code: func (p *Pget) CheckMirrors(ctx context.Context, url string, ch *Ch) {
  
  	res, err := ctxhttp.Head(ctx, http.DefaultClient, url)
  	if err != nil {
  		ch.Err <- errors.Wrap(err, "failed to head request: "+url)
  		return
  	}
  
  	if res.Header.Get("Accept-Ranges") != "bytes" {
  		ch.Err <- errors.Errorf("not supported range access: %s", url)
  		return
  	}
  
  	// To perform with the correct "range access"
  	// get the last url in the redirect
  	_url := res.Request.URL.String()
  	if isNotLastURL(_url, url) {
  		p.TargetURLs = append(p.TargetURLs, _url)
  	} else {
  		p.TargetURLs = append(p.TargetURLs, url)
  	}
  
  	// get of ContentLength
  	if res.ContentLength <= 0 {
  		ch.Err <- errors.New("invalid content length")
  		return
  	}
  	ch.Size <- uint(res.ContentLength)
  }
docs: // CheckMirrors method check be able to range access. also get redirected url.