Update PerfSession and SessionManager to identify Legacy sessions.

firebase-perf/firebase-perf.gradle

@@ -70,13 +70,15 @@ android {
         buildConfigField("String", "TRANSPORT_LOG_SRC", "String.valueOf(\"FIREPERF\")")
         buildConfigField("Boolean", "ENFORCE_DEFAULT_LOG_SRC", "Boolean.valueOf(false)")
         buildConfigField("String", "FIREPERF_VERSION_NAME", "String.valueOf(\"" + property("version") + "\")")
+        buildConfigField("Boolean", "ENFORCE_LEGACY_SESSIONS", "Boolean.valueOf(false)")
 
         if (project.hasProperty("fireperfBuildForAutopush")) {
             // This allows the SDK to be built for "Autopush" env when the mentioned flag
             // (-PfireperfBuildForAutopush) is passed in the gradle build command (of either the
             // SDK or the Test App).
             buildConfigField("String", "TRANSPORT_LOG_SRC", "String.valueOf(\"FIREPERF_AUTOPUSH\")")
             buildConfigField("Boolean", "ENFORCE_DEFAULT_LOG_SRC", "Boolean.valueOf(true)")
+            buildConfigField("Boolean", "ENFORCE_LEGACY_SESSIONS", "Boolean.valueOf(true)")
         }
 
         minSdkVersion project.minSdkVersion

firebase-perf/src/main/java/com/google/firebase/perf/FirebasePerformance.java

@@ -34,7 +34,7 @@
 import com.google.firebase.perf.config.RemoteConfigManager;
 import com.google.firebase.perf.logging.AndroidLogger;
 import com.google.firebase.perf.logging.ConsoleUrlGenerator;
-import com.google.firebase.perf.logging.DebugEnforcementCheck;
+import com.google.firebase.perf.logging.FirebaseSessionsEnforcementCheck;
 import com.google.firebase.perf.metrics.HttpMetric;
 import com.google.firebase.perf.metrics.Trace;
 import com.google.firebase.perf.session.FirebasePerformanceSessionSubscriber;
@@ -44,8 +44,8 @@
 import com.google.firebase.perf.util.ImmutableBundle;
 import com.google.firebase.perf.util.Timer;
 import com.google.firebase.remoteconfig.RemoteConfigComponent;
-import com.google.firebase.sessions.BuildConfig;
 import com.google.firebase.sessions.api.FirebaseSessionsDependencies;
+import com.google.firebase.sessions.api.SessionSubscriber;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.net.URL;
@@ -96,6 +96,8 @@ public class FirebasePerformance implements FirebasePerformanceAttributable {
   // once during initialization and cache it.
   private final ImmutableBundle mMetadataBundle;
 
+  private final SessionSubscriber sessionSubscriber;
+
   /** Valid HttpMethods for manual network APIs */
   @StringDef({
     HttpMethod.GET,
@@ -169,9 +171,10 @@ public static FirebasePerformance getInstance() {
       this.mPerformanceCollectionForceEnabledState = false;
       this.configResolver = configResolver;
       this.mMetadataBundle = new ImmutableBundle(new Bundle());
+      this.sessionSubscriber = new FirebasePerformanceSessionSubscriber(false);
       return;
     }
-    DebugEnforcementCheck.setEnforcement(BuildConfig.DEBUG);
+    FirebaseSessionsEnforcementCheck.setEnforcement(BuildConfig.ENFORCE_LEGACY_SESSIONS);
 
