Wiki codelab, complete with tests.

R=r, rsc, gri
CC=golang-dev
http://codereview.appspot.com/887045

21 files changed, 2513 insertions, 0 deletions

diff --git a/doc/codelab/wiki/Makefile b/doc/codelab/wiki/Makefile
new file mode 100644
index 000000000..76ab5c5bc
--- /dev/null
+++ b/doc/codelab/wiki/Makefile
@@ -0,0 +1,29 @@
+# Copyright 2010 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.
+
+include ../../../src/Make.$(GOARCH)
+
+all: index.html
+
+# ugly hack to deal with whitespaces in $GOROOT
+nullstring :=
+space := $(nullstring) # a space at the end
+QUOTED_GOROOT:=$(subst $(space),\ ,$(GOROOT))
+
+include $(QUOTED_GOROOT)/src/Make.common
+
+CLEANFILES+=index.html srcextract.bin htmlify.bin
+
+index.html: srcextract.bin htmlify.bin
+	awk '/^!/{system(substr($$0,2)); next} {print}' "$$@" < wiki.html > index.html
+
+test: final.bin
+	./test.sh
+	rm -f final.6 final.bin
+
+%.bin: %.$O
+	$(QUOTED_GOBIN)/$(LD) -o $@ $<
+%.$O: 
+	$(QUOTED_GOBIN)/$(GC) $*.go
+
diff --git a/doc/codelab/wiki/edit.html b/doc/codelab/wiki/edit.html
new file mode 100644
index 000000000..71a919496
--- /dev/null
+++ b/doc/codelab/wiki/edit.html
@@ -0,0 +1,6 @@
+<h1>Editing {title}</h1>
+
+<form action="/save/{title}" method="POST">
+<div><textarea name="body" rows="20" cols="80">{body|html}</textarea></div>
+<div><input type="submit" value="Save"></div>
+</form>
diff --git a/doc/codelab/wiki/final-noclosure.go b/doc/codelab/wiki/final-noclosure.go
new file mode 100644
index 000000000..d4ce71560
--- /dev/null
+++ b/doc/codelab/wiki/final-noclosure.go
@@ -0,0 +1,100 @@
+package main
+
+import (
+	"http"
+	"io/ioutil"
+	"os"
+	"regexp"
+	"template"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.Error) {
+	filename := title + ".txt"
+	body, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &page{title: title, body: body}, nil
+}
+
+func viewHandler(c *http.Conn, r *http.Request) {
+	title, err := getTitle(c, r)
+	if err != nil {
+		return
+	}
+	p, err := loadPage(title)
+	if err != nil {
+		http.Redirect(c, "/edit/"+title, http.StatusFound)
+		return
+	}
+	renderTemplate(c, "view", p)
+}
+
+func editHandler(c *http.Conn, r *http.Request) {
+	title, err := getTitle(c, r)
+	if err != nil {
+		return
+	}
+	p, err := loadPage(title)
+	if err != nil {
+		p = &page{title: title}
+	}
+	renderTemplate(c, "edit", p)
+}
+
+func saveHandler(c *http.Conn, r *http.Request) {
+	title, err := getTitle(c, r)
+	if err != nil {
+		return
+	}
+	body := r.FormValue("body")
+	p := &page{title: title, body: []byte(body)}
+	err = p.save()
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(c, "/view/"+title, http.StatusFound)
+}
+
+func renderTemplate(c *http.Conn, tmpl string, p *page) {
+	t, err := template.ParseFile(tmpl+".html", nil)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	err = t.Execute(p, c)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+	}
+}
+
+const lenPath = len("/view/")
+
+var titleValidator = regexp.MustCompile("^[a-zA-Z0-9]+$")
+
+func getTitle(c *http.Conn, r *http.Request) (title string, err os.Error) {
+	title = r.URL.Path[lenPath:]
+	if !titleValidator.MatchString(title) {
+		http.NotFound(c, r)
+		err = os.NewError("Invalid Page Title")
+	}
+	return
+}
+
+func main() {
+	http.HandleFunc("/view/", viewHandler)
+	http.HandleFunc("/edit/", editHandler)
+	http.HandleFunc("/save/", saveHandler)
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/final-noerror.go b/doc/codelab/wiki/final-noerror.go
new file mode 100644
index 000000000..3b699452a
--- /dev/null
+++ b/doc/codelab/wiki/final-noerror.go
@@ -0,0 +1,52 @@
+package main
+
+import (
+	"http"
+	"io/ioutil"
+	"os"
+	"template"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.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 editHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, err := loadPage(title)
+	if err != nil {
+		p = &page{title: title}
+	}
+	t, _ := template.ParseFile("edit.html", nil)
+	t.Execute(p, c)
+}
+
+func viewHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := loadPage(title)
+	t, _ := template.ParseFile("view.html", nil)
+	t.Execute(p, c)
+}
+
+func main() {
+	http.HandleFunc("/view/", viewHandler)
+	http.HandleFunc("/edit/", editHandler)
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/final-parsetemplate.go b/doc/codelab/wiki/final-parsetemplate.go
new file mode 100644
index 000000000..93b956b9d
--- /dev/null
+++ b/doc/codelab/wiki/final-parsetemplate.go
@@ -0,0 +1,90 @@
+package main
+
+import (
+	"http"
+	"io/ioutil"
+	"os"
+	"regexp"
+	"template"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.Error) {
+	filename := title + ".txt"
+	body, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &page{title: title, body: body}, nil
+}
+
+func viewHandler(c *http.Conn, r *http.Request, title string) {
+	p, err := loadPage(title)
+	if err != nil {
+		http.Redirect(c, "/edit/"+title, http.StatusFound)
+		return
+	}
+	renderTemplate(c, "view", p)
+}
+
+func editHandler(c *http.Conn, r *http.Request, title string) {
+	p, err := loadPage(title)
+	if err != nil {
+		p = &page{title: title}
+	}
+	renderTemplate(c, "edit", p)
+}
+
+func saveHandler(c *http.Conn, r *http.Request, title string) {
+	body := r.FormValue("body")
+	p := &page{title: title, body: []byte(body)}
+	err := p.save()
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(c, "/view/"+title, http.StatusFound)
+}
+
+func renderTemplate(c *http.Conn, tmpl string, p *page) {
+	t, err := template.ParseFile(tmpl+".html", nil)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	err = t.Execute(p, c)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+	}
+}
+
+const lenPath = len("/view/")
+
+var titleValidator = regexp.MustCompile("^[a-zA-Z0-9]+$")
+
+func makeHandler(fn func(*http.Conn, *http.Request, string)) http.HandlerFunc {
+	return func(c *http.Conn, r *http.Request) {
+		title := r.URL.Path[lenPath:]
+		if !titleValidator.MatchString(title) {
+			http.NotFound(c, r)
+			return
+		}
+		fn(c, r, title)
+	}
+}
+
+func main() {
+	http.HandleFunc("/view/", makeHandler(viewHandler))
+	http.HandleFunc("/edit/", makeHandler(editHandler))
+	http.HandleFunc("/save/", makeHandler(saveHandler))
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/final-template.go b/doc/codelab/wiki/final-template.go
new file mode 100644
index 000000000..481cda1e6
--- /dev/null
+++ b/doc/codelab/wiki/final-template.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"http"
+	"io/ioutil"
+	"os"
+	"template"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.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 editHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, err := loadPage(title)
+	if err != nil {
+		p = &page{title: title}
+	}
+	renderTemplate(c, "view", p)
+}
+
+func viewHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := loadPage(title)
+	renderTemplate(c, "edit", p)
+}
+
+func saveHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	body := r.FormValue("body")
+	p := &page{title: title, body: []byte(body)}
+	p.save()
+	http.Redirect(c, "/view/"+title, http.StatusFound)
+}
+
+func renderTemplate(c *http.Conn, tmpl string, p *page) {
+	t, _ := template.ParseFile(tmpl+".html", nil)
+	t.Execute(p, c)
+}
+
+func main() {
+	http.HandleFunc("/view/", viewHandler)
+	http.HandleFunc("/edit/", editHandler)
+	http.HandleFunc("/save/", saveHandler)
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/final.go b/doc/codelab/wiki/final.go
new file mode 100644
index 000000000..0186729c2
--- /dev/null
+++ b/doc/codelab/wiki/final.go
@@ -0,0 +1,93 @@
+package main
+
+import (
+	"http"
+	"io/ioutil"
+	"os"
+	"regexp"
+	"template"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.Error) {
+	filename := title + ".txt"
+	body, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &page{title: title, body: body}, nil
+}
+
+func viewHandler(c *http.Conn, r *http.Request, title string) {
+	p, err := loadPage(title)
+	if err != nil {
+		http.Redirect(c, "/edit/"+title, http.StatusFound)
+		return
+	}
+	renderTemplate(c, "view", p)
+}
+
+func editHandler(c *http.Conn, r *http.Request, title string) {
+	p, err := loadPage(title)
+	if err != nil {
+		p = &page{title: title}
+	}
+	renderTemplate(c, "edit", p)
+}
+
+func saveHandler(c *http.Conn, r *http.Request, title string) {
+	body := r.FormValue("body")
+	p := &page{title: title, body: []byte(body)}
+	err := p.save()
