Using Templates in Golang (Go Template)

Go Template

Golang provides a feature called Go Template, which allows binding various data or exporting manipulated strings according to a specified format.

text/template package

• This package is one of the two standard library packages used for processing text-based templates and is commonly used when text needs to be generated according to a fixed format or specific logic.
• An example of using the text/template package to export text according to a fixed format is shown below.

package main 

import ( 
	"os" 
	"log"
	"text/template" 
) 

type Person struct { 
	Name string 
	Age int 
} 

func main() { 
	t := template.New("hello") 
	t, err = t.Parse("Hello {{.Name}}, you are {{.Age}} years old.\n") 
	if err != nil {
		log.Error(err)
	}
	p := Person{Name: "GiraffeWithCode", Age: 27} 
	t.Execute(os.Stdout, p) 
}

As seen in the code, it is easy to guess that each field like Name and Age in the Person struct will be bound to each element of the template string "Hello {{.Name}}, you are {{.Age}} years old.\n".

Running the above code will yield the following result.

Result

Hello GiraffeWithCode, you are 27 years old.

Loops

Loops can also be implemented using range.

package main

import (
    "os"
    "log"
    "text/template"
)

type Person struct {
    Name string
    Age  int
    Cars []string
}

const (
	tmpl = `Hello {{.Name}}, you are {{.Age}} years old. You have {{range .Cars}}{{.}}, {{end}}`
)

func main() {
    t := template.New("hello")
    t, err := t.Parse("Hello {{.Name}}, you are {{.Age}} years old.\n")
    if err != nil {
        log.Fatal(err)
    }

    t, err = t.Parse("")
    if err != nil {
        log.Fatal(err)
    }

    p := Person{Name: "GiraffeWithCode", Age: 27, Cars: []string{"BMW", "Audi", "Benz"}}
    t.Execute(os.Stdout, p)
}

Result

Hello GiraffeWithCode, you are 27 years old. You have BMW, Audi, Benz,

Conditionals

Conditionals can be implemented using if.

package main

import (
    "os"
    "log"
    "text/template"
)

type Person struct {
    Name string
    Age  int
    Cars []string
}

const (
    tmpl = `Hello {{.Name}}, you are {{.Age}} years old. You have {{range .Cars}}{{.}}, {{end}}{{if .Cars}}{{else}}no car{{end}}`
)

func main() {
    t := template.New("hello")
    t, err := t.Parse(tmpl)
    if err != nil {
        log.Fatal(err)
    }

    p := Person{Name: "GiraffeWithCode", Age: 27, Cars: []string{"BMW", "Audi", "Benz"}}
    t.Execute(os.Stdout, p)
}

Result

Hello GiraffeWithCode, you are 27 years old. You have BMW, Audi, Benz

text/template vs html/template

Both the text/template package and the html/template package are standard libraries used for processing text-based templates.

The main difference between these two packages lies in their safety in the context of HTML.

1. text/template: Designed to handle plain text. Templates processed using this package will not have special escape processing if the generated strings are used as HTML.

2. html/template: Designed to securely handle HTML content. This package automatically escapes strings safely in the context of HTML, JavaScript, CSS, URLs, etc., to prevent web attacks like Cross-Site Scripting (XSS). (It performs a similar role to the JS library DOMPurify.)

Reference

• Working with text/template and html/template