04 The server

Create server.js:

// server.js
const { grpc, proto } = require("./load");

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

const server = new grpc.Server();
server.addService(proto.Greeter.service, { SayHello: sayHello });
server.bindAsync(
  "0.0.0.0:50051",
  grpc.ServerCredentials.createInsecure(),
  () => console.log("Greeter listening on :50051"),
);

How it works:

Line	What it does
require("./load")	Gets the grpc runtime and the proto package bindings.
sayHello	Implements the SayHello RPC. call.request.name is the field from HelloRequest. callback(null, {...}) sends HelloReply.
new grpc.Server()	Creates a bare gRPC server.
addService	Registers the Greeter service using proto.Greeter.service (the descriptor) and maps each method name to a handler function.
bindAsync	Binds to all interfaces on port 50051 with no TLS. The callback fires once the port is open.

The handler signature is (call, callback):

• call.request — the deserialized HelloRequest.
• callback(error, response) — call with null error and the HelloReply object.

Next: 05 The client