A template generates output from fixed text, data substitutions, and actions. For HTTP pages, Go’s html/template replaces strings written directly to a ResponseWriter with structured HTML that is easier to maintain. Use text/template for plain-text output such as email. section 9.0 section 9.2
In an HTML file, {{.Title}} prints a field from the data passed to Execute. An action can also control output: {{range .Comments}} repeats markup for each comment, and {{end}} closes the range. Inside the range, fields such as {{.Text}} refer to the current comment. section 9.1.1
Listing 9.2 Using a simple HTML template
package main
import (
"html/template" #1
"net/http"
)
type Page struct {
Title, Content string
}
func displayPage(w http.ResponseWriter, r *http.Request) {
p := &Page{ #2
Title: "An Example", #2
Content: "Have fun stormin' da castle.", #2
} #2
t := template.Must(template.ParseFiles("templates
/simple.html")) #3
t.Execute(w, p) #4
}
func main() {
http.HandleFunc("/", displayPage) #5
http.ListenAndServe(":8080", nil) #5
}
A complete HTTP handler parses an HTML file, constructs page data, and executes the template into the response. section 9.1.1
Choose html/template when rendering HTML with untrusted data. It escapes inserted values according to their context: a value in a URL query and one in visible page text need different treatment. The security model trusts the template but not data supplied through its variables; text/template does not add that HTML-aware escaping. section 9.1.1 section 9.2
Keep data generation in application code and display formatting in the template. For formatting not provided by built-in functions, register a function with template.FuncMap before parsing. A date-formatting function can then be used as {{.Date | dateFormat "Jan 2, 2006"}}. Parsing at a suitable point outside repeated rendering can also reduce processing work. section 9.1.2 section 9.0
Listing 9.5 Adding template functions
package main
import (
"html/template"
"net/http"
"time"
)
var tpl = `<!DOCTYPE HTML> #1
<html>
<head>
<meta charset="utf-8">
<title>Date Example</title>
</head>
<body>
<p>{{.Date | dateFormat "Jan 2, 2006"}}</p> #2
</body>
</html>`
var funcMap = template.FuncMap{ #3
"dateFormat": dateFormat, #3
} #3
func dateFormat(layout string, d time.Time) string { #4
return d.Format(layout) #4
} #4
func serveTemplate(res http.ResponseWriter, req *http.Request) {
t := template.New("date") #5
t.Funcs(funcMap) #6
t.Parse(tpl) #7
data := struct{ Date time.Time }{ #8
Date: time.Now(),
} #8
t.Execute(res, data) #9
} #8
func main() { #8
http.HandleFunc("/", serveTemplate) #10
http.ListenAndServe(":8080", nil) #8
} #8
The date example connects the template pipeline to a Go function registered through FuncMap. section 9.1.2
For plain-text email, execute a text/template into a buffer, then send the resulting content through a mail client. Injected values are not automatically HTML-escaped; use escaping functions if the output requires them. HTML email can instead use html/template. section 9.2
