In Memory Message Queue Adapter

DRY Castore MessageQueue definition using FastQ.

📥 Installation

``bash


npm

npm install @castore/in-memory-message-queue-adapter

yarn

yarn add @castore/in-memory-message-queue-adapter
`

This package has @castore/core as peer dependency, so you will have to install it as well:

`bash


npm

npm install @castore/core

yarn

yarn add @castore/core
`

👩‍💻 Usage

The simplest way to use this adapter is to use the attachTo static method:

`ts
import { InMemoryMessageQueueAdapter } from '@castore/in-memory-message-queue-adapter';

const messageQueueAdapter =
InMemoryMessageQueueAdapter.attachTo(appMessageQueue);
`

This will make your messageQueueAdapter inherit from your appMessageQueue types while plugging them together 🙌

You can also instanciate one on its own, but notice the code duplication:

`ts
import type { MessageQueueMessage } from '@castore/core';
import { InMemoryMessageQueueAdapter } from '@castore/in-memory-message-queue-adapter';

const messageQueueAdapter = new InMemoryMessageQueueAdapter<
MessageQueueMessage
>();

appMessageQueue.messageQueueAdapter = messageQueueAdapter;
`

🤖 Set worker

You can provide an async worker for the queue at construction time, or in context later:

`ts
const messageQueueAdapter = InMemoryMessageQueueAdapter.attachTo(
appMessageQueue,
{
worker: async message => {
// 🙌 Correctly typed!
const { eventStoreId, event } = message;
},
},
);

// 👇 Alternatively
const messageQueueAdapter = new InMemoryMessageQueueAdapter<
MessageQueueMessage
>({
worker: async message => {
// 🙌 Correctly typed!
const { eventStoreId, event } = message;
},
});

// 👇 Also alternatively
messageQueueAdapter.worker = async message => {
// 🙌 Correctly typed!
const { eventStoreId, event } = message;
};
`

> Only one worker at a time can be set up

For more control, the worker has access to more context through its second argument:

`ts
messageQueueAdapter.worker = async (message, context) => {
const { eventStoreId, event } = message;
const {
// 👇 See "Retry policy" section below
attempt,
retryAttemptsLeft,
// 👇 If event is replayed
replay,
} = context;

...
};
`

♻️ Retry policy

This adapter will retry failed messages handling. You can specify a different retry policy than the default one via its constructor arguments:

- retryAttempts (?number = 2): The maximum number of retry attempts for a message in case of worker execution failure. If all the retries fail, the error is logged with console.error, and the message ignored.
- retryDelayInMs (?number = 30000): The minimum delay in milliseconds between the worker execution failure and its first retry.
- retryBackoffRate (?number = 2): A factor applied to the retryDelayInMs at each subsequent retry.

`ts
const messageQueueAdapter = InMemoryMessageQueueAdapter.attachTo(appMessageQueue, {
retryAttempts: 3,
retryDelayInMs: 10000,
retryBackoffRate: 1.5,
});

// 👇 Alternatively
const messageQueueAdapter = new InMemoryMessageQueueAdapter<
MessageQueueMessage
>({
retryAttempts: 3,
retryDelayInMs: 10000,
retryBackoffRate: 1.5,
});
``

For instance, if the worker is continously failing for a specific message, the sequence of code execution (with the default retry policy) will look like this:

- Worker execution: ❌ Failure
- _30 seconds of delay_
- Worker execution: ❌ Failure
- _60 seconds of delay (30x2)_
- Worker execution: ❌ Failure
- _No more retry attempt, error is logged_