进入loadPage问题：无效的内存地址或nil指针取消引用

Question

I'm following the golang.org tutorial on building a wiki page (https://golang.org/doc/articles/wiki/#tmp_4) and everything runs fine until I've gotten the above error message during step "Using net/http to serve wiki pages". I've got a text.txt file in src/github.com/user/gowiki/test.txt but loadPage(title) doesn't seem to be accessing the test.txt file. Any help is greatly appreciated. Thanks!

   package main

import (
    "fmt"
    "io/ioutil"
    "net/http"
)

type Page struct {
    Title string
    Body  []byte
}

func (p *Page) save() error {
    filename := p.Title + ".txt"
    return ioutil.WriteFile(filename, p.Body, 0600)
}

func loadPage(title string) (*Page, error) {
    filename := title + ".txt"
    body, err := ioutil.ReadFile(filename)
    if err != nil {
        return nil, err
    }
    return &Page{Title: title, Body: body}, nil
}

func viewHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/view/"):]
    p, _ := loadPage(title)
    fmt.Fprintf(w, "<h1>%s</h1><div>%s</div>", p.Title, p.Body)
}

func main() {
    http.HandleFunc("/view/", viewHandler)
    http.ListenAndServe(":8080", nil)
}

Answer 1

You are not checking the error returned by loadPage() in viewHandler() so if loadPage() can't load the file and returns nil with an error, viewHandler() tries to use that nil to obtain the page title and body and that's what causing the panic.

It works fine if loadPage() can read the file, though.