Add self-update, including in Docker

Sandbar can install new releases itself using Reef's selfupdate, automatically with
SANDBAR_AUTO_UPDATE=1 or from a button on the Account page. In a container the new binary is
written to <data>/bin and takes over from the image at start, until the image catches up.
Tags now publish a Gitea release with archives and SHA256SUMS as well as the image.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

cmd/sandbar/main.go

@@ -18,6 +18,7 @@ import (
 
 	"git.veillax.com/Veillax/reef/dotenv"
 	"git.veillax.com/Veillax/reef/secretbox"
+	"git.veillax.com/Veillax/reef/selfupdate"
 	"git.veillax.com/Veillax/sandbar/internal/sandbar"
 )
 
@@ -45,6 +46,7 @@ func main() {
 	data := flag.String("data", env("SANDBAR_DATA", "./sandbar-data"), "directory for the database")
 	url := flag.String("url", env("SANDBAR_URL", ""), "public URL (used for links in notifications)")
 	flag.String("env", ".env", "file to read secrets and settings from")
+	autoUpdate := flag.Bool("auto-update", os.Getenv("SANDBAR_AUTO_UPDATE") == "1", "check for new releases every few hours and update and restart by itself (Linux and macOS, including Docker)")
 	genkey := flag.Bool("genkey", false, "print a new random SANDBAR_MASTER_KEY and exit")
 	showVersion := flag.Bool("version", false, "print the version and exit")
 	flag.Parse()
@@ -58,6 +60,9 @@ func main() {
 		return
 	}
 
+	// In a container, an update lives on the data volume and takes over from the image.
+	sandbar.UseNewerOverlay(*data, version, log.Printf)
+
 	key, err := masterKey(*data)
 	if err != nil {
 		log.Fatal(err)
@@ -72,20 +77,40 @@ func main() {
 	}
 	defer st.Close()
 
+	var hs *http.Server
 	atoi := func(k string) int { n, _ := strconv.Atoi(os.Getenv(k)); return n }
-	srv := sandbar.New(sandbar.Options{
+	var srv *sandbar.Server
+	srv = sandbar.New(sandbar.Options{
 		DataDir:      *data,
 		URL:          strings.TrimRight(*url, "/"),
 		MetricsToken: os.Getenv("SANDBAR_METRICS_TOKEN"),
 		MessageDays:  atoi("SANDBAR_MESSAGE_DAYS"),
 		CheckDays:    atoi("SANDBAR_CHECK_DAYS"),
+		Version:      version,
+		AutoUpdate:   *autoUpdate,
+		UpdateServer: os.Getenv("SANDBAR_UPDATE_SERVER"),
+		UpdateRepo:   os.Getenv("SANDBAR_UPDATE_REPO"),
+		Restart: func(exe string) error {
+			// Let go of the port and the database, then become the new binary. If that fails, exit
+			// so the container or service manager starts it again, now from the new file.
+			hs.Close()
+			srv.Close()
+			st.Close()
+			err := selfupdate.Restart(exe)
+			log.Printf("could not restart into %s, exiting: %v", exe, err)
+			os.Exit(1)
+			return err
+		},
 		SMTP: sandbar.SMTPConfig{Host: os.Getenv("SANDBAR_SMTP_HOST"), Port: os.Getenv("SANDBAR_SMTP_PORT"),
 			User: os.Getenv("SANDBAR_SMTP_USER"), Password: os.Getenv("SANDBAR_SMTP_PASSWORD"), From: env("SANDBAR_SMTP_FROM", "sandbar@localhost")},
 	}, st)
 	srv.BootstrapAdmin(os.Getenv("SANDBAR_ADMIN_EMAIL"), os.Getenv("SANDBAR_ADMIN_PASSWORD"))
 	srv.Start()
+	if *autoUpdate {
+		go srv.RunAutoUpdate(context.Background())
+	}
 
-	hs := &http.Server{Addr: *listen, Handler: srv.Handler(), ReadHeaderTimeout: 10 * time.Second, IdleTimeout: 2 * time.Minute}
+	hs = &http.Server{Addr: *listen, Handler: srv.Handler(), ReadHeaderTimeout: 10 * time.Second, IdleTimeout: 2 * time.Minute}
 	go func() {
 		log.Printf("sandbar %s listening on %s", version, *listen)
 		if err := hs.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {