Fixed promhttp Instrument* handlers.

Unfortunately optionality is important as not every e.g. ObserverVec implements exemplar (e.g. summary).

For counters this is not that needed - but changed for consistency and readability.

Signed-off-by: bwplotka <bwplotka@gmail.com>

prometheus/promhttp/instrument_client.go

@@ -78,7 +78,11 @@ func InstrumentRoundTripperCounter(counter *prometheus.CounterVec, next http.Rou
 			for label, resolve := range rtOpts.extraLabelsFromCtx {
 				l[label] = resolve(resp.Request.Context())
 			}
-			counter.With(l).(prometheus.ExemplarAdder).AddWithExemplar(1, rtOpts.getExemplarFn(r.Context()))
+			if rtOpts.getExemplarFn == nil {
+				counter.With(l).Inc()
+			} else {
+				counter.With(l).(prometheus.ExemplarAdder).AddWithExemplar(1, rtOpts.getExemplarFn(r.Context()))
+			}
 		}
 		return resp, err
 	}
@@ -122,7 +126,12 @@ func InstrumentRoundTripperDuration(obs prometheus.ObserverVec, next http.RoundT
 			for label, resolve := range rtOpts.extraLabelsFromCtx {
 				l[label] = resolve(resp.Request.Context())
 			}
-			obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(time.Since(start).Seconds(), rtOpts.getExemplarFn(r.Context()))
+
+			if rtOpts.getExemplarFn == nil {
+				obs.With(l).Observe(time.Since(start).Seconds())
+			} else {
+				obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(time.Since(start).Seconds(), rtOpts.getExemplarFn(r.Context()))
+			}
 		}
 		return resp, err
 	}

prometheus/promhttp/instrument_server.go

@@ -80,6 +80,11 @@ func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler, op
 			for label, resolve := range hOpts.extraLabelsFromCtx {
 				l[label] = resolve(r.Context())
 			}
+
+			if hOpts.getExemplarFn == nil {
+				obs.With(l).Observe(time.Since(now).Seconds())
+				return
+			}
 			obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(time.Since(now).Seconds(), hOpts.getExemplarFn(r.Context()))
 		}
 	}
@@ -91,6 +96,11 @@ func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler, op
 		for label, resolve := range hOpts.extraLabelsFromCtx {
 			l[label] = resolve(r.Context())
 		}
+
+		if hOpts.getExemplarFn == nil {
+			obs.With(l).Observe(time.Since(now).Seconds())
+			return
+		}
 		obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(time.Since(now).Seconds(), hOpts.getExemplarFn(r.Context()))
 	}
 }
@@ -130,6 +140,11 @@ func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler,
 			for label, resolve := range hOpts.extraLabelsFromCtx {
 				l[label] = resolve(r.Context())
 			}
+
+			if hOpts.getExemplarFn == nil {
+				counter.With(l).Inc()
+				return
+			}
 			counter.With(l).(prometheus.ExemplarAdder).AddWithExemplar(1, hOpts.getExemplarFn(r.Context()))
 		}
 	}
@@ -141,6 +156,11 @@ func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler,
 		for label, resolve := range hOpts.extraLabelsFromCtx {
 			l[label] = resolve(r.Context())
 		}
+
+		if hOpts.getExemplarFn == nil {
+			counter.With(l).Inc()
+			return
+		}
 		counter.With(l).(prometheus.ExemplarAdder).AddWithExemplar(1, hOpts.getExemplarFn(r.Context()))
 	}
 }
@@ -183,7 +203,12 @@ func InstrumentHandlerTimeToWriteHeader(obs prometheus.ObserverVec, next http.Ha
 			for label, resolve := range hOpts.extraLabelsFromCtx {
 				l[label] = resolve(r.Context())
 			}
-			obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(time.Since(now).Seconds(), hOpts.getExemplarFn(r.Context()))
+
+			if hOpts.getExemplarFn == nil {
+				obs.With(l).Observe(time.Since(now).Seconds())
+			} else {
+				obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(time.Since(now).Seconds(), hOpts.getExemplarFn(r.Context()))
+			}
 		})
 		next.ServeHTTP(d, r)
 	}
@@ -227,6 +252,11 @@ func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler,
 			for label, resolve := range hOpts.extraLabelsFromCtx {
 				l[label] = resolve(r.Context())
 			}
+
+			if hOpts.getExemplarFn == nil {
+				obs.With(l).Observe(float64(size))
+				return
+			}
 			obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(float64(size), hOpts.getExemplarFn(r.Context()))
 		}
 	}
@@ -239,6 +269,11 @@ func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler,
 		for label, resolve := range hOpts.extraLabelsFromCtx {
 			l[label] = resolve(r.Context())
 		}
+
+		if hOpts.getExemplarFn == nil {
+			obs.With(l).Observe(float64(size))
+			return
+		}
 		obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(float64(size), hOpts.getExemplarFn(r.Context()))
 	}
 }
@@ -279,6 +314,11 @@ func InstrumentHandlerResponseSize(obs prometheus.ObserverVec, next http.Handler
 		for label, resolve := range hOpts.extraLabelsFromCtx {
 			l[label] = resolve(r.Context())
 		}
+
+		if hOpts.getExemplarFn == nil {
+			obs.With(l).Observe(float64(d.Written()))
+			return
+		}
 		obs.With(l).(prometheus.ExemplarObserver).ObserveWithExemplar(float64(d.Written()), hOpts.getExemplarFn(r.Context()))
 	})
 }

prometheus/promhttp/option.go

@@ -37,7 +37,6 @@ type options struct {
 
 func defaultOptions() *options {
 	return &options{
-		getExemplarFn:      func(ctx context.Context) prometheus.Labels { return nil },
 		extraLabelsFromCtx: map[string]LabelValueFromCtx{},
 	}
 }