code: func (gs *genericStore) canAddChannel(name string) error {
  	if gs.channels[name] != nil {
  		return ErrAlreadyExists
  	}
  	if gs.limits.MaxChannels > 0 && len(gs.channels) >= gs.limits.MaxChannels {
  		return ErrTooManyChannels
  	}
  	return nil
  }
docs: // canAddChannel returns true if the current number of channels is below the limit.
  // If a channel named `channelName` alreadt exists, an error is returned.
  // Store lock is assumed to be locked.