Fetching and hashing a file from a URL in a Zapier code action in JavaScript

I was looking for a way to hash files manipulated in a Zapier code action and since Zapier does not provide such crypto transforms by default, I went on to implement it in Javascript.

The code below does this:

1. fetch the file from a public URL
2. hash said file using sha256
3. return the hash in the output

const crypto = require('crypto');
    
return fetch(inputData.fileUrl)
  .then((res)=>{
    console.log(res.ok);
    console.log(res.status);
    console.log(res.statusText);
    return res.buffer()
  })
  .then((buffer)=>{
    const hash = crypto.createHash('sha256');
    hash.update(buffer);
    callback (null, {"hashValue":hash.digest('hex')});
  })
  .catch(callback)

I am basically calling 'fetch' on the S3 URL, returning the result as a buffer() call on the response object. I then create a 'crypto' object from said buffer, from which I create a sha256 hash and hex digest.

Note: Javascript code actions in Zapier can only take strings as input parameters, so any files you want to hash need to transit through a storage space (e.g. AWS S3 bucket) that has a publicly accessible URL. If you manipulate private/sensitive data, you may want to delete the file in a subsequent action in your zap. Beware also of non ascii characters in the URL (e.g. fetching from AWS S3 returns a 403 Forbidden error if your URL includes such characters as '€')

I hope Zapier users will find this useful, e.g. to automate workflows where you need to ensure file data integrity (accounting, invoicing ...)