s3-etag

S3 ETAG

Generate an accurate S3 ETAG for any file (including multipart).

Installation

npm install s3-etag

(TypeScript type definitions are included in the package.)

Usage

import { generateETag } from 's3-etag';

// Simple MD5 hash of contents for non-multipart files
const etag = generateETag(absoluteFilePath);

// MD5 hash of combined contents & part number (see below) for multipart files
const partSizeInBytes = 10 * 1024 * 1024; // 10mb
const etag = generateETag(absoluteFilePath, partSizeInBytes);

How It Works

This is a Node.js implementation of this algorithm.

At a high level:

• If no partSizeInBytes is specified, return MD5 hash of file contents
• If partSizeInBytes is specified:
  • Generate parts by comparing partSizeInBytes to the file size
  • Read each part from the file, MD5 hash the part, and append it to a global combined hash
  • Once all parts are processed, generate a new MD5 from the global combined hash, and suffix with the amount of parts

License

See LICENSE.md.