写一个使用JSON作为序列化协议的gRPC通信的客户端和服务端

下面是一个使用JSON作为序列化协议的gRPC通信的客户端和服务端的示例，其中定义了一个名为`HelloWorld`的简单服务，客户端发送一个名为`name`的字符串，服务端返回一个包含`Hello, name!`的字符串：

#### 服务端

#include <iostream>
#include <memory>
#include <string>

#include <grpcpp/grpcpp.h>
#include <grpcpp/server.h>
#include <grpcpp/server_builder.h>
#include <grpcpp/server_context.h>

#include "helloworld.grpc.pb.h"

using grpc::Server;
using grpc::ServerBuilder;
using grpc::ServerContext;
using grpc::Status;
using helloworld::HelloRequest;
using helloworld::HelloReply;
using helloworld::Greeter;

class GreeterServiceImpl final : public Greeter::Service {
    Status SayHello(ServerContext* context, const HelloRequest* request,
                    HelloReply* reply) override {
        std::string prefix("Hello, ");
        reply->set_message(prefix + request->name());
        return Status::OK;
    }
};

void RunServer() {
    std::string server_address("0.0.0.0:50051");
    GreeterServiceImpl service;

    grpc::EnableDefaultHealthCheckService(true);
    grpc::reflection::InitProtoReflectionServerBuilderPlugin();
    ServerBuilder builder;
    builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
    builder.RegisterService(&service);
    std::unique_ptr<Server> server(builder.BuildAndStart());
    std::cout << "Server listening on " << server_address << std::endl;
    server->Wait();
}

int main(int argc, char** argv) {
    RunServer();
    return 0;
}

#### 客户端

#include <iostream>
#include <memory>
#include <string>

#include <grpcpp/grpcpp.h>
#include <grpcpp/ext/proto_server_reflection_plugin.h>
#include <grpcpp/health_check_service_interface.h>

#include "helloworld.grpc.pb.h"

using grpc::Channel;
using grpc::ClientContext;
using grpc::Status;
using helloworld::HelloRequest;
using helloworld::HelloReply;
using helloworld::Greeter;

class GreeterClient {
public:
    GreeterClient(std::shared_ptr<Channel> channel)
        : stub_(Greeter::NewStub(channel)) {}

    std::string SayHello(const std::string& name) {
        HelloRequest request;
        request.set_name(name);

        HelloReply reply;
        ClientContext context;

        std::string serializedRequest, serializedReply;
        grpc::SerializationTraits<HelloRequest>::serialize(request, &serializedRequest);
        Status status = stub_->CallRPC("SayHello", serializedRequest, &serializedReply);

        if (status.ok()) {
            grpc::SerializationTraits<HelloReply>::deserialize(serializedReply, &reply);
            return reply.message();
        } else {
            std::cout << "RPC failed: " << status.error_message() << std::endl;
            return "";
        }
    }

private:
    std::unique_ptr<Greeter::Stub> stub_;
};

int main(int argc, char** argv) {
    std::string name("World");

    GreeterClient greeter(grpc::CreateChannel("localhost:50051", grpc::InsecureChannelCredentials()));
    std::string reply = greeter.SayHello(name);
    std::cout << "Received: " << reply << std::endl;

    return 0;
}

在这个例子中，我们使用了`grpc::SerializationTraits`类将请求和响应对象序列化为JSON字符串。`GreeterClient`类实现了客户端的逻辑，`SayHello`函数发送一个`HelloRequest`对象到服务端，并返回一个包含`Hello, name!`的字符串。在`main`函数中，我们使用`CreateChannel`函数创建一个与服务端通信的通道，并使用`GreeterClient`类进行通信。