code: function xfer (res, files, cb) {
      var file = files.shift();
  
      if (!file) {
          return cb(null);
      }
  
      fs.createReadStream(file
      ).on("data", function (chunk) {
          res.write(chunk);
      }).on("error", cb
      ).on("close", function xferClose () {
          xfer(res, files, cb);
      });
  }
docs: Implementation of the actual file transfer.