Stop hiding read failures on web

packages/file_picker_web/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Fixed picking files on Safari (macOS and iOS) never returning the selection. [#2222](https://github.com/vicajilau/flutter_file_picker/issues/2222)
 - Fixed a selection being reported as cancelled when the window regained focus before the `change` event.
+- Fixed `readAsBytes()` and `readAsByteStream()` hiding read failures. A failed stream now emits an error instead of ending early with a truncated file. [#2229](https://github.com/vicajilau/flutter_file_picker/issues/2229)
 
 ## 4.0.0
 

packages/file_picker_web/lib/src/platform_file_web_fetch.dart

@@ -26,38 +26,40 @@ extension type _ReadResult(JSObject _) implements JSObject {
   external JSUint8Array? get value;
 }
 
-/// Attempts to fetch bytes from a web-only path (`blob:` or `data:` URL).
+/// Fetches the bytes of a web-only path (`blob:` or `data:` URL).
 ///
 /// Returns the full file bytes (`Uint8List`) using `fetch(...).arrayBuffer()`
-/// for `blob:` URLs, or parses `data:` URIs. Returns `null` if fetching fails
-/// or if [path] is empty or not a valid web URL.
-Future<Uint8List?> fetchBytesFromWebPath(String? path) async {
-  if (path == null || path.isEmpty) return null;
-
-  try {
-    if (path.startsWith('data:')) {
-      return Uri.parse(path).data?.contentAsBytes();
-    }
+/// for `blob:` URLs, or parses `data:` URIs. Returns `null` if [path] is not a
+/// web URL, so the caller can fall back to another source. Throws if the
+/// content of a web URL cannot be read.
+Future<Uint8List?> fetchBytesFromWebPath(String path) async {
+  if (!_isWebPath(path)) return null;
+
+  if (path.startsWith('data:')) {
+    final uriData = Uri.parse(path).data;
 
-    if (path.startsWith('blob:')) {
-      final response = _Response(await _fetchJs(path.toJS).toDart);
-      final buffer = await response.arrayBuffer().toDart;
-      return buffer.toDart.asUint8List();
+    if (uriData == null) {
+      return null;
     }
-  } catch (_) {
-    return null;
+
+    return uriData.contentAsBytes();
   }
 
-  return null;
+  final response = _Response(await _fetchJs(path.toJS).toDart);
+  final buffer = await response.arrayBuffer().toDart;
+  return buffer.toDart.asUint8List();
 }
 
+bool _isWebPath(String path) =>
+    path.startsWith('blob:') || path.startsWith('data:');
+
 /// Attempts to create a streaming `Stream<Uint8List>` from a web-only path
 /// (`blob:` or `data:` URL).
 ///
-/// Returns `null` when streaming isn't possible and the caller should
-/// fall back to [fetchBytesFromWebPath].
-Stream<Uint8List>? fetchStreamFromWebPath(String? path) {
-  if (path == null || path.isEmpty) return null;
+/// Returns `null` if [path] is not a web URL, so the caller can fall back to
+/// another source. Read failures are emitted as errors on the stream.
+Stream<Uint8List>? fetchStreamFromWebPath(String path) {
+  if (!_isWebPath(path)) return null;
 
   return _streamFromWebPath(path);
 }
@@ -67,43 +69,37 @@ Stream<Uint8List>? fetchStreamFromWebPath(String? path) {
 /// Uses `Response.body` (`ReadableStream`) when available; otherwise falls
 /// back to a single in-memory `arrayBuffer()` chunk.
 Stream<Uint8List> _streamFromWebPath(String path) async* {
-  try {
-    if (path.startsWith('data:')) {
-      final bytes = Uri.parse(path).data?.contentAsBytes();
-      if (bytes != null) {
-        yield bytes;
-      }
-      return;
+  if (path.startsWith('data:')) {
+    final uriData = Uri.parse(path).data;
+
+    if (uriData == null) {
+      throw FormatException('Invalid data: URL', path);
     }
 
-    if (path.startsWith('blob:')) {
-      final jsResponse = await _fetchJs(path.toJS).toDart;
+    yield uriData.contentAsBytes();
+    return;
+  }
 
-      final response = _Response(jsResponse);
-      final body = response.body;
+  final response = _Response(await _fetchJs(path.toJS).toDart);
+  final body = response.body;
 
-      // If there's no streaming body, fallback to arrayBuffer()
-      if (body == null) {
-        final buffer = await response.arrayBuffer().toDart;
-        yield buffer.toDart.asUint8List();
-        return;
-      }
+  // If there's no streaming body, fallback to arrayBuffer()
+  if (body == null) {
+    final buffer = await response.arrayBuffer().toDart;
+    yield buffer.toDart.asUint8List();
+    return;
+  }
 
-      final readable = _ReadableStream(body);
-      final reader = _Reader(readable.getReader());
+  final readable = _ReadableStream(body);
+  final reader = _Reader(readable.getReader());
 
-      while (true) {
-        final jsResultObj = await reader.read().toDart;
-        final result = _ReadResult(jsResultObj);
-        if (result.done) break;
+  while (true) {
+    final result = _ReadResult(await reader.read().toDart);
+    if (result.done) break;
 
-        final arr = result.value;
-        if (arr == null) break;
+    final arr = result.value;
+    if (arr == null) break;
 
-        yield arr.toDart;
-      }
-    }
-  } catch (_) {
-    return;
+    yield arr.toDart;
   }
 }

packages/file_picker_web/test/web_platform_file_read_test.dart

@@ -0,0 +1,62 @@
+@TestOn('browser')
+library;
+
+import 'dart:convert';
+import 'dart:js_interop';
+import 'dart:typed_data';
+
+import 'package:file_picker_web/file_picker_web.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:web/web.dart';
+
+void main() {
+  final content = Uint8List.fromList(utf8.encode('hello file_picker'));
+
+  String createBlobUrl() => URL.createObjectURL(Blob([content.toJS].toJS));
+
+  WebPlatformFile fileAt(String url) =>
+      WebPlatformFile(name: 'a.txt', uri: Uri.parse(url));
+
+  test('readAsBytes() reads a blob URL', () async {
+    final url = createBlobUrl();
+    addTearDown(() => URL.revokeObjectURL(url));
+
+    expect(await fileAt(url).readAsBytes(), content);
+  });
+
+  test('readAsBytes() throws when the blob URL cannot be read', () async {
+    final url = createBlobUrl();
+    URL.revokeObjectURL(url);
+
+    await expectLater(fileAt(url).readAsBytes(), throwsA(anything));
+  });
+
+  test('readAsByteStream() reads a blob URL', () async {
+    final url = createBlobUrl();
+    addTearDown(() => URL.revokeObjectURL(url));
+
+    final chunks = await fileAt(url).readAsByteStream().toList();
+    expect(chunks.expand((chunk) => chunk).toList(), content);
+  });
+
+  test(
+    'readAsByteStream() emits an error when the blob URL cannot be read',
+    () async {
+      final url = createBlobUrl();
+      URL.revokeObjectURL(url);
+
+      await expectLater(
+        fileAt(url).readAsByteStream().toList(),
+        throwsA(anything),
+      );
+    },
+  );
+
+  test('readAsBytes() and readAsByteStream() read a data URL', () async {
+    final url = Uri.dataFromBytes(content).toString();
+
+    expect(await fileAt(url).readAsBytes(), content);
+    final chunks = await fileAt(url).readAsByteStream().toList();
+    expect(chunks.expand((chunk) => chunk).toList(), content);
+  });
+}