feat(admin): ask the panel to restart, from verdande's own settings

A container cannot replace its own image from the inside, so "update" is really
"ask whoever owns the container to recreate it" — Yggdrasil pulls `:latest` on the
way, which is what makes a restart an update at all. This removes the second
browser tab, not the panel's authority: the panel still does the work and still
records who asked.

Three settings, needed together, and the page names whichever are missing — an
operator reading "not configured" should not have to go and find out which of
three. The token is never sent to a browser; the page is told only whether it is
set.

Answers 202 rather than waiting. The panel stops this container as part of
answering, so the reply may never arrive, and a request cut off mid-flight is the
successful case wearing a failure's clothes. The interface believes neither answer
and polls /healthz until it responds.

Administrators only, and sessions only. A leaked API token that could restart the
server is a denial of service in one request.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/config/config.go

@@ -38,6 +38,22 @@ type Config struct {
 	// the deal its operator made by self-hosting.
 	UpdateCheck bool
 
+	// The Yggdrasil panel this instance runs under, so it can ask to be restarted
+	// from its own interface rather than from another browser tab.
+	//
+	// A container cannot replace its own image from the inside. Restarting is the
+	// panel's job — it recreates the container and pulls `:latest` on the way — so
+	// what this needs is a way to ask. All three are required together; any one
+	// alone cannot do anything.
+	//
+	// The token is a panel credential with control over that server. Anybody who
+	// can read this environment can restart it, which is true of anybody with the
+	// host anyway. It is never sent to a browser: the settings page is told only
+	// whether it is set.
+	PanelURL      string
+	PanelToken    string
+	PanelServerID string
+
 	// TrashRetention is how long a soft-deleted task or project stays recoverable.
 	TrashRetention time.Duration
 
@@ -69,6 +85,9 @@ func Load() (*Config, error) {
 		Dev:            envBool("VERDANDE_DEV", false),
 
 		GmailClientID:     env("VERDANDE_GMAIL_CLIENT_ID", ""),
+		PanelURL:          strings.TrimSuffix(env("VERDANDE_PANEL_URL", ""), "/"),
+		PanelToken:        env("VERDANDE_PANEL_TOKEN", ""),
+		PanelServerID:     env("VERDANDE_PANEL_SERVER_ID", ""),
 		GmailClientSecret: env("VERDANDE_GMAIL_CLIENT_SECRET", ""),
 		UpdateCheck:       envBool("VERDANDE_UPDATE_CHECK", false),
 	}

