httptransport: add instrumentation helper

Signed-off-by: Hank Donnay <hdonnay@redhat.com>

httptransport/instrumentation.go

@@ -0,0 +1,37 @@
+package httptransport
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+)
+
+type wrapper struct {
+	RequestCount    *prometheus.CounterVec
+	RequestSize     *prometheus.HistogramVec
+	ResponseSize    *prometheus.HistogramVec
+	RequestDuration *prometheus.HistogramVec
+	InFlight        *prometheus.GaugeVec
+}
+
+func (m *wrapper) init() {
+	prometheus.MustRegister(m.RequestCount, m.RequestSize, m.ResponseSize, m.RequestDuration, m.InFlight)
+}
+
+func (m *wrapper) wrap(tag string, h http.Handler) http.Handler {
+	// Add the route tag for traces
+	return otelhttp.WithRouteTag(tag,
+		// Stack all these metrics handlers.
+		promhttp.InstrumentHandlerCounter(m.RequestCount.MustCurryWith(prometheus.Labels{"handler": tag}),
+			promhttp.InstrumentHandlerRequestSize(m.RequestSize.MustCurryWith(prometheus.Labels{"handler": tag}),
+				promhttp.InstrumentHandlerResponseSize(m.ResponseSize.MustCurryWith(prometheus.Labels{"handler": tag}),
+					promhttp.InstrumentHandlerDuration(m.RequestDuration.MustCurryWith(prometheus.Labels{"handler": tag}),
+						promhttp.InstrumentHandlerInFlight(m.InFlight.WithLabelValues(tag),
+							h))))))
+}
+
+func (m *wrapper) wrapFunc(tag string, h http.HandlerFunc) http.Handler {
+	return m.wrap(tag, h)
+}