Prevent a nats message from being redelivered during processing

hold.go

// This function can be called to start a hold on a message for processing on Jetstream.
// The interval should be shorter than the message ack timeout.
// The parentCancel can be used to provide a cancellation function for processing in the event that we cannot set InProgress
// The function return should be named release by the caller, and can be used to unlock message processing after a successful ACK/NAK

func HoldMessage(ctx context.Context, msg *nats.Msg, interval time.Duration, parentCancel context.CancelFunc) context.CancelFunc {
	ctx, release := context.WithCancel(ctx)
	if interval < 1 { 
		return release
	}
	var exit bool
	go func() {
		for {
			select {
			case <- time.After(interval):
				if err := msg.InProgress() ; err != nil {
					release()
					if parentCancel != nil {
						parentCancel()
						exit = true
					}
				}
			case <-ctx.Done():
				exit = true
			}
			if exit {
				break
			}
		}
		release()
	}()
	return release
}