Use manual foreground detection to trigger network reconnect

firebase-firestore/CHANGELOG.md

@@ -1,4 +1,8 @@
 # Unreleased
+- [changed] Increases the aggressiveness of network retires when an app's
+  foreground status changes.
+
+# 23.0.1
 - [changed] The SDK now tries to immediately establish a connection to the
   backend when the app enters the foreground.
 

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/remote/RemoteStoreTest.java

@@ -81,16 +81,16 @@ public ImmutableSortedSet<DocumentKey> getRemoteKeysForTarget(int targetId) {
     RemoteStore remoteStore =
         new RemoteStore(callback, localStore, datastore, testQueue, connectivityMonitor);
 
-    waitFor(testQueue.enqueue(() -> remoteStore.forceEnableNetwork()));
+    waitFor(testQueue.enqueue(remoteStore::forceEnableNetwork));
     drain(testQueue);
     networkChangeSemaphore.drainPermits();
 
     connectivityMonitor.goOffline();
     waitFor(networkChangeSemaphore);
     drain(testQueue);
-
-    waitFor(testQueue.enqueue(() -> remoteStore.forceEnableNetwork()));
     networkChangeSemaphore.drainPermits();
+
+    waitFor(testQueue.enqueue(remoteStore::forceEnableNetwork));
     connectivityMonitor.goOnline();
     waitFor(networkChangeSemaphore);
   }

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/AndroidConnectivityMonitor.java

@@ -17,27 +17,35 @@
 import static com.google.firebase.firestore.util.Assert.hardAssert;
 
 import android.annotation.TargetApi;
+import android.app.Activity;
+import android.app.Application;
 import android.content.BroadcastReceiver;
+import android.content.ComponentCallbacks2;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
+import android.content.res.Configuration;
 import android.net.ConnectivityManager;
 import android.net.Network;
 import android.os.Build;
+import android.os.Bundle;
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
-import com.google.android.gms.common.api.internal.BackgroundDetector;
 import com.google.firebase.firestore.util.Consumer;
+import com.google.firebase.firestore.util.Logger;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * Android implementation of ConnectivityMonitor. Parallel implementations exist for N+ and pre-N.
  *
  * <p>Implementation note: Most of the code here was shamelessly stolen from
  * https://github.com/grpc/grpc-java/blob/master/android/src/main/java/io/grpc/android/AndroidChannelBuilder.java
  */
-public final class AndroidConnectivityMonitor
-    implements ConnectivityMonitor, BackgroundDetector.BackgroundStateChangeListener {
+public final class AndroidConnectivityMonitor implements ConnectivityMonitor {
+
+  private static final String LOG_TAG = "AndroidConnectivityMonitor";
 
   private final Context context;
   @Nullable private final ConnectivityManager connectivityManager;
@@ -78,34 +86,72 @@ private void configureNetworkMonitoring() {
       final DefaultNetworkCallback defaultNetworkCallback = new DefaultNetworkCallback();
       connectivityManager.registerDefaultNetworkCallback(defaultNetworkCallback);
       unregisterRunnable =
-          new Runnable() {
-            @Override
-            public void run() {
-              connectivityManager.unregisterNetworkCallback(defaultNetworkCallback);
-            }
-          };
+          () -> connectivityManager.unregisterNetworkCallback(defaultNetworkCallback);
     } else {
       NetworkReceiver networkReceiver = new NetworkReceiver();
       @SuppressWarnings("deprecation")
       IntentFilter networkIntentFilter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
       context.registerReceiver(networkReceiver, networkIntentFilter);
-      unregisterRunnable =
-          new Runnable() {
-            @Override
-            public void run() {
-              context.unregisterReceiver(networkReceiver);
-            }
-          };
+      unregisterRunnable = () -> context.unregisterReceiver(networkReceiver);
     }
   }
 
   private void configureBackgroundStateListener() {
-    BackgroundDetector.getInstance().addListener(this);
+    Application applicationContext = (Application) context.getApplicationContext();
+    final AtomicBoolean inBackground = new AtomicBoolean();
+
+    // Manually register an ActivityLifecycleCallback. Android's BackgroundDetector only notifies
+    // when it is certain that the app transitioned from background to foreground. Instead, we
+    // want to be notified whenever there is a slight chance that this transition happened.
+    applicationContext.registerActivityLifecycleCallbacks(
+        new Application.ActivityLifecycleCallbacks() {
+          @Override
+          public void onActivityCreated(@NonNull Activity activity, Bundle savedInstanceState) {}
+
+          @Override
+          public void onActivityStarted(@NonNull Activity activity) {}
+
+          @Override
+          public void onActivityResumed(@NonNull Activity activity) {
+            if (inBackground.compareAndSet(true, false)) {
+              raiseForegroundNotification();
+            }
+          }
+
+          @Override
+          public void onActivityPaused(@NonNull Activity activity) {}
+
+          @Override
+          public void onActivityStopped(@NonNull Activity activity) {}
+
+          @Override
+          public void onActivitySaveInstanceState(
+              @NonNull Activity activity, @NonNull Bundle outState) {}
+
+          @Override
+          public void onActivityDestroyed(@NonNull Activity activity) {}
+        });
+
+    applicationContext.registerComponentCallbacks(
+        new ComponentCallbacks2() {
+          @Override
+          public void onTrimMemory(int level) {
+            if (level == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {
+              inBackground.set(true);
+            }
+          }
+
+          @Override
+          public void onConfigurationChanged(@NonNull Configuration newConfig) {}
+
+          @Override
+          public void onLowMemory() {}
+        });
   }
 
-  @Override
-  public void onBackgroundStateChanged(boolean background) {
-    if (!background && isConnected()) {
+  public void raiseForegroundNotification() {
+    Logger.debug(LOG_TAG, "App has entered the foreground.");
+    if (isConnected()) {
       raiseCallbacks(/* connected= */ true);
     }
   }

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/OnlineStateTracker.java

@@ -88,6 +88,11 @@ interface OnlineStateCallback {
     shouldWarnClientIsOffline = true;
   }
 
+  /** Returns the current online state. */
+  OnlineState getState() {
+    return state;
+  }
+
   /**
    * Called by RemoteStore when a watch stream is started (including on each backoff attempt).
    *

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/RemoteStore.java

@@ -214,14 +214,29 @@ public void onClose(Status status) {
                 // Porting Note: Unlike iOS, `restartNetwork()` is called even when the network
                 // becomes unreachable as we don't have any other way to tear down our streams.
 
+                // We only invoke restartNetwork() when the network status differs from our online
+                // state. This prevents frequent reconnects as the callback is invoked whenever
+                // the app reaches the foreground.
+                if (networkStatus.equals(NetworkStatus.REACHABLE)
+                    && onlineStateTracker.getState().equals(OnlineState.ONLINE)) {
+                  return;
+                }
+
+                if (networkStatus.equals(NetworkStatus.UNREACHABLE)
+                    && onlineStateTracker.getState().equals(OnlineState.OFFLINE)) {
+                  return;
+                }
+
                 // If the network has been explicitly disabled, make sure we don't accidentally
                 // re-enable it.
-                if (canUseNetwork()) {
-                  // Tear down and re-create our network streams. This will ensure the backoffs are
-                  // reset.
-                  Logger.debug(LOG_TAG, "Restarting streams for network reachability change.");
-                  restartNetwork();
+                if (!canUseNetwork()) {
+                  return;
                 }
+
+                // Tear down and re-create our network streams. This will ensure the backoffs are
+                // reset.
+                Logger.debug(LOG_TAG, "Restarting streams for network reachability change.");
+                restartNetwork();
               });
         });
   }