add chapter 15.6 (#682)

eBook/examples/chapter_15/wiki/ANewPage.txt

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+Testing input of new page!
+Go Go Go !

eBook/examples/chapter_15/wiki/TestPage.txt

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+This is a sample Page.

eBook/examples/chapter_15/wiki/edit.html

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+<h1>Editing {{.Title |html}}</h1>
+
+<form action="/save/{{.Title |html}}" method="POST">
+<div><textarea name="body" rows="20" cols="80">{{printf "%s" .Body|html}}</textarea></div>
+<div><input type="submit" value="Save"></div>
+</form>

eBook/examples/chapter_15/wiki/page.txt

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+Hello Go - World !!!
+This works great.

eBook/examples/chapter_15/wiki/page1.txt

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+This is a test!!

eBook/examples/chapter_15/wiki/page5.txt

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+Page5 is hereby started.
+This is a first addition.
+2nd addition.

eBook/examples/chapter_15/wiki/view.html

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+<h1>{{.Title |html}}</h1>
+
+<p>[<a href="/edit/{{.Title |html}}">edit</a>]</p>
+
+<div>{{printf "%s" .Body |html}}</div>

eBook/examples/chapter_15/wiki/wiki.go

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+package main
+
+import (
+	"net/http"
+	"io/ioutil"
+	"log"
+	"regexp"
+	"text/template"
+)
+
+const lenPath = len("/view/")
+
+var titleValidator = regexp.MustCompile("^[a-zA-Z0-9]+$")
+var templates = make(map[string]*template.Template)
+var err error
+
+type Page struct {
+	Title string
+	Body  []byte
+}
+
+func init() {
+	for _, tmpl := range []string{"edit", "view"} {
+		templates[tmpl] = template.Must(template.ParseFiles(tmpl + ".html"))
+	}
+}
+
+func main() {
+	http.HandleFunc("/view/", makeHandler(viewHandler))
+	http.HandleFunc("/edit/", makeHandler(editHandler))
+	http.HandleFunc("/save/", makeHandler(saveHandler))
+	err := http.ListenAndServe("localhost:8080", nil)
+	if err != nil {
+		log.Fatal("ListenAndServe: ", err.Error())
+	}
+}
+
+func makeHandler(fn func(http.ResponseWriter, *http.Request, string)) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		title := r.URL.Path[lenPath:]
+		if !titleValidator.MatchString(title) {
+			http.NotFound(w, r)
+			return
+		}
+		fn(w, r, title)
+	}
+}
+
+func viewHandler(w http.ResponseWriter, r *http.Request, title string) {
+	p, err := load(title)
+	if err != nil { // page not found
+		http.Redirect(w, r, "/edit/"+title, http.StatusFound)
+		return
+	}
+	renderTemplate(w, "view", p)
+}
+
+func editHandler(w http.ResponseWriter, r *http.Request, title string) {
+	p, err := load(title)
+	if err != nil {
+		p = &Page{Title: title}
+	}
+	renderTemplate(w, "edit", p)
+}
+
+func saveHandler(w http.ResponseWriter, r *http.Request, title string) {
+	body := r.FormValue("body")
+	p := &Page{Title: title, Body: []byte(body)}
+	err := p.save()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(w, r, "/view/"+title, http.StatusFound)
+}
+
+func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
+	err := templates[tmpl].Execute(w, p)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	}
+}
+
+func (p *Page) save() error {
+	filename := p.Title + ".txt"
+	// file created with read-write permissions for the current user only
+	return ioutil.WriteFile(filename, p.Body, 0600)
+}
+
+func load(title string) (*Page, error) {
+	filename := title + ".txt"
+	body, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &Page{Title: title, Body: body}, nil
+}

eBook/examples/chapter_15/wiki/wiki_part1.go

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+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+)
+
+type Page struct {
+	Title string
+	Body  []byte
+}
+
+func (p *Page) save() error {
+	filename := p.Title + ".txt"
+	return ioutil.WriteFile(filename, p.Body, 0600)
+}
+
+func load(title string) (*Page, error) {
+	filename := title + ".txt"
+	body, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &Page{Title: title, Body: body}, nil
+}
+
+func main() {
+	p1 := &Page{Title: "TestPage", Body: []byte("This is a sample Page.")}
+	p1.save()
+	p2, _ := load("TestPage")
+	fmt.Println(string(p2.Body))
+}

eBook/examples/chapter_15/wiki/wiki_part2.go

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+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/http"
+)
+
+type Page struct {
+	Title string
+	Body  []byte
+}
+
+func (p *Page) save() error {
+	filename := p.Title + ".txt"
+	return ioutil.WriteFile(filename, p.Body, 0600)
+}
+
+func load(title string) (*Page, error) {
+	filename := title + ".txt"
+	body, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &Page{Title: title, Body: body}, nil
+}
+
+const lenPath = len("/view/")
+
+func viewHandler(w http.ResponseWriter, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := load(title)
+	fmt.Fprintf(w, "<h1>%s</h1><div>%s</div>", p.Title, p.Body)
+}
+
+func main() {
+	http.HandleFunc("/view/", viewHandler)
+	http.ListenAndServe(":8080", nil)
+}