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(c, "/view/"+title, http.StatusFound)
+}
+
+var templates = make(map[string]*template.Template)
+
+func init() {
+	for _, tmpl := range []string{"edit", "view"} {
+		templates[tmpl] = template.MustParseFile(tmpl+".html", nil)
+	}
+}
+
+func renderTemplate(c *http.Conn, tmpl string, p *page) {
+	err := templates[tmpl].Execute(p, c)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+	}
+}
+
+const lenPath = len("/view/")
+
+var titleValidator = regexp.MustCompile("^[a-zA-Z0-9]+$")
+
+func makeHandler(fn func(*http.Conn, *http.Request, string)) http.HandlerFunc {
+	return func(c *http.Conn, r *http.Request) {
+		title := r.URL.Path[lenPath:]
+		if !titleValidator.MatchString(title) {
+			http.NotFound(c, r)
+			return
+		}
+		fn(c, r, title)
+	}
+}
+
+func main() {
+	http.HandleFunc("/view/", makeHandler(viewHandler))
+	http.HandleFunc("/edit/", makeHandler(editHandler))
+	http.HandleFunc("/save/", makeHandler(saveHandler))
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/htmlify.go b/doc/codelab/wiki/htmlify.go
new file mode 100644
index 000000000..4a52e077f
--- /dev/null
+++ b/doc/codelab/wiki/htmlify.go
@@ -0,0 +1,12 @@
+package main
+
+import (
+	"os"
+	"template"
+	"io/ioutil"
+)
+
+func main() {
+	b, _ := ioutil.ReadAll(os.Stdin)
+	template.HTMLFormatter(os.Stdout, b, "")
+}
diff --git a/doc/codelab/wiki/http-sample.go b/doc/codelab/wiki/http-sample.go
new file mode 100644
index 000000000..11d5d7861
--- /dev/null
+++ b/doc/codelab/wiki/http-sample.go
@@ -0,0 +1,15 @@
+package main
+
+import (
+	"fmt"
+	"http"
+)
+
+func handler(c *http.Conn, r *http.Request) {
+	fmt.Fprintf(c, "Hi there, I love %s!", r.URL.Path[1:])
+}
+
+func main() {
+	http.HandleFunc("/", handler)
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/index.html b/doc/codelab/wiki/index.html
new file mode 100644
index 000000000..171b9b74f
--- /dev/null
+++ b/doc/codelab/wiki/index.html
@@ -0,0 +1,997 @@
+<div class="content">
+
+<h1>Writing Web Applications</h1>
+
+<h2>Introduction</h2>
+
+<p>
+Covered in this codelab:
+</p>
+<ul>
+<li>Creating a data structure with load and save methods</li>
+<li>Using the <code>http</code> package to build web applications
+<li>Using the <code>template</code> package to process HTML templates</li>
+<li>Using the <code>regexp</code> package to validate user input</li>
+<li>Using closures</li>
+</ul>
+
+<p>
+Assumed knowledge:
+</p>
+<ul>
+<li>Programming experience</li>
+<li>Understanding of basic web technologies (HTTP, HTML)</li>
+<li>Some UNIX command-line knowledge</li>
+</ul>
+
+<h2>Getting Started</h2>
+
+<p>
+At present, you need to have a Linux, OS X, or FreeBSD machine to run Go. If
+you don't have access to one, you could set up a Linux Virtual Machine (using 
+<a href="http://www.virtualbox.org/">VirtualBox</a> or similar) or a
+<a href="http://www.google.com/search?q=virtual+private+server">Virtual 
+Private Server</a>.
+</p>
+
+<p>
+Install Go (see the <a href="http://golang.org/doc/install.html">Installation Instructions</a>).
+</p>
+
+<p>
+Make a new directory for this codelab and cd to it:
+</p>
+
+<pre>
+$ mkdir ~/gowiki
+$ cd ~/gowiki
+</pre>
+
+<p>
+Create a file named <code>wiki.go</code>, open it in your favorite editor, and 
+add the following lines:
+</p>
+
+<pre>
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+)
+</pre>
+
+<p>
+Both <code>fmt</code> and <code>ioutil</code> are built-in packages that 
+we'll be using. Later, as we implement additional functionality, we will add 
+more packages to this <code>import</code> declaration.
+</p>
+
+<h2>Data Structures</h2>
+
+<p>
+Let's start by defining the data structures. A wiki consists of a series of
+interconnected pages, each of which has a title and a body (the page content).
+Here, we define <code>page</code> as a struct with two fields representing
+the title and body.
+</p>
+
+<pre>
+type page struct {
+	title	string
+	body	[]byte
+}
+</pre>
+
+<p>
+The type <code>[]byte</code> means "a <code>byte</code> slice". 
+(See <a href="http://golang.org/doc/effective_go.html#slices">Effective Go</a> 
+for more on slices.)  
+The <code>body</code> element is a <code>[]byte</code> rather than
+<code>string</code> because that is the type expected by the <code>io</code>
+libraries we will use, as you'll see below.
+</p>
+
+<p>
+The <code>page</code> struct describes how page data will be stored in memory. 
+But what about persistent storage? We can address that by creating a 
+<code>save</code> method on <code>page</code>:
+</p>
+
+<pre>
+func (p *page) save() os.Error {
+	filename := p.title + &#34;.txt&#34;
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+</pre>
+
+<p>
+This method's signature reads: "This is a method named <code>save</code> that
+takes as its receiver <code>p</code>, a pointer to <code>page</code> . It takes
+no parameters, and returns a value of type <code>os.Error</code>." 
+</p>
+
+<p>
+This method will save the <code>page</code>'s <code>body</code> to a text 
+file. For simplicity, we will use the <code>title</code> as the file name.
+</p>
+
+<p>
+The <code>save</code> method returns an <code>os.Error</code> value because
+that is the return type of <code>WriteFile</code> (a standard library function
+that writes a byte slice to a file).  The <code>save</code> method returns the
+error value, to let the application handle it should anything go wrong while
+writing the file.  If all goes well, <code>page.save()</code> will return
+<code>nil</code> (the zero-value for pointers, interfaces, and some other 
+types).
+</p>
+
+<p>
+The octal integer constant <code>0600</code>, passed as the third parameter to
+<code>WriteFile</code>, indicates that the file should be created with
+read-write permissions for the current user only. (See the Unix man page
+<code>open(2)</code> for details.)
+</p>
+
+<p>
+We will want to load pages, too:
+</p>
+
+<pre>
+func loadPage(title string) *page {
+	filename := title + &#34;.txt&#34;
+	body, _ := ioutil.ReadFile(filename)
+	return &amp;page{title: title, body: body}
+}
+</pre>
+
+<p>
+The function <code>loadPage</code> constructs the file name from
+<code>title</code>, reads the file's contents into a new
+<code>page</code>, and returns a pointer to that new <code>page</code>.
+</p>
+
+<p>
+Functions can return multiple values. The standard library function 
+<code>io.ReadFile</code> returns <code>[]byte</code> and <code>os.Error</code>. 
+In <code>loadPage</code>, error isn't being handled yet; the "blank identifier"
+represented by the underscore (<code>_</code>) symbol is used to throw away the
+error return value (in essence, assigning the value to nothing). 
+</p>
+
+<p>
+But what happens if <code>ReadFile</code> encounters an error?  For example,
+the file might not exist. We should not ignore such errors.  Let's modify the
+function to return <code>*page</code> and <code>os.Error</code>.
+</p>
+
+<pre>
+func loadPage(title string) (*page, os.Error) {
+	filename := title + &#34;.txt&#34;
+	body, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &amp;page{title: title, body: body}, nil
+}
+</pre>
+
+<p>
+Callers of this function can now check the second parameter; if it is
+<code>nil</code> then it has succesfully loaded a page. If not, it will be an
+<code>os.Error</code> that can be handled by the caller (see the <a
+href="http://golang.org/pkg/os/#Error">os package documentation</a> for 
+details).
+</p>
+
+<p>
+At this point we have a simple data structure and the ability to save to and
+load from a file. Let's write a <code>main</code> function to test what we've
+written:
+</p>
+
+<pre>
+func main() {
+	p1 := &amp;page{title: &#34;TestPage&#34;, body: []byte(&#34;This is a sample page.&#34;)}
+	p1.save()
+	p2, _ := loadPage(&#34;TestPage&#34;)
+	fmt.Println(string(p2.body))
+}
+</pre>
+
+<p>
+After compiling and executing this code, a file named <code>TestPage.txt</code>
+would be created, containing the contents of <code>p1</code>. The file would
+then be read into the struct <code>p2</code>, and its <code>body</code> element
+printed to the screen.
+</p>
+
+<p>
+You can compile and run the program like this: 
+</p>
+
+<pre>
+$ 8g wiki.go
+$ 8l wiki.8
+$ ./8.out
+This is a sample page.
+</pre>
+
+<p>
+(The <code>8g</code> and <code>8l</code> commands are applicable to
+<code>GOARCH=386</code>. If you're on an <code>amd64</code> system,
+subtitute 6's for the 8's.)
