TechQ, yet another project to learn Go

I’ve been coding for more than 10 years, and I’ve used a variety of languages, but when it comes to fill my pockets I code in Ruby.

I have been checking out Go for a while now. I like it’s simplicity while maintaining consistency across its methods and standard libraries. I have little experience with typed languages, but Go makes it feel easy, and the IDE tools it has makes it fun to use.

So what is this Tech Q I’m talking about? It’s a web application where I can randomly get questions for technical interviews I sometimes do at my work. I was looking to learn the following:

Embedding with go:embed¹ : I’m blown away with the idea you can compile statics in a binary. I tested go-bindata and packr, but Go introduced a way in 2021.
Serving paths with http: I’ve experimented with gorilla/mux² but wanted to use the http³ module.
Using gorm⁴ with SQLite⁵: I’ve been keeping an eye on this library for a while, wanted to give it a try using SQLite.
Organizing the app: I have experimented on how to modularize a Go application, but wanted to give it another go, to see what feels natural.
Last but not least, to deploy something: It’s been a while and it’s always fun.

Let’s dive into what I learned for each of these points.

Embedding with `go:embed`

Turns out you can use the directive //go:embed to access embedded files in a Go program. For this application I created the following structure.

resources
├── resources.go
├── static
│   ├── css
│   ├── fonts
│   └── images
└── templates
    ├── index.gohtml
    └── layout.gohtml

Where resources.go contains the following code:

package resources

import "embed"

var (
	//go:embed templates
	Templates embed.FS

	//go:embed static
	Statics embed.FS
)

This allows me to use the embedded files like this, for example the IndexHandler:

func IndexHandler(w http.ResponseWriter, r *http.Request) {
	// ...
	tpl, err := template.ParseFS(
		resources.Templates,
		"templates/index.gohtml",
		"templates/layout.gohtml",
	)
	// ...
}

For Statics, which can be fonts, images, CSS, etc. my handler looks like this:

func StaticHandler() http.Handler {
	var staticFS = http.FS(resources.Statics)
	return http.FileServer(staticFS)
}

Finally, since my handlers are pointing to either / in the case of the IndexHandler and /statics/ for the StaticHandler, I can access for example a CSS file from a layout with /statics/css/styles.css.

While developing the application I even embedded a CSV file, the SQLite database itself, and images, just to try it out. It’s nice.

Serving paths with `http`

My server skills are still a mess, and I’m still copying and pasting some code I’ve used before. But I learned something this time, take a look at this code:

func NewServer(port string) *Server {
	mux := http.NewServeMux()
	httpServer := &http.Server{Addr: ":" + port, Handler: mux}

	s := &Server{
		httpServer: httpServer,
	}

	mux.HandleFunc("/", indexHandler)

	return s
}

func indexHandler(w http.ResponseWriter, r *http.Request) {
	log.Println("indexHandler called")
}

Whenever I visited localhost:3000 I would get two log lines for the indexHandler. I was confused so I added more information to the log line:

func IndexHandler(w http.ResponseWriter, r *http.Request) {
	log.Println("indexHandler called", r.URL.Path)
}

Which logged:

indexHandler called /
indexHandler called /favicon.ico

That’s a request from me and the browser looking for / and /favicon.ico. The documentation about NewServerMux says the following⁶:

Note that since a pattern ending in a slash names a rooted subtree, the pattern “/” matches all paths not matched by other registered patterns, not just the URL with Path == “/”.

Which makes sense, that’s the kind of flexibility I like. This small patch achieved what I was looking for to only match GET at /.

func IndexHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" || r.URL.Path != "/" {
		w.WriteHeader(http.StatusNotFound)
		return
	}
}

Using `gorm` with SQLite

I’m used to Ruby on Rails⁷ and its wonderfully bloated ActiveRecord and ActiveModel. Don’t get me wrong, I love it, but when it comes to use other ORMs like gorm, you feel there’s something missing, like migrations and seeds in my case.

