import type { Plugin } from './app';
import type { Context } from './http';
/** A rate-limit counter store: record a hit, report the count + reset time. */
export interface RateLimitStore {
    /**
     * Record a hit for `key` in a `windowMs` window; returns the running count and
     * milliseconds until the window resets.
     *
     * @param key - the bucket key identifying the client
     * @param windowMs - length of the fixed window, in milliseconds
     */
    hit(key: string, windowMs: number): {
        count: number;
        resetMs: number;
    } | Promise<{
        count: number;
        resetMs: number;
    }>;
}
/**
 * In-memory fixed-window counter, one window per key — the default
 * {@link rateLimit} store. Counts live in a single process and vanish on
 * restart, so it only limits per instance; use a shared store (e.g. Redis)
 * to enforce one limit across several instances.
 *
 * @returns a {@link RateLimitStore} backed by an in-process map
 */
export declare function memoryRateLimitStore(): RateLimitStore;
/** Options for {@link rateLimit}. */
export interface RateLimitOptions {
    /** Max requests permitted per window; the next request in the same window gets `429`. Required. */
    limit: number;
    /** Length of the fixed window, in milliseconds; the count resets once it elapses. Required. */
    windowMs: number;
    /** Bucket key for a request. Default: the `X-Forwarded-For` header, else `"global"`. */
    keyBy?: (ctx: Context) => string;
    /** Counter store. Default: an in-memory fixed window. */
    store?: RateLimitStore;
}
/**
 * Plugin: limit how many requests a client may make in a time window, replying
 * `429 Too Many Requests` (with `Retry-After`) once the limit is exceeded. Every
 * response carries `X-RateLimit-Limit`/`X-RateLimit-Remaining`. Bucket clients
 * with `keyBy` (default: the `X-Forwarded-For` header); swap the in-memory
 * counter for a shared `store` (e.g. Redis) in a multi-instance deployment.
 *
 * ```ts
 * const app = await createApp({
 *   plugins: [rateLimit({ limit: 100, windowMs: 60_000 })],
 * })
 * ```
 *
 * @param options - `limit` and `windowMs` are required; `keyBy` and `store`
 *   default to per-`X-Forwarded-For` bucketing and an in-memory fixed window
 * @returns a plugin that enforces the limit with `429` and rate-limit headers
 */
export declare function rateLimit(options: RateLimitOptions): Plugin;
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