fix(replay): start a new session on opt-in whenever replay was wanted

.changeset/opt-in-new-session-when-replay-wanted.md

@@ -0,0 +1,6 @@
+---
+"posthog": patch
+"posthog-android": patch
+---
+
+Fix session replay recording into the opted-out session when a linked feature flag or pending remote config delayed its restart after `optIn()`.

posthog/src/main/java/com/posthog/PostHog.kt

@@ -458,7 +458,8 @@ public class PostHog private constructor(
                     sessionReplayHandler = it
 
                     if (startSessionReplay) {
-                        startSessionReplayInternal(resumeCurrent = resumeSessionReplay)
+                        // setup() resumes the current session and optIn() has already started a new one
+                        startSessionReplayInternal(resumeCurrent = resumeSessionReplay, rotateSession = false)
                     }
                 } else if (it is PostHogSurveysHandler) {
                     surveysHandler = it
@@ -1364,6 +1365,12 @@ public class PostHog private constructor(
             }
 
             if (wasOptedOut) {
+                // rotate even if the linked flag or remote config then holds replay off, so a later start
+                // doesn't resume the session that was active while opted out
+                if (sessionReplayWanted) {
+                    PostHogSessionManager.endSession()
+                    PostHogSessionManager.startSession()
+                }
                 installIntegrations(resumeSessionReplay = false, startSessionReplay = sessionReplayWanted, surveys = surveys)
                 // install re-arms each integration from local config; re-apply the cached remote
                 // config (e.g. exception autocapture turned off remotely) instead of waiting for a reload
@@ -2527,7 +2534,10 @@ public class PostHog private constructor(
         }
     }
 
-    private fun startSessionReplayInternal(resumeCurrent: Boolean) {
+    private fun startSessionReplayInternal(
+        resumeCurrent: Boolean,
+        rotateSession: Boolean = !resumeCurrent,
+    ) {
         if (!isEnabled()) {
             return
         }
@@ -2552,8 +2562,10 @@ public class PostHog private constructor(
 
                 it.start(true)
             } else {
-                endSession()
-                startSession()
+                if (rotateSession) {
+                    endSession()
+                    startSession()
+                }
 
                 if (!shouldRecordSession()) {
                     return

posthog/src/test/java/com/posthog/PostHogTest.kt

@@ -1508,6 +1508,46 @@ internal class PostHogTest {
         sut.close()
     }
 
+    @Test
+    fun `optIn starts a new session when replay is wanted but its flag holds it off`() {
+        val http = mockHttp()
+        val url = http.url("/")
+        val integration = PostHogSessionReplayHandlerFake(false)
+
+        val sut = getSut(url.toString(), sessionReplay = true, preloadFeatureFlags = false, integration = integration)
+        val sessionAtOptOut = sut.getSessionId()
+
+        sut.optOut()
+        integration.reset()
+        sut.optIn()
+
+        assertFalse(integration.startCalled)
+        assertNotEquals(sessionAtOptOut, sut.getSessionId())
+
+        sut.close()
+    }
+
+    @Test
+    fun `optIn keeps the session when the app stopped replay before opting out`() {
+        val http = mockHttp()
+        val url = http.url("/")
+        val integration = PostHogSessionReplayHandlerFake(false)
+        val myPrefs = PostHogMemoryPreferences()
+        myPrefs.setValue(SESSION_REPLAY, emptyMap<String, String>())
+
+        val sut =
+            getSut(url.toString(), sessionReplay = true, cachePreferences = myPrefs, preloadFeatureFlags = false, integration = integration)
+        sut.stopSessionReplay()
+        val sessionAtOptOut = sut.getSessionId()
+
+        sut.optOut()
+        sut.optIn()
+
+        assertEquals(sessionAtOptOut, sut.getSessionId())
+
+        sut.close()
+    }
+
     @Test
     fun `flags-loaded replay start can't land after a concurrent optOut`() {
         val http = mockHttp()