I created a method to connect to the database:

var DB *gorm.DB

func ConnectDatabase() {
	database, _ := gorm.Open(sqlite.Open("./data/database.db"), &gorm.Config{})
	DB = database
}

And three methods to conviniently manage the database with my Questions struct.

func DropDB(db *gorm.DB) {
	db.Migrator().DropTable(&models.Question{})
}

func CreateDB(db *gorm.DB) {
	db.AutoMigrate(&models.Question{})
}

func SetupDB(db *gorm.DB) {
	DropDB(db)
	CreateDB(db)
}

For the seeds I found this awesome article from Redha Juanda⁸, I adapted a method to read from a TXT file with the questions I needed.

func (s Seed) QuestionSeed() {
	file, _ := os.Open("db/seeds/questions.txt")
	defer file.Close()
	scanner := bufio.NewScanner(file)

	for scanner.Scan() {
		line := scanner.Text()
		s.db.Create(&models.Question{Body: line})
	}
}

I used this code⁹ to handle arguments using flag and adapted it to my needs.

func HandleArgs() {
	flag.Parse()
	args := flag.Args()

	if len(args) >= 1 {
		switch args[0] {
		case "seed":
			db.ExecuteSeed(db.DB, args[1:]...)
			os.Exit(0)
		case "create":
			db.CreateDB(db.DB)
			os.Exit(0)
		case "drop":
			db.DropDB(db.DB)
			os.Exit(0)
		case "setup":
			db.SetupDB(db.DB)
			db.ExecuteSeed(db.DB)
			os.Exit(0)
		}
	}
}

Allowing me to execute them like this:

$ go run main.go create
$ go run main.go seed # or seed QuestionSeed

Organizing the app

I learned in my csgo_exporter¹⁰ project how to organize a Prometheus Exporter, or at least what its usually done. For this case I took a similar approach but trying not to put everything in the internal folder.

I kept config because it makes sense. db and seeds in the same directory to maintain database logic in one place. resources as I mentioned before it’s where the statics are. And internal is everything that has to do with business logic.

.
├── config
├── data
├── db
│   └── seeds
├── internal
│   ├── handlers
│   ├── models
│   └── server
└── resources
    ├── static
    │   ├── css
    │   ├── fonts
    │   └── images
    └── templates

Now that I’m writing this maybe the server package needs to be outside internal? Or maybe inside config? Trivialities, but I like this kind of stuff.

Deploy something

Feels good to deploy, no? I have an instance in DigitalOcean¹¹ instance full of Docker containers with Traefik¹² as a reverse proxy. The easiest way for me is to create an image and set it up with Docker Compose.

I really like this Dockerfile, it’s very similar to the one in the csgo_exporter.

ARG IMAGE=scratch
ARG OS=linux
ARG ARCH=amd64

FROM golang:1.18.1-alpine3.15 as builder

WORKDIR /go/src/github.com/kinduff/techq

RUN apk --no-cache --virtual .build-deps add git alpine-sdk sqlite

COPY . .

RUN go mod download
RUN GOOS=$OS GOARCH=$ARCH go build -a -ldflags '-linkmode external -extldflags "-static"' -o binary .

FROM $IMAGE

LABEL name="techq"

WORKDIR /root/
COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
COPY --from=builder /go/src/github.com/kinduff/techq/binary techq

EXPOSE 3000

CMD ["./techq"]

This generates a compressed image of ~8MB. The Docker Compose file is trivial.

TechQ in the browser

You can see the final result at TechQ.kinduff.com ⧉ and the source code at github.com/kinduff/techq ⧉.

Hope you enjoyed this blog post, it was really fun to write and I’m always happy to share what I know and what I’m learning.

See you next time!

Footnotes

TechQ, yet another project to learn Go

Embedding with go:embed

Serving paths with http

Using gorm with SQLite

Organizing the app

Deploy something

Embedding with `go:embed`

Serving paths with `http`

Using `gorm` with SQLite