Step 1 — Set up the project

1# 1. create the project
2mkdir shortener && cd shortener
3go mod init github.com/you/shortener
4
5# 2. folders and empty files
6mkdir -p cmd/api internal/transport/web
7touch cmd/api/main.go internal/transport/web/respond.go
8
9# 3. write the two files below, then
10# (go mod tidy adds and removes dependencies; see "Modules and tooling")
11go mod tidy
12go run ./cmd/api
13
14# 4. in a second terminal
15curl -s localhost:8080/healthz
16curl -si -X POST localhost:8080/healthz | head -1   # 405, for free

1package web
2
3import (
4	"encoding/json"
5	"net/http"
6)
7
8// JSON writes v as the response body with the given status code.
9func JSON(w http.ResponseWriter, status int, v any) {
10	w.Header().Set("Content-Type", "application/json")
11	w.WriteHeader(status)              // headers first, then status, then body
12	if v != nil {
13		json.NewEncoder(w).Encode(v)
14	}
15}
16
17// Error writes one consistent error shape, so clients never have to guess.
18func Error(w http.ResponseWriter, status int, msg string) {
19	JSON(w, status, map[string]string{"error": msg})
20}

1package main
2
3import (
4	"log/slog"
5	"net/http"
6	"os"
7	"time"
8
9	"github.com/you/shortener/internal/transport/web"
10)
11
12func main() {
13	if err := run(); err != nil {
14		slog.Error("fatal", "err", err)
15		os.Exit(1)                     // the only os.Exit in the program
16	}
17}
18
19func run() error {
20	mux := http.NewServeMux()
21
22	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
23		web.JSON(w, 200, map[string]string{"status": "ok"})
24	})
25
26	srv := &http.Server{
27		Addr:              ":8080",
28		Handler:           mux,
29		ReadHeaderTimeout: 5 * time.Second,
30		ReadTimeout:       15 * time.Second,
31		WriteTimeout:      30 * time.Second,
32	}
33
34	slog.Info("listening", "addr", srv.Addr)
35	return srv.ListenAndServe()
36}

1go run ./cmd/api
2
3# in another terminal
4curl -s localhost:8080/healthz
5# {"status":"ok"}