fix: Don't do network calls when apps are in background (#730)

Addresses #724

The other task needed to close this ticket is to have endpoint apps bind and unbind from the Gateway when they are in the foreground/background.

app/src/androidTest/java/tech/relaycorp/gateway/background/endpoint/EndpointPreRegistrationServiceTest.kt

@@ -8,7 +8,6 @@ import android.os.Message
 import android.os.Messenger
 import androidx.test.core.app.ApplicationProvider.getApplicationContext
 import androidx.test.rule.ServiceTestRule
-import kotlinx.coroutines.test.UnconfinedTestDispatcher
 import kotlinx.coroutines.test.runTest
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertNotNull
@@ -45,7 +44,7 @@ class EndpointPreRegistrationServiceTest {
     lateinit var internetGatewayPreferences: InternetGatewayPreferences
 
     private val coroutineContext
-        get() = app.backgroundScope.coroutineContext + UnconfinedTestDispatcher()
+        get() = (getApplicationContext() as App).backgroundContext
 
     @Before
     fun setUp() {
@@ -117,7 +116,7 @@ class EndpointPreRegistrationServiceTest {
         internetGatewayPreferences.setRegistrationState(RegistrationState.ToDo)
 
         val serviceIntent = Intent(
-            getApplicationContext<Context>(),
+            getApplicationContext(),
             EndpointPreRegistrationService::class.java,
         )
         val binder = serviceRule.bindService(serviceIntent)

app/src/androidTest/java/tech/relaycorp/gateway/background/endpoint/GatewaySyncServiceParcelCollectionTest.kt

@@ -6,14 +6,14 @@ import androidx.test.rule.ServiceTestRule
 import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.take
-import kotlinx.coroutines.test.UnconfinedTestDispatcher
 import kotlinx.coroutines.test.runTest
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Rule
 import org.junit.Test
+import tech.relaycorp.gateway.App
 import tech.relaycorp.gateway.data.model.RecipientLocation
 import tech.relaycorp.gateway.domain.StoreParcel
 import tech.relaycorp.gateway.pdc.local.PDCServer
@@ -45,7 +45,7 @@ class GatewaySyncServiceParcelCollectionTest {
     lateinit var storeParcel: StoreParcel
 
     private val coroutineContext
-        get() = UnconfinedTestDispatcher()
+        get() = (getApplicationContext() as App).backgroundContext
 
     @Before
     fun setUp() {
@@ -55,6 +55,7 @@ class GatewaySyncServiceParcelCollectionTest {
 
     @After
     fun tearDown() {
+        serviceRule.unbindService()
         Thread.sleep(3000) // Wait for netty to properly stop, to avoid a RejectedExecutionException
     }
 

app/src/androidTest/java/tech/relaycorp/gateway/background/endpoint/GatewaySyncServiceParcelDeliveryTest.kt

@@ -10,6 +10,7 @@ import org.junit.Assert.assertEquals
 import org.junit.Before
 import org.junit.Rule
 import org.junit.Test
+import tech.relaycorp.gateway.App
 import tech.relaycorp.gateway.data.database.StoredParcelDao
 import tech.relaycorp.gateway.data.disk.FileStore
 import tech.relaycorp.gateway.data.model.MessageAddress
@@ -41,6 +42,9 @@ class GatewaySyncServiceParcelDeliveryTest {
     @Inject
     lateinit var storedParcelDao: StoredParcelDao
 
+    private val coroutineContext
+        get() = (getApplicationContext() as App).backgroundContext
+
     @Before
     fun setUp() {
         AppTestProvider.component.inject(this)
@@ -49,11 +53,12 @@ class GatewaySyncServiceParcelDeliveryTest {
 
     @After
     fun tearDown() {
+        serviceRule.unbindService()
         Thread.sleep(3000) // Wait for netty to properly stop, to avoid a RejectedExecutionException
     }
 
     @Test
-    fun parcelDelivery_validParcel() = runTest {
+    fun parcelDelivery_validParcel() = runTest(coroutineContext) {
         setGatewayCertificate(PDACertPath.PRIVATE_GW)
         val recipientId = "0deadbeef"
         val recipientInternetAddress = "example.org"
@@ -76,7 +81,7 @@ class GatewaySyncServiceParcelDeliveryTest {
     }
 
     @Test(expected = RejectedParcelException::class)
-    fun parcelDelivery_invalidParcel() = runTest {
+    fun parcelDelivery_invalidParcel() = runTest(coroutineContext) {
         val fiveMinutesAgo = ZonedDateTime.now().minusMinutes(5)
         val recipientId = "0deadbeef"
         val recipientInternetAddress = "example.org"

app/src/androidTest/java/tech/relaycorp/gateway/test/TestApp.kt

@@ -1,5 +1,6 @@
 package tech.relaycorp.gateway.test
 
+import kotlinx.coroutines.test.UnconfinedTestDispatcher
 import tech.relaycorp.gateway.App
 import tech.relaycorp.gateway.TestAppModule
 
@@ -8,6 +9,8 @@ open class TestApp : App() {
         .testAppModule(TestAppModule(this))
         .build() as AppTestComponent
 
