(feat) Add a network status listener to restart DataStore after the network comes online

aws-datastore/build.gradle

@@ -31,6 +31,7 @@ dependencies {
 
     testImplementation project(path: ':testmodels')
     testImplementation project(path: ':testutils')
+    testImplementation project(path: ':aws-datastore')
     testImplementation dependency.jsonassert
     testImplementation dependency.junit
     testImplementation dependency.mockito

aws-datastore/src/main/AndroidManifest.xml

@@ -15,5 +15,8 @@
 -->
 
 <manifest package="com.amplifyframework.datastore"
-    xmlns:android="http://schemas.android.com/apk/res/android" />
+    xmlns:android="http://schemas.android.com/apk/res/android" >
+
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+</manifest>
 

aws-datastore/src/main/java/com/amplifyframework/datastore/AWSDataStorePlugin.java

@@ -47,6 +47,7 @@
 import com.amplifyframework.datastore.storage.StorageItemChange;
 import com.amplifyframework.datastore.storage.sqlite.SQLiteStorageAdapter;
 import com.amplifyframework.datastore.syncengine.Orchestrator;
+import com.amplifyframework.datastore.syncengine.ReachabilityMonitor;
 import com.amplifyframework.hub.HubChannel;
 import com.amplifyframework.logging.Logger;
 
@@ -90,6 +91,8 @@ public final class AWSDataStorePlugin extends DataStorePlugin<Void> {
 
     private final boolean isSyncRetryEnabled;
 
+    private final ReachabilityMonitor reachabilityMonitor;
+
     private AWSDataStorePlugin(
             @NonNull ModelProvider modelProvider,
             @NonNull SchemaRegistry schemaRegistry,
@@ -100,6 +103,7 @@ private AWSDataStorePlugin(
         this.authModeStrategy = AuthModeStrategyType.DEFAULT;
         this.userProvidedConfiguration = userProvidedConfiguration;
         this.isSyncRetryEnabled = userProvidedConfiguration != null && userProvidedConfiguration.getDoSyncRetry();
+        this.reachabilityMonitor = ReachabilityMonitor.Companion.create();
         // Used to interrogate plugins, to understand if sync should be automatically turned on
         this.orchestrator = new Orchestrator(
             modelProvider,
@@ -130,6 +134,9 @@ private AWSDataStorePlugin(@NonNull Builder builder) throws DataStoreException {
             SQLiteStorageAdapter.forModels(schemaRegistry, modelProvider) :
             builder.storageAdapter;
         this.categoryInitializationsPending = new CountDownLatch(1);
+        this.reachabilityMonitor = builder.reachabilityMonitor == null ?
+            ReachabilityMonitor.Companion.create() :
+            builder.reachabilityMonitor;
 
         // Used to interrogate plugins, to understand if sync should be automatically turned on
         this.orchestrator = new Orchestrator(
@@ -255,6 +262,33 @@ public void configure(
             event -> InitializationStatus.SUCCEEDED.toString().equals(event.getName()),
             event -> categoryInitializationsPending.countDown()
         );
+
+        reachabilityMonitor.configure(context);
+        observeNetworkStatus();
+    }
+
+    /**
+     * Start the datastore when the network is available, and stop the datastore when it is not
+     * available.
+     */
+    private void observeNetworkStatus() {
+        reachabilityMonitor.getObservable()
+            .doOnNext(networkIsAvailable -> {
+                if (networkIsAvailable) {
+                    LOG.info("Network available, start datastore");
+                    start(
+                        (Action) () -> { },
+                        ((e) -> LOG.error("Error starting datastore plugin after network event: " + e))
+                    );
+                } else {
+                    LOG.info("Network lost, stop datastore");
+                    stop(
+                        (Action) () -> { },
+                        ((e) -> LOG.error("Error stopping datastore plugin after network event: " + e))
+                    );
+                }
+            })
+            .subscribe();
     }
 
     @WorkerThread
@@ -657,6 +691,7 @@ public static final class Builder {
         private ApiCategory apiCategory;
         private AuthModeStrategyType authModeStrategy;
         private LocalStorageAdapter storageAdapter;
+        private ReachabilityMonitor reachabilityMonitor;
         private boolean isSyncRetryEnabled;
 
         private Builder() {}
@@ -714,6 +749,17 @@ Builder storageAdapter(LocalStorageAdapter storageAdapter) {
             return this;
         }
 
+        /**
+         * Package-private method to allow for injection of a ReachabilityMonitor for testing purposes.
+         * @param reachabilityMonitor An instance that implements LocalStorageAdapter.
+         * @return Current builder instance, for fluent construction of plugin.
+         */
+        @VisibleForTesting
+        Builder reachabilityMonitor(ReachabilityMonitor reachabilityMonitor) {
+            this.reachabilityMonitor = reachabilityMonitor;
+            return this;
+        }
+
         /**
          * Sets the authorization mode strategy which will be used by DataStore sync engine
          * when interacting with the API plugin.

