[hw-1] implement cart service

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

@@ -0,0 +1,23 @@
+package round_trippers
+
+import (
+	"net/http"
+
+	"github.com/rs/zerolog/log"
+)
+
+type LogRoundTripper struct {
+	rt http.RoundTripper
+}
+
+func NewLogRoundTripper(rt http.RoundTripper) http.RoundTripper {
+	return &LogRoundTripper{
+		rt: rt,
+	}
+}
+
+func (l *LogRoundTripper) RoundTrip(r *http.Request) (*http.Response, error) {
+	log.Debug().Msgf("%s called", r.URL.String())
+
+	return l.rt.RoundTrip(r)
+}

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

@@ -0,0 +1,67 @@
+package round_trippers
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/rs/zerolog/log"
+)
+
+type RetryRoundTripper struct {
+	rt              http.RoundTripper
+	maxRetries      int
+	initialDelaySec int
+}
+
+func NewRetryRoundTripper(rt http.RoundTripper, maxRetries int, initialDelaySec int) http.RoundTripper {
+	return &RetryRoundTripper{
+		rt:              rt,
+		maxRetries:      maxRetries,
+		initialDelaySec: initialDelaySec,
+	}
+}
+
+func (rrt *RetryRoundTripper) RoundTrip(r *http.Request) (*http.Response, error) {
+	var resp *http.Response
+	var err error
+
+	for attempt := 0; attempt <= rrt.maxRetries; attempt++ {
+		if attempt > 0 {
+			// exponential retry time (e.g.: [1s, 2s, 4s])
+			delay := time.Duration(rrt.initialDelaySec<<uint(attempt-1)) * time.Second
+
+			log.Debug().Msgf("retrying, delay=%d", delay)
+
+			timer := time.NewTimer(delay)
+
+			select {
+			case <-timer.C:
+			case <-r.Context().Done():
+				timer.Stop()
+
+				return nil, r.Context().Err()
+			}
+		}
+
+		resp, err = rrt.rt.RoundTrip(r)
+		if err != nil {
+			return nil, err
+		}
+
+		switch resp.StatusCode {
+		case http.StatusTooManyRequests, 420:
+			resp.Body.Close()
+
+			if attempt == rrt.maxRetries {
+				return nil, fmt.Errorf("request returned %d after %d retries", resp.StatusCode, rrt.maxRetries)
+			}
+
+			continue
+		default:
+			return resp, nil
+		}
+	}
+
+	return resp, err
+}