+    override val backgroundContext = UnconfinedTestDispatcher()
+
     override fun onCreate() {
         super.onCreate()
         component.inject(this)

app/src/main/java/tech/relaycorp/gateway/App.kt

@@ -44,8 +44,10 @@ open class App : Application() {
         }
     }
 
+    open val backgroundContext = Dispatchers.IO
+
     @VisibleForTesting
-    val backgroundScope = CoroutineScope(Dispatchers.IO)
+    val backgroundScope get() = CoroutineScope(backgroundContext)
 
     @Inject
     lateinit var foregroundAppMonitor: ForegroundAppMonitor

app/src/main/java/tech/relaycorp/gateway/AppModule.kt

@@ -7,6 +7,7 @@ import android.net.ConnectivityManager
 import android.net.wifi.WifiManager
 import dagger.Module
 import dagger.Provides
+import kotlin.coroutines.CoroutineContext
 
 @Module
 open class AppModule(
@@ -34,4 +35,7 @@ open class AppModule(
 
     @Provides
     fun wifiManager() = app.getSystemService(Context.WIFI_SERVICE) as WifiManager
+
+    @Provides
+    fun backgroundCoroutineContext(): CoroutineContext = app.backgroundContext
 }

app/src/main/java/tech/relaycorp/gateway/domain/publicsync/PublicSync.kt

@@ -5,9 +5,11 @@ import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.delay
-import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.flatMapLatest
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.launch
 import tech.relaycorp.gateway.background.ConnectionState
 import tech.relaycorp.gateway.background.ConnectionStateObserver
@@ -45,22 +47,26 @@ class PublicSync
         combine(
             foregroundAppMonitor.observe(),
             pdcServerStateManager.observe(),
-            connectionStateObserver.observe(),
             // Retry registration and sync every minute in case there's a failure
             interval(1.minutes),
-        ) { foregroundState, pdcState, connectionState, _ ->
-            if (
-                connectionState is ConnectionState.InternetWithGateway && (
+        ) { foregroundState, pdcState, _ -> Pair(foregroundState, pdcState) }
+            .flatMapLatest { (foregroundState, pdcState) ->
+                if (
                     foregroundState == ForegroundAppMonitor.State.Foreground ||
-                        pdcState == PDCServer.State.Started
-                    )
-            ) {
-                startSync()
-            } else {
-                stopSync()
+                    pdcState == PDCServer.State.Started
+                ) {
+                    connectionStateObserver.observe()
+                        .map { it is ConnectionState.InternetWithGateway }
+                } else {
+                    flowOf(false)
+                }
+            }.collect { syncShouldBeRunning ->
+                if (syncShouldBeRunning) {
+                    startSync()
+                } else {
+                    stopSync()
+                }
             }
-        }
-            .collect()
     }
 
     suspend fun syncOneOff() {

app/src/main/java/tech/relaycorp/gateway/pdc/local/PDCServer.kt

@@ -6,21 +6,22 @@ import io.ktor.server.engine.embeddedServer
 import io.ktor.server.netty.Netty
 import io.ktor.server.routing.routing
 import io.ktor.server.websocket.WebSockets
-import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
 import tech.relaycorp.gateway.pdc.local.routes.EndpointRegistrationRoute
 import tech.relaycorp.gateway.pdc.local.routes.PDCServerRoute
 import tech.relaycorp.gateway.pdc.local.routes.ParcelCollectionRoute
 import tech.relaycorp.gateway.pdc.local.routes.ParcelDeliveryRoute
 import javax.inject.Inject
+import kotlin.coroutines.CoroutineContext
 import kotlin.time.Duration.Companion.seconds
 
 class PDCServer
 @Inject constructor(
     private val stateManager: PDCServerStateManager,
     endpointRegistrationRoute: EndpointRegistrationRoute,
-    parcelCollectionRoute: ParcelCollectionRoute,
+    private val parcelCollectionRoute: ParcelCollectionRoute,
     parcelDeliveryRoute: ParcelDeliveryRoute,
+    private val backgroundContext: CoroutineContext,
 ) {
 
     private val server by lazy {
@@ -37,15 +38,16 @@ class PDCServer
     }
 
     suspend fun start() {
-        withContext(Dispatchers.IO) {
+        withContext(backgroundContext) {
             server.start(false)
         }
         stateManager.set(State.Started)
     }
 
     suspend fun stop() {
-        withContext(Dispatchers.IO) {
-            server.stop(0, CALL_DEADLINE.inWholeMilliseconds)
+        withContext(backgroundContext) {
+            parcelCollectionRoute.stop()
+            server.stop(1000, CALL_DEADLINE.inWholeMilliseconds)
         }
         stateManager.set(State.Stopped)
     }

app/src/main/java/tech/relaycorp/gateway/pdc/local/routes/ParcelCollectionRoute.kt

@@ -56,6 +56,10 @@ class ParcelCollectionRoute
         }
     }
 
+    fun stop() {
+        asyncJob.cancel()
+    }
+
     private suspend fun DefaultWebSocketServerSession.handle() {
         if (call.request.header(HEADER_ORIGIN) != null) {
             // The client is most likely a (malicious) web page