internal/httpapi/panel_handlers.go

@@ -0,0 +1,105 @@
+package httpapi
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"time"
+)
+
+// Asking the panel to restart this instance.
+//
+// A container cannot replace its own image from the inside, so "update" is really
+// "ask whoever owns the container to recreate it" — Yggdrasil pulls `:latest` on
+// the way, which is what makes a restart an update at all.
+//
+// The alternative was a second browser tab: read the version here, go to the
+// panel, find the server, press Restart. This removes the tab, not the panel's
+// authority — the panel still does the work and still records who asked.
+//
+// Administrators only, and sessions only. A leaked API token that could restart
+// the server is a denial of service in one request, and the whole point of the
+// session rule elsewhere in this file is that a stolen token must not be able to
+// do things only a person at a keyboard should.
+
+type panelStatusJSON struct {
+	// Configured is all three settings being present. The token itself is never
+	// sent: the page needs to know whether the button can work, not what the
+	// credential is.
+	Configured bool   `json:"configured"`
+	PanelURL   string `json:"panel_url,omitempty"`
+	// Why it cannot work, when it cannot. An operator reading "not configured"
+	// should not have to go and find out which of three things is missing.
+	Missing []string `json:"missing,omitempty"`
+}
+
+func (s *Server) panelStatus() panelStatusJSON {
+	var missing []string
+	if s.cfg.PanelURL == "" {
+		missing = append(missing, "VERDANDE_PANEL_URL")
+	}
+	if s.cfg.PanelToken == "" {
+		missing = append(missing, "VERDANDE_PANEL_TOKEN")
+	}
+	if s.cfg.PanelServerID == "" {
+		missing = append(missing, "VERDANDE_PANEL_SERVER_ID")
+	}
+	return panelStatusJSON{
+		Configured: len(missing) == 0,
+		PanelURL:   s.cfg.PanelURL,
+		Missing:    missing,
+	}
+}
+
+func (s *Server) handlePanelStatus(w http.ResponseWriter, r *http.Request) {
+	writeJSON(w, http.StatusOK, s.panelStatus())
+}
+
+func (s *Server) handleRestartFromPanel(w http.ResponseWriter, r *http.Request) {
+	status := s.panelStatus()
+	if !status.Configured {
+		writeError(w, http.StatusServiceUnavailable, CodeInternal,
+			fmt.Sprintf("this instance cannot restart itself: %v are not set", status.Missing))
+		return
+	}
+
+	user := userFrom(r.Context())
+	s.log.Info("restart requested from the interface", "user", user.ID, "server", s.cfg.PanelServerID)
+
+	// A short timeout of its own. The panel stops this container as part of
+	// answering, so the reply may never arrive — that is not a failure, and a
+	// request that hung waiting for it would look like one.
+	ctx, cancel := context.WithTimeout(context.WithoutCancel(r.Context()), 10*time.Second)
+	defer cancel()
+
+	url := fmt.Sprintf("%s/api/servers/%s/restart", s.cfg.PanelURL, s.cfg.PanelServerID)
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, nil)
+	if err != nil {
+		s.internal(w, r, "build panel request", err)
+		return
+	}
+	req.Header.Set("Authorization", "Bearer "+s.cfg.PanelToken)
+
+	resp, err := (&http.Client{Timeout: 10 * time.Second}).Do(req)
+	if err != nil {
+		// Including "the panel killed us mid-reply", which is the successful case
+		// wearing a failure's clothes. The interface polls /healthz rather than
+		// believing either answer, so this only has to be honest about what it saw.
+		s.log.Warn("panel restart call did not complete", "err", err)
+		writeJSON(w, http.StatusAccepted, map[string]any{
+			"restarting": true,
+			"note":       "the panel did not answer; it may already be restarting this container",
+		})
+		return
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode >= 400 {
+		s.log.Error("panel refused the restart", "status", resp.StatusCode)
+		writeError(w, http.StatusBadGateway, CodeInternal,
+			fmt.Sprintf("the panel refused: HTTP %d — check VERDANDE_PANEL_TOKEN has control of this server", resp.StatusCode))
+		return
+	}
+
+	writeJSON(w, http.StatusAccepted, map[string]any{"restarting": true})
+}

