@message-queue-toolkit/amqp/README.md

AMQP adapter for message-queue-toolkit

# AMQP (Advanced Message Queuing Protocol)

The library provides support for both direct exchanges and topic exchanges.

> **_NOTE:_** Check [README.md](../../README.md) for transport-agnostic library documentation.

## Publishers

Use `AbstractAmqpQueuePublisher` to implement direct exchange and `AbstractAmqpTopicPublisher` for topic exchange.

See [test publisher](test/publishers/AmqpPermissionPublisher.ts) for an example of implementation.

## Consumers

Use `AbstractAmqpQueueConsumer` to implement direct exchange and `AbstractAmqpTopicConsumer` for topic exchange.

See [test consumer](test/consumers/AmqpPermissionConsumer.ts) for an example of implementation.

## Automatic Reconnects

`message-queue-toolkit` automatically reestablishes connections for all publishers and consumers via `AmqpConnectionManager` mechanism.

Example:

```ts
export const TEST_AMQP_CONFIG: AmqpConfig = {
  vhost: '',
  hostname: 'localhost',
  username: 'guest',
  password: 'guest',
  port: 5672,
  useTls: false,
}

const amqpConnectionManager = new AmqpConnectionManager(config, logger)
await amqpConnectionManager.init()

const publisher = new TestAmqpPublisher(
  { amqpConnectionManager },
  {
    // other amqp options
  },
)
await publisher.init()

const consumer = new TestAmqpConsumer(
  { amqpConnectionManager },
  {
    // other amqp options
  },
)
await consumer.start()

// break connection, to simulate unexpected disconnection in production
await (await amqpConnectionManager.getConnection()).close()

const message = {
  // some test message
}

// This will fail, but will trigger reconnection within amqpConnectionManager
publisher.publish(message)

// eventually connection is reestablished and propagated across all the AMQP services that use same amqpConnectionManager

// This will succeed and consumer, which also received new connection, will be able to consume it
publisher.publish(message)
```

## Lazy instantiation

By default `message-queue-toolkit/amqp` will lazily instantiate publishers before the publish in case they weren't instantiated before. This may result in system not failing fast when connection to AMQP cannot be established, as instantiation happens asynchronously. In case that is an undesirable behaviour, you can set parameter `isLazyInitEnabled` to false either directly for a publisher, or as one of the `newPublisherOptions` parameters for the `AmqpQueuePublisherManager`.

In case when lazy instantiation is disabled, publishers should be initialized explicitly by using an async `AmqpQueuePublisherManager.initRegisteredPublishers()` method. It also has an optional `publishers?: string[]` argument, which can be used to only initialize some specific publishers.