code: func insertUpstreamUserAgent(upstreamUA string, dockerUA string) string {
  	charsToEscape := `();\`
  	upstreamUAEscaped := escapeStr(upstreamUA, charsToEscape)
  	return fmt.Sprintf("%s UpstreamClient(%s)", dockerUA, upstreamUAEscaped)
  }
docs: // insertUpstreamUserAgent adds the upstream client useragent to create a user-agent
  // string of the form:
  //   $dockerUA UpstreamClient($upstreamUA)