code: func (h *RequestHeader) AddBytesK(key []byte, value string) {
  	h.Add(b2s(key), value)
  }
docs: // AddBytesK adds the given 'key: value' header.
  //
  // Multiple headers with the same key may be added with this function.
  // Use SetBytesK for setting a single header for the given key.