code: func newEventCacheKey(chConfig fab.ChannelCfg, opts ...options.Opt) (*eventCacheKey, error) {
  	params := defaultParams()
  	options.Apply(params, opts)
  
  	h := sha256.New()
  	if _, err := h.Write([]byte(params.getOptKey())); err != nil {
  		return nil, err
  	}
  	hash := h.Sum([]byte(chConfig.ID()))
  
  	return &eventCacheKey{
  		channelConfig: chConfig,
  		key:           string(hash),
  		opts:          opts,
  	}, nil
  }
docs: // newEventCacheKey returns a new eventCacheKey