Streaming files from AWS S3 using NodeJS Stream API with Typescript

import {Readable, ReadableOptions} from 'stream';import type {S3} from 'aws-sdk';export class SmartStream extends Readable {    _currentCursorPosition = 0; // Holds the current starting position for our range queries    _s3DataRange = 64 * 1024; // Amount of bytes to grab    _maxContentLength: number; // Total number of bites in the file    _s3: S3; // AWS.S3 instance    _s3StreamParams: S3.GetObjectRequest; // Parameters passed into s3.getObject method    constructor(        parameters: S3.GetObjectRequest,        s3: S3,        maxLength: number,        // You can pass any ReadableStream options to the NodeJS Readable super class here        // For this example we wont use this, however I left it in to be more robust        nodeReadableStreamOptions?: ReadableOptions    ) {        super(nodeReadableStreamOptions);        this._maxContentLength = maxLength;        this._s3 = s3;        this._s3StreamParams = parameters;    }    _read() {        if (this._currentCursorPosition > this._maxContentLength) {            // If the current position is greater than the amount of bytes in the file            // We push null into the buffer, NodeJS ReadableStream will see this as the end of file (EOF) and emit the 'end' event            this.push(null);        } else {            // Calculate the range of bytes we want to grab            const range = this._currentCursorPosition + this._s3DataRange;            // If the range is greater than the total number of bytes in the file            // We adjust the range to grab the remaining bytes of data            const adjustedRange = range < this._maxContentLength ? rangeEnd : this._maxContentLength;            // Set the Range property on our s3 stream parameters            this._s3StreamParams.Range = `bytes=${this._currentCursorPosition}-${adjustedRange}`;            // Update the current range beginning for the next go             this._currentCursorPosition = adjustedRange + 1;            // Grab the range of bytes from the file            this._s3.getObject(this._s3StreamParams, (error, data) => {                if (error) {                    // If we encounter an error grabbing the bytes                    // We destroy the stream, NodeJS ReadableStream will emit the 'error' event                    this.destroy(error);                } else {                    // We push the data into the stream buffer                    this.push(data.Body);                }            });        }    }}

import {SmartStream} from <Path to SmartStream file>;export async function createAWSStream(): Promise<SmartStream> {    return new Promise((resolve, reject) => {        const bucketParams = {            Bucket: <Your Bucket>,            Key: <Your Key>        }        try {            const s3 = resolveS3Instance();            s3.headObject(bucketParams, (error, data) => {                if (error) {                    throw error;                }                // After getting the data we want from the call to s3.headObject                // We have everything we need to instantiate our SmartStream class                // If you want to pass ReadableOptions to the Readable class, you pass the object as the fourth parameter                const stream = new SmartStream(bucketParams, s3, data.ContentLength);                resolve(stream);            });        } catch (error) {            reject(error)        }    });}