add chapter 15.8 (#685)

eBook/examples/chapter_15/elaborated_webserver.go

@@ -0,0 +1,148 @@
+//Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+package main
+
+import (
+	"bytes"
+	"expvar"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+)
+
+// hello world, the web server
+var helloRequests = expvar.NewInt("hello-requests")
+
+// flags:
+var webroot = flag.String("root", "/home/user", "web root directory")
+
+// simple flag server
+var booleanflag = flag.Bool("boolean", true, "another flag for testing")
+
+// Simple counter server. POSTing to it will set the value.
+type Counter struct {
+	n int
+}
+
+// a channel
+type Chan chan int
+
+func main() {
+	flag.Parse()
+	http.Handle("/", http.HandlerFunc(Logger))
+	http.Handle("/go/hello", http.HandlerFunc(HelloServer))
+	// The counter is published as a variable directly.
+	ctr := new(Counter)
+	expvar.Publish("counter", ctr)
+	http.Handle("/counter", ctr)
+	// http.Handle("/go/", http.FileServer(http.Dir("/tmp"))) // uses the OS filesystem
+	http.Handle("/go/", http.StripPrefix("/go/", http.FileServer(http.Dir(*webroot))))
+	http.Handle("/flags", http.HandlerFunc(FlagServer))
+	http.Handle("/args", http.HandlerFunc(ArgServer))
+	http.Handle("/chan", ChanCreate())
+	http.Handle("/date", http.HandlerFunc(DateServer))
+	err := http.ListenAndServe(":12345", nil)
+	if err != nil {
+		log.Panicln("ListenAndServe:", err)
+	}
+}
+
+func Logger(w http.ResponseWriter, req *http.Request) {
+	log.Print(req.URL.String())
+	w.WriteHeader(404)
+	w.Write([]byte("oops"))
+}
+
+func HelloServer(w http.ResponseWriter, req *http.Request) {
+	helloRequests.Add(1)
+	io.WriteString(w, "hello, world!\n")
+}
+
+// This makes Counter satisfy the expvar.Var interface, so we can export
+// it directly.
+func (ctr *Counter) String() string { return fmt.Sprintf("%d", ctr.n) }
+
+func (ctr *Counter) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	switch req.Method {
+	case "GET": // increment n
+		ctr.n++
+	case "POST": // set n to posted value
+		buf := new(bytes.Buffer)
+		io.Copy(buf, req.Body)
+		body := buf.String()
+		if n, err := strconv.Atoi(body); err != nil {
+			fmt.Fprintf(w, "bad POST: %v\nbody: [%v]\n", err, body)
+		} else {
+			ctr.n = n
+			fmt.Fprint(w, "counter reset\n")
+		}
+	}
+	fmt.Fprintf(w, "counter = %d\n", ctr.n)
+}
+
+func FlagServer(w http.ResponseWriter, req *http.Request) {
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	fmt.Fprint(w, "Flags:\n")
+	flag.VisitAll(func(f *flag.Flag) {
+		if f.Value.String() != f.DefValue {
+			fmt.Fprintf(w, "%s = %s [default = %s]\n", f.Name, f.Value.String(), f.DefValue)
+		} else {
+			fmt.Fprintf(w, "%s = %s\n", f.Name, f.Value.String())
+		}
+	})
+}
+
+// simple argument server
+func ArgServer(w http.ResponseWriter, req *http.Request) {
+	for _, s := range os.Args {
+		fmt.Fprint(w, s, " ")
+	}
+}
+
+func ChanCreate() Chan {
+	c := make(Chan)
+	go func(c Chan) {
+		for x := 0; ; x++ {
+			c <- x
+		}
+	}(c)
+	return c
+}
+
+func (ch Chan) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	io.WriteString(w, fmt.Sprintf("channel send #%d\n", <-ch))
+}
+
+// exec a program, redirecting output
+func DateServer(rw http.ResponseWriter, req *http.Request) {
+	rw.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	r, w, err := os.Pipe()
+	if err != nil {
+		fmt.Fprintf(rw, "pipe: %s\n", err)
+		return
+	}
+
+	p, err := os.StartProcess("/bin/date", []string{"date"}, &os.ProcAttr{Files: []*os.File{nil, w, w}})
+	defer r.Close()
+	w.Close()
+	if err != nil {
+		fmt.Fprintf(rw, "fork/exec: %s\n", err)
+		return
+	}
+	defer p.Release()
+	io.Copy(rw, r)
+	wait, err := p.Wait()
+	if err != nil {
+		fmt.Fprintf(rw, "wait: %s\n", err)
+		return
+	}
+	if !wait.Exited() {
+		fmt.Fprintf(rw, "date: %v\n", wait)
+		return
+	}
+}