Metrics

A metric middleware is helpful to track and aggregate metrics whenever you invoke client.Publish(), the call is first passed through the chain of middlewares and then published to broker.

publish_metrics.go

func main() {
    var client *courier.Client

    pm := &promCollector{}

    client.UsePublisherMiddleware(pm.publisherMiddleware)
}

type promCollector struct {
    attemps *prometheus.CounterVec
    errors  *prometheus.CounterVec
    success *prometheus.CounterVec
}

func (p *promCollector) publisherMiddleware(next courier.Publisher) courier.Publisher {
    return courier.PublisherFunc(func(ctx context.Context, topic string, data interface{}, opts ...courier.Option) error {
        p.attemps.With(prometheus.Labels{}).Inc()

        if err := next.Publish(ctx, topic, data, opts...); err != nil {
            p.errors.With(prometheus.Labels{}).Inc()

            return err
        }

        p.success.With(prometheus.Labels{}).Inc()

        return nil
    })
}