Passing custom proto message using WithDetails() from gRPC status package

Question

I have been recently experimenting with gRPC error handling and wanted to pass in my own proto message to the client (defining my own error details and internal error codes). After searching around, found out couple of examples that uses WithDetails() in gRPC status package to attach custom metadata. I started implementing the same as follows

gRPC proto message

message ErrorInfo {
    int64 error_code = 1;
    string error_message = 2;
    string resource_name = 3;
}

Server-side implementation

// Frame the error message
        st := status.New(codes.NotFound, "object not found")
        errInfo := &api.ErrorInfo {
            ErrorCode: 100,
            ErrorMessage: "Fetching credential failed",
            ResourceName: req.GetBackupLocation().GetCloudCredential(),
        }
        var err error
        st, err = st.WithDetails(errInfo)
        if err != nil {
            // If this errored, it will always error
            // here, so better panic so we can figure
            // out why than have this silently passing.
            panic(fmt.Sprintf("Unexpected error attaching metadata: %v", err))
        }

        return  st.Err()

Client-side implementation

fmt.Printf("line 76 err :%v", err)
                st := status.Convert(err)
                for _, detail := range st.Details() {
                    switch t := detail.(type) {
                    case *api.ErrorInfo:
                        fmt.Printf("error code: %v", t.GetErrorCode())
                        fmt.Printf("error msg: %v", t.GetErrorMessage())
                        fmt.Printf("resource name: %v", t.GetResourceName())
                    }
                }

When i run the code, it hit the Panic() added in the server code which means WithDetails() errored out.

For proceeding further, removed panic on server side, with this client throws the following error

:any: message type "" isn't linked inerror

Questions:

• Does WithDetails() only work for googleapis/rpc/errdetails standard gRPC proto definition and not with custom proto?

• Looking at the proto files and code implementation, I don't see anything specific to gRPC errdetails package.

• When I tried with the proto message from this package, it's working fine.

[ Note: i am using gogo protobuf]

Can any one please let know what is that i am missing here?

Answer 1

I was facing a similar error (any: message type "" isn't linked in *errors.errorString). In my case it was due to grpc.Status API.

If you're using gogo proto you need to import/use

"github.com/gogo/status"

Instead of

"google.golang.org/grpc/status"

Answer 2

From my point of view, mixing business logic errors with transport errors should not be considered as a good practice, even if GRPC API allows it. Adding special Result or Error structure to every response (with your own set of fields and codes) is much more clean and flexible way to report about request handling state.