+</p>
+
+<p>
+<a href="part1.go">Click here to view the code we've written so far.</a>
+</p>
+
+<h2>Introducing the <code>http</code> package (an interlude)</h2>
+
+<p>
+Here's a full working example of a simple web server:
+</p>
+
+<pre>
+package main
+
+import (
+	&#34;fmt&#34;
+	&#34;http&#34;
+)
+
+func handler(c *http.Conn, r *http.Request) {
+	fmt.Fprintf(c, &#34;Hi there, I love %s!&#34;, r.URL.Path[1:])
+}
+
+func main() {
+	http.HandleFunc(&#34;/&#34;, handler)
+	http.ListenAndServe(&#34;:8080&#34;, nil)
+}
+</pre>
+
+<p>
+The <code>main</code> function begins with a call to 
+<code>http.HandleFunc</code>, which tells the <code>http</code> package to 
+handle all requests to the web root (<code>"/"</code>) with 
+<code>handler</code>. 
+</p>
+
+<p>
+It then calls <code>http.ListenAndServe</code>, specifying that it should
+listen on port 8080 on any interface (<code>":8080"</code>). (Don't
+worry about its second parameter, <code>nil</code>, for now.)
+This function will block until the program is terminated.
+</p>
+
+<p>
+The function <code>handler</code> is of the type <code>http.HandlerFunc</code>.
+It takes an <code>http.Conn</code> and <code>http.Request</code> as its 
+arguments.
+</p>
+
+<p>
+An <code>http.Conn</code> is the server end of an HTTP connection; by writing 
+to it, we send data to the HTTP client.
+</p>
+
+<p>
+An <code>http.Request</code> is a data structure that represents the client
+HTTP request.  The string <code>r.URL.Path</code> is the path component
+of the request URL.  The trailing <code>[1:]</code> means
+"create a sub-slice of <code>Path</code> from the 1st character to the end." 
+This drops the leading "/" from the path name.
+</p>
+
+<p>
+If you run this program and access the URL: 
+</p>
+<pre>http://localhost:8080/monkeys</pre>
+<p>
+the program would present a page containing:
+</p>
+<pre>Hi there, I love monkeys!</pre>
+
+<h2>Using <code>http</code> to serve wiki pages</h2>
+
+<p>
+To use the <code>http</code> package, it must be imported:
+</p>
+
+<pre>
+import (
+	"fmt"
+	<b>"http"</b>
+	"io/ioutil"
+)
+</pre>
+
+<p>
+Let's create a handler to view a wiki page: 
+</p>
+
+<pre>
+const lenPath = len(&#34;/view/&#34;)
+
+func viewHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := loadPage(title)
+	fmt.Fprintf(c, &#34;&lt;h1&gt;%s&lt;/h1&gt;&lt;div&gt;%s&lt;/div&gt;&#34;, p.title, p.body)
+}
+</pre>
+
+<p>
+First, this function extracts the page title from <code>r.URL.Path</code>,
+the path component of the request URL. The global constant 
+<code>lenPath</code> is the length of the leading <code>"/view/"</code>
+component of the request path.
+The <code>Path</code> is re-sliced with <code>[lenPath:]</code> to drop the 
+first 6 characters of the string. This is because the path will invariably 
+begin with <code>"/view/"</code>, which is not part of the page title.
+</p>
+
+<p>
+The function then loads the page data, formats the page with a string of simple 
+HTML, and writes it to <code>c</code>, the <code>http.Conn</code>. 
+</p>
+
+<p>
+Again, note the use of <code>_</code> to ignore the <code>os.Error</code> 
+return value from <code>loadPage</code>. This is done here for simplicity
+and generally considered bad practice. We will attend to this later.
+</p>
+
+<p>
+To use this handler, we create a <code>main</code> function that
+initializes <code>http</code> using the <code>viewHandler</code> to handle
+any requests under the path <code>/view/</code>.
+</p>
+
+<pre>
+func main() {
+	http.HandleFunc(&#34;/view/&#34;, viewHandler)
+	http.ListenAndServe(&#34;:8080&#34;, nil)
+}
+</pre>
+
+<p>
+<a href="part2.go">Click here to view the code we've written so far.</a>
+</p>
+
+<p>
+Let's create some page data (as <code>test.txt</code>), compile our code, and
+try serving a wiki page:
+</p>
+
+<pre>
+$ echo "Hello world" &gt; test.txt
+$ 8g wiki.go
+$ 8l wiki.8
+$ ./8.out
+</pre>
+
+<p>
+With this web server running, a visit to <code><a
+href="http://localhost:8080/view/test">http://localhost:8080/view/test</a></code>
+should show a page titled "test" containing the words "Hello world".
+</p>
+
+<h2>Editing pages</h2>
+
+<p>
+A wiki is not a wiki without the ability to edit pages. Let's create two new
+handlers: one named <code>editHandler</code> to display an 'edit page' form,
+and the other named <code>saveHandler</code> to save the data entered via the
+form.
+</p>
+
+<p>
+First, we add them to <code>main()</code>: 
+</p>
+
+<pre>
+func main() {
+	http.HandleFunc(&#34;/view/&#34;, viewHandler)
+	http.HandleFunc(&#34;/edit/&#34;, editHandler)
+	http.HandleFunc(&#34;/save/&#34;, saveHandler)
+	http.ListenAndServe(&#34;:8080&#34;, nil)
+}
+</pre>
+
+<p>
+The function <code>editHandler</code> loads the page 
+(or, if it doesn't exist, create an empty <code>page</code> struct), 
+and displays an HTML form.
+</p>
+
+<pre>
+func editHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, err := loadPage(title)
+	if err != nil {
+		p = &amp;page{title: title}
+	}
+	fmt.Fprintf(c, &#34;&lt;h1&gt;Editing %s&lt;/h1&gt;&#34;+
+		&#34;&lt;form action=\&#34;/save/%s\&#34; method=\&#34;POST\&#34;&gt;&#34;+
+		&#34;&lt;textarea name=\&#34;body\&#34;&gt;%s&lt;/textarea&gt;&lt;br&gt;&#34;+
+		&#34;&lt;input type=\&#34;submit\&#34; value=\&#34;Save\&#34;&gt;&#34;+
+		&#34;&lt;/form&gt;&#34;,
+		p.title, p.title, p.body)
+}
+</pre>
+
+<p>
+This function will work fine, but all that hard-coded HTML is ugly.
+Of course, there is a better way.
+</p>
+ 
+<h2>The <code>template</code> package</h2>
+
+<p>
+The <code>template</code> package is part of the Go standard library.  We can
+use <code>template</code> to keep the HTML in a separate file, allowing
+us to change the layout of our edit page without modifying the underlying Go
+code.
+</p>
+
+<p>
+First, we must add <code>template</code> to the list of imports:
+</p>
+
+<pre>
+import (
+	"http"
+	"io/ioutil"
+	"os"
+	<b>"template"</b>
+)
+</pre>
+
+<p>
+Let's create a template file containg the HTML form. 
+Open a new file named <code>edit.html</code>, and add the following lines:
+</p>
+
+<pre>
+&lt;h1&gt;Editing {title}&lt;/h1&gt;
+
+&lt;form action=&#34;/save/{title}&#34; method=&#34;POST&#34;&gt;
+&lt;div&gt;&lt;textarea name=&#34;body&#34; rows=&#34;20&#34; cols=&#34;80&#34;&gt;{body|html}&lt;/textarea&gt;&lt;/div&gt;
+&lt;div&gt;&lt;input type=&#34;submit&#34; value=&#34;Save&#34;&gt;&lt;/div&gt;
+&lt;/form&gt;
+</pre>
+
+<p>
+Modify <code>editHandler</code> to use the template, instead of the hard-coded
+HTML:
+</p>
+
+<pre>
+func editHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, err := loadPage(title)
+	if err != nil {
+		p = &amp;page{title: title}
+	}
+	t, _ := template.ParseFile(&#34;edit.html&#34;, nil)
+	t.Execute(p, c)
+}
+</pre>
+
+<p>
+The function <code>template.ParseFile</code> will read the contents of 
+<code>edit.html</code> and return a <code>*template.Template</code>. 
+</p>
+
+<p>
+The method <code>t.Execute</code> replaces all occurrences of 
+<code>{title}</code> and <code>{body}</code> with the values of 
+<code>p.title</code> and <code>p.body</code>, and writes the resultant
+HTML to the <code>http.Conn</code>.
+</p>
+
+<p>
+Note that we've used <code>{body|html}</code> in the above template.  
+The <code>|html</code> part asks the template engine to pass the value
+<code>body</code> through the <code>html</code> formatter before outputting it,
+which escapes HTML characters (such as replacing <code>&gt;</code> with 
+<code>&amp;gt;</code>). 
+This will prevent user data from corrupting the form HTML. 
+</p>
+
+<p>
+Now that we've removed the <code>fmt.Sprintf</code> statement, we can remove
+<code>"fmt"</code> from the <code>import</code> list.
