code: func (r *Registry) GetClientFunc(stream string) (func(*Peer, string, bool) (Client, error), error) {
  	r.clientMu.RLock()
  	defer r.clientMu.RUnlock()
  
  	f := r.clientFuncs[stream]
  	if f == nil {
  		return nil, fmt.Errorf("stream %v not registered", stream)
  	}
  	return f, nil
  }
docs: // GetClient accessor for incoming streamer constructors