package main

...

func main() {
    addr := flag.String("addr", ":4000", "HTTP network address")
    dsn := flag.String("dsn", "web:pass@/snippetbox?parseTime=true", "MySQL data source name")
    flag.Parse()

    logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

    db, err := openDB(*dsn)
    if err != nil {
        logger.Error(err.Error())
        os.Exit(1)
    }
    defer db.Close()

    templateCache, err := newTemplateCache()
    if err != nil {
        logger.Error(err.Error())
        os.Exit(1)
    }

    formDecoder := form.NewDecoder()

    sessionManager := scs.New()
    sessionManager.Store = mysqlstore.New(db)
    sessionManager.Lifetime = 12 * time.Hour

    app := &application{
        logger:         logger,
        snippets:       &models.SnippetModel{DB: db},
        templateCache:  templateCache,
        formDecoder:    formDecoder,
        sessionManager: sessionManager,
    }

    // Initialize a new http.Server struct. We set the Addr and Handler fields so
    // that the server uses the same network address and routes as before.
    srv := &http.Server{
        Addr:    *addr,
        Handler: app.routes(),
    }

    logger.Info("starting server", "addr", srv.Addr)

    // Call the ListenAndServe() method on our new http.Server struct to start 
    // the server.
    err = srv.ListenAndServe()
    logger.Error(err.Error())
    os.Exit(1)
}

...