+</p>
+
+<p>
+While we're working with templates, let's create a template for our
+<code>viewHandler</code> called <code>view.html</code>:
+</p>
+
+<pre>
+&lt;h1&gt;{title}&lt;/h1&gt;
+
+&lt;p&gt;[&lt;a href=&#34;/edit/{title}&#34;&gt;edit&lt;/a&gt;]&lt;/p&gt;
+
+&lt;div&gt;{body}&lt;/div&gt;
+</pre>
+
+<p>
+Modify <code>viewHandler</code> accordingly:
+</p>
+
+<pre>
+func viewHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := loadPage(title)
+	t, _ := template.ParseFile(&#34;view.html&#34;, nil)
+	t.Execute(p, c)
+}
+</pre>
+
+<p>
+Notice that we've used almost exactly the same templating code in both
+handlers. Let's remove this duplication by moving the templating code
+to its own function:
+</p>
+
+<pre>
+func viewHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := loadPage(title)
+	renderTemplate(c, &#34;edit&#34;, p)
+}
+
+func editHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, err := loadPage(title)
+	if err != nil {
+		p = &amp;page{title: title}
+	}
+	renderTemplate(c, &#34;view&#34;, p)
+}
+
+func renderTemplate(c *http.Conn, tmpl string, p *page) {
+	t, _ := template.ParseFile(tmpl+&#34;.html&#34;, nil)
+	t.Execute(p, c)
+}
+</pre>
+
+<p>
+The handlers are now shorter and simpler. 
+</p>
+
+<h2>Handling non-existent pages</h2>
+
+<p>
+What if you visit <code>/view/APageThatDoesntExist</code>? The program will 
+crash. This is because it ignores the error return value from
+<code>loadPage</code>. Instead, if the requested page doesn't exist, it should 
+redirect the client to the edit page so the content may be created:
+</p>
+
+<pre>
+func viewHandler(c *http.Conn, r *http.Request, title string) {
+	p, err := loadPage(title)
+	if err != nil {
+		http.Redirect(c, &#34;/edit/&#34;+title, http.StatusFound)
+		return
+	}
+	renderTemplate(c, &#34;view&#34;, p)
+}
+</pre>
+
+<p>
+The <code>http.Redirect</code> function adds an HTTP status code of 
+<code>http.StatusFound</code> (302) and a <code>Location</code>
+header to the HTTP response.
+</p>
+
+<h2>Saving pages</h2>
+
+<p>
+The function <code>saveHandler</code> will handle the form submission. 
+</p>
+
+<pre>
+func saveHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	body := r.FormValue(&#34;body&#34;)
+	p := &amp;page{title: title, body: []byte(body)}
+	p.save()
+	http.Redirect(c, &#34;/view/&#34;+title, http.StatusFound)
+}
+</pre>
+
+<p>
+The page title (provided in the URL) and the form's only field, 
+<code>body</code>, are stored in a new <code>page</code>. 
+The <code>save()</code> method is then called to write the data to a file,
+and the client is redirected to the <code>/view/</code> page.
+</p>
+
+<p>
+The value returned by <code>FormValue</code> is of type <code>string</code>.
+We must convert that value to <code>[]byte</code> before it will fit into 
+the <code>page</code> struct.  We use <code>[]byte(body)</code> to perform
+the conversion.
+</p>
+
+<h2>Error handling</h2>
+
+<p>
+There are several places in our program where errors are being ignored.  This
+is bad practice, not least because when an error does occur the program will
+crash.  A better solution is to handle the errors and return an error message
+to the user. That way if something does go wrong, the server will continue to
+function and the user will be notified.
+</p>
+
+<p>
+First, let's handle the errors in <code>renderTemplate</code>:
+</p>
+
+<pre>
+func renderTemplate(c *http.Conn, tmpl string, p *page) {
+	t, err := template.ParseFile(tmpl+&#34;.html&#34;, nil)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	err = t.Execute(p, c)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+	}
+}
+</pre>
+
+<p>
+The <code>http.Error</code> function sends a specified HTTP response code 
+(in this case "Internal Server Error") and error message.
+Already the decision to put this in a separate function is paying off.
+</p>
+
+<p>
+Now let's fix up <code>saveHandler</code>:
+</p>
+
+<pre>
+func saveHandler(c *http.Conn, r *http.Request, title string) {
+	body := r.FormValue(&#34;body&#34;)
+	p := &amp;page{title: title, body: []byte(body)}
+	err := p.save()
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(c, &#34;/view/&#34;+title, http.StatusFound)
+}
+</pre>
+
+<p>
+Any errors that occur during <code>p.save()</code> will be reported 
+to the user.
+</p>
+
+<h2>Template caching</h2>
+
+<p>
+There is an inefficiency in this code: <code>renderTemplate</code> calls 
+<code>ParseFile</code> every time a page is rendered. 
+A better approach would be to call <code>ParseFile</code> once for each 
+template at program initialization, and store the resultant 
+<code>*Template</code> values in a data structure for later use.
+</p>
+
+<p>
+First we create a global map named <code>templates</code> in which to store 
+our <code>*Template</code> values, keyed by <code>string</code> 
+(the template name):
+</p>
+
+<pre>
+var templates = make(map[string]*template.Template)
+</pre>
+
+<p>
+Then we create an <code>init</code> function, which will be called before
+<code>main</code> at program initialization. The function
+<code>template.MustParseFile</code> is a convenience wrapper around
+<code>ParseFile</code> that does not return an error code; instead, it panics
+if an error is encountered. A panic is appropriate here; if the templates can't
+be loaded the only sensible thing to do is exit the program.
+</p
+
+<pre>
+func init() {
+	for _, tmpl := range []string{&#34;edit&#34;, &#34;view&#34;} {
+		templates[tmpl] = template.MustParseFile(tmpl+&#34;.html&#34;, nil)
+	}
+}
+</pre>
+
+<p>
+A <code>for</code> loop is used with a <code>range</code> statement to iterate 
+over an array constant containing the names of the templates we want parsed.
+If we were to add more templates to our program, we would add their names to 
+that array.
+</p>
+
+<p>
+We then modify our <code>renderTemplate</code> function to call 
+the <code>Execute</code> method on the appropriate <code>Template</code> from 
+<code>templates</code>:
+
+<pre>
+func renderTemplate(c *http.Conn, tmpl string, p *page) {
+	err := templates[tmpl].Execute(p, c)
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+	}
+}
+</pre>
+
+<h2>Validation</h2>
+
+<p>
+As you may have observed, this program has a serious security flaw: a user
+can supply an arbitrary path to be read/written on the server. To mitigate
+this, we can write a function to validate the title with a regular expression.
+</p>
+
+<p>
+First, add <code>"regexp"</code> to the <code>import</code> list.
+Then we can create a global variable to store our validation regexp:
+</p>
+
+<pre>
+var titleValidator = regexp.MustCompile(&#34;^[a-zA-Z0-9]+$&#34;)
+</pre>
+
+<p>
+The function <code>regexp.MustCompile</code> will parse and compile the 
+regular expression, and return a <code>regexp.Regexp</code>. 
+<code>MustCompile</code>, like <code>template.MustParseFile</code>,
+is distinct from <code>Compile</code> in that it will panic if 
+the expression compilation fails, while <code>Compile</code> returns an 
+<code>os.Error</code> as a second parameter. 
+</p>
+
+<p>
+Now, let's write a function that extracts the title string from the request 
+URL, and tests it against our <code>titleValidator</code> expression:
+</p>
+
+<pre>
+func getTitle(c *http.Conn, r *http.Request) (title string, err os.Error) {
+	title = r.URL.Path[lenPath:]
+	if !titleValidator.MatchString(title) {
+		http.NotFound(c, r)
+		err = os.NewError(&#34;Invalid Page Title&#34;)
+	}
+	return
+}
+</pre>
+
+<p>
+If the title is valid, it will be returned along with a <code>nil</code>
+error value.  If the title is invalid, the function will write a 
+"404 Not Found" error to the HTTP connection, and return an error to the 
+handler. 
+</p>
+
+<p>
+Let's put a call to <code>getTitle</code> in each of the handlers:
+</p>
+
+<pre>
+func viewHandler(c *http.Conn, r *http.Request) {
+	title, err := getTitle(c, r)
+	if err != nil {
+		return
+	}
+	p, err := loadPage(title)
+	if err != nil {
+		http.Redirect(c, &#34;/edit/&#34;+title, http.StatusFound)
+		return
+	}
+	renderTemplate(c, &#34;view&#34;, p)
+}
+
+func editHandler(c *http.Conn, r *http.Request) {
+	title, err := getTitle(c, r)
+	if err != nil {
+		return
+	}
+	p, err := loadPage(title)
+	if err != nil {
+		p = &amp;page{title: title}
+	}
+	renderTemplate(c, &#34;edit&#34;, p)
+}
+
+func saveHandler(c *http.Conn, r *http.Request) {
+	title, err := getTitle(c, r)
+	if err != nil {
+		return
+	}
+	body := r.FormValue(&#34;body&#34;)
+	p := &amp;page{title: title, body: []byte(body)}
+	err = p.save()
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(c, &#34;/view/&#34;+title, http.StatusFound)
+}
+</pre>
+
+<h2>Introducing Function Literals and Closures</h2>
+
+<p>
+Catching the error condition in each handler introduces a lot of repeated code.
+What if we could wrap each of the handlers in a function that does this 
+validation and error checking? Go's 
+<a href="http://golang.org/doc/go_spec.html#Function_declarations">function 
+literals</a> provide a powerful means of abstracting functionality 
+that can help us here.
