make a proxy to convert http download file name in express

express_download_name_proxy.js

var request = require('request');

function setDownloadName(req, res, fileName) {
    var userAgent = (req.headers['user-agent'] || '').toLowerCase();
    if (userAgent.indexOf('chrome') > -1) {
        res.setHeader('Content-Disposition', 'attachment; filename=' + encodeURIComponent(fileName));
    } else if (userAgent.indexOf('firefox') >-1) {
        res.setHeader('Content-Disposition', 'attachment; filename*="utf8\'\'' + encodeURIComponent(fileName) + '"');
    } else {
        res.setHeader('Content-Disposition', 'attachment; filename=' + new Buffer(fileName).toString('binary'));
    }
}
/**
 * make a proxy to convert http download file name
 *  eg.
 *      if browser request: /download-proxy?url=http://domain/not-readable-file.png&name=readable-file.png,
 *      then will get a download attachment named readable-file.png
 */
function downloadProxy(req, res) {
    req.setEncoding('utf8');

    var url = req.query.url;
    var name = req.query.name;

    setDownloadName(req, res, name);

    var stream = request.get(url).pipe(res);

    stream.on('error', function (err) {
        res.send(500, err);
    });
}

module.exports = function (app) {
    app.get('/download-proxy', downloadProxy);
};

This won't work unless res/req are global vars, right?