feat(react-native): link new sessions to the one they replace via session.previous_id

sdk/@launchdarkly/observability-react-native/src/client/ObservabilityClient.test.ts

@@ -1,6 +1,10 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { ObservabilityClient } from './ObservabilityClient'
 import { Platform } from 'react-native'
+import {
+	SESSION_RESUME_THRESHOLD_MS,
+	SESSION_STORAGE_KEY,
+} from '../constants/sessions'
 
 describe('ObservabilityClient — stop during async init', () => {
 	beforeEach(() => {
@@ -155,4 +159,32 @@ describe('ObservabilityClient — platform attributes on the Resource', () => {
 			'device.model.identifier': 'user-model',
 		})
 	})
+
+	it('carries session.previous_id when a new session replaces a stale one', async () => {
+		const now = Date.now()
+		localStorage.setItem(
+			SESSION_STORAGE_KEY,
+			JSON.stringify({
+				sessionId: 'stale-session-id',
+				startTime: now - SESSION_RESUME_THRESHOLD_MS * 2,
+				lastActivityTime: now - SESSION_RESUME_THRESHOLD_MS - 1_000,
+				reloadCount: 0,
+			}),
+		)
+		try {
+			const attributes = await buildInitializedResource()
+
+			expect(attributes['session.previous_id']).toBe('stale-session-id')
+			expect(attributes['session.id']).not.toBe('stale-session-id')
+		} finally {
+			localStorage.clear()
+		}
+	})
+
+	it('omits session.previous_id when there was no previous session', async () => {
+		localStorage.clear()
+		const attributes = await buildInitializedResource()
+
+		expect(attributes).not.toHaveProperty('session.previous_id')
+	})
 })

sdk/@launchdarkly/observability-react-native/src/client/SessionManager.test.ts

@@ -156,6 +156,80 @@ describe('SessionManager session preservation', () => {
 		expect(mgr.getResumeInfo().reloadCount).toBe(0)
 	})
 
+	it('links a session started after a stale one via session.previous_id', async () => {
+		const store = new MemoryStore()
+		const now = Date.now()
+		store.seed({
+			sessionId: 'stale-session-id',
+			startTime: now - SESSION_RESUME_THRESHOLD_MS * 2,
+			lastActivityTime: now - SESSION_RESUME_THRESHOLD_MS - 1_000,
+			reloadCount: 0,
+		})
+
+		const mgr = new SessionManager({}, store)
+		await mgr.initialize()
+
+		expect(mgr.getPreviousSessionId()).toBe('stale-session-id')
+		expect(mgr.getSessionAttributes()).toEqual({
+			'session.id': mgr.getSessionInfo().sessionId,
+			'session.start_time': mgr.getSessionInfo().startTime.toString(),
+			'session.previous_id': 'stale-session-id',
+		})
+		// The next load links to this session, not the one before it.
+		expect(store.read().sessionId).toBe(mgr.getSessionInfo().sessionId)
+	})
+
+	it('links a session started by a cold start via session.previous_id', async () => {
+		const store = new MemoryStore()
+		const now = Date.now()
+		store.seed({
+			sessionId: 'prev-session-id',
+			startTime: now - 60_000,
+			lastActivityTime: now - 1_000,
+			reloadCount: 0,
+		})
+
+		const mgr = new SessionManager(
+			{ getProcessStartTimeMs: () => now - 500 },
+			store,
+		)
+		await mgr.initialize()
+
+		expect(mgr.getSessionAttributes()['session.previous_id']).toBe(
+			'prev-session-id',
+		)
+	})
+
+	it('omits session.previous_id when the session is resumed', async () => {
+		const store = new MemoryStore()
+		const now = Date.now()
+		store.seed({
+			sessionId: 'prev-session-id',
+			startTime: now - 60_000,
+			lastActivityTime: now - 1_000,
+			reloadCount: 0,
+		})
+
+		const mgr = new SessionManager({}, store)
+		await mgr.initialize()
+
+		expect(mgr.getSessionInfo().sessionId).toBe('prev-session-id')
+		expect(mgr.getPreviousSessionId()).toBeUndefined()
+		expect(mgr.getSessionAttributes()).not.toHaveProperty(
+			'session.previous_id',
+		)
+	})
+
+	it('omits session.previous_id when nothing was persisted', async () => {
+		const mgr = new SessionManager({}, new MemoryStore())
+		await mgr.initialize()
+
+		expect(mgr.getPreviousSessionId()).toBeUndefined()
+		expect(mgr.getSessionAttributes()).not.toHaveProperty(
+			'session.previous_id',
+		)
+	})
+
 	it('does not resume without a persistent store', async () => {
 		const mgr = new SessionManager({}, noOpStore)
 		await mgr.initialize()

sdk/@launchdarkly/observability-react-native/src/client/SessionManager.ts

@@ -61,6 +61,9 @@ export class SessionManager {
 		reloadCount: 0,
 	}
 	private lastPersistAt = 0
+	// The persisted session this JS load replaced (stale or cold start), so
+	// the new session's telemetry can link back to it as `session.previous_id`.
+	private previousSessionId?: string
 
 	constructor(options?: Options, store?: SessionStore) {
 		this.options = {
@@ -110,6 +113,7 @@ export class SessionManager {
 				startTime: Date.now(),
 			}
 			this.resumeInfo = { reloaded: false, elapsedMs: 0, reloadCount: 0 }
+			this.previousSessionId = undefined
 		}
 	}
 
@@ -161,6 +165,9 @@ export class SessionManager {
 			// completes.
 			this.reloadCount = 0
 			this.resumeInfo = { reloaded: false, elapsedMs: 0, reloadCount: 0 }
+			if (previous && previous.sessionId !== this.sessionInfo.sessionId) {
+				this.previousSessionId = previous.sessionId
+			}
 
 			if (this.options.debug && isColdStart) {
 				console.log(
@@ -271,10 +278,22 @@ export class SessionManager {
 		return { ...this.sessionInfo }
 	}
 
+	/**
+	 * The ID of the persisted session this JS load replaced with a new one
+	 * (the previous session timed out, or the app cold started). Undefined
+	 * when the session was resumed or nothing was persisted.
+	 */
+	public getPreviousSessionId(): string | undefined {
+		return this.previousSessionId
+	}
+
 	public getSessionAttributes(): Record<string, string> {
 		return {
 			'session.id': this.sessionInfo.sessionId,
 			'session.start_time': this.sessionInfo.startTime.toString(),
+			...(this.previousSessionId
+				? { 'session.previous_id': this.previousSessionId }
+				: {}),
 		}
 	}