HTTP 重试与退避：客户端最小策略（JS 与 Go 对照）

async function fetchWithRetry(url, max=5) {
  let delay = 200; // ms
  for (let i=1; i<=max; i++) {
    try { return await fetch(url); }
    catch (e) { if (i===max) throw e; }
    await new Promise(r => setTimeout(r, delay));
    delay = Math.min(delay * 2, 5000);
  }
}

func GetWithRetry(url string, max int) (*http.Response, error) {
  delay := 200 * time.Millisecond
  for i := 1; i <= max; i++ {
    resp, err := http.Get(url)
    if err == nil && resp.StatusCode < 500 { return resp, err }
    if i == max { return resp, err }
    time.Sleep(delay)
    if delay < 5*time.Second { delay *= 2 }
  }
  return nil, fmt.Errorf("retry failed")
}