@nestjstools/messaging-nats-extension

A NestJS library for managing asynchronous and synchronous messages with support for buses, handlers, channels, and consumers. This library simplifies building scalable and decoupled applications by facilitating robust message handling pipelines while ensuring flexibility and reliability.

Documentation

https://nestjstools.gitbook.io/nestjstools-messaging-docs

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Installation

npm install @nestjstools/messaging @nestjstools/messaging-nats-extension 

or

yarn add @nestjstools/messaging @nestjstools/messaging-nats-extension

Nats Integration: Messaging Configuration Example

---

Simple Config for nats messaging

import { Module } from '@nestjs/common';
import { MessagingModule } from '@nestjstools/messaging';
import { SendMessageHandler } from './handlers/send-message.handler';
import { MessagingNatsExtensionModule, NatsChannelConfig } from "@nestjstools/messaging-nats-extension";

@Module({
  imports: [
    MessagingNatsExtensionModule, // Importing the Nats extension module
    MessagingModule.forRoot({
      buses: [
        {
          name: 'nats-message.bus',
          channels: ['nats-message'],
        },
      ],
      channels: [
        new NatsChannelConfig({
          name: 'nats-message',
          enableConsumer: true, // Enable if you want to consume messages
          connectionUris: ['nats://localhost:4222'],
          subscriberName: 'nats-core',
        }),
      ],
      debug: true, // Optional: Enable debugging for Messaging operations
    }),
  ],
})
export class AppModule {}

Config for Nats with JetStream

import { Module } from '@nestjs/common';
import { MessagingModule } from '@nestjstools/messaging';
import { SendMessageHandler } from './handlers/send-message.handler';
import { MessagingNatsExtensionModule, NatsJetStreamChannelConfig } from "@nestjstools/messaging-nats-extension";

@Module({
  imports: [
    MessagingNatsExtensionModule, // Importing the Nats extension module
    MessagingModule.forRoot({
      buses: [
        {
          name: 'nats-message.bus',
          channels: ['nats-channel-jetstream'],
        },
      ],
      channels: [
        new NatsJetStreamChannelConfig({
          name: 'nats-channel-jetstream',                  // Unique channel name in your app
          connectionUris: ['nats://localhost:4222'],       // URI of your NATS server
          enableConsumer: true,                            // Enables message consumer
          streamConfig: {
            streamName: 'event-steam',                     // Name of the JetStream stream
            deliverSubjects: ['my_app_command.*'],         // Subjects for stream
            autoUpdate: true,                              // Allow stream config update at app startup
          },
          consumerConfig: {
            durableName: 'nats-durable_name',              // Persistent consumer name (track offset)
            subject: 'my_app_command.*',                   // Specific subject this consumer listens to
            autoUpdate: true,                              // Allow consumer config update
          },
        }),
      ],
      debug: true, // Optional: Enable debugging for Messaging operations
    }),
  ],
})
export class AppModule {}

Dispatch messages via bus (example)

import { Controller, Get } from '@nestjs/common';
import { CreateUser } from './application/command/create-user';
import { IMessageBus, MessageBus, RoutingMessage } from '@nestjstools/messaging';

@Controller()
export class AppController {
  constructor(
    @MessageBus('nats-message.bus') private natsMessageBus: IMessageBus,
  ) {}

  @Get('/nats')
  createUser(): string {
    this.natsMessageBus.dispatch(new RoutingMessage(new CreateUser('John FROM Nats'), 'my_app_command.create_user'));

    return 'Message sent';
  }
}

Handler for your message

import { CreateUser } from '../create-user';
import { IMessageBus, IMessageHandler, MessageBus, MessageHandler, RoutingMessage, DenormalizeMessage } from '@nestjstools/messaging';

@MessageHandler('my_app_command.create_user')
export class CreateUserHandler implements IMessageHandler<CreateUser>{

  handle(message: CreateUser): Promise<void> {
    console.log(message);
    // TODO Logic there
  }
}

📨 Communicating Beyond a NestJS Application (Cross-Language Messaging)

To enable communication with a Handler from services written in other languages, follow these steps:

1. Publish a Message to the queue

2. Include the Routing Key Header Your message must include a header attribute named messaging-routing-key. The value should correspond to the routing key defined in your NestJS message handler:

   @MessageHandler('my_app_command.create_user') // <-- Use this value as the routing key

3. You're Done! Once the message is published with the correct routing key, it will be automatically routed to the appropriate handler within the NestJS application.

---

Routing Strategy

Message routing behavior depends on the value of subscriberName:

• Static Routing: If subscriberName is a specific subject (e.g., 'order.created'), all messages will be published directly to that subject.

• Wildcard Routing: If subscriberName contains a wildcard (e.g., 'order.*' or 'order.>'), the system uses message.messageRoutingKey as the publish subject instead. This enables dynamic routing based on the actual message type or topic.

Example

// If subscriberName is 'order.*'
subscriberName = 'order.*';
message.messageRoutingKey = 'order.created';

// The message will be published to 'order.created'

or JetStream

// If JetStream deliverSubjects is ['order.*']
subject = 'order.*'; // from consumer
message.messageRoutingKey = 'order.created';

// The message will be published to 'order.created'

This strategy allows you to use a single subscriber to handle a range of message types dynamically.

---

Configuration Options

NatsChannel

Property	Description	Default Value
name	The name of the NATS channel (e.g., 'nats-message').
enableConsumer	Whether to enable message consumption (i.e., process incoming messages).	true
connectionUris	An array of NATS server URIs to connect to (e.g., ['nats://localhost:4222']).
subscriberName	A unique identifier for the subscriber (used in queue group subscriptions).

---

Note: NATS supports many configurations for streams, consumers, and subjects. If this setup doesn’t fit your specific use case, you can create your own custom NATS channel — this package and repository provide base classes that you can fork and modify to suit your needs.

Real world working example with RabbitMQ & Redis - but might be helpful to understand how it works

https://github.com/nestjstools/messaging-rabbitmq-example