How to copy a large file from SFTP server to AWS S3 using lambda?

functions: {
    downloadXMLFile: {
      handler: "handler.downloadXMLFile",
      timeout: 900,
      memorySize: 5120,
      ephemeralStorageSize: 1024,
      events: [
        {
          http: {
            method: 'get',
            path: 'downloadXMLFile',
          },
        }
      ]
    }
  }

import { parseString } from 'xml2js';
import { S3 } from "aws-sdk";
import ClientFtp from 'ssh2-sftp-client';
import fs from "fs";

const s3 = new S3({
  accessKeyId: process.env.AWS_ACCESS_KEY,
  secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY
});

export const downloadXMLFile: Handler = async (_event: APIGatewayEvent) => { 
  try {
    
    const d = new Date();
    const today = `${d.getDate()}-${d.getMonth()+1}-${d.getFullYear()}`
    const sftp = new ClientFtp();
    
    return sftp
      .connect({
        host: process.env.SFTP_HOST,
        username: process.env.SFTP_USER,
        privateKey: sftpSSHKey,
      })
      .then(async () => {
        await sftp.fastGet("/upload/feed.xml", "/tmp/feed.xml");
        const xmlData = fs.readFileSync("/tmp/feed.xml", "utf-8");
        const jsonData = await parseXml(xmlData);

        await uploadtoS3({
          Bucket: process.env.FEED_BUCKET,
          Body: JSON.stringify(jsonData),
          ContentType: "application/json",
          Key: `${today}/feed.json`,
        });

        await uploadtoS3({
          Bucket: process.env.FEED_BUCKET,
          Body: xmlData.toString(),
          ContentType: "application/xml",
          Key: `${today}/feed.xml`,
        });

        return formatJSONResponse({
          message: "File downloaded and transformed successfully!",
        });
      })
      .catch((err) => {
        console.log("Catch Error: ", err);
        throw new Error(err);
      });
    
  } catch (error) {
    console.log(error);
    return internalServerError(error);
  }
  
}

export async function parseXml (xmlString: string) : Promise<any> {
  return await new Promise((resolve, reject) => parseString(xmlString, (err, jsonData) => {
    if (err) {
      reject(err);
    }
    resolve(jsonData);
  }));
}

export async function uploadtoS3(s3Data: S3.PutObjectRequest) {
  console.info("---- UPLODAING TO S3", s3Data.Bucket, s3Data.Key);

  try {
    return await s3.upload(s3Data).promise();
  } catch (error) {
    console.log(error);
    return error;
  }
}