/**
 * A streaming body that yields what `body` does, with `project` applied to
 * each value the router sends as a line of JSON: that is any but strings and
 * binary data, which it sends as they are.
 *
 * Nothing is read from `body` before the result is, which it may never be:
 * the router stops a body it does not send (e.g. for a HEAD request) unread.
 */
export declare function mapStreamingBody(body: any, project: (value: unknown) => unknown): any;