import type {
RateLimiter,
RateLimitResult,
RateLimitConfig,
RateLimiterState,
} from "../types.js";
/**
* Sliding Window Rate Limiter
*
* Tracks individual request timestamps and counts requests in a sliding window.
* More accurate than fixed window but uses more memory.
*/
export class SlidingWindowRateLimiter implements RateLimiter {
private timestamps: number[] = [];
private config: RateLimitConfig;
constructor(config: RateLimitConfig) {
this.config = config;
}
check(): RateLimitResult {
if (!this.config.enabled) {
return { allowed: true, headers: {} };
}
const now = Date.now();
const windowStart = now - this.config.windowMs;
// Remove expired timestamps
this.timestamps = this.timestamps.filter((t) => t > windowStart);
const currentCount = this.timestamps.length;
const remaining = Math.max(0, this.config.maxRequests - currentCount - 1);
// Calculate when the oldest request will expire
const oldestTimestamp = this.timestamps[0];
const resetInSeconds = oldestTimestamp
? Math.ceil((oldestTimestamp + this.config.windowMs - now) / 1000)
: Math.ceil(this.config.windowMs / 1000);
const headers: Record<string, string> = {
"x-ratelimit-limit-requests": String(this.config.maxRequests),
"x-ratelimit-remaining-requests": String(Math.max(0, remaining)),
"x-ratelimit-reset-requests": `${resetInSeconds}s`,
};
if (currentCount >= this.config.maxRequests) {
const resetInMs = oldestTimestamp
? oldestTimestamp + this.config.windowMs - now
: this.config.windowMs;
return {
allowed: false,
retryAfter: resetInSeconds,
headers: {
...headers,
"retry-after": String(resetInSeconds),
"retry-after-ms": String(Math.max(0, resetInMs)),
},
};
}
// Record this request
this.timestamps.push(now);
return { allowed: true, headers };
}
reset(): void {
this.timestamps = [];
}
getState(): RateLimiterState {
const now = Date.now();
const windowStart = now - this.config.windowMs;
const activeCount = this.timestamps.filter((t) => t > windowStart).length;
return {
strategy: "sliding-window",
currentCount: activeCount,
maxCount: this.config.maxRequests,
windowStartMs: windowStart,
};
}
updateConfig(config: Partial<RateLimitConfig>): void {
this.config = { ...this.config, ...config };
}
}
