@nestjstools/messaging

A NestJS library for managing asynchronous and synchronous messages (service bus) 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.

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Features

• Message Buses: Define multiple buses for commands, events, and queries to streamline message routing.
• Handlers: Easily register and manage handlers for processing messages.
• Channels: Support for in-memory channels and easy extension to create custom channel implementations tailored to your needs.
• Consumers: Run message consumers to process queued messages asynchronously, ensuring system reliability and fault tolerance.
• Middleware Support: Add custom middleware for message transformation such like validation, logging - do whatever you want.
• Debug Mode: Enable enhanced logging and debugging capabilities for development.
• Extensibility: Creating new channels is straightforward, allowing developers to expand and integrate with external systems or protocols effortlessly.
• Concurrent Handler Execution: Messages dispatched to multiple handlers are processed concurrently, improving performance and responsiveness across your system.

Channels

• Redis channel adapter
• RabbitMQ channel adapter
• Amazon SQS channel adapter
• Google PubSub channel Adapter
• Nats channel Adapter

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Documentation

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

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Example project based on RaabitMQ example

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

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Installation

npm install @nestjstools/messaging

or

yarn add @nestjstools/messaging

Getting Started

Basic Usage (In-memory)

import { MessagingModule, InMemoryChannelConfig } from '@nestjstools/messaging';
import { SendMessageHandler } from './handlers/send-message.handler';


@Module({
  imports: [
    MessagingModule.forRoot({
      buses: [
        {
          name: 'message.bus',
          channels: ['my-channel'],
        },
      ],
      channels: [
        new InMemoryChannelConfig({
          name: 'my-channel',
          middlewares: [],
        }),
      ],
      debug: true,
    }),
  ],
})
export class AppModule {}

Define a Message & Message Handler

Create a new handler that processes specific message

Define your message

export class SendMessage {
  constructor(
    public readonly content: string,
  ) {
  }
}

Define your message handler

import { SendMessage } from './send-message';
import { MessageResponse, MessageHandler, IMessageHandler } from '@nestjstools/messaging';
import { Injectable } from '@nestjs/common';

// You can define multiple routing messages on the same handler: @MessageHandler('your.message', 'your.message2')
@Injectable()
@MessageHandler('your.message')
export class SendMessageHandler implements IMessageHandler<SendMessage> {
   // If you want to receive the message as a properly typed instance (not just a raw object),
   // use the `@DenormalizeMessage()` decorator on the parameter:
   // async handle(@DenormalizeMessage() message: SendMessage): Promise<MessageResponse | void> {

  async handle(message: SendMessage): Promise<object | void> {
    console.log(message.content);
    // Example handling logic
  }
}

Next Step: Dispatching a Message

Messages can be dispatched from anywhere in your application—whether from services, controllers, or other components. Here’s an example using an HTTP endpoint:

import { Controller, Get } from '@nestjs/common';
import { MessageBus, IMessageBus, RoutingMessage } from '@nestjstools/messaging';
import { SendMessage } from './test/send-message';


@Controller()
export class AppController {
  //You can inject every bus which you defined in configuration
  constructor(@MessageBus('message.bus') private readonly messageBus: IMessageBus) {}

  @Get()
  async dispatchMessage(): Promise<string> {
    // Dispatching a SendMessage instance with a route
    await this.messageBus.dispatch(
      new RoutingMessage(new SendMessage('Message from HTTP request'), 'your.message'),
    );

    return 'Message dispatched successfully!';
  }
}

Flow:

1. Flexible Dispatching:

   • You can call the dispatch method from any layer (e.g., controller, service, or scheduled job). This example uses an HTTP GET endpoint for demonstration.

2. @MessageBus Decorator:

   • Injects the particular message bus (identified by its name, message.bus) into the AppController.

3. Routing and Payload:

   • Wrap the payload (SendMessage) in a RoutingMessage to specify its route (your.message), which ensures the message is handled by the appropriate handler.

4. HTTP Trigger:

   • This implementation illustrates an entry point triggered via an HTTP request, showcasing how simple it is to connect the messaging system to a web interface.

⚠️ Warning!

🚨 Important Notice: You can return responses from handlers, but currently, it only works with the InMemoryChannel. This behavior may not function as expected if multiple handlers are processing a single message.

🛠️ Please ensure you're using a compatible setup when working with multiple handlers, as this could result in unexpected behavior.

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Normalizers

What is a Normalizer? A Normalizer is a component that transforms messages between different formats. It ensures that messages are correctly encoded when sent and properly decoded when received. This is particularly useful in messaging systems where messages need to be serialized and deserialized efficiently.

