Embedding files in Go using the "embed" package

The most exciting feature for me in the Go 1.16 release is the new “embed” package which allows you to embed a file contents as part of the Go application binary.

This ability so far was most easily available via using various third party packages and they worked great. You could also use go generate to roll out your own solution, if needed. However, now having this facility in the form of a standard library package is great news.

Let’s see how we can use it.

First of course, download and install Go as per the instructions

Demo - Embedding a template

As an example of a file that we want to embed, let’s consider a Go template which generates Go source code:

# We want to embed this
package main

import "fmt"

func main() {
    fmt.Printf("Hello World - Welcome to {{.Name}}'s World")
}

The file above is stored in the directory templates as a file main.go.tmpl. To embed the above file contents, we would write the following code using the embed package:

package main

import _ "embed"

//go:embed templates/main.go.tmpl
var tmplMainGo []byte

The key here is of course:

//go:embed templates/main.go.tmpl
var tmplMainGo []byte

This makes the contents of the above template available as a slice of bytes in the tmplMainGo variable.

We can then access the template as follows:

tmpl, err := tmpl.Parse(string(tmplMainGo))
...

You can see the working demo here. Clone the repository and run the following steps:

$ go build

$ ./go-embed 
package main

import "fmt"

func main() {
    fmt.Printf("Hello World - Welcome to Jane's World")
}

Notes

The embed package also currently supports embedding an file system tree via the embed.FS type. See the package docs for the details.