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Token Bucket Rate Limiter in Go

Implement a token bucket rate limiter that refills at a configured rate and allows a burst, guarding handlers against traffic spikes.

GoResilience

Code

snippet
package limiter

import (
	"sync"
	"time"
)

type TokenBucket struct {
	mu         sync.Mutex
	capacity   float64
	tokens     float64
	refillRate float64
	last       time.Time
}

func NewTokenBucket(capacity, refillPerSecond float64) *TokenBucket {
	return &TokenBucket{
		capacity:   capacity,
		tokens:     capacity,
		refillRate: refillPerSecond,
		last:       time.Now(),
	}
}

func (b *TokenBucket) Allow(cost float64) bool {
	b.mu.Lock()
	defer b.mu.Unlock()
	now := time.Now()
	b.tokens = min(b.capacity, b.tokens+now.Sub(b.last).Seconds()*b.refillRate)
	b.last = now
	if b.tokens >= cost {
		b.tokens -= cost
		return true
	}
	return false
}

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