当网页应用的处理函数发生 panic，服务器会简单地终止运行。这可不妙：网页服务器必须是足够健壮的程序，能够承受任何可能的突发问题。
首先能想到的是在每个处理函数中使用 defer/recover，不过这样会产生太多的重复代码。13.5节 使用闭包的错误处理模式是更优雅的方案。我们把这种机制应用到前一章的简单网页服务器上。实际上，它可以被简单地应用到任何网页服务器程序中。
为增强代码可读性，我们为页面处理函数创建一个类型：

  1. type HandleFnc func(http.ResponseWriter, *http.Request)

我们的错误处理函数应用了13.5节 的模式，成为 logPanics 函数：

  1. func logPanics(function HandleFnc) HandleFnc {
  2.     return func(writer http.ResponseWriter, request *http.Request) {
  3.         defer func() {
  4.             if x := recover(); x != nil {
  5.                 log.Printf("[%v] caught panic: %v", request.RemoteAddr, x)
  6.             }
  7.         }()
  8.         function(writer, request)
  9.     }
  10. }

然后我们用 logPanics 来包装对处理函数的调用：

  1. http.HandleFunc("/test1", logPanics(SimpleServer))
  2. http.HandleFunc("/test2", logPanics(FormServer))

处理函数现在可以恢复 panic 调用，类似13.5节 中的错误检测函数。完整代码如下：
示例 15.11 robust_webserver.go

  1. package main
  3. import (
  4.     "io"
  5.     "log"
  6.     "net/http"
  7. )
  9. const form = `<html><body><form action="#" method="post" name="bar">
  10.         <input type="text" name="in"/>
  11.         <input type="submit" value="Submit"/>
  12.     </form></html></body>`
  14. type HandleFnc func(http.ResponseWriter, *http.Request)
  16. /* handle a simple get request */
  17. func SimpleServer(w http.ResponseWriter, request *http.Request) {
  18.     io.WriteString(w, "<h1>hello, world</h1>")
  19. }
  21. /* handle a form, both the GET which displays the form
  22.    and the POST which processes it.*/
  23. func FormServer(w http.ResponseWriter, request *http.Request) {
  24.     w.Header().Set("Content-Type", "text/html")
  25.     switch request.Method {
  26.     case "GET":
  27.         /* display the form to the user */
  28.         io.WriteString(w, form)
  29.     case "POST":
  30.         /* handle the form data, note that ParseForm must
  31.            be called before we can extract form data*/
  32.         //request.ParseForm();
  33.         //io.WriteString(w, request.Form["in"][0])
  34.         io.WriteString(w, request.FormValue("in"))
  35.     }
  36. }
  38. func main() {
  39.     http.HandleFunc("/test1", logPanics(SimpleServer))
  40.     http.HandleFunc("/test2", logPanics(FormServer))
  41.     if err := http.ListenAndServe(":8088", nil); err != nil {
  42.         panic(err)
  43.     }
  44. }
  46. func logPanics(function HandleFnc) HandleFnc {
  47.     return func(writer http.ResponseWriter, request *http.Request) {
  48.         defer func() {
  49.             if x := recover(); x != nil {
  50.                 log.Printf("[%v] caught panic: %v", request.RemoteAddr, x)
  51.             }
  52.         }()
  53.         function(writer, request)
  54.     }
  55. }

链接