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/* SPDX-License-Identifier: MIT
*
* Copyright (C) 2017-2022 WireGuard LLC. All Rights Reserved.
*/
package ratelimiter
import (
"net/netip"
"sync"
"time"
)
const (
packetsPerSecond = 20
packetsBurstable = 5
garbageCollectTime = time.Second
packetCost = 1000000000 / packetsPerSecond
maxTokens = packetCost * packetsBurstable
)
type RatelimiterEntry struct {
mu sync.Mutex
lastTime time.Time
tokens int64
}
type Ratelimiter struct {
mu sync.RWMutex
timeNow func() time.Time
stopReset chan struct{} // send to reset, close to stop
table map[netip.Addr]*RatelimiterEntry
}
func (rate *Ratelimiter) Close() {
rate.mu.Lock()
defer rate.mu.Unlock()
if rate.stopReset != nil {
close(rate.stopReset)
}
}
func (rate *Ratelimiter) Init() {
rate.mu.Lock()
defer rate.mu.Unlock()
if rate.timeNow == nil {
rate.timeNow = time.Now
}
// stop any ongoing garbage collection routine
if rate.stopReset != nil {
close(rate.stopReset)
}
rate.stopReset = make(chan struct{})
rate.table = make(map[netip.Addr]*RatelimiterEntry)
stopReset := rate.stopReset // store in case Init is called again.
// Start garbage collection routine.
go func() {
ticker := time.NewTicker(time.Second)
ticker.Stop()
for {
select {
case _, ok := <-stopReset:
ticker.Stop()
if !ok {
return
}
ticker = time.NewTicker(time.Second)
case <-ticker.C:
if rate.cleanup() {
ticker.Stop()
}
}
}
}()
}
func (rate *Ratelimiter) cleanup() (empty bool) {
rate.mu.Lock()
defer rate.mu.Unlock()
for key, entry := range rate.table {
entry.mu.Lock()
if rate.timeNow().Sub(entry.lastTime) > garbageCollectTime {
delete(rate.table, key)
}
entry.mu.Unlock()
}
return len(rate.table) == 0
}
func (rate *Ratelimiter) Allow(ip netip.Addr) bool {
var entry *RatelimiterEntry
// lookup entry
rate.mu.RLock()
entry = rate.table[ip]
rate.mu.RUnlock()
// make new entry if not found
if entry == nil {
entry = new(RatelimiterEntry)
entry.tokens = maxTokens - packetCost
entry.lastTime = rate.timeNow()
rate.mu.Lock()
rate.table[ip] = entry
if len(rate.table) == 1 {
rate.stopReset <- struct{}{}
}
rate.mu.Unlock()
return true
}
// add tokens to entry
entry.mu.Lock()
now := rate.timeNow()
entry.tokens += now.Sub(entry.lastTime).Nanoseconds()
entry.lastTime = now
if entry.tokens > maxTokens {
entry.tokens = maxTokens
}
// subtract cost of packet
if entry.tokens > packetCost {
entry.tokens -= packetCost
entry.mu.Unlock()
return true
}
entry.mu.Unlock()
return false
}
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