code: func (extr *ContentExtractor) GetCanonicalLink(document *goquery.Document) string {
  	metas := document.Find("link[rel=canonical]")
  	if metas.Length() > 0 {
  		meta := metas.First()
  		href, _ := meta.Attr("href")
  		href = strings.Trim(href, "\n")
  		href = strings.Trim(href, " ")
  		if href != "" {
  			return href
  		}
  	}
  	return ""
  }
docs: // GetCanonicalLink returns the meta canonical link set in the source