+</p>
+
+<p>
+First, we re-write the function definition of each of the handlers to accept
+a title string:
+</p>
+
+<pre>
+func viewHandler(c, *http.Conn, r *http.Request, title string)
+func editHandler(c, *http.Conn, r *http.Request, title string)
+func saveHandler(c, *http.Conn, r *http.Request, title string)
+</pre>
+
+<p>
+Now let's define a wrapper function that <i>takes a function of the above
+type</i>, and returns a function of type <code>http.HandlerFunc</code>
+(suitable to be passed to the function <code>http.HandleFunc</code>):
+</p>
+
+<pre>
+func makeHandler(fn func (*http.Conn, *http.Request, string)) http.HandlerFunc {
+	return func(c *http.Conn, r *http.Request) {
+		// Here we will extract the page title from the Request,
+		// and call the provided handler 'fn'
+	}
+}
+</pre>
+
+<p>
+The returned function is called a closure because it encloses values defined
+outside of it. In this case, the variable <code>fn</code> (the single argument
+to <code>makeHandler</code>) is enclosed by the closure. The variable
+<code>fn</code> will be one of our save, edit, or view handlers.
+</p>
+
+<p>
+Now we can take the code from <code>getTitle</code> and use it here
+(with some minor modifications):
+</p>
+
+<pre>
+func makeHandler(fn func(*http.Conn, *http.Request, string)) http.HandlerFunc {
+	return func(c *http.Conn, r *http.Request) {
+		title := r.URL.Path[lenPath:]
+		if !titleValidator.MatchString(title) {
+			http.NotFound(c, r)
+			return
+		}
+		fn(c, r, title)
+	}
+}
+</pre>
+
+<p>
+The closure returned by <code>makeHandler</code> is a function that takes
+an <code>http.Conn</code> and <code>http.Request</code> (in other words,
+an <code>http.HandlerFunc</code>). 
+The closure extracts the <code>title</code> from the request path, and
+validates it with the <code>titleValidator</code> regexp. If the
+<code>title</code> is invalid, an error will be written to the
+<code>Conn</code> using the <code>http.NotFound</code> function. 
+If the <code>title</code> is valid, the enclosed handler function
+<code>fn</code> will be called with the <code>Conn</code>,
+<code>Request</code>, and <code>title</code> as arguments.
+</p>
+
+<p>
+Now we can wwrap the handler functions with <code>makeHandler</code> in 
+<code>main</code>, before they are registered with the <code>http</code> 
+package:
+</p>
+
+<pre>
+func main() {
+	http.HandleFunc(&#34;/view/&#34;, makeHandler(viewHandler))
+	http.HandleFunc(&#34;/edit/&#34;, makeHandler(editHandler))
+	http.HandleFunc(&#34;/save/&#34;, makeHandler(saveHandler))
+	http.ListenAndServe(&#34;:8080&#34;, nil)
+}
+</pre>
+
+<p>
+Finally we remove the calls to <code>getTitle</code> from the handler functions,
+making them much simpler:
+</p>
+
+<pre>
+func viewHandler(c *http.Conn, r *http.Request, title string) {
+	p, err := loadPage(title)
+	if err != nil {
+		http.Redirect(c, &#34;/edit/&#34;+title, http.StatusFound)
+		return
+	}
+	renderTemplate(c, &#34;view&#34;, p)
+}
+
+func editHandler(c *http.Conn, r *http.Request, title string) {
+	p, err := loadPage(title)
+	if err != nil {
+		p = &amp;page{title: title}
+	}
+	renderTemplate(c, &#34;edit&#34;, p)
+}
+
+func saveHandler(c *http.Conn, r *http.Request, title string) {
+	body := r.FormValue(&#34;body&#34;)
+	p := &amp;page{title: title, body: []byte(body)}
+	err := p.save()
+	if err != nil {
+		http.Error(c, err.String(), http.StatusInternalServerError)
+		return
+	}
+	http.Redirect(c, &#34;/view/&#34;+title, http.StatusFound)
+}
+</pre>
+
+<h2>Try it out!</h2>
+
+<p>
+<a href="final.go">Click here to view the final code listing.</a>
+</p>
+
+<p>
+Recompile the code, and run the app:
+</p>
+
+<pre>
+$ 8g wiki.go
+$ 8l wiki.8
+$ ./8.out
+</pre>
+
+<p>
+Visiting <a href="http://localhost:8080/ANewPage">http://localhost:8080/ANewPage</a>
+should present you with the page edit form. You should then be able to 
+enter some text, click 'Save', and be redirected to the newly created page.
+</p>
+
+<h2>Other tasks</h2>
+
+<p>
+Here are some simple tasks you might want to tackle on your own:
+</p>
+
+<ul>
+<li>Store templates in <code>tmpl/</code> and page data in <code>data/</code>.
+<li>Add a handler to make the web root redirect to 
+	<code>/view/FrontPage</code>.</li>
+<li>Spruce up the page templates by making them valid HTML and adding some
+	CSS rules.</li>
+<li>Implement inter-page linking by converting instances of 
+	<code>[PageName]</code> to <br>
+	<code>&lt;a href="/view/PageName"&gt;PageName&lt;/a&gt;</code>.
+	(hint: you could use <code>regexp.ReplaceAllFunc</code> to do this)
+	</li>
+</ul>
+
+</div>
diff --git a/doc/codelab/wiki/notemplate.go b/doc/codelab/wiki/notemplate.go
new file mode 100644
index 000000000..a61d905e3
--- /dev/null
+++ b/doc/codelab/wiki/notemplate.go
@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+	"http"
+	"io/ioutil"
+	"os"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.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(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := loadPage(title)
+	fmt.Fprintf(c, "<h1>%s</h1><div>%s</div>", p.title, p.body)
+}
+
+func editHandler(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, err := loadPage(title)
+	if err != nil {
+		p = &page{title: title}
+	}
+	fmt.Fprintf(c, "<h1>Editing %s</h1>"+
+		"<form action=\"/save/%s\" method=\"POST\">"+
+		"<textarea name=\"body\">%s</textarea><br>"+
+		"<input type=\"submit\" value=\"Save\">"+
+		"</form>",
+		p.title, p.title, p.body)
+}
+
+func main() {
+	http.HandleFunc("/view/", viewHandler)
+	http.HandleFunc("/edit/", editHandler)
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/part1-noerror.go b/doc/codelab/wiki/part1-noerror.go
new file mode 100644
index 000000000..39e8331e3
--- /dev/null
+++ b/doc/codelab/wiki/part1-noerror.go
@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) *page {
+	filename := title + ".txt"
+	body, _ := ioutil.ReadFile(filename)
+	return &page{title: title, body: body}
+}
+
+func main() {
+	p1 := &page{title: "TestPage", body: []byte("This is a sample page.")}
+	p1.save()
+	p2 := loadPage("TestPage")
+	fmt.Println(string(p2.body))
+}
diff --git a/doc/codelab/wiki/part1.go b/doc/codelab/wiki/part1.go
new file mode 100644
index 000000000..f3678baa5
--- /dev/null
+++ b/doc/codelab/wiki/part1.go
@@ -0,0 +1,33 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.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, _ := loadPage("TestPage")
+	fmt.Println(string(p2.body))
+}
diff --git a/doc/codelab/wiki/part2.go b/doc/codelab/wiki/part2.go
new file mode 100644
index 000000000..c2c29dc3b
--- /dev/null
+++ b/doc/codelab/wiki/part2.go
@@ -0,0 +1,40 @@
+package main
+
+import (
+	"fmt"
+	"http"
+	"io/ioutil"
+	"os"
+)
+
+type page struct {
+	title string
+	body  []byte
+}
+
+func (p *page) save() os.Error {
+	filename := p.title + ".txt"
+	return ioutil.WriteFile(filename, p.body, 0600)
+}
+
+func loadPage(title string) (*page, os.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(c *http.Conn, r *http.Request) {
+	title := r.URL.Path[lenPath:]
+	p, _ := loadPage(title)
+	fmt.Fprintf(c, "<h1>%s</h1><div>%s</div>", p.title, p.body)
+}
+
+func main() {
+	http.HandleFunc("/view/", viewHandler)
+	http.ListenAndServe(":8080", nil)
+}
diff --git a/doc/codelab/wiki/srcextract.go b/doc/codelab/wiki/srcextract.go
new file mode 100644
index 000000000..607375183
--- /dev/null
+++ b/doc/codelab/wiki/srcextract.go
@@ -0,0 +1,73 @@
+package main
+
+import (
+	"bytes"
+	"flag"
+	"go/parser"
+	"go/printer"
+	"go/ast"
+	"log"
+	"os"
+)
+
+var (
+	srcFn   = flag.String("src", "", "source filename")
+	getName = flag.String("name", "", "func/type name to output")
+	html    = flag.Bool("html", true, "output HTML")
+	showPkg = flag.Bool("pkg", false, "show package in output")
+)
+
+func main() {
+	// handle input
+	flag.Parse()
+	if *srcFn == "" || *getName == "" {
+		flag.Usage()
+		os.Exit(2)
+	}
+	// load file
+	file, err := parser.ParseFile(*srcFn, nil, nil, 0)
+	if err != nil {
+		log.Exit(err)
+	}
+	// create printer
+	p := &printer.Config{
+		Mode:     0,
+		Tabwidth: 8,
+		Styler:   nil,
+	}
+	if *html {
+		p.Mode = printer.GenHTML
+	}
+	// create filter
+	filter := func(name string) bool {
+		return name == *getName
+	}
+	// filter
+	if !ast.FilterFile(file, filter) {
+		os.Exit(1)
+	}
+	b := new(bytes.Buffer)
+	p.Fprint(b, file)
+	// drop package declaration
+	if !*showPkg {
+		for {
+			c, err := b.ReadByte()
+			if c == '\n' || err != nil {
+				break
+			}
+		}
+	}
+	// drop leading newlines
+	for {
+		b, err := b.ReadByte()
+		if err != nil {
+			break
+		}
+		if b != '\n' {
+			os.Stdout.Write([]byte{b})
+			break
+		}
+	}
+	// output
+	b.WriteTo(os.Stdout)
+}
diff --git a/doc/codelab/wiki/test.sh b/doc/codelab/wiki/test.sh
new file mode 100755
index 000000000..5b752fe3c
--- /dev/null
+++ b/doc/codelab/wiki/test.sh
@@ -0,0 +1,24 @@
+#1/bin/bash
+
+./final.bin &
+wiki_pid=$!
