naive-cache.go

type Cache struct {
	kv map[string]*bufio.Reader
	http.RoundTripper
}

func (c *Cache) RoundTrip(req *http.Request) (*http.Response, error) {
	if req.Method != "GET" {
		return c.RoundTrip(req)
	}

	v, ok := c.kv[req.URL.String()]
	if ok {
		// return cached
		return http.ReadResponse(v, nil)

	}

	resp, err := c.RoundTripper.RoundTrip(req)
	if err != nil {
		return resp, err
	}

	body, err := httputil.DumpResponse(resp, true)
	if err != nil {
		return resp, err
	}

	r := bufio.NewReader(bytes.NewReader(body))
	c.kv[req.URL.String()] = r

	return resp, err
}

func main() {
	c := &http.Client{
		Transport: &Cache{
			RoundTripper: http.DefaultTransport,
			kv:           make(map[string]*bufio.Reader),
		},
	}

	req, err := http.NewRequest("GET", "https://www.google.com", nil)
	if err != nil {
		log.Fatalf("Could not create request")
	}

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	req = req.WithContext(ctx)
	resp, err := c.Do(req)
	if err != nil {
		log.Fatalln(err)
	}
	resp.Body.Close()

	log.Println(resp)
}