Node.js: Pipe ouput of request into crypto.hash

Question

I would like to compute the hash of a resource (e.g., a PDF) from a URL. To this end, I wrote

const computeHash = co.wrap(function* main(url) {
  const response = yield promisify(request)(url);
  // assume response.status === 200
  const buf = new Uint8Array(response.arrayBuffer);
  const hash = crypto.createHash('sha1');
  hash.update(buf, 'binary');
  return hash.digest('hex');
});

to be used

const hash = yield computeHash('http://arxiv.org/pdf/1001.1234v3.pdf');

What I like about the code:

• It's a generator, so I can yield it. Just a step away from async/await.

What I don't like:

• It doesn't correctly compute the hash. :)
• The request is completed and the response body as a whole piped into the hash function. I'd rather pipe the output of request into the hash function.

Any hints?

Answer 1

crypto.createHash() provides a Hash instance that currently supports two interfaces: legacy (update() and digest()) and streaming. You don't have to do anything special to use either one, so to stream the response to the hashing stream it's as simple as:

var hasher = crypto.createHash('sha1');
hasher.setEncoding('hex');
request(url).pipe(hasher).on('finish', function() {
  console.log('Hash is', hasher.read());
});

That's how you'd do it with normal callbacks, but I am not sure how you'd work yield into that as I'm not familiar enough with generators and the like.