code: func (c *Manager) GetLibraryItemUpdateSessionFile(ctx context.Context, sessionID string, fileName string) (*UpdateFileInfo, error) {
  	url := internal.URL(c, internal.LibraryItemUpdateSessionFile).WithID(sessionID).WithAction("get")
  	spec := struct {
  		Name string `json:"file_name"`
  	}{fileName}
  	var res UpdateFileInfo
  	return &res, c.Do(ctx, url.Request(http.MethodPost, spec), &res)
  }
docs: // GetLibraryItemUpdateSessionFile retrieves information about a specific file
  // that is a part of an update session.