main.go

// A small HTTP server that demonstrates routing, JSON, slog, middleware
// and graceful shutdown using only the standard library.
package main

import (
	"context"
	"encoding/json"
	"errors"
	"flag"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"
)

type pingResp struct {
	Status string `json:"status"`
}

type echoResp struct {
	Echo string `json:"echo"`
}

func ping(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(pingResp{Status: "ok"})
}

func echo(w http.ResponseWriter, r *http.Request) {
	msg := r.URL.Query().Get("msg")
	if msg == "" {
		http.Error(w, "missing 'msg' query parameter", http.StatusBadRequest)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(echoResp{Echo: msg})
}

func loggingMiddleware(logger *slog.Logger) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			start := time.Now()
			next.ServeHTTP(w, r)
			logger.Info("request",
				slog.String("method", r.Method),
				slog.String("path", r.URL.Path),
				slog.Duration("dur", time.Since(start)),
			)
		})
	}
}

func main() {
	addr := flag.String("addr", ":8080", "listen address")
	flag.Parse()

	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))

	mux := http.NewServeMux()
	mux.HandleFunc("GET /ping", ping)
	mux.HandleFunc("GET /echo", echo)

	srv := &http.Server{
		Addr:              *addr,
		Handler:           loggingMiddleware(logger)(mux),
		ReadHeaderTimeout: 5 * time.Second,
	}

	go func() {
		logger.Info("server starting", slog.String("addr", *addr))
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			logger.Error("server failed", slog.Any("err", err))
			os.Exit(1)
		}
	}()

	stop := make(chan os.Signal, 1)
	signal.Notify(stop, syscall.SIGINT, syscall.SIGTERM)
	<-stop
	logger.Info("shutdown signal received")

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := srv.Shutdown(ctx); err != nil {
		logger.Error("graceful shutdown failed", slog.Any("err", err))
	}
	logger.Info("bye")
}