Uploading with FormData throws a TypeError: type 'List<int>' is not a subtype of type 'Uint8List' of 'value' about dio

[fromlabs]

Yes I've already tried your solution and it works.

Meanwhile I found a workaround on my code:

dio.MultipartFile.fromBytes(
  Uint8List.fromList(fileData),
  filename: fileName,
  contentType: contentType,
),

Thanks @AlexV525!

[AlexV525]

Huge thanks for your inputs!

[fromlabs]

I think is related to:

• #2184
• #2186

I suppose the problem is in form_data.dart:

final controller = StreamController<Uint8List>(sync: false);

...

Future<void>(() async {
  for (final file in files) {
    writeUtf8('--$boundary$_rn');
    writeUtf8(_headerForFile(file));
    await writeStreamToSink(file.value.finalize(), controller);
    writeLine();
  }
}).then((_) {
  writeUtf8('--$boundary--$_rn');
}).whenComplete(() {
  controller.close();
});

multipart_file.dart
Stream<List<int>> finalize();

Calling writeStreamToSink(Stream<List<int>>, StreamController<Uint8List>) throws a TypeError because is trying to add List<int> to a Uint8List sink.

[AlexV525]

@fromlabs Could you try updating the implementation to below solve the problem?

Future<void>(() async {
  for (final file in files) {
    writeUtf8('--$boundary$_rn');
    writeUtf8(_headerForFile(file));
    await writeStreamToSink<Uint8List>(
      file.value
          .finalize()
          .map((e) => e is Uint8List ? e : Uint8List.fromList(e)),
      controller,
    );
    writeLine();
  }
}).then((_) {
  writeUtf8('--$boundary--$_rn');
}).whenComplete(() {
  controller.close();
});

[AlexV525]

@fromlabs Are you able to extract a minimal reproducible example? I'm wondering why the issue (if it exists) escapes from our tests.

[fromlabs]

I think because formdata_test.dart doesn't test directly MultipartFile.fromBytes with real List<int>, but tests just MultipartFile.fromString, MultipartFile.fromFile and MultipartFile.fromFileSync which work under the hood with Uint8List.