WithBuffer(n int) SubOpt {
return func(conf *subconf) {
conf.buffer = n
}
}
func subscribe[T any](matcher func(*T) bool, opts ...SubOpt) (*BufferedSubscription[T], error) {
sub, err := reporter.bus.Subscribe(new(T))
if err != nil {
return nil, err
}
ctx, cancel := context.WithCancel(context.Background())
conf := newSubconf(opts...)
bs := &BufferedSubscription[T]{
cancel: cancel,
result: make(chan T, conf.buffer),
full: make(chan struct{}),
}
go bs.run(ctx, sub, matcher)
return bs, nil
}
// Subscribe to the objects of type T.
func Subscribe[T any](opts ...SubOpt) (*BufferedSubscription[T], error) {
return subscribe[T](nil, opts...)
}
// SubscribeMatched subscribes and filters results before adding them to the Out channel.
func SubscribeMatched[T any](matcher func(*T) bool, opts ...SubOpt) (*BufferedSubscription[T], error) {
return subscribe(matcher, opts...)
}
// BufferedSubscription is meant to be used by API subscribers.
//
// Majority of the events are published on the critical consensus path, and they
// can't block consensus progress if consumer is slow.
// To account for slow consumer each subscription maintains an internal buffer
// with specific events, if this buffer overflows consumer should be dropped
// and stream restarted.
type BufferedSubscription[T any] struct {
cancel func()
result chan T
full chan struct{}
}
// Close non-blocking close of the subscription.
func (sub *BufferedSubscription[T]) Close() {
sub.cancel()
}
// Out is a channel with subscription results.
func (sub *BufferedSubscription[T]) Out() <-chan T {
return sub.result
}
// Full is closed if subscriptions buffer overflows.
func (sub *BufferedSubscription[T]) Full() <-chan struct{} {
return sub.full
}
func (sub *BufferedSubscription[T]) run(ctx context.Context, s Subscription, matcher func(*T) bool) {
defer s.Close()
for {
select {
case <-ctx.Done():
return
case evt := <-s.Out():
typed := evt.(T)
if matcher != nil && !matcher(&typed) {
break
}
select {
case sub.result <- typed:
default:
close(sub.full)
return
}
}
}
}