     TransportManager.getInstance()
         .initialize(firebaseApp, firebaseInstallationsApi, transportFactoryProvider);
@@ -186,8 +189,8 @@ public static FirebasePerformance getInstance() {
     sessionManager.setApplicationContext(appContext);
 
     mPerformanceCollectionForceEnabledState = configResolver.getIsPerformanceCollectionEnabled();
-    FirebaseSessionsDependencies.register(
-        new FirebasePerformanceSessionSubscriber(isPerformanceCollectionEnabled()));
+    sessionSubscriber = new FirebasePerformanceSessionSubscriber(isPerformanceCollectionEnabled());
+    FirebaseSessionsDependencies.register(sessionSubscriber);
 
     if (logger.isLogcatEnabled() && isPerformanceCollectionEnabled()) {
       logger.info(
@@ -463,4 +466,9 @@ private static ImmutableBundle extractMetadata(Context appContext) {
   Boolean getPerformanceCollectionForceEnabledState() {
     return mPerformanceCollectionForceEnabledState;
   }
+
+  @VisibleForTesting
+  SessionSubscriber getSessionSubscriber() {
+    return sessionSubscriber;
+  }
 }

firebase-perf/src/main/java/com/google/firebase/perf/logging/DebugEnforcementCheck.kt → firebase-perf/src/main/java/com/google/firebase/perf/logging/FirebaseSessionsEnforcementCheck.kt

@@ -16,15 +16,19 @@
 
 package com.google.firebase.perf.logging
 
-class DebugEnforcementCheck {
+import com.google.firebase.perf.session.PerfSession
+import com.google.firebase.perf.session.isLegacy
+
+class FirebaseSessionsEnforcementCheck {
   companion object {
     /** When enabled, failed preconditions will cause assertion errors for debugging. */
     @JvmStatic var enforcement: Boolean = false
     private var logger: AndroidLogger = AndroidLogger.getInstance()
 
-    public fun checkSession(isAqsAvailable: Boolean, failureMessage: String) {
-      if (!isAqsAvailable) {
-        Companion.logger.debug(failureMessage)
+    @JvmStatic
+    fun checkSession(session: PerfSession, failureMessage: String) {
+      if (session.isLegacy()) {
+        logger.debug("legacy session ${session.sessionId()}: $failureMessage")
         assert(!enforcement) { failureMessage }
       }
     }

firebase-perf/src/main/java/com/google/firebase/perf/session/FirebasePerformanceSessionSubscriber.kt

@@ -16,10 +16,10 @@
 
 package com.google.firebase.perf.session
 
+import com.google.firebase.perf.logging.FirebaseSessionsEnforcementCheck
 import com.google.firebase.perf.session.gauges.GaugeManager
 import com.google.firebase.perf.v1.ApplicationProcessState
 import com.google.firebase.sessions.api.SessionSubscriber
-import java.util.UUID
 
 class FirebasePerformanceSessionSubscriber(override val isDataCollectionEnabled: Boolean) :
   SessionSubscriber {
@@ -28,15 +28,10 @@ class FirebasePerformanceSessionSubscriber(override val isDataCollectionEnabled:
 
   override fun onSessionChanged(sessionDetails: SessionSubscriber.SessionDetails) {
     val currentPerfSession = SessionManager.getInstance().perfSession()
+    // TODO(b/394127311): Add logic to deal with app start gauges.
+    FirebaseSessionsEnforcementCheck.checkSession(currentPerfSession, "onSessionChanged")
 
-    // A [PerfSession] was created before a session was started.
-    if (!currentPerfSession.isAqsReady) {
-      GaugeManager.getInstance()
-        .logGaugeMetadata(currentPerfSession.sessionId(), ApplicationProcessState.FOREGROUND)
-      return
-    }
-
-    val updatedSession = PerfSession.createWithId(UUID.randomUUID().toString())
+    val updatedSession = PerfSession.createWithId(sessionDetails.sessionId)
     SessionManager.getInstance().updatePerfSession(updatedSession)
     GaugeManager.getInstance()
       .logGaugeMetadata(updatedSession.sessionId(), ApplicationProcessState.FOREGROUND)

