fix: make possible adding custom attributes to the shipped otelhttp client metrics - open-telemetry#5084

Author: Ionut Zailic

instrumentation/net/http/otelhttp/handler.go

@@ -219,8 +219,10 @@ func (h *middleware) serveHTTP(w http.ResponseWriter, r *http.Request, next http
 		},
 	})
 
-	labeler := &Labeler{}
-	ctx = injectLabeler(ctx, labeler)
+	labeler, found := LabelerFromContext(ctx)
+	if !found {
+		ctx = InjectLabeler(ctx, labeler)
+	}
 
 	next.ServeHTTP(w, r.WithContext(ctx))
 

instrumentation/net/http/otelhttp/labeler.go

@@ -48,7 +48,7 @@ type labelerContextKeyType int
 
 const lablelerContextKey labelerContextKeyType = 0
 
-func injectLabeler(ctx context.Context, l *Labeler) context.Context {
+func InjectLabeler(ctx context.Context, l *Labeler) context.Context {
 	return context.WithValue(ctx, lablelerContextKey, l)
 }
 

instrumentation/net/http/otelhttp/transport.go

@@ -148,8 +148,10 @@ func (t *Transport) RoundTrip(r *http.Request) (*http.Response, error) {
 		ctx = httptrace.WithClientTrace(ctx, t.clientTrace(ctx))
 	}
 
-	labeler := &Labeler{}
-	ctx = injectLabeler(ctx, labeler)
+	labeler, found := LabelerFromContext(ctx)
+	if !found {
+		ctx = InjectLabeler(ctx, labeler)
+	}
 
 	r = r.Clone(ctx) // According to RoundTripper spec, we shouldn't modify the origin request.