//?core/limit/periodlimit.go
const?periodScript?=?`local?limit?=?tonumber(ARGV[1])
local?window?=?tonumber(ARGV[2])
local?current?=?redis.call("INCRBY",?KEYS[1],?1)
if?current?==?1?then
????redis.call("expire",?KEYS[1],?window)
end
if?current?<?limit?then
????return?1
elseif?current?==?limit?then
????return?2
else
????return?0
end`

type?(
????//?PeriodOption?defines?the?method?to?customize?a?PeriodLimit.
????PeriodOption?func(l?*PeriodLimit)
????//?A?PeriodLimit?is?used?to?limit?requests?during?a?period?of?time.
????PeriodLimit?struct?{
????????period?????int??//?窗口大小，單位?s
????????quota??????int??//?請求上限
????????limitStore?*redis.Redis
????????keyPrefix??string???//?key?前綴
????????align??????bool
????}
)
//?NewPeriodLimit?returns?a?PeriodLimit?with?given?parameters.
func?NewPeriodLimit(period,?quota?int,?limitStore?*redis.Redis,?keyPrefix?string,
????opts?...PeriodOption)?*PeriodLimit?{
????limiter?:=?&PeriodLimit{
????????period:?????period,
????????quota:??????quota,
????????limitStore:?limitStore,
????????keyPrefix:??keyPrefix,
????}
????for?_,?opt?:=?range?opts?{
????????opt(limiter)
????}
????return?limiter
}

//?key?就是需要被限制的資源標(biāo)識
func?(h?*PeriodLimit)?Take(key?string)?(int,?error)?{
????return?h.TakeCtx(context.Background(),?key)
}
//?TakeCtx?requests?a?permit?with?context,?it?returns?the?permit?state.
func?(h?*PeriodLimit)?TakeCtx(ctx?context.Context,?key?string)?(int,?error)?{
????resp,?err?:=?h.limitStore.EvalCtx(ctx,?periodScript,?[]string{h.keyPrefix?+?key},?[]string{
????????strconv.Itoa(h.quota),
????????strconv.Itoa(h.calcExpireSeconds()),
????})
????if?err?!=?nil?{
????????return?Unknown,?err
????}
????code,?ok?:=?resp.(int64)
????if?!ok?{
????????return?Unknown,?ErrUnknownCode
????}
????switch?code?{
????case?internalOverQuota:?//?超過上限
????????return?OverQuota,?nil
????case?internalAllowed:???//?未超過，允許訪問
????????return?Allowed,?nil
????case?internalHitQuota:??//?正好達(dá)到限流上限
????????return?HitQuota,?nil
????default:
????????return?Unknown,?ErrUnknownCode
????}
}