3 Things You May Not Know About The Go Template Engine

3 Things You May Not Know About The Go
Template Engine Chang Sau Sheong Feb 2015

Obligatory stuﬀ

What is a template engine?

Where’s Go template engine? Logic-‐less Go template
engine Embedded logic Mustache, Handlebars etc JSP, Haml, Jade etc

How does the Go template engine work?

text/template html/template

Parse template Execute template

<!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Go Web
Programming</title> </head> <body> {{ . }} </body> </html>

package main import ( "net/http" "html/template" ) func process(w http.ResponseWriter,
r *http.Request) { t, _ := template.ParseFiles("tmpl.html") t.Execute(w, "Hello World!") } func main() { server := http.Server{ Addr: "127.0.0.1:8080", } http.HandleFunc("/process", process) server.ListenAndServe() }

The Go template engine is kinda cool

1. Pipelines

<!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/ html; charset=utf-8"> <title>Go
Web Programming</title> </head> <body> {{ 12.3456 | printf "%.2f" }} </body> </html>

2. FuncTons

func formatDate(t time.Time) string { layout := "2006-01-02" return t.Format(layout)
} func process(w http.ResponseWriter, r *http.Request) { funcMap := template.FuncMap { "fdate": formatDate } t := template.New("tmpl.html").Funcs(funcMap) t, _ = t.ParseFiles("tmpl.html") t.Execute(w, time.Now()) }

<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Go Web Programming</title> </head>
<body> <div>The date/time is {{ fdate . }}</div> </body> </html>

<body> <div>The date/time is {{ . | fdate }}</div> </body> </html>

3. Context aware

func process(w http.ResponseWriter, r *http.Request) { t, _ := template.ParseFiles("tmpl.html")
content := `I asked: <i>"What's up?"</i>` t.Execute(w, content) }

<body> <div>{{ . }}</div> <div><a href="/{{ . }}">Path</a></div> <div><a href="/?q={{ . }}">Query</a></div> <div><a onclick="f('{{ . }}')">Onclick</a></div> </body> </html>

<body> <div>I asked: <i>"What's up?"</ i></div> <div><a href="/I%20asked:%20%3ci%3e%22What%27s%20up? %22%3c/i%3e">Path</a></div> <div><a href="/?q=I%20asked%3a%20%3ci%3e%22What%27s %20up%3f%22%3c%2fi%3e">Query</a></div> <div><a onclick="f('I asked: \x3ci\x3e\x22What\x27s up?\x22\x3c\/i\x3e')">Onclick</a></div> </body> </html>

Context Content Original text I asked: <i>"What's up?"</i> {{ .
}} I asked: <i>"What's up?"</i> <a href="/{{ . }}"> I%20asked:%20%3ci%3e%22What%27s%20up?%22%3c/i%3e <a href="/?q={{ . }}"> I%20asked%3a%20%3ci%3e%22What%27s%20up%3f%22%3c %2fi%3e <a onclick="{{ . }}"> I asked: \x3ci\x3e\x22What\x27s up?\x22\x3c\/i\x3e

XSS Demo

hWp://manning.com/chang

Thank you sausheong@gmail.com @sausheong

3 Things You May Not Know About The Go Template...

3 Things You May Not Know About The Go Template Engine

Sau Sheong Chang

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