code: public static function buildHttpClient(
          LoopInterface $loop,
          $connector = null
      ) {
          if (class_exists(HttpClientFactory::class)) {
              // if HttpClientFactory class exists, use old behavior for backwards compatibility
              return static::buildHttpClient04($loop, $connector);
          } else {
              return static::buildHttpClient05($loop, $connector);
          }
      }
docs: Build a React Http Client.
  
  @param LoopInterface                       $loop
  @param ConnectorInterface|DnsResolver|null $connector Only pass this argument if you need to customize DNS
  behaviour. With react http client v0.5, pass a connector,
  with v0.4 this must be a DnsResolver.
  
  @return HttpClient