aws-datastore/src/main/java/com/amplifyframework/datastore/syncengine/ReachabilityMonitor.kt

@@ -0,0 +1,130 @@
+/*
+ * Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file 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.amplifyframework.datastore.syncengine
+
+import android.content.Context
+import android.net.ConnectivityManager
+import android.net.ConnectivityManager.NetworkCallback
+import android.net.Network
+import androidx.annotation.VisibleForTesting
+import com.amplifyframework.datastore.DataStoreException
+import io.reactivex.rxjava3.core.Observable
+import io.reactivex.rxjava3.core.ObservableEmitter
+import io.reactivex.rxjava3.core.ObservableOnSubscribe
+import java.util.concurrent.TimeUnit
+
+/**
+ * The ReachabilityMonitor is responsible for watching the network status as provided by the OS.
+ * It returns an observable that publishes "true" when the network becomes available and "false" when
+ * the network is lost.  It publishes the current status on subscription.
+ *
+ * ReachabilityMonitor does not try to monitor the DataStore websockets or the status of the AppSync service.
+ *
+ * The network changes are debounced with a 250 ms delay to allow some time for one network to connect after another
+ * network has disconnected (for example, wifi is lost, then cellular connects) to reduce thrashing.
+ */
+internal interface ReachabilityMonitor {
+    fun configure(context: Context)
+    @VisibleForTesting
+    fun configure(context: Context, connectivityProvider: ConnectivityProvider)
+
+    companion object {
+        fun create(): ReachabilityMonitor {
+            return ReachabilityMonitorImpl(ProdSchedulerProvider())
+        }
+
+        fun createForTesting(baseSchedulerProvider: SchedulerProvider): ReachabilityMonitor {
+            return ReachabilityMonitorImpl(baseSchedulerProvider)
+        }
+    }
+    fun getObservable(): Observable<Boolean>
+}
+
+private class ReachabilityMonitorImpl constructor(val schedulerProvider: SchedulerProvider) : ReachabilityMonitor {
+    private var emitter: ObservableOnSubscribe<Boolean>? = null
+
+    override fun configure(context: Context) {
+        return configure(context, DefaultConnectivityProvider())
+    }
+
+    override fun configure(context: Context, connectivityProvider: ConnectivityProvider) {
+        emitter = ObservableOnSubscribe { emitter ->
+            val callback = getCallback(emitter)
+            connectivityProvider.registerDefaultNetworkCallback(context, callback)
+            // Provide the current network status upon subscription.
+            emitter.onNext(connectivityProvider.hasActiveNetwork)
+        }
+    }
+
+    override fun getObservable(): Observable<Boolean> {
+        emitter?.let { emitter ->
+            return Observable.create(emitter)
+                .subscribeOn(schedulerProvider.io())
+                .debounce(250, TimeUnit.MILLISECONDS, schedulerProvider.computation())
+        } ?: run {
+            throw DataStoreException(
+                "ReachabilityMonitor has not been configured.",
+                "Call ReachabilityMonitor.configure() before calling ReachabilityMonitor.getObservable()"
+            )
+        }
+    }
+
+    private fun getCallback(emitter: ObservableEmitter<Boolean>): NetworkCallback {
+        return object : NetworkCallback() {
+            override fun onAvailable(network: Network) {
+                emitter.onNext(true)
+            }
+            override fun onLost(network: Network) {
+                emitter.onNext(false)
+            }
+        }
+    }
+}
+
+/**
+ * This interface puts an abstraction layer over ConnectivityManager. Since ConnectivityManager
+ * is a concrete class created within context.getSystemService() it can't be overridden with a test
+ * implementation, so this interface works around that issue.
+ */
+internal interface ConnectivityProvider {
+    val hasActiveNetwork: Boolean
+    fun registerDefaultNetworkCallback(context: Context, callback: NetworkCallback)
+}
+
+private class DefaultConnectivityProvider : ConnectivityProvider {
+
+    private var connectivityManager: ConnectivityManager? = null
+
+    override val hasActiveNetwork: Boolean
+        get() = connectivityManager?.let { it.activeNetwork != null }
+            ?: run {
+                throw DataStoreException(
+                    "ReachabilityMonitor has not been configured.",
+                    "Call ReachabilityMonitor.configure() before calling ReachabilityMonitor.getObservable()"
+                )
+            }
+
+    override fun registerDefaultNetworkCallback(context: Context, callback: NetworkCallback) {
+        connectivityManager = context.getSystemService(ConnectivityManager::class.java)
+        connectivityManager?.let { it.registerDefaultNetworkCallback(callback) }
+            ?: run {
+                throw DataStoreException(
+                    "ConnectivityManager not available",
+                    "No recovery suggestion is available"
+                )
+            }
+    }
+}

aws-datastore/src/main/java/com/amplifyframework/datastore/syncengine/SchedulerProvider.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file 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.amplifyframework.datastore.syncengine
+
+import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers
+import io.reactivex.rxjava3.core.Scheduler
+import io.reactivex.rxjava3.schedulers.Schedulers
+
+/**
+ * This interface provides a way to give custom schedulers to RX observables for testing.
+ */
+interface SchedulerProvider {
+    fun io(): Scheduler
+    fun computation(): Scheduler
+    fun ui(): Scheduler
+}
+
+class ProdSchedulerProvider : SchedulerProvider {
+    override fun computation() = Schedulers.computation()
+    override fun ui() = AndroidSchedulers.mainThread()
+    override fun io() = Schedulers.io()
+}

aws-datastore/src/test/java/com/amplifyframework/datastore/AWSDataStorePluginTest.java

