code: func UnaryServerInterceptor(opts ...Option) grpc.UnaryServerInterceptor {
  	o := evaluateOptions(opts)
  	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
  		newCtx := newTagsForCtx(ctx)
  		if o.requestFieldsFunc != nil {
  			setRequestFieldTags(newCtx, o.requestFieldsFunc, info.FullMethod, req)
  		}
  		return handler(newCtx, req)
  	}
  }
docs: // UnaryServerInterceptor returns a new unary server interceptors that sets the values for request tags.