grpc/rpcerror/grpc.go
func UnaryServerInterceptor(fn ConvertFunc) grpc.UnaryServerInterceptor {
	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
		resp, err = handler(ctx, req)
		return resp, fn(err)
	}
}
func UnaryServerInterceptor(fn ConvertFunc) grpc.UnaryServerInterceptor {
	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
		resp, err = handler(ctx, req)
		return resp, fn(err)
	}
}
// UnaryServerInterceptor applies fn to errors returned by server.