+
+cleanup() {
+	kill $wiki_pid
+	rm -f test_*.out Test.txt
+	exit ${1:-1}
+}
+trap cleanup INT
+
+sleep 1
+
+curl -s -o test_edit.out http://localhost:8080/edit/Test 
+cmp test_edit.out test_edit.good || cleanup 1
+curl -s -o /dev/null -d body=some%20content http://localhost:8080/save/Test
+cmp Test.txt test_Test.txt.good || cleanup 1
+curl -s -o test_view.out http://localhost:8080/view/Test
+cmp test_view.out test_view.good || cleanup 1
+
+echo "Passed"
+cleanup 0
+
diff --git a/doc/codelab/wiki/test_Test.txt.good b/doc/codelab/wiki/test_Test.txt.good
new file mode 100644
index 000000000..f0eec86f6
--- /dev/null
+++ b/doc/codelab/wiki/test_Test.txt.good
@@ -0,0 +1 @@
+some content
\ No newline at end of file
diff --git a/doc/codelab/wiki/test_edit.good b/doc/codelab/wiki/test_edit.good
new file mode 100644
index 000000000..36c6dbb73
--- /dev/null
+++ b/doc/codelab/wiki/test_edit.good
@@ -0,0 +1,6 @@
+<h1>Editing Test</h1>
+
+<form action="/save/Test" method="POST">
+<div><textarea name="body" rows="20" cols="80"></textarea></div>
+<div><input type="submit" value="Save"></div>
+</form>
diff --git a/doc/codelab/wiki/test_view.good b/doc/codelab/wiki/test_view.good
new file mode 100644
index 000000000..07e8edb22
--- /dev/null
+++ b/doc/codelab/wiki/test_view.good
@@ -0,0 +1,5 @@
+<h1>Test</h1>
+
+<p>[<a href="/edit/Test">edit</a>]</p>
+
+<div>some content</div>
diff --git a/doc/codelab/wiki/view.html b/doc/codelab/wiki/view.html
new file mode 100644
index 000000000..a46622d01
--- /dev/null
+++ b/doc/codelab/wiki/view.html
@@ -0,0 +1,5 @@
+<h1>{title}</h1>
+
+<p>[<a href="/edit/{title}">edit</a>]</p>
+
+<div>{body}</div>
diff --git a/doc/codelab/wiki/wiki.html b/doc/codelab/wiki/wiki.html
new file mode 100644
index 000000000..b3525f73b
--- /dev/null
+++ b/doc/codelab/wiki/wiki.html
@@ -0,0 +1,783 @@
+<div class="content">
+
+<h1>Writing Web Applications</h1>
+
+<h2>Introduction</h2>
+
+<p>
+Covered in this codelab:
+</p>
+<ul>
+<li>Creating a data structure with load and save methods</li>
+<li>Using the <code>http</code> package to build web applications
+<li>Using the <code>template</code> package to process HTML templates</li>
+<li>Using the <code>regexp</code> package to validate user input</li>
+<li>Using closures</li>
+</ul>
+
+<p>
+Assumed knowledge:
+</p>
+<ul>
+<li>Programming experience</li>
+<li>Understanding of basic web technologies (HTTP, HTML)</li>
+<li>Some UNIX command-line knowledge</li>
+</ul>
+
+<h2>Getting Started</h2>
+
+<p>
+At present, you need to have a Linux, OS X, or FreeBSD machine to run Go. If
+you don't have access to one, you could set up a Linux Virtual Machine (using 
+<a href="http://www.virtualbox.org/">VirtualBox</a> or similar) or a
+<a href="http://www.google.com/search?q=virtual+private+server">Virtual 
+Private Server</a>.
+</p>
+
+<p>
+Install Go (see the <a href="http://golang.org/doc/install.html">Installation Instructions</a>).
+</p>
+
+<p>
+Make a new directory for this codelab and cd to it:
+</p>
+
+<pre>
+$ mkdir ~/gowiki
+$ cd ~/gowiki
+</pre>
+
+<p>
+Create a file named <code>wiki.go</code>, open it in your favorite editor, and 
+add the following lines:
+</p>
+
+<pre>
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+)
+</pre>
+
+<p>
+Both <code>fmt</code> and <code>ioutil</code> are built-in packages that 
+we'll be using. Later, as we implement additional functionality, we will add 
+more packages to this <code>import</code> declaration.
+</p>
+
+<h2>Data Structures</h2>
+
+<p>
+Let's start by defining the data structures. A wiki consists of a series of
+interconnected pages, each of which has a title and a body (the page content).
+Here, we define <code>page</code> as a struct with two fields representing
+the title and body.
+</p>
+
+<pre>
+!./srcextract.bin -src=part1.go -name=page
+</pre>
+
+<p>
+The type <code>[]byte</code> means "a <code>byte</code> slice". 
+(See <a href="http://golang.org/doc/effective_go.html#slices">Effective Go</a> 
+for more on slices.)  
+The <code>body</code> element is a <code>[]byte</code> rather than
+<code>string</code> because that is the type expected by the <code>io</code>
+libraries we will use, as you'll see below.
+</p>
+
+<p>
+The <code>page</code> struct describes how page data will be stored in memory. 
+But what about persistent storage? We can address that by creating a 
+<code>save</code> method on <code>page</code>:
+</p>
+
+<pre>
+!./srcextract.bin -src=part1.go -name=save
+</pre>
+
+<p>
+This method's signature reads: "This is a method named <code>save</code> that
+takes as its receiver <code>p</code>, a pointer to <code>page</code> . It takes
+no parameters, and returns a value of type <code>os.Error</code>." 
+</p>
+
+<p>
+This method will save the <code>page</code>'s <code>body</code> to a text 
+file. For simplicity, we will use the <code>title</code> as the file name.
+</p>
+
+<p>
+The <code>save</code> method returns an <code>os.Error</code> value because
+that is the return type of <code>WriteFile</code> (a standard library function
+that writes a byte slice to a file).  The <code>save</code> method returns the
+error value, to let the application handle it should anything go wrong while
+writing the file.  If all goes well, <code>page.save()</code> will return
+<code>nil</code> (the zero-value for pointers, interfaces, and some other 
+types).
+</p>
+
+<p>
+The octal integer constant <code>0600</code>, passed as the third parameter to
+<code>WriteFile</code>, indicates that the file should be created with
+read-write permissions for the current user only. (See the Unix man page
+<code>open(2)</code> for details.)
+</p>
+
+<p>
+We will want to load pages, too:
+</p>
+
+<pre>
+!./srcextract.bin -src=part1-noerror.go -name=loadPage
+</pre>
+
+<p>
+The function <code>loadPage</code> constructs the file name from
+<code>title</code>, reads the file's contents into a new
+<code>page</code>, and returns a pointer to that new <code>page</code>.
+</p>
+
+<p>
+Functions can return multiple values. The standard library function 
+<code>io.ReadFile</code> returns <code>[]byte</code> and <code>os.Error</code>. 
+In <code>loadPage</code>, error isn't being handled yet; the "blank identifier"
+represented by the underscore (<code>_</code>) symbol is used to throw away the
+error return value (in essence, assigning the value to nothing). 
+</p>
+
+<p>
+But what happens if <code>ReadFile</code> encounters an error?  For example,
+the file might not exist. We should not ignore such errors.  Let's modify the
+function to return <code>*page</code> and <code>os.Error</code>.
+</p>
+
+<pre>
+!./srcextract.bin -src=part1.go -name=loadPage
+</pre>
+
+<p>
+Callers of this function can now check the second parameter; if it is
+<code>nil</code> then it has succesfully loaded a page. If not, it will be an
+<code>os.Error</code> that can be handled by the caller (see the <a
+href="http://golang.org/pkg/os/#Error">os package documentation</a> for 
+details).
