Kiruna is a simple, powerful library for building and optimizing fullstack Go applications, with live browser refresh and excellent dev-prod parity. It's sort of like Vite, but for Go apps.
- Automatic smart rebuilds and browser refreshes
- Instant hot reloading for CSS files (without a full page refresh)
- Highly configurable to support any use case
- Glob pattern file watching
- Granular build hooks with customizable timing strategies
- Static asset hashing and embedding
- Basic CSS bundling and minification
- Critical CSS inlining
- Safely serve public static assets with immutable cache headers
Dev-time reloads are smart and fast. Based on the type of file you edit and your associated configuration options, Kiruna will do the minimum amount of work necessary to get your changes to your browser as quickly as possible.
Kiruna has a few lightweight runtime helpers for referencing hashed static assets from Go code and templates (e.g., Kiruna.GetPublicURL("favicon.ico")) and for including your CSS in your HTML templates (e.g., Kiruna.GetCriticalCSSStyleElement(), Kiruna.GetStyleSheetLinkElement()). They have zero third-party dependencies and are aggressively cached whenever possible, so you can feel free to call them even in the hot path of your application.
Kiruna is completely decoupled from any specific frameworks or libraries, so you can use it with any Go server framework or router you choose, or just use the standard library. Moreover, unlike some alternatives, Kiruna doesn't require you to install any tooling on your machine. It is orchestrated solely from inside your repo and its dependencies.
Let's get a Kiruna project set up from scratch. This should only take a few minutes to complete. The only prerequisite is that you have Go installed on your machine.
Start by initializing a new Go module in an empty directory, replacing your-module-name with your own module name:
go mod init your-module-nameThen run the following commands to create the necessary directories and files for your project:
# Scaffold directories
mkdir -p cmd/app cmd/build cmd/dev
mkdir -p static/private static/public/prehashed
mkdir -p styles/critical styles/normal
mkdir -p dist/kiruna internal/platform
# Create placeholder files
touch cmd/app/main.go cmd/build/main.go cmd/dev/main.go
touch static/private/index.go.html
touch styles/critical/main.css styles/normal/main.css
touch dist/kiruna/x dist/dist.go internal/platform/kiruna.goNow copy this into your dist/dist.go file:
package dist
import "embed"
//go:embed kiruna
var FS embed.FSNow copy this into your internal/platform/kiruna.go file, replacing your-module-name with your own module name:
package platform
import (
"your-module-name/dist"
"github.com/sjc5/kiruna"
)
var Kiruna = kiruna.New(&kiruna.Config{
DistFS: dist.FS,
EntryPoint: "cmd/app/main.go",
})Now go get Kiruna and tidy up:
go get github.com/sjc5/kiruna
go mod tidyNow copy this into your static/private/index.go.html file:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
{{.Kiruna.GetCriticalCSSStyleElement}} {{.Kiruna.GetStyleSheetLinkElement}}
</head>
<body>
<div>
<h1>Hello, world!</h1>
<p>Hello from "static/private/index.go.html"</p>
</div>
{{.Kiruna.GetRefreshScript}}
</body>
</html>And now copy this into your cmd/app/main.go file, replacing your-module-name with your own module name:
package main
import (
"fmt"
"html/template"
"net/http"
"your-module-name/internal/platform"
"github.com/sjc5/kiruna"
)
func main() {
// Health check endpoint
http.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
w.WriteHeader(http.StatusOK)
w.Write([]byte("OK"))
})
// Serve static files from "dist/kiruna/static/public" directory, accessible at "/public/"
http.Handle("/public/", platform.Kiruna.MustGetServeStaticHandler("/public/", true))
// Serve an HTML file using html/template
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
FS, err := platform.Kiruna.GetPrivateFS()
if err != nil {
fmt.Println(err)
http.Error(w, "Error loading template", http.StatusInternalServerError)
return
}
tmpl, err := template.ParseFS(FS, "index.go.html")
if err != nil {
fmt.Println(err)
http.Error(w, "Error loading template", http.StatusInternalServerError)
return
}
err = tmpl.Execute(w, struct{ Kiruna *kiruna.Kiruna }{
Kiruna: platform.Kiruna,
})
if err != nil {
http.Error(w, "Error executing template", http.StatusInternalServerError)
}
})
port := kiruna.MustGetPort()
fmt.Printf("Starting server on: http://localhost:%d\n", port)
http.ListenAndServe(fmt.Sprintf(":%d", port), nil)
}And copy this into your cmd/build/main.go file, replacing your-module-name with your own module name:
package main
import "your-module-name/internal/platform"
func main() {
err := platform.Kiruna.Build()
if err != nil {
panic(err)
}
}This file is what you'll want to run when you're ready to build for production. Running go run ./cmd/build will build your project and save your binary to dist/bin/main. Assuming you used DistFS to embed your static assets, you can now run your binary from anywhere on the build machine, and it will serve your static assets from the embedded filesystem. If you chose not to embed your static assets, you'll just need to make sure that the binary is a sibling of the dist/kiruna directory in order to serve your static assets from disk.
