You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.go
    path of file: ./repos/nano/examples/cluster
    
    the code of the file until where you have to start completion: package main

import (
	"log"
	"net/http"

    
func runMaster(args *cli.Context) error {
	listen := args.String("listen")
	if listen == "" {
		return errors.Errorf("master listen address cannot empty")
	}

	webDir := filepath.Join(srcPath(), "master", "web")
	log.Println("Nano master server web content directory", webDir)
	log.Println("Nano master listen address", listen)
	log.Println("Open http://127.0.0.1:12345/web/ in browser")

	http.Handle("/web/", http.StripPrefix("/web/", http.FileServer(http.Dir(webDir))))
	go func() {
		if err := http.ListenAndServe(":12345", nil); err != nil {
			panic(err)
		}
	}()

	// Register session closed callback
	session.Lifetime.OnClosed(master.OnSessionClosed)

	// Startup Nano server with the specified listen address
	nano.Listen(listen,
		nano.WithMaster(),
		nano.WithComponents(master.Services),
		nano.WithSerializer(json.NewSerializer()),
		nano.WithDebugMode(),
		nano.WithUnregisterCallback(func(m cluster.Member) {
			log.Println("Todo alarm unregister:", m.String())
		}),
	)

	return nil
}