# 15.5 确保网页应用健壮
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](13.5.md)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：
```go
type HandleFnc func(http.ResponseWriter, *http.Request)
```
我们的错误处理函数应用了 [13.5 节](13.5.md)的模式，变成了以下的 `logPanics()` 函数：
```go
func logPanics(function HandleFnc) HandleFnc {
return func(writer http.ResponseWriter, request *http.Request) {
defer func() {
if x := recover(); x != nil {
log.Printf("[%v] caught panic: %v", request.RemoteAddr, x)
}
}()
function(writer, request)
}
}
```
然后我们用 `logPanics()` 来包装对处理函数的调用：
```go
http.HandleFunc("/test1", logPanics(SimpleServer))
http.HandleFunc("/test2", logPanics(FormServer))
```
处理函数现在可以恢复 panic 调用，类似 [13.5 节](13.5.md)中的错误检测函数。完整代码如下：
示例 15.11 [robust_webserver.go](examples/chapter_15/robust_webserver.go)
```go
package main
import (
"io"
"log"
"net/http"
)
const form = `<html><body><form action="#" method="post" name="bar">
<input type="text" name="in"/>
<input type="submit" value="Submit"/>
</form></html></body>`
type HandleFnc func(http.ResponseWriter, *http.Request)
/* handle a simple get request */
func SimpleServer(w http.ResponseWriter, request *http.Request) {
io.WriteString(w, "<h1>hello, world</h1>")
}
/* handle a form, both the GET which displays the form
and the POST which processes it.*/
func FormServer(w http.ResponseWriter, request *http.Request) {
w.Header().Set("Content-Type", "text/html")
switch request.Method {
case "GET":
/* display the form to the user */
io.WriteString(w, form)
case "POST":
/* handle the form data, note that ParseForm must
be called before we can extract form data*/
//request.ParseForm();
//io.WriteString(w, request.Form["in"][0])
io.WriteString(w, request.FormValue("in"))
}
}
func main() {
http.HandleFunc("/test1", logPanics(SimpleServer))
http.HandleFunc("/test2", logPanics(FormServer))
if err := http.ListenAndServe(":8088", nil); err != nil {
panic(err)
}
}
func logPanics(function HandleFnc) HandleFnc {
return func(writer http.ResponseWriter, request *http.Request) {
defer func() {
if x := recover(); x != nil {
log.Printf("[%v] caught panic: %v", request.RemoteAddr, x)
}
}()
function(writer, request)
}
}
```
## 链接
- [目录](directory.md)
- 上一节：[写一个简单的网页应用](15.4.md)
- 下一节：[用模板编写网页应用](15.6.md)