Note
Oftentimes you'll want to handle compilation of your Go binary yourself. In such cases, you can use platform.Kiruna.BuildWithoutCompilingGo() instead of platform.Kiruna.Build(). This will run all the same Kiruna-specific processing (static asset hashing, etc.) but will stop short of producing an executable.
Now copy this into your cmd/dev/main.go file, replacing your-module-name with your own module name:
package main
import (
"your-module-name/internal/platform"
"github.com/sjc5/kiruna"
)
func main() {
platform.Kiruna.MustStartDev(&kiruna.DevConfig{
HealthcheckEndpoint: "/healthz",
WatchedFiles: kiruna.WatchedFiles{{Pattern: "**/*.go.html"}},
})
}Now try running the dev server:
go run ./cmd/devIf you copied everything correctly, you should see some logging, with a link to your site on localhost, either at port 8080 or some fallback port. If you see an error, double check that you copied everything correctly.
Now paste the following into your styles/critical/main.css file, and hit save:
body {
background-color: darkblue;
color: white;
}If you leave your browser open and your dev server running, you should see the changes reflected in your browser nearly instantly via hot CSS reloading. Notice that the CSS above is being inlined into your document head. This is because it is in the styles/critical directory.
Now let's make sure your normal stylesheet is also working. Copy this into your styles/normal/main.css file:
h1 {
color: red;
}When you hit save, this should also hot reload.
Note
You can put multiple css stylesheets into the styles/critical and styles/normal directories. In each case, the CSS will be minified and concatenated in alphabetical order by filename.
Now let's try editing your html template at static/private/index.go.html.
Find the line that says <h1>Hello, world!</h1> (line 10) and change it to: <h1 style="color: green;">Hello, world!</h1>.
When you hit save, your browser page should automatically refresh itself. This happens because of the {Pattern: "**/*.go.html"} item in the kiruna.WatchedFiles slice in cmd/dev/main.go. If you were to remove that item and restart your dev server, the page would not reload when you save your html file (if you don't believe me, go give it a try).
When you want to watch different file types, you can add them to the kiruna.WatchedFiles slice using glob patterns, and there are a whole bunch of ways to tweak this to get your desired reload behavior and sequencing, including callbacks and more. Feel free to explore your auto-complete options here or dive into the Kiruna source code to learn more.
If desired, you can bootstrap a new .gitignore file by running the following:
echo "dist/*\n\!dist/dist.go" > .gitignoreIf you're just looking for automatic Go application rebuilds only, without automatic browser refreshes or static asset build tooling, then Kiruna may be overkill for you, and you could just use Air instead.
That said, you can put Kiruna into a simpler ServerOnly mode if you want, which skips the frontend-targeted build steps and just does automatic Go application rebuilds.
In either case, one benefit of Kiruna over Air is that it doesn't require you to install any tooling on your machine. It is orchestrated solely from inside your repo and its dependencies. So when a new developer joins your team, they can just clone your repo and be ready to rock as soon as they run go mod tidy (instead of needing to install and configure Air on their machine first).
Copyright 2024 Samuel J. Cook. Licensed under the BSD 3-Clause License.