错误

```go package main import ( "html/template" "io" "io/ioutil" "log" "net/http" "os" "path" "runtime/debug" ) const ( ListDir = 0x0001 UPLOAD_DIR = "./uploads" TEMPLATE_DIR = "./views" ) var templates = make(map[string]*template.Template) func init() { fileInfoArr, err := ioutil.ReadDir(TEMPLATE_DIR) check(err) var templateName, templatePath, tmpl string for _, fileInfo := range fileInfoArr { templateName = fileInfo.Name() if ext := path.Ext(templateName); ext != ".html" { continue } templatePath = TEMPLATE_DIR + "/" + templateName log.Println("Loading template:", templatePath) t := template.Must(template.ParseFiles(templatePath)) templates[tmpl] = t } } func check(err error) { if err != nil { panic(err) } } func renderHtml(w http.ResponseWriter, templ string, locals map[string]interface{}) { err := templates[templ].Execute(w, locals) check(err) } func isExists(path string) bool { _, err := os.Stat(path) if err == nil { return true } return os.IsExist(err) } func uploadHandler(w http.ResponseWriter, r *http.Request) { if r.Method == "GET" { renderHtml(w, "upload", nil) } if r.Method == "POST" { f, h, err := r.FormFile("image") check(err) filename := h.Filename defer f.Close() t, err := ioutil.TempFile(UPLOAD_DIR, filename) check(err) defer t.Close() _, err = io.Copy(t, f) check(err) http.Redirect(w, r, "/view?id="+filename, http.StatusFound) } } func viewHandler(w http.ResponseWriter, r *http.Request) { var imageId, imagePath string imageId = r.FormValue("id") imagePath = UPLOAD_DIR + "/" + imageId if exists := isExists(imagePath); !exists { http.NotFound(w, r) return } w.Header().Set("Content-Type", "image") http.ServeFile(w, r, imagePath) } func listHandler(w http.ResponseWriter, r *http.Request) { fileInfoArr, err := ioutil.ReadDir("./uploads") check(err) locals := make(map[string]interface{}) images := []string{} for _, fileInfo := range fileInfoArr { images = append(images, fileInfo.Name()) } locals["images"] = images renderHtml(w, "list", locals) } func safeHandler(fn http.HandlerFunc) http.HandlerFunc { return func(w http.ResponseWriter, r *http.Request) { defer func() { if e, ok := recover().(error); ok { http.Error(w, err.Error(), http.StatusInternalServerError) //或者输出自定义的50x错误页面 //w.WriteHeader(http.StatusInternalServerError) //renderHtml(w,"error",e) //logging log.Println("WARN:panic in %v. - %v", fn, e) log.Println(string(debug.Stack())) } }() fn(w, r) } } func staticDirHandler(mux *http.ServeMux, prefix string, staticDir string, flags int) { mux.HandleFunc(prefix, func(w http.ResponseWriter, r *http.Request) { file := staticDir + r.URL.Path[len(prefix)-1:] if (flags & ListDir) == 0 { if exists := isExists(file); !exists { http.NotFound(w, r) return } } http.ServeFile(w, r, file) }) } func main() { mux := http.NewServeMux() staticDirHandler(mux, "/assets", "./public", 0) mux.HandleFunc("/", safeHandler(listHandler)) mux.HandleFunc("/view", safeHandler(viewHandler)) mux.HandleFunc("/upload", safeHandler(uploadHandler)) err := http.ListenAndServe(":8080", mux) if err != nil { log.Fatal("ListenAndServe: ", err.Error()) } } ``` undefined: err in err.Error