Getting Started #
In this article I am going to show you how to embed static files inside a Go binary. Embedding files can serve many purposes such as embedding a React app and serving it over http all inside a single Go binary.
Embed a single file #
We will start by embedding a single file and print it out to standard output.
Let's prepare a simple index.html static file.
<html> <head> <title>Embedded File</title> </head> <body> <h1>Hello from Go!</h1> </body> </html>index.html
Write the Go code to embed the file.
package main import ( _ "embed" "fmt" ) //go:embed index.html var staticFile string func main() { fmt.Println(staticFile) }main.go
For embedding to work you need three things:
- Import the
embedpackage (import _ "embed"). - A variable to hold the data of embedded file (
var staticFile string). - Using comment specify which file to import
//go:embed index.html. The comment goes right above the variable.
Note: Both main.go and index.html are in the same directory. Go will look for the file relative to the main.go file.
Build the binary using go build and run it, the html file will be the output.
<head>
<title>Embedded File</title>
</head>
<body>
<h1>Hello from Go!</h1>
</body>
</html>
There are 3 valid types for the variable that holds embedded file: string, []byte and embed.FS.
Embed a directory #
Instead of embedding a single file, we can embed an entire directory.
Let's prepare a directory, create a new static folder and place the index.html file in it.
Create a new page.html file in the static folder.
<html> <head> <title>Embedded File</title> </head> <body> <h1>Page</h1> </body> </html>static/page.html
So the folder structure looks like this.
static
|- index.html
|- page.html
main.go
Since we are embedding a directory we will use embed.FS type here.
package main import ( "embed" "fmt" ) //go:embed static var fs embed.FS func main() { files, _ := fs.ReadDir("static") for _, f := range files { fmt.Println(f.Name()) } }main.go
embed.FS has a function called ReadDir that lists the content of a directory, in the above code example we list all the files inside the static folder.
The output will be:
index.html
page.html
Reading one of the files from the directory
package main import ( "embed" "fmt" ) //go:embed static var fs embed.FS func main() { file, _ := fs.ReadFile("static/index.html") // 👈 fmt.Println(string(file)) }main.go
Embed multiple directories #
You can go one step ahead and embed multiple folders. Let's create a new static2 folder and paste the same index.html folder.
package main import ( "embed" "fmt" ) //go:embed static static2 var fs embed.FS func main() { files, _ := fs.ReadDir(".") for _, f := range files { fmt.Println(f.Name()) } }main.go
In the embedding comment, specify another folder separated with a space //go:embed static static2.
The output will be:
static
static2
Serve embedded directory over http #
We can take advantage of this embedding feature and serve our static files over http using.
package main import ( "embed" "net/http" ) //go:embed static var fs embed.FS func main() { http.Handle("/", http.FileServer(http.FS(fs))) http.ListenAndServe(":8080", nil) }main.go
Visit http://localhost:8080/static/index.html in your browser to see the file in action.
Read more about embed package and its functionality on the official docs here.
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