internal/httpapi/panel_test.go

@@ -0,0 +1,131 @@
+package httpapi
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/kristianwind/verdande/internal/config"
+)
+
+// Restarting is administrators only, and sessions only. A leaked API token that
+// could restart the server is a denial of service in one request.
+func TestRestartingIsAdminsOnlyAndSessionsOnly(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+	other := ts.newUser(t, "anden@example.dk", "Anden")
+
+	for _, path := range []string{"/api/v1/panel", "/api/v1/panel/restart"} {
+		method := "GET"
+		if path != "/api/v1/panel" {
+			method = "POST"
+		}
+		if resp, _ := other.do(t, method, path, nil); resp.StatusCode != http.StatusForbidden {
+			t.Errorf("%s as an ordinary user: status %d, want 403", path, resp.StatusCode)
+		}
+	}
+
+	admin, err := ts.db.UserByEmail(t.Context(), "kristian@example.dk")
+	if err != nil {
+		t.Fatal(err)
+	}
+	token := ts.apiToken(t, admin.ID)
+	req, _ := http.NewRequest("POST", ts.URL+"/api/v1/panel/restart", nil)
+	req.Header.Set("Authorization", "Bearer "+token)
+	resp, err := (&http.Client{}).Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusForbidden {
+		t.Errorf("restart with an admin's API token: status %d, want 403", resp.StatusCode)
+	}
+}
+
+// Unconfigured, it says which of the three settings are missing rather than
+// "not configured" — an operator should not have to go and find out which.
+func TestAnUnconfiguredPanelSaysWhatIsMissing(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+
+	_, status := ts.do(t, "GET", "/api/v1/panel", nil)
+	if status["configured"] != false {
+		t.Fatalf("configured = %v on an instance with no panel settings", status["configured"])
+	}
+	missing, _ := status["missing"].([]any)
+	if len(missing) != 3 {
+		t.Errorf("missing = %v, want all three settings named", missing)
+	}
+
+	resp, body := ts.do(t, "POST", "/api/v1/panel/restart", nil)
+	if resp.StatusCode != http.StatusServiceUnavailable {
+		t.Errorf("restart with nothing configured: status %d, want 503", resp.StatusCode)
+	}
+	if body["error"] == nil {
+		t.Error("the refusal says nothing about why")
+	}
+}
+
+// Configured, it calls the panel with a bearer token and reports what came back.
+func TestARestartCallsThePanelWithItsToken(t *testing.T) {
+	var gotPath, gotAuth string
+	panel := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotPath, gotAuth = r.URL.Path, r.Header.Get("Authorization")
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer panel.Close()
+
+	ts := newTestServerWith(t, func(cfg *config.Config) {
+		cfg.PanelURL = panel.URL
+		cfg.PanelToken = "hemmelig"
+		cfg.PanelServerID = "abc-123"
+	})
+	ts.bootstrap(t)
+
+	_, status := ts.do(t, "GET", "/api/v1/panel", nil)
+	if status["configured"] != true {
+		t.Fatalf("configured = %v with all three set", status["configured"])
+	}
+	// The token is a credential and must never reach a browser.
+	for key, value := range status {
+		if s, ok := value.(string); ok && s == "hemmelig" {
+			t.Errorf("the panel token was sent to the client in %q", key)
+		}
+	}
+
+	resp, _ := ts.do(t, "POST", "/api/v1/panel/restart", nil)
+	if resp.StatusCode != http.StatusAccepted {
+		t.Fatalf("restart: status %d, want 202", resp.StatusCode)
+	}
+	if gotPath != "/api/servers/abc-123/restart" {
+		t.Errorf("called %q", gotPath)
+	}
+	if gotAuth != "Bearer hemmelig" {
+		t.Errorf("Authorization = %q", gotAuth)
+	}
+}
+
+// A panel that refuses is reported as the panel refusing, not as this server
+// breaking: the fix is a token with control of that server, and saying "internal
+// error" would send somebody looking in the wrong place.
+func TestAPanelThatRefusesIsReportedAsSuch(t *testing.T) {
+	panel := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, "forbidden", http.StatusForbidden)
+	}))
+	defer panel.Close()
+
+	ts := newTestServerWith(t, func(cfg *config.Config) {
+		cfg.PanelURL = panel.URL
+		cfg.PanelToken = "forkert"
+		cfg.PanelServerID = "abc-123"
+	})
+	ts.bootstrap(t)
+
+	resp, body := ts.do(t, "POST", "/api/v1/panel/restart", nil)
+	if resp.StatusCode != http.StatusBadGateway {
+		t.Errorf("a refusing panel: status %d, want 502", resp.StatusCode)
+	}
+	if msg, _ := body["error"].(string); msg == "" {
+		t.Error("the refusal does not say what to check")
+	}
+}

internal/httpapi/server.go

@@ -347,6 +347,11 @@ func New(cfg *config.Config, db *store.DB, log *slog.Logger, web fs.FS) *Server
 			r.Group(func(r chi.Router) {
 				r.Use(s.requireSession, s.requireAdmin)
 				r.Get("/errors", s.handleListErrors)
+				// Restarting this instance from its own interface. The panel does
+				// the work — a container cannot replace its own image — and pulls
+				// `:latest` on the way, which is what makes a restart an update.
+				r.Get("/panel", s.handlePanelStatus)
+				r.Post("/panel/restart", s.handleRestartFromPanel)
 				// A backup file is a complete copy of the database, so this whole
 				// group is sessions-only as well as administrators-only: a leaked
 				// token must not be able to download everybody's data.