Unknown gRPC error with no error message - gRPC-web and goproxy

Question

I'm trying to build a web application with the following stack:

• Flutter/Dart
• Go/goproxy
• gRPC
• MongoDB

I was able to successfully define and compile a protobuf into Dart and Go, however now that I'm trying to integrate the UI with the backend, I am running into the following issue:

Error: gRPC Error (code: 2, codeName: UNKNOWN, message:
null, details: [], rawResponse: null, trailers: {})

Here is my client code:

import 'package:grpc/grpc_web.dart';

import 'package:proj/protos/cards.pb.dart';
import 'package:proj/protos/cards.pbgrpc.dart';

class FiltersService {
  static ResponseFuture<Filters> getFilters() {
    GrpcWebClientChannel channel =
        GrpcWebClientChannel.xhr(Uri.parse('http://localhost:9000'));

    FiltersServiceClient clientStub = FiltersServiceClient(
      channel,
    );

    return clientStub.getFilters(Void());
  }
}

The server controller code:

const (
    port = 9000
)

var (
    grpcServer *grpc.Server
)


func StartServer() {
    log.Println("Starting server")
    listener, err := net.Listen("tcp", fmt.Sprintf(":%v", port))
    if err != nil {
        log.Fatalf("Unable to listen to port %v\n%v\n", port, err)
    }

    repositories.ConnectToMongoDB()

    grpcServer = grpc.NewServer()
    registerServices()
    grpcWebServer := grpcweb.WrapServer(grpcServer)

    httpServer := &http.Server{
        Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
            if r.ProtoMajor == 2 {
                grpcWebServer.ServeHTTP(w, r)
            } else {
                w.Header().Set("Access-Control-Allow-Origin", "*")
                w.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
                w.Header().Set("Access-Control-Allow-Headers", "Accept, Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization, X-User-Agent, X-Grpc-Web")
                w.Header().Set("grpc-status", "")
                w.Header().Set("grpc-message", "")
                if grpcWebServer.IsGrpcWebRequest(r) {
                    grpcWebServer.ServeHTTP(w, r)
                }
            }
        }),
    }

    httpServer.Serve(listener)

}

// Register services defined in protobufs to call from UI
func registerServices() {
    cardsService := &services.CardsService{}
    protos.RegisterCardsServiceServer(grpcServer, cardsService)

    filtersService := &services.FiltersService{}
    protos.RegisterFiltersServiceServer(grpcServer, filtersService)
}

I can tell that the server is receiving the request properly, and when I output the response of the service, I am getting the expected response.

Here is the service I am calling:

func (service *FiltersService) GetFilters(ctx context.Context, void *protos.Void) (*protos.Filters, error) {
    filters := repositories.GetFilters()
    return converters.FiltersStructToFiltersProtoConverter(filters), nil
}

When I output the response of converters.FiltersStructToFiltersProtoConverter(filters), I get the correct output, so it looks like there's still an issue with the way my server is set up.

I know this isn't a lot of info to go on, however I'm not sure what other information you may need, but can add as needed.