code: func (s *IssuesService) ListLabelsByIssue(ctx context.Context, owner string, repo string, number int, opt *ListOptions) ([]*Label, *Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/issues/%d/labels", owner, repo, number)
  	u, err := addOptions(u, opt)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	// TODO: remove custom Accept header when this API fully launches.
  	req.Header.Set("Accept", mediaTypeLabelDescriptionSearchPreview)
  
  	var labels []*Label
  	resp, err := s.client.Do(ctx, req, &labels)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return labels, resp, nil
  }
docs: // ListLabelsByIssue lists all labels for an issue.
  //
  // GitHub API docs: https://developer.github.com/v3/issues/labels/#list-labels-on-an-issue