code: func (p *Proxy) addToEndpointList(ctx context.Context, r string) error {
  	rgx, err := regexp.Compile(r)
  	if err == nil {
  		p.mutex.Lock()
  		p.endpointBlackList = append(p.endpointBlackList, rgx)
  		p.mutex.Unlock()
  	}
  	return err
  }
docs: // addToEndpointList compiles regex and adds it to an endpointList
  // if regex is valid
  // use t to choose list type: true for whitelist false for blacklist