Give a starting Chromium longer to observe the browser location timezone

server/cmd/api/api/browser_location.go

@@ -21,6 +21,11 @@ import (
 
 const (
 	browserLocationApplyTimeout = 5 * time.Second
+	// browserLocationStartupTimeout bounds how long after its DevTools endpoint
+	// comes up Chromium may take to notice /etc/localtime being replaced. Until
+	// then it ignores the replacement, and one restoring a slow saved tab can
+	// take longer than browserLocationApplyTimeout.
+	browserLocationStartupTimeout = 10 * time.Second
 	// browserLocationRoundTimeout bounds how long one attempt waits for
 	// Chromium's acknowledgements before it sends the location again.
 	browserLocationRoundTimeout = 1500 * time.Millisecond
@@ -143,7 +148,7 @@ func (s *ApiService) startBrowserLocationReconcileLocked(bundle oapi.BrowserLoca
 
 func (s *ApiService) reconcileBrowserLocation(ctx context.Context, bundle oapi.BrowserLocationBundle) {
 	started := time.Now()
-	deadline := started.Add(browserLocationApplyTimeout)
+	deadline := browserLocationDeadline(started, s.chromiumSince())
 	for {
 		if ctx.Err() != nil || !s.browserLocationCurrent(bundle) {
 			return
@@ -183,8 +188,9 @@ func (s *ApiService) reconcileBrowserLocation(ctx context.Context, bundle oapi.B
 				s.browserLocation.lastError = err.Error()
 				s.browserLocation.failures.Add(1)
 			}
+			components := s.browserLocation.components
 			s.browserLocationMu.Unlock()
-			logger.FromContext(ctx).Error("browser location did not converge", "error", err, "generation", bundle.Generation)
+			logger.FromContext(ctx).Error("browser location did not converge", "error", err, "generation", bundle.Generation, "components", components)
 			return
 		}
 		s.browserLocation.retries.Add(1)
@@ -196,6 +202,27 @@ func (s *ApiService) reconcileBrowserLocation(ctx context.Context, bundle oapi.B
 	}
 }
 
+// browserLocationDeadline is when an attempt that started at started stops
+// retrying: browserLocationApplyTimeout after it started, or
+// browserLocationStartupTimeout after Chromium's DevTools endpoint came up at
+// chromiumSince, whichever is later.
+func browserLocationDeadline(started, chromiumSince time.Time) time.Time {
+	deadline := started.Add(browserLocationApplyTimeout)
+	if startup := chromiumSince.Add(browserLocationStartupTimeout); startup.After(deadline) {
+		return startup
+	}
+	return deadline
+}
+
+// chromiumSince is when the running Chromium's DevTools endpoint came up, or
+// the zero time if it is unknown.
+func (s *ApiService) chromiumSince() time.Time {
+	if s.upstreamMgr == nil {
+		return time.Time{}
+	}
+	return s.upstreamMgr.Since()
+}
+
 // watchPendingRenderers follows the renderers that were pending when bundle
 // applied until they acknowledge it. If the browser then reports a component
 // that didn't converge, the location is no longer applied and is sent again.
@@ -597,7 +624,7 @@ func browserLocationError(message string) *string {
 // waitBrowserLocationApplied waits until the running browser confirms bundle,
 // or reports why it didn't.
 func (s *ApiService) waitBrowserLocationApplied(ctx context.Context, bundle oapi.BrowserLocationBundle) error {
-	ctx, cancel := context.WithTimeout(ctx, browserLocationApplyTimeout+time.Second)
+	ctx, cancel := context.WithDeadline(ctx, browserLocationDeadline(time.Now(), s.chromiumSince()).Add(time.Second))
 	defer cancel()
 	ticker := time.NewTicker(25 * time.Millisecond)
 	defer ticker.Stop()

server/cmd/api/api/browser_location_test.go

@@ -499,6 +499,42 @@ func TestSetBrowserLocationAllowsPendingRenderers(t *testing.T) {
 	assert.Equal(t, 1, status.Components.RenderersPending)
 }
 
+// Chromium ignores /etc/localtime being replaced until it has finished
+// starting, which restoring a slow saved tab delays past
+// browserLocationApplyTimeout. A location sent to a Chromium that just started
+// keeps replacing it until Chromium observes it.
+func TestSetBrowserLocationWaitsForStartingChromiumToObserveTimezone(t *testing.T) {
+	service := newBrowserLocationStateService(t)
+	observesFrom := time.Now().Add(browserLocationApplyTimeout + 500*time.Millisecond)
+	var observed atomic.Bool
+	previous := setBrowserLocaltime
+	setBrowserLocaltime = func(string) error {
+		if time.Now().After(observesFrom) {
+			observed.Store(true)
+		}
+		return nil
+	}
+	t.Cleanup(func() { setBrowserLocaltime = previous })
+	fakeLocationChromium(t, service, func() map[string]any {
+		return map[string]any{"renderersConverged": true, "renderersPending": 0, "timezoneConverged": observed.Load()}
+	})
+
+	resp := service.applyBrowserLocation(context.Background(), testLocationBundle(1))
+
+	require.IsType(t, oapi.SetBrowserLocation200JSONResponse{}, resp, "error: %s", snapshotError(service))
+	assert.True(t, observed.Load())
+}
+
+func TestBrowserLocationDeadline(t *testing.T) {
+	started := time.Now()
+
+	assert.Equal(t, started.Add(browserLocationApplyTimeout), browserLocationDeadline(started, time.Time{}), "an unknown Chromium gets the apply timeout")
+	settled := started.Add(-time.Minute)
+	assert.Equal(t, started.Add(browserLocationApplyTimeout), browserLocationDeadline(started, settled), "a Chromium past startup gets the apply timeout")
+	starting := started.Add(-time.Second)
+	assert.Equal(t, starting.Add(browserLocationStartupTimeout), browserLocationDeadline(started, starting), "a starting Chromium gets until it is past startup")
+}
+
 func TestBrowserLocationConfirmed(t *testing.T) {
 	converged := oapi.BrowserLocationComponents{Browser: true, Timezone: true, Renderers: true, NetworkContexts: true}
 	pending := converged

server/lib/devtoolsproxy/proxy.go

@@ -101,6 +101,9 @@ type UpstreamManager struct {
 	logger      *slog.Logger
 
 	currentURL atomic.Value // string
+	// currentSince is when currentURL last changed, in wall-clock Unix
+	// nanoseconds.
+	currentSince atomic.Int64
 
 	startOnce  sync.Once
 	stopOnce   sync.Once
@@ -154,10 +157,21 @@ func (u *UpstreamManager) Current() string {
 	return val
 }
 
+// Since returns when the current upstream URL was discovered, or the zero
+// time if none has been.
+func (u *UpstreamManager) Since() time.Time {
+	since := u.currentSince.Load()
+	if since == 0 {
+		return time.Time{}
+	}
+	return time.Unix(0, since)
+}
+
 func (u *UpstreamManager) setCurrent(url string) {
 	prev := u.Current()
 	if url != "" && url != prev {
 		u.logger.Info("devtools upstream updated", slog.String("url", url))
+		u.currentSince.Store(time.Now().UnixNano())
 		u.currentURL.Store(url)
 		// Broadcast update to subscribers without blocking. If a subscriber's
 		// channel buffer (size 1) is full, replace the buffered value with the