firebase-perf/src/main/java/com/google/firebase/perf/session/FirebaseSessionsHelper.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.perf.session
+
+import com.google.firebase.perf.util.Constants
+import java.util.UUID
+
+/** Identifies whether the [PerfSession] is legacy or not. */
+fun PerfSession.isLegacy(): Boolean {
+  return this.sessionId().isLegacy()
+}
+
+/** Identifies whether the string is from a legacy [PerfSession]. */
+fun String.isLegacy(): Boolean {
+  return this.startsWith(Constants.UNDEFINED_AQS_ID_PREFIX)
+}
+
+/** Creates a valid session ID for [PerfSession] that can be predictably identified as legacy. */
+fun createLegacySessionId(): String {
+  val uuid = UUID.randomUUID().toString().replace("-", "")
+  return uuid.replaceRange(
+    0,
+    Constants.UNDEFINED_AQS_ID_PREFIX.length,
+    Constants.UNDEFINED_AQS_ID_PREFIX
+  )
+}

firebase-perf/src/main/java/com/google/firebase/perf/session/PerfSession.java

@@ -24,51 +24,43 @@
 import com.google.firebase.perf.util.Timer;
 import com.google.firebase.perf.v1.SessionVerbosity;
 import java.util.List;
-import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 
 /** Details of a session including a unique Id and related information. */
 public class PerfSession implements Parcelable {
   private final Timer creationTime;
   private final String sessionId;
   private boolean isGaugeAndEventCollectionEnabled = false;
-  public final boolean isAqsReady;
 
   /*
    * Creates a PerfSession object and decides what metrics to collect.
    */
   public static PerfSession createWithId(@Nullable String aqsSessionId) {
-    String sessionId;
-    Boolean isAqsReady;
-    if (aqsSessionId != null) {
-      sessionId = aqsSessionId;
-      isAqsReady = true;
-    } else {
-      sessionId = UUID.randomUUID().toString().replace("-", "");
-      isAqsReady = false;
+    String sessionId = aqsSessionId;
+    if (sessionId == null) {
+      sessionId = FirebaseSessionsHelperKt.createLegacySessionId();
     }
-    PerfSession session = new PerfSession(sessionId, new Clock(), isAqsReady);
-    session.setGaugeAndEventCollectionEnabled(shouldCollectGaugesAndEvents(sessionId));
+    PerfSession session = new PerfSession(sessionId, new Clock());
+    session.setGaugeAndEventCollectionEnabled(session.shouldCollectGaugesAndEvents());
     return session;
   }
 
   /** Creates a PerfSession with the provided {@code sessionId} and {@code clock}. */
   @VisibleForTesting(otherwise = VisibleForTesting.PACKAGE_PRIVATE)
-  public PerfSession(String sessionId, Clock clock, boolean isAqsReady) {
+  public PerfSession(String sessionId, Clock clock) {
     this.sessionId = sessionId;
-    this.isAqsReady = isAqsReady;
     creationTime = clock.getTime();
   }
 
   private PerfSession(@NonNull Parcel in) {
     super();
     sessionId = in.readString();
     isGaugeAndEventCollectionEnabled = in.readByte() != 0;
-    isAqsReady = in.readByte() != 0;
     creationTime = in.readParcelable(Timer.class.getClassLoader());
   }
 
   /** Returns the sessionId for the given session. */
+  @NonNull
   public String sessionId() {
     return sessionId;
   }
@@ -160,10 +152,11 @@ public static com.google.firebase.perf.v1.PerfSession[] buildAndSort(
   }
 
   /** If true, Session Gauge collection is enabled. */
-  public static boolean shouldCollectGaugesAndEvents(String sessionId) {
+  public boolean shouldCollectGaugesAndEvents() {
     ConfigResolver configResolver = ConfigResolver.getInstance();
     return configResolver.isPerformanceMonitoringEnabled()
-        && (Math.abs(sessionId.hashCode() % 100) < configResolver.getSessionsSamplingRate() * 100);
+        && (Math.abs(this.sessionId.hashCode() % 100)
+            < configResolver.getSessionsSamplingRate() * 100);
   }
 
