Reset the cache when the partial file is deleted mid-download

CHANGELOG.md

@@ -1,3 +1,9 @@
+## Unreleased
+
+### Fixes
+
+* Fixed a partial cache file deleted mid-download (by the device's cache management, say) failing every request for what it held until the download ended: the download wrote on into the deleted file. A request now resets the cache, and waits for its range to download again.
+
 ## 0.3.1
 
 ### Fixes

lib/src/cache_stream/http_cache_stream.dart

@@ -118,6 +118,20 @@ class HttpCacheStream {
       }
     }
 
+    //Deleted while it downloads (by the device's cache management, say), the
+    //partial cache file takes the download's writes into a file no response can
+    //open, until the download ends. Reset, the download starts again, and the
+    //request waits for its range.
+    final activeDownloader = _cacheDownloader;
+    final cacheDeleted = activeDownloader != null &&
+        !activeDownloader.isClosed &&
+        activeDownloader.filePosition > 0 &&
+        !await files.activeCacheFile().exists();
+    if (cacheDeleted) {
+      await _resetCache(InvalidCacheSizeException(
+          sourceUrl, -1, responseHeaders?.sourceLength ?? 0));
+    }
+
     final rangeThreshold = config.rangeRequestSplitThreshold;
     if (rangeThreshold != null &&
         range.start >= rangeThreshold &&
@@ -132,7 +146,9 @@ class HttpCacheStream {
     final streamRequest = StreamRequest.construct(range);
     final downloader = _cacheDownloader;
 
-    if (downloader != null && downloader.processRequest(streamRequest)) {
+    if (!cacheDeleted &&
+        downloader != null &&
+        downloader.processRequest(streamRequest)) {
       return streamRequest.response; //Request was processed immediately
     } else {
       _queuedRequests

test/e2e/partial_deleted_test.dart

@@ -0,0 +1,70 @@
+import 'dart:async';
+import 'dart:typed_data';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:http_cache_stream/http_cache_stream.dart';
+import 'package:http_cache_stream/src/etc/extensions/file_extensions.dart';
+
+import '../support/harness.dart';
+import '../support/payload.dart';
+
+/// The partial cache file deleted while it downloads (by the device's cache
+/// management, say): the download writes on into the deleted file, where no
+/// response can open what it holds. A request resets the cache, and its range
+/// downloads again.
+void main() {
+  late CacheTestHarness h;
+
+  setUp(() async {
+    h = CacheTestHarness();
+    await h.setUp();
+  });
+
+  tearDown(() => h.tearDown());
+
+  Future<Uint8List> read(HttpCacheStream stream, int start, int end) async {
+    final response = await stream.request(start: start, end: end);
+    final builder = BytesBuilder(copy: false);
+    await for (final chunk in response.stream) {
+      builder.add(chunk);
+    }
+    return builder.takeBytes();
+  }
+
+  test('a range it had downloaded is read again after the file was deleted',
+      () async {
+    final half = h.origin.payload.length ~/ 2;
+    final bodyGate = Completer<void>();
+    h.origin
+      ..responseBodyGate = bodyGate
+      ..responseBodyGateAfterBytes = half;
+    final stream = h.manager.createStream(h.origin.url('/deleted.mp3'));
+    final reachedHalf = Completer<void>();
+    final errors = <Object>[];
+    final subscription = stream.cacheStateStream.listen((state) {
+      if (state.position >= half && !reachedHalf.isCompleted) {
+        reachedHalf.complete();
+      }
+    }, onError: errors.add);
+    final download = stream.download();
+    await reachedHalf.future.timeout(const Duration(seconds: 5));
+    final partial = stream.files.partial;
+    for (var i = 0; i < 100 && (partial.lengthSyncOrNull() ?? 0) < half; i++) {
+      await Future<void>.delayed(const Duration(milliseconds: 10));
+    }
+    await partial.delete();
+
+    final bytes =
+        await read(stream, 1000, 9000).timeout(const Duration(seconds: 10));
+    expect(bytes, Uint8List.sublistView(h.origin.payload, 1000, 9000));
+    expect(errors.whereType<InvalidCacheSizeException>().map((e) => e.size),
+        contains(-1),
+        reason: 'the deletion is reported');
+
+    bodyGate.complete();
+    final file = await download.timeout(const Duration(seconds: 15));
+    expect(Payload.hash(await file.readAsBytes()), h.payloadHash);
+    await subscription.cancel();
+    await stream.dispose(force: true);
+  });
+}