Method getClientHeader

src/Server/GRPCServer.cpp:409–416

        }

        std::optional<String> getClientHeader(const String & key) const
        {
            const auto & client_metadata = grpc_context.client_metadata();
            auto it = client_metadata.find(key);
            if (it != client_metadata.end())
                return String{it->second.data(), it->second.size()};
            return std::nullopt;
        }

        void setTransportCompression(const TransportCompression & transport_compression)
        {