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https://github.com/unknwon/the-way-to-go_ZH_CN.git
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add chapter 15.8 (#685)
This commit is contained in:
marjune
ᴊ. ᴄʜᴇɴ
243
eBook/15.8.md
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243
eBook/15.8.md
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@@ -0,0 +1,243 @@
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# 15.8 精巧的多功能网页服务器
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为进一步深入理解 `http` 包以及如何构建网页服务器功能，让我们来学习和体会下面的例子：先列出代码，然后给出不同功能的实现方法，程序输出显示在表格中。
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示例 15.20 [elaborated_webserver.go](examples/chapter_15/elaborated_webserver.go)
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```go
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package main
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import (
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"bytes"
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"expvar"
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"flag"
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"fmt"
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"io"
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"log"
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"net/http"
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"os"
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"strconv"
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)
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// hello world, the web server
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var helloRequests = expvar.NewInt("hello-requests")
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// flags:
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var webroot = flag.String("root", "/home/user", "web root directory")
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// simple flag server
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var booleanflag = flag.Bool("boolean", true, "another flag for testing")
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// Simple counter server. POSTing to it will set the value.
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type Counter struct {
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n int
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}
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// a channel
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type Chan chan int
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func main() {
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flag.Parse()
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http.Handle("/", http.HandlerFunc(Logger))
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http.Handle("/go/hello", http.HandlerFunc(HelloServer))
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// The counter is published as a variable directly.
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ctr := new(Counter)
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expvar.Publish("counter", ctr)
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http.Handle("/counter", ctr)
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// http.Handle("/go/", http.FileServer(http.Dir("/tmp"))) // uses the OS filesystem
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http.Handle("/go/", http.StripPrefix("/go/", http.FileServer(http.Dir(*webroot))))
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http.Handle("/flags", http.HandlerFunc(FlagServer))
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http.Handle("/args", http.HandlerFunc(ArgServer))
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http.Handle("/chan", ChanCreate())
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http.Handle("/date", http.HandlerFunc(DateServer))
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err := http.ListenAndServe(":12345", nil)
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if err != nil {
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log.Panicln("ListenAndServe:", err)
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}
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}
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func Logger(w http.ResponseWriter, req *http.Request) {
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log.Print(req.URL.String())
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w.WriteHeader(404)
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w.Write([]byte("oops"))
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}
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func HelloServer(w http.ResponseWriter, req *http.Request) {
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helloRequests.Add(1)
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io.WriteString(w, "hello, world!\n")
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}
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// This makes Counter satisfy the expvar.Var interface, so we can export
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// it directly.
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func (ctr *Counter) String() string { return fmt.Sprintf("%d", ctr.n) }
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func (ctr *Counter) ServeHTTP(w http.ResponseWriter, req *http.Request) {
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switch req.Method {
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case "GET": // increment n
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ctr.n++
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case "POST": // set n to posted value
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buf := new(bytes.Buffer)
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io.Copy(buf, req.Body)
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body := buf.String()
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if n, err := strconv.Atoi(body); err != nil {
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fmt.Fprintf(w, "bad POST: %v\nbody: [%v]\n", err, body)
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} else {
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ctr.n = n
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fmt.Fprint(w, "counter reset\n")
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}
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}
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fmt.Fprintf(w, "counter = %d\n", ctr.n)
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}
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func FlagServer(w http.ResponseWriter, req *http.Request) {
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w.Header().Set("Content-Type", "text/plain; charset=utf-8")
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fmt.Fprint(w, "Flags:\n")
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flag.VisitAll(func(f *flag.Flag) {
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if f.Value.String() != f.DefValue {
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fmt.Fprintf(w, "%s = %s [default = %s]\n", f.Name, f.Value.String(), f.DefValue)
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} else {
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fmt.Fprintf(w, "%s = %s\n", f.Name, f.Value.String())
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}
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})
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}
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// simple argument server
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func ArgServer(w http.ResponseWriter, req *http.Request) {
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for _, s := range os.Args {
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fmt.Fprint(w, s, " ")
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}
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}
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func ChanCreate() Chan {
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c := make(Chan)
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go func(c Chan) {
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for x := 0; ; x++ {
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c <- x
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}
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}(c)
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return c
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}
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func (ch Chan) ServeHTTP(w http.ResponseWriter, req *http.Request) {
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io.WriteString(w, fmt.Sprintf("channel send #%d\n", <-ch))
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}
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// exec a program, redirecting output
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func DateServer(rw http.ResponseWriter, req *http.Request) {
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rw.Header().Set("Content-Type", "text/plain; charset=utf-8")
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r, w, err := os.Pipe()
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if err != nil {
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fmt.Fprintf(rw, "pipe: %s\n", err)
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return
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}
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p, err := os.StartProcess("/bin/date", []string{"date"}, &os.ProcAttr{Files: []*os.File{nil, w, w}})
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defer r.Close()
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w.Close()
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if err != nil {
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fmt.Fprintf(rw, "fork/exec: %s\n", err)
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return
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}
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defer p.Release()
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io.Copy(rw, r)
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wait, err := p.Wait()
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if err != nil {
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fmt.Fprintf(rw, "wait: %s\n", err)
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return
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}
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if !wait.Exited() {
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fmt.Fprintf(rw, "date: %v\n", wait)
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return
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}
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}
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```
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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Logger | http://localhost:12345/ （根） | oops
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`Logger` 处理函数用 `w.WriteHeader(404)` 来输出 “404 Not Found”头部。
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此项技术通常很有用，无论何时服务器执行代码产生错误，都可以应用类似这样的代码：
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```go
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if err != nil {
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w.WriteHeader(400)
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return
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}
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```
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另外利用 `logger` 包的函数，针对每个请求在服务器端命令行打印日期、时间和 URL。
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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HelloServer | http://localhost:12345/go/hello | hello, world!
