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Go embed

last modified April 11, 2024

In this article we show to access embedded files from within a running Go program.

The embed package allows to access static files such as images and HTML files from within a running Go binary. It was introduced in Go 1.16.

Go embed a text file

In the first example, we embed a text file into a slice of bytes.

data/words.txt

sky
blue
rock
water
array
karma
falcon

We have a few words in the text file.

main.go

package main
import (
 "bytes"
 _ "embed"
 "fmt"
)
var (
 //go:embed data/words.txt
 data []byte
)
func main() {
 fmt.Println(string(data))
 fmt.Println("----------------------")
 words := bytes.Split(data, []byte{'\n'})
 for _, w := range words {
 fmt.Println(string(w))
 }
}

We embed a text file into the program and print the data.

var (
 //go:embed data/words.txt
 data []byte
)

Embedding is done by using the //go:embed directive above the variable declaration.

$ go build
$ ./txtfile.exe
sky
blue
rock
water
array
karma
falcon
----------------------
sky
blue
rock
water
array
karma
falcon

Go embed multiple files

In the following example, we embed two text files.

data/langs.txt

Perl
Raku
F#
Clojure
Go
C#

This is the langs.txt file.

data/words.txt

sky
blue
rock
falcon
war
tree
storm
cup

This is the words.txt file.

main.go

package main
import (
 "embed"
 "fmt"
)
//go:embed data/*
var f embed.FS
func main() {
 langs, _ := f.ReadFile("data/langs.txt")
 fmt.Println(string(langs))
 words, _ := f.ReadFile("data/words.txt")
 fmt.Println(string(words))
}

We embed two text files and print their contents.

//go:embed data/*
var f embed.FS

With the * wildcard character, we embed all files within the data directory.

$ go build
$ ./files.exe
Perl
Raku
F#
Clojure
Go
C#
sky
blue
rock
falcon
war
tree
storm
cup

Go embed static files

In the following example, we embed static files into a binary of a web application.

public/index.html

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>Home</title>
</head>
<body>
 <p>
 Home page
 </p>
</body>
</html>

This is the index.html file.

public/about.html

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>About</title>
</head>
<body>
 <p>
 About page
 </p>
</body>
</html>

This is the about.html file.

main.go

package main
import (
 "embed"
 "io/fs"
 "net/http"
)
//go:embed public
var content embed.FS
func handler() http.Handler {
 fsys := fs.FS(content)
 html, _ := fs.Sub(fsys, "public")
 return http.FileServer(http.FS(html))
}
func main() {
 mux := http.NewServeMux()
 mux.Handle("/", handler())
 http.ListenAndServe(":8080", mux)
}

The code example runs a server which serves two static files. We embed a whole directory.

//go:embed public
var content embed.FS

The embed.FS allows to embed a tree of files.

func handler() http.Handler {
 fsys := fs.FS(content)
 html, _ := fs.Sub(fsys, "public")
 return http.FileServer(http.FS(html))
}

The handler serves static files from the public directory. In Go, the http.FileServer is used to serve static content.

Source

Go embed package - reference

In this article we have showed how to access static files from within a running Go program using the embed package.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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