code: func (e *Engine) syncRPC() {
  	// TODO(jsing): Make this default to IPv6, if configured.
  	addr := &net.TCPAddr{
  		IP:   e.config.Node.IPv4Addr,
  		Port: e.config.SyncPort,
  	}
  	ln, err := net.ListenTCP("tcp", addr)
  	if err != nil {
  		log.Fatalf("Listen failed: %v", err)
  	}
  
  	go e.syncServer.serve(ln)
  
  	<-e.shutdownRPC
  	ln.Close()
  	e.shutdownRPC <- true
  }
docs: // syncRPC starts a server to handle synchronisation RPCs via a TCP socket.