Context: I want a handler to throw the 404 html page even when using a FileServer function to handle views folder.

• Problem: When I try to send a wrong path to my server (i.e: using Postman), I always get the default “404 Page not found” text instead of my custom HTML page.

• GitHub Link for the project if you want to know how I structured my code

• Current Implementation:

Using the default file handler from the Go Chi documentation:

// FileServer conveniently sets up a http.FileServer handler to serve
// static files from a http.FileSystem.
func fileServerSetup(r chi.Router, path string, root http.FileSystem) {
    log := config.GetLogger()

    if strings.ContainsAny(path, "{}*") {
        log.Error("FileServer does not permit any URL parameters.")
    }

    if path != "/" && path[len(path)-1] != '/' {
        r.Get(path, http.RedirectHandler(path+"/", http.StatusMovedPermanently).ServeHTTP)
        path += "/"
    }
    path += "*"

    r.Get(path, func(w http.ResponseWriter, r *http.Request) {
        routeContext := chi.RouteContext(r.Context())
        pathPrefix := strings.TrimSuffix(routeContext.RoutePattern(), "/*")
        fs := http.StripPrefix(pathPrefix, http.FileServer(root))
        fs.ServeHTTP(w, r)
    })
}

And this is my server’s related configuration:

type Server struct {
    Router    *chi.Mux
    EnvConfig *config.EnvConfig
}

type ServerDefinition interface {
    New() (server *Server)
    MountViewsFolder() error
    ApplyMiddleWares()
    MountHandlers()
}

func (s *Server) New() (server *Server) {
    server = &Server{}
    server.Router = chi.NewRouter()
    server.EnvConfig = config.LoadEnv()
    pigeon.GetSmtp()
    return server
}

func (s *Server) MountViewsFolder() error {
    workDir, err := os.Getwd()

    if err != nil {
        return err
    }

    filesDir := http.Dir(filepath.Join(workDir, "public/views"))
    fileServerSetup(s.Router, "/", filesDir)

    return nil
}

func (s *Server) MountHandlers() {
    s.Router.NotFound(func(w http.ResponseWriter, r *http.Request) {
        http.ServeFile(w, r, "public/views/404.tmpl")
    })

    s.Router.Get("/swagger/*", httpSwagger.Handler(
        httpSwagger.URL(
            fmt.Sprintf("http://%s:%d/swagger/doc.json",
                s.EnvConfig.Host,
                s.EnvConfig.Port,
            )),
    ))

    // Auth
    s.Router.Route("/auth", func(r chi.Router) {
        r.Post("/login", auth.LoginReq)
        r.With(md.RefreshVerify).Group(func(r chi.Router) {
            r.Post("/refresh-token", auth.RefreshTheAccessToken)
        })
    })

    // Sign up
    s.Router.Route("/signup", func(r chi.Router) {
        r.Use(middleware.AllowContentType("application/json"))
        r.Post("/", signup.Register)
        r.Post("/verify-email", signup.VerifyEmail)
        r.Put("/reset-code", signup.ResetVerifyCode)
    })

    // User
    s.Router.Route("/user", func(r chi.Router) {
        r.Use(middleware.AllowContentType("application/json"))
        r.Use(md.AccessVerify)
        r.Get("/", user.GetAllUsers)
        r.Put("/", user.UpdateUser)
        r.With(httpin.NewInput(user.UserIdPath{})).Group(func(ru chi.Router) {
            ru.Get("/{userId}", user.GetUserById)
            ru.Delete("/{userId}", user.DeleteUserById)
        })
    })
}

• Expected Result: get the custom 404 html page I made whenever I hit a wrong URI from my backend.
• Preview of how things should have been if the above code was to work (I commented out the MountViewsFolder function to test the 404):