Microservices interaction with external services

[purplefish32]

I'm submitting a...

[ ] Regression 
[X ] Bug report
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

When using nestjs as a NATS microservice, the nats payload (data), when using the @MessagePattern decorator, is always undefined.

  @MessagePattern('sms.send')
  test(data: any) {
    console.log('function called OK');
    console.log(data); // Allways undefined
  }

In the provided example I can log "function called OK" but data is allways undefined.

Here is my main.ts

import { NestFactory } from '@nestjs/core';
import { Transport } from '@nestjs/microservices';
import { AppModule } from './app.module';

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

I have tried both regular strings and json encoded objects as valid payloads.

Expected behavior

data should not be undefined

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

Environment

Nest version: X.Y.Z

 
For Tooling issues:
- Node version: XX  
- Platform:  

Others:

[kamilmysliwiec]

Please, provide a minimal repository which reproduces your issue.

[purplefish32]

Here you are, it is a verry basic example. https://github.com/purplefish32/nest-nats
instructions are in the README file.
By the way I used nest cli to generate the app.

[purplefish32]

The @EventPattern decorator, has exactly the same problem, I have updated my repo with an example.

[purplefish32]

A Ha!

I am on to something: if I change my simple nats emitter from

nats.publish('sms.send', JSON.stringify({ message: "JSON payload!" }));

to

nats.publish('sms.send', JSON.stringify({ data: "JSON payload!" }));

I recieve the proper paload.

This is both undocumented and IMHO not the correct way to handle a NATS payload.
A NATS payload can be any type of string, not necesairily JSON, and the JSON can be any format.

My payloads are usualy formated like this :

{ "entity": "..." }

[purplefish32]

@kamilmysliwiec I would love to provide a pull request to fix this issue, but I am a Lerna noob and have no idea how to get the package.json of my test repo to use @nest/microservices from my fork instead of the one published on npm.

Is there a way to point directly to my github or do I have to use a private npm repo to publish my changes ?

[kamilmysliwiec]

Nest wraps every message exchanged by microservices with its own structure understandable by the framework (hence, data property is required). As far as I understand, you want to communicate with Nest microservice using an external service that is not built on top of Nest. We need to provide better docs for that, thanks for pointing this out.

[purplefish32]

I dont think it is a documentation issue, I think is the way that Nest microservices communicate via NATS is incorrect in that a NATS payload should be by default an arbitairy string not an opiniated JSON object.

[purplefish32]

IMHO, the nats-server should be initialised as a sting by default, or JSON via a new option

example:

const app = await NestFactory.createMicroservice(ApplicationModule, {
  transport: Transport.NATS,
  options: {
    url: 'nats://localhost:4222',
    json: true // New option
  },
});

And in the case of a JSON paload : data used in @MessagePattern and @EventPattern should be the root object of the JSON payload, not the object.data

@MessagePattern('sms.send')
  test(data: {} : null {
    console.log(data)
  }

I hope I am clear in my explanaition :)

Otherwise It means that every other non Nest NATS serivce must conform to the nestjs spec. which is a shame.

[kamilmysliwiec]

Nest needs to use particular JSON shape in order to stay cohesive between other transport layers. This JS object is serialized to string (stringified JSON) under the hood and sent through the network.

Otherwise It means that every other non Nest NATS serivce must conform to the nestjs spec. which is a shame.

Yes, this is exactly what it means and I don't think this is "a shame".

IMHO, the nats-server should be initialised as a sting by default, or JSON via a new option

This is something that we could potentially add in the future

[amh4r]

@kamilmysliwiec

Are there any plans to allow custom shape? I'd like to migrate our services to NestJS, but we currently use this shape:

{
  type,          // Equivalent of NestJS "pattern"
  appId,         // Some data specific to our platform.
  loginUserId,   // Some data specific to our platform.
  payload,       // Equivalent of NestJS "data"
}

So far, this is really the only hurdle for our migration to NestJS. Awesome framework!

[EDIT]

Is there a way to add translation logic for messages? I tried using an Interceptor, but undefined is the only element in the context.args array. Looks like Nest is pulling out the data property before the Interceptor is called.