Read a file line by line using Lambda / S3

Question

I want to read a file line by line located on S3. I tried the following code which I found searching online, but the Lambda function is exiting without invoking any of the readline callbacks. What am I doing wrong?

const aws = require('aws-sdk');
const s3 = new aws.S3({ apiVersion: '2006-03-01' });
const readline = require('readline');

exports.handler = async (event, context, callback) => {
    const bucket = event.Records[0].s3.bucket.name;
    const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
    const params = {
        Bucket: bucket,
        Key: key,
    };

    const s3ReadStream = s3.getObject(params).createReadStream();

    const rl = readline.createInterface({
      input: s3ReadStream,
      terminal: false
    });

    rl.on('line', (line) => {
      console.log(`Line from file: ${line}`);
    });
    rl.on('error', () => {
        console.log('error');
    });
    rl.on('close', function () {
        console.log('closed');
        context.succeed();
    });
    console.log('done');
};

Answer 1

I've found the problem. It's being awhile that I haven't coded on Lambda and I thought it would only exit when context was called. I'm now waiting for the promise to be resolved (or rejected which I'll implement later).

const aws = require('aws-sdk');
const s3 = new aws.S3({ apiVersion: '2006-03-01' });
const readline = require('readline');

exports.handler = async (event, context, callback) => {
    const bucket = event.Records[0].s3.bucket.name;
    const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
    const params = {
        Bucket: bucket,
        Key: key,
    };
    const s3ReadStream = s3.getObject(params).createReadStream();

    const rl = readline.createInterface({
      input: s3ReadStream,
      terminal: false
    });

    let myReadPromise = new Promise((resolve, reject) => {

        rl.on('line', (line) => {
          console.log(`Line from file: ${line}`);
        });
        rl.on('error', () => {
            console.log('error');
        });
        rl.on('close', function () {
            console.log('closed');
            resolve();
        });
    });

    try { await myReadPromise; }
    catch(err) {
        console.log('an error has occurred');
    }

    console.log('done reading!');
};