How to receive a multipart file send from flutter in .net c# api

[sumchans]

Hello all,

I am stuck on this error for a few days now.

What I am trying to do send in a list of user selected files as bytes from a flutter application to a .net graphql api using the hotchocolate package.

This is my flutter code where I prepare the files to be sent. Just posting a bit of it -

        for (var image in images) {
          var byteData = File(image.path).readAsBytesSync();
          widget.user.files.add(MultipartFile.fromBytes(
            'photo',
            byteData,
            filename: '${DateTime.now().toUtc()}-${image.name}',
            contentType: MediaType("image", "jpg"),
          ));
        }

After adding the files to the list I call the below button press event to send the files which calls the mutation method

onPressed: () async {
                    final result =
                        await GraphQLInstance().fileUploadMutation(widget.user);
                    }

final _fileUploadMutation = """
    mutation(\$containerName: String, \$files: [Upload]) {
      uploadFiles(containerName: \$containerName, files: \$files) {
        status
      }
    }
    """;
  Future<bool> fileUploadMutation(User user) async {
    user.id = '+141600000';
    String containerName = user.id.substring(
        1); // removing the '+' sign at the beginning of the phone number
    QueryResult result = await _client().mutate(
      MutationOptions(document: gql(_fileUploadMutation), variables: {
        "containerName": containerName,
        "files": user.files
      } 
          ),
    );
    print(result);
    if (result.hasException) {
      print(result.exception?.graphqlErrors[0].message);
    } else if (result.data != null) {
      user.avatarUrl = result.data!['UploadFiles'][0];
      return true;
    }
    return false;
  }

And finally here the api method that gets called. The api call works as I tested that other ways.

public async Task<String> UploadFiles(string containerName, List<IFile> files)
{
     Console.WriteLine(containerName);
     return "Success";
}

This is what I noticed after the api call -

• If I send the files argument to the api from the client the api runs without errors, but I dont see the console.writeline statement printed out and also I get the below exception on the client as well.
• If I don't send the files argument to the api from the client the api runs without errors, then I see the console.writeline statement printed out.

After the call to the api this is exception I see on the client -