javascript - How to use CORS to access an iframe

Question

When a user prints, my server generate a PDF, and I do this to show the print dialog for the PDF.

$('<iframe type="application/pdf"></iframe>').attr('src', url).load(function() {
    var iframe = this;
    setTimeout(function() { //Chrome PDF viewer shows "Loading..." forever otherwise
        iframe.contentWindow.print();
        $(iframe).remove(); //gc
    }, 50);
}).appendTo('body');

But now I am hosting the PDFs on S3. I get

Uncaught SecurityError: Blocked a frame with origin "https://localhost" from
accessing a frame with origin "https://my-bucket.s3.amazonaws.com".
Protocols, domains, and ports must match.

I presume I need to add CORS headers.

I have

Access-Control-Allow-Methods: GET, HEAD
Access-Control-Allow-Origin: *

What am I missing?

Answer 1

Paul - CORS does not apply when attempting to programmatically access content from a cross-origin iframe. If you want to access content from an iframe on a different domain, you will need to make use of the Web Messaging API (window.postMessage & the onmessage event) to communicate between your page and the iframe.