code: function(foundInCacheSeed, fullPath, data, compiled, next) {
              if (foundInCacheSeed) {
                debugLog("Found resource in cache seed: " + cacheUrl)
                if (data) {
                  async.waterfall([
                    function(next) {
                      if (url.match(/\.css$/)) {
                        processStylesheet(rootUrl, version, url, data, timeout,
                          onCacheMiss, next);
                      } else {
                        next(null, data);
                      }
                    },
                  ], function(err, data) {
                    if (err) return next(err);
                    writeToFile(filePath, data, function(err, fullPath) {
                      next(err, fullPath, data, compiled, null);
                    });
                  });
                } else {
                  next(null, fullPath, data, compiled, null);
                }
              } else {
                getServerResource(next);
              }
            }
docs: get from server or write to cache if necessary