//?core/limit/tokenlimit.go
//?生成?token?速率
script?=?`local?rate?=?tonumber(ARGV[1])
//?通容量
local?capacity?=?tonumber(ARGV[2])
//?當前時間戳
local?now?=?tonumber(ARGV[3])
//?請求數(shù)量
local?requested?=?tonumber(ARGV[4])
//?需要多少秒才能把桶填滿
local?fill_time?=?capacity/rate
//?向下取整，ttl?為填滿時間?2?倍
local?ttl?=?math.floor(fill_time*2)
//?當前桶剩余容量，如果為?nil，說明第一次使用，賦值為桶最大容量
local?last_tokens?=?tonumber(redis.call("get",?KEYS[1]))
if?last_tokens?==?nil?then
????last_tokens?=?capacity
end
//?上次請求時間戳，如果為?nil?則賦值?0
local?last_refreshed?=?tonumber(redis.call("get",?KEYS[2]))
if?last_refreshed?==?nil?then
????last_refreshed?=?0
end
//?距離上一次請求的時間跨度
local?delta?=?math.max(0,?now-last_refreshed)
//?距離上一次請求的時間跨度能生成的?token?數(shù)量和桶內剩余?token?數(shù)量的和
//?與桶容量比較，取二者的小值
local?filled_tokens?=?math.min(capacity,?last_tokens+(delta*rate))
//?判斷請求數(shù)量和桶內?token?數(shù)量的大小
local?allowed?=?filled_tokens?>=?requested
//?被請求消耗掉之后，更新剩余?token?數(shù)量
local?new_tokens?=?filled_tokens
if?allowed?then
????new_tokens?=?filled_tokens?-?requested
end
//?更新?redis?token
redis.call("setex",?KEYS[1],?ttl,?new_tokens)
//?更新?redis?刷新時間
redis.call("setex",?KEYS[2],?ttl,?now)
return?allowed`

//?A?TokenLimiter?controls?how?frequently?events?are?allowed?to?happen?with?in?one?second.
type?TokenLimiter?struct?{
????//?生成?token?速率
????rate???????????int
????//?桶容量
????burst??????????int
????store??????????*redis.Redis
????//?桶?key
????tokenKey???????string
????//?桶刷新時間?key
????timestampKey???string
????rescueLock?????sync.Mutex
????//?redis?健康標識
????redisAlive?????uint32
????//?redis?健康監(jiān)控啟動狀態(tài)
????monitorStarted?bool
????//?內置單機限流器
????rescueLimiter??*xrate.Limiter
}
//?NewTokenLimiter?returns?a?new?TokenLimiter?that?allows?events?up?to?rate?and?permits
//?bursts?of?at?most?burst?tokens.
func?NewTokenLimiter(rate,?burst?int,?store?*redis.Redis,?key?string)?*TokenLimiter?{
????tokenKey?:=?fmt.Sprintf(tokenFormat,?key)
????timestampKey?:=?fmt.Sprintf(timestampFormat,?key)
????return?&TokenLimiter{
????????rate:??????????rate,
????????burst:?????????burst,
????????store:?????????store,
????????tokenKey:??????tokenKey,
????????timestampKey:??timestampKey,
????????redisAlive:????1,
????????rescueLimiter:?xrate.NewLimiter(xrate.Every(time.Second/time.Duration(rate)),?burst),
????}
}

