Address PR feedback

middleware/http_tracing.go

@@ -130,7 +130,7 @@ func HTTPGRPCTracingInterceptor(router *mux.Router) grpc.UnaryServerInterceptor
 }
 
 func httpOperationNameFunc(r *http.Request) string {
-	routeName := ExtractRouteName(r)
+	routeName := ExtractRouteName(r.Context())
 	return getOperationName(routeName, r)
 }
 

middleware/instrument.go

@@ -118,7 +118,7 @@ func (i Instrument) Wrap(next http.Handler) http.Handler {
 // We do all this as we do not wish to emit high cardinality labels to
 // prometheus.
 func (i Instrument) getRouteName(r *http.Request) string {
-	route := ExtractRouteName(r)
+	route := ExtractRouteName(r.Context())
 	if route == "" {
 		route = "other"
 	}

middleware/route_injector.go

@@ -35,11 +35,13 @@ func WithRouteName(r *http.Request, routeName string) *http.Request {
 	return r.WithContext(ctx)
 }
 
-// ExtractRouteName returns the route name associated with this request.
+// ExtractRouteName returns the route name associated with this request that was previously injected by the
+// RouteInjector middleware or WithRouteName.
+//
 // This is the same route name used for trace and metric names, and is already suitable for use as a Prometheus label
 // value.
-func ExtractRouteName(r *http.Request) string {
-	routeName, ok := r.Context().Value(contextKeyRouteName).(string)
+func ExtractRouteName(ctx context.Context) string {
+	routeName, ok := ctx.Value(contextKeyRouteName).(string)
 	if !ok {
 		return ""
 	}

middleware/route_injector_test.go

@@ -28,7 +28,7 @@ func TestRouteInjector(t *testing.T) {
 			actualRouteName := ""
 
 			handler := func(_ http.ResponseWriter, r *http.Request) {
-				actualRouteName = ExtractRouteName(r)
+				actualRouteName = ExtractRouteName(r.Context())
 			}
 
 			router := mux.NewRouter()