84 lines
3.4 KiB
Go
84 lines
3.4 KiB
Go
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// Copyright (c) 2016 Uber Technologies, Inc.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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package utils
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import (
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"sync"
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"time"
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)
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// RateLimiter is a filter used to check if a message that is worth itemCost units is within the rate limits.
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type RateLimiter interface {
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CheckCredit(itemCost float64) bool
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}
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type rateLimiter struct {
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sync.Mutex
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creditsPerSecond float64
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balance float64
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maxBalance float64
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lastTick time.Time
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timeNow func() time.Time
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}
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// NewRateLimiter creates a new rate limiter based on leaky bucket algorithm, formulated in terms of a
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// credits balance that is replenished every time CheckCredit() method is called (tick) by the amount proportional
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// to the time elapsed since the last tick, up to max of creditsPerSecond. A call to CheckCredit() takes a cost
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// of an item we want to pay with the balance. If the balance exceeds the cost of the item, the item is "purchased"
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// and the balance reduced, indicated by returned value of true. Otherwise the balance is unchanged and return false.
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//
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// This can be used to limit a rate of messages emitted by a service by instantiating the Rate Limiter with the
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// max number of messages a service is allowed to emit per second, and calling CheckCredit(1.0) for each message
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// to determine if the message is within the rate limit.
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//
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// It can also be used to limit the rate of traffic in bytes, by setting creditsPerSecond to desired throughput
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// as bytes/second, and calling CheckCredit() with the actual message size.
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func NewRateLimiter(creditsPerSecond, maxBalance float64) RateLimiter {
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return &rateLimiter{
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creditsPerSecond: creditsPerSecond,
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balance: maxBalance,
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maxBalance: maxBalance,
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lastTick: time.Now(),
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timeNow: time.Now}
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}
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func (b *rateLimiter) CheckCredit(itemCost float64) bool {
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b.Lock()
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defer b.Unlock()
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// calculate how much time passed since the last tick, and update current tick
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currentTime := b.timeNow()
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elapsedTime := currentTime.Sub(b.lastTick)
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b.lastTick = currentTime
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// calculate how much credit have we accumulated since the last tick
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b.balance += elapsedTime.Seconds() * b.creditsPerSecond
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if b.balance > b.maxBalance {
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b.balance = b.maxBalance
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}
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// if we have enough credits to pay for current item, then reduce balance and allow
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if b.balance >= itemCost {
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b.balance -= itemCost
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return true
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}
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return false
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}
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