You can use it to make it works with:

• protobuf
• Custom JSONs
• Base64
• Any custom format

import { Injectable } from '@nestjs/common';
import { MessagingNormalizer, MessageNormalizer } from '@nestjstools/messaging';
import { Buffer } from 'buffer';

@Injectable()
@MessagingNormalizer()
export class Base64Normalizer implements MessageNormalizer {
  denormalize(message: string | object, type: string): Promise<object> {
    if (typeof message === 'object') {
      throw new Error('Message must be a string!');
    }
    return Promise.resolve(JSON.parse(Buffer.from(message, 'base64').toString('utf-8')));
  }

  normalize(message: object, type: string): Promise<string> {
    const jsonString = JSON.stringify(message);
    return Promise.resolve(Buffer.from(jsonString, 'utf-8').toString('base64'));
  }
}

How It Works

Normalization (normalize)

• Converts a JSON object to a Base64 string before sending.

Denormalization (denormalize)

• Decodes the Base64 string back into a JSON object after receiving.

You can define a Normalizer per Channel

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⤵️ Middlewares

A middleware in the context of the MessagingModule is a function that processes messages as they pass through the message pipeline. The middleware can intercept, modify, or log messages before they are handled by the respective message handler. This is particularly useful for logging, authentication, validation, or any other pre-processing step before the actual business logic is applied.

Each channel in the messaging system has its own set of middlewares, and these middlewares are executed in order when a message is dispatched through the respective channel.

How to Use Middleware in Messaging Channels:

To use middleware, you need to:

1. Define the middleware class that implements the Middleware interface, which contains the process method that processes the message.
2. Attach the middleware to a specific channel via the channel configuration.

Example Middleware Code:

Here's an example middleware class that logs a message when the middleware is applied.

import { Injectable } from '@nestjs/common';
import { Middleware, RoutingMessage } from '@nestjstools/messaging';

@Injectable()
@MessagingMiddleware()
export class TestMiddleware implements Middleware {
   async process(message: RoutingMessage, context: MiddlewareContext): Promise<MiddlewareContext> {
      console.log('!!!! WORKS');  // Log or process the message here

      return await context.next().process(message, context); //TODO call `next()` method from `MiddlewareContext` to process next middleware
   }
}

Attaching Middleware to a Channel:

Now that we've defined the middleware, it needs to be attached to a specific channel in the MessagingModule configuration. Here's how you would configure the middleware for a channel:

import { MessagingModule, AmqpChannelConfig, InMemoryChannelConfig } from '@nestjstools/messaging';
import { TestMiddleware } from './middlewares/test.middleware';
import { SendMessageHandler } from './handlers/send-message.handler';

@Module({
  imports: [
    MessagingModule.forRoot({
      buses: [
        {
          name: 'message.bus',
          channels: ['my-channel'],
        },
      ],
      channels: [
        new InMemoryChannelConfig({
          name: 'my-channel',
          middlewares: [TestMiddleware],  // Attach TestMiddleware to this channel
        }),
        new AmqpChannelConfig({
          name: 'amqp-command',
          connectionUri: 'amqp://guest:guest@localhost:5672/',
          exchangeName: 'my_app_command.exchange',
          bindingKeys: ['my_app.command.#'],
          exchangeType: ExchangeType.TOPIC,
          queue: 'my_app.command',
          autoCreate: true,
          enableConsumer: true,
          middlewares: [TestMiddleware],  // Attach TestMiddleware to this AMQP channel
        }),
      ],
      debug: true,
    }),
  ],
})
export class AppModule {}

Explanation of How It Works:

1. Middleware Class:

   • A Middleware is a class that implements the next method. In this case, the TestMiddleware simply logs '!!!! WORKS' and allows the message to continue.

2. Message Pipeline:

   • When a message is dispatched, it passes through the series of middlewares configured for its channel.
   • The middlewares execute in the order they're listed for the channel, and each next method decides what happens to the message—whether it continues or gets transformed.

3. Channel-Specific Middlewares:

   • Each channel can have its own set of middlewares defined in the channel's configuration (e.g., InMemoryChannelConfig and AmqpChannelConfig).
   • This allows flexible control of how messages are processed depending on the channel, enabling different logic for each transport mechanism (in-memory vs. RabbitMQ).

Benefits of Using Middlewares:

• Separation of Concerns: Middlewares help encapsulate cross-cutting concerns like logging, validation, and authentication, making the code cleaner.
• Reusability: A middleware can be reused across different channels to perform the same actions on various messages.
• Custom Logic: You can apply custom transformations, logging, or other types of business logic to messages as they move through the pipeline.

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🔰 ExceptionListener

The ExceptionListener provides a centralized way to handle exceptions thrown during asynchronous message processing from any channel in your messaging system.

By decorating a class with @MessagingExceptionListener() and implementing the ExceptionListener interface, you can intercept and respond to any unhandled exception occurring during message handling — whether it's logging, reporting, retries, or custom recovery logic.

Example Use Case: You can log the error, send a notification, or trigger fallback logic whenever a message handler throws an exception.

