review: fix lcp capture

Author: archandatta

server/lib/cdpmonitor/computed.go

@@ -78,15 +78,19 @@ func (s *computedState) navSnapshot() (json.RawMessage, map[string]string) {
 }
 
 // navDataWith merges extra fields into the current nav payload.
+// Nav context fields (session_id, target_id, etc.) always take precedence over
+// caller-supplied extra so a page-controlled payload cannot forge nav identity.
 func (s *computedState) navDataWith(extra map[string]any) json.RawMessage {
-	base := make(map[string]any)
+	result := make(map[string]any)
+	maps.Copy(result, extra)
 	if s != nil {
 		d, _ := s.navSnapshot()
+		base := make(map[string]any)
 		_ = json.Unmarshal(d, &base)
+		maps.Copy(result, base)
 	}
-	maps.Copy(base, extra)
-	result, _ := json.Marshal(base)
-	return result
+	out, _ := json.Marshal(result)
+	return out
 }
 
 func stopTimer(t *time.Timer) {

server/lib/cdpmonitor/domains.go

@@ -45,7 +45,7 @@ func (m *Monitor) enableDomains(ctx context.Context, sessionID string, targetTyp
 	}
 
 	if _, err := m.send(ctx, "PerformanceTimeline.enable", map[string]any{
-		"eventTypes": []string{timelineEventLayoutShift},
+		"eventTypes": []string{timelineEventLayoutShift, timelineEventLCP},
 	}, sessionID); err != nil && ctx.Err() == nil {
 		m.log.Warn("cdpmonitor: failed to enable PerformanceTimeline", "session", sessionID, "err", err)
 	}

server/lib/cdpmonitor/handlers.go

@@ -208,41 +208,50 @@ func (m *Monitor) handleBindingCalled(p cdpRuntimeBindingCalledParams, sessionID
 	m.publishEvent(header.Type, events.CategoryInteraction, events.Source{Kind: events.KindCDP}, "Runtime.bindingCalled", cs.navDataWith(payloadMap), sessionID)
 }
 
-// handleTimelineEvent processes PerformanceTimeline layout-shift events.
+// handleTimelineEvent processes PerformanceTimeline layout-shift and LCP events.
 func (m *Monitor) handleTimelineEvent(p cdpPerformanceTimelineEventAddedParams, sessionID string) {
-	if p.Event.Type != timelineEventLayoutShift {
-		return
-	}
-	// source_frame_id is the frame where the shift occurred; distinct from nav
-	// context's frame_id (the top-level navigated frame).
-	ev := map[string]any{
-		"source_frame_id": p.Event.FrameID,
-		"time":           p.Event.Time,
-		"duration":       p.Event.Duration,
-	}
-	var shift cdpLayoutShiftDetails
-	if p.Event.LayoutShiftDetails != nil && json.Unmarshal(p.Event.LayoutShiftDetails, &shift) == nil {
-		ev["layout_shift_details"] = map[string]any{
-			"score":            shift.Score,
-			"had_recent_input": shift.HadRecentInput,
+	switch p.Event.Type {
+	case timelineEventLayoutShift:
+		// source_frame_id is the frame where the shift occurred; distinct from nav
+		// context's frame_id (the top-level navigated frame).
+		ev := map[string]any{
+			"source_frame_id": p.Event.FrameID,
+			"time":            p.Event.Time,
+			"duration":        p.Event.Duration,
 		}
-	}
-	var lcp cdpLcpDetails
-	if p.Event.LcpDetails != nil && json.Unmarshal(p.Event.LcpDetails, &lcp) == nil {
-		ev["lcp_details"] = map[string]any{
-			"render_time": lcp.RenderTime,
-			"load_time":   lcp.LoadTime,
-			"size":        lcp.Size,
-			"element_id":  lcp.ElementID,
-			"url":         lcp.URL,
-			"node_id":     lcp.NodeID,
+		var shift cdpLayoutShiftDetails
+		if p.Event.LayoutShiftDetails != nil && json.Unmarshal(p.Event.LayoutShiftDetails, &shift) == nil {
+			ev["layout_shift_details"] = map[string]any{
+				"score":            shift.Score,
+				"had_recent_input": shift.HadRecentInput,
+			}
 		}
-	}
-	cs := m.computedFor(sessionID)
-	data := cs.navDataWith(ev)
-	m.publishEvent(EventLayoutShift, events.CategoryPage, events.Source{Kind: events.KindCDP}, "PerformanceTimeline.timelineEventAdded", data, sessionID)
-	if cs != nil {
-		cs.onLayoutShift()
+		cs := m.computedFor(sessionID)
+		data := cs.navDataWith(ev)
+		m.publishEvent(EventLayoutShift, events.CategoryPage, events.Source{Kind: events.KindCDP}, "PerformanceTimeline.timelineEventAdded", data, sessionID)
+		if cs != nil {
+			cs.onLayoutShift()
+		}
+
+	case timelineEventLCP:
+		ev := map[string]any{
+			"source_frame_id": p.Event.FrameID,
+			"time":            p.Event.Time,
+		}
+		var lcp cdpLcpDetails
+		if p.Event.LcpDetails != nil && json.Unmarshal(p.Event.LcpDetails, &lcp) == nil {
+			ev["lcp_details"] = map[string]any{
+				"render_time": lcp.RenderTime,
+				"load_time":   lcp.LoadTime,
+				"size":        lcp.Size,
+				"element_id":  lcp.ElementID,
+				"url":         lcp.URL,
+				"node_id":     lcp.NodeID,
+			}
+		}
+		cs := m.computedFor(sessionID)
+		data := cs.navDataWith(ev)
+		m.publishEvent(EventLCP, events.CategoryPage, events.Source{Kind: events.KindCDP}, "PerformanceTimeline.timelineEventAdded", data, sessionID)
 	}
 }
 

server/lib/cdpmonitor/types.go

@@ -25,6 +25,7 @@ const (
 	EventDOMContentLoaded     = "page_dom_content_loaded" // Page.domContentEventFired
 	EventPageLoad             = "page_load"               // Page.loadEventFired
 	EventLayoutShift          = "page_layout_shift"       // PerformanceTimeline event of type "layout-shift"
+	EventLCP                  = "page_lcp"                // PerformanceTimeline event of type "largest-contentful-paint"
 	EventTabOpened            = "page_tab_opened"         // Target.attachedToTarget for type=page
 )
 
@@ -62,8 +63,10 @@ const (
 	MetadataKeyTargetType   = "target_type"
 )
 
-// CDP PerformanceTimeline event type for layout shifts.
-const timelineEventLayoutShift = "layout-shift"
+const (
+	timelineEventLayoutShift = "layout-shift"
+	timelineEventLCP         = "largest-contentful-paint"
+)
 
 // CDP target type for browser pages (as opposed to workers, iframes, etc.).
 const targetTypePage = "page"