   /**
@@ -187,7 +180,6 @@ public int describeContents() {
   public void writeToParcel(@NonNull Parcel out, int flags) {
     out.writeString(sessionId);
     out.writeByte((byte) (isGaugeAndEventCollectionEnabled ? 1 : 0));
-    out.writeByte((byte) (isAqsReady ? 1 : 0));
     out.writeParcelable(creationTime, 0);
   }
 

firebase-perf/src/main/java/com/google/firebase/perf/session/SessionManager.java

@@ -19,7 +19,7 @@
 import androidx.annotation.Keep;
 import androidx.annotation.VisibleForTesting;
 import com.google.firebase.perf.application.AppStateMonitor;
-import com.google.firebase.perf.logging.DebugEnforcementCheck;
+import com.google.firebase.perf.logging.FirebaseSessionsEnforcementCheck;
 import com.google.firebase.perf.session.gauges.GaugeManager;
 import com.google.firebase.perf.v1.ApplicationProcessState;
 import com.google.firebase.perf.v1.GaugeMetadata;
@@ -49,8 +49,8 @@ public static SessionManager getInstance() {
 
   /** Returns the currently active PerfSession. */
   public final PerfSession perfSession() {
-    DebugEnforcementCheck.Companion.checkSession(
-        perfSession.isAqsReady, "Access perf session from manger without aqs ready");
+    FirebaseSessionsEnforcementCheck.checkSession(
+        perfSession, "Access perf session from manger without aqs ready");
 
     return perfSession;
   }
@@ -82,8 +82,8 @@ public void setApplicationContext(final Context appContext) {
    * @see PerfSession#isSessionRunningTooLong()
    */
   public void stopGaugeCollectionIfSessionRunningTooLong() {
-    DebugEnforcementCheck.Companion.checkSession(
-        perfSession.isAqsReady,
+    FirebaseSessionsEnforcementCheck.checkSession(
+        perfSession,
         "Session is not ready while trying to stopGaugeCollectionIfSessionRunningTooLong");
 
     if (perfSession.isSessionRunningTooLong()) {
@@ -107,6 +107,8 @@ public void updatePerfSession(PerfSession perfSession) {
 
     this.perfSession = perfSession;
 
+    // TODO(b/394127311): Update/verify behavior for Firebase Sessions.
+
     synchronized (clients) {
       for (Iterator<WeakReference<SessionAwareObject>> i = clients.iterator(); i.hasNext(); ) {
         SessionAwareObject callback = i.next().get();
@@ -159,8 +161,8 @@ public void unregisterForSessionUpdates(WeakReference<SessionAwareObject> client
   }
 
   private void startOrStopCollectingGauges(ApplicationProcessState appState) {
-    DebugEnforcementCheck.Companion.checkSession(
-        perfSession.isAqsReady, "Session is not ready while trying to startOrStopCollectingGauges");
+    FirebaseSessionsEnforcementCheck.checkSession(
+        perfSession, "Session is not ready while trying to startOrStopCollectingGauges");
 
     if (perfSession.isGaugeAndEventCollectionEnabled()) {
       gaugeManager.startCollectingGauges(perfSession, appState);

firebase-perf/src/main/java/com/google/firebase/perf/util/Constants.java

@@ -22,6 +22,10 @@ public class Constants {
   public static final String PREFS_NAME = "FirebasePerfSharedPrefs";
   public static final String ENABLE_DISABLE = "isEnabled";
 
+  // A non-hex character guarantees it isn't an AQS generated UUID.
+  // https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.uuid/-uuid/
+  public static final String UNDEFINED_AQS_ID_PREFIX = "z";
+
   public static final double MIN_SAMPLING_RATE = 0.0;
   public static final double MAX_SAMPLING_RATE = 1.0;
 

firebase-perf/src/test/java/com/google/firebase/perf/session/FirebaseSessionsTestHelper.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.perf.session
+
+import com.google.firebase.perf.util.Clock
+
+fun createTestSession(suffix: Int): PerfSession {
+  // TODO(b/394127311): Add a method to verify legacy behavior.
+  // only hex characters and so it's AQS.
+  return PerfSession(testSessionId(suffix), Clock())
+}
+
+fun testSessionId(suffix: Int): String = "abc$suffix"