Example ExceptionListener Code:

import { Injectable } from '@nestjs/common';
import { ExceptionListener, MessagingExceptionListener, ExceptionContext } from '@nestjstools/messaging';

@MessagingExceptionListener()
export class CustomExceptionListener implements ExceptionListener {
   onException(context: ExceptionContext): Promise<void> {
      console.log(`Here I can handle exception If I want and do some action`);
   }
}

Configuration options

Here’s a table with the documentation for the MessagingModule.forRoot configuration you requested, breaking it into buses, channels (with descriptions of both channels), and their respective properties, descriptions, and default values:

MessagingModule.forRoot Configuration

Property	Description	Default Value
buses	Array of message buses that define routing and processing of messages.	[] (empty array by default)
channels	Array of channel configurations used by the message buses.	[] (empty array by default)
debug	Enables or disables debug mode for logging additional messages.	false
logging	Enables or disables logging for bus activity (e.g., message dispatch).	true

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Buses

Property	Description	Default Value
name	Name of the message bus (e.g., 'command.message-bus').
channels	List of channel names to be used by this bus (e.g., 'my-channel').	[]

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Channels

InMemoryChannelConfig

Property	Description	Default Value
name	Name of the in-memory channel (e.g., 'my-channel').
middlewares	List of middlewares to apply to the channel.	[]
avoidErrorsForNotExistedHandlers	Avoid errors if no handler is available for the message.	false
normalizer	Set your custom normalizer for messages

Creating Your Own Channel and Bus

This process allows you to define and integrate a custom Channel and MessageBus for your application, giving you complete flexibility and control over how messages are processed, dispatched, and consumed. Each step provides the necessary building blocks to create your own transport layer with full integration into the MessagingModule.

1. Create a ChannelConfig

A ChannelConfig class holds the configuration required to establish a stable connection to your service (e.g., RabbitMQ, Redis, etc.). Your class should implement the ChannelConfig interface and define necessary data like the channel name and middlewares.

export class YourChannelConfig implements ChannelConfig {
  public readonly name: string;
  public readonly middlewares: object[];

  constructor({ name, middlewares }: AmqpChannelConfig) {
    this.name = name;
    this.middlewares = middlewares ?? [];  // Default to empty array if no middlewares provided
  }
}

2. Create a Channel

Next, create a class that implements the Channel interface. This class will serve as your DataSource and utilize the configuration you defined in the ChannelConfig class.

export class YourChannel extends Channel {}

3. Create a ChannelFactory

A ChannelFactory is responsible for creating instances of your custom Channel class. It implements the IChannelFactory interface and ensures proper injection into your app.

@Injectable()
@ChannelFactory(YourChannel)
export class YourChannelFactory implements IChannelFactory<YourChannelConfig> {
   create(channelConfig: YourChannelConfig): Channel {
      return new YourChannel(channelConfig);
   }
}

4. Create a MessageBus

The MessageBus handles the dispatching of messages in your system. Create a class implementing the IMessageBus interface to send messages to your custom service (e.g., RabbitMQ, Redis, etc.).

export class YourMessageBus implements IMessageBus {
  constructor(private readonly yourChannel: YourChannel) {}

  async dispatch(message: RoutingMessage): Promise<MessageResponse | void> {
    // Write your logic here to dispatch the message to your channel (e.g., RabbitMQ)
  }
}

5. Create a MessageBusFactory

The MessageBusFactory creates instances of your MessageBus and ensures it's properly integrated with your Channel. It implements the IMessageBusFactory interface.

@Injectable()
@MessageBusFactory(YourChannel)
export class YourMessageBusFactory implements IMessageBusFactory<YourChannel> {
  create(channel: YourChannel): IMessageBus {
    return new YourMessageBus(channel);  // Return a new instance of your message bus
  }
}

6. Create a Consumer MessageConsumer

A consumer receives and processes messages. Create a class that implements the IMessagingConsumer interface and handle the message processing within the consume method.

@Injectable()
@MessageConsumer(YourChannel)
export class YourMessagingConsumer implements IMessagingConsumer<YourChannel> {
  async consume(dispatcher: ConsumerMessageDispatcher, channel: YourChannel): Promise<void> {
    // Logic to consume a message...
    //TODO dispatcher.dispatch(new ConsumerMessage(...));

    return Promise.resolve();
  }

  async onError(errored: ConsumerDispatchedMessageError, channel: YourChannel): Promise<void> {
    // Handle error if message processing fails
    return Promise.resolve();
  }
}

7. Add Custom MessageOptions to Your Bus (Optional)

You can create custom message options for your message.

export class YourMessageOptions implements MessageOptions {
  constructor(public readonly middlewares: Middleware[] = []) {}
}

Classes with Injectable() decorator must be defined as providers in somewhere in application.

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