code: func (whisper *Whisper) getPeer(peerID []byte) (*Peer, error) {
  	whisper.peerMu.Lock()
  	defer whisper.peerMu.Unlock()
  	for p := range whisper.peers {
  		id := p.peer.ID()
  		if bytes.Equal(peerID, id[:]) {
  			return p, nil
  		}
  	}
  	return nil, fmt.Errorf("Could not find peer with ID: %x", peerID)
  }
docs: // getPeer retrieves peer by ID