WIP allow disk to continue after fetcher ends

This prototypes a change where if Fetcher is a Flow and never emits, we can fallback to SoT. This change does break another test we have (StoreTest#testFreshUsesOnlyNetwork) which ensures that we don't use disk for fresh requests. These two use cases seems at odds as I can also anticipate some users expecting to see disk resutls if network returns an error. Issue: #185
MobileNativeFoundation · Jul 2, 2020 · cc4dea7 · cc4dea7
1 parent 61762f2
commit cc4dea7
Show file tree

Hide file tree

Showing 3 changed files with 32 additions and 2 deletions.
diff --git a/buildsystem/dependencies.gradle b/buildsystem/dependencies.gradle
@@ -8,7 +8,6 @@ ext.versions = [
 
         // Plugins
         androidGradlePlugin         : '4.0.0',
-        androidGradlePlugin         : '4.0.0-beta05',
         dokkaGradlePlugin           : '0.10.0',
         ktlintGradle                : '9.1.1',
         spotlessGradlePlugin        : '3.26.1',

diff --git a/store/src/main/java/com/dropbox/android/external/store4/impl/RealStore.kt b/store/src/main/java/com/dropbox/android/external/store4/impl/RealStore.kt
@@ -34,6 +34,7 @@ import kotlinx.coroutines.FlowPreview
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.emitAll
 import kotlinx.coroutines.flow.flow
+import kotlinx.coroutines.flow.onCompletion
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.flow.onStart
 import kotlinx.coroutines.flow.transform
@@ -161,7 +162,10 @@ internal class RealStore<Key : Any, Input : Any, Output : Any>(
     ): Flow<StoreResponse<Output>> {
         val diskLock = CompletableDeferred<Unit>()
         val networkLock = CompletableDeferred<Unit>()
-        val networkFlow = createNetworkFlow(request, networkLock)
+        val networkFlow = createNetworkFlow(request, networkLock).onCompletion {
+            // if network finishes, always unlock the disk to let the rest of the machinery continue
+            diskLock.complete(Unit)
+        }
         if (!request.shouldSkipCache(CacheType.DISK)) {
             diskLock.complete(Unit)
         }

diff --git a/store/src/test/java/com/dropbox/android/external/store4/impl/FlowStoreTest.kt b/store/src/test/java/com/dropbox/android/external/store4/impl/FlowStoreTest.kt
@@ -40,6 +40,7 @@ import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.filter
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.flow
+import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.test.TestCoroutineScope
 import kotlinx.coroutines.test.runBlockingTest
@@ -628,6 +629,32 @@ class FlowStoreTest {
             fetcher1Job.cancelAndJoin()
         }
 
+    @Test
+    fun `GIVEN Flow Fetcher WHEN it completes with 0 emissions THEN SourceOfTruth should load`() {
+        // see https://github.com/dropbox/Store/issues/185
+        testScope.runBlockingTest {
+            val persister = InMemoryPersister<Int, String>()
+            persister.write(3, "local")
+            val pipeline = StoreBuilder.from(
+                    fetcher = Fetcher.ofFlow {
+                        flowOf<String>()
+                    },
+                    sourceOfTruth = persister.asSourceOfTruth()
+            ).build()
+            assertThat(pipeline.stream(
+                    StoreRequest.fresh(3)
+            )).emitsExactly(
+                    StoreResponse.Loading(
+                            origin = ResponseOrigin.Fetcher
+                    ),
+                    StoreResponse.Data(
+                            origin = ResponseOrigin.SourceOfTruth,
+                            value = "local"
+                    )
+            )
+        }
+    }
+
     suspend fun Store<Int, String>.get(request: StoreRequest<Int>) =
         this.stream(request).filter { it.dataOrNull() != null }.first()