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template: add example to demonstrate template blocks
Fixes golang/go#14285 Change-Id: I3b32b7fc19960a77778e84cba2a0a95b49dbdf16 Reviewed-on: https://go-review.googlesource.com/19443 Reviewed-by: Rob Pike <[email protected]> Reviewed-by: Chris Broadfoot <[email protected]> Reviewed-by: Russ Cox <[email protected]>
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‎README.md‎

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@@ -50,3 +50,8 @@ A trivial "Hello, world" App Engine application intended to be used as the
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starting point for your own code.
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_Note_: The `goapp` tool is part of the [Google App Engine SDK for Go](https://cloud.google.com/appengine/downloads#Google_App_Engine_SDK_for_Go).
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### [template][template/] ([godoc](//godoc.org/github.com/golang/example/template))
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A trivial web server that demonstrates the use of the
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[`template` package](https://golang.org/pkg/text/template/)'s `block` feature.

‎template/image.tmpl‎

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{{define "content"}}
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<div id="image">
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<img src="{{.URL}}" title="{{.Title}}" alt="{{.Title}}">
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</div>
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{{end}}
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{{define "sidebar"}}
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<a href="/">Back</a>
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{{end}}

‎template/index.tmpl‎

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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>{{.Title}}</title>
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<style>
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body {
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font-family: sans-serif;
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}
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h1 {
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background: #ddd;
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}
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#sidebar {
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float: right;
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}
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</style>
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</head>
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<body>
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<h1>{{.Title}}</h1>
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<div id="sidebar">
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{{block "sidebar" .}}
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<h2>Links</h2>
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{{/* The dashes in the following template directives
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ensure the generated HTML of this list contains no
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extraneous spaces or line breaks. */}}
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<ul id="sidebar">
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{{- range .Links}}
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<li><a href="{{.URL}}">{{.Title}}</a></li>
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{{- end}}
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</ul>
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{{end}}
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</div>
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{{block "content" .}}
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<div id="content">
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{{.Body}}
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</div>
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{{end}}
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</body>
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</html>

‎template/main.go‎

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/*
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Copyright 2016 Google Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Command template is a trivial web server that uses the text/template (and
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// html/template) package's "block" feature to implement a kind of template
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// inheritance.
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//
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// It should be executed from the directory in which the source resides,
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// as it will look for its template files in the current directory.
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package main
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import (
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"html/template"
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"log"
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"net/http"
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"strings"
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)
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func main() {
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http.HandleFunc("/", indexHandler)
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http.HandleFunc("/image/", imageHandler)
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log.Fatal(http.ListenAndServe("localhost:8080", nil))
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}
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// indexTemplate is the main site template.
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// The default template includes two template blocks ("sidebar" and "content")
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// that may be replaced in templates derived from this one.
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var indexTemplate = template.Must(template.ParseFiles("index.tmpl"))
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// Index is a data structure used to populate an indexTemplate.
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type Index struct {
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Title string
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Body string
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Links []Link
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}
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type Link struct {
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URL, Title string
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}
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// indexHandler is an HTTP handler that serves the index page.
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func indexHandler(w http.ResponseWriter, r *http.Request) {
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data := &Index{
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Title: "Image gallery",
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Body: "Welcome to the image gallery.",
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}
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for name, img := range images {
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data.Links = append(data.Links, Link{
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URL: "/image/" + name,
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Title: img.Title,
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})
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}
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if err := indexTemplate.Execute(w, data); err != nil {
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log.Println(err)
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}
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}
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// imageTemplate is a clone of indexTemplate that provides
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// alternate "sidebar" and "content" templates.
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var imageTemplate = template.Must(template.Must(indexTemplate.Clone()).ParseFiles("image.tmpl"))
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// Image is a data structure used to populate an imageTemplate.
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type Image struct {
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Title string
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URL string
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}
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// imageHandler is an HTTP handler that serves the image pages.
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func imageHandler(w http.ResponseWriter, r *http.Request) {
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data, ok := images[strings.TrimPrefix(r.URL.Path, "/image/")]
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if !ok {
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http.NotFound(w, r)
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return
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}
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if err := imageTemplate.Execute(w, data); err != nil {
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log.Println(err)
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}
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}
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// images specifies the site content: a collection of images.
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var images = map[string]*Image{
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"go": {"The Go Gopher", "https://golang.org/doc/gopher/frontpage.png"},
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"google": {"The Google Logo", "https://www.google.com/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png"},
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}

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