//?Allow?is?shorthand?for?AllowN(time.Now(),?1).
func?(lim?*TokenLimiter)?Allow()?bool?{
????return?lim.AllowN(time.Now(),?1)
}
//?AllowCtx?is?shorthand?for?AllowNCtx(ctx,time.Now(),?1)?with?incoming?context.
func?(lim?*TokenLimiter)?AllowCtx(ctx?context.Context)?bool?{
????return?lim.AllowNCtx(ctx,?time.Now(),?1)
}
//?AllowN?reports?whether?n?events?may?happen?at?time?now.
//?Use?this?method?if?you?intend?to?drop?/?skip?events?that?exceed?the?rate.
//?Otherwise,?use?Reserve?or?Wait.
func?(lim?*TokenLimiter)?AllowN(now?time.Time,?n?int)?bool?{
????return?lim.reserveN(context.Background(),?now,?n)
}
//?AllowNCtx?reports?whether?n?events?may?happen?at?time?now?with?incoming?context.
//?Use?this?method?if?you?intend?to?drop?/?skip?events?that?exceed?the?rate.
//?Otherwise,?use?Reserve?or?Wait.
func?(lim?*TokenLimiter)?AllowNCtx(ctx?context.Context,?now?time.Time,?n?int)?bool?{
????return?lim.reserveN(ctx,?now,?n)
}

func?(lim?*TokenLimiter)?reserveN(ctx?context.Context,?now?time.Time,?n?int)?bool?{
????//?判斷?Redis?健康狀態(tài)，如果?Redis?故障，則使用進程內限流器
????if?atomic.LoadUint32(&lim.redisAlive)?==?0?{
????????return?lim.rescueLimiter.AllowN(now,?n)
????}
????//?執(zhí)行限流腳本
????resp,?err?:=?lim.store.EvalCtx(ctx,
????????script,
????????[]string{
????????????lim.tokenKey,
????????????lim.timestampKey,
????????},
????????[]string{
????????????strconv.Itoa(lim.rate),
????????????strconv.Itoa(lim.burst),
????????????strconv.FormatInt(now.Unix(),?10),
????????????strconv.Itoa(n),
????????})
????//?redis?allowed?==?false
????//?Lua?boolean?false?->?r?Nil?bulk?reply
????if?err?==?redis.Nil?{
????????return?false
????}
????if?errors.Is(err,?context.DeadlineExceeded)?||?errors.Is(err,?context.Canceled)?{
????????logx.Errorf("fail?to?use?rate?limiter:?%s",?err)
????????return?false
????}
????if?err?!=?nil?{
????????logx.Errorf("fail?to?use?rate?limiter:?%s,?use?in-process?limiter?for?rescue",?err)
????????//?如果有異常的話，會啟動進程內限流
????????lim.startMonitor()
????????return?lim.rescueLimiter.AllowN(now,?n)
????}
????code,?ok?:=?resp.(int64)
????if?!ok?{
????????logx.Errorf("fail?to?eval?redis?script:?%v,?use?in-process?limiter?for?rescue",?resp)
????????lim.startMonitor()
????????return?lim.rescueLimiter.AllowN(now,?n)
????}
????//?redis?allowed?==?true
????//?Lua?boolean?true?->?r?integer?reply?with?value?of?1
????return?code?==?1
}

func?(lim?*TokenLimiter)?startMonitor()?{
????lim.rescueLock.Lock()
????defer?lim.rescueLock.Unlock()
????//?需要加鎖保護，如果程序已經(jīng)啟動了，直接返回，不要重復啟動
????if?lim.monitorStarted?{
????????return
????}
????lim.monitorStarted?=?true
????atomic.StoreUint32(&lim.redisAlive,?0)
????go?lim.waitForRedis()
}
func?(lim?*TokenLimiter)?waitForRedis()?{
????ticker?:=?time.NewTicker(pingInterval)
????//?更新監(jiān)控進程的狀態(tài)
????defer?func()?{
????????ticker.Stop()
????????lim.rescueLock.Lock()
????????lim.monitorStarted?=?false
????????lim.rescueLock.Unlock()
????}()
????for?range?ticker.C?{
????????//?對?redis?進行健康監(jiān)測，如果?redis?服務恢復了
????????//?則更新?redisAlive?標識，并退出?goroutine
????????if?lim.store.Ping()?{
????????????atomic.StoreUint32(&lim.redisAlive,?1)
????????????return
????????}
????}
}