Embedding files in Go using the "embed" package
Go 1.16 Beta 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 Beta 1
If you have Go installed already, run:
$ go get golang.org/dl/go1.16beta1
# Substitute ~/go/bin with your GOBIN path if you have
# one set explicitly
$ ~/go/bin/go1.16beta1 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
$ ~/go/bin/go1.16beta1 version
go version go1.16beta1 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.
Notes
If you don’t like the embed
package being imported for its side-effects,
this may change before the final release. See
here for
the details.
The embed
package also currently supports embedding an file system tree via
the embed.FS
type. See the package docs for the
details.