code: func SortLogger(outputLogger log.Logger, keys ...string) log.Logger {
  	indices := make(map[string]int, len(keys))
  	for i, k := range keys {
  		indices[k] = i
  	}
  	return log.LoggerFunc(func(keyvals ...interface{}) error {
  		sortKeyvals(indices, keyvals)
  		return outputLogger.Log(keyvals...)
  	})
  }
docs: // Provides a logger that sorts key-values with keys in keys before other key-values