code: func SerializeMetadataHeader(meta map[string]string) string {
  	header := ""
  	for key, value := range meta {
  		valueBase64 := base64.StdEncoding.EncodeToString([]byte(value))
  		header += key + " " + valueBase64 + ","
  	}
  
  	// Remove trailing comma
  	if len(header) > 0 {
  		header = header[:len(header)-1]
  	}
  
  	return header
  }
docs: // SerializeMetadataHeader serializes a map of strings into the Upload-Metadata
  // header format used in the response for HEAD requests.
  // e.g. Upload-Metadata: name bHVucmpzLnBuZw==,type aW1hZ2UvcG5n