    static ChunkSpec invalidPayload(uint8_t flags, bool valid_message) {
      ChunkSpec spec;
      spec.valid = true;
      spec.data = serializeResponse(grpc::health::v1::HealthCheckResponse::SERVING);
      spec.data[0] = flags;
      if (!valid_message) {
        const size_t kGrpcHeaderSize = 5;
        for (size_t i = kGrpcHeaderSize; i < spec.data.size(); i++) {
          // Fill payload with some random data.
          spec.data[i] = i % 256;
        }
      }
      return spec;
    }
    static ChunkSpec invalidPayload(uint8_t flags, bool valid_message) {
      ChunkSpec spec;
      spec.valid = true;
      spec.data = serializeResponse(grpc::health::v1::HealthCheckResponse::SERVING);
      spec.data[0] = flags;
      if (!valid_message) {
        const size_t kGrpcHeaderSize = 5;
        for (size_t i = kGrpcHeaderSize; i < spec.data.size(); i++) {
           
          spec.data[i] = i % 256;
        }
      }
      return spec;
    }