snapshot of https://github.com/ThreeDotsLabs/watermill.git (master, 2026-09-15; blobs > 131072B omitted)

components/metrics/handler.go

@@ -0,0 +1,92 @@
+package metrics
+
+import (
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus"
+
+	"github.com/ThreeDotsLabs/watermill/message"
+)
+
+var (
+	handlerLabelKeys = []string{
+		labelKeyHandlerName,
+		labelSuccess,
+	}
+
+	// defaultHandlerExecutionTimeBuckets are one order of magnitude smaller than default buckets (5ms~10s),
+	// because the handler execution times are typically shorter (µs~ms range).
+	defaultHandlerExecutionTimeBuckets = []float64{
+		0.0005,
+		0.001,
+		0.0025,
+		0.005,
+		0.01,
+		0.025,
+		0.05,
+		0.1,
+		0.25,
+		0.5,
+		1,
+	}
+)
+
+// HandlerPrometheusMetricsMiddleware is a middleware that captures Prometheus metrics.
+type HandlerPrometheusMetricsMiddleware struct {
+	handlerExecutionTimeSeconds *prometheus.HistogramVec
+	additionalLabels            []MetricLabel
+}
+
+// Middleware returns the middleware ready to be used with watermill's Router.
+func (m HandlerPrometheusMetricsMiddleware) Middleware(h message.HandlerFunc) message.HandlerFunc {
+	return func(msg *message.Message) (msgs []*message.Message, err error) {
+		now := time.Now()
+		ctx := msg.Context()
+		labels := prometheus.Labels{
+			labelKeyHandlerName: message.HandlerNameFromCtx(ctx),
+		}
+		for _, lb := range m.additionalLabels {
+			labels[lb.Label] = lb.ComputeValueFn(ctx)
+		}
+
+		defer func() {
+			if err != nil {
+				labels[labelSuccess] = "false"
+			} else {
+				labels[labelSuccess] = "true"
+			}
+			m.handlerExecutionTimeSeconds.With(labels).Observe(time.Since(now).Seconds())
+		}()
+
+		return h(msg)
+	}
+}
+
+// NewRouterMiddleware returns new middleware.
+func (b PrometheusMetricsBuilder) NewRouterMiddleware() HandlerPrometheusMetricsMiddleware {
+	var err error
+	m := HandlerPrometheusMetricsMiddleware{
+		additionalLabels: b.additionalLabels,
+	}
+
+	if b.HandlerBuckets == nil {
+		b.HandlerBuckets = defaultHandlerExecutionTimeBuckets
+	}
+
+	m.handlerExecutionTimeSeconds, err = b.registerHistogramVec(prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Namespace: b.Namespace,
+			Subsystem: b.Subsystem,
+			Name:      "handler_execution_time_seconds",
+			Help:      "The total time elapsed while executing the handler function in seconds",
+			Buckets:   b.HandlerBuckets,
+		},
+		toLabelsSlice(handlerLabelKeys, b.additionalLabels),
+	))
+	if err != nil {
+		panic(errors.Wrap(err, "could not register handler execution time metric"))
+	}
+
+	return m
+}