AWSの「サーバーレスのウェブアプリケーションを構築する」の「サーバーレスバックエンドを構築する」をNodeJS 18.x以降で対応する

はじめに

AWSのDeveloper試験を受験しようと手を動かしながら勉強中だが、以下リンク先でNodeJS 16.xでないと動かないプログラムがサンプルとして置かれている。
https://aws.amazon.com/jp/getting-started/hands-on/build-serverless-web-app-lambda-apigateway-s3-dynamodb-cognito/module-3/
しかし、ap-northeast-1で選択できるNodeJSはすでに18.x以降のものしかなかった。
とりあえずもろもろサンプルから置き換えて実装し、ひとまず動くところまで確認できたので残しておく。

さっそくブツを

// 書き換えポイント このimport群
import { createRequire } from 'module';
const require = createRequire(import.meta.url);
const randomBytes = require('crypto').randomBytes;
import { PutCommand, DynamoDBDocument } from '@aws-sdk/lib-dynamodb';
import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
const ddb = DynamoDBDocument.from(new DynamoDBClient({ region: "ap-northeast-1" }));

const fleet = [
  {
      Name: 'Angel',
      Color: 'White',
      Gender: 'Female',
  },
  {
      Name: 'Gil',
      Color: 'White',
      Gender: 'Male',
  },
  {
      Name: 'Rocinante',
      Color: 'Yellow',
      Gender: 'Female',
  },
];

// 書き換えポイント このhandlerの定義の仕方
export const handler = (event, context, callback) => {
  if (!event.requestContext.authorizer) {
    errorResponse('Authorization not configured', context.awsRequestId, callback);
    return;
  }

  const rideId = toUrlString(randomBytes(16));
  console.log('Received event (', rideId, '): ', event);

  // Because we're using a Cognito User Pools authorizer, all of the claims
  // included in the authentication token are provided in the request context.
  // This includes the username as well as other attributes.
  const username = event.requestContext.authorizer.claims['cognito:username'];

  // The body field of the event in a proxy integration is a raw string.
  // In order to extract meaningful values, we need to first parse this string
  // into an object. A more robust implementation might inspect the Content-Type
  // header first and use a different parsing strategy based on that value.
  const requestBody = JSON.parse(event.body);

  const pickupLocation = requestBody.PickupLocation;

  const unicorn = findUnicorn(pickupLocation);

  recordRide(rideId, username, unicorn).then(_ => {
    callback(null, {
      statusCode: 201,
      body: JSON.stringify({
          RideId: rideId,
          Unicorn: unicorn,
          Eta: '30 seconds',
          Rider: username,
      }),
      headers: {
          'Access-Control-Allow-Origin': '*',
      },
  });
  }).catch((err) => {
    console.error(err);

    // If there is an error during processing, catch it and return
    // from the Lambda function successfully. Specify a 500 HTTP status
    // code and provide an error message in the body. This will provide a
    // more meaningful error response to the end client.
    errorResponse(err.message, context.awsRequestId, callback)
  });;
};

// This is where you would implement logic to find the optimal unicorn for
// this ride (possibly invoking another Lambda function as a microservice.)
// For simplicity, we'll just pick a unicorn at random.
function findUnicorn(pickupLocation) {
  console.log('Finding unicorn for ', pickupLocation.Latitude, ', ', pickupLocation.Longitude);
  return fleet[Math.floor(Math.random() * fleet.length)];
}

// 書き換えポイント このFunction
async function recordRide(rideId, username, unicorn) {
  const command = new PutCommand({
    TableName: 'Rides',
    Item: {
        RideId: rideId,
        User: username,
        Unicorn: unicorn,
        RequestTime: new Date().toISOString(),
    },
  });
  const response = await ddb.send(command)
  return response;
}

function toUrlString(buffer) {
  return buffer.toString('base64')
      .replace(/\+/g, '-')
      .replace(/\//g, '_')
      .replace(/=/g, '');
}

function errorResponse(errorMessage, awsRequestId, callback) {
callback(null, {
  statusCode: 500,
  body: JSON.stringify({
    Error: errorMessage,
    Reference: awsRequestId,
  }),
  headers: {
    'Access-Control-Allow-Origin': '*',
  },
});
}

終わりに

自分がどう実装したか忘れる自信しかなかったのでQiitaに備忘録として残しておくことを目的としているが、同じように迷った誰かの助けになったらそれはそれで嬉しいです。