code: func GzipHandler(h http.Handler) http.Handler {
  	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  		if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") || w.Header().Get("Content-Encoding") != "" || w.Header().Get("Vary") != "" {
  			h.ServeHTTP(w, r)
  			return
  		}
  		w.Header().Set("Content-Encoding", "gzip")
  		w.Header().Set("Vary", "Accept-Encoding")
  		gz := gzip.NewWriter(w)
  		defer gz.Close()
  		h.ServeHTTP(&gzipResponseWriter{
  			Writer:         gz,
  			ResponseWriter: w,
  		}, r)
  	})
  }
docs: // Gzips response body if the request says it'll allow it.