Refactor session manager (#717)

* factor out interface

* move session api to its own top module. make implementations internal.

* spotless

* use impl, fix compile

core/build.gradle.kts

@@ -63,8 +63,9 @@ android {
 
 dependencies {
     implementation(project(":instrumentation:android-instrumentation"))
-    implementation(project(":services"))
     implementation(project(":common"))
+    implementation(project(":services"))
+    implementation(project(":session"))
 
     implementation(libs.androidx.core)
 

core/src/main/java/io/opentelemetry/android/OpenTelemetryRumBuilder.java

@@ -33,6 +33,8 @@
 import io.opentelemetry.android.internal.services.ServiceManager;
 import io.opentelemetry.android.internal.services.ServiceManagerImpl;
 import io.opentelemetry.android.internal.services.periodicwork.PeriodicWorkService;
+import io.opentelemetry.android.internal.session.SessionIdTimeoutHandler;
+import io.opentelemetry.android.internal.session.SessionManagerImpl;
 import io.opentelemetry.android.session.SessionManager;
 import io.opentelemetry.android.session.SessionProvider;
 import io.opentelemetry.api.baggage.propagation.W3CBaggagePropagator;
@@ -302,7 +304,7 @@ public OpenTelemetryRum build() {
                 new BufferDelegatingSpanExporter();
 
         SessionManager sessionManager =
-                SessionManager.create(timeoutHandler, config.getSessionTimeout().toNanos());
+                SessionManagerImpl.create(timeoutHandler, config.getSessionTimeout().toNanos());
 
         OpenTelemetrySdk sdk =
                 OpenTelemetrySdk.builder()
@@ -373,6 +375,8 @@ private void initializeExporters(
         }
         initializationEvents.spanExporterInitialized(spanExporter);
 
+        SessionManager sessionManager =
+                SessionManagerImpl.create(timeoutHandler, config.getSessionTimeout().toNanos());
         bufferedDelegatingLogExporter.setDelegate(logsExporter);
 
         bufferDelegatingSpanExporter.setDelegate(spanExporter);

core/src/main/java/io/opentelemetry/android/SdkPreconfiguredRumBuilder.kt

@@ -10,6 +10,8 @@ import io.opentelemetry.android.instrumentation.AndroidInstrumentation
 import io.opentelemetry.android.instrumentation.AndroidInstrumentationLoader
 import io.opentelemetry.android.instrumentation.InstallationContext
 import io.opentelemetry.android.internal.services.ServiceManager
+import io.opentelemetry.android.internal.session.SessionIdTimeoutHandler
+import io.opentelemetry.android.internal.session.SessionManagerImpl
 import io.opentelemetry.android.session.SessionManager
 import io.opentelemetry.sdk.OpenTelemetrySdk
 
@@ -19,7 +21,7 @@ class SdkPreconfiguredRumBuilder
         private val application: Application,
         private val sdk: OpenTelemetrySdk,
         private val timeoutHandler: SessionIdTimeoutHandler = SessionIdTimeoutHandler(),
-        private val sessionManager: SessionManager = SessionManager(timeoutHandler = timeoutHandler),
+        private val sessionManager: SessionManager = SessionManagerImpl(timeoutHandler = timeoutHandler),
         private val discoverInstrumentations: Boolean,
         private val serviceManager: ServiceManager,
     ) {

core/src/main/java/io/opentelemetry/android/internal/session/SessionIdTimeoutHandler.kt

