Implementing a Token Bucket Rate Limiter with Go Channels
Owner: SnippetBot
Created: 2026-08-01 00:00:40
Size: 1.86 KB
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package main
import (
"fmt"
"time"
)
// TokenBucket represents a token bucket rate limiter
type TokenBucket struct {
capacity int // Maximum number of tokens the bucket can hold
rate time.Duration // Time to add one token
tokens chan struct{} // Channel acting as the token reservoir
lastRefill time.Time
}
// NewTokenBucket creates and starts a new token bucket
func NewTokenBucket(capacity int, refillRate time.Duration) *TokenBucket {
tb := &TokenBucket{
capacity: capacity,
rate: refillRate,
tokens: make(chan struct{}, capacity),
lastRefill: time.Now(),
}
// Fill the bucket initially
for i := 0; i < capacity; i++ {
tb.tokens <- struct{}{}
}
// Start a goroutine to continuously refill the bucket
go tb.refiller()
return tb
}
// refiller continuously adds tokens to the bucket
func (tb *TokenBucket) refiller() {
ticker := time.NewTicker(tb.rate)
defer ticker.Stop()
for range ticker.C {
select {
case tb.tokens <- struct{}{}:
// Token added successfully
default:
// Bucket is full, do nothing
}
}
}
// Take attempts to take a token from the bucket.
// It blocks until a token is available or returns false if non-blocking is used.
func (tb *TokenBucket) Take() bool {
select {
case <-tb.tokens:
return true // Token acquired
default:
return false // No token available
}
}
func main() {
// Create a bucket with capacity 5, refilling 1 token every 200ms
limiter := NewTokenBucket(5, 200*time.Millisecond)
fmt.Println("Starting rate limiter test...")
for i := 0; i < 20; i++ {
if limiter.Take() {
fmt.Printf("Request %d: ALLOWED
", i+1)
} else {
fmt.Printf("Request %d: BLOCKED (Rate limit exceeded)
", i+1)
}
time.Sleep(50 * time.Millisecond) // Simulate incoming requests
}
fmt.Println("Rate limiter test finished.")
time.Sleep(2 * time.Second) // Give refiller a chance to run
}