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99 lines
3.0 KiB
Markdown
99 lines
3.0 KiB
Markdown
# 15.5 确保网页应用健壮
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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。
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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。
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为增强代码可读性，我们为页面处理函数创建一个类型：
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```go
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type HandleFnc func(http.ResponseWriter, *http.Request)
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```
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我们的错误处理函数应用了[13.5节](13.5.md) 的模式，成为 `logPanics` 函数：
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```go
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func logPanics(function HandleFnc) HandleFnc {
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return func(writer http.ResponseWriter, request *http.Request) {
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defer func() {
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if x := recover(); x != nil {
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log.Printf("[%v] caught panic: %v", request.RemoteAddr, x)
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}
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}()
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function(writer, request)
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}
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}
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```
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然后我们用 `logPanics` 来包装对处理函数的调用：
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```go
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http.HandleFunc("/test1", logPanics(SimpleServer))
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http.HandleFunc("/test2", logPanics(FormServer))
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```
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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：
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示例 15.11 [robust_webserver.go](examples/chapter_15/robust_webserver.go)
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```go
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package main
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import (
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"io"
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"log"
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"net/http"
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)
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const form = `<html><body><form action="#" method="post" name="bar">
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<input type="text" name="in"/>
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<input type="submit" value="Submit"/>
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</form></html></body>`
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type HandleFnc func(http.ResponseWriter, *http.Request)
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/* handle a simple get request */
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func SimpleServer(w http.ResponseWriter, request *http.Request) {
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io.WriteString(w, "<h1>hello, world</h1>")
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}
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/* handle a form, both the GET which displays the form
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and the POST which processes it.*/
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func FormServer(w http.ResponseWriter, request *http.Request) {
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w.Header().Set("Content-Type", "text/html")
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switch request.Method {
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case "GET":
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/* display the form to the user */
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io.WriteString(w, form)
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case "POST":
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/* handle the form data, note that ParseForm must
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be called before we can extract form data*/
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//request.ParseForm();
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//io.WriteString(w, request.Form["in"][0])
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io.WriteString(w, request.FormValue("in"))
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}
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}
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func main() {
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http.HandleFunc("/test1", logPanics(SimpleServer))
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http.HandleFunc("/test2", logPanics(FormServer))
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if err := http.ListenAndServe(":8088", nil); err != nil {
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panic(err)
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}
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}
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func logPanics(function HandleFnc) HandleFnc {
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return func(writer http.ResponseWriter, request *http.Request) {
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defer func() {
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if x := recover(); x != nil {
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log.Printf("[%v] caught panic: %v", request.RemoteAddr, x)
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}
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}()
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function(writer, request)
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}
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}
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```
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## 链接
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- [目录](directory.md)
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- 上一节：[写一个简单的网页应用](15.4.md)
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- 下一节：[用模板编写网页应用](15.6.md)
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