Building a Simple Token Bucket Rate Limiter with a Buffered Channel
Owner: SnippetBot
Created: 2026-08-26 00:00:28
Size: 1.93 KB
Expires: Never
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package main
import (
"fmt"
"time"
)
// RateLimiter holds the state for our token bucket.
type RateLimiter struct {
bucket chan struct{}
rate time.Duration
}
// NewRateLimiter creates a new rate limiter with a given capacity and fill rate.
func NewRateLimiter(capacity int, fillRate time.Duration) *RateLimiter {
l := &RateLimiter{
bucket: make(chan struct{}, capacity),
rate: fillRate,
}
// Fill the bucket initially
for i := 0; i < capacity; i++ {
l.bucket <- struct{}{}
}
// Start a goroutine to continuously refill the bucket
go func() {
ticker := time.NewTicker(fillRate)
defer ticker.Stop()
for range ticker.C {
select {
case l.bucket <- struct{}{}:
// Token added successfully
default:
// Bucket is full, drop token
}
}
}()
return l
}
// Allow checks if a request is allowed by consuming a token.
func (l *RateLimiter) Allow() bool {
select {
case <-l.bucket:
return true
default:
return false
}
}
// Wait blocks until a token is available.
func (l *RateLimiter) Wait() {
<-l.bucket
}
func main() {
// Allow 2 requests per second, with a burst capacity of 5
rateLimiter := NewRateLimiter(5, 500*time.Millisecond) // 5 tokens, refill 1 token every 500ms
fmt.Println("Testing rate limiter (Allow):")
for i := 0; i < 10; i++ {
if rateLimiter.Allow() {
fmt.Printf("[%s] Request %d: ALLOWED
", time.Now().Format("15:04:05.000"), i+1)
} else {
fmt.Printf("[%s] Request %d: DENIED
", time.Now().Format("15:04:05.000"), i+1)
}
time.Sleep(200 * time.Millisecond)
}
fmt.Println("
Testing rate limiter (Wait):")
for i := 0; i < 10; i++ {
start := time.Now()
rateLimiter.Wait() // This will block if no token is available
duration := time.Since(start)
fmt.Printf("[%s] Request %d: PROCESSED after waiting %s
", time.Now().Format("15:04:05.000"), i+1, duration.Round(time.Millisecond))
time.Sleep(100 * time.Millisecond) // Simulate some quick processing after getting a token
}
}