import type {
RateLimiter,
RateLimitResult,
RateLimitConfig,
RateLimiterState,
} from "../types.js";
/**
* Fixed Window Rate Limiter
*
* Allows N requests per fixed time window. Window resets completely when it expires.
* Simple but can allow 2x burst at window boundaries.
*/
export class FixedWindowRateLimiter implements RateLimiter {
private requestCount = 0;
private windowStart = Date.now();
private config: RateLimitConfig;
constructor(config: RateLimitConfig) {
this.config = config;
}
check(): RateLimitResult {
if (!this.config.enabled) {
return { allowed: true, headers: {} };
}
const now = Date.now();
// Reset window if expired
if (now - this.windowStart >= this.config.windowMs) {
this.windowStart = now;
this.requestCount = 0;
}
this.requestCount++;
const remaining = Math.max(0, this.config.maxRequests - this.requestCount);
const resetInSeconds = Math.ceil(
(this.config.windowMs - (now - this.windowStart)) / 1000,
);
const headers: Record<string, string> = {
"x-ratelimit-limit-requests": String(this.config.maxRequests),
"x-ratelimit-remaining-requests": String(remaining),
"x-ratelimit-reset-requests": `${resetInSeconds}s`,
};
if (this.requestCount > this.config.maxRequests) {
const resetInMs = this.config.windowMs - (now - this.windowStart);
return {
allowed: false,
retryAfter: resetInSeconds,
headers: {
...headers,
"retry-after": String(resetInSeconds),
"retry-after-ms": String(Math.max(0, resetInMs)),
},
};
}
return { allowed: true, headers };
}
reset(): void {
this.requestCount = 0;
this.windowStart = Date.now();
}
getState(): RateLimiterState {
return {
strategy: "fixed-window",
currentCount: this.requestCount,
maxCount: this.config.maxRequests,
windowStartMs: this.windowStart,
};
}
updateConfig(config: Partial<RateLimitConfig>): void {
this.config = { ...this.config, ...config };
// Reset if window size changed
if (config.windowMs !== undefined) {
this.reset();
}
}
}
