Calculate or get file integrity

Question

There is any way to get or calculate the file integrity hash?

e.g:

<script src="https://code.jquery.com/jquery-3.6.1.min.js" integrity="sha256-o88AwQnZB+VDvE9tvIXrMQaPlFFSUTR+nldQm1LuPXQ=" crossorigin="anonymous"></script>

For the script above the browser calculate the file sha256 and comparing it to the given attribute integrity o88AwQnZB+VDvE9tvIXrMQaPlFFSUTR+nldQm1LuPXQ=.

So my question is if I can get the browser calculation for the real file (the one that the client received) via web api or something like that?

I read about Request.integrity at https://developer.mozilla.org/en-US/docs/Web/API/Request/integrity but wen i try to use it i get an empty string.

const myRequest = new Request('https://code.jquery.com/jquery-3.6.1.min.js');
const myIntegrity = myRequest.integrity;

Answer 1

There is a site for Subresource Integrity (SRI) hashtag generation - https://www.srihash.org/

Or it can be generated manually with openssl. Like openssl dgst -sha512 -binary myfile.js | openssl base64 -A. Then add a constant sha512- before the hash to get the proper value for the integrity attribute.