MEAN : Serve File from GridFs

Question

I am using MEAN stack and I am trying to serve a file stored using Mongo GridFs.

This is the code I have tried so far.

exports.getFile = function(req, res) {
  var fileId = req.params.fileId;

  gfs.findOne({ _id: fileId }, function (err, file) {
    if (err) { res.status(500).send(err) }
    console.log('file meta', file);
    res.header("Content-Type", file.contentType);

    var readstream = gfs.createReadStream({
      filename: file.filename
    });
    //error handling, e.g. file does not exist
    readstream.on('error', function (err) {
      console.log('An error occurred!', err);
      throw err;
    });
    readstream.on('close', function(file) {
      console.log('file content', file);
    });
    readstream.pipe(res);
  });
};

This is what I get on console:

file meta { _id: 566c0b6ddfb625ae52ce99c7,
  filename: 'profile_picture_by_kyo_tux-d4hrimy.png',
  contentType: 'binary/octet-stream',
  length: 0,
  chunkSize: 261120,
  uploadDate: Sat Dec 12 2015 17:26:29 GMT+0530 (IST),
  aliases: null,
  metadata: null,
  md5: 'd41d8cd98f00b204e9800998ecf8427e' }
file content undefined
GET /api/users/file/566c0b6ddfb625ae52ce99c7 200 9ms

I am not getting the file on webpage. What am I doing wrong?