Invalidate async cache on exception (#132)

himamis · web-flow · commit 6d2de25f208b · 2020-10-22T16:51:57.000+02:00
* Invalidate async cache on exception

When the callback throws an exception, the startStaleTime was not called, so the cache was not refreshed. Because of this, future calls to this cache returned with the exception.
diff --git a/lib/src/async_cache.dart b/lib/src/async_cache.dart
@@ -60,12 +60,12 @@ class AsyncCache<T> {
     if (_cachedStreamSplitter != null) {
       throw StateError('Previously used to cache via `fetchStream`');
     }
-    if (_cachedValueFuture == null) {
-      _cachedValueFuture = callback();
-      await _cachedValueFuture;
+    final result = _cachedValueFuture ??= callback();
+    try {
+      return await result;
+    } finally {
       _startStaleTimer();
     }
-    return _cachedValueFuture!;
   }
 
   /// Returns a cached stream from a previous call to [fetchStream], or runs
diff --git a/test/async_cache_test.dart b/test/async_cache_test.dart
@@ -158,4 +158,16 @@ void main() {
     }));
     expect(cache.fetchStream(call).toList(), completion(['1', '2', '3']));
   });
+
+  test('should invalidate even if the future throws an exception', () async {
+    cache = AsyncCache.ephemeral();
+
+    Future<String> throwingCall() async => throw Exception();
+    await expectLater(cache.fetch(throwingCall), throwsA(isException));
+    // To let the timer invalidate the cache
+    await Future.delayed(Duration(milliseconds: 5));
+
+    Future<String> call() async => 'Completed';
+    expect(await cache.fetch(call), 'Completed', reason: 'Cache invalidates');
+  });
 }

Original file line number	Diff line number	Diff line change
`@@ -60,12 +60,12 @@ class AsyncCache<T> {`
`60`	`60`	`if (_cachedStreamSplitter != null) {`
`61`	`61`	throw StateError('Previously used to cache via `fetchStream`');
`62`	`62`	`}`
`63`		`- if (_cachedValueFuture == null) {`
`64`		`- _cachedValueFuture = callback();`
`65`		`- await _cachedValueFuture;`
	`63`	`+ final result = _cachedValueFuture ??= callback();`
	`64`	`+ try {`
	`65`	`+ return await result;`
	`66`	`+ } finally {`
`66`	`67`	`_startStaleTimer();`
`67`	`68`	`}`
`68`		`- return _cachedValueFuture!;`
`69`	`69`	`}`
`70`	`70`
`71`	`71`	`/// Returns a cached stream from a previous call to [fetchStream], or runs`