netwatch/internal/server/server.go

// Package server provides the HTTP server lifecycle,
// including startup, routing, and graceful shutdown. The
// process lifetime is owned by fx: shutdown is requested
// through fx.Shutdowner so every component's OnStop hook runs
// in dependency order.
package server

import (
	"context"
	"fmt"
	"log/slog"
	"net/http"
	"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/getsentry/sentry-go"
	"github.com/go-chi/chi/v5"
	"go.uber.org/fx"
)

// sentryFlushTimeout is how long shutdown waits for Sentry to send
// what it still holds.
const sentryFlushTimeout = 2 * time.Second

// 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
	Shutdowner fx.Shutdowner
}

// Server is the top-level HTTP server orchestrator.
type Server struct {
	h          *handlers.Handlers
	httpServer *http.Server
	log        *slog.Logger
	mw         *middleware.Middleware
	params     Params
	router     *chi.Mux
	shutdowner fx.Shutdowner
}

// 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()
	s.shutdowner = params.Shutdowner

	err := s.enableSentry()
	if err != nil {
		return nil, err
	}

	lc.Append(fx.Hook{
		OnStart: func(_ context.Context) error {
			// Build the router and http.Server synchronously
			// here, before spawning the serving goroutine, so
			// httpServer is fully constructed by the time OnStop
			// (or an early signal) can read it. fx guarantees
			// OnStart returns before OnStop runs, so no
			// synchronization or nil check is needed at shutdown.
			s.SetupRoutes()
			s.httpServer = s.newHTTPServer()

			go s.listenAndServe()

			return nil
		},
		OnStop: func(ctx context.Context) error {
			return s.shutdown(ctx)
		},
	})

	return s, nil
}

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

// enableSentry sets Sentry up when SENTRY_DSN is set, so that
// SetupRoutes can report panics to it. With SENTRY_DSN empty it does
// nothing. A DSN Sentry refuses stops the start.
func (s *Server) enableSentry() error {
	if s.params.Config.SentryDSN == "" {
		return nil
	}

	err := sentry.Init(sentry.ClientOptions{
		Dsn:     s.params.Config.SentryDSN,
		Release: s.params.Globals.Appname + "-" + s.params.Globals.Version,
	})
	if err != nil {
		return fmt.Errorf("SENTRY_DSN: %w", err)
	}

	s.log.Info("sentry error reporting activated")

	return nil
}

// shutdown gracefully stops the HTTP server within the
// deadline of the context fx provides for OnStop, then gives
// Sentry, if set up, time to send what it still holds.
func (s *Server) shutdown(ctx context.Context) error {
	err := s.httpServer.Shutdown(ctx)

	if s.params.Config.SentryDSN != "" {
		sentry.Flush(sentryFlushTimeout)
	}

	if err != nil {
		s.log.Error("server clean shutdown failed", "error", err)

		return err
	}

	s.log.Info("server stopped")

	return nil
}