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Basically, fakelag was counting the time imposed by its own sleeps as though the user had themselves paused for that amount of time. Therefore, if a user sent a large number of consecutive commands, every other command would pause for the expected throttle interval, but the subsequent command would be processed instantly (you'd get two back-to-back commands). This resulted in throttled users being able to send at double the expected rate.
95 lines
2.5 KiB
Go
95 lines
2.5 KiB
Go
// Copyright (c) 2018 Shivaram Lingamneni <slingamn@cs.stanford.edu>
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// released under the MIT license
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package irc
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import (
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"time"
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)
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// fakelag is a system for artificially delaying commands when a user issues
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// them too rapidly
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type FakelagState uint
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const (
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// initially, the client is "bursting" and can send n commands without
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// encountering fakelag
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FakelagBursting FakelagState = iota
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// after that, they're "throttled" and we sleep in between commands until
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// they're spaced sufficiently far apart
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FakelagThrottled
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)
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// this is intentionally not threadsafe, because it should only be touched
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// from the loop that accepts the client's input and runs commands
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type Fakelag struct {
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window time.Duration
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burstLimit uint
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throttleMessagesPerWindow uint
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cooldown time.Duration
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nowFunc func() time.Time
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sleepFunc func(time.Duration)
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state FakelagState
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burstCount uint // number of messages sent in the current burst
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lastTouch time.Time
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}
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func NewFakelag(window time.Duration, burstLimit uint, throttleMessagesPerWindow uint, cooldown time.Duration) *Fakelag {
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return &Fakelag{
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window: window,
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burstLimit: burstLimit,
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throttleMessagesPerWindow: throttleMessagesPerWindow,
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cooldown: cooldown,
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nowFunc: time.Now,
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sleepFunc: time.Sleep,
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state: FakelagBursting,
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}
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}
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// register a new command, sleep if necessary to delay it
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func (fl *Fakelag) Touch() {
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if fl == nil {
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return
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}
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now := fl.nowFunc()
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// XXX if lastTouch.IsZero(), treat it as "very far in the past", which is fine
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elapsed := now.Sub(fl.lastTouch)
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fl.lastTouch = now
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if fl.state == FakelagBursting {
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// determine if the previous burst is over
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if elapsed > fl.cooldown {
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fl.burstCount = 0
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}
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fl.burstCount++
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if fl.burstCount > fl.burstLimit {
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// reset burst window for next time
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fl.burstCount = 0
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// transition to throttling
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fl.state = FakelagThrottled
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// continue to throttling logic
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} else {
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return
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}
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}
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if fl.state == FakelagThrottled {
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if elapsed > fl.cooldown {
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// let them burst again
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fl.state = FakelagBursting
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return
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}
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// space them out by at least window/messagesperwindow
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sleepDuration := time.Duration((int64(fl.window) / int64(fl.throttleMessagesPerWindow)) - int64(elapsed))
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if sleepDuration > 0 {
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fl.sleepFunc(sleepDuration)
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// the touch time should take into account the time we slept
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fl.lastTouch = fl.nowFunc()
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}
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}
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}
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