netwatch/backend/internal/server/server.go

// Package server provides the HTTP server lifecycle,
// including startup, routing, signal handling, and graceful
// shutdown.
package server

import (
	"context"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"sneak.berlin/go/netwatch/internal/config"
	"sneak.berlin/go/netwatch/internal/globals"
	"sneak.berlin/go/netwatch/internal/handlers"
	"sneak.berlin/go/netwatch/internal/logger"
	"sneak.berlin/go/netwatch/internal/middleware"

	"github.com/go-chi/chi/v5"
	"go.uber.org/fx"
)

// Params defines the dependencies for Server.
type Params struct {
	fx.In

	Config     *config.Config
	Globals    *globals.Globals
	Handlers   *handlers.Handlers
	Logger     *logger.Logger
	Middleware *middleware.Middleware
}

// Server is the top-level HTTP server orchestrator.
type Server struct {
	cancelFunc  context.CancelFunc
	exitCode    int
	h           *handlers.Handlers
	httpServer  *http.Server
	log         *slog.Logger
	mw          *middleware.Middleware
	params      Params
	router      *chi.Mux
	startupTime time.Time
}

// New creates a Server and registers lifecycle hooks for
// starting and stopping it.
func New(
	lc fx.Lifecycle,
	params Params,
) (*Server, error) {
	s := new(Server)
	s.params = params
	s.mw = params.Middleware
	s.h = params.Handlers
	s.log = params.Logger.Get()

	lc.Append(fx.Hook{
		OnStart: func(_ context.Context) error {
			s.startupTime = time.Now().UTC()

			// The fx OnStart context is scoped to startup and is
			// cancelled once the hook returns; run() derives its
			// own context instead of inheriting this one.
			go func() { //nolint:contextcheck // see comment above
				s.run()
			}()

			return nil
		},
		OnStop: func(_ context.Context) error {
			if s.cancelFunc != nil {
				s.cancelFunc()
			}

			return nil
		},
	})

	return s, nil
}

// ServeHTTP delegates to the chi router.
func (s *Server) ServeHTTP(
	w http.ResponseWriter,
	r *http.Request,
) {
	s.router.ServeHTTP(w, r)
}

func (s *Server) run() {
	exitCode := s.serve()
	os.Exit(exitCode)
}

func (s *Server) serve() int {
	// Declared up front because the multi-assign below also writes
	// s.cancelFunc, so := cannot be used.
	var ctx context.Context //nolint:wsl // see comment above

	ctx, s.cancelFunc = context.WithCancel(
		context.Background(),
	)

	go func() {
		c := make(chan os.Signal, 1)

		signal.Ignore(syscall.SIGPIPE)
		signal.Notify(c, os.Interrupt, syscall.SIGTERM)

		sig := <-c
		s.log.Info("signal received", "signal", sig)

		if s.cancelFunc != nil {
			s.cancelFunc()
		}
	}()

	go func() {
		s.serveUntilShutdown()
	}()

	<-ctx.Done()
	s.cleanShutdown()

	return s.exitCode
}

const shutdownTimeout = 5 * time.Second

func (s *Server) cleanShutdown() {
	s.exitCode = 0

	ctxShutdown, shutdownCancel := context.WithTimeout(
		context.Background(),
		shutdownTimeout,
	)
	defer shutdownCancel()

	err := s.httpServer.Shutdown(ctxShutdown)
	if err != nil {
		s.log.Error(
			"server clean shutdown failed",
			"error", err,
		)
	}

	s.log.Info("server stopped")
}