Express endpoint to retrieve file from MongoDB GridFS

file.js

exports.get = function(req, res) {
    var db = new mongo.Db('downloadr', new mongo.Server("127.0.0.1", 27017, {}), {safe: false, strict: false});

    db.open(function (err) {
        if (err) return handleError(err);
        var gfs = Grid(db, mongo);

        gfs
        // create a read stream from gfs...
        .createReadStream({ _id: req.param('fileId') })
        .on('error', function() {
            res.send(500, 'failed to retrieve file.');
        })
        // and pipe it to Express' response
        .pipe(res);
    });
};