report frozen period duration

Author: bcaudan

packages/rum-core/src/domain/contexts/sessionContext.ts

@@ -1,5 +1,6 @@
 import type { ContextValue } from '@datadog/browser-core'
 import {
+  toServerDuration,
   DISCARDED,
   HookNames,
   SKIPPED,
@@ -12,6 +13,7 @@ import {
 } from '@datadog/browser-core'
 import type { RumSessionManager } from '../rumSessionManager'
 import { SessionReplayState, SessionType } from '../rumSessionManager'
+import type { PageStateServerEntry } from '../../rawRumEvent.types'
 import { RumEventType } from '../../rawRumEvent.types'
 import type { RecorderApi } from '../../boot/rumPublicApi'
 import type { DefaultRumEventAttributes, DefaultTelemetryEventAttributes, Hooks } from '../hooks'
@@ -38,6 +40,7 @@ export function startSessionContext(
     const eventDuration = elapsed(startTime, relativeNow())
     const wasInFrozenState = pageStateHistory.wasInPageStateDuringPeriod(PageState.FROZEN, startTime, eventDuration)
     if (isSessionExpired || (wasInFrozenState && eventType !== RumEventType.VIEW)) {
+      const pageStatesForPeriod = pageStateHistory.findPageStatesForPeriod(startTime, eventDuration)!
       // monitor-until: 2026-01-01
       addTelemetryDebug('Event sent after session expiration or frozen page state', {
         debug: {
@@ -49,14 +52,26 @@ export function startSessionContext(
             ? Number(session.expire) - relativeToClocks(startTime).timeStamp
             : undefined,
           wasInFrozenState,
-          pageStateDuringEventDuration: pageStateHistory.findPageStatesForPeriod(
-            startTime,
-            eventDuration
-          ) as ContextValue,
+          pageStateDuringEventDuration: pageStatesForPeriod as ContextValue,
+          sumFrozenDuration: wasInFrozenState ? computeSumFrozenDuration(pageStatesForPeriod) : undefined,
         },
       })
     }
 
+    /**
+     * Compute a frozen period duration by looking at the frozen entry start time and the next entry start time
+     */
+    function computeSumFrozenDuration(pageStates: PageStateServerEntry[]) {
+      let sum = 0
+      for (let i = 0; i < pageStates.length; i++) {
+        if (pageStates[i].state === PageState.FROZEN) {
+          const nextStateStart = pageStates[i + 1] ? pageStates[i + 1].start : toServerDuration(relativeNow())
+          sum += nextStateStart - pageStates[i].start
+        }
+      }
+      return sum
+    }
+
     let hasReplay
     let sampledForReplay
     let isActive