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包 `expvar` 可以创建（Int，Float 和 String 类型）变量，并将它们发布为公共变量。它会在 HTTP URL `/debug/vars` 上以 JSON 格式公布。通常它被用于服务器操作计数。`helloRequests` 就是这样一个 `int64` 变量，该处理函数对其加 1，然后写入“hello world!”到浏览器。
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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Counter | http://localhost:12345/counter | counter = 1
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Counter | 刷新（GET 请求） | counter = 2
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计数器对象 `ctr` 有一个 `String()` 方法，所以它实现了 `expvar.Var` 接口。这使其可以被发布，尽管它是一个结构体。`ServeHTTP` 函数使 `ctr` 成为处理器，因为它的签名正确实现了 `http.Handler` 接口。
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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FileServer | http://localhost:12345/go/ggg.html | 404 page not found
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`FileServer(root FileSystem) Handler` 返回一个处理器，它以 `root` 作为根，用文件系统的内容响应 HTTP 请求。要获得操作系统的文件系统，用 `http.Dir`，例如：
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```go
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http.Handle("/go/", http.FileServer(http.Dir("/tmp")))
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```
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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FlagServer | http://localhost:12345/flags | Flags: boolean = true root = /home/rsc
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该处理函数使用了 `flag` 包。`VisitAll` 函数迭代所有的标签（flag），打印它们的名称、值和默认值（当不同于“值”时）。
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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ArgServer | http://localhost:12345/args | ./elaborated_webserver.exe
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该处理函数迭代 `os.Args` 以打印出所有的命令行参数。如果没有指定则只有程序名称（可执行程序的路径）会被打印出来。
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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Channel | http://localhost:12345/chan | channel send #1
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Channel | 刷新 | channel send #2
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每当有新请求到达，通道的 `ServeHTTP` 方法从通道获取下一个整数并显示。由此可见，网页服务器可以从通道中获取要发送的响应，它可以由另一个函数产生（甚至是客户端）。下面的代码片段正是一个这样的处理函数，但会在 30 秒后超时：
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```go
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func ChanResponse(w http.ResponseWriter, req *http.Request) {
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timeout := make (chan bool)
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go func () {
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time.Sleep(30e9)
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timeout <- true
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}()
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select {
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case msg := <-messages:
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io.WriteString(w, msg)
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case stop := <-timeout:
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return
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}
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}
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```
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处理函数 | 调用 URL | 浏览器获得响应
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--------|----------|---------------
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DateServer | http://localhost:12345/date | 显示当前时间（由于是调用 /bin/date，仅在 Unix 下有效）
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可能的输出：`Thu Sep 8 12:41:09 CEST 2011`。
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`os.Pipe()` 返回一对相关联的 `File`，从 `r` 读取数据，返回已读取的字节数来自于 `w` 的写入。函数返回这两个文件和错误，如果有的话：
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```go
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func Pipe() (r *File, w *File, err error)
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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：[探索 template 包](15.7.md)
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- 下一节：[用 rpc 实现远程过程调用](15.9.md)
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148
eBook/examples/chapter_15/elaborated_webserver.go
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148
eBook/examples/chapter_15/elaborated_webserver.go
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@@ -0,0 +1,148 @@
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//Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"bytes"
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"expvar"
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"flag"
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"fmt"
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"io"
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"log"
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"net/http"
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"os"
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"strconv"
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)
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// hello world, the web server
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var helloRequests = expvar.NewInt("hello-requests")
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// flags:
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var webroot = flag.String("root", "/home/user", "web root directory")
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// simple flag server
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var booleanflag = flag.Bool("boolean", true, "another flag for testing")
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// Simple counter server. POSTing to it will set the value.
