Embedding static files in 2021 has become a bit easier since the release of Go 1.16. The new release comes with a new module embed which provides a handy set of interface and methods to attach static files in go binaries
Let’s have a short look at how to use this.
First of all, you will need Go 1.16
$ go get golang.org/dl/go1.16rc1
$ go1.16rc1 download
$ go1.16rc1 version
go version go1.16rc1
Now before we do that, let’s create a project directory
$ tree
.
├── assets
│ └── report.html
├── sample.txt
└── static-demo.go
Our code will be in static-demo.go
Go provides us with 3 ways to embed content:
- On type
string - On type
byte - On type
FS
Let’s explore each one of these one by one
package main
import (
_ "embed"
"fmt"
)
func main() {
//go:embed sample.txt
var s string
fmt.Println(s)
}
To specify what variable holds our static file, go directive //go:embed is used followed by the name of file or a pattern to embed. Note that there must be no space between // and go because that is a regular one line comment in Go.
The //go:embed directive requires importing “embed”, even when using a string or []byte & since we are not referring to the embed module directly we are using a blank _ import. In our code we are embedding a text file sample.txt here is what it contains
This is a sample file
with multiple lines
and 🐧️ emojis too!
Now lets execute our code to see if actually works
$ go run static-demo.go
This is a sample file
with multiple lines
and 🐧️ emojis too!
Ok that’s pretty cool (dodge this Javascript!). Now lets see how to share some data to a text file
package main
import (
"embed"
"fmt"
"html/template"
"os"
)
func main() {
//go:embed assets/*
var assetData embed.FS
t, err := template.ParseFS(assetData, "assets/report.html")
if err != nil {
fmt.Println(err)
}
templateData := struct {
Title string
}{
Title: "File inside Go",
}
t.Execute(os.Stdout, templateData)
}
embed.FS enables us to embed a tree of static files i.e in our case the assets directory as dictated by the directive //go:embed assets/* which contains a file report.html with following contents
<html>
<head>
<title>{{$.Title}}</title>
</head>
<body>
<h1>Go is cool af!</h1>
</body>
</html>
Patterns in the go directive cannot contain ‘.’ or ‘..’ path elements nor begin with a leading slash. To match everything in the current directory, use ‘*’
A FS (file system) in Go is a read-only collection of files, usually initialized with a //go:embed directive.
template.ParseFS takes a FS as first argument followed by a list of glob patterns,
Running this prints out our title correctly inside the HTML template.
$ go run static-demo.go
<html>
<head>
<title>File inside Go</title>
</head>
<body>
<h1>Go is cool af!</h1>
</body>
</html>
It worked!
Embedding files inside the binaries itself opens up emense out of opportunities that we would see as this feature gets stable
Top comments (2)
Thank you for this post , in
sample.txt auto embed to
sstring ?For byte embed what do it?
Hi Javad, Sorry for the late reply. I just saw your comment
You just need to declare a
bytevariable to do this