Feature request: idempotent decorator for Lambda handler

[saragerion]

Use Case

Users who write their Lambda functions as classes should be able to make their function handler idempotent via decorator.

Solution/User Experience

import { LambdaInterface } from '@aws-lambda-powertools/commons';
import { 
  idempotentHandler,
  DynamoDBPersistenceLayer,
  IdempotencyConfig,
} from '@aws-lambda-powertools/idempotency';

const config = new IdempotencyConfig({...});
const ddbPersistenceLayer = new DynamoDBPersistenceLayer({...});

class Lambda implements LambdaInterface {
  // Decorate your handler class method
  @idempotentHandler({
    persistenceStore: ddbPersistenceLayer,
    config
  })
  public async handler(_event: unknown, _context: unknown): Promise<void> {
    /* ...Function logic here... */
  }
}

export const handlerClass = new Lambda();
export const handler = handlerClass.handler.bind(handlerClass);

The idempotentHandler decorator should be able to decorate an handler method of a LambdaInterface class, both async and sync. The decorator should accept an object with mandatory persistenceStore and an optional config one. The former should be an instance of any class that extends BasePersistenceLayer, while the latter should be an instance of the class IdempotencyConfig.

Following the Powertools for Python implementation, the decorator should:

• return early if the POWERTOOLS_IDEMPOTENCY_DISABLED env variable has a truthy value (using EnvironmentVariableService)
• use the provided config object or instantiate a new one if none is passed
• register the Lambda context into the config object (used to manage timeouts)
• instantiate an IdempotencyHandler
• call & return the IdempotencyHandler.handle() method

This last step will ensure that the IdempotencyHandler will perform all the actions needed to make the function idempotent.

Alternative solutions

No response

Acknowledgment

• This feature request meets Lambda Powertools Tenets
• Should this be considered in other Lambda Powertools languages? i.e. Python, Java