1. 定义 .proto 文件

首先，创建一个 .proto 文件，定义服务和消息：

syntax = "proto3";

package helloworld;

service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply) {}
  rpc SayHelloAgain (HelloRequest) returns (HelloReply) {}
}

message HelloRequest {
  string name = 1;
}

message HelloReply {
  string message = 1;
}

### 2. 实现服务器

创建 `greeter_server.js` 文件，包含服务的实现：

```javascript
const grpc = require('@grpc/grpc-js');
const protoLoader = require('@grpc/proto-loader');
const packageDefinition = protoLoader.loadSync('helloworld.proto', {
  keepCase: true,
  longs: String,
  enums: String,
  defaults: true,
  oneofs: true
});
const helloProto = grpc.loadPackageDefinition(packageDefinition).helloworld;

function sayHello(call, callback) {
  callback(null, { message: 'Hello ' + call.request.name });
}

function sayHelloAgain(call, callback) {
  callback(null, { message: 'Hello again, ' + call.request.name });
}

function main() {
  const server = new grpc.Server();
  server.addService(helloProto.Greeter.service, { sayHello: sayHello, sayHelloAgain: sayHelloAgain });
  server.bindAsync('0.0.0.0:50051', grpc.ServerCredentials.createInsecure(), () => {
    server.start();
  });
}

main();

3. 实现客户端

创建 greeter_client.js 文件，包含客户端的实现：

const grpc = require('@grpc/grpc-js');
const protoLoader = require('@grpc/proto-loader');
const packageDefinition = protoLoader.loadSync('helloworld.proto', {
  keepCase: true,
  longs: String,
  enums: String,
  defaults: true,
  oneofs: true
});
const helloProto = grpc.loadPackageDefinition(packageDefinition).helloworld;

function main() {
  const client = new helloProto.Greeter('localhost:50051', grpc.credentials.createInsecure());
  client.sayHello({ name: 'World' }, (err, response) => {
    if (err) console.error(err);
    else console.log('Greeting:', response.message);
  });
  client.sayHelloAgain({ name: 'World' }, (err, response) => {
    if (err) console.error(err);
    else console.log('Greeting:', response.message);
  });
}

main();

4. 运行服务器和客户端

确保你已经安装了所有必要的依赖：

npm install @grpc/grpc-js @grpc/proto-loader

然后，分别运行服务器和客户端：

node greeter_server.js
node greeter_client.js