Embedding Files In Go Using The "Embed" Package

March 3, 2021, 3:09 a.m.

#tutorial #golangp #rogramming

Go 1.16 Release Candidate 1 was announced recently and the most exciting feature for me in this 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. I will keep this post updated as the 1.16 release evolves.

Getting Go 1.16 RC 1

If you have Go installed already, run:

$ go get golang.org/dl/go1.16rc1

# Substitute ~/go/bin with your GOBIN path if you have
# one set explicitly
$ ~/go/bin/go1.16rc1 download 
...

After the above command finishes execution, you will now be able to access the 1.16 go tool:

# Substitute ~/go/bin with your GOBIN path if you have
# one set explicitly or GOBIN is not in your PATH
$ ~/go/bin/go1.16rc1 version
go version go1.16rc1 darwin/amd64

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:

# Substitute ~/go/bin with your GOBIN path if you have
# one set explicitly or GOBIN is not in your PATH

$ ~/go/bin/go1.16rc1 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.