安全重试与退避策略（指数退避/抖动/幂等）最佳实践

一、退避与抖动function backoff(baseMs: number, attempt: number, maxMs: number): number { const exp = Math.min(maxMs, baseMs * Math.pow(2, attempt)) const jitter = Math.random() * exp * 0.5 return Math.floor(exp * 0.75 + jitter) } 二、幂等与计数头type Req = { headers: Record<string, string | undefined> } type Res = { setHeader: (k: string, v: string) => void; status: (n: number) => Res; end: (b?: string) => void } function validIdem(k: string): boolean { return /^[A-Za-z0-9_\-\.]{8,128}$/.test(k) } 三、重试封装type Task = () => Promise<Response> async function safeRetry(task: Task, attempts: number, baseMs: number, maxMs: number, onAttempt?: (i: number, delayMs: number) => void): Promise<Response> { let last: any for (let i = 0; i < attempts; i++) { try { const r = await task() if (r.status < 500 && r.status !== 429) return r const retryAfter = Number(r.headers.get('Retry-After') || '0') const delay = retryAfter > 0 ? retryAfter * 1000 : backoff(baseMs, i, maxMs) onAttempt?.(i + 1, delay) await new Promise(res => setTimeout(res, delay)) last = r } catch (e) { const delay = backoff(baseMs, i, maxMs) onAttempt?.(i + 1, delay) await new Promise(res => setTimeout(res, delay)) last = e } } throw last } 四、服务端协同function setRetryHeaders(res: Res, retryAfterSec: number, count: number) { res.setHeader('Retry-After', String(retryAfterSec)) res.setHeader('X-Retry-Count', String(count)) } 五、整合与验收指数退避与抖动限制雪崩；遵循`Retry-After`优先；最大延迟与尝试次数受控。幂等键校验与计数头可用；与断路器/速率限制协同避免级联失败。审计记录包含尝试次数与延迟；失败策略清晰（>=500或429重试）。