Multipart Upload to S3 and Cloudflare R2 with Node.js

import {
  S3Client,
  CreateMultipartUploadCommand,
  UploadPartCommand,
  CompleteMultipartUploadCommand,
  AbortMultipartUploadCommand,
} from '@aws-sdk/client-s3';
import fs from 'fs';

const s3 = new S3Client({
  region: 'auto',
  endpoint: process.env.R2_ENDPOINT, // e.g. https://<accountId>.r2.cloudflarestorage.com
  credentials: {
    accessKeyId: process.env.AWS_ACCESS_KEY_ID!,
    secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY!,
  },
});

export async function uploadLargeFileToR2(filePath: string, bucket: string, key: string) {
  const PART_SIZE = 10 * 1024 * 1024; // 10MB per part (must be >= 5MB for S3/R2)
  const fileStats = fs.statSync(filePath);
  const fileStream = fs.createReadStream(filePath, { highWaterMark: PART_SIZE });

  // 1. Initiate Multipart Upload
  const init = await s3.send(
    new CreateMultipartUploadCommand({
      Bucket: bucket,
      Key: key,
    })
  );
  const uploadId = init.UploadId;

  const uploadedParts: { PartNumber: number; ETag: string }[] = [];
  let partNumber = 1;

  try {
    for await (const chunk of fileStream) {
      console.log(`Uploading part ${partNumber}...`);

      const partResult = await s3.send(
        new UploadPartCommand({
          Bucket: bucket,
          Key: key,
          UploadId: uploadId,
          PartNumber: partNumber,
          Body: chunk,
        })
      );

      uploadedParts.push({
        PartNumber: partNumber,
        ETag: partResult.ETag!,
      });

      partNumber++;
    }

    // 2. Complete Upload
    await s3.send(
      new CompleteMultipartUploadCommand({
        Bucket: bucket,
        Key: key,
        UploadId: uploadId,
        MultipartUpload: {
          Parts: uploadedParts.sort((a, b) => a.PartNumber - b.PartNumber),
        },
      })
    );

    console.log('Upload successfully completed!');
  } catch (error) {
    console.error('Upload failed. Aborting multipart upload...', error);
    await s3.send(
      new AbortMultipartUploadCommand({
        Bucket: bucket,
        Key: key,
        UploadId: uploadId,
      })
    );
    throw error;
  }
}