@@ -0,0 +1,81 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.android.internal.session
+
+import io.opentelemetry.android.internal.services.applifecycle.ApplicationStateListener
+import io.opentelemetry.sdk.common.Clock
+import java.time.Duration
+
+/**
+ * This class encapsulates the following criteria about the sessionId timeout:
+ *
+ *
+ *  * If the app is in the foreground sessionId should never time out.
+ *  * If the app is in the background and no activity (spans) happens for >15 minutes, sessionId
+ * should time out.
+ *  * If the app is in the background and some activity (spans) happens in <15 minute intervals,
+ * sessionId should not time out.
+ *
+ *
+ * Consequently, when the app spent >15 minutes without any activity (spans) in the background,
+ * after moving to the foreground the first span should trigger the sessionId timeout.
+ */
+internal class SessionIdTimeoutHandler(
+    private val clock: Clock,
+    private val sessionTimeout: Duration,
+) : ApplicationStateListener {
+    @Volatile
+    private var timeoutStartNanos: Long = 0
+
+    @Volatile
+    private var state = State.FOREGROUND
+
+    // for testing
+    @JvmOverloads
+    internal constructor(sessionTimeout: Duration = DEFAULT_SESSION_TIMEOUT) : this(
+        Clock.getDefault(),
+        sessionTimeout,
+    )
+
+    override fun onApplicationForegrounded() {
+        state = State.TRANSITIONING_TO_FOREGROUND
+    }
+
+    override fun onApplicationBackgrounded() {
+        state = State.BACKGROUND
+    }
+
+    fun hasTimedOut(): Boolean {
+        // don't apply sessionId timeout to apps in the foreground
+        if (state == State.FOREGROUND) {
+            return false
+        }
+        val elapsedTime = clock.nanoTime() - timeoutStartNanos
+        return elapsedTime >= sessionTimeout.toNanos()
+    }
+
+    fun bump() {
+        timeoutStartNanos = clock.nanoTime()
+
+        // move from the temporary transition state to foreground after the first span
+        if (state == State.TRANSITIONING_TO_FOREGROUND) {
+            state = State.FOREGROUND
+        }
+    }
+
+    private enum class State {
+        FOREGROUND,
+        BACKGROUND,
+
+        /** A temporary state representing the first event after the app has been brought back.  */
+        TRANSITIONING_TO_FOREGROUND,
+    }
+
+    companion object {
+        @JvmField
+        val DEFAULT_SESSION_TIMEOUT: Duration = Duration.ofMinutes(15)
+    }
+}

core/src/main/java/io/opentelemetry/android/session/SessionManager.kt → core/src/main/java/io/opentelemetry/android/internal/session/SessionManagerImpl.kt

@@ -3,21 +3,24 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-package io.opentelemetry.android.session
+package io.opentelemetry.android.internal.session
 
-import io.opentelemetry.android.SessionIdTimeoutHandler
+import io.opentelemetry.android.session.Session
+import io.opentelemetry.android.session.SessionIdGenerator
+import io.opentelemetry.android.session.SessionManager
+import io.opentelemetry.android.session.SessionObserver
+import io.opentelemetry.android.session.SessionStorage
 import io.opentelemetry.sdk.common.Clock
 import java.util.Collections.synchronizedList
 import java.util.concurrent.TimeUnit
 
-internal class SessionManager(
+internal class SessionManagerImpl(
     private val clock: Clock = Clock.getDefault(),
     private val sessionStorage: SessionStorage = SessionStorage.InMemory(),
     private val timeoutHandler: SessionIdTimeoutHandler,
     private val idGenerator: SessionIdGenerator = SessionIdGenerator.DEFAULT,
     private val sessionLifetimeNanos: Long = TimeUnit.HOURS.toNanos(4),
-) : SessionProvider,
-    SessionPublisher {
+) : SessionManager {
     // TODO: Make thread safe / wrap with AtomicReference?
     private var session: Session = Session.NONE
     private val observers = synchronizedList(ArrayList<SessionObserver>())
@@ -70,8 +73,8 @@ internal class SessionManager(
         fun create(
             timeoutHandler: SessionIdTimeoutHandler,
             sessionLifetimeNanos: Long,
-        ): SessionManager =
-            SessionManager(
+        ): SessionManagerImpl =
+            SessionManagerImpl(
                 timeoutHandler = timeoutHandler,
                 sessionLifetimeNanos = sessionLifetimeNanos,
             )

core/src/test/java/io/opentelemetry/android/OpenTelemetryRumBuilderTest.java

@@ -42,6 +42,7 @@
 import io.opentelemetry.android.internal.services.applifecycle.AppLifecycleService;
 import io.opentelemetry.android.internal.services.applifecycle.ApplicationStateListener;
 import io.opentelemetry.android.internal.services.visiblescreen.VisibleScreenService;
+import io.opentelemetry.android.internal.session.SessionIdTimeoutHandler;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.common.KeyValue;
 import io.opentelemetry.api.common.Value;