Exit with the shutdown's code and wait for image processing (closes #86)

fx alone handles SIGINT and SIGTERM; the server's own handler, which
only cancelled a context that fx's stop did not wait for, is gone.
runApp starts the fx app, waits for a signal or a shutdown request,
stops the app and returns the exit code, which main passes to os.Exit.
A listen error asks fx to shut down with exit code 1. A Sentry DSN that
cannot be used fails the server's start hook, so fx stops what had
already started. The server's stop hook stops the HTTP server, then
waits for the images still being processed, both within
ShutdownTimeout; images still being processed after that are logged and
fail the stop, so the exit code is 1.

Model: opus-5-5

internal/server/server.go

@@ -3,12 +3,10 @@ package server
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log/slog"
 	"net/http"
-	"os"
-	"os/signal"
-	"syscall"
 	"time"
 
 	"github.com/getsentry/sentry-go"
@@ -27,6 +25,10 @@ const (
 	SentryFlushTimeout = 2 * time.Second
 )
 
+// errStillProcessing is returned by the server's stop hook when images are
+// still being processed once ShutdownTimeout has passed.
+var errStillProcessing = errors.New("images still being processed at shutdown")
+
 // Params defines dependencies for Server.
 type Params struct {
 	fx.In
@@ -36,6 +38,7 @@ type Params struct {
 	Config     *config.Config
 	Middleware *middleware.Middleware
 	Handlers   *handlers.Handlers
+	Shutdowner fx.Shutdowner
 }
 
 // Server is the main HTTP server.
@@ -45,59 +48,58 @@ type Server struct {
 	globals       *globals.Globals
 	mw            *middleware.Middleware
 	h             *handlers.Handlers
+	shutdowner    fx.Shutdowner
 	startupTime   time.Time
-	exitCode      int
 	sentryEnabled bool
-	cancelFunc    context.CancelFunc
 	httpServer    *http.Server
 	router        *chi.Mux
 }
 
-// New creates a new Server instance.
+// New creates a new Server instance. Its start hook starts Sentry and the
+// HTTP server; its stop hook, which fx runs on SIGINT, SIGTERM or a
+// shutdown request, shuts them down.
 func New(lc fx.Lifecycle, params Params) (*Server, error) {
 	s := &Server{
-		log:     params.Logger.Get(),
-		config:  params.Config,
-		globals: params.Globals,
-		mw:      params.Middleware,
-		h:       params.Handlers,
+		log:        params.Logger.Get(),
+		config:     params.Config,
+		globals:    params.Globals,
+		mw:         params.Middleware,
+		h:          params.Handlers,
+		shutdowner: params.Shutdowner,
 	}
 
 	lc.Append(fx.Hook{
-		OnStart: func(ctx context.Context) error {
+		OnStart: func(_ context.Context) error {
 			s.startupTime = time.Now()
-			go s.Run(context.WithoutCancel(ctx))
 
-			return nil
-		},
-		OnStop: func(_ context.Context) error {
-			if s.cancelFunc != nil {
-				s.cancelFunc()
+			err := s.enableSentry()
+			if err != nil {
+				return err
 			}
 
+			s.SetupRoutes()
+			s.httpServer = s.newHTTPServer()
+
+			go s.serveUntilShutdown()
+
 			return nil
 		},
+		OnStop: s.cleanShutdown,
 	})
 
 	return s, nil
 }
 
-// Run starts the server.
-func (s *Server) Run(ctx context.Context) {
-	s.enableSentry()
-	s.serve(ctx)
-}
-
 // MaintenanceMode returns whether maintenance mode is enabled.
 func (s *Server) MaintenanceMode() bool {
 	return s.config.MaintenanceMode
 }
 
-func (s *Server) enableSentry() {
+func (s *Server) enableSentry() error {
 	s.sentryEnabled = false
 
 	if s.config.SentryDSN == "" {
-		return
+		return nil
 	}
 
 	err := sentry.Init(sentry.ClientOptions{
@@ -105,55 +107,42 @@ func (s *Server) enableSentry() {
 		Release: fmt.Sprintf("%s-%s", s.globals.Appname, s.globals.Version),
 	})
 	if err != nil {
-		s.log.Error("sentry init failure", "error", err)
-		os.Exit(1)
+		return fmt.Errorf("sentry init failure: %w", err)
 	}
 
 	s.log.Info("sentry error reporting activated")
 	s.sentryEnabled = true
+
+	return nil
 }
 
-func (s *Server) serve(ctx context.Context) int {
-	ctx, cancelFunc := context.WithCancel(ctx)
-	s.cancelFunc = cancelFunc
+// cleanShutdown stops the HTTP server, waits for the images still being
+// processed, then flushes Sentry. The first two share ShutdownTimeout. It
+// returns errStillProcessing when images are still being processed after
+// that, as their work is abandoned.
+func (s *Server) cleanShutdown(ctx context.Context) error {
+	s.log.Info("shutting down")
 
-	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 s.serveUntilShutdown()
-
-	<-ctx.Done()
-	s.cleanShutdown(ctx)
-
-	return s.exitCode
-}
-
-func (s *Server) cleanShutdown(ctx context.Context) {
-	s.exitCode = 0
-
-	ctxShutdown, shutdownCancel := context.WithTimeout(
-		context.WithoutCancel(ctx), ShutdownTimeout)
+	ctxShutdown, shutdownCancel := context.WithTimeout(ctx, ShutdownTimeout)
 	defer shutdownCancel()
 
-	if s.httpServer != nil {
-		err := s.httpServer.Shutdown(ctxShutdown)
-		if err != nil {
-			s.log.Error("server clean shutdown failed", "error", err)
-		}
+	err := s.httpServer.Shutdown(ctxShutdown)
+	if err != nil {
+		s.log.Error("server clean shutdown failed", "error", err)
 	}
 
+	stillProcessing := s.h.WaitForProcessing(ctxShutdown)
+
 	if s.sentryEnabled {
 		sentry.Flush(SentryFlushTimeout)
 	}
+
+	if stillProcessing > 0 {
+		s.log.Error("images still being processed at shutdown",
+			"count", stillProcessing)
+
+		return errStillProcessing
+	}
+
+	return nil
 }