Using net/http to serve

承上篇文章，針對wiki 檔案進行http的操作

增加view 功能

  1. 增加一個function，將request URL中的/view/ 過濾，取其後面的值作為文章title
  2. 呼叫 loadPage function
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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)
}
  1. 接著，在main function 中去設定view 路由
  2. 並設定聽port 8080
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func main() {
	http.HandleFunc("/view/", viewHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
}

Editing Pages

  1. 增加編輯和儲存的路由
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func main() {
	http.HandleFunc("/view/", viewHandler)
    http.HandleFunc("/edit/", editHandler)
    http.HandleFunc("/save/", saveHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
}
  1. 增加編輯 function
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func editHandler(w http.ResponseWriter, r *http.Request) {
	title := r.URL.Path[len("/edit/"):]
	p, err := loadPage(title)
	if err != nil {
		p = &Page{Title: title}
	}
	fmt.Fprintf(w, "<h1>Editing %s</h1>"+
		"<form action=\"/save/%s\" method=\"POST\">"+
		"<textarea name=\"body\">%s</textarea><br>"+
		"<input type=\"submit\" value=\"Save\">"+
		"</form>",
		p.Title, p.Title, p.Body)
}

但使用 html hardcode有點醜陋

  1. 所以可以使用html/template package
  • 建立一個edit.html
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<h1>Editing {{.Title}}</h1>

<form action="/save/{{.Title}}" method="POST">
<div><textarea name="body" rows="20" cols="80">{{printf "%s" .Body}}</textarea></div>
<div><input type="submit" value="Save"></div>
</form>
  1. 將 edit function 改成使用 html
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func editHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/edit/"):]
    p, err := loadPage(title)
    if err != nil {
        p = &Page{Title: title}
    }
    t, _ := template.ParseFiles("edit.html")
    t.Execute(w, p)
}

template.ParseFiles會讀取 html 內的內容然後 return *template.Template

  1. 也可以將 view 轉成使用 html 檔案
  • view.html
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<h1>{{.Title}}</h1>

<p>[<a href="/edit/{{.Title}}">edit</a>]</p>

<div>{{printf "%s" .Body}}</div>
  • viewHandler
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func viewHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/view/"):]
    p, _ := loadPage(title)
    t, _ := template.ParseFiles("view.html")
    t.Execute(w, p)
}
  1. 將重複使用的程式共用 function
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func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
    t, _ := template.ParseFiles(tmpl + ".html")
    t.Execute(w, p)
}

然後將 viewHandler 和改成使用這個 function

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func viewHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/view/"):]
    p, _ := loadPage(title)
    renderTemplate(w, "view", p)
}
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func editHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/edit/"):]
    p, err := loadPage(title)
    if err != nil {
        p = &Page{Title: title}
    }
    renderTemplate(w, "edit", p)
}

處理不存在的Pages

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func viewHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/view/"):]
    p, err := loadPage(title)
    if err != nil {
        http.Redirect(w, r, "/edit/"+title, http.StatusFound)
        return
    }
    renderTemplate(w, "view", p)
}

Saving pages

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func saveHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/save/"):]
    body := r.FormValue("body")
    p := &Page{Title: title, Body: []byte(body)}
    p.save()
    http.Redirect(w, r, "/view/"+title, http.StatusFound)
}

FormValue return type string. 需要轉換值為 []byte 去符合 Page struct

Error Handling

Handle the error in renderTemplate

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func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
    t, err := template.ParseFiles(tmpl + ".html")
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    err = t.Execute(w, p)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
    }
}

fix up saveHandler

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func saveHandler(w http.ResponseWriter, r *http.Request) {
    title := r.URL.Path[len("/save/"):]
    body := r.FormValue("body")
    p := &Page{Title: title, Body: []byte(body)}
    err := p.save()
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    http.Redirect(w, r, "/view/"+title, http.StatusFound)
}

Template caching

建立一個全域變數
var templates = template.Must(template.ParseFiles("edit.html", "view.html"))

修改renderTemplate function

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func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
    err := templates.ExecuteTemplate(w, tmpl+".html", p)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
    }
}

Validation

增加regex的格式驗證
var validPath = regexp.MustCompile("^/(edit|save|view)/([a-zA-Z0-9]+)$")

增加function使用validPath去驗證title

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func getTitle(w http.ResponseWriter, r *http.Request) (string, error) {
    m := validPath.FindStringSubmatch(r.URL.Path)
    if m == nil {
        http.NotFound(w, r)
        return "", errors.New("Invalid Page Title")
    }
    return m[2], nil // The title is the second subexpression.
}

將 getTitle function 加入 handlers裡

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func viewHandler(w http.ResponseWriter, r *http.Request) {
    title, err := getTitle(w, r)
    if err != nil {
        return
    }
    p, err := loadPage(title)
    if err != nil {
        http.Redirect(w, r, "/edit/"+title, http.StatusFound)
        return
    }
    renderTemplate(w, "view", p)
}
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func editHandler(w http.ResponseWriter, r *http.Request) {
    title, err := getTitle(w, r)
    if err != nil {
        return
    }
    p, err := loadPage(title)
    if err != nil {
        p = &Page{Title: title}
    }
    renderTemplate(w, "edit", p)
}
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func saveHandler(w http.ResponseWriter, r *http.Request) {
    title, err := getTitle(w, r)
    if err != nil {
        return
    }
    body := r.FormValue("body")
    p := &Page{Title: title, Body: []byte(body)}
    err = p.save()
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    http.Redirect(w, r, "/view/"+title, http.StatusFound)
}

Literals and Closures

在每個handler中抓取error的情況會使用很多重複的程式碼，可以將每個handlers中的error 和 validation 用一個function包起來

  1. 將每個handler function 加上title string
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func viewHandler(w http.ResponseWriter, r *http.Request, title string)
func editHandler(w http.ResponseWriter, r *http.Request, title string)
func saveHandler(w http.ResponseWriter, r *http.Request, title string)
  1. 定義function
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func makeHandler(fn func(http.ResponseWriter, *http.Request, string)) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        m := validPath.FindStringSubmatch(r.URL.Path) //extract the page title from the Request
        if m == nil {
            http.NotFound(w, r)
            return
        }
        fn(w, r, m[2]) //call the provided handler 'fn'
    }
}

這個return function 是一個closure(閉包)
這個閉包會取得request 路徑上的title, 然後透過TitleValidator驗證他的格式
若title不合法，則error會寫入 ResponseWriter (http.NotFound)
若合法，則此function fn 會被呼叫

  1. 將makeHandler加至 main function
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func main() {
    http.HandleFunc("/view/", makeHandler(viewHandler))
    http.HandleFunc("/edit/", makeHandler(editHandler))
    http.HandleFunc("/save/", makeHandler(saveHandler))

    log.Fatal(http.ListenAndServe(":8080", nil))
}
  1. 從handler function裡移除getTitle

REFERENCES