I get gRPC Invalid UTF-8 when I make a request to gRPC endpoint from Flutter app

Issue

I am trying to connect a Flutter app to gRPC server.
It used to work fine in my older laptop, but now I always get this error when I try to make a request to an endpoint:

gRPC Error (code: 13, codeName: INTERNAL, message: grpc: error unmarshalling request: string field contains invalid UTF-8, details: [], rawResponse: null)

when I use another gRPC client, such as bloomRPC, the call is successful and I get the correct data.
The Flutter app call does not even reach the endpoint service (I put a println there to test it, and it does not print anything when I make a call from the Flutter app, but it does print it when using bloomRPC).

This is my client connection code:

class GrpcClient {
  late ClientChannel client;
  static final GrpcClient _connection = GrpcClient._connect();

  factory GrpcClient() => _connection;
  
  GrpcClient._connect(){
    client = ClientChannel(
     "10.0.2.2",
      port: 8080,
      options: ChannelOptions(credentials: ChannelCredentials.insecure(), connectionTimeout:Duration(seconds: 10))
    );

  }
}

I run the server with GODEBUG=http2debug=2 go run .. I got this output when I made the call from Bloom:

2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote SETTINGS len=6, settings: MAX_FRAME_SIZE=16384
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read SETTINGS len=36, settings: ENABLE_PUSH=0, MAX_CONCURRENT_STREAMS=0, INITIAL_WINDOW_SIZE=4194304, MAX_FRAME_SIZE=4194304, MAX_HEADER_LIST_SIZE=8192, UNKNOWN_SETTING_65027=1
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read WINDOW_UPDATE len=4 (conn) incr=4128769
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read PING len=8 ping="\x00\x00\x00\x00\x00\x00\x00\x00"
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote SETTINGS flags=ACK len=0
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read HEADERS flags=END_HEADERS stream=1 len=259
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote PING flags=ACK len=8 ping="\x00\x00\x00\x00\x00\x00\x00\x00"
2021/12/27 22:23:52 http2: decoded hpack field header field ":scheme" = "http"
2021/12/27 22:23:52 http2: decoded hpack field header field ":method" = "POST"
2021/12/27 22:23:52 http2: decoded hpack field header field ":authority" = "localhost:8080"
2021/12/27 22:23:52 http2: decoded hpack field header field ":path" = "/protofiles.UserService/GetUserById"
2021/12/27 22:23:52 http2: decoded hpack field header field "te" = "trailers"
2021/12/27 22:23:52 http2: decoded hpack field header field "content-type" = "application/grpc"
2021/12/27 22:23:52 http2: decoded hpack field header field "user-agent" = "grpc-node/1.24.7 grpc-c/8.0.0 (windows; chttp2; ganges)"
2021/12/27 22:23:52 http2: decoded hpack field header field "grpc-accept-encoding" = "identity,deflate,gzip"
2021/12/27 22:23:52 http2: decoded hpack field header field "accept-encoding" = "identity,gzip"
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read WINDOW_UPDATE stream=1 len=4 incr=5
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read DATA flags=END_STREAM stream=1 len=122 data="\x00\x00\x00\x00u\ns\b\x05\x12\x05Hello\x1a$1bcc4186-3a63-4a22-8dac-c144d6d0eb49\"\x05Hello*\x05Hello0\x00:\x04\b\x14\x10\nB\x05HelloJ\x05HelloR\x04\b\x14\x10\nZ\b\b\x14\x10\x01\x18\x01 \x00`\x14h\x14p\x14x\x14\x82\x01\"
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read WINDOW_UPDATE len=4 (conn) incr=5
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote WINDOW_UPDATE len=4 (conn) incr=122
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote PING len=8 ping="\x02\x04\x10\x10\t\x0e\a\a"
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read PING flags=ACK len=8 ping="\x02\x04\x10\x10\t\x0e\a\a"
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: read SETTINGS flags=ACK len=0
Hello
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote HEADERS flags=END_HEADERS stream=1 len=14
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote DATA stream=1 len=192 data="\x00\x00\x00\x00\xbb\n\xb8\x01\b\x05\x12\tHajjivsky
2021/12/27 22:23:52 http2: Framer 0xc0000a6000: wrote HEADERS flags=END_STREAM|END_HEADERS stream=1 len=24

And this output from the Dart application:

2021/12/27 22:25:25 http2: Framer 0xc0002b2000: wrote SETTINGS len=6, settings: MAX_FRAME_SIZE=16384
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: read SETTINGS len=6, settings: ENABLE_PUSH=0
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: wrote SETTINGS flags=ACK len=0
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: read SETTINGS flags=ACK len=0
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: read HEADERS flags=END_HEADERS stream=1 len=169
2021/12/27 22:25:25 http2: decoded hpack field header field ":method" = "POST"
2021/12/27 22:25:25 http2: decoded hpack field header field ":scheme" = "http"
2021/12/27 22:25:25 http2: decoded hpack field header field ":path" = "/protofiles.UserService/GetUserById"
2021/12/27 22:25:25 http2: decoded hpack field header field ":authority" = "10.0.2.2:8080"
2021/12/27 22:25:25 http2: decoded hpack field header field "content-type" = "application/grpc"
2021/12/27 22:25:25 http2: decoded hpack field header field "te" = "trailers"
2021/12/27 22:25:25 http2: decoded hpack field header field "user-agent" = "dart-grpc/2.0.0"
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: read DATA stream=1 len=69 data="\x00\x00\x00\x00@\n>\b\x05\x12\x00\x1a\x00\"\x00(\x002\f\b\xa4\xa6\xa8\x8e\x06\x10\xa0\xb7\x93\xf1\x01:\x00B\x00J\f\b\xa4\xa6\xa8\x8e\x06\x10\xf0ɒ\xf1\x01R\b\b\x00\x10\x00\x18\x00 \x00X\x00`\x00h\x00p\x00z\x00"
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: wrote WINDOW_UPDATE len=4 (conn) incr=69
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: wrote PING len=8 ping="\x02\x04\x10\x10\t\x0e\a\a"
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: read DATA flags=END_STREAM stream=1 len=0 data=""
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: wrote HEADERS flags=END_STREAM|END_HEADERS stream=1 len=90
2021/12/27 22:25:25 http2: Framer 0xc0002b2000: read PING flags=ACK len=8 ping="\x02\x04\x10\x10\t\x0e\a\a"

This is the proto message & endpoint:

message User{
    int64 id = 1;
    string username = 2;
    string auth_user_id = 3;
    string email = 4;
    string display_name = 5;
    Gender gender = 6;
}
func (u *UserService) GetUserById(ctx context.Context, in *protofiles.GetUserRequest) (*protofiles.GetUserResponse, error) {
    user, err := u.store.GetByID(in.User.Id)
    if err != nil {
        return &protofiles.GetUserResponse{}, err
    }
    return &protofiles.GetUserResponse{User: models.UserHelper.ToProto(user)}, nil
}

Solution

After several hours of trial and error, I finally figured out what the problem was, it like many other bugs it turned out to be a stupid one.
The order of the tags in the proto file’s message has been changed (a new field was added at the top and all of the other fields were pushed downward). The server was using the new definition, while the client was using the old one. When the client tried to call an endpoint, the tags did not match.

All I had to do is re-generate the files for the client stub.

Answered By – Ali Alhajji

Answer Checked By – Robin (FlutterFixes Admin)

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