NestJS NATS请求 - 响应

Question

I'm trying to use NestJS and the NATS microservice. There is good documentation for setting up a basic request-response.

What I did is the following:

Ran a local NATS server.

Set up my main.ts to connect to the server:

async function bootstrap() {
  const app = await NestFactory.createMicroservice(AppModule, {
    options: {
      url: "nats://localhost:4222",
    },
    transport: Transport.NATS,
  });
  app.listen(() => console.log("Microservice is listening"));
}
bootstrap();

Created a ClientProxyFactory to send back messages:

export const NatsClientProvider: Provider = {
  inject: [ConfigService],
  provide: NatsClientProviderId,
  useFactory: async (config: ConfigService) =>
    ClientProxyFactory.create({
      options: {
        servers: config.getNatsConfig().servers,
      },
      transport: Transport.NATS,
    }),
};

Set up a controller app.controller.ts to respond to a certain pattern:

@Controller()
export class AppController {
  constructor(
    private readonly appService: AppService,
    @Inject(NatsClientProviderId) private readonly natsClient: ClientProxy,
  ) {}

  @MessagePattern("hello")
  async getHello(data: string) {
    console.log("data: ", data);
    console.log("getHello!!");
    await this.natsClient.send("hello", this.appService.getHello());
    return this.appService.getHello();
  }

  async onModuleInit() {
    await this.natsClient.connect();
    console.log("Nats connected!");
  }

Set up a test file to try sending a request-response message:

import { connect } from "ts-nats";

async function start() {
  const nc = await connect({
    servers: ["nats://localhost:4222"],
  });

  const msg = await nc.request("hello", 5000, "me");
  console.log("msg: ", msg);
}

start();

When I run my Nest app, I can see the subscription created properly in the NATS server logs.

When I run the test.ts file, it times out with NatsError: Request timed out. . However, I can see my console logs (although the data is undefined even though I am specifying it in the published message.

Neither the return nor the client.send methods are working to receive messages back from the app.

Any help is appreciated!

EDIT: Still looking into and stuck on this issue. In the "Sending Messages" section of the Microservice docs , it says "The pattern has to be equal to this one defined in the @MessagePattern() decorator while payload is a message that we want to transmit to another microservice.". If I do that, the Nest app detects the message it sends and gets stuck in an infinite loop of sending a message and receiving the same message back and forth to itself forever.

Answer 1

When using the ClientProxy, send and emit return Observables. You need to "activate" those for them to do anything. So you can either subscribe to them, or change it to a Promise.

since you are using await you probably want to do

await this.natsClient.send("hello", this.appService.getHello()).toPromise();

Answer 2

To avoid the infinite loop in your controller, remove the natsClient.send statement. MessagePattern will automatically send a reply with the data you return from the function, in your case this.appService.getHello() :

@MessagePattern("hello")
async getHello(data: string) {
  console.log("data: ", data);
  return "Hello World!";
}

Nest requires you to send a long an id attribute (any string is fine) for it to be able to reply to a message. Just include it in the data json:

// Nest expects the data to have the following structure
const reply = await nc.request("hello", 500, JSON.stringify({ data: "Hello", id: "myid" }));
console.log({ reply });

In your nest log, you'll see the following log entry:

data: Hello

In your test script, you'll see this:

{ reply:
   { subject: '_INBOX.GJGL6RJFYXKMCF8CWXO0HB.GJGL6RJFYXKMCF8CWXO0B5',
     sid: 1,
     reply: undefined,
     size: 50,
     data: '{"err":null,"response":"Hello World!","id":"myid"}' 
} }