Handling Errors and Status Codes

st, ok := status.FromError(err)
if ok {
    fmt.Println(st.Code(), st.Message())
    for _, d := range st.Details() {
        switch info := d.(type) {
        case *errdetails.BadRequest:
            // handle field violations
        case *errdetails.RetryInfo:
            time.Sleep(info.RetryDelay.AsDuration())
        }
    }
}

// in proto:
message AppError {
  string code = 1;
  string trace_id = 2;
}

st, _ := status.New(codes.Internal, "db down").
    WithDetails(&AppError{Code: "DB_001", TraceId: traceID})
return st.Err()

switch status.Code(err) {
case codes.NotFound:
    return defaultUser(), nil
case codes.Unavailable, codes.DeadlineExceeded:
    return retry()
default:
    return nil, err
}

func toStatus(err error) error {
    switch {
    case errors.Is(err, repo.ErrNotFound):
        return status.Error(codes.NotFound, "not found")
    case errors.Is(err, repo.ErrConflict):
        return status.Error(codes.AlreadyExists, "exists")
    case errors.Is(err, context.DeadlineExceeded):
        return status.Error(codes.DeadlineExceeded, "deadline")
    default:
        return status.Error(codes.Internal, "internal")
    }
}