+</p>
+
+<p>
+At this point we have a simple data structure and the ability to save to and
+load from a file. Let's write a <code>main</code> function to test what we've
+written:
+</p>
+
+<pre>
+!./srcextract.bin -src=part1.go -name=main
+</pre>
+
+<p>
+After compiling and executing this code, a file named <code>TestPage.txt</code>
+would be created, containing the contents of <code>p1</code>. The file would
+then be read into the struct <code>p2</code>, and its <code>body</code> element
+printed to the screen.
+</p>
+
+<p>
+You can compile and run the program like this: 
+</p>
+
+<pre>
+$ 8g wiki.go
+$ 8l wiki.8
+$ ./8.out
+This is a sample page.
+</pre>
+
+<p>
+(The <code>8g</code> and <code>8l</code> commands are applicable to
+<code>GOARCH=386</code>. If you're on an <code>amd64</code> system,
+subtitute 6's for the 8's.)
+</p>
+
+<p>
+<a href="part1.go">Click here to view the code we've written so far.</a>
+</p>
+
+<h2>Introducing the <code>http</code> package (an interlude)</h2>
+
+<p>
+Here's a full working example of a simple web server:
+</p>
+
+<pre>
+!./htmlify.bin < http-sample.go
+</pre>
+
+<p>
+The <code>main</code> function begins with a call to 
+<code>http.HandleFunc</code>, which tells the <code>http</code> package to 
+handle all requests to the web root (<code>"/"</code>) with 
+<code>handler</code>. 
+</p>
+
+<p>
+It then calls <code>http.ListenAndServe</code>, specifying that it should
+listen on port 8080 on any interface (<code>":8080"</code>). (Don't
+worry about its second parameter, <code>nil</code>, for now.)
+This function will block until the program is terminated.
+</p>
+
+<p>
+The function <code>handler</code> is of the type <code>http.HandlerFunc</code>.
+It takes an <code>http.Conn</code> and <code>http.Request</code> as its 
+arguments.
+</p>
+
+<p>
+An <code>http.Conn</code> is the server end of an HTTP connection; by writing 
+to it, we send data to the HTTP client.
+</p>
+
+<p>
+An <code>http.Request</code> is a data structure that represents the client
+HTTP request.  The string <code>r.URL.Path</code> is the path component
+of the request URL.  The trailing <code>[1:]</code> means
+"create a sub-slice of <code>Path</code> from the 1st character to the end." 
+This drops the leading "/" from the path name.
+</p>
+
+<p>
+If you run this program and access the URL: 
+</p>
+<pre>http://localhost:8080/monkeys</pre>
+<p>
+the program would present a page containing:
+</p>
+<pre>Hi there, I love monkeys!</pre>
+
+<h2>Using <code>http</code> to serve wiki pages</h2>
+
+<p>
+To use the <code>http</code> package, it must be imported:
+</p>
+
+<pre>
+import (
+	"fmt"
+	<b>"http"</b>
+	"io/ioutil"
+)
+</pre>
+
+<p>
+Let's create a handler to view a wiki page: 
+</p>
+
+<pre>
+!./srcextract.bin -src=part2.go -name=lenPath
+
+!./srcextract.bin -src=part2.go -name=viewHandler
+</pre>
+
+<p>
+First, this function extracts the page title from <code>r.URL.Path</code>,
+the path component of the request URL. The global constant 
+<code>lenPath</code> is the length of the leading <code>"/view/"</code>
+component of the request path.
+The <code>Path</code> is re-sliced with <code>[lenPath:]</code> to drop the 
+first 6 characters of the string. This is because the path will invariably 
+begin with <code>"/view/"</code>, which is not part of the page title.
+</p>
+
+<p>
+The function then loads the page data, formats the page with a string of simple 
+HTML, and writes it to <code>c</code>, the <code>http.Conn</code>. 
+</p>
+
+<p>
+Again, note the use of <code>_</code> to ignore the <code>os.Error</code> 
+return value from <code>loadPage</code>. This is done here for simplicity
+and generally considered bad practice. We will attend to this later.
+</p>
+
+<p>
+To use this handler, we create a <code>main</code> function that
+initializes <code>http</code> using the <code>viewHandler</code> to handle
+any requests under the path <code>/view/</code>.
+</p>
+
+<pre>
+!./srcextract.bin -src=part2.go -name=main
+</pre>
+
+<p>
+<a href="part2.go">Click here to view the code we've written so far.</a>
+</p>
+
+<p>
+Let's create some page data (as <code>test.txt</code>), compile our code, and
+try serving a wiki page:
+</p>
+
+<pre>
+$ echo "Hello world" &gt; test.txt
+$ 8g wiki.go
+$ 8l wiki.8
+$ ./8.out
+</pre>
+
+<p>
+With this web server running, a visit to <code><a
+href="http://localhost:8080/view/test">http://localhost:8080/view/test</a></code>
+should show a page titled "test" containing the words "Hello world".
+</p>
+
+<h2>Editing pages</h2>
+
+<p>
+A wiki is not a wiki without the ability to edit pages. Let's create two new
+handlers: one named <code>editHandler</code> to display an 'edit page' form,
+and the other named <code>saveHandler</code> to save the data entered via the
+form.
+</p>
+
+<p>
+First, we add them to <code>main()</code>: 
+</p>
+
+<pre>
+!./srcextract.bin -src=final-noclosure.go -name=main
+</pre>
+
+<p>
+The function <code>editHandler</code> loads the page 
+(or, if it doesn't exist, create an empty <code>page</code> struct), 
+and displays an HTML form.
+</p>
+
+<pre>
+!./srcextract.bin -src=notemplate.go -name=editHandler
+</pre>
+
+<p>
+This function will work fine, but all that hard-coded HTML is ugly.
+Of course, there is a better way.
+</p>
+ 
+<h2>The <code>template</code> package</h2>
+
+<p>
+The <code>template</code> package is part of the Go standard library.  We can
+use <code>template</code> to keep the HTML in a separate file, allowing
+us to change the layout of our edit page without modifying the underlying Go
+code.
+</p>
+
+<p>
+First, we must add <code>template</code> to the list of imports:
+</p>
+
+<pre>
+import (
+	"http"
+	"io/ioutil"
+	"os"
+	<b>"template"</b>
+)
+</pre>
+
+<p>
+Let's create a template file containg the HTML form. 
+Open a new file named <code>edit.html</code>, and add the following lines:
+</p>
+
+<pre>
+!./htmlify.bin < edit.html
+</pre>
+
+<p>
+Modify <code>editHandler</code> to use the template, instead of the hard-coded
+HTML:
+</p>
+
+<pre>
+!./srcextract.bin -src=final-noerror.go -name=editHandler
+</pre>
+
+<p>
+The function <code>template.ParseFile</code> will read the contents of 
+<code>edit.html</code> and return a <code>*template.Template</code>. 
+</p>
+
+<p>
+The method <code>t.Execute</code> replaces all occurrences of 
+<code>{title}</code> and <code>{body}</code> with the values of 
+<code>p.title</code> and <code>p.body</code>, and writes the resultant
+HTML to the <code>http.Conn</code>.
+</p>
+
+<p>
+Note that we've used <code>{body|html}</code> in the above template.  
+The <code>|html</code> part asks the template engine to pass the value
+<code>body</code> through the <code>html</code> formatter before outputting it,
+which escapes HTML characters (such as replacing <code>&gt;</code> with 
+<code>&amp;gt;</code>). 
+This will prevent user data from corrupting the form HTML. 
+</p>
+
+<p>
+Now that we've removed the <code>fmt.Sprintf</code> statement, we can remove
+<code>"fmt"</code> from the <code>import</code> list.
+</p>
+
+<p>
+While we're working with templates, let's create a template for our
+<code>viewHandler</code> called <code>view.html</code>:
+</p>
+
+<pre>
+!./htmlify.bin < view.html
+</pre>
+
+<p>
+Modify <code>viewHandler</code> accordingly:
+</p>
+
+<pre>
+!./srcextract.bin -src=final-noerror.go -name=viewHandler
+</pre>
+
+<p>
+Notice that we've used almost exactly the same templating code in both
+handlers. Let's remove this duplication by moving the templating code
+to its own function:
+</p>
+
+<pre>
+!./srcextract.bin -src=final-template.go -name=viewHandler
+
+!./srcextract.bin -src=final-template.go -name=editHandler
+
+!./srcextract.bin -src=final-template.go -name=renderTemplate
+</pre>
+
+<p>
+The handlers are now shorter and simpler. 
+</p>
+
+<h2>Handling non-existent pages</h2>
+
+<p>
+What if you visit <code>/view/APageThatDoesntExist</code>? The program will 
+crash. This is because it ignores the error return value from
+<code>loadPage</code>. Instead, if the requested page doesn't exist, it should 
+redirect the client to the edit page so the content may be created:
+</p>
+
+<pre>
+!./srcextract.bin -src=final.go -name=viewHandler
+</pre>
+
+<p>
+The <code>http.Redirect</code> function adds an HTTP status code of 
+<code>http.StatusFound</code> (302) and a <code>Location</code>
+header to the HTTP response.
+</p>
+
+<h2>Saving pages</h2>
+
+<p>
+The function <code>saveHandler</code> will handle the form submission. 
