code: func (b *b2dReleaseGetter) getReleaseURL(apiURL string) (string, error) {
  	if apiURL == "" {
  		apiURL = defaultURL
  	}
  
  	// match github (enterprise) release urls:
  	// https://api.github.com/repos/../../releases or
  	// https://some.github.enterprise/api/v3/repos/../../releases
  	re := regexp.MustCompile("(https?)://([^/]+)(/api/v3)?/repos/([^/]+)/([^/]+)/releases")
  	matches := re.FindStringSubmatch(apiURL)
  	if len(matches) != 6 {
  		// does not match a github releases api URL
  		return apiURL, nil
  	}
  
  	scheme, host, org, repo := matches[1], matches[2], matches[4], matches[5]
  	if host == "api.github.com" {
  		host = "github.com"
  	}
  
  	tag, err := b.getReleaseTag(apiURL)
  	if err != nil {
  		return "", err
  	}
  
  	log.Infof("Latest release for %s/%s/%s is %s", host, org, repo, tag)
  	bugURL, ok := AUFSBugB2DVersions[tag]
  	if ok {
  		log.Warnf(`
  Boot2Docker %s has a known issue with AUFS.
  See here for more details: %s
  Consider specifying another storage driver (e.g. 'overlay') using '--engine-storage-driver' instead.
  `, tag, bugURL)
  	}
  	url := fmt.Sprintf("%s://%s/%s/%s/releases/download/%s/%s", scheme, host, org, repo, tag, b.isoFilename)
  	return url, nil
  }
docs: // getReleaseURL gets the latest release URL of Boot2Docker.