EZ4: Topic

It uses the power of reflection to provide a contract that determines how to build and connect topic components.

Getting started

Install

npm install @ez4/topic @ez4/local-topic @ez4/aws-topic -D

Create topic

// file: topic.ts
import type { Environment, Service } from '@ez4/common';
import type { Topic } from '@ez4/topic';

// MyTopic message
type MyTopicMessage = {
  foo: string;
  bar: number;
};

// MyTopic declaration
export declare class MyTopic extends Topic.Service<MyTopicMessage> {
  subscriptions: [
    Topic.UseSubscription<{
      handler: typeof eventHandler;
    }>
  ];

  variables: {
    myVariable: Environment.Variable<'MY_VARIABLE'>;
  };

  services: {
    otherService: Environment.Service<OtherService>;
    variables: Environment.ServiceVariables;
  };
}

// MyTopic message handler
export function eventHandler(request: Topic.Incoming<MyTopicMessage>, context: Service.Context<MyTopic>): void {
  const { otherService, variables } = context;
  const { message } = request;

  // Access message contents
  message.foo;

  // Access injected services
  otherService.call();

  // Access injected variables
  variables.myVariable;
}

Use topic

// file: handler.ts
import type { Service } from '@ez4/common';
import type { MyTopic } from './topic';

// Any other handler that has injected MyTopic service
export async function anyHandler(_request: any, context: Service.Context<DummyService>) {
  const { myTopic } = context;

  await myTopic.sendMessage({
    foo: 'foo',
    bar: 123
  });
}

Topic properties

Service

| Name | Type | Description | | ------------- | ----------------------- | ----------------------------------------------------- | | fifoMode | Topic.UseFifoMode<> | Enable and configure the FIFO mode options. | | subscriptions | Topic.UseSubscription<> | All subscriptions associated to the topic. | | variables | object | Environment variables associated to all subscription. | | services | object | Injected services associated to all subscription. |

Use type helpers for fifoMode and subscriptions properties.

Subscriptions (Function)

| Name | Type | Description | | ------------ | -------- | ----------------------------------------------------- | | listener | function | Life-cycle listener function for the subscription. | | handler | function | Entry-point handler function for the subscription. | | variables | object | Environment variables associated to the subscription. | | logRetention | integer | Log retention (in days) for the handler. | | timeout | integer | Maximum execution time (in seconds) for the handler. | | memory | integer | Memory available (in megabytes) for the handler. |

Subscriptions (Queue)

| Name | Type | Description | | ------- | --------------------- | ------------------------------- | | service | Environment.Service<> | Reference to the queue service. |

Examples

• Get started with topic
• Importing topic

Providers

• Local provider
• AWS provider

License

MIT License