+</p>
+
+<pre>
+!./srcextract.bin -src=final-template.go -name=saveHandler
+</pre>
+
+<p>
+The page title (provided in the URL) and the form's only field, 
+<code>body</code>, are stored in a new <code>page</code>. 
+The <code>save()</code> method is then called to write the data to a file,
+and the client is redirected to the <code>/view/</code> page.
+</p>
+
+<p>
+The value returned by <code>FormValue</code> is of type <code>string</code>.
+We must convert that value to <code>[]byte</code> before it will fit into 
+the <code>page</code> struct.  We use <code>[]byte(body)</code> to perform
+the conversion.
+</p>
+
+<h2>Error handling</h2>
+
+<p>
+There are several places in our program where errors are being ignored.  This
+is bad practice, not least because when an error does occur the program will
+crash.  A better solution is to handle the errors and return an error message
+to the user. That way if something does go wrong, the server will continue to
+function and the user will be notified.
+</p>
+
+<p>
+First, let's handle the errors in <code>renderTemplate</code>:
+</p>
+
+<pre>
+!./srcextract.bin -src=final-parsetemplate.go -name=renderTemplate
+</pre>
+
+<p>
+The <code>http.Error</code> function sends a specified HTTP response code 
+(in this case "Internal Server Error") and error message.
+Already the decision to put this in a separate function is paying off.
+</p>
+
+<p>
+Now let's fix up <code>saveHandler</code>:
+</p>
+
+<pre>
+!./srcextract.bin -src=final.go -name=saveHandler
+</pre>
+
+<p>
+Any errors that occur during <code>p.save()</code> will be reported 
+to the user.
+</p>
+
+<h2>Template caching</h2>
+
+<p>
+There is an inefficiency in this code: <code>renderTemplate</code> calls 
+<code>ParseFile</code> every time a page is rendered. 
+A better approach would be to call <code>ParseFile</code> once for each 
+template at program initialization, and store the resultant 
+<code>*Template</code> values in a data structure for later use.
+</p>
+
+<p>
+First we create a global map named <code>templates</code> in which to store 
+our <code>*Template</code> values, keyed by <code>string</code> 
+(the template name):
+</p>
+
+<pre>
+!./srcextract.bin -src=final.go -name=templates
+</pre>
+
+<p>
+Then we create an <code>init</code> function, which will be called before
+<code>main</code> at program initialization. The function
+<code>template.MustParseFile</code> is a convenience wrapper around
+<code>ParseFile</code> that does not return an error code; instead, it panics
+if an error is encountered. A panic is appropriate here; if the templates can't
+be loaded the only sensible thing to do is exit the program.
+</p
+
+<pre>
+!./srcextract.bin -src=final.go -name=init
+</pre>
+
+<p>
+A <code>for</code> loop is used with a <code>range</code> statement to iterate 
+over an array constant containing the names of the templates we want parsed.
+If we were to add more templates to our program, we would add their names to 
+that array.
+</p>
+
+<p>
+We then modify our <code>renderTemplate</code> function to call 
+the <code>Execute</code> method on the appropriate <code>Template</code> from 
+<code>templates</code>:
+
+<pre>
+!./srcextract.bin -src=final.go -name=renderTemplate
+</pre>
+
+<h2>Validation</h2>
+
+<p>
+As you may have observed, this program has a serious security flaw: a user
+can supply an arbitrary path to be read/written on the server. To mitigate
+this, we can write a function to validate the title with a regular expression.
+</p>
+
+<p>
+First, add <code>"regexp"</code> to the <code>import</code> list.
+Then we can create a global variable to store our validation regexp:
+</p>
+
+<pre>
+!./srcextract.bin -src=final-noclosure.go -name=titleValidator
+</pre>
+
+<p>
+The function <code>regexp.MustCompile</code> will parse and compile the 
+regular expression, and return a <code>regexp.Regexp</code>. 
+<code>MustCompile</code>, like <code>template.MustParseFile</code>,
+is distinct from <code>Compile</code> in that it will panic if 
+the expression compilation fails, while <code>Compile</code> returns an 
+<code>os.Error</code> as a second parameter. 
+</p>
+
+<p>
+Now, let's write a function that extracts the title string from the request 
+URL, and tests it against our <code>titleValidator</code> expression:
+</p>
+
+<pre>
+!./srcextract.bin -src=final-noclosure.go -name=getTitle
+</pre>
+
+<p>
+If the title is valid, it will be returned along with a <code>nil</code>
+error value.  If the title is invalid, the function will write a 
+"404 Not Found" error to the HTTP connection, and return an error to the 
+handler. 
+</p>
+
+<p>
+Let's put a call to <code>getTitle</code> in each of the handlers:
+</p>
+
+<pre>
+!./srcextract.bin -src=final-noclosure.go -name=viewHandler
+
+!./srcextract.bin -src=final-noclosure.go -name=editHandler
+
+!./srcextract.bin -src=final-noclosure.go -name=saveHandler
+</pre>
+
+<h2>Introducing Function Literals and Closures</h2>
+
+<p>
+Catching the error condition in each handler introduces a lot of repeated code.
+What if we could wrap each of the handlers in a function that does this 
+validation and error checking? Go's 
+<a href="http://golang.org/doc/go_spec.html#Function_declarations">function 
+literals</a> provide a powerful means of abstracting functionality 
+that can help us here.
+</p>
+
+<p>
+First, we re-write the function definition of each of the handlers to accept
+a title string:
+</p>
+
+<pre>
+func viewHandler(c, *http.Conn, r *http.Request, title string)
+func editHandler(c, *http.Conn, r *http.Request, title string)
+func saveHandler(c, *http.Conn, r *http.Request, title string)
+</pre>
+
+<p>
+Now let's define a wrapper function that <i>takes a function of the above
+type</i>, and returns a function of type <code>http.HandlerFunc</code>
+(suitable to be passed to the function <code>http.HandleFunc</code>):
+</p>
+
+<pre>
+func makeHandler(fn func (*http.Conn, *http.Request, string)) http.HandlerFunc {
+	return func(c *http.Conn, r *http.Request) {
+		// Here we will extract the page title from the Request,
+		// and call the provided handler 'fn'
+	}
+}
+</pre>
+
+<p>
+The returned function is called a closure because it encloses values defined
+outside of it. In this case, the variable <code>fn</code> (the single argument
+to <code>makeHandler</code>) is enclosed by the closure. The variable
+<code>fn</code> will be one of our save, edit, or view handlers.
+</p>
+
+<p>
+Now we can take the code from <code>getTitle</code> and use it here
+(with some minor modifications):
+</p>
+
+<pre>
+!./srcextract.bin -src=final.go -name=makeHandler
+</pre>
+
+<p>
+The closure returned by <code>makeHandler</code> is a function that takes
+an <code>http.Conn</code> and <code>http.Request</code> (in other words,
+an <code>http.HandlerFunc</code>). 
+The closure extracts the <code>title</code> from the request path, and
+validates it with the <code>titleValidator</code> regexp. If the
+<code>title</code> is invalid, an error will be written to the
+<code>Conn</code> using the <code>http.NotFound</code> function. 
+If the <code>title</code> is valid, the enclosed handler function
+<code>fn</code> will be called with the <code>Conn</code>,
+<code>Request</code>, and <code>title</code> as arguments.
+</p>
+
+<p>
+Now we can wwrap the handler functions with <code>makeHandler</code> in 
+<code>main</code>, before they are registered with the <code>http</code> 
+package:
+</p>
+
+<pre>
+!./srcextract.bin -src=final.go -name=main
+</pre>
+
+<p>
+Finally we remove the calls to <code>getTitle</code> from the handler functions,
+making them much simpler:
+</p>
+
+<pre>
+!./srcextract.bin -src=final.go -name=viewHandler
+
+!./srcextract.bin -src=final.go -name=editHandler
+
+!./srcextract.bin -src=final.go -name=saveHandler
+</pre>
+
+<h2>Try it out!</h2>
+
+<p>
+<a href="final.go">Click here to view the final code listing.</a>
+</p>
+
+<p>
+Recompile the code, and run the app:
+</p>
+
+<pre>
+$ 8g wiki.go
+$ 8l wiki.8
+$ ./8.out
+</pre>
+
+<p>
+Visiting <a href="http://localhost:8080/ANewPage">http://localhost:8080/ANewPage</a>
+should present you with the page edit form. You should then be able to 
+enter some text, click 'Save', and be redirected to the newly created page.
+</p>
+
+<h2>Other tasks</h2>
+
+<p>
+Here are some simple tasks you might want to tackle on your own:
+</p>
+
+<ul>
+<li>Store templates in <code>tmpl/</code> and page data in <code>data/</code>.
+<li>Add a handler to make the web root redirect to 
+	<code>/view/FrontPage</code>.</li>
+<li>Spruce up the page templates by making them valid HTML and adding some
+	CSS rules.</li>
+<li>Implement inter-page linking by converting instances of 
+	<code>[PageName]</code> to <br>
+	<code>&lt;a href="/view/PageName"&gt;PageName&lt;/a&gt;</code>.
+	(hint: you could use <code>regexp.ReplaceAllFunc</code> to do this)
+	</li>
+</ul>
+
+</div>