[hw-7] add metrics, tracing

cart/internal/app/app.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/rs/zerolog"
 	"github.com/rs/zerolog/log"
 	"google.golang.org/grpc"
@@ -90,6 +91,7 @@ func (app *App) setupCartService() (*service.CartService, error) {
 	// Product service client
 	transport := http.DefaultTransport
 	transport = round_trippers.NewLogRoundTripper(transport)
+	transport = round_trippers.NewMetricsRoundTripper(transport)
 	transport = round_trippers.NewRetryRoundTripper(transport, productsRetryAttemptsDefault, productsInitialDelaySecDefault)
 
 	httpClient := http.Client{
@@ -133,7 +135,11 @@ func (app *App) BootstrapHandlers(cartService *service.CartService) http.Handler
 	mx.HandleFunc("DELETE /user/{user_id}/cart/{sku_id}", s.DeleteItemHandler)
 	mx.HandleFunc("DELETE /user/{user_id}/cart", s.DeleteItemsByUserIDHandler)
 
-	h := middlewares.NewTimerMiddleware(mx)
+	mx.Handle("GET /metrics", promhttp.Handler())
+
+	h := middlewares.NewTracingMiddleware(mx)
+	h = middlewares.NewMetricsMiddleware(h)
+	h = middlewares.NewTimerMiddleware(h)
 
 	return h
 }