import type {
RateLimiter,
RateLimitResult,
RateLimitConfig,
RateLimiterState,
} from "../types.js";
/**
* Leaky Bucket Rate Limiter
*
* Requests enter a queue that "leaks" at a constant rate.
* If the queue is full, requests are rejected.
* Provides very smooth, consistent output rate.
*/
export class LeakyBucketRateLimiter implements RateLimiter {
private queue: number[] = []; // timestamps of queued requests
private lastLeak: number;
private config: RateLimitConfig;
constructor(config: RateLimitConfig) {
this.config = config;
this.lastLeak = Date.now();
}
private leak(): void {
const now = Date.now();
const elapsed = (now - this.lastLeak) / 1000; // seconds
const leakCount = Math.floor(elapsed * this.config.refillRate);
if (leakCount > 0) {
// Remove leaked requests from queue
this.queue = this.queue.slice(leakCount);
this.lastLeak = now;
}
}
check(): RateLimitResult {
if (!this.config.enabled) {
return { allowed: true, headers: {} };
}
this.leak();
const queueSpace = this.config.bucketCapacity - this.queue.length;
const headers: Record<string, string> = {
"x-ratelimit-limit-requests": String(this.config.bucketCapacity),
"x-ratelimit-remaining-requests": String(queueSpace),
};
if (this.queue.length >= this.config.bucketCapacity) {
// Queue is full, calculate when space will be available
const timeToNextSlotSeconds = 1 / this.config.refillRate;
const timeToNextSlotMs = Math.ceil(timeToNextSlotSeconds * 1000);
return {
allowed: false,
retryAfter: Math.ceil(timeToNextSlotSeconds),
headers: {
...headers,
"retry-after": String(Math.ceil(timeToNextSlotSeconds)),
"retry-after-ms": String(timeToNextSlotMs),
},
};
}
// Add request to queue
this.queue.push(Date.now());
return { allowed: true, headers };
}
reset(): void {
this.queue = [];
this.lastLeak = Date.now();
}
getState(): RateLimiterState {
this.leak(); // Update before reporting
return {
strategy: "leaky-bucket",
queueLength: this.queue.length,
capacity: this.config.bucketCapacity,
};
}
updateConfig(config: Partial<RateLimitConfig>): void {
this.config = { ...this.config, ...config };
}
}
