constructor({permanentMaxAge, getSubdirectoryURL}) {
        /** @private */
        this.permanentMaxAge = permanentMaxAge;

        this.getSubdirectoryURL = getSubdirectoryURL;

        /** @private */
        this.router = express.Router();
        /** @private @type {Object.<string, {fromRegex: RegExp, to: string, options: {permanent: boolean}}>} */
        this.redirects = {};

        this.handleRequest = this.handleRequest.bind(this);
    }
@param {object} config
@param {number} config.permanentMaxAge
@param {function} config.getSubdirectoryURL