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type Counter struct {
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n int
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}
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// a channel
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type Chan chan int
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func main() {
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flag.Parse()
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http.Handle("/", http.HandlerFunc(Logger))
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http.Handle("/go/hello", http.HandlerFunc(HelloServer))
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// The counter is published as a variable directly.
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ctr := new(Counter)
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expvar.Publish("counter", ctr)
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http.Handle("/counter", ctr)
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// http.Handle("/go/", http.FileServer(http.Dir("/tmp"))) // uses the OS filesystem
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http.Handle("/go/", http.StripPrefix("/go/", http.FileServer(http.Dir(*webroot))))
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http.Handle("/flags", http.HandlerFunc(FlagServer))
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http.Handle("/args", http.HandlerFunc(ArgServer))
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http.Handle("/chan", ChanCreate())
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http.Handle("/date", http.HandlerFunc(DateServer))
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err := http.ListenAndServe(":12345", nil)
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if err != nil {
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log.Panicln("ListenAndServe:", err)
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}
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}
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func Logger(w http.ResponseWriter, req *http.Request) {
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log.Print(req.URL.String())
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w.WriteHeader(404)
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w.Write([]byte("oops"))
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}
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func HelloServer(w http.ResponseWriter, req *http.Request) {
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helloRequests.Add(1)
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io.WriteString(w, "hello, world!\n")
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}
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// This makes Counter satisfy the expvar.Var interface, so we can export
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// it directly.
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func (ctr *Counter) String() string { return fmt.Sprintf("%d", ctr.n) }
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func (ctr *Counter) ServeHTTP(w http.ResponseWriter, req *http.Request) {
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switch req.Method {
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case "GET": // increment n
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ctr.n++
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case "POST": // set n to posted value
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buf := new(bytes.Buffer)
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io.Copy(buf, req.Body)
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body := buf.String()
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if n, err := strconv.Atoi(body); err != nil {
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fmt.Fprintf(w, "bad POST: %v\nbody: [%v]\n", err, body)
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} else {
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ctr.n = n
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fmt.Fprint(w, "counter reset\n")
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}
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}
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fmt.Fprintf(w, "counter = %d\n", ctr.n)
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}
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func FlagServer(w http.ResponseWriter, req *http.Request) {
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w.Header().Set("Content-Type", "text/plain; charset=utf-8")
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fmt.Fprint(w, "Flags:\n")
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flag.VisitAll(func(f *flag.Flag) {
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if f.Value.String() != f.DefValue {
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fmt.Fprintf(w, "%s = %s [default = %s]\n", f.Name, f.Value.String(), f.DefValue)
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} else {
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fmt.Fprintf(w, "%s = %s\n", f.Name, f.Value.String())
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}
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})
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}
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// simple argument server
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func ArgServer(w http.ResponseWriter, req *http.Request) {
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for _, s := range os.Args {
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fmt.Fprint(w, s, " ")
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}
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}
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func ChanCreate() Chan {
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c := make(Chan)
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go func(c Chan) {
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for x := 0; ; x++ {
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c <- x
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}
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}(c)
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return c
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}
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func (ch Chan) ServeHTTP(w http.ResponseWriter, req *http.Request) {
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io.WriteString(w, fmt.Sprintf("channel send #%d\n", <-ch))
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}
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// exec a program, redirecting output
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func DateServer(rw http.ResponseWriter, req *http.Request) {
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rw.Header().Set("Content-Type", "text/plain; charset=utf-8")
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r, w, err := os.Pipe()
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if err != nil {
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fmt.Fprintf(rw, "pipe: %s\n", err)
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return
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}
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p, err := os.StartProcess("/bin/date", []string{"date"}, &os.ProcAttr{Files: []*os.File{nil, w, w}})
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defer r.Close()
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w.Close()
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if err != nil {
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fmt.Fprintf(rw, "fork/exec: %s\n", err)
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return
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}
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defer p.Release()
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io.Copy(rw, r)
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wait, err := p.Wait()
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if err != nil {
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fmt.Fprintf(rw, "wait: %s\n", err)
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return
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}
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if !wait.Exited() {
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fmt.Fprintf(rw, "date: %v\n", wait)
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return
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}
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}
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