[hw-7] add metrics, tracing

cart/internal/infra/http/round_trippers/metrics.go

@@ -0,0 +1,37 @@
+package round_trippers
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"route256/cart/internal/infra/http/metrics"
+)
+
+type MetricsRoundTripper struct {
+	rt http.RoundTripper
+}
+
+func NewMetricsRoundTripper(rt http.RoundTripper) http.RoundTripper {
+	return &MetricsRoundTripper{
+		rt: rt,
+	}
+}
+
+func (m *MetricsRoundTripper) RoundTrip(r *http.Request) (*http.Response, error) {
+	start := time.Now()
+	resp, err := m.rt.RoundTrip(r)
+
+	status := "error"
+
+	if resp != nil {
+		status = strconv.Itoa(resp.StatusCode)
+	}
+
+	url := r.URL.Path
+
+	metrics.IncOutboundRequestCount(r.Method, url, status)
+	metrics.StoreOutboundRequestDuration(r.Method, url, status, time.Since(start))
+
+	return resp, err
+}