Fix double-counting bug in promhttp.InstrumentRoundTripperCounter (#1118)

Signed-off-by: Dave Henderson <[email protected]>

Signed-off-by: Dave Henderson <[email protected]>

Author: hairyhenderson

prometheus/promhttp/instrument_client.go

@@ -78,7 +78,6 @@ func InstrumentRoundTripperCounter(counter *prometheus.CounterVec, next http.Rou
 				1,
 				rtOpts.getExemplarFn(r.Context()),
 			)
-			counter.With(labels(code, method, r.Method, resp.StatusCode, rtOpts.extraMethods...)).Inc()
 		}
 		return resp, err
 	}

prometheus/promhttp/instrument_client_test.go

@@ -25,6 +25,7 @@ import (
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
 
 	dto "github.com/prometheus/client_model/go"
 	"google.golang.org/protobuf/proto"
@@ -250,6 +251,19 @@ func TestClientMiddlewareAPI_WithRequestContext(t *testing.T) {
 			t.Errorf("metric family %s must not be empty", mf.GetName())
 		}
 	}
+
+	// make sure counters aren't double-incremented (see #1117)
+	expected := `
+		# HELP client_api_requests_total A counter for requests from the wrapped client.
+		# TYPE client_api_requests_total counter
+		client_api_requests_total{code="200",method="get"} 1
+	`
+
+	if err := testutil.GatherAndCompare(reg, strings.NewReader(expected),
+		"client_api_requests_total",
+	); err != nil {
+		t.Fatal(err)
+	}
 }
 
 func TestClientMiddlewareAPIWithRequestContextTimeout(t *testing.T) {