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Fix: JetStream ackWait timer starts before handler due to pre-buffering (#609) #37

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Fix: JetStream ackWait timer starts before handler due to pre-buffering (#609) #37

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11 changes: 8 additions & 3 deletions pkg/jetstream/consumer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -126,11 +126,16 @@ func consume(ctx context.Context,
) (chan *message.Message, error) {
output := make(chan *message.Message)

// TODO: this is the closest analog to callback based subscriptions in watermill-nats/pkg/nats
// add support for batching pull consumers using consumer.Fetch / FetchNoWait
// Use Fetch with PullMaxMessages=1 to avoid pre-buffering.
// consumer.Consume() pre-fetches messages internally, causing the NATS ackWait
// clock to start ticking before the handler sees the message. Over time,
// a backlog causes NATS to redeliver messages that were still being processed.
fetchOpts := append([]jetstream.PullConsumeOpt{}, pullConsumeOpts...)
fetchOpts = append(fetchOpts, jetstream.PullMaxMessages(1))

cc, err := consumer.Consume(func(msg jetstream.Msg) {
cb(ctx, msg, output)
}, pullConsumeOpts...)
}, fetchOpts...)
if err != nil {
return nil, fmt.Errorf("failed to start jetstream consumer: %w", err)
}
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