4

We want to return one object/struct with one property as empty list/array/slice in golang to client(browser). from the go code we are returning empty slice of len=0 and capacity=0, but through protobuf this key is getting deleted or set as a nil and removed.

protobuf code

syntax = "proto3";
package version1;
message ToDo {
     int64 id = 1 ;
     string title = 2;
}
message ReadAllResponse{
     repeated   ToDo  toDos = 1 ;
}

golang code:

list := make([]*version1.ToDo, 0) //[]*version1.ToDo{}
output:= version1.ReadAllResponse{
        ToDos: list,
        Api:   "v1",
    }

I am getting actual output as {api: "v1"} but expected should come as {api: "v1",todos:[]}

Please help/suggest us in fixing the protobuf or golang syntax.

dev2
  • 117
  • 2
  • 10
  • Are you calling your grpc service directly from the browser (with grpc-web or something), or are you calling grpc-gateway (https://github.com/grpc-ecosystem/grpc-gateway) ? – erikbozic Sep 13 '19 at 21:28
  • I am calling the service as http end point from browser and backend proxy this request through grpc-gateway . – dev2 Sep 13 '19 at 21:31

1 Answers1

6

Your array field gets lost when grpc-gateway serializes the proto struct to json with jsonpb serializer.

Fortunately the gateway exposes a way to configure the jsonpb serializer when setting up the gateway:

mux := runtime.NewServeMux(runtime.WithMarshalerOption(runtime.MIMEWildcard, &runtime.JSONPb{ EmitDefaults:true}))

The &runtime.JSONPb{ EmitDefaults:true} option should do what you want.

erikbozic
  • 1,605
  • 1
  • 16
  • 21
  • Thanks a lot, It was big help. – dev2 Sep 13 '19 at 21:42
  • for the future Reference of issue.. https://github.com/grpc-ecosystem/grpc-gateway/issues/233 . https://jbrandhorst.com/post/gopherjs-client-grpc-server-4/ – dev2 Sep 13 '19 at 21:53