@@ -192,7 +192,6 @@ public void startInApiMode() throws JSONException, AmplifyException {
 
         dataStoreReadyObserver.await();
         subscriptionsEstablishedObserver.await();
-        networkStatusObserver.await();
 
         assertRemoteSubscriptionsStarted();
     }

aws-datastore/src/test/java/com/amplifyframework/datastore/syncengine/ReachabilityMonitorTest.kt

@@ -0,0 +1,72 @@
+package com.amplifyframework.datastore.syncengine
+
+import android.content.Context
+import android.net.ConnectivityManager
+import android.net.Network
+import com.amplifyframework.datastore.DataStoreException
+import io.reactivex.rxjava3.core.BackpressureStrategy
+import io.reactivex.rxjava3.schedulers.TestScheduler
+import io.reactivex.rxjava3.subscribers.TestSubscriber
+import java.util.concurrent.TimeUnit
+import org.junit.Test
+import org.mockito.Mockito.mock
+
+class ReachabilityMonitorTest {
+
+    // Test that calling getObservable() without calling configure() first throws a DataStoreException
+    @Test(expected = DataStoreException::class)
+    fun testReachabilityConfigThrowsException() {
+        ReachabilityMonitor.create().getObservable()
+    }
+
+    // Test that the debounce and the event publishing in ReachabilityMonitor works as expected.
+    // Events that occur within 250 ms of each other should be debounced so that only the last event
+    // of the sequence is published.
+    @Test
+    fun testReachabilityDebounce() {
+        var callback: ConnectivityManager.NetworkCallback? = null
+
+        val connectivityProvider = object : ConnectivityProvider {
+            override val hasActiveNetwork: Boolean
+                get() = run {
+                    return true
+                }
+            override fun registerDefaultNetworkCallback(
+                context: Context,
+                callback2: ConnectivityManager.NetworkCallback
+            ) {
+                callback = callback2
+            }
+        }
+
+        val mockContext = mock(Context::class.java)
+        // TestScheduler allows the virtual time to be advanced by exact amounts, to allow for repeatable tests
+        val testScheduler = TestScheduler()
+        val reachabilityMonitor = ReachabilityMonitor.createForTesting(TestSchedulerProvider(testScheduler))
+        reachabilityMonitor.configure(mockContext, connectivityProvider)
+
+        // TestSubscriber allows for assertions and awaits on the items it observes
+        val testSubscriber = TestSubscriber<Boolean>()
+        reachabilityMonitor.getObservable()
+            // TestSubscriber requires a Flowable
+            .toFlowable(BackpressureStrategy.BUFFER)
+            .subscribe(testSubscriber)
+
+        val network = mock(Network::class.java)
+        // Should provide initial network state (true) upon subscription (after debounce)
+        testScheduler.advanceTimeBy(251, TimeUnit.MILLISECONDS)
+        callback!!.onAvailable(network)
+        callback!!.onAvailable(network)
+        callback!!.onLost(network)
+        // Should provide false after debounce
+        testScheduler.advanceTimeBy(251, TimeUnit.MILLISECONDS)
+        callback!!.onAvailable(network)
+        // Should provide true after debounce
+        testScheduler.advanceTimeBy(251, TimeUnit.MILLISECONDS)
+        callback!!.onAvailable(network)
+        // Should provide true after debounce
+        testScheduler.advanceTimeBy(251, TimeUnit.MILLISECONDS)
+
+        testSubscriber.assertValues(true, false, true, true)
+    }
+}

aws-datastore/src/test/java/com/amplifyframework/datastore/syncengine/TestSchedulerProvider.kt

@@ -0,0 +1,16 @@
+package com.amplifyframework.datastore.syncengine
+
+import io.reactivex.rxjava3.schedulers.Schedulers
+import io.reactivex.rxjava3.schedulers.TestScheduler
+
+class TrampolineSchedulerProvider : SchedulerProvider {
+    override fun computation() = Schedulers.trampoline()
+    override fun ui() = Schedulers.trampoline()
+    override fun io() = Schedulers.trampoline()
+}
+
+class TestSchedulerProvider(private val scheduler: TestScheduler) : SchedulerProvider {
+    override fun computation() = scheduler
+    override fun ui() = scheduler
+    override fun io() = scheduler
+}