How to use the pn/fs.createReadStream function in pn

return createServer((req, res) => {
        const [, fixture, query] = /^\/([^?]+)(\?.*)?$/.exec(req.url);

        const headers = { "Content-Type": "text/html" };
        if (query === "?charset=csiso88598e") {
          headers["Content-Type"] = "text/html;charset=csiso88598e";
        }

        res.writeHead(200, headers);
        fs.createReadStream(fixturePath(fixture)).pipe(res);
      }).then(s => {
        server = s;