export interface ETagOptions {
    /** Emit a weak validator (`W/"…"`). Default `true` - it's a content hash, not a byte-for-byte promise. */
    readonly weak?: boolean;
    /** Maximum response bytes to hash. Default `1_000_000`; larger responses pass through unchanged. */
    readonly maxBytes?: number;
}
/**
 * A {@link defineRouterPlugin} plugin that adds a content-hash `ETag` to `GET` `200` responses and returns
 * **`304 Not Modified`** when the client's `If-None-Match` matches - saving bandwidth on unchanged
 * responses. Built on the portable `onResponseBody` tier: the hook receives the final
 * framework-serialized bytes on every runtime with nothing drained, so the middleware stays on
 * Node's direct writer. Handler-returned raw `Response`s (streams, proxied fetches) use a capped,
 * replaying fallback so oversized bodies remain intact. Idempotent.
 */
export declare function etag(options?: ETagOptions): import("@nifrajs/core").IdentityPlugin<never>;
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